OPTICAL FILTER, LASER MODULE, AND WAVELENGTH LOCKEOPTICAL FILTER, LASER MODULE, AND WAVELENGTH LOCKER MODULE R MODULE

摘要

On a second thermo-module there are disposed a prism, an optical filter, and a sub-mount, via a base respectively. On the front side of the sub-mount, there are disposed a first photodetector and a second photodetector. The optical filter is structured with a crystal member that satisfies a condition that .alpha. + (1/n0) x (.DELTA.n/.DELTA.T) becomes no t more than 3.5, where .alpha. is a coefficient of linear expansion, no is a refractive index at a normal temperature, and On is a change of a refractive index corresponding to a temperature variation .alpha.T.