Abstract: The invention provides an optical communication system (10) comprising a plurality of mutually interconnected bi-directional optical waveguide rings (20, 30, 40, 50, 60) in which radiation modulated with communication traffic propagates. The radiation is partitioned into 32 distinct wavebands. Interfaces (70, 80, 90, 100, 110, 120) are included in the system (10) where communication traffic propagating in the rings transfers from one ring to another. Each interface (70) is capable of providing an all-optical waveband reconfigurable communication link between the rings (20, 30, 40, 50, 60). At each interface (70), conversion of optical radiation to corresponding electrical signals is not required when transferring communication traffic from one ring to another, thereby providing the system (10) with a potentially larger communication bandwidth compared to conventional optical communication systems.

Abstract: The invention provides a radiation power equalizer for an optical communication system, the equalizer characterized in that it includes: (a) an optical demultiplexer (300) for partitioning information-bearing radiation received at the equalizer into one or more radiation components corresponding to wavelength division multiplexed communication channels of the system; (b) a liquid crystal cell array (310) for selectively transmitting or attenuating said one or more radiation components; (c) an optical multiplexer (330) for combining one or more of the radiation components transmitted or attenuated through the cell array (310) to provide combined radiation; (d) a transmitter erbium-doped fiber amplifier (70) coupled to a PIN diode detector array (120) for measuring radiation power present in said one or more of the radiation components included in the combined radiation and generating one or more corresponding component radiation power indicative signals; and (e) a control module (130) for receiving said one or

Abstract: A signal transmission system has a number of wave division multiplex optical carriers linking a number of switching units arranged in a closed ring network. The carriers are amplified to compensate for loss and attenuation, but the ring gain of each carrier must be less than unity to prevent unwanted signal oscillation. An automatic gain control arrangement is operative for each optical carrier which is detected as being present at a switching unit, and the gain control is disabled for each carrier which is detected as being absent.

Abstract: The invention provides a radiation power equalizer for an optical communication system, the equalizer characterized in that it includes: (a) an optical demultiplexer (300) for partitioning information-bearing radiation received at the equalizer into one or more radiation components corresponding to wavelength division multiplexed communication channels of the system; (b) a liquid crystal cell array (310) for selectively transmitting or attenuating said one or more radiation components; (c) an optical multiplexer (330) for combining one or more of the radiation components transmitted or attenuated through the cell array (310) to provide combined radiation; (d) a transmitter erbium-doped fiber amplifier (70) coupled to a PIN diode detector array (120) for measuring radiation power present in said one or more of the radiation components included in the combined radiation and generating one or more corresponding component radiation power indicative signals; and (e) a control module (130) for receiving said one or

Abstract: Optical switching arrangement for switching a number of optical signals, consists of a thermo-optic switch having a number of heaters which are heated by passing electrical current through them. The mark-space ratio of current supplied from a constant voltage source is varied to provide constant power to the heaters to compensate for resistance changes in the heaters.

Abstract: The invention provides an optical communication system (10) comprising a plurality of mutually interconnected bi-directional optical waveguide rings (20, 30, 40, 50, 60) in which radiation modulated with communication traffic propagates. The radiation is partitioned into 32 distinct wavebands. Interfaces (70, 80, 90, 100, 110, 120) are included in the system (10) where communication traffic propagating in the rings transfers from one ring to another. Each interface (70) is capable of providing an all-optical waveband reconfigurable communication link between the rings (20, 30, 40, 50, 60). At each interface (70), conversion of optical radiation to corresponding electrical signals is not required when transferring communication traffic from one ring to another, thereby providing the system (10) with a potentially larger communication bandwidth compared to conventional optical communication systems.

Abstract: A method of, and an apparatus for, operating an optical modulator employ an optical attenuation versus voltage response which is cyclic and which includes an input to which the application of a bias voltage moves the modulator's response along the voltage axis to maintain the modulator's response at a desired voltage position. The apparatus comprises a bias voltage generator for generating a bias voltage which comprises the sum of a first and a second voltage component. The first component is fixed during normal operation and is selected to correspond to the expected bias voltage required for maintaining the modulator's response at a desired voltage position. The apparatus further comprises circuitry for detecting the position of the modulator's response and adjusting the second voltage component to maintain the response at the desired voltage position.