Abstract: A reconfigurable optical add drop module has a coarse demultiplexer, for outputting sub bands of wavelengths, a fine mux/demux, for adding and/or dropping wavelengths, a coarse multiplexer, for remultiplexing the sub bands, an optical switch in between the coarse demultiplexer and the fine mux/demux, to switch the sub bands for pass through, or for add/drop. Reconfiguration can be remote, automatic, with less interruption to traffic. By switching sub bands rather than individual wavelengths, the number of switches can be reduced, and consequently losses, and space requirements can be reduced. Also, upgrading from pass through to add drop, of one or more sub bands is easier. Hence initial capital cost of nodes and the cost of upgrading can be reduced, since there is less need to provide redundant add drop capacity initially. Mid stage access enables external components to be added to the optical path for the sub bands.

Abstract: An optical demultiplexer has a coarse filter 41,43,45 and a plurality of arrayed waveguide gratings (AWGs) 49 connected to respective outputs of the coarse filter 41,43,45. The AWGs are of like design with a plurality of configurations and are arranged to have a configuration corresponding to be frequency range output on the respective output. The device can be used in WDM systems.

Abstract: A planar dispersion compensator for an optical signal is provided. The compensator decomposes an inputted optical signal into N component signals separated by a fractional wavelength &dgr;&lgr;. Each component signal has its path-length adjusted to induce a sufficient phase shift between input and output to change the group delay of the optical signal when recombined from each of the component signals. In this manner, pulse broadening can be compensated by selectively varying the induced phase shifts to produce the desired level of opposite group delay.

Abstract: The invention is directed to an optical grating device which is capable of processing at least two optical signals concurrently, comprising a plurality of input waveguides, a plurality of output waveguides, a first free propagating region and a second free propagating region, and a composite light pathway. These are arranged such that a first input waveguide and a first output waveguide are connected to said first region; a second input waveguide and a second output waveguide are connected to said second region; and said first region and said second region are connected by the composite light pathway. Light input along the first input waveguide is able to pass through the composite light pathway to be output through the second output waveguide and light input along the second input waveguide is able to pass through the composite light pathway to be output through the first output waveguide.

Abstract: An optical waveguide device for guiding an optical signal comprising a substrate, a waveguide extending at least partially across the substrate, and at least two slots extending transversely across the waveguide. The separation between the slots, the direction of propagation of the optical signal in the waveguide, is substantially ( n ⁢   ⁢ Δ ⁢   ⁢ λ 2 ) , where n is an odd integer and &Dgr;&lgr; the difference in wavelength of the radiation and guided modes of the optical signal resolved in the direction of propagation.

Abstract: An optical demultiplexer has a coarse filter 41,43,45 and a plurality of arrayed waveguide gratings (AWGs) 49 connected to respective outputs of the coarse filter 41,43,45. The AWGs are of like design with a plurality of configurations and are arranged to have a configuration corresponding to be frequency range output on the respective output. The device can be used in WDM systems.

Abstract: An arrayed waveguide grating device 1 has a substrate 1 with an array 41 of waveguides extending across the substrate between an input coupler 37 and an output coupler 39. At least one input waveguide 31 extends between an input end for coupling to an input signal and the input coupler 37 and at least one output waveguide extends between an output end for coupling to an output signal and the output coupler 39. The input end or ends of the at least one input waveguide and the output end or ends of the at least one output waveguide are brought to the same edge 35 of the substrate.

Abstract: It is found that the use of a multimode interference (MMI) section to flatten the pass-bands of an arrayed waveguide grating (AWG) multiplexer/demultiplexer or comb filter device introduces undesirable wavelength dispersion into those pass-bands if that MMI section mixes modes of more than two different orders, and if the grating of that device is a ‘uniform’ grating whose waveguides are equally (minimally) attenuating, and in which the optical path length difference between each adjacent pair of waveguides 40 of the array is the same.

Abstract: An optical comb filter is constructed from a monolithic arrangement of two identical integrated optics format arrayed waveguide diffraction gratings connected back-to-back via a star coupler incorporating a field stop (spatial filter0. Alternatively, only one of the diffraction gratings is employed in conjunction with a combined field stop and retro-reflector, the other end of the diffraction grating being optically coupled with one port of an optical circulator.

Abstract: It is found that the use of a multimode interference (MMI) section to flatten the pass-bands of an arrayed waveguide grating (AWG) multiplexer/demultiplexer or comb filter introduces undesirable non-linear wavelength dispersion into those pass-bands if that MMI section mixes modes of more than two different orders. This dispersion can be substantially compensated by the use of a tandem arrangement of two AWGs with MMIs of differing length chosen to provide complementary dispersions. In the case of a comb filter, an equivalent compensation can be achieved by arranging for the light to make a second passage through the AWG in the reverse direction.

Abstract: An injection laser array has 2.sup.n output elements (1) coupled by Y couplers (2, 4, 6) and (n-1) in sets of intermediate elements to a single element (7) in a tree configuration. The face end of the single element is provided with a high reflectivity coating (8) while those of the 2.sup.n output elements are provided with low a reflectivity coating (9).