基于纳米光纤的光学法布里-珀罗谐振腔腔内模场的表征

Characterization of mode field distribution in optical Fabry-Perot cavity based on nanofiber

光学法布里-珀罗(F-P)谐振腔、粒子、微纳机械振子三者结合的复合腔光力学系统在基本物理问题、量子信息、精密测量等方面的研究和应用中越来越引起大家的重视.本文将纳米光纤置于光学F-P谐振腔的腔模中,探究了纳米光纤对光学F-P谐振腔精细度的影响,并通过测量纳米光纤引起的光学F-P谐振腔内腔损耗随纳米光纤位置的关系直接获得光学F-P谐振腔的腰斑半径,从而进一步实现了对光学F-P谐振腔腔内模场分布的无损表征.此方法可以用于在纳米光纤表面装载的发光粒子与光学F-P谐振腔耦合的精确控制,也为集合光子、粒子、声子的复合腔光力学研究提供了良好的平台.

The composite cavity optomechanical system combining optical Fabry-Perot(F-P)cavities,particles,and micro/nano mechanical oscillators is becoming more significant in the researches and applications of the fundamental physics,quantum information processing,and precision measurement.Characterizing the mode field distribution of optical F-P cavity is significant prior to the application of optical F-P cavity.In this paper,we propose and demonstrate a method to measure the waist of an optical F-P cavity and to characterize the mode field distribution of the optical F-P cavity by using a nanofiber nondestructively.In experiment,a nanofiber is placed in the mode of the optical F-P cavity with a fineness of around 1500.The optical F-P cavity is composed of two mirrors each with high reflectivity of 99.8%.The radius of curvature of the each mirror is 50 mm.The cavity length is(80±4)mm.The nanofiber is fabricated from a single-mode fiber by the flame-brush method.The nanofiber diameter is around 440 nm.The transmission spectra of the optical F-P cavity are measured by scanning the cavity length.The free spectrum ranges and the inner cavity losses can be obtained from the transmission spectra.First,the influence of the nanofiber on the optical F-P cavity fineness is investigated.The fineness as a function of nanofiber position along the radial direction of the optical F-P cavity is measured.The fineness caused by the nanofiber decreases to a minimum value of about 240.Second,it is investigated that the optical F-P cavity inner loss caused by the nanofiber as a function of the nanofiber position along the radial direction of the optical F-P cavity when the nanofiber is placed at the waist of the optical F-P cavity.The inner loss of the optical F-P cavity caused by the nanofiber is related to the intensity distribution of the optical F-P cavity mode field,which is predicted theoretically.Thus,by making the Gaussian fitting of the optical F-P cavity inner loss as a function of the nanofiber position,we can obtain a waist radius of the optical F-P cavity to be(72±1)μm.This is in good agreement with the theoretical calculation.Finally,the mode field distribution of the optical F-P cavity along the cavity axis is characterized.This method can be used for precisely controlling the coupling between the particles on the surface of nanofiber and optical F-P cavity.Besides,this method provides a good platform for studying the hybrid optomechanical system combining cavities,photons and quantum emitters.