Variable wavelength semiconductor laser

Claim 1

A semiconductor laser comprising: an active filter region including a diffraction grating formed along a first light emitting layer and equipped with a band-pass type filter function; gain adjustment regions for adjusting an optical gain, each having a second light emitting layer formed of a semiconductor which is the same as or different from that of the first light emitting layer; and waveguide regions, each having a waveguide coupled to the active filter region or one of the gain adjustment regions with high efficiency; in which the gain adjustment regions and the waveguide regions are integrated on a single substrate on both sides of the active filter region substantially symmetrically with respect thereto; a laser resonator is formed by providing a pair of reflecting end facets or reflectors at both ends of the assembly of the gain adjustment regions, the active filter region and the waveguide regions; the gain adjustment regions, the active filter region and the waveguide regions are electrically isolated from one another and are each provided with an electrode; and the oscillation wavelength of the semiconductor laser is changed by changing the refractive indices of the respective regions through voltage application or current injection to the electrodes, thereby producing a narrow-line-width, single-wavelength oscillation output light of a wavelength which agrees with the transmission wavelength of the active filter region dependent on preset refractive indices of the respective regions.