Patent ID: 6954477

Claim:
A ridge-waveguide type semiconductor laser device comprising: an active region between upper and lower cladding layers; a stripe-shaped ridge formed in an upper portion of at least said upper cladding layer, said ridge having side surfaces; and an insulating film functioning as a current constriction layer, said insulating film being formed on said side surfaces of said ridge; wherein, on the assumption that an effective refractive index difference Δn between an effective refractive index n eff1 of said ridge for an oscillation wavelength, that an effective refractive index n eff2 of a portion on each of both sides of said ridge for the oscillation wavelength is Δn=n eff1 −n eff2 , and a ridge width is W; at least one of a kind and thickness of said insulating film, a thickness of an electrode film on said insulating film, a ridge height, a kind of said upper cladding layer, and a thickness of a remaining layer portion, located on each of both the sides of said ridge, of said upper cladding layer is set such that a combination of W and Δn is located in a specific Δn-W region on X-Y coordinates on which W (μm) is plotted on the X-axis and Δn is plotted on the Y-axis, said specific Δn-W region being defined so as to satisfy the following three equations: Δ n ≦−0.004 ×W +0.0123, (1) W≧1.0 μm, and (2) Δn≧0.0056. (3)