Patent ID: 7483470

Claim:
A semiconductor laser comprising: a substrate made of InP; an active layer including a multiquantum well structure formed above the substrate, the active layer having a width and a thickness which are constant in a direction of a resonator length L, the width of the active layer being in a range of 7 to 14 μm; and an n-type cladding layer made of InGaAsP and a p-type cladding layer made of InP which are formed above the substrate with the active layer interposed therebetween, a bandgap wavelength of the InGaAsP of the n-type cladding layer being in a range between 0.96 μm and 0.98 μm, wherein the n-type cladding layer made of InGaAsP has a refractive index that is higher than a refractive index of the p-type cladding layer made of InP, so that distribution of light generated in the active layer is biased to the n-type cladding layer to suppress an increase of optical loss due to inter valance band absorption in the p-type cladding layer, and wherein light which oscillates only in a fundamental lateral mode to be emitted from an exit facet is configured to be optically coupled with an external single mode optical fiber without generation of a higher lateral mode, and the light emitted from the exit facet has a spot size such that a ratio of a horizontal size to a vertical size of the spot size is in a range of 1:0.65 to 1:1.35.