Research On Key Technologies Of High Sensitivity Space Laser Communication Based On Single Photon Detection And PPM Modulation

With the rapid development of laser communication technology and the arrival of the5 G era,there is a higher demand for space laser communication.For example,the transmitter needs to have higher speed,higher power,tunable;the receiver needs to have higher sensitivity,more compact and portable,stronger anti-interference ability and so on;the communication system needs to be more precise and more reliable,higher gain transceiver antenna and faster aiming,more precise capture,longer tracking technology.In order to provide a new idea for the realization of high sensitivity space laser communication,this dissertation combines two technologies of single photon detection and pulse position modulation,and adopts a new method of avalanche suppression that combines a gating circuit and a feedback quenching circuit,and an insert frame header method for pulse position modulation is designed.First of all,this dissertation briefly introduces the classification of single photon detector and several working modes.The principle of gated single photon detection is explained in detail and the calculation method of signal-to-noise ratio without post-pulse is derived,and it is found that it is related to the photon detection efficiency,the number of photogenerated carriers,and the number of gates,in-depth analysis of some important parameter characteristics of APD.The pulse position modulation is analyzed in terms of principle,practicality,advantages and disadvantages,and the relationship between the error time slot rate and the signal-to-noise ratio is deduced.It is found that the error time slot rate is not only related to the signal-to-noise ratio,but also related to the modulation order.Finally,it is found that most communication systems are accustomed to adopting single pulse position modulation which is easy to implement.Secondly,this dissertation designs and simulates the laser communication system.And designs the laser emitting unit,laser receiving unit,signal processing unit;the avalanche suppression method adopted can not only quench avalanches quickly,reduce dark counts,but also extend the average service life of the detector;the pulse position modulation and demodulation process was simulated by field programmable gate array,which verified the effectiveness and feasibility of the new method.Then,on this basis,a 1550 nm pulse position modulation laser communication experiment was built,and the performance of the single photon detector under different parameter in this experiment was tested.The results show that when the detection efficiency is 25%,the trigger delay is 8.00 ns,the gate width is 5.0ns and the death time is 0.1?s,the single photon detector has the best performance under the experimental conditions.Finally,under the best parameters,the detection sensitivity of single photon detectors with different modulation rates was tested.The results show that the communication sensitivity is-51.8d Bm when the communication code rate is 1Mbps;the communication sensitivity is-41.0d Bm when the communication code rate is 4Mbps,which realizes high sensitivity space laser communication.