Variable-wavelength semiconductor laser device controlled by strength of electric field applied to wavelength selection element

A variable-wavelength semiconductor laser device comprising:

• a tapered-stripe semiconductor laser amplifier which is constructed to emit a first light from a first end surface, receive a second light from the first surface thereof, and emit a third light from a second surface thereof, wherein said third light maintains a transmittance of a p-polarization component close to 100% resulting in a high output laser light;
• a wavelength selection unit which is constructed to receive the first light, selects a wavelength from among a plurality of wavelengths included in the first light according to strength of an electric field applied to the wavelength selection unit, and returns to the tapered-stripe semiconductor laser amplifier a portion of the first light having the selected wavelength as the second light, wherein said wavelength selection unit includes a birefringent filter containing at least one birefringent element made of a material exhibiting an electrooptic effect, and a mirror which reflects the first light after the first light has passed through the birefringent filter;
• and
• an electric field applying unit which applies said electric field to said wavelength selection unit, wherein said electric field applying unit includes a pair of electrodes which are formed so that portions of said birefringent filter through which said first light passes are located between the pair of electrodes, and a unit for applying the electric field between the pair of electrodes.