A semiconductor laser amplifier using waveguides

A semiconductor laser has a semiconductor optical amplifier 11 with first and second semiconductor waveguides 18, 19. The first waveguide forms at least part of a first optical path in the amplifier between reflectors, and the second waveguide is optically coupled to the first waveguide in the optical amplifier. A laser output is connected to a second optical path formed at least in part by the second waveguide 19. Alternatively, one of the reflectors may be a reflective grating 25 which provides substantially total reflection. One of the reflectors in the amplifier may be provided by coating one end facets 20 of the optical amplifier in gold. The waveguides may be formed as part of an integrated semiconductor amplifier. The waveguides may be rib waveguides forming a four port evanescent coupler. The semiconductor amplifier 11 may a rectangular chip mounted in a recesss 12 in an integrated circuit optoelectronic device 13. The laser may be in the form of an external cavity arrangement or may be a distributed feedback laser.