基于二次强度调制的激光测距系统

Laser ranging system based on double intensity modulation

本文提出的二次强度调制测距系统可以实现绝对距离的测量,其利用马赫曾德尔强度调制器代替二次偏振调制测距中的电光相位调制器,通过对信号的光强进行二次调制来进行测距.相比于二次偏振调制测距,二次强度调制测距无需考虑测距系统中的偏振态问题,简化了系统结构,提高了系统的稳定性.经过相关理论推导以及实验验证:二次强度调制测距系统的输出光强与调制频率成余弦关系,并且可以直接测量调制器到目标物体之间的绝对距离,系统的频率稳定度、相对测距精度皆达到10^(-7)量级.本文提出的测距系统量程达到100 m,相对测距精度稳定在10^(-7)量级.采用摇摆法快速测距,避免了直接扫频寻找光强极小值点对应的频率,数据刷新率达到2 kHz.二次强度调制测距系统测距速度快,同时兼顾了较大的量程与较好的测距精度,系统结构简单,易于搭建,具有广阔的应用前景.

Long-range,high-precision,and high-refresh rate absolute distance measurement based on double intensity modulation is proposed and experimentally demonstrated.In this scheme,a Mach-Zehnder modulator is utilized to perform bidirectional modulation by a reversible optical path.In the Mach-Zehnder modulator,interference demodulation is completed by bidirectional modulated light with time difference.By adjusting the driving frequency of the modulator,the curve of light intensity versus driving frequency is achieved.Consequently,the distance to be measured can be obtained by extracted the frequency interval between two adjacent light intensity minimum points.In the traditional double polarization modulation ranging,the optical carrier is polarized by a polarizing beam splitter(PBS)before phase modulator.Moreover,a quarter wave or Faraday rotating mirror need to be placed to adjust the polarization in front of the target object.Therefore,the polarization state is an indispensable factor in the traditional double polarization modulation ranging.Due to the advantage of the intensity modulation,absolute distance measurement is achieved without additional polarization control,greatly simplifying the system.Theoretical analysis of the system is developed,which is then demonstrated by experiments.In the experiments,we achieved the following results.Firstly,the relationship between the intensity of the output light of the system and the modulation frequency is theoretically analyzed,which proved to be a cosine form.Secondly,swing method is introduced to realize high-speed absolute distance measurement during the analytical distance algorithm,and we achieved a refresh rate of 2 kHz in the experiments.Thirdly,the relationship between measurement ranging precision and frequency stability is analyzed.When the modulation frequency is 8.9 GHz,the experimentally measured frequency stability is on the order of 10^(-7).And when the distance to be measured is 2.73 m,the standard deviation of ranging reaches 1μm,which represents the precision of the system.That is,the relative measurement precision is also on the order of 10^(-7),which is consistent with theoretical analysis.Finally,when the distance to be measured increases from 1.57 m to 100.83 m,the measurement precision increases from 1μm to 30μm.It is worth mentioning that the relative measurement precision of the system is always stable in the order of 10^(-7).Our scheme has some significant advantages,such as long-range,high-precision,high-refresh rate,and a simple and compact configuration.Moreover,our method can be used in important applications such as precision instruments,metrology,and aerospace.