Abstract: A polarisation beam splitter (1) comprises a substrate (2) and a branched waveguide (3) formed on top of the substrate (2) and having a main portion (4) and two branch portions (5) and (6) with gradual splitting angles relative to the main portion (4) for conducting respective polarisation components along respective axes. One of the branch portions (5) is formed with a dielectric coating (7) in the region in which the branch portion (5) splits off from the main portion (4). The dielectric coating (7) serves to stress or de-stress the branch portion (5) in the region of the branching junction relative to the branch portion (6), such that different polarisation components in the main portion (4) are split apart along respective branch portions (5) and (6) by the resulting differential birefringence. Such an arrangement, which may also be applied to a combiner, is advantageous since it provides efficient splitting of polarisation components and is easily fabricated.

Abstract: A planar waveguide module has integrally formed thereon a waveguide and, in sequence along the optical transmission path, a first LOA, a 90° polarisation rotator, a VOA and a second LOA. The LOAs and are gain-clamped SOAs having linear gain responses over the required wavelength range. In the absence of the polarisation rotator the PDGs of the LOAs would be added together to provide an overall PDG of approximately twice the PDG of a single LOA. However the inclusion of the polarisation rotator between the LOAs causes a substantial reduction in the overall PDG. If TE polarised light is supplied to the first LOA, the polarisation rotator will cause TM polarised light to be supplied to LOA, and accordingly the overall gain of the module will equal Gain(TE, LOA 3)+Gain(TM, LOA 7)−attenuation.

Abstract: An optical waveguide structure formed on an optical chip comprising a first waveguide layer 3 of a first material supported on a substrate 7 and a second waveguide layer 6 of a second material supported on the first waveguide layer 3. The first waveguide layer 3 is separated from the substrate 7 by an optical confinement layer 8 and the second waveguide layer 6 is separated from the first waveguide layer 3 by an etch-stop layer 9. The etch-stop layer 9 is thin compared to the thickness of the first waveguide layer 3 and/or the second waveguide layer 6 and is of a material which enables it to act as an etch-stop when features are etched in the second waveguide layer 6.