High-Sensitivity Homodyne Coherent Detection Of Laser Pulse Echo

Since the laser was invented in the 1960 s,it has advantages of high coherence and good monochromaticity and directionality to used as a light source.It has been applied to the field of coherent detection,and it has gradually received more and more attentions by scholars at home and abroad.Compared with other detection technologies,laser coherent detection technology has longer transmission distance and higher detection sensitivity.Laser coherent detection technology is widely used in radar,ranging,speed measurement and other aspects,which has a wide range of application prospects.By mixing the local oscillator light and the signal light at the laser coherent detection system's receiving end,and demodulating the mixing,it can recover the signal.In the laser coherent detection system,the photocurrent output through the coherent mixing process is proportional to the product of the local oscillator laser power and the signal laser power.In order to improve the sensitivity of the optical receiver and the signal transmission distance,the local oscillator can be increased within a certain range.The power of the laser can further improve the detection sensitivity of the coherent detection system.According to the differences of detection principles,laser detection technology can be divided into direct detection and coherent(heterodyne/homodyne)detection.Compared with direct detection,coherent detection relies on more complex detection devices and coherent light sources.However,coherent detection technology has the advantages of strong detection capability and high signal-to-noise ratio,and can achieve relatively high sensitivity detection for weak laser signals.Under the same conditions,the quantum noise limit signal-to-noise ratio of direct detection is half of that of coherent detection,and it is easily affected by the detection device in actual work,and it is difficult to reach the limit;however,when the power of the local oscillation laser of coherent detection system is very strong,the signal-to-noise ratio can approach the theoretical limit.The sensitivity of a laser coherent detection system can be expressed by the minimum optical power that the system can be received.It is a very important indicator to measure the quality of a coherent detection system.With a higher detection sensitivity,the detection system can distinguish weaker optical signals.In the laser coherent detection system,the laser echo signal reflected by the detection target is usually relatively weak,and considering the influence of factors such as atmospheric attenuation,background light interference,and the detection system's own noise,the sensitivity of the coherent detection system is greatly compared with the theoretical value,and it is difficult to detect long-distance targets.In order to improve the detection sensitivity in a coherent detection system,in addition to appropriately increasing the optical power of the local oscillator laser,it is also necessary to suppress the noise in the detection system.In order to extract the weak pulse laser echo signal from the system noise,it is necessary to design a highsensitivity laser pulse detection system to meet the requirements of detection distance?detection accuracy and other indicators.