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Issue 26,
pp. 26965-26977
•https://doi.org/10.1364/OE.18.026965
Study of different spectral regions and delay bandwidth relation in slow light photonic crystal waveguides
H. Kurt, K. Üstün, and L. Ayas
H. Kurt,* K. Üstün, and L. Ayas
Department of Electrical and Electronics Engineering TOBB University of Economics and Technology 06560, Turkey
*Corresponding author: hkurt@etu.edu.tr
H Kurt
K Üstün
L Ayas
H. Kurt, K. Üstün, and L. Ayas, "Study of different spectral regions and delay bandwidth relation in slow light photonic crystal waveguides," Opt. Express 18, 26965-26977 (2010)
Improvement of delay-bandwidth product in photonic crystal slow-light waveguides
Ran Hao, et al.
Novel slow light waveguide with controllable delay-bandwidth product and utra-low dispersion
Ultra slow light achievement in photonic crystals by merging coupled cavities with waveguides
Kadir Üstün, et al.
Photonic Crystals and Devices
Light matter interactions
Photonic crystal waveguides
Slow light
Slow light applications
Waveguide modes
Photonic crystal waveguides (130.5296)
Photonic crystals (160.5298)
Dispersion (260.2030)
Original Manuscript: August 30, 2010
Revised Manuscript: October 27, 2010
Manuscript Accepted: December 6, 2010
2. Slow light photonic crystal waveguide structure and frequency domain analysis
3. Time domain analysis of slow light propagation in photonic crystal waveguide
4. Optimization of figure of merit and loss analysis
Suppl. Mat. (1)
We investigate slow light propagation in monomode photonic crystal waveguides with different spectral features such as constant group index, high bandwidth and low group velocity dispersion. The form of the waveguide mode alters dramatically and spans three different spectral intervals by tuning the size of the boundary holes. Namely, slope of the band gap guided mode changes sign from negative to positive toward the Brillouin zone edge. In between there is a transition region where modes have nearly zero slopes. Maximum group index occurs at these turning points at the expense of high dispersion and narrow bandwidth. The apparent trade-off relationship between group index and bandwidth is revealed systematically. We show that as the radius of the innermost hole is increased above a certain value, the former one decreases and the latter one increases both exponentially but with a different ratio. The product of average group index and bandwidth is defined as a figure of merit which reaches up to a value of approximately 0.30 after a detailed parametric search. The findings of the frequency domain analysis obtained by plane wave expansion method are confirmed via finite-difference time-domain study.
©2010 Optical Society of America
Endeavoring to reduce the speed of light may seem to be against the high speed optical communication occurring at close proximity to the speed of light. However, in some circumstances it is imperative to manipulate the speed of light in a controlled manner. For example, nonlinear optics, optical memories, buffers, delay lines and electro- and magneto-optic effects may gain benefit from slow light phenomena due to enhanced light-matter interaction and spatial compression of optical pulses [1–6]. Consequently, the concept of tailoring the speed of light has been an intense research area. The approaches in terms of underlying fundamentals can be mainly grouped into two categories. The first group utilizes the material dispersion in atomic media or solid-state systems. The second category belongs to the structural dispersion of specially designed photonic devices [7–9]. The pioneering studies in the field have been exploited the first type of slow light mechanism which achieved a record breaking speed of 17 m/s [10]. The two major problems associated with these approaches are the limited bandwidth nature and the practical constraints due to the requirement of special environments [11]. Carefully engineered dielectric structures show great promise to tame and manipulate the speed of light by lowering speed many orders of magnitude even though that value is still far beyond the achievement of the approaches belonging the first group.
The beauty of reducing speed of light based upon structural dispersion comes from the relatively easy engineering of the complex structures at will. Photonic crystals (PC) are periodic dielectric structures that may exhibit band gap phenomena so that we can modify them by inducing defects of certain type to obtain cavities and waveguides [12]. As a result, light can be confined in the desired regions or guided through certain symmetry directions. Photonic crystal waveguides (PCW) show dispersive characteristics so that the group velocity varies enormously within a certain k-space. The two regions which have low group velocities are near the Brillouin zone edges, namely, (kx, ky) = (0, 0)2π/a or (0, 0.5)2π/a. But near these points, band shape resembles quadratic behavior which naturally accompanies large group velocity dispersion (GVD) and small bandwidth. As a result, the optical signal gets distorted after propagating a certain distance [13]. One solution to tackle with the GVD lies behind the idea of obtaining flat bands. So having high group index (ng) values with small GVD and large bandwidth are important research objectives [14–29] because of the diverse applications of slow light as mentioned above. One crucial aspect that should be kept in mind while obtaining flat bands with constant slopes is the relatively simple structures that can be easily realized. In this work, we obtain different families of dispersion diagrams which ensure large and constant group index in addition to high bandwidth operation. This aspect of the work consists of one part of the study.
The second part as explained later in the paper is to explore systematically the trade-off relation between bandwidth and group index. We emphasized the importance of side rows of holes to reduce the speed of light. The band shape changes dramatically when the innermost holes' radii reach a certain value as the rest of the background holes' radii are kept constant. An inverse relation persists between the bandwidth and average group index. One may have either a large group index value of 590 or a small value of 14 with the corresponding normalized bandwidths of 5.35×10−5 and 0.011, respectively for a certain filling factor. As we can see later, while one parameter diminishes by more than one order of magnitude the other parameter increases by more than two orders of magnitude. In the previous studies, attention was given to the flat-band creation and a figure of merit is defined as the product of "average group index and bandwidth". The trade-off relation between the two parameters was mentioned in previous studies but none of them reported an exponential dependency. Flat-band occurs at two different spectral regions, one is close to dielectric band and the second region is close to air band. In between the two regions, there is a slow light waveguide mode whose band slope is almost zero. This in turn yields the most dispersive mode but at the same time the largest group index. The optimization of group index and bandwidth product was carried out in one of the flat bands region and a value of approximately 0.30 is obtained. The finite-difference time-domain (FDTD) method is used to verify propagation of slow light pico-second optical pulse [30]. An appropriate bandwidth of optical pulse (12 nm) is at 1550 nm selected and relevant parameters are extracted by the time-of-flight method. Both index and band gap guided modes are excited and the pulse separation in time domain was observed.
The intact photonic crystal (PC) used in this paper is a two dimensional structure with triangular lattice air holes in dielectric background as shown in Fig. 1 . The air hole radius is rb=0.30a, where a is the lattice constant and background refractive index is 3.46. The symmetry directions are also shown in the figure. The waveguide is constructed by filling the center holes with the same background dielectric material along ΓΚ direction. The dispersion diagram of the PCW as shown in Fig. 2 is calculated by plane wave expansion method [31] using MIT's freely available software MPB. The waveguide mode of even type is represented by a solid line. The odd mode is also included in the figure as a dashed-line. The group index value that corresponds to the waveguide mode is demonstrated in Fig. 3 . The group index is defined as ng=c/vg, where c is the speed of light. The group velocity as represented by vg is the first order derivative of waveguide mode, i.e., vg=|∂ω/∂k|. Due to the polarization sensitivity of 2D PCs only TE modes (electric fields are in the plane) are considered in the study.
Fig. 1 The representative picture of the investigated slow light photonic crystal waveguide. The holes inside the rectangles with dashed lines are subject to size variation. Their radii are represented byrd. The radii of the remaining holes in background are rb=0.30a and the relative permittivity of dielectric material is 12. The two insets on the right and left hand sides show the two defined variables, rbandrd, respectively.
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Fig. 2 The defect bands of the dispersion diagram of PCW. Solid- and dashed-lines correspond to even and odd modes, respectively. The radii of holes in the first rows and background are rb = rd = 0.30a.
Fig. 3 The group index spectrum of photonic crystal waveguide with respect to normalized frequency.
Considering the out-of-plane losses, we focus on only region of interest in the reciprocal space where mode stays under the light line. This part of the region is apparent if we only present dispersion diagrams within the interval from k=0.25(2π/a) to band-edge. Figure 3 shows group index variation of a regular PCW. As evident from this plot, it diverges very fast at the close proximity of cut-off frequency. The two main problems of such a waveguide mode are the narrow bandwidth operation and high GVD. The way of eliminating these problems lies behind the idea of obtaining flat-bands (non-zero, constant slope). Flat bands with small slopes provide constant group index and have very low GVD.
As the field distribution of the guided mode is highest in the center of the waveguide and decreases along transverse to propagation direction, the first rows of holes affect the field distribution and the dispersion diagram more than the second and third rows. Therefore, in this study we modified the side rows holes' size and changed symmetrically their radii along the waveguide.
The dispersion diagram of PCW contains various curves as shown in Fig. 4 when we change the first row of holes' radii from rd=0.20a to 0.4750a with an incremental step of 0.0125a. The background holes radii are kept constant at rb=0.30a. Within the resolution of our parameter scan, we realized that when hole radius is around 0.36a and beyond that first flat-band region emerges in the dispersion diagram. For the values of hole radii between 0.30a and 0.36a, the waveguide mode is very dispersive and there is no signature of flat-band region. The second flat-band regime occurs when rd takes values around 0.20a. Most of the previous studies targeted to tune geometric parameters within a small interval. Hence, some of the general trends that may be captured were unrevealed. As a result, large structural variations reveal important observations. The first observation in the dispersion diagram which is also a trivial one is the bands movement to higher/lower frequencies as we increase/decrease the side row of holes' radii. The band flattens as the waveguide mode comes close to continuum of dielectric band. The flatness disappears and mode becomes highly dispersive at intermediate values ofrd due to hyperbolic forms of bands. We will demonstrate later in the paper that, there is always a turning point (rd=0.35a, designated with a marker in the figure) as we change the filling factor of the PC by altering rd. This is the second important observation that can be drawn from the dispersion diagram. The slope of the band is almost zero at the turning point and below/above this value the bands have negative/positive slopes. The upward movement speed increases even though the amount of increment is kept the same. The three spectral intervals are roughly separated by double-arrows in Fig. 4. While the lower and upper parts contain flat-band regions suitable for slow light application the middle part is highly dispersive.
Fig. 4 Evolution of dispersion curves of photonic crystal waveguide with changing boundary holes' size. The background holes have radii of rb=0.30a and first row of holes' radii are varied from rd=0.20a to0.4750a.
To gather group index variation of the bands in the three regions, we prepared Fig. 5 . The band which has the smallest slope is also indicated with a marker. There are two interesting regimes in the figure in terms of slow light perspective. Bands with constant group indices appear both at lower and upper parts of the spectrum. The first one is close to dielectric band continuum states. On the contrary, the second part is close to continuum states of the air band. The same types of lines correspond to same modes in the plots of ω(k) and ng(ω) in Figs. 4 and 5, respectively. Hence, the two figures complement each other. The useful low dispersion area in Fig. 4 can be easily detected by inspecting Fig. 5. The constant group index regions plotted with red-dotted lines imitate a U-shaped behavior which is the region of low GVD. We selected three representative points (shown with arrows) in the group index spectrum where the corresponding group indices are 27.9, 43.4 and 10.4, respectively to investigate e-field distributions. The result is shown in Fig. 6 . The e-field penetrates more towards transverse to propagation direction in Fig. 6(a) than the rest. The field components reach up to the 4th row. This is because of the relevant mode closeness to dielectric continuum states. On the other hand, it decays very quickly over the 1st and 2nd rows for the other two cases in Figs. 6(b) and 6(c). The unique behavior of e-field distributions for different bands tells us that one may play with the rows up to 3rd or 4th row to engineer slow light in lower part of the spectrum. However, 1st and 2nd row have the most pronouncing role to manipulate mode shape for slow light in the upper part of the group index spectrum.
Fig. 5 Group index spectrum of bands in Fig. 4. The three arrows show the spectral points whose electric field distributions are presented in Fig. 6. The double arrow indicates the interval of a group of modes that have large GVD.
Fig. 6 Electric field distributions of three cases are prepared. (a) (rb, rd)=(0.30a, 0.20a), (b) (rb, rd)=(0.30a, 0.35a) and (c) (rb, rd)=(0.30a, 0.4625a). The wave vector is fixed at k=0.40 (2π/a)for the three cases.
The nice behavioral change between group index and bandwidth in the upper part of the group index spectrum (Fig. 5) directed us to extract quantitative values. We re-produced group index variation for rd changing from 0.3625a to 0.45a keeping rb fixed at 0.30a. Different y-scales are used in Figs. 7(a) and 7(b). From these plots, constant-group index and the corresponding bandwidth values are extracted. We can see that there are constant group index regions with different bandwidths. The ng values are U-shaped and the bottom of this U shape is very appropriate for obtaining constant group index with small GVD and high bandwidth. We extracted the value of minimum group index and bandwidth from Fig. 7. The bandwidth is defined as Δω/ω0, where Δω is the difference between maximum and minimum frequencies and ω0 is the center frequency of the U-shape. The maximum and minimum frequencies are determined so that corresponding ng values are within the 10% of the minimum group index. The corresponding variations of bandwidth and group index are shown in Figs. 8(a) and 8(b), respectively. As we can see, while bandwidth increases exponentially, the group index decreases also exponentially but with a different decay rate.
Fig. 7 (a) Group index vs. frequency plots for rdvalues ranging from 0.3625a to 0.40a. (b) Group index vs. frequency plots for rdvalues from 0.4125a to 0.45a.
Fig. 8 (a) The bandwidth variation corresponding to an interval such that group index does not exceed 10% of the local minima. (b) The constant group index dependency with respect to holes' radii.
Since the group index and bandwidth values are inversely proportional, we had to determine a figure of merit (FOM). We first evaluated average group index and bandwidth values and then defined the product of them as a FOM. The result is shown in Fig. 9 . The FOM increases almost five times reaching a value of 0.16 as we increase air holes radii of the first rows from 0.3625a to 0.45a.
Fig. 9 The average group index and bandwidth product dependency to boundary hole size variation.
The GVD graph calculated by evaluating ∂2k/∂ω2 is depicted in Figs. 10(a) and 10(b) for radii of holes 0.3875a and 0.45a, respectively. The low GVD reduces down to the order of 105 ps2/km. We should note that GVD changes symmetrically with positive and negative parts which can be used for dispersion compensation application.
Fig. 10 The group velocity dispersion relation of the slow light PCW for (a) rd=0.3875a and (b) rd=0.45a.
In this section, the slow light results are reinforced by the time domain study using FDTD method. It allows us to visualize slow light propagation inside PCW. The structure length is taken to be 300a. The computational domain is surrounded by perfectly matched layer boundary condition. Different detection points are placed throughout the structure and the distance between each detection point is 32a. We made simulations on the structure with side row radii equal to 0.4375a. The central frequency of Gaussian source is fixed at ωa/2πc=0.2452with a normalized bandwidth of 0.001. We excited the slow light mode by sending a tilted input source. After a certain distance which is proportional to the difference between the slopes of the waveguide mode at two different k points, the separation of the input pulse into fast (index-guided) and slow modes (band-gap guided) is easily observable.
The group index extraction is performed by tracing arrival times of the central peaks of the slow light. The lattice constant a is fixed at 380 nm targeting the optical regime of 1550 nm. The bandwidths of the input pulse and constant group index region are approximately 6.3 nm and 12.6 nm, respectively. The pulse is allowed to propagate for more than 10000 a/c time. By measuring delay time of the pulses at different locations, we obtain Fig. 11(a) . The slope of the curve which approximates FDTD data gives group index value of ng=22.85. The delay time information of the first detection point is scaled to zero time to take it as a reference. This number is very close to the frequency domain result of ng=20.59. It takes 8.69 ps for the input pulse to travel 300a length PCW. The delay time can be increased either by using longer PCW or using different rod radii value. By using different rod radii for innermost holes, larger group index value can be attained at the expense of narrowing the bandwidth.
Fig. 11 (a) A part of the computational domain employed in the FDTD study is shown as an inset in the figure. The side rows of holes radii are 0.4375a. The length of the PCW is 300a and the distance between two detection points is 32a. Time domain data are stored at equally placed detection points along waveguide centerline. Lines with circular and square markers indicate slow light's and fast light's delay time data, respectively. (b)-(e) Time domain optical pulse evolutions of slow light at four selected propagation distances.
Figure 11(a) also indicates time delay information for fast light. As can be seen from Fig. 7(b), fast light has a smaller group index (lower tail part of dispersion line). As a result, the slope of the curve corresponding to fast light is almost three times smaller than slow light. The temporal evolutions of slow light optical pulses while propagating down the waveguide are presented in Figs. 11(b)–11(e) at four selected detection points, 32a, 96a, 160a and 224a, respectively. The absence of broadening and distortion in the pulse waveforms are an indication of negligible GVD. The fast light reaches the end of the waveguide earlier than slow light. Hence, the reflected portion of it interferes with the traveling slow light. As a result, a small broadening in the pulse form appears only in Figs. 11(d) and 11(e).
The pulse propagation through PCW is presented in Fig. 12 . There are two detection windows used for the observation of light propagation, one is placed in the middle of the waveguide while the other one is located at the end of the waveguide. First fast light appears at the observation plane as expected due to small group index as compared with the slow light which has almost three times larger group index. As can be seen from Fig. 12(a), e-field distribution resembles well the index guided mode pattern. After certain time delay, the slow light arrives with distinct field patterns such as diffusing more towards the transverse direction and appearing beating patterns along the longitudinal direction as indicated in Fig. 12(b). To prove further the dispersion free propagation of the slow light, we provided another snap-shot of the e-field of slow light at the end of the waveguide. That means the field in Fig. 12(b) is allowed to travel almost a distance of 300a to reach the end of the waveguide. It can be seen from the plot in Fig. 12(c) that the pulse propagation does not suffer from any group velocity dispersion. Media 1 shows the optical pulse propagation along the waveguide.
Fig. 12 (Media 1) Light propagation through PCW. (a) The time snap-shots of the fast and slow light are shown in (a) and (b), respectively. (c) The spatial field distribution of slow light in (b) after propagating until the end of the waveguide.
The previous analyses were performed by keeping background holes' radii at rb=0.30a. It is worth considering the other cases where rb takes values smaller and larger than 0.30a. As a result, we consider the change in the figure of merit when we scan different combinations of rb and rd.
Figure 13(a) shows the color-map plot of average group index and bandwidth product with respect to rb and rd. The FOM value reaches up to 0.30 at the upper right corner of the figure where rb and rd take larger values, 0.42a and 0.48a, respectively. To underpin the constituent parameters variation clearly, we show group index and bandwidth variation along the dotted line which corresponds to rb=0.36ain Figs. 13(b) and c. The insets show the enlarged view of the selected portions. When group index takes the largest value for certain rd, the corresponding bandwidth is at the smallest value. Hence, defined FOM is a signature designating the inverse relation between the two parameters. The optimizations were performed only considering the first two rows of holes. It may be possible to enhance FOM further if one considers also the role of second row of holes. If higher FOM is sought for, one should use larger rb and rd values. On the other hand, larger group index with small bandwidth is available for various rb values when rd is kept relatively smaller. FOM values in the previous studies can be as low as on the order of 0.01 [28] and may increase up to 0.85 by judicious waveguide design [26]. The FOM of the present work as compared to them stays within an intermediate value.The parametric scan of radii allowed us to identify one additional feature of slow light PCW. For each radius of background holes, there is a certain rd value of first row of holes where the bands have the smallest slope (close to zero within the numerical resolution). The U-shaped group index region starts to appear above this rd value. Table 1 shows the specific rd values which are transition regions between lower flat bands and upper flat bands. The modes are highly dispersive at and around these rd values. When we increase rb from 0.28a to 0.38a, the turning points first decrease and then start to increase. Table 1 informs us which region to search for slow light with flat band if we fix the filing factor of PCW. The turning point is reminiscent of the existence of lower flat band. As we increase rb above 0.38a, continuum states of dielectric band intervene strongly with the waveguide mode and lower flat band disappears. Hence the trend in Table 1 can be presented up to a certain rb value.
Fig. 13 Average group index and bandwidth product map of slow light photonic crystal waveguide. The filling factor changes with rb, and two sides air holes are altered by parameter rd. (b) and (c) indicate group index and bandwidth variation, respectively when rbis fixed at 0.36a.
Table 1. Turning point variation
A detailed loss analysis is out of the scope of the present work. However, to have an idea on the performance of the proposed slow light structure under the loss, we performed some additional work. Among the various loss mechanisms that may occur in PCW, we focused on the loss due to backward scattering. For this purpose, we introduced randomly varying hole diameters within an interval of 0.4375a±0.01a. Such randomness may occur as a consequence of an imperfect structure fabrication. The background radii of holes are kept constant at rb=0.30a. The expected group index value of the waveguide without inclusion of loss parameter is ng=22.85. However, uniformly distributed and randomly varying hole diameters' should modify the dispersion curve. As a result, group index may increase or decrease correspondingly. The length of the perturbed part within the PCW is varied up to 40a while keeping the rest of the structure unchanged. The result is presented in Fig. 14 . The estimated loss coefficient extracted within the limited resolution of FDTD discretization is approximately 0.05dB/a. At first glance, such a loss value may seem to be high if a comparison is made with the literature [14]. However, careful examination of the way of introducing fabrication loss component into the current analysis provides a reasonable explanation. The holes' radii of first rows are artificially perturbed from the original value, 0.437a to 0.4275a and 0.4475a (extreme cases). In these situations, dispersion analyses yield constant group indices of the following values 26.92 and 14.56 with different band widths. As compared to the loss free case, group index change occurs within a large interval of 20.59 ± (~6). Besides, slow light waveguide mode moves to higher/lower frequencies and in some cases there may be no overlap between the constant group index regions. As a result, slow light mode excited for ng=20.59 faces with a huge scattering loss due to group index mismatch and band movement. Uniformly distributed perturbation parameters also exaggerate the fabrication disorder loss. Instead, a more realistic distribution such as Gaussian distribution can be adapted. Finally, field distribution of the slow light mode plays a crucial role for the loss amount. Strongly concentrated fields especially around the perturbed area are more amenable to high loss. It is possible to tailor the disorder induced losses in slow light waveguides by manipulating appropriately the locations of the e-field concentration [32]. The electric field concentration should be distributed at regions where disordered places do not overlap with the high intensity of the field. The out of plane losses in PCWs will not be a major concern as long as the operating spectral region is selected to be below the light line [33,34]. In the present work, slow light region appears below the light as can be seen from Fig. 2.
Fig. 14 The logarithmic plot of the disorder induced losses versus length of slow light waveguide. The solid line is a fitting curve to discrete data points.
In conclusion, we have studied tuning of group index and bandwidth values by means of obtaining flat dispersion curves in a simplistic manner. We performed detailed analysis to engineer the dispersion and show that complete scan of parameters is very beneficial for slow light concept to identify and categorize different spectral trends that appear in dispersion diagrams. The frequency domain calculations confirm that when the radii of the side rows of holes increase above certain value for each rb then unique properties in the waveguide mode appear due to the interaction with continuum states (from below/above: dielectric/air band). The inverse exponential relation between group index and bandwidth is explored. The defined figure of merit shows increment with respect to increase in the radii of the side rows of holes reaching a value of approximately 0.30. The group velocity of 0.0017c is achieved in the modified photonic crystal waveguide. The transmissions of pico-second optical pulses were realized by time domain study. The presented results obtained by simple geometrical modifications via detailed parameter scan guide us how to obtain large bandwidth, constant group index and low GVD for slow light applications.
The authors gratefully acknowledge the financial support of the Scientific and Technological Research Council of Turkey (TUBITAK), Project no: 108T717. HK also acknowledges support from the Turkish Academy of Sciences Distinguished Young Scientist Award (TUBA GEBIP).
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30. A. Taflove, Computational Electrodynamics – The Finite-Difference Time Domain Method. Norwood, MA: Artech House, 2000.
31. S. G. Johnson and J. D. Joannopoulos, "Block-iterative frequency-domain methods for Maxwell's equations in a planewave basis," Opt. Express 8(3), 173–190 (2001). [CrossRef] [PubMed]
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33. E. Kuramochi, M. Notomi, S. Hughes, A. Shinya, T. Watanabe, and L. Ramunno, "Disorder-induced scattering loss of line-defect waveguides in photonic crystal slabs," Phys. Rev. B 72(16), 161318 (2005). [CrossRef]
34. M. Notomi, A. Shinya, S. Mitsugi, E. Kuramochi, and H. Ryu, "Waveguides, resonators and their coupled elements in photonic crystal slabs," Opt. Express 12(8), 1551–1561 (2004). [CrossRef] [PubMed]
R. W. Boyd, D. J. Gauthier, and A. L. Gaeta, "Applications of slow light in telecommunications," Opt. Photon. News 17(4), 18–23 (2006).
T. F. Krauss, "Why do we need slow light," Nat. Photonics 2(8), 448–450 (2008).
T. Baba, "Slow light in photonic crystals," Nat. Photonics 2(8), 465–473 (2008).
F. Xia, L. Sekaric, and Y. Vlasov, "Ultracompact optical buffers on a silicon chip," Nat. Photonics 1(1), 65–71 (2007).
T. Tanabe, M. Notomi, S. Mitsugi, A. Shinya, and E. Kuramochi, "Fast bistable all-optical switch and memory on a silicon photonic crystal on-chip," Opt. Lett. 30(19), 2575–2577 (2005).
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J. B. Khurgin, "Slow light in various media: a tutorial," Adv. Opt. Photon. 2(3), 287–318 (2010).
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R. S. Tucker, P.-C. Ku, and C. J. Chang-Hasnain, "Slow-light optical buffers-capabilities and fundamental limitations," J. Lightwave Technol. 23(12), 4046–4066 (2005).
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M. Notomi, K. Yamada, A. Shinya, J. Takahashi, C. Takahashi, and I. Yokohama, "Extremely large group-velocity dispersion of line-defect waveguides in photonic crystal slabs," Phys. Rev. Lett. 87(25), 253902 (2001).
L. H. Frandsen, A. V. Lavrinenko, J. Fage-Pedersen, and P. I. Borel, "Photonic crystal waveguides with semi-slow light and tailored dispersion properties," Opt. Express 14(20), 9444–9450 (2006).
Y. Hamachi, S. Kubo, and T. Baba, "Slow light with low dispersion and nonlinear enhancement in a lattice-shifted photonic crystal waveguide," Opt. Lett. 34(7), 1072–1074 (2009).
M. D. Settle, R. J. P. Engelen, M. Salib, A. Michaeli, L. Kuipers, and T. F. Krauss, "Flatband slow light in photonic crystals featuring spatial pulse compression and terahertz bandwidth," Opt. Express 15(1), 219–226 (2007).
A. Yu. Petrove and M. Eich, "Zero dispersion at small group velocities in photonic crystal waveguides," Appl. Phys. Lett. 85(21), 4866–4868 (2004).
H. Kurt, H. Benisty, T. Melo, O. Khayam, and C. Cambournac, "Slow-light regime and critical coupling in highly multimode corrugated waveguides," J. Opt. Soc. Am. B 25(12), C1–C14 (2008).
J. Ma and C. Jiang, "Demonstration of Ultraslow Modes in Asymmetric Line-Defect Photonic Crystal Waveguides," IEEE Photon. Technol. Lett. 20(14), 1237–1239 (2008).
J. Hou, D. Gao, H. Wu, R. Hao, and Z. Zhou, "Flat Band Slow Light in Symmetric Line Defect Photonic Crystal Waveguides," IEEE Photon. Technol. Lett. 21(20), 1571–1573 (2009).
J. Li, T. P. White, L. O'Faolain, A. Gomez-Iglesias, and T. F. Krauss, "Systematic design of flat band slow light in photonic crystal waveguides," Opt. Express 16(9), 6227–6232 (2008).
S. Rawal, R. K. Sinha, and R. M. De La Rue, "Slow light miniature devices with ultra-flattened dispersion in silicon-on-insulator photonic crystal," Opt. Express 17(16), 13315–13325 (2009).
R. Hao, E. Cassan, H. Kurt, X. Le Roux, D. Marris-Morini, L. Vivien, H. Wu, Z. Zhou, and X. Zhang, "Novel slow light waveguide with controllable delay-bandwidth product and utra-low dispersion," Opt. Express 18(6), 5942–5950 (2010).
O. Khayam and H. Benisty, "General recipe for flatbands in photonic crystal waveguides," Opt. Express 17(17), 14634–14648 (2009).
R. Hao, E. Cassan, H. Kurt, J. Hou, X. Le Roux, D. Marris-Morini, L. Vivien, G. Dingshan, Z. Zhou, and X. Zhang, "Novel Kind of Semislow Light Photonic Crystal Waveguides With Large Delay-Bandwidth Product," IEEE Photon. Technol. Lett. 22(11), 844–846 (2010).
L. Dai and C. Jiang, "Ultrawideband Low Dispersion Slow Light Waveguides," J. Lightwave Technol. 27(14), 2862–2868 (2009).
L. Dai and C. Jiang, "Photonic crystal slow light waveguides with large delay-bandwidth product," Appl. Phys. B 95(1), 105–111 (2009).
J. Ma and C. Jiang, "Flatband slow light in asymmetric line-defect photonic crystal waveguide featuring low group velocity and dispersion," IEEE J. Quantum Electron. 44(8), 763–769 (2008).
F. Wang, J. Ma, and C. Jiang, "Dispersionless slow wave in novel 2-D photonic crystal line defect waveguides," J. Lightwave Technol. 26(11), 1381–1386 (2008).
A. Taflove, Computational Electrodynamics – The Finite-Difference Time Domain Method. Norwood, MA: Artech House, 2000.
S. G. Johnson and J. D. Joannopoulos, "Block-iterative frequency-domain methods for Maxwell's equations in a planewave basis," Opt. Express 8(3), 173–190 (2001).
A. Petrov, M. Krause, and M. Eich, "Backscattering and disorder limits in slow light photonic crystal waveguides," Opt. Express 17(10), 8676–8684 (2009).
E. Kuramochi, M. Notomi, S. Hughes, A. Shinya, T. Watanabe, and L. Ramunno, "Disorder-induced scattering loss of line-defect waveguides in photonic crystal slabs," Phys. Rev. B 72(16), 161318 (2005).
M. Notomi, A. Shinya, S. Mitsugi, E. Kuramochi, and H. Ryu, "Waveguides, resonators and their coupled elements in photonic crystal slabs," Opt. Express 12(8), 1551–1561 (2004).
Baba, T.
Behroozi, C.
Behroozi, C. H.
Benisty, H.
Borel, P. I.
Boyd, R. W.
Cambournac, C.
Cassan, E.
Chang-Hasnain, C. J.
Dai, L.
De La Rue, R. M.
Dingshan, G.
Dutton, Z.
Eich, M.
Engelen, R. J. P.
Fage-Pedersen, J.
Frandsen, L. H.
Gaeta, A. L.
Gao, D.
Gauthier, D. J.
Gomez-Iglesias, A.
Hamachi, Y.
Hao, R.
Harris, S.
Hau, L.
Hau, L. V.
Hou, J.
Hughes, S.
Jiang, C.
Joannopoulos, J. D.
Johnson, S. G.
Khayam, O.
Khurgin, J. B.
Krause, M.
Krauss, T. F.
Ku, P.-C.
Kubo, S.
Kuipers, L.
Kuramochi, E.
Kurt, H.
Lavrinenko, A. V.
Le Roux, X.
Li, J.
Liu, C.
Ma, J.
Marris-Morini, D.
Melo, T.
Michaeli, A.
Mitsugi, S.
Mori, D.
Notomi, M.
O'Faolain, L.
Petrov, A.
Petrove, A. Yu.
Ramunno, L.
Rawal, S.
Ryu, H.
Salib, M.
Sekaric, L.
Settle, M. D.
Shinya, A.
Sinha, R. K.
Takahashi, C.
Takahashi, J.
Tanabe, T.
Tucker, R. S.
Vivien, L.
Vlasov, Y.
Wang, F.
Watanabe, T.
White, T. P.
Wu, H.
Xia, F.
Yamada, K.
Yokohama, I.
Zhang, X.
Zhou, Z.
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Fig. 1 The representative picture of the investigated slow light photonic crystal waveguide. The holes inside the rectangles with dashed lines are subject to size variation. Their radii are represented by r d . The radii of the remaining holes in background are r b = 0.30 a and the relative permittivity of dielectric material is 12. The two insets on the right and left hand sides show the two defined variables, r b and r d , respectively.
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Fig. 2 The defect bands of the dispersion diagram of PCW. Solid- and dashed-lines correspond to even and odd modes, respectively. The radii of holes in the first rows and background are r b = r d = 0.30a.
Fig. 4 Evolution of dispersion curves of photonic crystal waveguide with changing boundary holes' size. The background holes have radii of r b = 0.30 a and first row of holes' radii are varied from r d = 0.20 a to 0.4750 a .
Fig. 6 Electric field distributions of three cases are prepared. (a) ( r b , r d ) = ( 0.30 a , 0.20 a ) , (b) ( r b , r d ) = ( 0.30 a , 0.35 a ) and (c) ( r b , r d ) = ( 0.30 a , 0.4625 a ) . The wave vector is fixed at k = 0.40 ( 2 π / a ) for the three cases.
Fig. 7 (a) Group index vs. frequency plots for r d values ranging from 0.3625a to 0.40a. (b) Group index vs. frequency plots for r d values from 0.4125a to 0.45a.
Fig. 10 The group velocity dispersion relation of the slow light PCW for (a) r d = 0.3875 a and (b) r d = 0.45 a .
Fig. 13 Average group index and bandwidth product map of slow light photonic crystal waveguide. The filling factor changes with r b , and two sides air holes are altered by parameter r d . (b) and (c) indicate group index and bandwidth variation, respectively when r b is fixed at 0.36a.
Table 1 Turning point variation
James Leger, Editor-in-Chief
Turning point variation
r b / a
r d / a 0.3625 0.3500 0.3375 0.350< r d / a <0.3625 0.3625 0.375< r d / a <0.3875


text:
Home Biography Some Shocking Facts About John Holmes!
Some Shocking Facts About John Holmes!
John Holmes net worth
If you adore watching adult movies, you must be familiar with John Holmes. He was an American pornographic star who had appeared in more than 570 movies in a short period. He is considered to be the first adult male star. Apart from being an adult star, he had tried his hand at several things to make a living for himself. John Holmes net worth, death and personal life are mentioned in the article ahead!
If you are his fan and are curious to know some facts about him, stay tuned. Read the article to the end. The article will give you some of the facts about his life that you might not know!
He spent his childhood with his three siblings, with whom he shared a mother. His mother then married another man. He lived with his stepfather until his stepbrother came into the scene. After the birth of his stepbrother, his stepfather overlooked him and his siblings.
He felt isolated and neglected at home, so he left home at 16 and became a part of the American Military. He has served as an army man in Germany. In 1963 he left the Military and moved to Carolina, where his wife was waiting for him.
Read this Career of Bolo Yeung.
He tied a knot with his nurse-wife in 1964, and the marriage ended in the late 1980s. His first wife died in 2012. During his time in Carolina, he had worked at different levels to sustain himself.
When he earned an average amount by driving an Ambulance, his female neighbour introduced him to this cinematic world. He was intriguing, and he wanted to mint money, so he instantly agreed. After earning his first handsome amount, he made a profession in this field.
When he was working day in and day out in Carolina to make a living for himself, he became a pneumothorax patient. He had other breathing and physiological issues too.
John Holmes net worth is approximately 10,000 dollars. He had earned this proportion via his adult films and some passive business ventures.
His blockbuster movies include 'Devil in Miss Jones' and 'Bad Throat'. One of his characters, Johnny Wadd, made him a household name. This character earned him massive success and made him financially stable.
At the peak of his career, he started feeling depressed and lonely. His extreme anxiety, depression and lack of sleep led him to drug addiction which escalated with each passing year leading to his divorce and failed business ventures.
His last film was The Devil In Mr Holmes. In 1988 at the delicate age of 43, he died of HIV after being hospitalised for five months. Doctors proclaimed that he had encephalitis, cardiac arrest and candidiasis, which led to his death.
John Holmes net worth is approximately 10k dollars which he earned from doing adult films and some other side businesses. He had two wives. He spent the last five months of his life in the hospital, where he was admitted to treat HIV. He lost the battle to HIV in 1988 at the age of 43.
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Built in 1829, Sunny Bank Mills is based in Yorkshire between Leeds and Bradford. It was founded by a group of local clothiers who invested together to purchase land and to build a woollen scribbling and fulling mill, known as The Farsley Club Mill. Whilst the production of textiles at the mill ended in 2008, the magnificent buildings have been restored to an exceptionally high standard and are now a 'creative space for business', with numerous small businesses based there. The Gaunt family has been involved with Sunny Bank for six generations, and are still as active today.
The looms and the dyehouse may have gone but Sunny Bank Mills, once a thriving textile manufacturer, can still inform and educate people about the history and the future of the textile industry. Since the closure of the works and the trading name Edwin Woodhouse being sold on, the family have been keen to ensure that the mill continues to provide employment for the local community. The development of the mill into business units is linked to the archive of artefacts that the mill still holds.
The archive represents a unique look at 180 years of cloth produced at the mill, and is an incredible historic textile mill collection.
Established over the last two years, the archive houses more than 60,000 lengths of fabric, 8,000 original designs and 5,000 wool-dyeing recipe cards. There are also shelves of leather-bound ledgers and cash books, each detailing the rise and fall of this once great industry and dozens of letters, photographs and personal documents relating to the men and women whose hard work and dedication built the company, but who ultimately couldn't save it from closure.
As part of making this archive work for the future the SDC together with Bulmer and Lumb worked with archive curator Rachel Moaby and the volunteers at Sunny Bank Mills to use the opportunity of heritage days not only to look at the heritage but also to inform about the industry that still survives (and thrives!) in Yorkshire and other parts of the UK. Based in Bradford, Bulmer and Lumb have been 'experts in colour for almost a century' and continue today as one of the UK's leading textile manufacturers.
The SDC provided samples of natural dyes such as logwood which was used extensively by the dyehouse to dye their fabrics and early examples of synthetic dyes from its own archive.
There is evidence that Sunny Bank Mills had its own loose stock dyehouse as well as using commission dyers and then appeared to use top dyeing probably as a way of improving the quality of the yarn produced. They were one of the first dyehouses in the UK to use yarn dyeing for worsted yarns. Bulmer and Lumb kindly supplied examples of wool going through the process from raw wool through to tops and illustrated both top dyeing and yarn dyeing as still carried out at their factory in Bradford.
The archive is open to visitors on the first Wednesday of every month and the recent Heritage Day was part of a regular series of events. Over 500 people attended over three days and while marvelling at the history and tales of days gone past were fascinated by the current industry still remaining in West Yorkshire and especially the fact that the SDC with its long history and Bulmer and Lumb continue to thrive and work together.
And the name Sunny Bank? This comes from a piece of land at the back of the buildings where the sun always shines.


text:
Why Joe Biden's Reading of an Irish Poem Went Viral
November 19, 2020 Topic: Politics Blog Brand: The Reboot Tags: Joe BidenPoetryWounded WarriorIrish LiteratureCommunity
In drawing on this verse, Biden implicitly pitched himself as the man poised to mediate healing and defend "the soul of America" after caustic wounding.
by Mark Libin
Following president-elect Joe Biden's victory in the United States, a campaign video of him reading Irish poet Seamus Heaney's verse adaptation of an ancient Greek play went viral.
The video features Biden reading the verse over a montage of images both of Biden on the campaign trail and scenes from across the U.S. related to the past divisive and charged year characterized by protests and the pandemic.
Biden had long adopted this famous Heaney quote as a signature piece. He cited it when he first ran in the 2008 presidential primaries, and on occasions when he spoke as vice-president.
The verse is from The Cure at Troy, Heaney's 1990 version of Philoctetes, the play by Sophocles about the Greek hero Philoctetes who, during the Trojan war, suffers from a festering foot caused by a snakebite. The chorus in the play, aiming towards social healing, recites the lines that have become part of Biden's political repertoire.
In drawing on this verse, Biden implicitly pitched himself as the man poised to mediate healing and defend "the soul of America" after caustic wounding. Meanwhile, President Donald Trump clung to the lyrics of "The Snake," a song popularized by soul singer Al Wilson and written by Oscar Brown Jr., singer-songwriter and civil rights activist. Trump recited the lyrics at numerous rallies as well as this year's Conservative Political Action Conference, prompting criticism from Brown's daughter, Africa Brown, who told CBC radio that "what Donald Trump stands for, and what my father stands for, are in such opposition."
The song tells the cautionary story of a woman who nurses a near-frozen snake back to health in her home, only to have the reptile fatally bite her in recovery. Trump appropriated the song as a not-so-subtle dog whistle to convey an anti-immigration, xenophobic message to his Republican base.
Wounded warrior
Heaney conceived of The Cure at Troy as a drama about reconciliation, about following one's conscience but also about setting personal feelings aside for the sake of the common good.
In the play, Philoctetes, on his way to fight the Trojan War, has been stranded on a desert island for 10 years, abandoned by Odysseus, whose crew could not bear the noxious smell of his wound.
Now, Odysseus returns with Achilles' son, Neoptolemus, because it has been prophesized that the Greeks will only prevail over Troy through the use of Hercules' bow and arrow, now in Philoctetes' possession.
After Heaney published The Cure at Troy, its resonance with the Troubles in Northern Ireland was immediately recognized, particularly in its lyrical denouement: after Neoptolemus realizes that Odysseus' advice to trick Philoctetes out of the bow goes against his conscience, he returns to apologize and reconcile with the wounded warrior.
Hope on this side of the grave
Neoptolemus urges Philoctetes similarly to relinquish his past grievances and return to the Greek army, be healed and help conquer Troy:
"Stop just licking your wounds," urges Neoptolemus, "Start seeing things."
Philoctetes finally agrees. The play's chorus recites the lines that Biden has returned to:
"History says, Don't hope
On this side of the grave.
But then, once in a lifetime
The longed-for tidal wave
Of justice can rise up
And hope and history rhyme."
Inspired leaders
The call to renounce vengeful thoughts embodied a national desire for peace and reconciliation in Northern Ireland, so that when Mary Robinson was elected president of Ireland in 1990, she recited Heaney's prophetic lines in her inauguration speech.
Similarly, when President Bill Clinton visited Northern Ireland in 1995 to commemorate the earlier ceasefire announcement that preceded the eventual Good Friday Agreement of 1998 — what the BBC called "the beginning of the end" of the conflict — he also quoted Heaney.
Biden also recited the lines of the chorus at his speech accepting the nomination at the Democratic National Convention in August.
Significantly, it's not central characters in this ancient drama who sound this call, but the chorus. The chorus surveys the noble characters and finds them wanting: "Shining with self-regard like polished stones," or "Licking their wounds / And flashing them around like decorations."
Biden has cannily pitched himself through this campaign as the political chorus: hating the divisiveness, the pettiness, the selfishness sharing the stage with him.
He calls for healing rather than vengeance, unity rather than division, and portrays himself as the figure that can bring together the "you and the me," the "it of it" all. He offers himself, through this poetic invocation, as a part of the healing ritual of a country hobbled by a snakebite, tricked, forsaken and left abandoned for years, wounded and bereft.
Biden appears to want to pick up Heaney's call for reconciliation and healing while pitching himself as one among the people.
'Double-take of feeling'
After U.S. media announced that Biden had won Pennsylvania and had enough electoral college votes to become president-elect, the Irish network RTÉ tweeted Biden's voice reading the lines over a montage of news footage in tribute.
The lines Biden has highlighted propose a hopeful view that renewed relationships are possible in human life. Biden's chorus invokes the "miracle self-healing / The utter, self-revealing / Double-take of feeling."
The "double-take of feeling" suggests an ability to change one's mind, to change directions, to forgive and reconcile as aspects of the fundamental changeability of human nature. For Biden, such possibilities animate hopes for "miracle" of "self-healing" needed in the country he is about to lead. These lines are short and direct iambic trimeter, a rhyme scheme often utilized by that other great poet of Irish politics, W.B. Yeats. The triple end-rhyme links them together in the reader's mind.
It is perhaps this layered capacity for empathy and for self-examination, for personal and political change, that would make "hope and history rhyme."
Mark Libin, Associate Professor, Department of English, Theatre, Film & Media, University of Manitoba


text:
Q: Azure Pipelines, dynamic number of steps based on variable output of previous job I'm trying to create a dynamic number of steps, based on the output value of a variable set in a previous job.
- stage: deploy
  jobs:
    - job: A
      steps:
      - bash: |
          echo "##vso[task.setvariable variable=myOutputVar;isoutput=true]this is a list"
        name: passOutput
    - job: B
      dependsOn: A
      variables:
        myVarFromJobA: $[ dependencies.A.outputs['passOutput.myOutputVar'] ]
      steps:
      - ${{ each env in split(variables.myVarFromJobA, ' ')}}:
        - script: echo "${{env}}"

When job A runs, the environment has myVarFromJobA set to this is a list correctly. However, I can't get a the template expression to evaluate based on the the variables new value. Instead, it does a split on the literal value of $[ dependencies.A.outputs['passOutput.myOutputVar'] ], rather than this is a list.

A: Because the "${{}}" is compile time expression, so it cannot evaluate the variable from previous job. For more information, you could refer to Runtime expression syntax.
If you want to split the variable, you could try to use the PowerShell script:
steps:
- task: PowerShell@2
  inputs:
    targetType: 'inline'
    script: |
      # Write your PowerShell commands here.
      echo $(myVarFromJobA)
      $results = "$(myVarFromJobA)".split(" ")
      foreach ($var in $results){
        Write-Host $var
      }

redpajama_set_name: RedPajamaStackExchange


Last month, two children started a small fire with a lighter in a church in Escondido. Luckily, the fast response from local law enforcement and firefighters prevented and casualties and significant fire damage to the church.
A few months before the church fire an Escondido home suffered from $500,000 in fire and smoke damage from a fire that spread from the garage into the home's heating ducts. It took an estimated 33 firefighters from multiple districts to completely extinguish the house fire.
Escondido sees its fair share of fires each year. In fact, fires can strike anyone at any time. According to the National Fire Prevention Association, an estimated 1.3 million fires break out in the United States each year. On average, there are over 3,000 deaths, 17,00 injuries and over 12 billion dollars in damages caused by house fires. These statistics show how important it is to follow fire prevention tips.
One of the easiest and most effective ways you can help keep your family safe is to invest in smoke detectors and alarms. Installing these units throughout your home in the manufacturer's recommended placements can mean the difference between life and death. You should have one smoke detector for each level of your Escondido home. Avoid placing your alarms near heating ducts, cold air returns, or above the stove – you end up with more false alarms this way. Airflow can also prevent the alarms from triggering.
It is crucial that smoke detectors and alarms are checked on a regular basis. When you start to hear that annoying beeping noise that your smoke alarm makes when the batteries are low – replace the batteries. Don't be that guy, you know the one that takes the batters out of the unit to get rid of the annoyance.
Fires caused by candles, cooking, portable heating units, and other similar accidents can be easily prevented.
Candles – When candles are lit do not leave the room before you put the candle out. With many of the items listed in this section, distraction and forgetfulness are big culprits in accidental fires.
You may want to invest in a battery operated or electric candle to avoid any accidents involved in candles getting knocked over.
Cooking – There are several fire damage risks when it comes to cooking. There are also several fire safety tips you can follow to prevent kitchen fire damage disasters.
Remove any clutter from your stove or cooking area. Dish towels, wooden utensils, and loose clothing are highly flammable.
Do not leave the stove unattended while cooking. Leaving the room to attend another task can lead to a forgotten pot of food boiling on the stove. As the water boils down the food starts to burn and can ignite causing a significant amount of smoke damage to your home.
Avoid using any kitchen appliances that have frayed or damaged wiring. Electrical fires can be difficult to extinguish.
Keep an eye on cooing temperatures when oil or grease is involved. If a grease fire does break out in your kitchen DO NOT use water to put out the flame. Attempt to remove all of the oxygen from the flame instead.
Portable Heating Units – If you are using a portable heating unit make sure the unit is 3 feet away from any flammable surface. If you have children in your home, make sure the area around the heating unit is a "kid-free" zone. Don't use portable heating units that have damaged or frayed wiring and when leaving a room make sure to turn the unit off.
For all our efforts to prevent fires, sometimes they do happen and we are so thankful for our local law enforcement and fire department for their quick thinking and fast action. There are also 24/7 emergency restoration companies that will arrive on the scene to assess the damage and start a plan of recovery. In the Escondido area, you can rely on JNT Restoration for any fire or smoke damage cleanup and restoration needs.


text:
Q: How Javascript is getting executed in browser by Javascript Engine? Question not for solution, Question to understand the system better
Experts! I know whenever you feed javascript code into javascript engine, It will execute by javascript engine immediately. Since, I haven't seen Engine's source code, I have few of questions as follows,
Let us assume I am loading couple of files from remote server namely FILE_1.js and FILE_2.js.
And the code in FILE_2.js is requiring some of the code in FILE_1.js. So I have included files as follows,
<script type="text/javascript" src="FILE_1.js" ></script>
<script type="text/javascript" src="FILE_2.js" ></script>

So hopefully, I have done what Javascript Engine requires. Here unfortunately I have written 5000KB of code in FILE_1.js, and however I have 5KB of code in FILE_2.js. Since server is multi-threaded definitely FILE_2.js will be loaded into my browser before FILE_1.js completed.
How javascript engine handle this?
And If moved the code from FILE_2.js to inline-script tag as follows, what are actions taken by javascript engine to manage this dependency?
<script type="text/javascript" src="FILE_1.js" ></script>
<script type="text/javascript" >
// Dependent code goes here
</script>

Note: I am not expecting single word answer Single Threaded. I just want to know deep who is manage issuing request either browser or javascript engine or common guy? if the request/response is handled by common guy, then how javascript engine aware about this?

A: When I post an answer about the behavior of code, I always like to go to two places:

*

*The specification

*The implementation

The specification:
The DOM API explicitly specifies scripts must be executed in order:

If the element has a src attribute, does not have an async attribute, and does not have the "force-async" flag set
The element must be added to the end of the list of scripts that will execute in order as soon as possible associated with the Document of the script element at the time the prepare a script algorithm started.

From 4.1 Scripting. Please check the list of exceptions to this rule before - having the defer or async attribute. This is specified well in 4.12.1.15.
This makes sense, imagine:
 //FILE_1.js
     var trololo = "Unicorn";
     ....
     // 1 million lines later
     trololo = "unicorn";
     var message = "Hello World";
//FILE_2.js
     alert(message); // if file 1 doesn't execute first, this throws a reference error.

It is generally better to use a module loader (that will defer script insertion and execution, and will manage dependencies correctly for you).
At the moment, the best approach is to use something like Browserify or RequireJS . In the future, we'll be able to use ECMAScript 6 modules.
The implementation:
Well, you mentioned it and I couldn't resist. So, if we check the Chromium blink source (still similar in WebKit):
bool ScriptLoader::prepareScript(const TextPosition& scriptStartPosition,
                                    LegacyTypeSupport supportLegacyTypes)
    {
    .....
    } else if (client->hasSourceAttribute() && // has src attribute
              !client->asyncAttributeValue() &&// and no `async` or `defer`
              !m_forceAsync                    // and it was not otherwise forced
              ) { // - woah, this is just like the spec
   m_willExecuteInOrder = true; // tell it to execute in order
   contextDocument->scriptRunner()->queueScriptForExecution(this,
                                                            m_resource,
                                      ScriptRunner::IN_ORDER_EXECUTION);

Great, so we can see in the source code that it adds them in order parsed - just like the specification says.
Let's see how a script runner does:
void ScriptRunner::queueScriptForExecution(ScriptLoader* scriptLoader,
                                          ResourcePtr<ScriptResource> resource,
                                          ExecutionType executionType){
     .....
     // Adds it in the order of execution, as we can see, this just
     // adds it to a queue
     case IN_ORDER_EXECUTION:
        m_scriptsToExecuteInOrder.append(PendingScript(element, resource.get()));
        break;
     }

And, using a timer, it fires them one by one when ready (or immediately, if nothing is pending):
 void ScriptRunner::timerFired(Timer<ScriptRunner>* timer)
 {
 ...
    scripts.swap(m_scriptsToExecuteSoon);
    for (size_t i = 0; i < size; ++i) {
    ....
        //fire!
        toScriptLoaderIfPossible(element.get())->execute(resource);
        m_document->decrementLoadEventDelayCount();
    }


text:
È stata la prima bambina afroamericana a desegregare la scuola elementare William Frantz, frequentata all'epoca solo da bianchi, in Louisiana, durante la crisi di desegregazione della scuola di New Orleans nel 1960.

Biografia

Primi anni di vita
Ruby Bridges è nata a Tylertown, Mississippi, da Abon e Lucille Bridges. Quando aveva quattro anni, la famiglia si trasferì a New Orleans, Louisiana. Nel 1960, quando aveva sei anni, i suoi genitori risposero a una richiesta della National Association for the Advancement of Colored People (NAACP) e la offrirono come volontaria per partecipare all'integrazione del sistema scolastico di New Orleans, anche se suo padre era titubante.

Integrazione
All'inizio del 1960, Ruby è stata una dei sei bambini neri di New Orleans a superare il test che stabiliva se potevano frequentare la scuola bianca William Frantz Elementary. Due dei sei decisero di rimanere alla loro vecchia scuola, Ruby andò a scuola da sola, e tre bambini furono trasferiti al McDonogh No. 19 e divennero noti come i Tre McDonogh. Ruby e sua madre furono scortate a scuola da ben quattro marshall federali durante l'intero primo anno di scuola.

Il padre di Ruby era inizialmente riluttante, mentre la madre sentiva la necessità non solo di dare alla figlia una migliore educazione, ma di "fare questo passo avanti... per tutti i bambini afro-americani". La donna convinse infine il marito a lasciarla andare alla scuola.

La sentenza del giudice J. Skelly Wright per il primo giorno delle scuole integrate a New Orleans, il 14 novembre 1960, fu commemorata da Norman Rockwell nel dipinto The Problem We All Live With (pubblicato su Look il 14 gennaio 1964). Come descrive Ruby stessa: "Salendo ho potuto vedere la folla, ma vivendo a New Orleans, in realtà ho pensato che fosse Mardi Gras. C'era una grande folla di persone al di fuori della scuola. Stavano lanciando cose e gridando, e questo tipo di cose succede a New Orleans al Mardi Gras". L'ex vice Marshall degli Stati Uniti Charles Burks ha poi ricordato: "Ha dimostrato molto coraggio. Non ha mai pianto né piagnucolato. Ha marciato come un piccolo soldato, siamo tutti molto orgogliosi di lei".

Non appena Ruby fu ammessa nella scuola, i genitori bianchi ritirarono i propri figli e tutti gli insegnanti si rifiutarono di lavorare finché un bambino di colore fosse stato iscritto. Solo una persona accettò di insegnare a Ruby: Barbara Henry, di Boston, Massachusetts. Per oltre un anno, Barbara Henry insegnò ad una classe composta dalla sola Ruby Bridges "come se stesse insegnando a un'intera classe".

Il primo giorno, Ruby e i suoi accompagnatori adulti trascorsero l'intera giornata nell'ufficio del preside, e il caos delle proteste impedì loro di andare in classe fino al secondo giorno. Il secondo giorno, tuttavia, uno studente bianco ruppe il boicottaggio ed entrò a scuola. Si trattava di un pastore metodista di 34 anni, Lloyd Anderson Foreman, che ha accompagnato sua figlia Pam di 5 anni attraverso la folla arrabbiata, dicendo: "Voglio semplicemente il privilegio di portare mia figlia a scuola". Pochi giorni dopo, altri genitori bianchi hanno iniziato a portare i loro figli, e le proteste hanno cominciato a calmarsi. Ogni mattina, mentre Ruby andava a scuola, una donna minacciava di avvelenarla. Per questo motivo, i Marshall statunitensi inviati dal Presidente Eisenhower, che supervisionavano la sicurezza dei Bridges, hanno permesso a Ruby di mangiare solo il cibo che portava da casa.

Lo psichiatra infantile Robert Coles si offrì volontariamente di fornire consulenza a Ruby durante il suo primo anno alla Frantz. Si incontrarono settimanalmente nella casa di Ruby e più tardi scrisse un libro per bambini, The Story of Ruby Bridges, per far conoscere la storia di Ruby.

La famiglia di Ruby soffrì per la decisione di mandarla alla William Frantz Elementary: suo padre perse il lavoro, il negozio di alimentari in cui la famiglia aveva sempre fatto la spesa non permetteva più loro di fare acquisti e i nonni, che erano mezzadri in Mississippi, furono espropriati della loro terra. Ruby aveva notato che molti altri nella comunità, sia bianchi che neri, mostravano sostegno in vari modi: alcune famiglie bianche continuavano a mandare i loro figli alla Frantz nonostante le proteste, un vicino di casa aveva fornito a suo padre un nuovo lavoro e le baby-sitter del posto consideravano lei e i familiari come protettori, al punto da camminare dietro l'auto dei marescialli federali durante i viaggi a scuola.

Vita adulta

Ruby Bridges, divenuta Ruby Bridges Hall dopo il matrimonio, vive ancora a New Orleans con suo marito, Malcolm Hall, e i loro quattro figli. Dopo la fine degli studi in un liceo desegregato, ha lavorato come agente di viaggio per 15 anni e in seguito è diventata madre a tempo pieno. Attualmente è presidente della Fondazione Ruby Bridges, che ha fondato nel 1999 per promuovere "i valori della tolleranza, del rispetto e dell'apprezzamento di tutte le differenze". Descrivendo la missione del gruppo, afferma, "il razzismo è una malattia degli adulti e dobbiamo smettere di usare i nostri figli per diffonderla".

Ruby Bridges Hall è il soggetto della canzone di Lori McKenna Ruby's Shoes. La sua lotta infantile alla William Frantz Elementary School è stata rappresentata nel film Ruby Bridges del 1998. La Bridges è stata interpretata dall'attrice Chaz Monet, e il film includeva anche Lela Rochon come madre di Ruby, Lucille "Lucy" Bridges; Michael Beach come il padre di Ruby, Abon Bridges; Penelope Ann Miller come insegnante di Ruby, la signora Barbara Henry; e Kevin Pollak come il dottor Robert Coles.

L'8 gennaio 2001, ha ricevuto la Presidential Citizens Medal dal presidente Bill Clinton.

Come centinaia di migliaia di persone nell'area di New Orleans, la Bridges ha perso la sua casa (a Eastern New Orleans) a causa delle catastrofiche inondazioni causate dal fallimento del sistema di sbarramento durante l'uragano Katrina nel 2005.

Nell'ottobre 2006, l'Alameda Unified School District in California ha dedicato una nuova scuola elementare a Ruby Bridges, e ha emesso un annuncio in suo onore, e nel novembre dello stesso anno è stata onorata nel Concerto contro l'odio della Lega Antidiffamazione. Nel 2007, il Museo dei bambini di Indianapolis ha inaugurato una nuova mostra che documenta la sua vita, insieme a quella di Anna Frank e di Ryan White.

Nel 2010, ha avuto una reunion per il 50º anno alla Frantz Elementary con Pam Foreman Testroet, che all'età di cinque anni era stata la prima bambina bianca a rompere il boicottaggio seguito alla frequentazione di Bridges in quella scuola.

Il 15 luglio 2011, la Bridges ha incontrato il presidente Barack Obama alla Casa Bianca, e durante la visione del suo dipinto fatto da Norman Rockwell in mostra le ha detto: "Penso che sia lecito affermare che se non fosse stato per voi ragazzi, forse non sarei stato qui e non ci staremmo guardando insieme".

Il 19 maggio 2012, la Bridges Hall ha ricevuto una laurea honoris causa dalla Università Tulane alla cerimonia di laurea annuale presso il Superdome.

Nel 2014, una statua di Ruby Bridges è stata inaugurata nel cortile della Scuola Elementare William Frantz.

Note

Bibliografia

Voci correlate
 Ruby Bridges, film per la tv del 1988

Altri progetti

Collegamenti esterni
 The Ruby Bridges Foundation
 This is the Problem We All Live With
 Ruby's Shoes su Songfacts.com
 Ruby Bridges (film TV del 1998)
 Debra Michals, "Ruby Bridges", National Women's History Museum, 2015

Attivisti afroamericani
Attivisti contro il razzismo

redpajama_set_name: RedPajamaWikipedia