Abstract: A narrow band laser transmitter comprising a semiconductor laser and an external optical resonator coupled by a coupling arrangement to the semiconductor laser characterized by the external optical resonator being a wavelength-selective fiber directional coupler in the form of a double core fiber whose cores have different refractive index discontinuities to the respective environments and different cross-sections. The laser transmitter is suitable for practical use, has a space-saving structure and is stable in operation.

Abstract: A sequential configuration of log.sub.2 n stages of birefringent elements are set forth. Each stage has a transfer function approximating a square wave, and successive stages have half periods. An input beam with n wavelength components would be demultiplexed into 2, 4 and finally n output beams at the output of the first, second, and log.sub.2 n stages, each output beam containing only one wavelength. Successive stages consist of two polarizing beam splitters between which is located their appropriate length of birefringent element to achieve the desired transfer function.

Abstract: The system comprises subscriber stations (1, 2) each comprising a semiconductor laser generator (4) provided with means (3, 5) for modulating its laser output by means of transmit signals and a heterodyned detection system consisting of a photoelectric receiver (15) optically coupled to a local oscillator (17), an exchange (32) comprising a computer (37) and dual cavity semiconductor laser transmitters (39) connected to the outputs (38) of the computer, a passive optical distributor (31), and optical fibers (16, 8) connecting the lasers (4) and receivers (15) of each station with the optical distributor (31), on the one hand, and the lasers (4) of each station to the exchange (32), on the other hand, the computer assigning an optical frequency for each requested call and the laser transmitters of the exchange being operable to lock the transmit optical frequency of the calling and the called station lasers (4, 104), via optical fiber lines (8), on the frequency assigned by the computer.

Abstract: A symbol generator is provided for generating a filtered analog waveform for use in phase modulating a carrier. A memory (30) is provided for storing predetermined waveform segments. The waveform segments are correlated with an input data stream. The data stream is converted to an address for the memory (30) to output a digital value to a D/A converter (122). The output of the D/A converter (122) is comprised of in-phase and quadrature-phase components which are input to a sample and hold circuit for generating the analog signals. The waveform segments are then sequentially assembled and input to a vector modulator (168).

Abstract: An n channel birefringent multiplexer/demultiplexer consists of log.sub.2 n sequences of birefringent crystal elements in Solc-type filter configuration. The configuration of polarizing beam splitters have one such beam splitter before the first sequence, one such beam splitter after the last sequence, and solely one such beam splitter between adjacent sequences of birefringent elements. With such multiplexer/demultiplexer horizontally and vertically polarized components of an input beam are separated at the input beam splitter, independently traverse all of the sequences of the birefringent elements and are recombined to form output beams only upon reaching the output beam splitter.

Abstract: A card, such as a credit card or identification card, includes electronic circuitry which permits its identification by an identifying device. More particularly, optical radiation is transmitted from the identifying device to the card to be identified. The radiation is modulated with information by a modulating device included in the card and is retransmitted to the identifying device.

Abstract: An optical fiber data link system comprising a controller and one or more stations, all of which are connected to one another by a series of optical fibers providing a single loop as a whole. At least one data input module and/or one data output module is connected to each station. The controller includes a light receiving element, a serial-parallel converter, an circuit for generating an address/data indicating signal, an address setting circuit, a parallel-serial converter and a luminous element. Each station includes a light receiving element, a serial-parallel converter, an address/data distinguish circuit, a parallel-serial converter and a luminous element. Each data input module includes an address decoder, a comparison circuit, a switch circuit, a data latch circuit and one or more input terminals. Each data output module includes an address decoder, a comparison circuit, a switch circuit, a data latch circuit and one or more output terminals.

Abstract: A timing control arrangement that dynamically controls the distribution of iming information in a distributed digital communication system. A reference timing signal is distributed from a reference master node to all other nodes in the system. The distribution is accomplished on a dynamic basis without the use of a central control. Each node is connected by links to at least one other node and each node receives timing signals from all of the links to which it is connected. Each node selects one of these signals as its timing reference by scanning the various signals it receives to identify the one signal that is applied via a link path that is the "closest" to the master reference node as indicated by information specifying the number of intermediate nodes through which the timing signal has traveled from the reference node to reach the receiving node.

Abstract: Filter quality is substantially improved (or complexity substantially reduced) in a digital PSK modem requiring an overall filter characteristic of the percent raised cosine type by using, in both the transmitter and the receiver, a filter having the same percent raised cosine response but at a higher cutoff frequency which satisfies the formula ##EQU1## where f.sub.f is the cutoff frequency (6 db) of the new filter, f.sub.o is one-half the baud rate of the modem, and .alpha. is the percent raised cosine expressed in decimal form.

Abstract: A multi-mode radio transceiver comprising a sequence of bi-directional circuit modules including a radio frequency input/output amplifier module (1), a radio frequency/baseband I and Q quadrature channel conversion module (2), an analogue/digital conversion module (3), a digital signal processor (4,5), and a digital signal input/output interface (6), with a control means (7) whereby for transmission a radio frequency signal is formed from analogue quadrature I and Q channel components of a digitized signal at baseband and translated to the radio transmission frequency and for reception the radio frequency signals are transformed into I and Q quadrature analogue components at baseband and subsequently digitized.

Abstract: Methods for modulating and demodulating digital data streams utilize a quadrature-quadrature phase shift keying data transmission arrangement to acheive a 100% increase in the bandwidth efficiency over known systems, such as minimum shift keying. Known arrangements utilize two dimensional data transmission. However, Q.sup.2 PSK, in accordance with the invention, provides four dimensional transmission which doubles the rate of data transmission for a given bandwidth, at the expense of approximately 45% increase in the average energy per bit. The input data stream is demultiplexed to form four demultiplexed data streams which are formed of demultiplexed data bits, each such stream being coded to form a stream of data words formed of a predetermined number of data pulses and a parity check bit. Each such data stream is combined with a signal having carrier and data pulse-shaping components.

Abstract: An optical communication system including repeaters which return a preamble signal to the receive line as soon as it detects a carrier on the transmit line of a single line optical bus. Therefore, transmission equipment can confirm data transmission quickly because the time delay between data transmission and its confirmation is decreased. The repeater also monitors a time delay associated with the return through a return loop of the transmitted data, and produces and transmits a failure signal when the time delay is longer than a predetermined value. The system also includes an optical transceiver connected between the optical bus and the transmission equipment which converts optical signals into electrical signals and visa versa and also adds the preamble signal to the front of data to be transmitted.

Abstract: Instead of an excitation pulse sequence producing circuit which is used according to prior art in calculating locations of excitation pulses and pulse amplitudes thereof, an excitation pulse sequence parameter producing circuit is used in a low bit-rate pattern coding device in recursively giving delays of the respective pulse locations to a discrete impulse response sequence to provide a system of delayed impulse responses and in transforming the delayed impulse response system into an orthogonal set of set elements. Meanwhile, the pulse locations are determined with element amplitudes or factors calculated for the respective system elements by the use of the system elements and each segment of a discrete pattern signal sequence. The pulse locations and the element amplitudes are used as parameters descriptive of the excitation pulses. Alternatively, the pulse locations are determined one at a time after quantization of each of the recursively determined element amplitudes.

Abstract: Partial response and quadrature partial response data transmission system characterized by increased transmission rate, lower signal-to-noise ratio, low cost and simpler hardware implementation than prior art systems. A steep filter (almost rectangular) is connected to the output of a cosine filter, forming a composite filter, wherein the cut-off frequency of the rectangular filter is less than the Nyquist frequency by a predetermined amount which is inversely proportional to the amount in percentage by which the data transmission rate exceeds the Nyquist rate. The system is thus capable of signalling at the Nyquist rate and greater, without requiring that channel filter parameters or the basic clock rate be adjusted. A smaller number of signal levels can be selected (as compared to previously existing methods) for spectrally efficient applications, and the resulting more robust system can also be used to transmit PAM, QAM, and other baseband or modulated signals.

Abstract: A system protocol for the composite shift key communication of binary signals in which a transmitting transceiver transmits a first summed signal having a first qualifying signal at a qualifying signal frequency Wqt as one of the summed signal components only when a binary signal is desired to be transmitted. The transmitting transceiver ceases transmission of the first qualifying signal Wqt as a transmitted signal or as a component of a composite summed signal when neither a binary zero nor a binary one is desired to be transmitted. The receiving transceiver signals to the transmitting transceiver when the binary signal transmission is being successfully received by transmitting thereto a second qualifying signal Wqr. The receiving transceiver drops the transmission of the second qualifying signal Wqr when the binary signal transmission is not being successfully received, or is being received with perceived errors therein.

Abstract: A frequency agile signal generator provided for emulating a communication signal of predetermined frequency and modulation characteristics including frequency hopping. The signal generator includes a digital controller such as a microprocessor or microcomputer for generating digital command signals specifying the desired characteristics of the output signal. In response to the digital command signals, a base digital frequency signal representing the desired base or center frequency of the output signal is generated by a number controlled oscillator in response to a digital frequency control signal. The digital command signals also control the generation of an analog modulation signal having desired modulation characteristics.

Abstract: A transmit/receive space diversity system communicates between transmitter-receivers at two separate sites. Each site has at least two antennas. Each antenna at a first one of the sites transmits a pilot signal, at differing frequencies. At the second or other site, all the pilot signals are received by each antenna, and the pilot signals are evaluated to determine which pilot-signal-receiving antenna is part of the lowest loss path between the sites. A data source at the second site is routed to the identified antenna for transmission of data signals back to the first site. At the first site, the data signals are received by all the antennas, and the best of the received data signals is routed to utilization apparatus. A data signal from the first site is transmitted to the second site, at which it is received by the selected antenna.

Abstract: A bidirectional fiber optic system is described in which at one terminal the output radiation of a light source (LED or semiconductor laser) is coupled through a small diameter hole in the active area of a photodiode into the core of a larger diameter transmission fiber. On the other hand, radiation propagating through the fiber in the opposite direction exits from the fiber with a large numerical aperture so that most of it is incident on the active area of the photodiode and little is lost through the hole. Also described are a number of photodiode configurations for use in such a system, as well as dual photodiodes to perform both signal detection and output monitoring functions. Further described are fiber optic sensing systems for monitoring such variables as blood pressure.

Abstract: An adaptive equalizer for data signals is allowed to start up and train in a wholly decision-directed mode but is precluded from converging to an incorrect state by inhibiting equalizer updating for equalizer output values which fall within a predetermined null zone.

Abstract: An apparatus for processing a digital signal which is transmitted from a transmit station by radio equipment and contains the same repetitive information employs the principle of decision by majority. A particular signal pattern with the least error rate is determined by majority. Noncoincident bits between the determined signal pattern and each of the repeatedly received patterns are counted and, then, the number of noncoincident bits is determined on each of a predetermined number of patterns which are selected by a selector out of the repeatedly received ones. When the number is smaller than a predetermined one, the pattern is allowed for processing. That is, the signal pattern is processed by measuring the bit error rate in a transmission path with the signal pattern equivalently used as a reference.