Abstract: An improved method is provided for fabricating a polarisation rotator in a rib waveguide having a propagation axis and opposite side walls. The method includes etching a pit in the substrate surface to form a recess in one of the side walls of the waveguide, during formation of the waveguide on the substrate surface, so as to provide an asymmetric waveguide section for imparting polarisation rotation to radiation propagated along the propagation axis. Preferably the pit is formed by a wet etching step forming an upper side surface within the recess that is inclined relative the waveguide side walls, and the waveguide side walls are formed by a dry etching step to extend perpendicularly to the substrate surface. In addition the dry etching step forms a lower side surface adjoining the upper side surface within the recess and tilted relative to the upper side surface.

Abstract: An optical device comprises a semiconductor structure including first and second ridge waveguides, each waveguide comprising a ridge extending across a surface of the semiconductor structure. The ridge of the first waveguide has a first height above a first region of the surface, and the ridge of the second waveguide has a second, greater, height above a second region of the surface. The semiconductor structure includes a multimode interference (MMI) region situated between the first and second ridge waveguides, which provides a transition between them. At least a part of the MMI region is tapered in width and/or at least a part of the first and/or second ridge waveguide is tapered in width in a direction extending away from the MMI region.

Abstract: The invention concerns a guided wave spatial filter (300) for receiving input radiation and outputting corresponding filtered output radiation, the filter comprising first and second waveguide sections (30, L3, L5) connected in series, the sections: (a) mutually matched for transmitting fundamental mode radiation components present in the input radiation therethrough to provide the output radiation; and (b) mutually mismatched for hindering higher-order mode radiation components present in the input radiation from propagating therethrough and contributing to the output radiation. The spatial filter (300) is implemented using rib waveguides (30) for the sections with associated relatively deeply and relatively shallowly etched structures (20, 310, 320) for imparting to the sections their radiation mode filtration characteristics.

Abstract: A Mach-Zehnder interferometer modulator for modulating a beam of laser light includes a pair of separate waveguides through which the laser light is passed after splitting in a splitting zone and after which the light is recombined in a merge zone. The waveguides are formed in a semiconductor material with one of the electrodes of each pair being formed in a doped layer while the other electrode, the top electrode, is a surface metalisation. The doped layer is trenched so that adjacent electrodes in the doped layer are electrically isolated from one another so that one of the electrodes in the doped layer can be connected with a different electrical polarity to the other electrode in the doped layer thereby permitting the connection of the pairs of electrodes in parallel anti-phase mode.

Abstract: A photonic integrated device having a substrate layer, epitaxial layers formed on said substrate layer and a guiding layer formed by one of the epitaxial layers. An optical waveguide is formed within the guiding layer. In the waveguide are a splitter (4) having at least two outputs, each output being transmitted to a Mach-Zehnder modulator (6, 8), the phase of the output of at least one modulator being shiftable, the signals being recombined to provide an optical phase shift key (PSK) output (14) wherein a trench is etched into the substrate layer between each pair of modulators to isolate the modulators from one another.

Abstract: The invention concerns a guided wave spatial filter (300) for receiving input radiation and outputting corresponding filtered output radiation, the filter comprising first and second waveguide sections (30, L3, L5) connected in series, the sections: (a) mutually matched for transmitting fundamental mode radiation components present in the input radiation therethrough to provide the output radiation; and (b) mutually mismatched for hindering higher-order mode radiation components present in the input radiation from propagating therethrough and contributing to the output radiation. The spatial filter (300) is implemented using rib waveguides (30) for the sections with associated relatively deeply and relatively shallowly etched structures (20, 310, 320) for imparting to the sections their radiation mode filtration characteristics.

Abstract: An optical modulator for producing a modulated optical output having a pre-determined frequency chirp comprises: optical splitting means for receiving and splitting an optical input signal to be modulated into two optical signals to pass along two waveguide arms (36, 38) made electro-optic material; and optical combining means for receiving and combining the two optical signals into said modulated optical output. At least one electrode pair (40/44, 42/44) is associated with each waveguide arm (36, 38), and is electrically connected in series such as to modulate the phase of said optical signals in antiphase in response to a single electrical signal (Vmod) applied thereto.