Abstract: A method for selecting a semiconductor laser exhibiting a desired relaxation oscillation frequency, including the steps of: (a) finding a correlation between a visibility of interference fringes of laser light generated by a sampled semiconductor laser and a relaxation oscillation frequency of the sampled semiconductor laser; and (b) measuring a visibility of interference fringes of laser light generated by each of semiconductor lasers to be subjected to selection and finding a relaxation oscillation frequency of that laser from the visibility thus measured with use of the correlation. This method is capable selecting semiconductor lasers exhibiting optimal high speed response characteristics for optical communications with less cost, avoiding a decrease in productivity for such lasers, and contributing to mass productivity therefor.

Abstract: A method for selecting a semiconductor laser is provided which contributes to improved productivity of a highly reliable semiconductor laser of prolonged lifetime, and which includes the steps of: (a) measuring highest peak intensity, Ia, and next highest peak intensity, Ib, of an interference fringes pattern of laser radiation of each semiconductor laser using an interferometer to find a damping ratio of visibility of the interference fringes pattern, .gamma.=Ib/Ia; and (b) selecting a semiconductor exhibiting self-pulsation by selecting a semiconductor laser which emits laser radiation whose damping ratio of visibility, .gamma., is 0.5 or less.

Abstract: The invention is directed to a semiconductor laser wherein the first embodiment is characterized in that the first upper portion cladding layer is assumed to be a double layer construction, the upper layer portion is assumed to be higher in carrier concentration than the lower layer portion, the series resistance component is restrained, so that the sequential direction voltage V.sub.F may be lowered without damaging the other characteristics such as oscillation start current I th and so on.

Abstract: The invention is directed to a semiconductor laser wherein the first embodiment is characterized in that the first upper portion cladding layer is assumed to be a double layer construction, the upper layer portion is assumed to be higher in carrier concentration than the lower layer portion, the series resistance component is restrained, so that the sequential direction voltage V.sub.F may be lowered without damaging the other characteristics such as oscillation start current I th and so on.