HETERODYNE DETECTION METHOD BY AMPLIFICATION DEGREE MODULATION OF AVALANCHE PHOTODIODE

摘要

PURPOSE:To reduce the number of parts, to simplify a circuit and to enable a high sensitivity of the heterodyne detection of an optical high-frequency signal by modulating the amplification degree of an avalanche photodiode by means of using the signal of a local oscillator. CONSTITUTION:A high-frequency signal from a local oscillator 20 of the frequency(fr) is placed upon a direct current power source 10 connected to an avalanche photodiode 40 by a coupler 30. Therefore the amplification degree of the diode 40 is modulated and the signal of a difference frequency fd=¦fs-fr¦ which is between the optical high frequency signal of the frequency (fs) and the frequency (fr) is generated inside the diode 40. The signal of the difference frequency (fd) is imputted in a measuring instrument 60 through a filter 50. Thus the circuit can be simplified by eliminating the need for the electric circuit element such as a mixer, etc. and moreover a slight optical high-frequency signal can be detected by raising the utilization efficiency of the signal.