Abstract: A multiwavelength transmitter comprises several laser sources (1) each configured to generate light of a different wavelength and a first array waveguide grating (2) arranged to direct light from each of the laser sources (1) into a first waveguide. The transmitter further comprises several electroabsorption modulators (7) each arranged to modulate light at one of the wavelengths with a respective data signal and a second array waveguide grating (6) arranged to direct each of said different wavelengths of light from the first waveguide to a respective one of the modulators (7). The optical modulators (7) are reflective optical modulators and the second array waveguide grating (6) is arranged to direct the modulated light reflected from each of the optical modulators (7) back into the first waveguide. An optical circulator (5) is provided in the first waveguide to couple modulated light from the second array waveguide grating (6) into an output waveguide.

Abstract: A multiwavelength transmitter comprises several laser sources (1) each configured to generate light of a different wavelength and a first array waveguide grating (2) arranged to direct light from each of the laser sources (1) into a first waveguide. The transmitter further comprises several electroabsorption modulators (7) each arranged to modulate light at one of the wavelengths with a respective data signal and a second array waveguide grating (6) arranged to direct each of said different wavelengths of light from the first waveguide to a respective one of the modulators (7). The optical modulators (7) are reflective optical modulators and the second array waveguide grating (6) is arranged to direct the modulated light reflected from each of the optical modulators (7) back into the first waveguide. An optical circulator (5) is provided in the first waveguide to couple modulated light from the second array waveguide grating (6) into an output waveguide.

Abstract: An optical filter is formed from at least two grating located in a waveguide region of a semiconductor optical device. Each grating has a multiple peak optical passband. The gratings are spaced apart in the waveguide region and form an optical cavity having a comb-filter characteristic. The gratings may be located in the active region of an optical gain element and in a preferred example are superstructure gratings (SSGs). A number of filters may be joined together in series.

Abstract: A semiconductor optical device, for example a laser, has a composite optical waveguide including a tapered, MQW active waveguide in optical contact with a substantially planar, passive waveguide. The fundamental optical mode supported by the composite waveguide varies along the length of the composite waveguide so that, in a laser, the laser mode is enlarged and is a better match to single mode optical fibre. A method for making such semiconductor optical devices is also disclosed.

Abstract: A semiconductor optical device, for example a laser, has a composite optical waveguide including a tapered, MQW active waveguide in optical contact with a substantially planar, passive waveguide. The fundamental optical mode supported by the composite waveguide varies along the length of the composite waveguide so that, in a laser, the laser mode is enlarged and is a better match to single mode optical fiber. A method for making such semiconductor optical devices is also disclosed.

Abstract: An optical filter is formed from at least two gratings (102,103) located in a waveguide region (104) of a` semiconductor optical device (101). Each grating has a multiple peak optical passband. The gratings are spaced apart in the waveguide region and form an optical cavity having a comb-filter characteristic. The gratings may be located in the active region of an optical gain element and in a preferred example are superstructure gratings (SSGs). A number of filters may be joined together in series.

Abstract: A semiconductor laser amplifier includes both a waveguide layer and an active layer. In use, an optical wave in the active layer interacts with the waveguiding layer to reduce the polarisation sensitivity of the amplifier. A short, thick active layer is not required, typical dimensions being 250 or 500 .mu.m long, by 0.2 .mu.m high. The mesa is typically about 2 .mu.m wide, but may be wider.

Abstract: In a semiconductor buried heterostructure laser having a mesa (2, 3, 4) and confinement layers (5, 6, 7) on a substrate (12), at least the lowermost of the confinement layers (5, 6, 7) is substantially planar up to the mesa. This is achieved by MOVPE growth of InP against lateral surfaces of the mesa (2, 3, 4) which are defined by distinct crystallographic planes of the material of the mesa. In particular (111) B InP planes are used. The laser is particularly for use in the field of optical communications.