Abstract: A nonreflective film is formed with a plurality of films having refractive indices higher than 1 and formed using a high-refractive index film (first film, third film, fifth film) and a low-refractive index film (second film, fourth film, sixth film, seventh film) respectively having refractive indices higher and lower than a square root of an effective refractive index of a semiconductor laser. The plurality of films are formed so as to have at least three kinds of compositions while each film is formed with a single composition, and to bring a real part and an imaginary part of an amplitude reflectance to zero as a whole. Therefore, a semiconductor optical device which can enhance a degree of freedom in a design of the nonreflective film can be provided even when a total film thickness of the plurality of films is different from a value &lgr;/4.

Abstract: A nonreflective film is formed with a plurality of films having refractive indices higher than 1 and formed using a high-refractive index film (first film, third film, fifth film) and a low-refractive index film (second film, fourth film, sixth film, seventh film) respectively having refractive indices higher and lower than a square root of an effective refractive index of a semiconductor laser. The plurality of films are formed so as to have at least three kinds of compositions while each film is formed with a single composition, and to bring a real part and an imaginary part of an amplitude reflectance to zero as a whole. Therefore, a semiconductor optical device which can enhance a degree of freedom in a design of the nonreflective film can be provided even when a total film thickness of the plurality of films is different from a value &lgr;/4.

Abstract: A multilayer film 1 obtained as a result of alternately laminating a first film 2 with a refractive index of n1 and a second film 3 with a refractive index of n2, the multilayer film 1 being formed such that the first film 2 is in contact with an end face of the semiconductor laser element 101. The first film 2 and the second film 3 satisfy relations expressed by the formulas n1<(nc)1/2 and n2>(nc)1/2. A reflectivity characteristic of the multilayer film 1 is such that a reflectivity of the multilayer film 1 is maximized at a wavelength &lgr;1 in a predetermined wavelength region and minimized at wavelengths &lgr;2 and &lgr;3 on a shorter-wavelength side and a longer-wavelength side of the wavelength &lgr;1, respectively.

Abstract: A semiconductor device and a photonic semiconductor device are disclosed wherein, if w is the thickness of a metal electrode layer covering a contact layer and current-unfed regions, D denotes the thickness of a plating layer on the metal electrode layer, the boundary between the contact layer and any one of the current-unfed regions is an origin, a direction from the origin into the device interior is a positive direction, and a direction from the origin toward any one of device facets is a negative direction, then a distance d between the origin and each facet of the plating layer satisfies (d/w)[1−w/(w+D)]<20.

Abstract: 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 &lgr;0 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 &lgr;0, 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.

Abstract: A semiconductor laser that has a large laser light aspect ratio, a high kink level, and a small variation in optical output efficiency. A semiconductor laser in which an increase in threshold current and a reduction in the optical output efficiency at an elevated temperature are prevented. The semiconductor laser includes a low refractive index layer between a guide layer and a cladding layer, and the total layer thickness of an active layer and the guide layer is not less than about 15% of an oscillation wavelength.

Abstract: A semiconductor device and a photonic semiconductor device are disclosed wherein, if it is assumed that “w” stands for the thickness of a metal electrode layer covering a contact layer and current-unfed regions, that “D” denotes the thickness of a plating layer formed on the metal electrode layer, that the boundary between the contact layer and any one of the current-unfed regions is taken as an origin, that a direction from the origin into the device interior is a positive direction, and that a direction from the origin toward any one of device facets is a negative direction, then a distance “d” between the origin and each facet of the plating layer is set to satisfy a relationship of d/w*[1−w/(w+D)]<20.