Abstract: A dc-coupled receiver for a shared optical system includes an input feedback amplifier circuit which establishes a dc reference baseline voltage level for incoming packets of data. A pair of sample-and-hold circuits are connected in parallel to receive and sample signals from the feedback amplifier circuit when no data is being transmitted and at the initial edge of incoming packets of data. A voltage divider circuit receiving signals from the sample-and-hold circuits establishes a dc slicing level for each incoming packet of data. An output feedback circuit can be added to compensate for offset error without affecting the performance of the sample-and-hold circuitry.

Abstract: An optical frequency division multiplexing network includes first optical communication paths connected to terminals, respectively, a second optical communication path connected to the outside and a node composed of a selection unit for selecting signals having optical frequencies to be sent to the plurality of terminals, respectively, from signals transmitted through the second optical communication path in optical frequency division multiplexing, a conversion unit for converting the selected signals into signals having a single optical frequency and an output unit for producing the converted signals to the terminals through the first optical communication paths, respectively.

Abstract: The present invention provides a wavelength division multiplexed optical communication system which includes an optical monitoring channel which is capable of surviving the failure of an optical amplifier. The optical communication system comprises a plurality of optical transmitters which optically communicate with an optical waveguide which carries the multiplexed optical transmission signal. At least one multiple-stage optical amplifier having at least first and second stages is positioned along said optical waveguide. The optical amplifier includes a first and second stages comprising doped fibers having a first gain wavelength band. An optical connecting element having a plurality of ports is positioned between the first and second stages.

Abstract: Spontaneous emission occurring in association with direct optical amplification using an erbium-doped optical fiber is modulated with an auxiliary signal, such as a supervisory signal, for transmission of the auxiliary signal. In a first aspect of the invention, the output of an optical amplifier is passed through a variable optical band-pass filter whose transmission characteristic is varied in accordance with the auxiliary signal, to modulate the spontaneous emission component contained in the optical amplifier output. In a second aspect of the invention, the output of the optical amplifier is separated by an optical branching device into a main optical signal and part of the spontaneous emission.

Abstract: A method and apparatus for reducing noise in optical communication systems, wherein the frequency of light output from a signal laser is modulated or dithered to broaden the optical spectrum of the signal laser. The broadening allows error-free data transmission within signal bands, despite the presence of optical beat interference. Different dithering tones are emitted by each laser in the network. The dithering tone for each signal laser in an optical network is chosen so that distortion resulting from the dithering tone falls outside the signal bands.

Abstract: The device comprises a first opto-optical gate for resynchronization and a second opto-optical gate for amplitude regeneration, the signal output by the first gate being applied to the control input of the second gate. The device also includes an opto-optical gate for regenerating contrast which receives a signal to be generated both on a source input and on a control input. The opto-optical gate is a three-input Mach-Zehnder interferometer, with each of the two branches thereof having a respective semiconductor optical amplifier.

Abstract: The short optical pulse generator is provided with a semiconductor laser which oscillates continuously at a single wavelength, a semiconductor electro-absorption type optical modulator which performs the intensity modulation of the output light from the laser, and a sinusoidal voltage generator and a DC voltage generator for driving the electro-absorption type optical modulator. A DC voltage is applied to the electro-absorption type optical modulator so that the output light from the laser is sufficiently extinguished. By applying a sinusoidal voltage to the optical modulator, short optical pulses are generated.

Abstract: Optical transmission systems in which interactive services, such as video-on-demand, are to be provided must be low in cost if the services are to find acceptance. This requires, among other things, that as little change to the structure of existing optical transmission systems as possible should be necessary.In the optical transmission system according to the invention, a first frequency-division multiplex signal (S.sub.T) is formed from subscriber-assigned video and telecommunications signals at a center (1). Cable television signals (S.sub.TV) are transmitted with light of a first wavelength, and the first frequency-division multiplex signal (S.sub.T) with light of a second wavelength, to at least one optical network termination (3). In the latter, the cable television signals (S.sub.TV) and the video signals are combined into a third frequency-division multiplex signal.

Abstract: An optical communication system in which the degradation of the signal-to-noise-ratio during transmission is alleviated. An optical signal from an optical transmitter is propagated over a transmission line comprising optical fibers and optical amplifiers, and received by an optical receiver. The signal-to-noise ratio is improved by inserting an injection-locked laser device at a specified point on the optical transmission line, improving the transmission characteristics of the optical communication system.

Abstract: A method and apparatus for receiving infrared signals are provided. The circuit includes preamplifier that includes an integrator that charges based on light detected by a photodiode. The circuit includes a warning circuit that generates a warning flag when the charge on the integrator exceeds a predetermined level. To prevent the integrator from saturation, digital logic resets the preamplifier by dumping the charge on the integrator in response to the warning signal. The digital logic is also configured to reset the integrator at predetermined intervals. When the incoming signal is encoded using pulse position modulation, the interval at which the integrator is reset is the length of a single time slot in the pulse position modulation frame. A sample and hold circuit is provided to hold a previous output of the preamplifier. The difference between the previous output of the preamplifier and the current output of the preamplifier is compared with a threshold voltage to detect pulses on the incoming signal.

Abstract: An optical fiber transmission line capable of suppressing the generation efficiency of four wave mixing in transmitting wavelength multiplex signal light. The transmission line employs a single mode optical fiber in which a zero dispersion wavelength is varied in the longitudinal direction of the optical fiber more largely than manufacturing variations in manufacturing conditions of the optical fiber. The use of this optical fiber as the transmission line suppresses the generation efficiency of four wave mixing in transmitting the wavelength multiplex signal light to allow the transmission of the wavelength multiplex signal light with a reduced crosstalk.

Abstract: An optical distribution network connects a downstream central office terminal to a number of upstream optical network units which service respective subscribers. Transmit and receive feeder fibers branch out to the optical network units. An optical carrier is modulated with an amplitude-varied signal including at least two different amplitude levels above a selected amplitude threshold, with at least one of the amplitude levels being selected so that it will not be reliably detected at the upstream end when a fiber in the path between the central office terminal and a destination optical network unit fails to meet a threshold power margin. The amplitude-varied optical signal is transmitted upstream to each destination optical network unit during, for example, a corresponding time slot. The portion of the signal containing the lower amplitude portions has no significance to the optical network units and is ignored.

Abstract: An optical multiplexing device spatially disburses collimated light from a fiber optic waveguide into individual wavelength bands, or multiplexes such individual wavelength bands to a common fiber optic waveguide or other destination. The optical multiplexing device has application for dense channel wavelength division multiplexing (WDM) systems for fiber optic telecommunications, as well as compact optical instrument design. Multiple wavelength light traveling in a fiber optic waveguide is separated into multiple narrow spectral bands directed to individual fiber optic carriers or detectors. An optical block has an optical port for passing the aforesaid multiple wavelength collimated light, and multiple ports arrayed in spaced relation to each other along a multiport surface of the optical block. A continuous, variable thickness, multi-cavity interference filter extends on the multiport surface of the optical block over the aforesaid multiple ports.

Abstract: The present invention relates to an apparatus for generating quasi equally spaced multi-channel frequencies using a frequency shifter. The optical multi-channel transmission system using OFDM or WDM can be provided with quasi equally spaced(unequally sequential spaced) frequencies on the basis of the functional relation among the frequency differences(n.sub.ij =n.sub.i -n.sub.j (i=j=1,2,3, . . . n)) of any two neighboring channels. Namely, after generating equally spaced frequencies by using a reference resonator, such as a Fiber Fabry Perot(FFP) resonator, each of the equally spaced frequencies is sequentially shifted by a frequency shifter, which generates and controls the quasi equally spaced(unequally sequential spaced) frequencies in order to effectively avoid crosstalk due to FFWM, and fully make use of the transmission bandwidth belonging to the low dispersion region of the optical fiber.

Abstract: A semiconductor optical device fabricating method for easily fabricating on a single substrate a plurality of distributed feedback lasers or distributed Bragg reflector lasers with uniform static and dynamic properties and individually different oscillation wavelengths. A plurality of pairs of stripe type insulating thin film masks are formed over that region of the semiconductor substrate which has optical waveguides formed therein for the lasers. Each pair of stripe type masks has a constant gap therebetween. With the masks in place, optical waveguide layers for the lasers are grown in crystallized fashion through metal organic vapor epitaxy. The stripe type masks in pairs differ dimensionally from one another.

Abstract: A portable electronic apparatus is provided with a plurality of infrared element connectors on the housing surfaces thereof. A detachable infrared emitting/receiving element is electrically connected to one selected from the infrared element connectors which is directed toward the opposite apparatus so as to provide the desired infrared connection. This causes the infrared transmission to be made without changing the direction of the apparatuses.

Abstract: A method and device for increasing the bandwidth of a drop line in a power line carrier communication system for facilitating high speed transmission of communication data. The drop line is divided into two sections, each containing both high frequency communication data components and low frequency power components. A high pass filter is provided for passing the high frequency components to a receiver device and a low pass filter is provided for passing the low frequency power components to an electrical system in a residence. The low pass filter is also used for blocking, from the drop line, high frequency noise generated by electrical appliances operating from the electrical system.

Abstract: An apparatus and method for use in an optical system. An in-line optical wavelength reference and control module (WRCM) is inserted in series with an optical fiber signal path between an input fiber and an output fiber. The WRCM includes an input lens, a multi-element grating and an output lens. The input lens couples an input optical signal from the input fiber into the multi-element grating. The multi-element grating includes low-efficiency gratings which reflect portions of the input optical signal having different predetermined characteristics to different detectors of a detector array, while transmitting the remaining portions of the input optical signal to the output lens. The output lens couples the transmitted portions of the optical signal back onto the optical signal path. The WRCM may thus be placed directly in series with an optical signal path.

Abstract: A system for transmitting optical power from a first location to a second location. The system includes a first light source at the first location which generates a first light beam. A power converter detects the first light beam at the second location. A first control circuit coupled to the power converter operates a second light source at the second location to generate a return safety light beam after detection of the first light beam. A photodetector detects the return safety light beam at the first location. A second control circuit is coupled between the photodetector and the first light source. The second control circuit detects the presence of the return safety light beam and operates the first light source to generate the first light beam at a first power level prior to detecting the return safety light beam and at a second power level, higher than the first power level, after detecting the return safety light beam.

Abstract: The optical regenerative circuit comprises: branching circuit for supplying a received optical data signal to two branch circuits; optical clock generator circuit for generating an optical clock signal from a first optical data signal, the first optical data signal being the optical data signal supplied to a first branch circuit of the two branch circuits; optical discriminating circuit for discriminating in an optical form a logic level of a second optical data signal in synchronization with the optical clock signal produced by the optical clock generator circuit, the second optical data signal being the optical data signal supplied to a second branch circuit of the two branch circuits; and variable-delay circuit for adjusting timings at which the second optical data signal and the optical clock signal are received by the optical discriminating circuit, by delaying a predetermined one of the first optical data signal, the second optical data signal and the optical clock signal so that the timings are synchro