| 摘要 |
An optical semiconductor device of the present invention comprises: a semiconductor laser having an equivalent refractive index of nc; and a low-reflective coating film disposed on one end face of the semiconductor laser; wherein the low-reflective coating film includes: a first-layer coating film having a refractive index of n1 and a film thickness of d1; and a second-layer coating film having a refractive index of n2 and a film thickness of d2; and wherein the low-reflective coating film is formed in such a way that when n0 and lambd0 denote a refractive index of a free space on a surface of the second-layer coating film and a given laser light wavelength of the semiconductor laser, respectively, both a real part and an imaginary part of an amplitude reflectance decided by the wavelength lambd0, the refractive indexes n1 and n2, and the film thickness d1 and d2 are zero, and only one of refractive indexes n1 and n2 is smaller than a square root of a product of said refractive. indexes nc and n0.
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