Patent ID: 7301974

Claim:
A wavelength monitoring device comprising: a semiconductor laser for emitting an optical signal that travels along a laser optical axis; a birefringent crystalline unit having a crystal optical axis inclined at an angle other than 90 degrees against a plane perpendicular to said laser optical axis and toward said laser optical axis, for receiving the optical signal emitted from said semiconductor laser and for outputting an optical signal having a polarized wave component of intensity corresponding to a wavelength of said received optical signal; and detecting means for detecting and monitoring the intensity of the polarized wave component of said optical signal output from said birefringent crystalline unit; wherein said birefringent crystalline unit is a single birefringent crystal; and wherein said birefringence crystal is formed of tellurium dioxide, and an angle between the crystal optical axis and the laser optical axis is 21.1 degrees.