Abstract: This paper introduces a method of measuring the absolute frequency response of photodetectors based on optical heterodyne.Through the mathematical derivation of absolute frequency response,the calculation formula of frequency response parameters of photodetector is obtained.And an optical heterodyne measurement system was designed to measure the frequency response of photodetector with high-response bandwidth of 67GHz at 1550nm.The accuracy and reliability of the system are verified by comparison with the high-precision optical wave component analyzer.The maximum deviation of the system is less than 0.8dB,and the measurement repeatability is better than 1%.This study can effectively solve the domestic test of frequency response parameters of (40～67)GHz photodetectors,especially the absolute frequency response,and is of great significance for the construction of frequency response calibration capacity of 67GHz photodetectors in China.

Key words: Photodetector, Absolute frequency response, Relative frequency response, Optical heterodyne