Abstract: An Optical Frequency Division Multiplexing system achieves close channel spacings and thus high density of communications channels in a particular frequency band by providing a very precise carrier frequency stabilization technique. Each laser-generated local carrier signal is locked to a corresponding reference signal. All of the reference signals are generated by a common tunable laser circuit that produces a sequence of bursts of successively higher frequencies determined by resonant points of a single Fabry-Perot filter. Each transceiver of the Optical Frequency Division Multiplexing system includes a frequency tracking circuit that converts received signals from the optical domain to the electrical domain and utilizes an intermediate frequency filter circuit and a servo control circuit to adjust the tunable laser frequency and lock it to the present reference frequency.

Abstract: Optical communication methods and apparatus are disclosed for transmitting two or more optical signals with different optical carrier frequencies on a single optical fiber with high spectral efficiency. Each optical carrier is typically modulated with multiple modulated subcarriers. In one embodiment, an optical phase modulator provides cancellation of second order intermodulation products in each optical signal, thereby permitting the optical carrier frequencies to be spaced by 2f.sub.max, where f.sub.max is the maximum modulation frequency. In another embodiment, a single sideband optical phase modulator provides cancellation of second order intermodulation products and one signal sideband, thereby permitting the optical carrier frequencies to be spaced by f.sub.max.

Abstract: Every subscriber node connected to an optical fiber comprises an access unit with a directional coupler which is controlled via an output amplifier, an optoelectric converter being connected subsequent to the directional coupler. Packets run on the fiber. The first bit of the packets indicates whether it is an empty packet (shown by "light" or "bright") or a data packet (shown by "no light" or "dark"). As soon as the node has prepared data for transmission in a buffer storage, a test is effected at each arriving packet as to whether or not it is an empty packet. For this purpose, the light of every first bit is guided to a L/I detector which carries out this test in a "flying" manner, while a no-light bit passes on to the outgoing fiber. If the L/I bit indicates a data packet, the control immediately switches the directional coupler to pass, so that the packet passes the node so as to be unchanged.

Abstract: An optical switch array is provided so as to connect a first group of M terminals capable of transmitting and receiving signals to and from a second group of N terminals, where M and N are respectively an integer of not less than 1.The optical switch array comprises first and second light-emitting devices, first and second light-receiving devices and first and second shutter arrays.The first and second light-emitting devices comprise M light sources driven in response to the signals input from the terminals of the first group and N light sources driven in response to the signals input from the terminals of the second group, respectively. The second light-emitting device is arranged in series with the first light-emitting device.The first and second light-receiving devices are arranged in a direction perpendicular to a predetermined direction in which the first and second light-emitting devices are arranged.

Abstract: Increasing the capacity of an existing lightwave transmission system can be accomplished by either increasing the bit rate or adding wavelength-multiplexed channels. Recent advances in erbium-doped fiber amplifier technology make the wavelength division multiplexed option particularly attractive. Unfortunately, because of nonuniform wavelength-dependent gain profile and saturation characteristic of erbium-doped fiber amplifiers, each channel of a wavelength-multiplexed system will experience a different optical gain which, in turn, can result in an excessive bit-error-rate performance in some channels. This invention is directed toward processing apparatus which selectively equalizes the optical gain or the optical signal-to-noise ratios of the channels of a wavelength-multiplexed optical transmission system. The output powers and the signal-to-noise ratios are selectively equalized by adjusting the optical input signal powers.

Abstract: An optical linear feedback shift register arrangement includes an optical encoding means implemented using a modified Sagnac switch. The encoding means encodes a received optical clock signal with a value derived from an exclusive-or of a first and second delayed version of an encoded signal received, respectively, at a first and second control ports. The resulting encoded clock signal, appearing at an output port, is then coupled through a first delay means to said first control port and coupled through a second delay means to said second control port. In another arrangement, an optical communication system utilizes the above-described linear feedback shift register to encode a data signal at a transmitter location and uses an identical linear feedback shift register at the receiver location to decode the encoded data signal.

Abstract: In a bidirectional light waveguide telecommunication system comprising telecommunication equipment that each respectively comprise a laser module whose monitor diode is also used as a receiving diode, the telecommunication equipment work in frequency-division multiplex in which a modulation circuit that precedes the laser transmitting diode converts the electrical transmission signal into a frequency band other than the frequency band occupied by the electrical reception signal. A frequency separating filter that follows the monitor diode is then connected, first of all, to a reception signal demodulator and, secondly, to a control circuit for setting the operating point of the laser transmitting diode.

Abstract: A supervisory circuit for optical repeaters has a selective decoder circuit for selecting and decoding either one of control signals for monitoring which are separated from individual transmission signals being propagated over the first channel and the second channel. When noise ascribable to a fault occurs on the first channel, a signal path connecting to the selective decoder circuit for inputting a control signal from the first channel is interrupted. Noise of this kind is detected in terms of an input signal level which does not lie in the frequency band of control signals.

Abstract: A network ring topology includes a plurality of entry and exit interfaces (100,110) disposed in administrative locations such as in an equipment room (53) and in riser and satellite closets (51, 57), and at stations. Interconnections between ports of sets of ports of the interfaces are made in the closets by jumpers (120--120) and either in a direct or in an inverted manner, the direct being between corresponding ports of corresponding sets of ports in interfaces. Inverted connections are made between two exit or between two entry interfaces in which input and output ports of corresponding rings are connected by jumpers. The interfaces are color coded and may be either entry or exit type to denote the arrangement of the ports. The interfaces and the color coding arrangement allow a craftperson to make connections in an administrative location without having to follow signals through the ring. For a dual ring counter rotating network, each interface necessarily include two sets of ports.

Abstract: An optical communication system for communicating information. The systems includes a source of continuous wave laser light and one or more acoustic beams whcih are frequency or amplitude modulated by data. The laser light beam and the acoustic beams are input to an acousto-optical modulator for producing an undiffracted laser light beam and one or more diffracted laser light beams. The diffracted laser light beams are frequently shifted from the undiffracted laser light beam and contain the data to be transmitted. The diffracted and undiffracted beams are combined and transmitted over an optical fiber for demodulation at a distant location by a receiver. The receiver includes a photodiode which heterodynes the diffracted and undiffracted beams and produces signals having the frequencies of the acoustic beams. Tuning circuitry separates the signals and demodulators reconstruct the data transmitted.

Abstract: In a system wherein a main channel of data is transmitted between two stations by means of an optical waveguide, an additional optical channel may be transmitted. Bits of the additional optical channel are inserted into the main channel at a transcoder in the transmitting station in place of bits of the main channel at defined spacings, known to the transcoder of the receiving station, with a bit rate lower than that of the main channel. The inserted bits are removed from the optical main channel at the receiving station. The bits of the additional optical channel inserted into the main channel are double bits that are identical to a forbidden bit combination that results during the recoding of an electrical AMI code into an optical CMI code. In the receiving station, the double bits of the main channel replaced by the bits of the additional optical channel are recovered by using sequential logic and memory to apply the fixed rules of the electrical AMI code.

Abstract: An interferometer, such as a fiberoptic Mach-Zehnder type, is equipped at a transmission end of the system with a phase modulator driven by a data-input signal to be transmitted; and at a reception end with another phase modulator driven by a large reference signal. Nonlinear dependence of output intensity on these signals yields an intensity component that is the product of the signals at the modulators; and in turn an electrical output-signal component at frequency equal to the difference between the data- and reference-signal frequencies. A servocontrolled phase bias holds the system near a minimum in overall light level, where nonlinearity is prominent while intensity-related noise is minimized.

Abstract: A remote controller capable of learning and later transmitting infrared signals transmitted by any other remote controller. The remote controller determines which of four modes of transmission a signal is transmitted in, including carrier mode, pulse mode, frequency shift keying mode and continuous wave mode. Once the type of signal is determined the controller learns each signal, saves them and later replays them to control a remote device.

Abstract: An optical receiving method utilizing polarization diversity is disclosed in which first and second reference lightwaves having different frequencies and having polarization planes substantially perpendicular to each other, are combined with a signal lightwave to form a combined lightwave. The combined lightwave is subjected to heterodyne detection to obtain a detection signal and the detection signal is separated into first and second intermediate-frequency signals having different carrier frequencies. The first and second intermediate-frequency signals are converted into first and second baseband signals, respectively, and the first and second baseband signals are added to obtain an output signal.

Abstract: A fully redundant safety interlock system is provided comprising, means for detecting the loss of light on a fiber optic link; controller means, coupled to said means for detecting, for determining the safety condition of the link based on the output of said means for detecting, and for controlling the radiant energy output of an optical transmitter, based on the determined safety condition, via redundant output control signals; and means, coupled to said controller means, responsive to said redundant control signals, for interconnecting the output of said controller means to transmitter drive circuitry to thereby adjust the radiant energy output by the transmitter. According to a preferred embodiment of the invention, the controller means includes an electronic implementation of two independent state machines, each of which redundantly determines the connection state of the optical link between two optical link cards.

Abstract: An optical communication system includes a transmitter for generating a subcarrier multiplexed optical signal, a receiver and an optical fiber for coupling the optical signal from the transmitter to the receiver. At the transmitter, an optical carrier is modulated with a composite modulation signal including a plurality of modulated microwave subcarriers to provide the optical signal. The receiver includes a local oscillator for generating a local light beam, a detector responsive to the received optical signal and the local light beam for providing a detected signal at an intermediate frequency, and a microwave receiver for demodulating the microwave subcarriers from the detected signal. The modulation index of the optical signal produced by each of the modulated microwave subcarriers is selected to permit transmission of a large number of high quality video channels. A quadrature detector can be used to eliminate second-order intermodulation products.

Abstract: Apparatus and method are disclosed for controlling the tone spacing (2.omega..sub.d) and output power level in an FSK lightwave transmitter. An arrangement is utilized which splits a tapped-off portion of the output data stream into two essentially equal components. A first component is then delayed and scrambled (polarization state) with respect to the second component. Self-heterodyning of the two signals results in forming a signal at the beat frequency, or tone spacing value. By comparing this beat frequency with a predetermined tone spacing value, adjustments may be made to the transmitter to maintain the desired tone spacing value. The self-heterodyned signal will also contain a component indicative of the data signal power level and may be utilized to adjust the transmitting device so as to maintain a constant power.

Abstract: A self-synchronizing infra-red communication system. The coding scheme involves transmitting a series of pulses, the separations between successive pulses representing the same data. Even though the separations between successive pulses all represent the same data, the separations are all different; it is this feature which allows for self-synchronization. Arrival times of successive pulses are recorded; the arrival times represent the receipt not only of transmitted pulses, but also of detected noise. The time differences between all arrival times (not only successive arrival times) are checked for consistency with predetermined allowable time-interval ranges which can separate successively transmitted pulses in a data sequence. When a sufficient number of such checks have been made, representing a sufficient degree of redundancy, it is possible to derive the data value represented by all of the pulse separations.

Abstract: To transmit a frequency-division multiplex signal occupying a broad frequency band, e.g., the 40-440 MHz cable television frequency band, over an optical-fiber transmission link, in the transmitter, the whole frequency band to be transmitted is converted by single-side-band amplitude modulation of a high-frequency carrier f.sub.0 to a higher-frequency band, e.g., 840-1240 MHz, which, referred to its lowest frequency, is less than one octave wide. Second-order intermodulations products, which usually result during electric-to-optical conversion, thus fall into unoccupied frequency ranges. At the receiving end, corresponding demodulation is performed employing either carrier recovery or a locally generated carrier. In a preferred embodiment, the frequency band to be transmitted is converted to the higher frequency band in several subbands.

Abstract: Device for optical heterodyne detection of an optical signal beam and an optical transmission system provided with such a device. An optical heterodyne detection device is described in which with the aid of three controllable elements (A, B and C), to influence the state of polarization and having a limited control range, such as Faraday rotators or birefringent electro-optical crystals, the state of polarization of radiation originating from a local oscillator (30) is made to correspond to the signal beam transmitted through a long-distance transmission fibre (10).