Abstract: A monitoring apparatus and method are provided for a communication system in which a central office communicates to at least one end unit using intermediate remote nodes. The remote node receives signals from both the central office and the end units. Each remote node can be equipped with apparatus for monitoring the integrity of paths of the communication system. The monitoring apparatus can include a mixing device that mixes received signals to produce combined signals. The received signals generally include a pilot signal sent from the central office and a data signal sent from the at least one end unit. The state of the communication system is analyzed based on the combined signals. If the combined signals includes only the data signal from the end unit, the path through which the pilot signal was sent is inoperative. If the combined signals includes only the pilot signal, the transmission path from the end unit over which the data signal is sent is inoperative.

Abstract: A control circuit for an injection laser provides a pre-bias current which prevents clipping induced errors in the laser output. An analog modulating signal is provided directly to the laser which receives the sum of a feedback current (Ifb) and a current source (Io) as the pre-bias current (Ipb). A monitor diode detects the laser light output and provides a current (Idet). A feedback circuit operates in a limited dynamic range, e.g. I.sub.l +/-40 mA or is incapable of outputting a negative current (Ifb>0). The feedback circuit responds to changes in Idet and adjusts the laser pre-bias current to hold Idet equal to a preset value, which effectively holds the laser's average output power constant. If the pre-bias current necessary to hold Idet fixed falls below some minimum level, Imin, the feedback circuit will run out of dynamic range and the laser's average power will increase. By preventing Ipb from falling below Imin clipping induced errors and distortion are avoided.

Abstract: A communication network and method is provided to communicate between a central office/head end and a plurality of end-units (EUs). A first transmission medium is connected between the central office and an intermediate node. A plurality of second transmission mediums are connected between the central office and a plurality of mini-fiber nodes. The intermediate node is also associated with each of the mini-fiber nodes such that an analog broadcast service may be sent over the first transmission medium to each of the mini-fiber nodes. Further, switched digital services and digital broadcast services are also sent over the second transmission mediums to each of the mini-fiber nodes. The mini-fiber nodes combine the signals and send the combined signals to a corresponding subset of EUs.

Abstract: A converter apparatus (Mini Fiber Node MFN) for use in a communication network (e.g., a coax network) includes a signal distribution unit (e.g., fiber node FN) for transmitting frequency-division multiplexed communication signals downstream over a coax cable to a node apparatus (amplifier) and via an access path to a plurality of end unit apparatuses connected thereto. The converter apparatus connects to the access path and receives downstream second FDM signals directly from the central office over an optical communication path and sends the second FDM signals to at least one end unit apparatus over the access path. The converter apparatus also receives upstream FDM signals from the at least one end unit apparatus over the access path and transmits the upstream FDM signals to the central office over the optical path. In another embodiment, the converter apparatus connects directly to the primary path to provide service to an end user apparatus connected in a "tapped-bus" arrangement.

Abstract: A method and apparatus for converting a non-return-to-zero (NRZ) voltage data stream into an optical data stream in return-to-zero (RZ) format, is disclosed comprising supplying a continuous optical signal to a modulator, driving the modulator with an NRZ voltage data stream and encoding either the NRZ data stream or the electrical output of the receiver. The modulator can be an interferometer, such as a Mach-Zehnder interferometer, or a directional coupler, for example.

Abstract: Critical placement and lengths of dispersion-compensating fiber maximize capacity in upgraded in-ground optical fiber communication systems. Higher per-channel bit rates in single-channel systems and in WDM systems are permitted.

Abstract: An apparatus and method for providing dispersion compensation for chromatic dispersion introduced in the signal conversion of an optical signal. An exemplary apparatus in accordance with the present invention includes a nonlinear conversion medium arranged within an optical signal path of the optical signal. The conversion medium receives the optical signal and generates a converted optical signal therefrom. At least one dispersion compensator is arranged within the signal path to provide an amount of chromatic dispersion suitable to offset a portion of the chromatic dispersion introduced in the converted signal by the nonlinear conversion medium. The nonlinear medium may be a length of dispersion-shifted fiber used to phase conjugate and/or frequency shift an input optical signal in an optical system utilizing, for example, optical phase conjugation to cancel the effects of fiber nonlinearities.

Abstract: An optical communication system and method are provided which utilize dispersion-induced FM to AM conversion with nonlinearity-induced AM stabilization. The system and method utilize a frequency modulated optical signal transmitter, a fiber span, an optical receiver which receives the transmitted optical signal and detects an AM signal resulting from dispersion-induced energy overlaps and voids in the optical signal, and one or more in-line amplifiers spaced within the optical fiber span. By adjusting the number, position and/or output power levels of the in-line amplifiers, stabilization of the energy voids and overlaps and resulting AM signal can be achieved, yielding a substantial increase in achievable transmission distance at a given bit rate.

Abstract: The present invention provides an apparatus and method for achieving bit rate distance products on the order of 200 Tbits/s-km in non-soliton optical communication using optical phase conjugation. The apparatus and method utilize phase conjugation and adjustments of in-line amplifier number, spacing, and/or output power in order to compensate for the interaction between first order dispersion and fiber nonlinearity dispersion effects in an optical fiber span. The present invention provides additional techniques for adjusting system parameters, such as dispersion-length products of first and second portions of the fiber span, in order to compensate for changes in first order dispersion resulting from non-zero second order dispersion. The method and apparatus also provide an improved multi-channel optical phase conjugation system design.

Abstract: External modulation is accomplished in a dual waveguide device wherein substantially identical input optical beams are supplied to the waveguides and wherein each waveguide through its electrode is subject to individual, mutually exclusive control. Modulation signals are applied to each waveguide via its separate electrode. Control signals are applied to each waveguide for adjusting the modulation chirp parameter to a desired fixed, non-zero value. Typically, the desired value of the chirp parameter is one which provides the lowest fiber dispersion penalty for the system. Modulated lightwave signals emerging from the waveguides are combined to form a single output signal suitable for transmission over an optical fiber. In one embodiment, Mach-Zehnder interferometer having separately controllable waveguides has its input coupled to a CW laser. Both III-V semiconductor and Ti:LiNbO.sub.