Abstract: In a maintenance system for a switch fabric in an optical switching network, a test signal is generated and multiplexed with the incoming traffic signal to form a composite signal. The composite signal is transmitted through the switch fabric via the traffic channel and then demultiplexed back into the traffic signal and the test signal, both of which are monitored by one or optical performance monitors. Thus, if the traffic signal is found to be defective, it is easy to determine whether the cause is the switch fabric or the incoming optical traffic signal that was already bad before entering the switch fabric.

Abstract: A method and circuit are presented for the all optical recovery of the clock signal from an arbitrary optical data signal. The method involves two stages. A first stage preprocesses the optical signal by converting a NRZ signal to a PRZ signal, or if the input optical signal is RZ, by merely amplifying it. In a preferred embodiment this stage is implemented via an integrated SOA in each arm of an asymmetric interferometric device. The output of the preprocessing stage is fed to a clock recovery stage, which consists of a symmetric interferometer that locks on to the inherent clock signal by using the second stage input signal to trigger two optical sources to self oscillate at the clock rate. In a preferred embodiment the second stage is implemented via SOAs integrated in the arms of an interferometer, with two DFB lasers as terminuses. The output of the interferometer is an optical clock signal at the clock rate of the original input.

Abstract: A system is provided for detecting the condition of a lamp, activating a permanent memory two-state display of the lamp condition, and displaying said condition during the daylight when no power is connected to the lamp. The system includes an electrical circuit powered by electricity drawn from power lines connected to the lamp such that the circuit is energized only when the lamp is supposed to be lighted. A rectifier transforms the alternating current of the power lines into a direct current for the circuit. The current of the power lines connected to the lamp is detected and measured when the lamp is supposed to be lighted in order to determine the condition of the lamp, and provide an appropriate signal for controlling switches within the circuit. Two alternative current pathways, each including a capacitor and a switch responsive to input from the current sensor, are provided in the circuit.

Abstract: The detecting circuit is used on cars to indicate the presence of emergency vehicles utilizing wailing sirens the instant invention residing in the unique circuitry itself to result in an extremely inexpensive electronics package for carrying out the desired function. Essentially, the circuit utilizes a band pass filter having a voltage tunable center frequency. Dominant frequencies in a sound spectrum received through the band pass filter are converted to voltages by means of a frequency to voltage converter and fed back to the band pass filter to shift the center frequency of the filter thereby tracking the dominant frequency signal. When the dominant frequency results from a wailing siren, the fed back voltage from the frequency to voltage converter constitutes a slowly continuously varying AC signal corresponding to the pitch variation of the siren. This signal is detected by a low pass filter and differentiating circuit to operate a flasher to indicate the presence of the siren.