An optical time domain reflectometry method and apparatus that employs Hadamard transforms to increase the signal-to-noise ratio. A sequence of N pulses of light corresponding to a Hadamard derived code are launched down a fiber optic cable for each of N such codes. Selected combinations of pulses of reflected light are transformed by a Hadamard derived matrix to a set of equations that are solved simultaneously to determine the power reflected from each of N points. Where a Hadamard code is used the average mean square error is reduced by a factor of 1/N. Where a simplex code is employed the average mean square error is reduced by a factor of 4N/(1+N).sup.2. In addition, N measurements of the power reflected at each point are computed and averaged.
A central equipment is connected by at least two optical fibers to a decentralized optical equipment and the central equipment creates an optical auxiliary signal which is transmitted together with an optical payload signal from the central equipment to the decentralized equipment. The optical auxiliary signal that is received in the decentralized optical equipment is rerouted and transmitted back to the central optical equipment via another optical fiber in addition to a second payload signal, and the reception of the optical auxiliary signal is optically monitored in the central optical equipment to determine if there is a breakage in either one of the fibers extending to the unit.
There is presented an apparatus and method of locating a reflective anomaly in an optical fiber. An optical generator is positioned at one end of a light path extending to and from a reflective anomaly in an optical fiber, and periodic pulses of light are injected into the fiber. A bend coupler containing directional optical detectors is clamped to the optical fiber in mid-span, between the optical generator and a reflective anomaly, and light energy is tapped. The coupler is capable of detecting and discriminating light travelling in both longitudinal directions. After signal conditioning and digitization, the light pulses are submitted to a logical network to initiate a timer that measures a time interval between the event of an interrogating light pulse, and its reflection, the result being memorized in a buffer. A microprocessor controls the system, and computes distance between the attached bend coupler and the reflective anomaly as a function of the memorized time interval. The result is then displayed for the user. The system enables a fault to be rapidly and accurately located in a multidrop installation without violating intermediate fibers.
The invention relates to a method of measuring the distance between a fixed point and an object, by the steps of: a) transmitting a light pulse (11) from the fixed point at a selected instant of transmission; b) periodically scanning of light intensity received at the fixed point and continuously storing, as a set of received scanned signal values, the scanned values at the scanning rate during a predetermined measuring time window (13) embracing the instant of reception of the light pulse reflected from the object; c) repeating steps a) and b) N number of times in order to obtain N number of sets of received signal values; d) summing the individual stored sets of received scanned signal values, set by set, to a summed scanned value set during a calculating window (14) following the N measuring time windows (13); e) repeating steps a) through d) in order to obtain a further summed scanning value set, whereby during or following step d) the further summed scanned value set is added, scanned value set by scanned value set, to the present summed scanned value set to actualize the latter, and whereby an equalizing portion of a summed scanned value set is optionally subtracted therefrom before and/or after the mentioned addition; f) searching within the summed scanned value set for significant scanning values which satisfy predetermined threshold values; g) repeating steps e) and f) until significant scanning values have been detected; and h) determining the looked-for distance from the position of the detected Significant scanning values in the summed scanned value set.
A system and method for high-speed parallel switching of digital data sequences using an all-optical technique is described. Each input digital data sequence is encoded into an optical pattern comprising of several cells. The encoded optical pattern can be of various sizes and shapes depending on cost and quality considerations. A unique modulating pattern is selected for each digital data sequence based on the destination address of that data sequence. Every cell of each encoded optical pattern is modulated using the selected modulating pattern to obtain a modulated-encoded optical pattern. Each modulated-encoded optical pattern corresponds to a specific input data sequence. All of the modulated-encoded optical patterns are superposed to obtain a composite modulated-encoded optical pattern. The composite pattern is optically broadcast to all possible outputs of the parallel switch. All the destination receivers simultaneously demodulate the composite pattern using the unique modulating pattern that corresponds to their destination address and thus extract the encoded data sequence sent to them. The demodulated-encoded data sequences are decoded back from optical to digital form and routed to their destination by conventional techniques.
