A whispering gallery mode resonator (WGMR) filter can narrow laser linewidth while significantly changing the output power characteristics of fiber laser system. It is found that traditional laser output power model is invalid. We report a correction model of a narrow linewidth fiber laser filtered with a WGMR to analyze its power. We believe that the loss of the laser system and the threshold gain increase caused by the WGMR filter lead to the predominate amplified spontaneous emission during the original laser period. According to that, we assume the correction coefficient is an exponential decay related to the Er-doped fiber length in the large loss situation, and we verify it experimentally. As a result, the correction model is valid for WGMR-filtered fiber laser.

We propose an absolute distance measurement method that employs heterodyne and superheterodyne combined interferometers to achieve synchronous detection and demodulation of multiwavelengths. Coarse and fine synthetic wavelengths are generated by a dual-longitudinal-mode He–Ne laser and four acoustic optical frequency shifters. Further, to improve phase synchronization measurement for multiwavelengths, we analyze the demodulation characteristics of coarse and fine measurement signals and adopt a demodulation method suitable for both signals. Experimental results demonstrate that the proposed method can achieve high-precision synchronous demodulation of multiwavelengths, and standard deviation is 1.7 × 10^-5 m in a range of 2 m.

为实现调频连续波（Frequency-modulated Continuous-wave，FMCW）激光雷达的高精度测量，针对激光雷达机械加工及装配过程中引入的几何结构误差，提出了基于激光雷达坐标测量误差的系统误差模型及误差修正方法。建立了激光雷达坐标系组，分析了空间坐标测量误差的来源。通过坐标系间的变换矩阵，实现了测量坐标的几何误差传递。然后，归并各坐标系的几何误差，建立了显式的激光雷达几何空间坐标误差表达式。并以此为基础，建立最小二乘优化目标，解算各项误差因子和修正后坐标。求得的误差因子可以用作后续坐标测量结果的修正。最后，基于该方法设计了一套以激光跟踪仪为高精度测量仪器、以靶球球心位置为标准点的标定场，使用激光跟踪仪与激光雷达测量相同位置的靶球完成系统误差修正。实验结果表明，经修正激光雷达空间距离测量的平均误差由0.044 8%下降到0.003 8%，误差极大值由4.17 mm下降到0.30 mm，验证了激光雷达几何结构误差标定和误差修正方法的有效性。

Laser ranging with frequency comb intermode beats (IMBs) has been suffering from random phase drifts (RPDs) for two decades. In this study, we reveal the influence of signal transmission path on the RPDs and propose a real-time suppression method using two IMBs of similar frequencies from different combs. As the two IMBs obtain similar RPDs during their transmission through same signal paths, the RPD of the original probing signal IMB is suppressed by deducting the RPD of the newly added local IMB in real time. In our experiments, a real-time suppression of RPDs is achieved using IMBs of 1001 and 1000 MHz. For the sampling time of 100 s, the effect of 19-fold suppression has been achieved. The proposed method provides a new solution for the long-standing phase drift problem in laser ranging with comb IMBs.

We propose a precision phase-generated-carrier (PGC) demodulation method with sub-nanometer resolution that avoids nonlinear errors in a laser wavelength sinusoidal modulation fiber-optic interferometer for long range dynamic displacement sensing. Using orthogonal detection and an AC-DC component extraction scheme, the PGC carrier phase delay (CPD) and laser intensity modulation phase delay can be obtained simultaneously to eliminate the nonlinear error from accompanied optical intensity modulation and CPD. Further, to realize long range displacement sensing, PGC phase modulation depth (PMD), determined by the laser wavelength modulation amplitude and the working distance of the interferometer, is required to maintain an optimal value during measurement, including initial position and dynamic movement. By combining frequency sweeping interference and modified PGC-arctan demodulation to measure real-time working distance, adaptive PMD technology is realized based on proportion control. We construct a fiber-optic Michelson and SIOS commercial interferometer for comparison and perform experiments to verify the feasibility of the proposed method. Experimental results demonstrate that an interferometer with sub-nanometer resolution and nanometer precision over a large range of 400 mm can be realized.