External resonator-type wavelength tunable laser device

摘要

The present invention provides an external resonator-type wavelength tunable laser device that can properly fulfill a wavelength tuning function even with the use of a planar wavelength tunable reflector involving a considerable level of residual reflection. The external resonator-type wavelength tunable laser device includes a planar reflection structure enabling a reflection spectral peak wavelength to be varied and a semiconductor element as a semiconductor gain medium. The semiconductor gain medium is composed of a multiple quantum well in which product &Ggr;·L of optical confinement constant &Ggr; and semiconductor gain medium length L (μm) of a gain layer is at least 25 μm and at most 40 μm and in which gain peak wavelength λ0 (nm) observed during carrier injected with a maximum modal gain equal to an internal loss of the semiconductor gain medium is larger than −3·&Dgr;R/2+(λc+35) and smaller than (−(&Ggr;·L)/7+8)·&Dgr;R+(−(&Ggr;·L)+λc+45). Here, &Dgr;R (dB) denotes a reflectance difference, and λc (nm) denotes a wavelength at a center of an operating wavelength range of the wavelength tunable laser device.