Performance Enhancement Of LCOS-WSS Based On Wavefront Distortion Compensation

With the development of optical communication technology,the demand of wavelength selector switches is increasing.The wavelength selective switch(WSS)based on liquid crystal on silicon(LCoS)spatial light modulator shows great application potential due to its high stability and flexible bandwidth operation capability.However,the wavefront distortion caused by aberration,LCoS spatial non-uniformity and other factors in the wavelength selective switch system will lead to the performance deterioration,such as insertion loss and crosstalk.This paper focuses on the measurement and compensation of wavefront distortion in LCoS-WSS optical system.Firstly,according to the functional requirements of wavelength selective switch,a4-port WSS based on LCoS is simulated and designed.And an array of optical fiber and microlens was fabricated.The experimental optical system was constructed and the performance parameters of the WSS were measured.The insertion loss is in the range of5.73 d B?10.57 d B,and the isolation is higher than 25 d B.This WSS also has the capabilities of central wavelength tuning and bandwidth tuning.The central wavelength tuning accuracy is 0.058 nm,and the minimum 3d B bandwidth tuning step is 0.024 nm.Secondly,in order to compensate the wavefront distortion in LCoS-WSS system,a method of model-based wavefront-free sensing is studied.Considering that the light spot on the LCoS surface is non-circular,the matrix orthogonalization method is used to transform the orthogonal Zernike polynomials in the unit circle to the orthogonal Zernike polynomials in the elliptic region.The new polynomial can characterize the wavefront in the elliptic spot region,and the wavefront correction method based on model can be applied in our LCoS-WSS system.Finally,wavefront correction technology based on model was used to correct the wavefront distortion of the wavelength selector switch system,so that LCoS can control the beam deflection angle in the WSS system as well as correct the wavefront distortion in the optical system.It is verified by experimental results that the wavefront correction technology can effectively improve the performance of the WSS system.The correction of wavefront distortion can reduce the insertion loss of each port of the WSS by 0.8d B?1.15 d B.