基于飞秒光梳多路同步锁相的多波长干涉实时绝对测距及其非模糊度量程分析

飞秒光梳被广泛用于时间频率技术和精密光谱测量,由其时频特性所衍生的绝对测距技术以可溯源、大尺寸、高精度等优点有望成为未来长度计量的最重要手段.本文提出了一种基于飞秒光梳多路同步锁相的多波长干涉实时绝对测距方法,使多个连续波激光器通过光学锁相环技术同步锁定到飞秒光梳梳模上,通过多路同步相位测量和小数重合算法最终实现绝对距离测量.所提测量方法不仅能保留传统激光干涉测距的高分辨力和精度,而且可溯源至时间频率基准,对高精度长度测量、尤其是对物理复现“米”的定义具有重要计量意义.测距实验证明,四波长干涉测距的非模糊度量程达到44.6 mm,折射率波动导致非模糊度量程变化为纳米量级;多波长干涉测距的非模糊度量程也受制于空气折射率的测量误差,多波长干涉绝对测距的非模糊度量程在实验室环境下可达数米、甚至几十米,并通过2米线性位移实验证明了多波长绝对测距的大量程和线性测量性能.

Real-time absolute distance measurement by multi-wavelength interferometry synchronously multi-channel phase-locked to frequency comb and analysis for the potential non-ambiguity range

Optical frequency combs of the femtosecond laser have been widely used in time-frequency technology and precision spectrum measurement.The absolute ranging technology derived from time-frequency characteristics of the optical frequency comb is expected to become the incomparable means of length metrology and distance measurement in the future due to its traceability to time-frequency standard and capability of large scale and high precision.This paper proposes a real-time absolute ranging method with multi-wavelength interferometry referenced to optical frequency comb,which enables multiple continuous-wave lasers to be synchronously calibrated to selected modes of the frequency comb by means of optical phase-locked loop.With synchronous phase measurement and calculation with excess fraction algorithm,absolute distance measurement by multiwavelength interferometry is ultimately fulfilled.The proposed measurement method can not only retain high resolution and high accuracy of traditional laser interferometry,but also can be traced to a time-frequency reference,which is of metrological significance to high-precision length and distance measurement,especially to the definition of“meter”for physical reproduction.Measured results for ranging experiments have proved that the non-ambiguity range of the four-wavelength interferometer reaches 44.6 mm,and fluctuations of air refractive index cause the non-ambiguity range change with the order of nanometers.Through theoretical analysis,it is pointed out that the non-ambiguity range of the multi-wavelength interferometer in the actual measurement environment is restricted by the calculated error of air refractive index,especially the estimation accuracy and fluctuation degree of the refractive index relationship between wavelengths.And in a good laboratory conditions,the non-ambiguity range of real-time absolute ranging by frequency-comb-calibrated multi-wavelength interferometry can reach several meters or even tens of meters.At the same time,a 2-meter linear displacement comparison has been carried out,the P.V.value of the residual errors for linear fitting is 36.1 nm,and such residual errors match the magnitude of uncertainty of air refractive index calculated by empirical formula,which prove that the multi-wavelength interferometry can perform meter-level absolute ranging.The proposed research can be directly applied to precision manufacturing of large-scale semiconductors up to several meters,and is beneficial to promoting the accuracy of laser ranging for space mission.