Abstract: A communications network having two complementary optical networks each connectable to a headend, each optical network comprising a plurality of periodic interleaving filters serially connected by optical waveguides such that an output port of one periodic interleaving filter is couple to an input port of another periodic interleaving filter, and wherein an input or output node of the network is formed by a non-serially connected input or output port of a periodic interleaving filter.

Abstract: A method for detecting power transients in a signal wavelength carried by an optical transmission medium in a band consisting of a first plurality of wavebands, such as a wavelength division multiplexed signal, comprises dividing the band into a second plurality of wavebands, equal to or less than the first plurality, and detecting power transients within each of the second plurality of wavebands. The power of each wavelength in the second plurality of wavebands is determined by detecting the power level in each second plurality of wavebands as a function of the contribution from each of the wavebands in the second plurality of wavebands to derive a plurality of simultaneous equations, equal in number to the second plurality of wavebands, and solving the plurality of simultaneous equations to determine the levels of each wave-length component of each waveband in the second plurality of wavebands. Correlation with error bursts detected in the optical receiver enable an audit of the error event to be conducted.

Abstract: An optical link 1 from one terminal A to another B has a series of spans 2 interconnecting nodes between the terminals A, B. Dispersion compensation means applies dispersion compensation to each span 2. Each span 2 contributes noise and the total noise in the link is result of the contributions from each span 2. The spans 2 may be normalised and the total noise in the link the sum of the contributions from each span. The amount of dispersion compensation applied to each span 2 by the dispersion compensation means is determined in accordance with the noise contribution of that span 2.

Abstract: In optical communication switching equipment there is a need to set up optical paths through the switch before there is an optical signal present. The present invention provides an optical switching apparatus comprising: an optical switch having a number of optical paths for switching optical channels; a demultiplexer coupled to said switch; a broadband light source coupled to said demultiplexer which distributes said light in said channels to enable correct alignment of said optical paths.

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.