Semiconductor laser

Claim 1

A semiconductor laser comprising: an active filter region (A₁) including a diffraction grating (5) formed along a first light emitting layer (4) and equipped with a band-pass type filter function; gain adjustment regions (B₁, B₂) for adjusting an optical gain, each having a second light emitting layer (3,3′) formed of a semiconductor which is the same as or different from that of the first light emitting layer (4); and waveguide regions (C₁, C₂) 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 (B₁,B₂) and the waveguide regions (C₁,C₂) are integrated on a single substrate on both sides of the active filter region (A₁) substantially symmetrically with respect thereto; a laser resonator is formed by providing a pair of reflecting end facets (9,9′) or reflectors (20,20′) 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 (15,16,17,18) 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.