Research On A Small Size Laser Ranging System For Human Eye Safety

Laser has a very wide range of applications in current human society,and it has been used in ranging since its birth.With the continuous development of laser and photodetector manufacturing technology,laser rangefinder has greatly improved volume and weight,and the use of many signal processing algorithms has also greatly improved the measurement accuracy.This article focuses on the missile end guidance and individual range finding equipment in the field of military applications,main to design a laser ranging module with small size,low power consumption,low cost and eye safe laser ranging module,using the module to replace electromagnetic ranging module in missile terminal guidance can effectively improve the anti-interference and hitting accuracy of missiles.In this paper,pulse time-of-flight ranging method is used as the system ranging method.Then,the system is modularized from top to bottom,and the system is divided into five modules:transmitter module,receiving module,optical module,signal processing module,and control module,decoupling the module as much as possible,which is convenient for later system upgrade and module replacement.In this paper,a transmitter module is designed based on a laser diode with a central wavelength of 1550nm and rated power of 40W,which makes the transmitting power reach the first-level laser safety standard and ensures the absolute safety of human eyes in the designed system.At the same time,the laser diode has more cost advantages than the laser.In order to minimize the parasitic inductance of the discharge circuit,on the one hand,the Nex FET^TM power MOSFET with special Kelvin Gate and 2ns rising time is selected as the switching device.On the other hand,microporous technology and power circuit separation are used to complete the discharge circuit layout in a space of 140mm².The transmitter module can generate pulse laser with a pulse width of 100ns,a rising time of 11ns and a peak power of 40W as required.At the same time,the repeated emission frequency of 10KHz enables the system to make multiple measurements in a short time.In this paper,considering that the echo signal is too weak,the APD with only 3n A dark current is selected as the photoelectric detector.At the same time,this paper designs a pre-transimpedance amplifier circuit based on the OPA858 op amp with the gain bandwidth product of up to 5.5GHz,which can provide millions of times of gain when it introduces extremely low noise and ensures the signal is not distorted.At the same time,this paper also introduces ADC to sample the echo signal.The digitized echo signal makes the application of subsequent algorithms possible and makes it possible for the system range to reach 1500m under the condition of 40W transmitting power.In this paper,the signal processing module and the control module are designed based on FPGA chip.The SNR of the echo signal is analyzed by the laser radar operating range equation,APD noise model and operational input noise model,and the echo signal model is established on this basis.By analyzing the echo signal model,a maximum value method is proposed to determine the pulse arrival time.This method can effectively avoid the influence of the amplitude change and waveform distortion on the measurement results.Aiming at the problem of insufficient range in the case of low transmission power,this paper refers to the radar signal processing algorithm and integrates the signal accumulation technology on the basis of the maximum value method.The simulation results show that this method can increase the effective range of the system from 700m to 1500m with the maximum measurement error not exceeding 2m under the condition of 20 accumulations.