Abstract: An optical communications system has a transmitter which uses modulation using multiple level phase and/or amplitude modulation, and is adaptable to provide modulation for different signals using different selections of the multiple levels. A receiver is able to perform demodulation from the multiple level phase and/or amplitude modulation, and is adaptable to provide demodulation of signals modulated using the different selections of the multiple levels. This provides an adaptive modulation system, so that different bit rates can be employed for different links.

Abstract: A wavelength division multiplex integrated optical transmitter and optical transmission system employing narrow band filters to dramatically improve tolerance to chromatic dispersion and thereby enable increased reach and/or data rates and a method of offering a communication service using such a transmitter or system.

Abstract: An optical array amplifier has a first light beam shaper, a first waveguide to guide an input optical signal consisting of a plurality of wavelengths to the first beam shaper, a diffracter illuminated by light from the first beam shaper to diffract the optical signal into individual wavelengths or groups of wavelengths, a second waveguide connected to a source of optical pump energy, a second beam shaper combining optical pump energy from the second waveguide with the diffracted signal wavelengths or groups of wavelengths without the pump energy impinging on the diffracter, so that a proportion of the optical pump energy is mixed with each of the wavelengths or groups of wavelengths, and to focus the mixed optical signals onto a third waveguide connected to an optical amplifier utilizing the pump energy to cause amplification of the individual wavelengths or groups of wavelengths mixed with the corresponding proportion of pump energy. The amplifier may be implemented as a planar waveguide device.

Abstract: An optical switch comprising switching means arranged to switch an optical signal by redirection of the optical beam path of said signal, wherein said optical switch is arranged to misalign the optical beam path so as to provide a predetermined optical output power. Thus a switch can be directly used to attenuate a signal, instead of utilising separate attenuators.

Abstract: An underwater telecommunications system has a first underwater cable for carrying data traffic, one or more underwater repeaters, and an underwater power network for supplying power to the repeaters. By providing a separate cable for some or all of the power supply, the power route may be made shorter, thus more power can be delivered, therefore more repeaters can be used, which enables more fiber pairs to be laid, and thus the capacity to be increased.

Abstract: A wavelength demultiplexer for demultiplexing optical signals carrying data, is also used to route a separate monitoring signal on to any of the demultiplexed output paths, by changing the wavelength of the monitoring signal. This enables optical paths through a switching arrangement to be verified or tested. A multiplexer at the output of the switching arrangement may be used to detect which of the output paths of the switching element has the monitoring signal. This saves the need for individual couplers to couple a monitoring signal on to each of the inputs, and off each of the outputs of the switching element. The saving in terms of component count, cost, and reduced size increases as the number of channels increases.

Abstract: An underwater telecommunications system has a first underwater cable for carrying data traffic, one or more underwater repeaters, and an underwater power network for supplying power to the repeaters. By providing a separate cable for some or all of the power supply, the power route may be made shorter, thus more power can be delivered, therefore more repeaters can be used, which enables more fiber pairs to be laid, and thus the capacity to be increased.

Abstract: An underwater data transmission system has a cable for carrying an optical signal to carry data, and a string of repeaters spaced apart along the cable, for transmitting the data along the cable, and is upgradeable in mid life by including an upgradeable repeater. The system may have a switchable loop to enable upgrading by adding an additional repeater to the loop and switching the loop into the data path. This enables the data capacity to be increased without needing to lift all the repeaters to the surface. This can enable the huge deployment costs of underwater systems to support several generations of advances in optical transmission systems. It makes more use of the usual twenty year design life of the physical infrastructure.

Abstract: Wave division multiplexers and demultiplexers utilizing fused fiber couplers and similar devices are expensive to implement. This is a barrier to deployment of optical networks particularly in the metro and access areas. The invention provides a cheaper design scheme to help overcome this problem. The invention provides an apparatus arranged to demultiplex a predetermined range and number of wavelengths comprising a plurality of devices each having at least one input port and two output ports, the output ports of each device having a periodic and complimentary series of minimum attenuation wavelength peaks, wherein the devices are arranged such that each demultiplexes a unique series of wavelengths, and wherein the apparatus comprises at least one device having a series of minimum attenuation wavelength peaks which do not correspond to the unique series of wavelengths the device is arranged to demultiplex.

Abstract: A unidirectional or bidirectional node for use in an optical communications network, a network consisting of such nodes and a method of maintaining a target loss around a ring. The node comprises one or more optical couplers as well as either or both of drop circuitry connected to an output port and add circuitry connected to an input port. This allows for changes to the wavelength plan without interruption of the ring traffic. If add circuitry is used, the wavelengths in the filtered add signal should be distinct from those of the incoming signal on the main optical path which is merged with the add signal. When separate fibers are used for transmitting and receiving data between a hub and nodes in a ring, the through loss of the couplers is reduced for upstream couplers, which increases the available loss to be assigned to the fiber. The method of maintaining a target loss around a ring relies on the known through loss of the coupler at each node to set the gain of an amplifier connected to the node.