Abstract: An improved demodulator and demodulation method usable in a coherence multiplexed, optical data transmission system. The demodulator comprises an interferometer and a signal processor. The interferometer has first and second arms having first ends coupled to receive radiation from an optical bus, and second ends connected to the signal processor. The path length difference between the arms is selected to approximately match that of a corresponding modulator, to within the coherence length of the optical carrier. The signal processor processes the optical signals emerging from the arms in combination, to produce a pair of electrical ouput signals. Linearly independent pairs of electrical ouput signals are produced for any two modulation signals that do not produce modulator optical path length differences that differ from one another by an integral multiple of a half wavelength of the optical carrier.

Abstract: The invention describes a method for optical communication of information between transmitter and receiver spatially separated from each other. The principle of heterodyne reception is utilized. A non-modulated optical carrier of a laser arranged on the receiving side is subdivided in a first fiber-optical coupler KE into two portions, the transmission path EMF and the local laser wave LL. In one branch, a displacement of frequency by the amount of .DELTA.f takes place. The non-modulated optical carrier passes through a one-mode fiber EMF in direction transmitting side and is modulated there with an effective signal in a modulator MOD (FIG. 1). This now modulated optical signal travels back to the receiving side, where it is converted with the local laser wave LL into an intermediate frequency band.

Abstract: A multipoint type MODEM communication system having a training device for adapting receiving parameters in a receiving MODEM to a characteristic of a telephone line connected to a sending MODEM in response to a training signal sent from the sending MODEM prior to the reception of data. The training signal includes a tone for gain control, a timing signal for pull-in synchronization, and at least two impulses for equalization and carrier phase control, which are superimposed on each other. A time between the first and the last impulses defines the characteristic of the telephone line which should be adjusted in the receiving MODEM.Additional guard impulses may be added prior to and/or after the impulses. A scramble signal also may be added after the impulses.In addition, a method for training the receiving MODEM is disclosed.

Abstract: Superheterodyne receivers for optical signals can be composed of two branches. The first branch contains a superheterodyne receiver in which the reception signal and the signal of a local oscillator are mixed in a traditional way; in the second receiver branch, the signal of the local oscillator experiences a 90.degree. phase rotation before the mixing. An optical triple coupler inventively serves for dividing the reception light and the light of the local laser onto both reception branches. This triple coupler can be manufactured as a triple fiber coupler or, on the other hand, has an integrated-optical triple coupler of lithium niobate, glass or of a III-V semiconductor.

Abstract: The present invention is an optical telecommunications system capable of setting up connections between particular pairs of subscriber stations. Illustratively, the Fourier components of radiation pulses produced in a first specific subscriber station are independently phase modulated in accordance with a predetermined code chosen so that the radiation pulse can be detected only in a second specific subscriber station.

Abstract: A multiplexed optical communication system comprising a source (12), a common optical bus (18, 20), a multiplexer (14) and a demultiplexer (16). The multiplexer comprises a plurality of modulators (50), each being formed in an electro-optic substrate and comprising a modulated arm (54) and a reference arm (56). Each arm comprises an optical waveguide, and the arms of each modulator have an optical path length difference LM(i) that is greater than the coherence length of the source, and that differs from the path length difference of each other modulator by an amount greater than the coherence length of the source. Each modulator also includes electrodes for varying the optical path length of its modulated arm based upon an electrical input signal representing an input data channel. The demultiplexer comprises a plurality of detectors, each having first and second detector arms, each detector arm comprising an optical waveguide.

Abstract: A coherence multiplexed optical signal transmission system in which modulation is introduced into the system by modulating the optical carrier or source signal, rather than by modulating the optical path length of an interferometer arm. The system comprises a transmitter and receiver interconnected by an optical bus. The transmitter comprises a plurality of transmitter interferometers, each transmitter interferometer including a modulated optical source. The transmitter interferometers have optical path length differences that are greater than the coherence length of the associated source, and that differ from one another by an amount greater than the source coherence length. The receiver comprises a plurality of receiver interferometers having path length differences matching those of the transmitter interferometers. Multiplexing and demultiplexing means are provided for coupling optical radiation between the bus and the interferometers.

Abstract: A data process system has a plurality of stations or terminals linked to a star coupler over cables comprising separate sending and receiving transmission lines, the cable shield being connected to system ground. To minimize bit error rate when a station is powered down, the transmitting differential amplifier at each terminal station is connected between a bias voltage and a virtual ground created by a pair of diodes connected in parallel, their anodes being connected to a voltage source through a current limiting resistor, the cathode of one diode being connected to system ground, the cathode of the other diode being connected to one side of the transmitting amplifier to define the virtual ground. To further enhance noise rejection, a balanced differential network is connected to the outputs of a transistor pair at the amplifier output to the differential wire transmission line.

Abstract: In a processing system (FIG. 1), peripheral boards (101-103) interconnected by a stack bus with a system board (100) each have an optical emitter (163) mounted on one face and an optical detector (162) mounted on the other face. The system board has an optical emitter mounted thereon. Emitters and detectors are arranged in a daisy-chain fashion: the emitter of one board faces the detector of the next board. To assign I.D.s (e.g. addresses) to boards, the system board turns on its emitter and transmits on the bus an I.D. The adjacent board's detector is illuminated and causes the board to latch the I.D. The system board turns off its emitter, signals the adjacent board to turn on its emitter, and transmits another I.D. on the bus. The next board's detector is thus illuminated and causes the board to latch the I.D. The system board performs the procedure for each peripheral board.

Abstract: A light communication equipment comprises a photo-sensor for sensing a modulated light signal, a processor for demodulating the light signal sensed by the photo-sensor and processing it, and a keyboard having a plurality of keys for instructing processing to the processor. The processor is housed in a housing and the keyboard is attached to the housing. The photo-sensor has a photo-sensing direction which is on a line extending from a longitudinal line on the keyboard.

Abstract: Optical heterodyne receivers for ASK-, PSK-, FSK-, and DPSK-modulated signals are disclosed which contain a polarization controller. The receiver contains a unit (Q, Q') which works on the difference-detector principle to eliminate the shot noise of the local oscillator (LO), which emits circularly polarized light. It further includes a quadrature demodulator (D, D', D") which, besides delivering the useful signal (N), provides polarization control signals (S.sub.E, S.sub.W) with which the ellipticity and the polarization angle of the received light (E.sub.S) are adjusted in such a way that the received light (E.sub.S) is linearly polarized at an angle of 45.degree. or 135.degree..

Abstract: A radio communications system is described in which analog voice signals are transmitted and received via single sideband amplitude modulation, and digital data signals are transmitted and received via narrowband frequency modulation in a single trunked radio system having dedicated channel bandwidths. The base station continuously transmits the FM signalling information on a dedicated control channel. The remote station transceiver initially acquires lock to the data channel FM carrier, which is then demodulated to determine the frequency of an assigned voice channel. The remote station then acquires lock to the single sideband pilot carrier on the appropriate voice channel. The controller incorporates a memory state for holding AFC for the mobile transmit frequency. In the preferred embodiment, the data channel incorporates 2400 bps FSK-FM data in a 6.

Abstract: In a digital information reproducing apparatus, a digital signal having passed through a band-limited transmission system is waveform-shaped at a threshold level controlled to its optimal value so that the information can be properly read out. The apparatus includes a threshold level control circuit for controlling the threshold level to shape the waveform of the input signal. This threshold level control circuit has a first control circuit for controlling the threshold level with reference to a read clock extracted from the input signal, and a second control circuit for controlling the threshold level of a shaped signal which is obtained by waveform-shaping the input signal so that the DC component of the shaped signal becomes a predetermined value. The control of the threshold level is performed by cooperation of the first and second control circuits.

Abstract: A high integrity optical data transmission system connecting a plurality of user I/O devices includes an optical path terminating at each user I/O device at a two port interface having a pair of optical transmitter and a pair of optical receivers for optically communicating the binary logic ONE and ZERO states and the system no data transmission state. A portion of the light transmitted over the optical path is fed back to the interface to control the transmitted light intensity. The two photodiode light receivers are closely matched in electrical characteristics and are biased by adjustable DC voltage sources so that the effects of photodiode dark currents on a trans-impedance amplifier are minimized.

Abstract: The relative intensity of the transmit beam and the local oscillator beam in a ladar diplexer can be continuously adjusted during operation by using a rotatable retardation plate with a slightly inclined "C" axis to turn a polarized laser beam into a composite beam having two components polarized in mutually perpendicular directions. The relative intensity of the components is adjustable by varying the inclination of the "C" axis. The composite beam is applied to the same polarizer element normally used to separate the return signal from the transmit beam. The polarizer acts as the beam splitter which separates the local oscillator beam from the transmit beam. The described configuration also saves one beam splitter and allows improved packaging and alignment of the diplexer.

Abstract: Disclosed are a pulse cancellation system and a pulse cancellation method for enhancing the effect of a small pulse superimposed on a large pulse, in the context of processing video signals in a circuit employing a compression video amplifier. The original waveform is delayed by a selected interval which is short as compared with the expected duration of pulses of interest in it, and the delayed waveform is subtracted from the original one to cancel the effect of those portions of pulses which are longer than the selected delay interval. Excursions of the resulting waveform which are on a selected side of a selected baseline can be removed, if desired. Alternative embodiments provide for selectively bypassing the delay and cancellation circuits, to feed the detector output directly to the compression amplifier in some cases, and for placing the small pulse enhancing circuit before the detector.

Abstract: An optical serial data bus for connecting logic cards used in a data processing system. The bus uses semiconductor lasers and PIN diodes as transmitters and receivers, transmitting through free space without the use of lenses or other optical elements. Each logic card communicates only with the adjacent cards on either side to minimize the transmission distance.

Abstract: A timing recovery apparatus for a burst mode communication receiver. The apparatus provides for optimum sampling and digitizing of received data at a plurality of data rates. In particular, a VCO is phase-locked to a local frequency reference prior to data being received. A reference timing preamble transmitted prior to the data is filtered and fed to the VCO causing it to injection lock such that the VCO becomes phase aligned with the preamble. The VCO is then permitted to "free run" during data transmission and continues to operate at substantially the same frequency. A synchronous divider and multiplexer, responsive to the VCO, allows selection of sampling clocks for the plurality of data rates. The divider is forced to a known state during VCO injection locking, to assure that the sampling clocks have maintained the proper phase for optimal sampling at the corresponding data rate. Further, means is provided to monitor the frequency of the VCO.

Abstract: An apparatus for discriminating an optical signal from others comprises a circuit for adding one of discriminating signals to a corresponding optical signal. The discriminating signal is of a frequency lower than a band of the optical signal. Therefore, the discriminating signal is easily detected by being passed through, for instance, a low-pass filter.An apparatus for tuning an optical wavelength filter used in apparatus for discriminating an optical signal from others comprises a circuit for frequency-modulating an optical signal by a first discriminating signal and for amplitude-modulating the optical signal by a second discriminating signal having a phase information of the first discriminating signal.

Abstract: An electronic device for a local area network of electronic apparatuses is characterized by a timer operatively associated with each apparatus, each timer being retriggerably responsive to the occurrence of a periodic feature of a code to assert a line driver for the period of the timer. The period of the timer is greater than the period of the feature.