US Patent 7177336 Semiconductor laser device

A semiconductor laser device having a waveguide constructed in a stack of layers including, on a substrate transparent and having a refractive index ns for laser light, a first clad layer of a refractive index nc1, a second clad layer of a refractive index nc2, a third clad layer of a refractive index nc3, a first conductivity type guide layer of a refractive index ng, an active quantum well layer, a second conductivity type guide layer, a second conductivity type clad layer, and a second conductivity type contact layer deposited in this order, wherein the waveguide has an effective refractive index ne, and a relationship of nc2<(nc1, nc3)<ne<(ns, ng) is satisfied.