The present invention relates to an integratedoptical circuit having a Bragg resonator evanescently coupled to a light guide and a photocell coupled to the Bragg resonator, and adapted to receive an optical signal transmitted in the light guide.
The article, Ivan P. Kaminow "FSK with direct detection in optical multiple-access FDM networks," I.E.E.E. Journal on Selected Areas in Communications, Volume 8, No. 6, pp. 1005-1014, (August 1990) discusses a non-coherently detecting optical network in which optical signals travel from a transmitter to a receiver. At the receiver, the optical signals are noncoherently detected and demodulated. To send signals back to the transmitter using the receiver, a laser is provided and transmits optical signals from the receiver to the transmitter. In addition, a star coupler is provided to connect several transmitters and several receivers.
Unpublished German Patent Application No. 41 42 922.2 also discusses providing an integrated-optical circuit for optical transmission systems in which a frequency multiplex method is employed and in which light of different frequencies are simultaneously conducted in a glass fiber. The circuit includes Bragg resonators coupled to a waveguide and photodiodes coupled to the Bragg resonators. This arrangement decouples and detects optical signals evanescently. The Bragg resonator described is suitable both as a frequency-selective modulator on the transmitter side and as a frequency-selective receiver and demodulator. For modulation/demodulation, the refractive index in the vicinity of the resonator is changed using the electro-optical effect.
The article, Hermann A. Haus, "Theory of Cascaded Quarter wave Shifted Distributed Feedback Resonators," I.E.E.E. Journal of Quantum Electronics, Volume 28, No. 1, pp. 205-213 (January 1992), describes the use of several feedback resonators on a light waveguide. These resonators are either evanescently coupled Bragg resonators for reflecting the signal, or are mounted on the light waveguide as a Bragg resonator for transmitting a signal. In addition, the article, O. Solgaard et al., "Pigtailed Single-Mode Fiber Optic Light Modulator in Silicone," I.E.E.E. Photonics Technology Letters, Volume 2, No. 9, pp. 640-642 (September 1990), describes a reflection modulator which electro-optically modulates and reflects an incoming signal.
Unfortunately, each of the above devices requires an active transmitting element such as a laser to transmit signals to a receiver. As a consequence, additional space and cost is required. Therefore, there is a need for an integrated-optical circuit in which optical modulated signals can be received and then transmitted without requiring an active transmitting element.