Wavelength-variable semiconductor laser light source

A wavelength-variable semiconductor laser light source comprising:

• a semiconductor laser whose one end face is coated with an antireflection film;
• a parallel sliding stage which moves in parallel with the optical axis of the semiconductor laser by a parallel sliding driver;
• a diffraction grating fixed on a rotating stage which is provided on the parallel sliding stage, the diffraction grating for inputting an outgoing light from the end face coated with the antireflection film so as to form an external resonator with the other end face of the semiconductor laser;
• a transformation mechanism for transforming the parallel motion of the parallel sliding stage into the rotational motion of the rotating stage;
• a light source for outputting light, the light source being fixed on the parallel sliding stage in a manner such that the axis of the light shifts in accordance with the parallel movement of the parallel sliding stage;
• a lens for expanding the light from the light source;
• a PSD for inputting the expanded light from the lens and outputting an electric signal which is proportional to an amount of the displacement of the expanded light, the displacement being caused by the parallel movement of the parallel sliding stage;
• a wavelength setting part for arbitrarily setting the oscillation wavelength of the semiconductor laser;
• and
• a comparator for comparing a set signal from the wavelength setting part with the electric signal from the PSD and feeding the result back to the parallel sliding driver.