Abstract: A range of tunable and switchable optical devices utilise liquid crystal variable wave plates to achieve tuning or switching of one or more parameters of the incident light. Such devices include various configurations of liquid crystal variable wave plates, birefringent walk off plates, birefringent wave plates, reflectors, lenses and others located in the light paths between optical fibres. A reciprocal optical component has a polarisation equaliser attached or adjacent to a fibre, or located between the fibre and a lens reducing the size and cost. Using equalisers with liquid crystal elements can avoid the need for separate liquid crystal devices for each of the polarisations. Switches, dynamic gain equalisers, attenuators, polarisation mode dispersion compensators and Fabry-Perot filters can also be created.

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. Portions of the substrate of the planar waveguide are removed to improve thermal responsiveness of the path-length adjustment means.

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: An assembly for combining the outputs from a group of n single mode optical fibres on to the photosensitive surface of a photodetector (1) has an adiabatically tapered bundle (2) of fibres (3) the small end of which is fusion spliced to one end of a length (4) of multimode fibre whose other end is optically coupled with the detector (1) by means of a lens (5).

Abstract: An arrayed waveguide device has an expansion rod for adjusting a position of the optical paths at a star coupler, by thermal expansion, to compensate for wavelength response dependence on temperature. A bearing surface parallel to a plane of the waveguides prevents movement out of the plane and allow movement along the bearing surface parallel to the plane. Thus small lateral movements can occur accurately without introducing losses through unwanted vertical movements using a passive mechanical arrangement. It a be used together with active thermal control, to give better compensating accuracy, or compensation for manufacturing variations. An optical component assembly has a substrate having one or more mating profiles, and first and second planar waveguide chips having mating profiles. During assembly, the mating profiles enable passive alignment of an optical coupling between is respective waveguides of the chips. A groove locates a fiber on the chip using passive alignment.

Abstract: An arrayed waveguide device comprises a plurality of input/output 2-dimensional optical waveguides optically that are coupled, by a radiative star coupler 1-dimensional waveguide region, with an arrayed waveguide grating constituted by a set of retro-reflector terminated 2-dimensional optical waveguides in side-by-side array so as to define a set of reflex optical paths extending from that star coupler region, each path being of incrementally greater optical path length from a shortest value at one side of the array to a longest value at the other.

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: 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. Portions of the substrate of the planar waveguide are removed to improve thermal responsiveness of the path-length adjustment means.

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: An optical multiplexer/demultiplexer with an improved spectral characteristic is provided by two diffraction gratings (61, 60) arranged optically in tandem, the gratings being arranged to provide free spectral ranges differing by a factor of at least two, and having a coupling between them that carries over into the second grating information concerning the dispersion afforded by the first grating.

Abstract: A dispersion compensator exhibiting low polarisation mode dispersion is constructed from a polarisation beam-splitter, a .pi./4 rotation Faraday rotator, and a matched pair of polarisation maintaining fibres provided with a matched pair of chirped Bragg reflection gratings. The waveguides are oriented with respect to the beam-splitter so that light reaching the waveguides from the beam-splitter via the rotator is launched into both waveguides with a polarisation state aligned with the same polarisation axis (i.e. both fast or both slow).

Abstract: A planar optical waveguide comprises at least two cladding layers on a substrate with at least one core layer disposed between the cladding layers. The overcladding layer of the two layers is doped in order to produce a thermal coefficient of expansion close to or equal to that of the substrate in order to reduce the polarisation sensitivity of the device.

Abstract: Optical fiber elements, such as narrow pass-band filters, dispersion equalizers, and channel dropping filters, are constructed from 2.times.2 single mode optical fiber fused tapered couplers having formed on one side of coupling regions Bragg distributed gratings in the two fibers from which the coupler is constructed. By making the gratings at a point where the fibers remain fused together in side-by-side contact it is ensured that they lie equidistant from the coupling region.

Abstract: During the photo-induced creation of a Bragg grating in a photosensitive optical fibre using the interference fringe pattern generated in the near field of a phase grating, the spacing between fibre and phase grating is modulated.

Abstract: Optical coupling between the end of a laser (10) mounted on a silica motherboard (12) and an optical fibre (11) is effected with the aid of a silicon platform (14) to which the end of the fibre (11) is secured. The motherboard (12) and fibre platform (11) are crystallographically etched to provide complementary mating profiles with a clearance of less than 10 .mu.m when alignment is established. While that alignment is maintained, resin (23) is introduced between motherboard and the fibre platform, and is cured. The minimal thickness of the cured resin minimises misalignments caused by resin shrinkage.

Abstract: An optical fibre amplifier in which a length of optically amplifying fibre is spliced between a pair of 2.times.2 tapered fused fibre couplers each constructed from a length of amplifier type profile fibre and a length of transmission type profile fibre. In each coupler, one of two constituent fibres has been pre-stretched so as to match the propagation constants of the two fibres within the coupling region of that coupler.

Abstract: A 1.times.N single mode optical waveguide coupler comprises a single input optical fibre (1), a slab-like mixer waveguide (3) and a plurality (N) of output optical fibres (2). As a result of interference effects light introduced into the mixer waveguide (3) via the centrally located input fibre (1) produces a linear array of output spots at various intervals along the length of the mixer waveguide. The length of the mixer waveguide is chosen such that the output optical fibres are aligned with one such array of output spots. The fibres may be adiabatically tapered to a smaller diameter in order to increase their modal spot size.

Abstract: An optical fibre star coupler in which the mixer element (11, 21, 45) exhibits optical gain. This allows the use of couplers having a relatively large number of outputs without the requirement for an excessive power level for any input signal.

Abstract: A non-circularly-symmetric intensity distribution is formed on a quadrant photodetector by coherently mixing two optical signals propagating in selected modes of different order. These modes are chosen either such that a change in relative phase of the two signals produces solely a rotation of the orientation of that intensity distribution, or such that a change in relative states of polarization produces this rotation.