Abstract: A method and apparatus for reducing nonlinear phase noise that is induced in an optical transmission system by the interaction of optical amplifier noise and Kerr effect. The apparatus includes an intensity-scaled nonlinear phase noise compensator. The phase noise compensator reduces the nonlinear phase noise by rotating a phase estimate by a scaled signal strength estimate for the optical signal or by comparing a complex estimate to curved regions having scaled nonlinear decision boundaries. The scale factor is derived from the number of spans in the transmission system. Another embodiment of the phase noise compensator uses the scaled signal strength for re-modulating an optical signal.

Abstract: An optical receiving apparatus according to the present invention comprises an optical signal branching circuit for receiving a signal light input from an optical transmission line, a discriminator for discriminating an output signal of the optical signal branch circuit, an evaluator for evaluating characteristics of another output signal of the optical signal branching circuit. The evaluator includes a saturable absorber for determining the discrimination threshold of the discriminator.

Abstract: Fault tolerance is provided in a cross-connect system having only duplicated switch fabrics, instead of the triplicated switch fabrics of the prior art. In addition to the two information switch fabrics, the cross-connect system has a relatively small code switch fabric which switches check-code signals generated at each input interface for each input signal sent to an information switch fabric. Fault-detection and error-recovery components in each output interface (1) generate local check-code signals for each outgoing signals received from an information switch fabric and (2) compare those local check-code signals to the corresponding check-code signal received from the code switch fabric to detect a failure and to select a healthy signal as the output signal for that output interface. In one embodiment, input and output interfaces are clustered, and the corresponding input and output check-code signals are multiplexed, for even greater savings in overhead (e.g.

Abstract: An optical pulse generator includes a single-wavelength light source, an electroabsorption optical modulator, a sine-wave voltage generator, a nonlinear circuit, and a DC voltage source. The single-wavelength light source outputs continuous, single-wavelength light. The electroabsorption optical modulator receives the single-wavelength light, modulates the single-wavelength light according to a pulse modulation signal, and outputs the modulated light as optical pulses. The sine-wave voltage generator generates an electrical signal having a sine waveform. The nonlinear circuit extracts only a waveform equal to or higher than a predetermined DC voltage from the sine waveform electrical signal. The DC voltage source adds a negative DC voltage to the electrical signal, from which only the waveform equal to or higher than the predetermined DC voltage is extracted by the nonlinear circuit, and applies the sum signal to the electroabsorption optical modulator as the pulse modulation signal.