SEMICONDUCTOR PHOTO DETECTOR

PURPOSE:To obtain an integrated photo detector capable of wavelength selection of variable wavelength by installing a wavelength selection mechanism and a semiconductor photo detector having a absorbent semiconductor layer, which wavelength selection mechanism can change the reflectivity of an optical waveguide and make the diffraction grating possible to selectively change the wavelength of light diffracted with higher order outside the optical waveguide. CONSTITUTION:A wavelength selection mechanism 2 and a semiconductor photo detector 3 are provided; the wavelength selection mechanism 2 has an optical waveguide 8 provided with an N-type region 4 and a P-type region 5; between them, a P-N junction is formed, and further a diffraction grating is arranged. Bias applying terminals 9a, 9b are arranged on the P-type region 5 and the N-type region 4 and are capable of applying bias to the P-N junction. The semiconductor photo detector 3 has an absorbent semiconductor layer 11 having a band gap wavelength longer than incident light. Thereby, an integrated photo detector 1 capable of wavelength selection of variable wavelength can be obtained.