课题组的微片激光（ML)回馈干涉仪，获国内外高度评价和多方应用。新需求：摆脱测量光直射被测目标的惯例，实现光纤柔性传输测量，适应狭小空间应用。挑战：大距离传输时温度、弯曲、外压力等引入的光纤长度变化会掩盖被测位移，使仪器失效。光纤难改，唯靠原理及系统创新：使用一对ML且其光束平行射入方解石，出射光为空间重合的平行(∥)和垂直(⊥)偏振光。光束穿过两个声光移频器后被移频1Ω，后耦合进长距离保偏光纤并传至尾端的格兰棱镜，∥和⊥光分离；∥光被反射回光纤再回ML内，只含光路内噪声信息;⊥光射向被测目标并携目标位移信息返回光纤再回到ML内，它同时含有光路噪声和目标位移信息；∥和⊥光都进入两激光器，光强被放大几个量级。因激光器内干涉只发生在同一激光器的出射光和回馈光之间，∥和⊥光不串扰；从⊥光的总相位改变中减去∥光的相位改变，留者仅为目标位移。预达指标：纳米分辨率，50米光纤，稳频精度10^-7。

The microchip laser feedback interferometer our group invented has been used by domestic and international universities and companies. All of the users speak highly of our instruments. The new requirements for improving such instruments mainly focus on the realization of flexible transmission and measurement based on optical fibre, which can enable such interferometers used in very narrow space,break through the limitations of traditional methods where the light signal from the interferometer is linearly projected on the surface of the target and no obstacel is allowed in the optical path. The challenges include avoiding changes of fiber's inner structure caused by the bend of fiber, the change of environmental temperature and stress,which lead to measurement errors. The principle innovation of this work is using two identical microchip lasers placed in parallel. The parallel laser beams go through a calcite crystal and become three light beams. The middle one contains a pare of light beams with orthognal polarizations, named as orthogonally-polarized light. The orthogonal light's frequencies have a Ω shift after going through two acousto optic frequency shifters. The light from frequency shifter is coupled into polarization maintaining optical fiber. On the output side of fiber, a polarization splitter is used to separate the orthogonally-polarized light beams. Because of the polarization splitter, reference light is reflected by reference target and carries reference signal which contains chaos of light path. Measurement light is reflected by the target and caries measurement signal which contains both chaos of light and displacement information of the target. The difference between reference and measurement lights is the displacement information of the target to be measured. The orthogonal light beams are back into lasers and amplified for several orders of magnitude. Feedback interference can only happen between one laser and its light, so two microchip lasers' interference will have no crosstalk. The goal of this research: high resolution in the order of nanometer, long transmission of 50 m using optical fiber, frequency stabilization of 10^-7.