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Chaos synchronization and communication in closed-loop semiconductor lasers subject to common chaotic phase-modulated feedback
Ning Jiang, Anke Zhao, Shiqin Liu, Chenpeng Xue, and Kun Qiu
Ning Jiang,* Anke Zhao, Shiqin Liu, Chenpeng Xue, and Kun Qiu
School of Information and Communication Engineering, University of Electronic Science and Technology of China, 2006 Xiyuan Avenue, Chengdu 611731, China
*Corresponding author: uestc_nj@uestc.edu.cn
N Jiang
A Zhao
S Liu
C Xue
K Qiu
Ning Jiang, Anke Zhao, Shiqin Liu, Chenpeng Xue, and Kun Qiu, "Chaos synchronization and communication in closed-loop semiconductor lasers subject to common chaotic phase-modulated feedback," Opt. Express 26, 32404-32416 (2018)
Injection-locking chaos synchronization and communication in closed-loop semiconductor lasers subject to phase-conjugate feedback (OE)
Key space enhancement of a chaos secure communication based on VCSELs with a common phase-modulated electro-optic feedback (OE)
Wideband complex-enhanced chaos generation using a semiconductor laser subject to delay-interfered self-phase-modulated feedback (OE)
Optical Communications and Interconnects
Laser coupling
Time lenses
Original Manuscript: August 21, 2018
Revised Manuscript: October 31, 2018
Manuscript Accepted: November 2, 2018
2. Principles and theoretical model
3. Influence of CCPMOF on characteristics of chaotic carrier
4. Chaos synchronization in closed-loop ECSLs subject to CCPMOF
5. Chaos communication and security discussion
We propose and demonstrate a closed-loop chaos system composed of external-cavity semiconductor lasers subject to common chaotic phase-modulated optical feedback (CCPMOF). The efficient-bandwidth and time-delay signature (TDS) characteristics of the chaotic carrier, the properties of chaos synchronization, as well as the performance and security of chaos communication are systematically investigated. The numerical results demonstrate that wideband chaotic carrier with effective TDS suppression can be easily obtained, high-quality chaos synchronization with considerable mismatch robustness, frequency detuning tolerance, and phase fluctuation tolerance can be achieved in a wide operation range, and high-speed chaos communication is available. With respect to the conventional closed-loop systems, the bandwidth and complexity of chaotic carrier is greatly enhanced, and the performances of chaos synchronization and communication are obviously improved.
Chaos synchronization and communication in external-cavity semiconductor lasers (ECSLs) have attracted great attention in the last decade for its physical security enhancement property [1–3]. In chaos-based communication systems based on ECSLs, message is usually embedded into the chaotic carrier at the transmitter end by the ways of chaos modulation, chaos masking, or chaos shift keying, and at the receiver end the message is recovered on the basis of chaos synchronization [4–6]. It has been theoretically and experimentally confirmed that there are two types of chaos synchronization can be achieved in the unidirectional coupling ECSL systems. One is the complete chaos synchronization and the other one is the generalized chaos synchronization. The physical mechanisms for these two types of chaos synchronization are based on the symmetric operation and the injection-locking effect, respectively [7,8].
Up to present, in most of chaotic ECSL systems, the feedback light is a linear delayed replica of the output light, which results in that the bandwidth of chaotic carrier is limited nearby the relaxation oscillation frequency (fRO) and the time delay signature (feedback delay time) is easily identified [9,10]. The limited bandwidth would restrict the transmission capacity of chaos communication system, and the TDS revealment would degrade the system security. In recent years, a lot of methods have been proposed to enhance the bandwidth and conceal the TDS of chaos in ECSLs, such as dual optical feedback [11], distributed feedback [12,13], phase-modulated feedback [5,14], delayed self-interference [15], electronic or optical heterodyning [16,17], coupling CW laser with chaotic laser [18], and propagating chaos generated by ECSL through optical time lens or optical fractional Fourier transformation module [19,20]. However, these studies are mainly focused on the stand-alone chaos sources, while the chaos synchronization and communication in the coupling chaos systems composed of these bandwidth-enhanced and TDS-concealed chaos sources are rarely investigated.
In this paper, we propose and demonstrate a closed-loop chaos synchronization system based on ECSLs subject to common chaotic phase-modulated optical feedback (CCPMOF). Simulation results demonstrate that with respect to the conventional closed-loop ECSL system, simultaneous bandwidth enhancement and effective TDS suppression for chaotic carrier can be achieved, high quality chaos synchronization can be performed much more easily, and the communication performance can be improved.
The configuration of closed-loop ECSL system subject to CCPMOF is illustrated in Fig. 1. Similar to the conventional closed-loop configuration [21], two twin ECSLs, namely master semiconductor laser (MSL) and slave semiconductor laser (SSL), are unidirectionally coupled with optical fiber. While differing from the conventional configurations, a phase modulator is deployed in the feedback loops of MSL and SSL, and the driving signals of phase modulators are distributed from a third chaotic ECSL which is referred as the driving semiconductor laser (DSL). The output of DSL is equally split into two parts, both of which are photo-detected, amplified and then respectively used as the driving signals of the phase modulators in the feedback loops of MSL and SSL. Under such a scenario, both of MSL and SSL suffer common chaotic phase-modulated optical feedback.
Fig. 1 Schematic of closed-loop ECSL system subject to common chaotic phase modulated feedback. DSL: driving semiconductor laser, MSL: master semiconductor laser, SSL: slave semiconductor laser, PM: phase modulator, OI: optical isolator, FC: fiber coupler, OC: optical circulator, PD: photodetector, R: reflector, Amp: electronic amplifier.
For the numerical purpose, we adopt the modified Lang-Kobayashi rate equations taking the feedback term and the injection term into consideration, to describe the dynamics of the ECSLs in the proposed scheme. The rate equations for DSL are written as [22]
(1)dEd(t)dt=12(1+iα)(Gd(t)−1τp)Ed(t)+kdEd(t−τd)exp(−iωdτd)+2βNd(t)χd(t),
(2)dNd(t)dt=Ide−Nd(t)τe−Gd(t)|Ed(t)|2.
While those for MSL and SSL are written as [21,23]
(3)dEm,s(t)dt=12(1+iα)(Gm,s(t)−1τp)Em,s(t)+kfEm,s(t−τf)exp(−iωm,sτf)exp(iϕPM(t))+σEm(t−τi)exp(−iωmτi)exp(iΔωt)+2βNm,s(t)χm,s(t),
(4)dNm,s(t)dt=Im,se−Nm,s(t)τe−Gm,s(t)|Em,s(t)|2.
(5)Gd,m,s(t)=g(Nd,m,s(t)−N0)1+ε|Ed,m,s(t)|2
(6)ϕPM(t)=A⋅Ν[|Ed(t-Δtd)|2]Vπ⋅π
(7)Ν(x)=x−xminxmax−xmin
In these equations, the subscripts d, m, and s stand for DSL, MSL, and SSL, respectively. E(t) denotes the slow-varying complex electric field, and N(t) denotes the carrier number in the laser cavity. e = 1.6 × 10−19 C is the electron charge. The optical gain G is defined in Eq. (5), wherein |E(t)|2 denotes the photon number in the cavity. kd and τd denote the feedback strength and time delay of DSL, respectively. kf and τf denote the feedback strength and time delay of MSL and SSL, respectively. σ and τi denote the coupling strength and flight time from MSL to SSL, respectively. ω=2πf is the angle frequency, and Δω=ωm−ωs is the detuning frequency between MSL and SSL. χ(t) is Gaussian noise source with unity variance and zero mean, which is adopted to model the spontaneous emission noise. The additional phase induced by the phase modulation (PM) is presented in Eq. (6), wherein A is the amplitude of driving signal, Ν[·] denotes normalizing the values of [·] into the range from 0 to 1, Δtd is the flight time from DSL to MSL and SSL, and Vπ is the half-wave voltage of phase modulator. The phase modulation index βPM is determined by A/Vπ. The normalization Ν[·] is mathematically defined in Eq. (7), wherein "min" and "max" mean the minimum and maximum values, respectively.
To quantitatively investigate the bandwidth and TDS characteristics of chaotic carrier in the proposed system, the efficient bandwidth and auto-correlation function (ACF) are calculated. The efficient bandwidth is defined as the span between the DC and the frequency where 80% of the energy is contained in the RF spectrum, as those in [9,18,19,24]. The ACF [A(∆t)] that measures how well the time series matches its time-shifted replica is defined as [15,16,25]
(8)A(Δt)=〈(I(t+Δt))−〈I(t+Δt)〉)⋅(I(t)−〈I(t)〉)〉(〈(I(t+Δt)−〈I(t+Δt)〉)2〉⋅〈(I(t)−〈I(t)〉)2〉)1/2,
where I(t) = |E(t)|2 is the intensity time series, I(t + ∆t) contains the time shift ∆t with respect to I(t), and <·> stands for the time averaging. Similarly, to quantify the chaos synchronization quality, the cross-correlation function (CCF) is defined as [6–8,26]
(9)C(Δt)=〈(Im(t+Δt))−〈Im(t+Δt)〉)⋅(Is(t)−〈Is(t)〉)〉(〈(Im(t+Δt)−〈Im(t+Δt)〉)2〉⋅〈(Is(t)−〈Is(t)〉)2〉)1/2
In our simulations, the rate equations are handled with the fourth-order Runge-Kutta algorithm. The intrinsic parameters of the lasers are set as the typical parameters reported in [27]: the wavelength λ=1550 nm, the linewidth enhancement factor α = 5, the differential gain parameter g=1.5×10−8 ps−1, the gain saturation coefficient ε=5×10−7, the spontaneous emission rate β=1.5×10−6 ns−1, the photon lifetime τp=2 ps, the carrier lifetime τe=2 ns and the transparent carrier number N0=1.5×108. The operation current I is set as I=2Ith, where Ith=14.7 mA is the threshold current. The feedback strength of DSL is chosen as kd=20 ns−1 and the feedback delay is set as τd = 3 ns. With these parameters, the DSL works in a chaotic regime. Unless otherwise stated, the feedback strength and delay of MSL and SSL are respectively set as kf=20 ns−1 and τf=5ns, the time delay of driving signal is set as Δtd=1 ns, and the flight time from MSL to SSL is set as τi=0 ns for the sake of simplicity.
3.1 Influence of CCPMOF on dynamic behaviors of ECSL
Firstly, we investigate the influence of CCPMOF on the dynamic behaviors of MSL and SSL. Since the dynamic behaviors of MSL and SSL are much similar for the symmetric configuration, here we only show the results of MSL for the sake of simplicity. Figure 2 shows the bifurcation maps of MSL under the feedback scenarios of COF and CCPMOF with different PM indexes. For the COF case, an obvious state transition process can be observed as the increase of feedback strength. The state of MSL changes from stable to quasiperiodic (multiple periodic) at about 5ns−1, and further changes to chaotic at about 7.5ns−1. Nevertheless, under the proposed CCPMOF scenario, it is apparent that no transition process occurs. Even when the feedback is weak [see the insets of Figs. 2(b)-2(d)], the output of ECSL is always chaotic. That is, it is very easy to get chaotic carrier for chaos communication with CCPMOF.
Fig. 2 Bifurcation maps of MSL with peak-to-peak intensity versus feedback strength, under the scenarios of (a) COF and CCPMOF with PM indexes of (b) 0.5, (c) 1, and (d) 2. The insets in (b)-(d) show the detail of bifurcation during the feedback strength range from 0 to 2ns−1.
Figure 3 shows the possibility distribution function (PDF) of the intensity of chaotic signals under the COF and CCPMOF scenarios with different feedback strengths. It is obvious that the PDF of chaos generated with COF does not have a Gaussian profile and the PDF is not symmetric. While in the CCPMOF case with identical feedback strength, the profile of PDF is similar to the Gaussian distribution, especially when the feedback strength is not very strong, as those shown in Figs. 3(b1) and 3(b2). Therefore, it can be concluded that with respect to COF, the CCPMOF here can optimize the PDF of the intensity of chaos, which is beneficial to obtaining a balanced bit ratio of "1" and "0" in the application of random bit generation [15].
Fig. 3 PDF of chaos under the scenarios of COF (first row) and CCPMOF (second row) with βPM = 1, for the cases with different feedback strengths of 10ns−1, 20ns−1, 30ns−1 and 40ns−1.
3.2 Bandwidth enhancement and TDS suppression induced by CCPMOF
It is well known that optical phase modulation with sinusoidal signal would induce infinite sidebands in optical spectrum. The chaotic PM driving signal here can be regarded as a superposition of sinusoidal signals with different frequencies, hence the chaotic PM would induce a mass of new frequency components into the feedback light, and consequently, the bandwidth of generated chaos would be enhanced. Moreover, since PM is a type of nonlinear modulation, the feedback in the present scheme is no longer a linear delayed replica of output of ECSL, then the external-cavity resonance would be weakened, and consequently, the TDS in chaotic carrier would be suppressed correspondingly. In this subsection, we concentrate on the bandwidth enhancement and TDS suppression properties of CCPMOF.
Figure 4 shows the temporal waveforms of intensities, as well as the corresponding RF spectra and ACF curves of the chaotic signals generated by the COF and the CCPMOF, in the case of identical feedback strength and feedback delay. Apparently, the chaotic pulses in the CCPMOF case [Fig. 4(b1)] are denser than those in the COF case [Fig. 4(a1)]. That is, the bandwidth is enhanced. This phenomenon can also be observed in the corresponding RF spectra shown in Figs. 4(a2) and 4(b2), where it is indicated that in the CCPMOF case the energy distributed nearby fRO is reduced, and the attenuation of frequency components higher than fRO is obviously smoother than that in the COF case. The efficient bandwidth in the COF case is 9.6 GHz, while that in the CCPMOF case is 14.6 GHz, the bandwidth has been enhanced by 5 GHz. On the other hand, in the COF case, there is an apparent peak appearing at the feedback delay position in the ACF curve, which means the TDS can be clearly identified. While in the proposed case, the ACF values except that at ∆t = 0 always maintain at a low level nearby 0, no distinguishable peak appears at the feedback delay position. That is, the TDS is totally concealed, and the complexity of chaotic carrier is greatly enhanced [10,25].
Fig. 4 Time series, RF spectra and ACF curves of chaos generated by COF and CCPMOF with identical feedback strength and delay. Here the feedback strength and feedback time delay for both of COF and CCPMOF are set as 20ns−1 and 5ns, respectively; the PM index is fixed as βPM = 1.
To further investigate the bandwidth enhancement and TDS suppression properties of CCPMOF, Fig. 5 shows the variations of efficient bandwidth and TDS value in ACF curve, as a function of the feedback strength and PM index. Here the TDS value is the value of the peak appearing at the feedback delay position in the ACF curve. As that shown in Fig. 5(a), for a fixed PM index, the efficient bandwidth gradually increases as the increase of feedback strength. Similarly, for a fixed feedback strength, a larger PM index can induce more significant bandwidth enhancement. On the other hand, as shown in Fig. 5(b), for a fixed PM index, the TDS value would gradually increase as the increase of feedback strength, and when the feedback strength is strong enough, the TDS may be revealed. While for a fixed feedback strength, the TDS value gets smaller and smaller, and finally it is suppressed at a low level nearby 0, as the increase of PM index. Repeating simulations with different PM indexes and different feedback strengths indicate that even though under strong feedback scenarios, the TDS can be totally concealed by properly enlarging the PM index. These phenomena are because that as the increase of PM index, more and more new frequency components are introduced into the feedback light, then the spectrum of feedback light would be gradually expanded, and the periodicity induced by external cavity resonance would be gradually weakened; consequently, the efficient bandwidth of chaotic carrier is correspondingly enhanced, and simultaneously the TDS is effectively suppressed.
Fig. 5 Efficient bandwidth (in GHz) and TDS value in ACF curve versus PM index βPM and feedback strength kf.
Overall, under the CCPMOF scenario, significant bandwidth enhancement and effective TDS suppression for chaotic carrier can be achieved by properly increasing the PM index. This can be implemented by increasing the gain of RF amplifier or adopting low half-wave voltage optical phase modulators. That is, it is easy to generate broadband chaotic carrier with effective TDS suppression for chaos communication in the proposed closed-loop ECSL system.
4.1 Influences of PM index and injection strength on chaos synchronization
Chaos synchronization is the basis of chaos-based communication, thus in this section we focus on the properties of chaos synchronization in the proposed closed-loop system consisting of ECSLs subject to CCPMOF. To quantitatively describe the level of chaos synchronization between MSL and SSL, we refer the case with a cross correlation coefficient [C(0) in Eq. (9)] larger than 0.95 as the high-quality chaos synchronization. Figure 6(a) shows the cross correlation between the chaotic signals generated by MSL and SSL in the space of PM index and injection strength. For the COF case (βPM = 0), high-quality chaos synchronization requires that the injection strength should be larger than a threshold of 36 ns−1. However, in the proposed system, in the case of βPM = 1, high quality chaos synchronization can be achieved when the injection strength is larger than 14 ns−1. Furthermore, as the increase of PM index, the threshold injection strength for high-quality synchronization would become smaller and smaller. When βPM = 2, the threshold injection strength is reduced as 5 ns−1, and when βPM = 3, it is further reduced as 2 ns−1. Apparently, in the proposed system, high-quality chaos synchronization is much easier to be achieved, and the operation region for the achievement of high-quality chaos synchronization is much wider, with respect to the COF closed-loop system. The prominent chaos synchronization property is due to that with the symmetric CCPMOF, an identical additional phase is added in both of the feedback light of MSL and SSL, with the affections of identical additional phases in the cavities of MSL and SSL, the phase difference between the outputs of MSL and SSL would be reduced, and stable phase locking between SSL and MSL can be more easily obtained, which then prompts the intensity locking and chaos synchronization in intensity [28]. As the increase of PM index, the phase difference between MSL and SSL would be further reduced, then the phase and intensity of SSL are more easily locked to those of MSL, and consequently, chaos synchronization is easier to be achieved.
Fig. 6 Cross correlations (CCs) for (a) MSL-SSL, (b) DSL-MSL, and (c) DSL-SSL versus the PM index βPM and the injection strength σ.
On the other hand, the cross correlation between the intensity of DSL [Id(t-Δtd)] and MSL (SSL) is also shown in Fig. 6(b) [Fig. 6(c)]. It is apparent that the correlation between DSL and MSL (SSL) always keeps at a very low level with a cross correlation coefficient smaller than 0.1. This is because the DSL chaos only affects the feedback phases of MSL and SSL, due to the nonlinearity of phase modulation, the feedback term in Eq. (1) shows a complex nonlinear relationship with the output of DSL, consequently, the evolutions of optical fields of MSL and SSL are incoherent with that of DSL. It is worth mentioning that this phenomenon is different from that in the scenario where the output of DSL is directly injected into MSL and SSL. Under that scenario, due to the injection-locking effect, the evolutions of MSL and SSL would be driven towards that of DSL, and consequently, the cross correlation between DSL and MSL (SSL) is rather high, they can even synchronize with each other, as long as the injection from DSL is sufficiently strong.
4.2 Mismatch robustness, detuning tolerance and phase fluctuation tolerance properties of chaos synchronization in CCPMOF closed-loop system
In practice, the intrinsic parameter mismatch, the frequency detuning and the phase fluctuations in injection and feedback paths would reduce the feasibility of chaos synchronization system, therefore it is essential to discuss their influences on the quality of chaos synchronization in the proposed system. Figure 7 shows the influences of intrinsic parameter mismatches of MSL and SSL on the chaos synchronization quality, for three indicative injection cases of σ = 20 ns−1, σ = 40 ns−1 and σ = 60 ns−1. Here the intrinsic parameters of DSL are fixed to the initial values, while the mismatches of MSL and SSL are introduced by decreasing the internal parameters α, g, and τp and accordingly increasing the parameters N0, ε, and τe of SSL by the same amount, as that reported in [27], which can be mathematically described as αm,s=(1−μm,s)α, gm,s=(1−μm,s)g, τpm,s=(1−μm,s)τp, N0m,s=(1+μm,s)N0, εm,s=(1+μm,s)ε, τem,s=(1+μm,s)τe, wherein μ stands for the mismatch ratio with respect to DSL. For the COF-based system, when the injection strength is weak, no chaos synchronization can be achieved as that shown in Figs. 7(a1), which has also been proved in Fig. 6; when the injection strength is nearby the threshold injection strength [see Fig. 7(b1)], high quality chaos synchronization can be achieved between MSL and SSL, but it is highly sensitive to mismatch between MSL and SSL; only when the injection strength is properly strong, as that shown in Fig. 7(c1), the chaos synchronization can be robust to certain mismatch. Nevertheless, in the CCPMOF-based system, high quality chaos synchronization can be always maintained in a relatively wide region where the mismatch of MSL is identical or similar to that of SSL. For the weak injection case shown in Figs. 7(a2)-7(a4), the robust mismatch range is above 10%. Moreover, the robust mismatch range would be gradually improved, as the increase of injection strength [Figs. 7(b2)-7(b4) and Figs. 7(c2)-7(c4)]. It is interesting to observe that positive mismatches for MSL and SSL would show better robustness with respect to the negative ones. This is because in a positive mismatch case, the parameters α, g, and τp of MSL and SSL are decreased, and the parameters N0, s, and τe are accordingly increased, which induces that the variations of carrier change get slower, the phase variations induced by chaotic PM is dominated to affect the phase variation in the laser cavity. Consequently, with the identical dominated additional chaotic feedback phases, stable phase locking for the injection-locking conditions reported in [28] can be more easily achieved, and then chaos synchronization can be preserved.
Fig. 7 Influences of intrinsic parameter mismatches of MSL and SSL on the quality of chaos synchronization in the COF configuration (first column) and the proposed CCPMOF-based system with βPM = 1 (second column), βPM = 2 (third column) and βPM = 3 (fourth column). The injection strengths in the first, second and third rows are set as 20 ns−1, 40 ns−1 and 60 ns−1, respectively.
Figure 8 shows the influence of frequency detuning of MSL and SSL on the quality of chaos synchronization, for the three indicative injection cases. The frequency detuning is introduced by fixing the operation frequency of DSL and tuning those of MSL and SSL. The frequency detuning between DSL and MSL is defined as Δfdm=fd−fm, and that between DSL and SSL is defined as Δfds=fd−fs, then the frequency detuning between MSL and SSL in Eq. (3) is Δω=ωm−ωs=2π(Δfds−Δfdm). It is obvious that in the CCPMOF-based system, high quality chaos synchronization can be preserved in a certain region where the frequency detuning of MSL is identical or similar to that of SSL. Even when the injection strength is weak [Figs. 8(a2)-8(a4)], the chaos synchronization can tolerate a frequency detuning beyond 10GHz. As the injection strength increases, the detuning tolerance would be enhanced. In the strong injection cases, the chaos synchronization can tolerate several tens of GHz frequency detuning [Figs. 8(b2)-8(b4) and Figs. 8(c2)-8(c4)]. The frequency detuning tolerance property qualitatively agrees with that occurs in the COF-based closed-loop system reported in [29], for the same synchronization mechanism based on the injection-locking effect. Nevertheless, in the COF system (the first column), considerable frequency detuning tolerance for high-quality chaos synchronization requires much stronger injection.
Fig. 8 Influences of frequency detuning of MSL and SSL on the quality of chaos synchronization in the COF configuration (first column) and the proposed CCPMOF-based system with βPM = 1 (second column), 2 (third column), and 3 (fourth column). The injection strengths in first row, second row, and third row are set as 20 ns−1, 40 ns−1 and 60 ns−1, respectively.
In practice, the phase fluctuations in injection light and feedback light of SSL are inevitable due to kinds of reasons, such as the imperfection of fiber, circumstance vibrations, etc, which may also degrade the quality of chaos synchronization. Here we summarize these phase fluctuations as an instantaneous phase noise in the injection for the sake of simplicity, and then the injection term in Eq. (3) is modified as σEm(t−τi)exp(−iωmτi(1+βpχp(t)))exp(iΔωt), wherein βp is the phase fluctuation strength which is defined as the ratio of phase fluctuation with respect to the injection phase, and χp(t) is a Gaussian noise source with unity variance and zero mean. Figure 9 shows the influences of phase fluctuation on the cross correlation between MSL and SSL, for the abovementioned three indicative injection cases. It is indicated that high quality chaos synchronization can be preserved as the phase fluctuation strength is smaller than −1.3dB. Repeating simulations with other injection strengths and PM indexes indicate that in the synchronization region of CCPMOF system, similar phase fluctuation tolerance can also be preserved.
Fig. 9 Influences of phase fluctuation between the injection and feedback of SSL on the cross correlation between MSL and SSL in the COF configuration and the proposed CCPMOF system with different PM indexes, for the injection cases of (a) σ = 20 ns−1, (b) σ = 40 ns−1, and (c) σ = 60 ns−1.
In general, with respect to the COF-based system, it is much easier to achieve stable high-quality chaos synchronization in the CCPMOF-based system, and the mismatch robustness and detuning tolerance properties would be enhanced as the increase of injection strength. In addition, it is worth noting that the results for the cases with different PM indexes are very similar, which indicates that the PM index does not obviously affect the mismatch robustness, the detuning tolerance, and the phase fluctuation tolerance of chaos synchronization.
5.1 Chaos communication in closed-loop ECSLs subject to CCPMOF
On the basis of the high-quality chaos synchronization, in this subsection we investigate the chaos communication in the proposed CCPMOF closed-loop system. Here the message is a random binary sequence, it is embedded into the chaotic carrier by the way of chaos modulation which is mathematically described as |Emm(t)|=|Em(t)|[1+Mm(t)], wherein Emm(t) denotes the modulated carrier, m(t) is the original message, M is the modulation index which determines the message amplitude in the modulated chaotic carrier, and it is chosen as 0.05 to guarantee that the message is well hidden in the chaotic carrier [21]. The message is recovered by the method of direct subtraction decoding which is described as m'(t)=LPF[|Emm(t)|2−|Es(t)|2], where LPF means the recovered message is filtered by a low-pass five-order Butterworth filter with a cut-off frequency equaling the message bit rate R. The communication performance is quantified by calculating the Q-factor of recovery message, which is defined as
(10)Q=<I1>−<I0>ε1+ε0
where <I1> and <I0> stand for the average power of bits "1" bit and "0", respectively; ε1 and ε0 are the corresponding standard deviations. A Q-factor value greater than 6 corresponds to a satisfactory BER about 10−9 [30]. Figure 10(a) shows the distribution of Q-factor of recovery message in the space of PM index βPM and message bit rate R. The results indicate that the range of satisfactory communication performance in the proposed system is obviously wider than that in conventional closed-loop system (βPM = 0), and moreover, this range gradually gets wider and wider as the increase of PM index. This phenomenon is attributed to that the CCPMOF simultaneously enhances the bandwidth of transmission chaotic carrier generated by MSL and that of the synchronous local chaotic carrier generated by SSL, then wider transmission bandwidth can be provided, and consequently, messages with higher rates can be successfully recovered with satisfactory Q-factors. The improvement of communication performance can also be directly observed by comparing the eye diagrams of recovery messages in the conventional system and the proposed system. As those shown in Figs. 10(b1)-10(c3), in the cases of identical bit rates, the eye diagrams in the proposed system open wider than those in the conventional system, especially when higher bit rate message is transmitted.
Fig. 10 (a) Q-factor of recovery message versus PM index βPM and message bit rate R. (b1)-(b3) show the eye diagrams of recovery message in the conventional closed-loop system, while (c1)-(c3) present those in the proposed scheme with βPM = 1. TB = 1/R is the bit period of message. The injection strength is σ = 40ns−1.
5.2 Security discussion
Finally, we turn to discuss the security of chaos communication in the CCPMOF closed-loop system. As aforementioned, the TDS can be effectively suppressed in the CCPMOF system. Therefore, it is difficult for the eavesdropper to guess the feedback delay of MSL and SSL from the transmission signal on the public channel. Figure 11(a) presents the influence of the feedback delay mismatch of SSL (with respect to the feedback delay of MSL) on the Q-factor of recovery message for the case of R = 4 Gbit/s. It is obvious the communication performance is extremely sensitive to the feedback delay mismatch between MSL and SSL. Similar results are also observed in repeating simulations with different values for R. It is indicated that a tiny feedback delay mismatch about 5ps that corresponds to a fiber length of 10−3m would induce the Q-factor decreasing from a satisfactory value 8.8 to 1.7 which indicates no useful message being recovered. Since the variation range of feedback delay can be rather large in practice, if the feedback delay is used as the private key, it is extremely difficult for the eavesdropper to intercept correct message, even if he holds a laser with parameters identical to MSL and SSL.
Fig. 11 (a) Variation of Q-factor versus the mismatch of feedback delay of SSL for the case of R = 4 Gbit/s and σ = 80ns−1. (b) Q-factors of legal recovery message and illegal intercepted messages under the typical attacks of DDLF and US, as a function of the message rate R. The third column shows the eye diagrams of (c1) the legal recovery messages, (d1) the DDLF attack-intercepted massages and (e1) the US attack-intercepted massages for the case of R = 2 Gbit/s, respectively; while the fourth column shows those for the case of R = 4 Git/s. The PM index is set as βPM = 1, and the injection strength for legal recovery is σ = 40ns−1, while that for the US attack is set as 100ns−1 to achieve chaos synchronization.
Furthermore, we consider two typical attack scenarios in chaos communication systems, namely the direct detection with linear filtering (DDLF) and the utilization of synchronization (US) [23,26,31]. For the first attack scenario, the eavesdropper uses a photodetector to capture the transmission chaotic carrier, and then adopts a five-order Butterworth low-pass filter with a cutoff frequency equaling the bit rate of message, to directly extract message from the public link from MSL to SSL. While under the US attack scenario, the eavesdropper firstly captures a transmission chaotic signal by splitting the public link, and then amplifies it and injects it into an attack semiconductor laser (ASL) to obtain chaos synchronization for illegal message interception. Here we consider the extremely serious case that the eavesdropper is equipped with an ASL that is totally identical to MSL and SSL (including the feedback parameters), except that there is no PM in the feedback loop. Figure 11(b) presents the Q-factor of legal recovery message and those of the messages intercepted by DDLF and US, versus the message bit rate R. Apparently, the Q-factors of intercepted messages fastly decrease as the increase of message rate. Under the DDLF scenario, the eavesdropper cannot intercept the message with a satisfactory Q-factor of 6, and when the bit rate is larger than 1.5 Gbit/s, no useful message can be recovered as those shown in Figs. 11(d1) and 11(d2). Repeating simulations with smaller message modulation indexes indicate that, by properly reducing the message modulation index, the Q-factor of message intercepted by DDLF would be further reduced. For the US attack scenario, when the message bit rate is lower than 4 Gbit/s, the eavesdropper may intercept partial message such as that shown in Fig. 11(e1), and even intercept the message with a satisfactory Q-factor larger than 6. However, when the bit rate is higher than 4 Gbit/s, no useful message can be recovered as that shown in Fig. 11(e2). Comparing with the legal recovery message, the intercepted messages show much higher BER. From this point of view, the security of message can be guaranteed by properly increasing the bit rate of message.
In practice, MSL and SSL are twin lasers manufactured on one chip, it is difficult for the eavesdropper to obtain an ASL identical to MSL and SSL, and hence more difficult for him to intercept message. Overall, without precise knowledge of the feedback time delay and the PM details in the feedback loop, the eavesdropper is not able to correctly intercept the message. In addition, by properly increasing the bit rate of message, the BER of intercepted messages would sharply increase, and the interception difficulty is further increased.
In summary, we have proposed a closed-loop chaos system composed of ECSLs subject to CCPMOF. The proposed system supports simultaneous bandwidth enhancement and effective TDS suppression for chaotic carrier, easy-to-implement chaos synchronization and high-speed chaos communication. It is demonstrated that with CCPMOF the chaotic carrier can be easily obtained even when the feedback strength is small, the efficient bandwidth of chaotic carrier can be significantly enhanced, and the TDS can be easily suppressed at a non-distinguishable level with proper selection of the PM index and the feedback strength. With respect to the conventional closed-loop ECSL system, high-quality chaos synchronization can be more easily achieved in a wide range of PM index and injection strength, a weak injection can achieve high-quality chaos synchronization with properly large PM indexes, and in the wide synchronization operation region, the chaos synchronization always shows considerable mismatch robustness, detuning tolerance and injection phase fluctuation tolerance. Moreover, the performance of chaos communication can be obviously improved, a higher bit rate transmission is available. Based on the prominent TDS suppression and communication performance improvement, the communication security can be guaranteed by using the feedback time delay as the private key or properly increasing the bit rate of message.
National Natural Science Foundation of China (NSFC) (61671119, 61471087); 111 Project (B14039).
1. M. Sciamanna and K. A. Shore, "Physics and applications of laser diode chaos," Nat. Photonics 9(3), 151–162 (2015). [CrossRef]
2. A. Argyris, D. Syvridis, L. Larger, V. Annovazzi-Lodi, P. Colet, I. Fischer, J. García-Ojalvo, C. R. Mirasso, L. Pesquera, and K. A. Shore, "Chaos-based communications at high bit rates using commercial fibre-optic links," Nature 438(7066), 343–346 (2005). [CrossRef] [PubMed]
3. N. Li, H. Susanto, B. Cemlyn, I. D. Henning, and M. J. Adams, "Secure communication systems based on chaos in optically pumped spin-VCSELs," Opt. Lett. 42(17), 3494–3497 (2017). [CrossRef] [PubMed]
4. J. Ke, L. Yi, G. Xia, and W. Hu, "Chaotic optical communications over 100-km fiber transmission at 30-Gb/s bit rate," Opt. Lett. 43(6), 1323–1326 (2018). [CrossRef] [PubMed]
5. C. Xue, N. Jiang, Y. Lv, C. Wang, G. Li, S. Lin, and K. Qiu, "Security-enhanced chaos communication with time-delay signature suppression and phase encryption," Opt. Lett. 41(16), 3690–3693 (2016). [CrossRef] [PubMed]
6. P. Li, J. G. Wu, Z. M. Wu, X. D. Lin, D. Deng, Y. R. Liu, and G. Q. Xia, "Bidirectional chaos communication between two outer semiconductor lasers coupled mutually with a central semiconductor laser," Opt. Express 19(24), 23921–23931 (2011). [CrossRef] [PubMed]
7. X. F. Li, W. Pan, B. Luo, and D. Ma, "Mismatch robustness and security of chaotic optical communications based on injection-locking chaos synchronization," IEEE J. Quantum Electron. 42(9), 953–960 (2006). [CrossRef]
8. J. Ohtsubo, "Chaos synchronization and chaotic signal masking in semiconductor lasers with optical feedback," IEEE J. Quantum Electron. 38(9), 1141–1154 (2002). [CrossRef]
9. A. B. Wang, Y. C. Wang, Y. B. Yang, M. J. Zhang, H. Xu, and B. J. Wang, "Generation of flat-spectrum wideband chaos by fiber ring resonator," Appl. Phys. Lett. 102(3), 031112 (2013). [CrossRef]
10. S. Y. Xiang, W. Pan, B. Luo, L. S. Yan, X. H. Zou, N. Li, and H. N. Zhu, "Wideband unpredictability-enhanced chaotic semiconductor lasers with dual-chaotic optical injections," IEEE J. Quantum Electron. 48(8), 1069–1076 (2012). [CrossRef]
11. J. G. Wu, G. Q. Xia, and Z. M. Wu, "Suppression of time delay signatures of chaotic output in a semiconductor laser with double optical feedback," Opt. Express 17(22), 20124–20133 (2009). [CrossRef] [PubMed]
12. Z. Q. Zhong, Z. M. Wu, and G. Q. Xia, "Experimental investigation on the time-delay signature of chaotic output from a 1550nm VCSEL subject to FBG feedback," Photon. Res. 5(1), 6–10 (2017). [CrossRef]
13. S. S. Li, Q. Liu, and S. C. Chan, "Distributed feedbacks for time-delay signature suppression of chaos generated from a semiconductor laser," IEEE Photonics J. 4(5), 1930–1935 (2012). [CrossRef]
14. S. L. Yan, "Enhancement of chaotic carrier bandwidth in a semiconductor laser transmitter using self-phase modulation in an optical fiber external round cavity," Chin. Sci. Bull. 55(11), 1007–1012 (2010). [CrossRef]
15. A. Wang, Y. Yang, B. Wang, B. Zhang, L. Li, and Y. Wang, "Generation of wideband chaos with suppressed time-delay signature by delayed self-interference," Opt. Express 21(7), 8701–8710 (2013). [CrossRef] [PubMed]
16. S. Y. Xiang, A. J. Wen, W. Pan, L. Lin, H. Zhang, H. Zhang, X. Guo, and J. Li, "Suppression of chaos time delay signature in a ring network consisting of three semiconductor lasers coupled with heterogeneous delays," J. Lightwave Technol. 34(18), 4221–4227 (2016). [CrossRef]
17. C. H. Cheng, Y. C. Chen, and F. Y. Lin, "Chaos time delay signature suppression and bandwidth enhancement by electrical heterodyning," Opt. Express 23(3), 2308–2319 (2015). [CrossRef] [PubMed]
18. Y. H. Hong, P. S. Spencer, and K. A. Shore, "Wideband chaos with time-delay concealment in vertical-cavity surface-emitting lasers with optical feedback and injection," IEEE J. Quantum Electron. 50(4), 236–242 (2014). [CrossRef]
19. N. Jiang, C. Wang, C. Xue, G. Li, S. Lin, and K. Qiu, "Generation of flat wideband chaos with suppressed time delay signature by using optical time lens," Opt. Express 25(13), 14359–14367 (2017). [CrossRef] [PubMed]
20. M. Cheng, L. Deng, H. Li, and D. Liu, "Enhanced secure strategy for electro-optic chaotic systems with delayed dynamics by using fractional Fourier transformation," Opt. Express 22(5), 5241–5251 (2014). [CrossRef] [PubMed]
21. D. Kanakidis, A. Argyris, A. Bogris, and D. Syvridis, "Influence of the decoding process on the performance of chaos encrypted optical communication systems," J. Lightwave Technol. 24(1), 335–341 (2006). [CrossRef]
22. R. Lang and K. Kobayashi, "External optical feedback effects on semiconductor injection laser properties," IEEE J. Quantum Electron. 16(3), 347–355 (1980). [CrossRef]
23. N. Jiang, C. Zhang, and K. Qiu, "Secure passive optical network based on chaos synchronization," Opt. Lett. 37(21), 4501–4503 (2012). [CrossRef] [PubMed]
24. F. Y. Lin and J. M. Liu, "Nonlinear dynamical characteristics of an optically-injected semiconductor laser subject to optoelectronic feedback," Opt. Commun. 221(1–3), 173–180 (2003). [CrossRef]
25. N. Li, W. Pan, A. Locquet, and D. S. Citrin, "Time-delay concealment and complexity enhancement of an external-cavity laser through optical injection," Opt. Lett. 40(19), 4416–4419 (2015). [CrossRef] [PubMed]
26. N. Jiang, C. P. Xue, Y. X. Lv, and K. Qiu, "Physical enhanced secure communication based on wavelength division multiplexing chaos synchronization of multimode semiconductor lasers," Nonlinear Dyn. 86(3), 1937–1949 (2016). [CrossRef]
27. A. Bogris, P. Rizomiliotis, K. E. Chlouverakis, A. Argyris, and D. Syvridis, "Feedback phase in optically generated chaos: a secret key for cryptographic application," IEEE J. Quantum Electron. 44(2), 119–124 (2008). [CrossRef]
28. A. Murakami, "Phase locking and chaos synchronization in injection-locked semiconductor lasers," IEEE J. Quantum Electron. 39(3), 438–447 (2003). [CrossRef]
29. R. Vincente, T. Perez, and C. R. Mirasso, "Open-versus closed-loop performance of synchronized chaotic external-cavity semiconductor lasers," IEEE J. Quantum Electron. 38(9), 1197–1204 (2002). [CrossRef]
30. A. Bogris, D. Kanakidis, A. Argyris, and D. Syvridis, "Performance characterization of a closed-loop chaotic communication system including fiber transmission in dispersion shifted fibers," IEEE J. Quantum Electron. 40(9), 1326–1336 (2004). [CrossRef]
31. A. Bogris, A. Argyris, and D. Syvridis, "Encryption efficiency analysis of chaotic communication systems based on photonic integrated chaotic circuits," IEEE J. Quantum Electron. 46(10), 1421–1429 (2010). [CrossRef]
M. Sciamanna and K. A. Shore, "Physics and applications of laser diode chaos," Nat. Photonics 9(3), 151–162 (2015).
A. Argyris, D. Syvridis, L. Larger, V. Annovazzi-Lodi, P. Colet, I. Fischer, J. García-Ojalvo, C. R. Mirasso, L. Pesquera, and K. A. Shore, "Chaos-based communications at high bit rates using commercial fibre-optic links," Nature 438(7066), 343–346 (2005).
N. Li, H. Susanto, B. Cemlyn, I. D. Henning, and M. J. Adams, "Secure communication systems based on chaos in optically pumped spin-VCSELs," Opt. Lett. 42(17), 3494–3497 (2017).
J. Ke, L. Yi, G. Xia, and W. Hu, "Chaotic optical communications over 100-km fiber transmission at 30-Gb/s bit rate," Opt. Lett. 43(6), 1323–1326 (2018).
C. Xue, N. Jiang, Y. Lv, C. Wang, G. Li, S. Lin, and K. Qiu, "Security-enhanced chaos communication with time-delay signature suppression and phase encryption," Opt. Lett. 41(16), 3690–3693 (2016).
P. Li, J. G. Wu, Z. M. Wu, X. D. Lin, D. Deng, Y. R. Liu, and G. Q. Xia, "Bidirectional chaos communication between two outer semiconductor lasers coupled mutually with a central semiconductor laser," Opt. Express 19(24), 23921–23931 (2011).
X. F. Li, W. Pan, B. Luo, and D. Ma, "Mismatch robustness and security of chaotic optical communications based on injection-locking chaos synchronization," IEEE J. Quantum Electron. 42(9), 953–960 (2006).
J. Ohtsubo, "Chaos synchronization and chaotic signal masking in semiconductor lasers with optical feedback," IEEE J. Quantum Electron. 38(9), 1141–1154 (2002).
A. B. Wang, Y. C. Wang, Y. B. Yang, M. J. Zhang, H. Xu, and B. J. Wang, "Generation of flat-spectrum wideband chaos by fiber ring resonator," Appl. Phys. Lett. 102(3), 031112 (2013).
S. Y. Xiang, W. Pan, B. Luo, L. S. Yan, X. H. Zou, N. Li, and H. N. Zhu, "Wideband unpredictability-enhanced chaotic semiconductor lasers with dual-chaotic optical injections," IEEE J. Quantum Electron. 48(8), 1069–1076 (2012).
J. G. Wu, G. Q. Xia, and Z. M. Wu, "Suppression of time delay signatures of chaotic output in a semiconductor laser with double optical feedback," Opt. Express 17(22), 20124–20133 (2009).
Z. Q. Zhong, Z. M. Wu, and G. Q. Xia, "Experimental investigation on the time-delay signature of chaotic output from a 1550nm VCSEL subject to FBG feedback," Photon. Res. 5(1), 6–10 (2017).
S. S. Li, Q. Liu, and S. C. Chan, "Distributed feedbacks for time-delay signature suppression of chaos generated from a semiconductor laser," IEEE Photonics J. 4(5), 1930–1935 (2012).
S. L. Yan, "Enhancement of chaotic carrier bandwidth in a semiconductor laser transmitter using self-phase modulation in an optical fiber external round cavity," Chin. Sci. Bull. 55(11), 1007–1012 (2010).
A. Wang, Y. Yang, B. Wang, B. Zhang, L. Li, and Y. Wang, "Generation of wideband chaos with suppressed time-delay signature by delayed self-interference," Opt. Express 21(7), 8701–8710 (2013).
S. Y. Xiang, A. J. Wen, W. Pan, L. Lin, H. Zhang, H. Zhang, X. Guo, and J. Li, "Suppression of chaos time delay signature in a ring network consisting of three semiconductor lasers coupled with heterogeneous delays," J. Lightwave Technol. 34(18), 4221–4227 (2016).
C. H. Cheng, Y. C. Chen, and F. Y. Lin, "Chaos time delay signature suppression and bandwidth enhancement by electrical heterodyning," Opt. Express 23(3), 2308–2319 (2015).
Y. H. Hong, P. S. Spencer, and K. A. Shore, "Wideband chaos with time-delay concealment in vertical-cavity surface-emitting lasers with optical feedback and injection," IEEE J. Quantum Electron. 50(4), 236–242 (2014).
N. Jiang, C. Wang, C. Xue, G. Li, S. Lin, and K. Qiu, "Generation of flat wideband chaos with suppressed time delay signature by using optical time lens," Opt. Express 25(13), 14359–14367 (2017).
M. Cheng, L. Deng, H. Li, and D. Liu, "Enhanced secure strategy for electro-optic chaotic systems with delayed dynamics by using fractional Fourier transformation," Opt. Express 22(5), 5241–5251 (2014).
D. Kanakidis, A. Argyris, A. Bogris, and D. Syvridis, "Influence of the decoding process on the performance of chaos encrypted optical communication systems," J. Lightwave Technol. 24(1), 335–341 (2006).
R. Lang and K. Kobayashi, "External optical feedback effects on semiconductor injection laser properties," IEEE J. Quantum Electron. 16(3), 347–355 (1980).
N. Jiang, C. Zhang, and K. Qiu, "Secure passive optical network based on chaos synchronization," Opt. Lett. 37(21), 4501–4503 (2012).
F. Y. Lin and J. M. Liu, "Nonlinear dynamical characteristics of an optically-injected semiconductor laser subject to optoelectronic feedback," Opt. Commun. 221(1–3), 173–180 (2003).
N. Li, W. Pan, A. Locquet, and D. S. Citrin, "Time-delay concealment and complexity enhancement of an external-cavity laser through optical injection," Opt. Lett. 40(19), 4416–4419 (2015).
N. Jiang, C. P. Xue, Y. X. Lv, and K. Qiu, "Physical enhanced secure communication based on wavelength division multiplexing chaos synchronization of multimode semiconductor lasers," Nonlinear Dyn. 86(3), 1937–1949 (2016).
A. Bogris, P. Rizomiliotis, K. E. Chlouverakis, A. Argyris, and D. Syvridis, "Feedback phase in optically generated chaos: a secret key for cryptographic application," IEEE J. Quantum Electron. 44(2), 119–124 (2008).
A. Murakami, "Phase locking and chaos synchronization in injection-locked semiconductor lasers," IEEE J. Quantum Electron. 39(3), 438–447 (2003).
R. Vincente, T. Perez, and C. R. Mirasso, "Open-versus closed-loop performance of synchronized chaotic external-cavity semiconductor lasers," IEEE J. Quantum Electron. 38(9), 1197–1204 (2002).
A. Bogris, D. Kanakidis, A. Argyris, and D. Syvridis, "Performance characterization of a closed-loop chaotic communication system including fiber transmission in dispersion shifted fibers," IEEE J. Quantum Electron. 40(9), 1326–1336 (2004).
A. Bogris, A. Argyris, and D. Syvridis, "Encryption efficiency analysis of chaotic communication systems based on photonic integrated chaotic circuits," IEEE J. Quantum Electron. 46(10), 1421–1429 (2010).
Adams, M. J.
Annovazzi-Lodi, V.
Argyris, A.
Bogris, A.
Cemlyn, B.
Chan, S. C.
Chen, Y. C.
Cheng, C. H.
Cheng, M.
Chlouverakis, K. E.
Citrin, D. S.
Colet, P.
Deng, D.
Deng, L.
Fischer, I.
García-Ojalvo, J.
Guo, X.
Henning, I. D.
Hong, Y. H.
Hu, W.
Jiang, N.
Kanakidis, D.
Ke, J.
Lang, R.
Larger, L.
Li, G.
Li, H.
Li, N.
Li, P.
Li, S. S.
Li, X. F.
Lin, F. Y.
Lin, S.
Lin, X. D.
Liu, D.
Liu, J. M.
Liu, Q.
Liu, Y. R.
Locquet, A.
Luo, B.
Lv, Y.
Lv, Y. X.
Ma, D.
Mirasso, C. R.
Murakami, A.
Ohtsubo, J.
Pan, W.
Perez, T.
Pesquera, L.
Qiu, K.
Rizomiliotis, P.
Sciamanna, M.
Shore, K. A.
Spencer, P. S.
Susanto, H.
Syvridis, D.
Vincente, R.
Wang, A.
Wang, A. B.
Wang, B.
Wang, B. J.
Wang, C.
Wang, Y. C.
Wen, A. J.
Wu, J. G.
Wu, Z. M.
Xia, G.
Xia, G. Q.
Xiang, S. Y.
Xue, C.
Xue, C. P.
Yan, L. S.
Yan, S. L.
Yang, Y.
Yang, Y. B.
Yi, L.
Zhang, B.
Zhang, C.
Zhang, H.
Zhang, M. J.
Zhong, Z. Q.
Zhu, H. N.
Zou, X. H.
Chin. Sci. Bull. (1)
IEEE J. Quantum Electron. (10)
IEEE Photonics J. (1)
Nonlinear Dyn. (1)
Opt. Commun. (1)
(1) d E d ( t ) d t = 1 2 ( 1 + i α ) ( G d ( t ) − 1 τ p ) E d ( t ) + k d E d ( t − τ d ) exp ( − i ω d τ d ) + 2 β N d ( t ) χ d ( t ) ,
(2) d N d ( t ) d t = I d e − N d ( t ) τ e − G d ( t ) | E d ( t ) | 2 .
(3) d E m , s ( t ) d t = 1 2 ( 1 + i α ) ( G m , s ( t ) − 1 τ p ) E m , s ( t ) + k f E m , s ( t − τ f ) exp ( − i ω m , s τ f ) exp ( i ϕ P M ( t ) ) + σ E m ( t − τ i ) exp ( − i ω m τ i ) exp ( i Δ ω t ) + 2 β N m , s ( t ) χ m , s ( t ) ,
(4) d N m , s ( t ) d t = I m , s e − N m , s ( t ) τ e − G m , s ( t ) | E m , s ( t ) | 2 .
(5) G d , m , s ( t ) = g ( N d , m , s ( t ) − N 0 ) 1 + ε | E d , m , s ( t ) | 2
(6) ϕ P M ( t ) = A ⋅ Ν [ | E d ( t - Δ t d ) | 2 ] V π ⋅ π
(7) Ν ( x ) = x − x min x m a x − x min
(8) A ( Δ t ) = 〈 ( I ( t + Δ t ) ) − 〈 I ( t + Δ t ) 〉 ) ⋅ ( I ( t ) − 〈 I ( t ) 〉 ) 〉 ( 〈 ( I ( t + Δ t ) − 〈 I ( t + Δ t ) 〉 ) 2 〉 ⋅ 〈 ( I ( t ) − 〈 I ( t ) 〉 ) 2 〉 ) 1 / 2 ,
(9) C ( Δ t ) = 〈 ( I m ( t + Δ t ) ) − 〈 I m ( t + Δ t ) 〉 ) ⋅ ( I s ( t ) − 〈 I s ( t ) 〉 ) 〉 ( 〈 ( I m ( t + Δ t ) − 〈 I m ( t + Δ t ) 〉 ) 2 〉 ⋅ 〈 ( I s ( t ) − 〈 I s ( t ) 〉 ) 2 〉 ) 1 / 2
(10) Q = < I 1 > − < I 0 > ε 1 + ε 0


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(ERGO) – In a remote village 50km north of the central Somali town of Dhusamareb town, Ali Abdikadir, a medical officer, is going to people's homes trying to control an outbreak of diarrhoea.
Since the closure last March of the health centre in Hananbur, after funding from the NGOSWISSO-KALMO ended, Abdikadir is providing the only available health service for this village of around 1,500 people.
With the assistance of a young boy, who helps carry his equipment, Ali walks door to door every morning armed with him sachets of oral rehydration solution sachets and drips to treat the sick people he encounters.
"I have no option but to move around as the health post in the village is not operating. The diarrhea outbreak is spreading fast so we need to move quickly to reduce its impact," Abdikadir told Radio Ergo.
Abdikadir said one person died in the village last week and 13 people are infected. He successfully treated another 10 patients.
"The area is very hot and has no clean water and these might be the factors leading to the spread of diarrhea," he said.
Abdikadirbuys medicines from Dhusamareb. Most of the patients are unable to pay for treatment immediately so he waits for them to pay when the can.
For patients he is unable to treat, Abdikadir refers them to the nearest towns of Dhusamareb or Adado.
HabibaDiriyehad to hire a vehicle to take five of her sick children to the hospital. Speaking to Radio Ergo from Dhusamarab, she said she had spent $250 on the children's treatment and now had to find means to return to the village.
The village has also been facing measles cases since December last year.
Fadumo Abdullahi, 55, told Radio Ergo eight of her children have been treated by Abdikadir for diarrhea this week.
Fadumo, who runs a tea kiosk, said she could not have afforded to take them to hospital.
"He helped us a lot because if it wasn't for him, we could not take the children to a hospital due to financial problems. In this village we have no hospital, so he treats my children," said Faduma.


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Excel Dryer Touts Virus Filtration, Donates Mobile Units
May 19, 2020 May 18, 2020 Joseph Bednar 230 Views Donates, Excel Dryer, Mobile Units, Virus Filtration, XLERATOR
Drying Times
By Joseph Bednar
When it comes to the XLERATOR, his company's signature hand dryer, filtration is nothing new, Bill Gagnon said.
"We've had an optional HEPA filtration system in it for years," said Gagnon, vice president of Excel Dryer in East Longmeadow. "The typical HEPA filtration test you do is performed with bacteria, and it's to particle sizes of .3 microns or larger. That's standard in the industry. We've done that test; we already had it."
One of the mobile units being delivered to the front lines of the COVID-19 fight.
But coronavirus isn't bacterial, as its name makes clear. And its typical particle size is around 120 nanometers, or 0.12 microns — much smaller than the bacterial particles the filter had already been tested for.
"When we heard about coronavirus, we wanted to get ahead of this and wanted to test our product and its effectiveness against viruses, so we sent our product to our testing laboratory partner in Minnesota and said we want to do a virus-specific test," Gagnon explained, adding that the lab put some 380 million virus particles through the system, "and basically zero came out the other end."
Well, not exactly zero, but pretty darn close; the dryer's filter lets through about one in 100,000 particles.
"This test shows our HEPA filtration system can filter [the virus] out of the airstream and gives the public assurance that it's safe to use hand dryers — because it is," Gagnon told HCN. "Hand dryers are a hygienic way to dry your hands. This was something we wanted to test for — something we thought was important."
On May 6, Excel Dryer hosted U.S. Rep. Richard Neal and local media to tour the company's manufacturing facility and tout the XLERATOR's virus-filtration capabilities — and an ongoing donation of 100 units, with HEPA filtration systems, to first responders and COVID-19 testing sites across the state.
"Talk about innovation and creativity — they established it," Neal said of Gagnon and his father, Excel President Denis Gagnon, who invented the popular XLERATOR. "These are 52 domestic manufacturing jobs to compete with supply chains all over the world. If we've learned one lesson from a pandemic, it's that relying on other parts of the world for our products and supplies is not a great idea."
Neal and his aide, William Tranghese, were involved in early discussions establishing Excel Dryer as an essential manufacturer in Massachusetts, making hand dryers that play a critical role in achieving proper hand hygiene. After all, thoroughly washing and completely drying hands are listed as the top defense against the spread of germs — including the novel coronavirus, which causes COVID-19 — by both the World Health Organization and the Centers for Disease Control and Prevention.
"Proper hand hygiene isn't just washing your hands, it's completely drying your hands," Denis Gagnon said following the factory tour. "When we originally added the HEPA filter as an option to the XLERATOR, we tested for bacteria. Because of the COVID outbreak, we retested the HEPA filter for its ability to filter viruses, and it literally filters 99.999% of viruses. So I think there's going to be healthy demand for HEPA-filter XLERATORs going forward."
Bending the Curve
Neal — who, like the Gagnons, Excel's employees, and guests, wore a face mask during his visit to the plant — touted hand washing as well, and said it's among the now-common practices, including social distancing, that are flattening the viral curve in Massachusetts.
U.S. Rep. Richard Neal (second from left) gets a factory tour with Excel Dryer's Denis Gagnon, Nancy Gagnon, and Bill Gagnon.
"The CDC and the WHO have all talked about the notion of hand hygiene, how important it is. I think we've seen in Massachusetts the curve beginning to bend," the congressman noted. "The stabilization — and a little bit of a decline — have had much to do with, I think, adhering to the recommendations of professional health people."
He particularly praised Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, as "the most reliable voice in America" on coronavirus and related matters. "Whenever I've received an invitation over these years in Washington to an event where he was the speaker, I went to hear what he had to say."
"If we've learned one lesson from a pandemic, it's that relying on other parts of the world for our products and supplies is not a great idea."
As for the COVID-19 progression, "there is some good news, but there is a ways to go," Neal went on. "Hot spots seem to be declining in the larger urban areas, but they seem to be moving to new places. So while we have better news in Boston, New York, and even here in Western Massachusetts, other areas of the country are likely to go through the outbreak that we've all witnessed here."
And if Excel can play a part in slowing the spread, all the better, Denis Gagnon said.
"We very much pride ourselves on making our product here in the United States," he noted. "It didn't take the inconvenience of disrupted supply chains to bring it back. We never wanted it to leave in the first place. As far as being a good corporate citizen, it's in our blood. We're happy to help in any way we can. This was kind of an impromptu solution, and I think it's going to help on the front lines."
Indeed, the 100 donated mobile units are already being shipped out, Bill Gagnon said, to police and fire facilities, testing sites, and places like the first-responder recovery center being operated by the Hampden County Sheriff's Office.
"If they test positive, they don't want to bring it home, so they get quality food and bedding and a place to get healthy and stay away from their families," he explained. "We're donating units there. We're just trying to find out where they'll make the biggest impact."
While the HEPA filters on the dryers are not new, the mobile units are. They came out of a conversation the Gagnons had with Neal and his staff about whether Excel's work is considered essential.
"In that conversation, I was talking about getting mobile units out to the front lines," Bill said, explaining that the company's stainless-steel supplier had built a wall to show off the product in a trade show booth. "They said, 'we can re-engineer that to be mobile, and we can get this thing out in the field.' Two days later, the prototype was created, and they drove it up here and dropped it off — it was amazing. Two weeks later, we had the first units being used out in the field.
"So it was an amazing new product innovation," he continued, "and we were working with the congressman's office and just trying to figure out, how can we help? How can we get this virus-filtering hand-hygiene solution into these facilities? And now it's here, and there's a lot of interest in it, and we think it can make a big difference."
After all, he explained, while experts like the CDC and Fauci tout proper hand hygiene as the best defense against the spread of germs, it's important to not forget the role of complete drying as well.
"Everyone talks about washing your hands for 20 seconds, but nobody talks about drying your hands," Bill said. "You have to completely dry them. Wet hands are 1,000 times more susceptible to pick up or transfer germs. Drying hands is critical."
Essentially Speaking
So are Excel's operations, even in the midst of an economic shutdown, he added.
"We were in the same situation of a lot of other small businesses; when the federal guidelines came out and it was up to the states to put out their guidances, there were a lot of general categories" for what constitutes an essential service during the pandemic, he explained.
Excel seemed to fit multiple categories, Bill told HCN; not only is hygiene important during a viral outbreak, but the company has contracts with the federal government to supply its product, which can boost a company's chances to be deemed essential.
"There's critical manufacturing, but for us, we're such a niche market, no one calls out hand dryers specifically," he went on. "But we felt like we fit under multiple categories, and that's why we reached out to Congressman Neal's office. We wanted to do everything we could to make sure we we're doing the right thing, and they helped us with that. And when the state of Massachusetts put out their second round, a revision to the essential-services list, hygiene actually had its own category … and we're certainly a critical part of that. So, yes, absolutely, we're essential."
And part of a mobile hand-drying solution that promises to reduce the spread of infection, Neal said. "There are simple things we can do in life to get through this, and they are going to be very important to us going forward."
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redpajama_set_name: RedPajamaCommonCrawl


Anba Markos, Metropolitan of Shubral-Kheima, Cairo, who is currently on a three-week pastoral visit to Riyadh, has been granted the Shield of Gratitude by Secretary-General of the Arab Festival of Tourist Information in the Kingdom of Saudi Arabia, Muhammed al-Amer. Mr Amer warmly welcomed Anba Markos in his "second home: Saudi Arabia".
For his part, Anba Markos expressed happiness at being in Riyadh, and thanked officials of the Saudi government and the Egyptian Embassy in Riyadh for the genuine brotherly love and warm reception they have given him.
Anba Markos is in Riyadh upon invitation by Crown Prince Mohammed Bin Salman, for a three-week pastoral visit which concludes on 17 December. During his visit, Anba Marcos held the first Coptic Mass in the Saudi Arabian capital, at the home of a Coptic worker in Riyadh. Mass was performed on a holy board which Anba Markos had brought with him from Cairo to use as an altar.
While in Riyadh, the Metropolitan met Mohammed al-Issa, Secretary-General of the Muslim World League. Attending were members of the Egyptian embassy in Riyadh. The Saudi-based MWL was for decades charged with spreading the strict Wahhabi school of Islam around the world, but Sheikh Issa recently said that those times were over and that his focus now aimed at annihilating extremist ideology.


text:
Rebecca Jarvis was named ABC News Chief Business and Economics Correspondent in April 2013. Deeply knowledgeable about financial news, she files reports for all ABC News programs and platforms, including "Good Morning America," "World News Tonight with David Muir" and "Nightline."
Before joining ABC News, Jarvis was co-host of "CBS This Morning: Saturday," Business and Economics correspondent for CBS News, and the founder, host and managing editor of "The Startup with Rebecca Jarvis" on CBSNews.com. She conducted wide-ranging interviews with the biggest names in business, including mega-investor Warren Buffett, Facebook's Sheryl Sandberg, Twitter founder Jack Dorsey, former Federal Reserve Chair Paul Volcker and Lloyd Blankfein from Goldman Sachs. In addition she covered the European debt crisis, the General Motors bankruptcy and the 2012 Presidential elections.
Prior to CBS News, Jarvis spent three years at CNBC reporting on market news from the New York Stock Exchange, NASDAQ and the New York Mercantile Exchange. She also contributed to MSNBC and NBC News, covering a range of stories from the Madoff scandal to the financial crisis, the collapse of Bear Stearns, Lehman Brothers and the sale of Merrill Lynch.
Jarvis began her journalism career writing for numerous publications, including Crain's Chicago Business and Business 2.0. She also has worked in investment banking and foreign currency trading.
A graduate from the University of Chicago, she holds a degree in economics and Constitutional law. A recipient of the University of Chicago Dean's Grant, she studied European banking and financial markets and the formation of the European Union at the Université Sciences Po in Paris, France.
Jarvis has received national recognition for her work with Colin Powell to empower children and improve communities. In 2000 she was named "One of Twenty Teens Who Will Change the World" by Teen People magazine and also named a "National Point of Light," receiving accolades from Presidents Bill Clinton and George H.W. Bush.


text:
Current: The Gaza Flotillas to Come: Some Ground Rules before Setting Out
The Gaza Flotillas to Come: Some Ground Rules before Setting Out
Amb. Alan Baker, June 5, 2011
Filed under: Hamas, International Law, Palestinians
Gaza Flotilla, hamas, international law, Israeli-Palestinian Conflict
Vol. 11, No. 3 June 5, 2011
An ostensibly civilian, humanitarian flotilla was employed in May 2010 to demonstratively breach the Israeli naval blockade of the Gaza coast. This flotilla was organized by the Turkish IHH, which has extensive links to extreme Islamic terror groups. Provoking a confrontation with Israel continues to be the primary aim.
Since May 2010, the Israeli government has altered the manner in which it administers the limitations on the transfer of goods to Gaza. It now specifically prohibits only those materials that might be taken and directed by Hamas and other terror groups in furtherance of their hostile purposes.
There is no humanitarian emergency among the civilian population in Gaza, and hence there can be no justification for conveying emergency shipments intended to alleviate an emergency that clearly does not exist. Any genuine wish to provide materials to the Gaza population can be directed through Israeli ports and the relevant authorities.
Hamas routinely fires missiles randomly at Israeli civilian targets. Thus a situation of ongoing armed conflict exists between Hamas and Israel, which has the prerogative to institute a naval and land blockade to prevent the introduction of weapons and materials that could serve belligerent purposes. Such a blockade is well established in international law and practice.
It is internationally accepted that any attempt to breach such a blockade may be prevented by Israeli naval patrols. Such a process may take place outside the area of the blockade if the declared intention of the flotilla is to violate the blockade. Furthermore, any vessel refusing to respond to the demands of the naval forces may be stopped forcefully.
Aiming to Provoke a Confrontation
Since the May 2010 wave of "flotillas" organized by Turkish and other groups, ostensibly conveying cargoes of vital and indispensible aid intended to reach the population of Gaza, much has been written and televised as to the real intentions of the organizers. Additionally, several enquiries have been instituted in order to analyze the legal, military, and other aspects of the flotilla affair and the way it was handled.
What seems to have been made very clear by the groups that organized the flotilla, especially the Turkish-led IHH terror-related organization, is the fact that the use of an ostensibly civilian, humanitarian flotilla and a huge PR campaign in order to demonstratively breach the Israeli naval blockade of the Gaza coast and thereby challenge Israel's policy regarding the Gaza Strip and provoke a confrontation with Israel, was clearly and continues to be the primary aim.
Conveying humanitarian goods to what was represented as a distressed Gaza population was a minor, secondary, and perhaps even incidental aim, at least among the most vocal participants in the flotilla, although there were indeed some who participated out of a bona fide belief in the importance of identifying themselves with, and trying to alleviate what they genuinely thought to be, a humanitarian crisis among the residents of Gaza.
The regrettable outcome of the May 2010 flotilla and the extensive international echo that still reverberates throughout the international community have nevertheless brought about a series of changes in the "situation on the ground."
The logic and aim of Israel's blockade is to prevent the Hamas terror organization presently administering Gaza from acquiring arms, ammunition, and other supplies that could contribute to hostile activities against Israel. Since May 2010, the Israeli government has altered the manner in which it administers the limitations on the transfer of goods to Gaza. It now specifically prohibits only those materials that might be taken and directed by Hamas and other terror groups in furtherance of their hostile purposes.
Furthermore, since the May 2010 flotilla incident and in light of the considerable publicity that has been given to the daily flow of goods and supplies into the Gaza Strip, it has become very clear to all that there is no humanitarian crisis in Gaza and all essential and other provisions are available to all residents.
On the other hand, the practical military and tactical implications and lessons of the May 2010 flotilla have been learned by Israel's military forces and the appropriate conclusions as to how to handle future flotillas have been reached and put into place.
Some Basic Facts
In light of these significant changes in the situation on the ground, one may wonder on what basis could future planned flotillas be justified and, in a similar vein, what might be the real intentions and motives of the organizers who are busy preparing the next flotilla touted for June 2011.
In this context, it might be pertinent to review some of the basic ground rules surrounding the flotilla phenomenon:
It is widely acknowledged that there is no humanitarian emergency among the civilian population in Gaza. Hence there can be no justification for conveying emergency shipments intended to alleviate an emergency that clearly does not exist. Most materials and foodstuffs are permitted to enter Gaza after examination by the Israeli authorities in order to prevent tactical materials from reaching Hamas and other terror groups. Any genuine wish to provide materials to the Gaza population can be directed through Israeli ports and the relevant authorities.
It is widely acknowledged that Gaza is independently administered by an internationally regarded terror organization – Hamas – that is sponsored and supplied with arms by Iran and that maintains an ongoing and actively hostile attitude towards Israel. The territory also serves as host to other terror groups such as the Islamic Jihad. Practically speaking, this hostility takes the form of incitement to terror through all levels of the population by all means of publicity – in kindergartens, schools, colleges, on the radio and television, and through the web. It involves the smuggling into the area and stockpiling of missiles, guns, and ammunition for use against Israel and its civilian population and the routine firing of such missiles randomly at Israeli civilian targets.
It is widely acknowledged that Israel does not hold the status of an "occupying power" in Gaza. In fact, Israel transferred its civilian powers and responsibilities over the Gaza Strip into the hands of the Palestinian Authority and withdrew its forces and civilians. The Palestinian Authority's control in Gaza was later usurped by Hamas, which turned the area into a base for mounting terror attacks against Israel.
Since such a terror organization is in sole and effective control of Gaza and directs ongoing and active hostilities against Israel and its civilians, it is widely acknowledged that a situation of ongoing armed conflict exists between Hamas, its associates, and Israel. In such a situation of armed conflict, Israel has the prerogative to institute a naval and land blockade with a view to prevent the introduction of weapons and materials that could serve the belligerent purposes of Hamas. The institution of such a blockade is well established in international law and practice.
It is internationally acknowledged that a naval blockade in such a situation, once instituted and maintained in accordance with the rules of international law with the appropriate public notification as to the area of sea that it covers, effective enforcement, impartiality and consideration of humanitarian needs of the population, is fully in accordance with accepted international law and practice.
Similarly, it is internationally accepted that any attempt to breach such a blockade by civilian or other vessels may be prevented by Israeli naval patrols, and the vessels involved may be stopped, searched, and sent to an Israeli port in order to check their cargoes. Such a process may take place outside the area of the blockade if the declared intention of the flotilla is to violate the blockade. Furthermore, any vessel refusing to respond to the demands of the naval forces may be stopped forcefully.
In light of all the above, there is good reason to assume that the instigators of the planned flotilla intending to set sail for Gaza in June 2011 would be hard put to justify themselves other than by admitting their real character and motives as a provocative and political demonstration.
Sponsorship, organization, and presence on such flotillas by terror organizations or their activists disguised as humanitarian groups will no longer deceive an international community which witnessed the May 2010 flotilla, the premeditated violence of its organizers, and the regrettable and tragic outcome.
While such demonstrations may well take place if only for their PR value, they will have to abide by internationally accepted rules and prove their bona fide nature in order to be considered as genuine.
Amb. Alan Baker, Director of the Institute for Contemporary Affairs at the Jerusalem Center for Public Affairs, is former Legal Adviser to Israel's Foreign Ministry and former Ambassador of Israel to Canada.
Iran and the Death of Palestinian Islamic Jihad (PIJ) Leaders


text:
Evaluation of Taiwan's Ma Ying-jeou
Taiwan's president, Ma Ying-jeou, has been in office for one year. After his first hundred days, he was criticized for not immediately turning Taiwan's economy around, as he had promised during the presidential campaign.
When Ma orchestrated a warming of cross strait relationship that led to signing a number of economic cooperation including the direct flight from the mainland to bring in tourists, he was immediately criticized for failing to attract 3000 tourists per day to Taiwan. This year, Taiwan is receiving the full daily quota of tourists from the mainland, the local economy is beginning to warm and discussion is now directed toward possible direct investment from the mainland.
Rather than giving any credit for the positive outcome by his administration, extreme pan green supporters are accusing Ma of prosecutorial persecution of Chen Shui Bian. Even though he has steadfastly stayed away from interfering with the judiciary process underway to examine the full extent of Chen's economic crime against the people of Taiwan, Chen's supporters accused him for doing so anyway.
Recently, I attended a conference at Stanford on state of the cross strait relations. The presenters and discussants were uniformedly courteous and genteel. None saw fit to point out Chen's singularly pivotal role in destroying Taiwan's economy during his eight year reign.
"It's the economy, stupid" has been the mantra that governed the success or failure of the last three U.S. president, including the current Obama Administration, but somehow this measure of a leader's effectiveness never applied to Chen.
Since the beginning of 2009, the Taiwan stock market has bounced back by 50%, the strongest recovery in Asia. The Stanford conference took little note and did not even speculate on whether Taiwan's economic recovery and its dependence on cooperation with the mainland will alter the dynamics of the question of independence vs. reunification vs. status quo.
For more information, a recent review of Ma's first year as president published by a major daily in Taiwan and is available in English.
Posted by George at 11:56 AM 1 comment:
America Remembers Tiananmen with "Humanitarian" Racism
In the West, "June 4" has become a shorthand reminder of the weeks of student-led protests that culminated in the tragic confrontation with China's People's Liberation Army ending on Beijing's Tiananmen Square in 1989.
While the bloody images from the streets of Beijing have seared the minds of America's TV audience, liusi, June 4 in Mandarin, is a distant memory inside China--so much has happened in the intervening 20 years that transformed China into an economic superpower.
An ironic and curious American reminder of the drama on Tiananmen Square can be found in the little known "The Chinese Student Protection Act" enacted in 1992 and an even more obscure provision in this Act.
Authored by then second-term Congresswoman Nancy Pelosi of San Francisco, the legislation was to provide a safe harbor by giving the Chinese students in the U.S., some of whom demonstrated in sympathy with their colleagues in China, the opportunity to apply for immediate permanent residency in America.
America has a long generous tradition toward people being persecuted by their own government by offering them asylum and the opportunity to build new lives in the U.S. Eastern Europeans in the 1950s, Cubans after Castro's 1959 revolution, and boat people from Southeast Asia and Soviet Jews in the 1970s are among those that come to mind.
Pelosi's student protection act took three years to get through Congress. The backroom dealings apparently necessitated charging the 55,000 green cards slots needed by the students as an "advance" against future quotas of employment-based green card applications made on behalf of Chinese professionals that American companies wanted to hire.
The purpose of employment-based green cards is to allow American companies to hold onto foreign professional talent and keep them in the U.S. This provision is motivated by national self-interest and has nothing to do with humanitarian action. Indeed, the success of Silicon Valley has been due to the foreign talent we have been able to attract and keep as they start new companies and create jobs.
There was no logical reason or justification to tie a humanitarian act to our ability to employ skilled immigrants from the same country. The case involving students from China was unique.
Every year the U.S. grants a maximum of 140,000 green cards to highly skilled foreign professional workers, not more than 9800 from any one country. In fact, the 9800 slots from any one country of origin are rarely all given away except for China and India; in these cases, there are always more highly qualified applicants waiting to get their green cards than available slots. Chinese professionals being sponsored for green cards typically earned advanced degrees from American universities in the sciences, medicine and engineering.
America's biggest sources of highly trained talent, needed to keep our companies on the leading edge, naturally come from the two countries with the largest population. (One can, of course, argue whether it makes sense to use the same fixed quota for China and India as for other much smaller countries.)
In the case with China, the quota is made even more restrictive because the Student Protection Act took away 1000 slots from China every year until all 55,000 have been offset. It will be another 14 years before the green cards for students have been "paid back."
Consequently, there is a log jam of Chinese with advanced degrees waiting for permanent residency in the US. Because of the offset, the average wait for a Chinese applying for a green card is over three years longer than for any other nationality.
Does it make any sense to make it harder for the professionals we want to keep, to stay in America? China's economy is on the ascendancy while ours is heading in the opposite direction. Why are we encouraging them to consider taking their talents back to China—or even Canada?
Chinese immigrants have had to face a history of exclusionary discrimination in order to live in America. This obscure provision of the Student Protection Act, which came to light only recently, seems rooted in the same racist mindset.
A group of Chinese professionals in America waiting for their green cards has formed the Legal Immigrant Association to ask Congress to repeal this discriminatory provision of the Chinese Student Protection Act. They are also seeking support from Chinese American communities.
With two prominent Chinese Americans serving in President Obama's cabinet, it should not be necessary to remind the people of America and members of Congress of the many contributions Chinese Americans have made in America.
This should be the right time to strike another racially discriminatory statute against the Chinese from our laws.
Posted by George at 5:57 PM 12 comments:
Labels: American politics, Chinese American Issues, U.S. China relations
America Remembers Tiananmen with "Humanitarian" Ra...


text:
Q: SQLDataSource DeleteCommand to get parameters I am having some problems passing parameters to a DELETE command, and cant seem to get a good understanding on how it works.
<asp:SqlDataSource ID="sdsPropertyList"
    runat="server"
    ProviderName="<%$ appSettings:ProviderName %>"
    ConnectionString="<%$ appSettings:ConnectionString %>"
    SelectCommand="selPropertyByAcntID"
    SelectCommandType="StoredProcedure"
    OnSelecting="sdsPropertyList_Selecting"
    OnSelected="sdsPropertyList_Selected"
    DeleteCommand="delPropertyByPropID"
    DeleteCommandType="StoredProcedure"
    OnDeleting="sdsPropertyList_Deleting"
    OnDeleted="sdsPropertyList_Deleted">
    <SelectParameters>
        <asp:Parameter Name="in_acntID" Type="Int32" DefaultValue="0" />
    </SelectParameters>
    <DeleteParameters>
        <asp:Parameter Name="in_acntID" Type="Int32" DefaultValue="0" />
        <asp:Parameter Name="in_propID" Type="Int32" DefaultValue="0" />
    </DeleteParameters>
</asp:SqlDataSource>

<asp:GridView ID="gvProperty" runat="server" DataSourceID="sdsPropertyList"
    AutoGenerateColumns="false" CssClass="gvPropList">
    <Columns>
        <asp:BoundField HeaderText="ID" InsertVisible="true" DataField="prop_id" ReadOnly="true" Visible="False" />
        <asp:BoundField HeaderText="Property" DataField="prop_title"
            ItemStyle-CssClass="gvPropTitle" >
        <ItemStyle CssClass="gvPropTitle" />
        </asp:BoundField>
        <asp:BoundField HeaderText="Units" DataField="unitCount"
            ItemStyle-CssClass="gvUnitCount" >
        <ItemStyle CssClass="gvUnitCount" />
        </asp:BoundField>
        <asp:BoundField DataField="prop_lastmodified" HeaderText="Last Modified"
            ItemStyle-CssClass="gvDate" DataFormatString="{0:M/dd/yyyy hh:mm tt}" >
        <ItemStyle CssClass="gvDate" />
        </asp:BoundField>
        <asp:TemplateField>
            <ItemTemplate>
                <asp:LinkButton ID="lbtnEdit" runat="server" CommandName="EditRecord" Text="Edit" CommandArgument='<%# Eval("prop_id") %>'></asp:LinkButton>
                <asp:LinkButton ID="lbtnDelete" runat="server" CommandName="Delete" Text="Delete" CommandArgument='<%# Eval("prop_id") %>'></asp:LinkButton>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField>
            <ItemTemplate>
                <asp:LinkButton ID="lbtnAdd" runat="server" CommandName="AddRecord" Text="Add" CommandArgument='<%# Eval("prop_id") %>'></asp:LinkButton>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
    <HeaderStyle CssClass="headerPropList"/>
    <RowStyle CssClass="gvPropRow" />
</asp:GridView>

protected void sdsPropertyList_Selecting(object sender, SqlDataSourceSelectingEventArgs e)
    {
        int userID = Convert.ToInt32(Page.User.Identity.Name);
        if (userID != 0)
            e.Command.Parameters["in_acntID"].Value = userID;
    }

protected void sdsPropertyList_Deleting(object sender, SqlDataSourceCommandEventArgs e)
    {
        int userID = Convert.ToInt32(Page.User.Identity.Name);
        if (userID != 0)
        {
            e.Command.Parameters["in_acntID"].Value = userID;
        }
    }

The SELECT statement is straightforward which requires one input parameter of userID.
However, the DELETE statement, requires 2 parameter inputs.
in_acntID = userID
in_propID = the boundfield datafield prop_id
What am I doing wrong? and should the CommandName and CommandArgument be passed at the ItemTemplate level if I have it defined at the SqlDataSource level?
I want the delete button to achieve the following:

*

*delete records from table(s) in DB

*remove the row from the gridview

UPDATE
After some additional research, I've found that, the NAME for parameters and HeaderText for Boundfield must be the same so that the values within your gridview can be used by the SQL commands of the datasource.
With the exception of the initial select commant, i have removed all the code behind references.
All is working corrently now.

A: According to the MSDN documentation, you need to specify the DataKeyNames on the gridView:
"Use the DataKeyNames property to specify the field or fields that represent the primary key of the data source. You must set the DataKeyNames property in order for the automatic update and delete features of the GridView control to work. The values of these key fields are passed to the data source control in order to specify the row to update or delete."

A: e.g.   if the id was in a listbox or dropdown
<DeleteParameters>
               <asp:ControlParameter ControlID="controlname" Name="id" PropertyName="SelectedValue" Type="Int32" />
                    </DeleteParameters>

i have used the above successfully for deleting . this could work for textboxes or labels. If you are handling the event , why not just take the entire delete process to the even handler ? Specify the entire sql setup including connection , command execution there . This method has also worked for me .

A: After some additional research, I've found that, the NAME for parameters and HeaderText for Boundfield must be the same so that the values within your gridview can be used by the SQL commands of the datasource.
With the exception of the initial select commant, i have removed all the code behind references.
All is working corrently now.
<asp:SqlDataSource ID="sdsPropertyList"
    runat="server"
    ProviderName="<%$ appSettings:ProviderName %>"
    ConnectionString="<%$ appSettings:ConnectionString %>"
    SelectCommand="selPropertyByAcntID"
    SelectCommandType="StoredProcedure"
    OnSelecting="sdsPropertyList_Selecting"
    DeleteCommand="delPropertyByPropID"
    DeleteCommandType="StoredProcedure"
    OnDeleted="sdsPropertyList_Deleted" >
    <SelectParameters>
        <asp:Parameter Name="acnt_id" Type="Int32" />
    </SelectParameters>
    <DeleteParameters>
        <asp:Parameter Name="acnt_id" Type="Int32" />
        <asp:Parameter Name="prop_id" Type="Int32" />
    </DeleteParameters>
</asp:SqlDataSource>
<asp:GridView ID="gvProperty" runat="server" DataSourceID="sdsPropertyList"
    AutoGenerateColumns="false" CssClass="gvPropList" DataKeyNames="acnt_id, prop_id">
    <Columns>
        <asp:BoundField HeaderText="acnt_id" InsertVisible="true" DataField="acnt_id" ReadOnly="true" Visible="False" />
        <asp:BoundField HeaderText="prop_id" InsertVisible="true" DataField="prop_id" ReadOnly="true" Visible="False" />
        <asp:BoundField HeaderText="Property" DataField="prop_title">
        <ItemStyle CssClass="gvPropTitle" />
        </asp:BoundField>
        <asp:BoundField HeaderText="Units" DataField="unitCount" >
        <ItemStyle CssClass="gvUnitCount" />
        </asp:BoundField>
        <asp:BoundField DataField="prop_lastmodified" HeaderText="Last Modified"
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Brentford take on Blackburn in their final game of the Championship season on Sunday knowing that a win will guarantee a top 10 finish.
Rovers, meanwhile, know that defeat will likely condemn them to the third tier of English football for the first time since they finished as third division runners up in 1980, unless Nottingham Forest lose by more at home to Ipswich.
Even a Blackburn victory may not be enough, depending on what happens at Forest's game with the Tractor Boys as well as Birmingham's trip to Bristol City.
GetWestLondon takes a look at the three clubs in the relegation mire and their recent history with the Bees.
Since Brentford were promoted to the Championship they have only picked up three points against Blackburn twice; both times in the 2014/15 season.
Last season saw the Bees draw 1-1 at Ewood Park, with Marco Djuricin picking up an injury that wrecked his season, and then lose 1-0 at Griffin Park in March against the 10-men of Rovers.
This season saw the Bees return from Lancashire with nothing after losing 3-2 in a topsy turvy game.
Blackburn is also the longest journey of the three sides in the relegation mire for the club and with travel distance set to increase after Brighton's promotion.
Of the sides in the relegation mire, Brentford's recent record against Nottingham Forest has been the best.
The Bees have triumphed in five of their six meetings with the Tricky Trees and drawn the other, coming from 2-0 down on Easter Monday to rescue a point under now Forest boss Mark Warburton.
Were the two-time European Champions to stay up and Warburton to remain in charge, it would certainly lead to an interesting fixture when the two sides were to meet given how the manager's relationship with Matthew Benham completely collapsed in 2015.
Travel wise, Nottingham is the middle of the three and is either one train or heading straight up the M1.
Brentford have only beaten Birmingham once in the six times they have met since winning promotion to the Championship.
The Blues have come out on top in four of those meetings, all of them managed by Gary Rowett. The Bees rescued a 1-1 draw when Lee Clark was in charge and won 3-1 at St Andrews on January 2 when Birmingham had Gianfranco Zola in charge after Rowett's unfair sacking.
Birmingham is, though, the shortest journey for Bees fans who can head up the M40 or take one train from two London terminals.
Who would Brentford fans rather not face next season? Have your say in our poll below.
Who would you like to see relegated from the Championship?