Abstract: A method and apparatus for generating signals representing a plurality (p) of n bit words corresponding to respective input signals. The apparatus comprises a basic word generator (7) for generating first signals representing m basic words (A-D) whereby the p words are the same as or are cyclic rearrangements of the n bits of the m basic words. Control means including combinatorial logic (33) determines the one of the p words corresponding to each input signal and generates corresponding control signals. Selection means including optical modulators (10-13, 20-25) are responsive to the control signals for selecting the appropriate first signal, if necessary after recycling by imposing selected delays, to constitute an output signal corresponding to the determined one of the p words.

Abstract: An optical logic device comprises a source of substantially constant, incoherent, optical power. Optical signal output means such as a waveguide switch receives the optical power from the source and has two output ports. The waveguide switch is responsive to electrical control signals selectively to generate optical signals on its output ports. A photodetector detects the logical condition of an optical input signal and generates a corresponding electrical control signal for controlling the waveguide switch. The arrangement is such that the optical condition of the output port is the logical complement of the logical condition represented by the optical input signal.

Abstract: A method and system for demultiplexing an optical signal having a bit rate in the order of GBit/second. The system comprising optical demultiplexing means including delay units and sampling devices such as optical modulators which are controlled at the Bit Rate so that the output signals of the optical modulators correspond to respective ones of the four channels of the original multiplexed signal. These demultiplexed signals may then be converted by regenerators into corresponding electrical signals.

Abstract: An electronic telephone exchange of the type employing time-space-time switching, has an optical fiber data link connecting the space and time switches. In order to meet the design requirements for use in a telephone exchange, the fiber optic link has to have fairly well defined performance parameters. In particular the overall diameter of the optical fibers employed in the optical fiber link lies between 180 and 250 microns, preferably 200 microns, and the core diameter of the optical fibers lies in the range 0.6 to 0.95 of the cladding diameter. Preferably the core diameter lies in the range 160-180 microns. The optical fiber link is characterized by the numerical aperture of the fiber, insertion loss of the fiber, sensitivity and dynamic range of detector, and the power output and extinction ratio of the transmitter.

Abstract: A signal level stabilizer includes two amplifier stages, each stage having a respective feed-back loop to control its gain. The gains of the amplifiers are varied in response to variations in the level of the input signal to give a substantially constant output signal. At low levels of the input signal the gain of one of the amplifiers only is varied in response to variations of the input signal and at high levels of the input signal the gain of the other amplifier is varied. The amplifiers may be part of a repeater in an optical communications linkage and one of the amplifiers may then be a photodiode and the other a power amplifier.