| 摘要 |
PROBLEM TO BE SOLVED: To enable a semiconductor laser included in an external resonator-type wavelength-variable laser, which oscillates in a single lateral mode and is coupled with an external optical system, to be improved in coupling efficiency with the external optical system so as to easily and stably control the wavelength of its laser radiation. SOLUTION: Lenses 103a and 103b, a reflecting mirror 104, and an etalon 102 are arranged on the side of the rear projection end face 100a of a semiconductor laser 100 oscillating in a single lateral mode for the formation of an external resonator-type wavelength-variable laser. The waveguide of the semiconductor laser 100 has a structure where its region within a distance of 50μm or so from the rear projection end face 100a decreases gradually in width from about 2μm to about 0.5μm toward the rear projection end face 100a. With this setup, a half band width is about 5μm at the rear projection end face 100a, and a laser beam is increased in diameter, and the semiconductor laser 100 is improved in its coupling efficiency with an external optical system.
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