Light detecting apparatus having a diffraction grating

摘要

A light detector provides wavelength tracking, monitoring or similar function by forming a diffraction grating in a light waveguide (4). Diffracted light from the waveguide is received by a light detecting device (11) having multiple detecting portions (PD1,...). Changes in the emission angle of the diffracted light caused by the wavelength or other fluctuation of the incident light are detected. The detected information can be used for wavelength tracking by injecting current into or applying a voltage to the waveguide to regulate the Bragg wavelength of the light waveguide, for monitoring and/or controlling the oscillation wavelength of a semiconductor laser or for other purposes.