Research On The Measurement Of The Residual Phase Noise Of Microwave Photonic Link

Microwave photonics technology is a newly emerging subject and it has been widely used in radio over fiber, radio astronomy, radar system and other applications. Microwave photonic link (MPL) can provide many advantages, such as low intrinsic loss, large bandwidth, reduced weight, increased immunity to electro-magnetic interference, and the potential for signal processing. Extensive research on the performance of MPL are undertaken. The structure and the principle of MPL are introduced. In this paper, the residual phase noises of the MPL and photodiode are primarily studied. A series of research work has been done and listed as follows:(1) The development process of the microwave photonics and the applications of MPL are reviewed. The main devices and the principle of external modulation MPL are introduced.(2)The current driver and constant temperature controller of laser is developed. Further more, the microwave photonic transmitter and receiver are designed. The experimental measurement shows that:In 9 hours, the output optical power of laser drifts less than 0.4%.(3) First, the concepts of phase noise and random signal processing are explained, and then the basic experimental method of phase noise measurement is introduced. Afterwards, the basic approach of cross-spectral phase noise measurement of the device under test (DUT) is introduced. The theory of this method is also simulated by Matlab.(4) High-performance radar systems have very stringent phase noise requirements on the MPL. The additional phase noise of microwave photonic link will reduce the sensitivity of the radar systems. A two-tone cross-correlation method is proposed to measure the residual phase noise of long-haul MPL. This method can eliminate the phase noise of measurement system introduced by the referencing source, which enable the measurement of residual phase noise of long-haul MPL. The theoretical model of this method is built and the experimental research on this method is also performed. The residual phase noise of lm,2km and 6km MPL are measured based on this method. The measurement results show that the residual phase noise of 6km MPL deteriorates 10dB than 1m MPL.(5) The photodiode is one of the core devices in the microwave photonic link and the residual phase noise of the photodiode will deteriorate the phase noise of the whole MPL. The two-tone cross-correlation method is used to measure the residual phase noise of the photodetector for the first time. Furthermore. the impacts of bias-voltage, input optical power and nonlinearity on the residual phase noise of the photodetector are analyzed in-depth. The measurements show that:a) the residual phase noise of photodiode decrease with the reverse-biased voltage. b) When the photodiode works at linear region, its residual phase noise does not change with the input optical power. When the photodiode works at the saturated nonlinear region, its residual phase noise increases with the input optical power, c) When the linearity of photodiode gets worsen, its residual phase noise will get larger.