Patent ID: 7265898

Claim:
A semiconductor optical amplifier formed from a vertical arrangement of substantially parallel material layers, the semiconductor optical amplifier amplifying an optical signal while confining it to an optical signal path substantially parallel to the material layers, the semiconductor optical amplifier comprising: a signal waveguide including a signal guiding layer, said signal waveguide vertically confining the optical signal around said signal guiding layer, said signal waveguide extending from an input facet to an output facet and defining said optical signal path therebetween; and a laser cavity including an active layer, said laser cavity being disposed between two end mirrors and defining a lasing path therebetween, said lasing path and said optical signal path vertically coinciding at an evanescent coupling region, said active layer and said signal guiding layer being vertically separated in said evanescent coupling region by at least one intervening layer; wherein said vertical separation between said active layer and said signal guiding layer in said evanescent coupling region is sufficiently small for an optical signal propagating along said signal guiding layer to be amplified by an evanescent coupling effect with said active layer.