Abstract: A semiconductor laser device includes a semiconductor laser element having a quantum well structure active layer having n levels of quantum states (n.gtoreq.2) from the first quantum level to the n-th quantum level in which the front facet reflectivity and the rear facet reflectivity are asymmetrical so that oscillation can occur at the n-th quantum level, a reflecting mirror having a reflectivity that causes oscillation of the semiconductor element to occur at a quantum level lower than the n-th quantum level, and a reflecting mirror moving unit for positioning the reflecting mirror in the neighborhood of the front facet or the rear facet of the semiconductor laser element. Therefore, a semiconductor laser device which can oscillate at two or more wavelengths with a simple construction is obtained.

Abstract: An improved optical fiber light-amplifier includes an amplifier optical fiber with a center core through which signal light is propagated, and a pumping light generating device which applies pumping light obliquely to the optical fiber. Pumping light is repetitively reflected within the optical fiber from portions of the optical fiber other than the interface between the core and regions surrounding the core. While pumping light is propagated through the fiber, it is absorbed by and excites the center core to amplify signal light being propagated through the optical fiber.

Abstract: A semiconductor laser device includes a semiconductor laser element having a quantum well structure active layer having n levels of quantum states (n<2) from the first quantum level to the n-th quantum level in which the front facet reflectivity and the rear facet reflectivity are asymmetrical so that oscillation can occur at the n-th quantum level, a reflecting mirror having a reflectivity that causes oscillation of the semiconductor element to occur at a quantum level lower than the n-th quantum level, and a reflecting mirror moving unit for positioning the reflecting mirror in the neighborhood of the front facet or the rear facet of the semiconductor laser element. Therefore, a semiconductor laser device which can oscillate at two or more wavelengths with a simple construction is obtained.

Abstract: A semiconductor laser device having a relative wide active region and a distributed Bragg reflector facet wherein a relative high reflectance region one third of the active region width is centrally disposed on a surface of the laser through which light is emitted.

Abstract: A semiconductor laser device provided with a broad light waveguide through which a higher order transverse oscillation modes can propagate, includes at least one of laser facet having a high reflectance region having a width of about 1/5 to 1/2 of the width of the light waveguide located at a central portion thereof and a low reflectance region having a lower reflectance than the high reflectance region located at both sides of the high reflectance region whereby higher order modes of oscillation can be suppressed.

Abstract: A bent waveguide for an optical integrated circuit includes a core region, cladding regions disposed at both sides of the core regoin forming a waveguide including a bent portion comprising the core region and the cladding region, a local waveguide region in the cladding region at the inner side of the bent portion. The local waveguide region has a larger refractive index than that of the core region or than that of the cladding region.