Investigation of balanced detection and receiver for coherent lidar

Signal detection plays a very important part in information times, which includes optical signal detection and electronic signal detection. Without question, 21 century is an optical times, so the importance of the optical signal detection becomes obvious. Optical detection includes direct detection and indirect detection (coherent detection). Direct detection is a method which only measures the amplitude of the signal and also be used in the measurement for strong signal. In contrast in indirect detection other parameters of the received electrical field can be modulated, such as its amplitude, frequency or phase. Coherent detection can be performed using two different techniques: heterodyne detection and homodyne detection. The coherent detection has much more sensitivity improvement over direct detection. However, some errors arise because of the two unstable signals, i.e., local beam and signal beam. Therefore, balanced detection technique can solve the question. In this paper, balanced detection technique was analyzed, which also was applied in signal measurement for lidar. Firstly, Mathematical modeling of the balanced detection process is deduced. Secondly, a numerical simulated system is established with software LABVIEW. Signal-to-noise ratio of the balanced detection is much two times than that of normal coherent detection technique. Furthermore, this balanced detection technique, which also be used in measurement for wind, not only Doppler shift can be obtained, but whether the Doppler shift is positive or negative can be distinguished, in other words, can know the direction of wind. Last but not least, the experiment results is well consisted with the simulated results, which shows that signal-to-noise ratio has been improved obviously.