Research On Programmable Wavelength Selective Switch Based On Liquid Crystal Spatial Light Modulator

Programmable wavelength selective switch(WSS)is one of the core optical devices of the next-generation reconfigurable optical add-drop multiplexer(ROADM)and optical cross-connect(OXC)in all-optical networks.It has Colorless,Directionless,Contentionless,Flexible Grid(CDCG)and other all-optical signal processing functions.So far,the ports number of commercial WSS is 1×20,the minimum channel bandwidth is 10 GHz,and the spectral tuning accuracy is 1GHz.The wavelength selective switch with a high port number can greatly reduce the complexity of system and the cost of construction,operation and maintenance of multi-dimensional optical nodes in all-optical networks.The WSS with higher spectral manipulation accuracy can greatly improve the network expansion function and networking flexibility of optical nodes.Therefore,WSS with high port count and fine spectral manipulation is a key to develop multi-dimensional optical cross-connect node technology in intelligent elastic optical networks.The current WSS is limited by multiple factors such as liquid crystal spatial light modulator pixel density,input/output port design and preparation,optical system design and imaging quality.The number of ports and the spectral resolution are limited.In this paper,we use 4K resolution liquid crystal spatial light modulator,improved optical system design and optimization of its internal optical components,the insertion loss is below 10 d B,and the spectral tuning accuracy is 7.5±1pm,the minimum channel bandwidth is 8.34 GHz,and the 1×120 port programmable wavelength selective switch with signal multiplexing function,the main work of this paper is as follows:1.Research on the key technology of the light field change during the beam transmission in the WSS system.The light field distribution of the fiber coupling microlens was analyzed and calculated when using microlenses with different focal lengths.The effect of the microlens structure on the input/output port loss in the WSS system is obtained.The calculation of the light field and the design of the fiber coupling microlens array provide a theoretical basis for WSS.2.The design of 128-port high-precision fiber-coupling micro-lens array with 127?m pitch is completed.According to the effective area of the liquid crystal spatial light modulator and the beam deflection range in WSS,a 128-port micro-lens array with a pitch of 127 ?m is designed and manufactured.A real-time loss detection system and coupling method for fiber-coupling microlens array were proposed and designed.The fiber array and the microlens array were precisely aligned one-to-one by using the real-time detection system.3.The working limitations of the liquid crystal spatial light modulator and the working principle of beam deflection are studied.The beam deflection characteristics of liquid crystal spatial light modulators were analyzed by using the electro-optical characteristics of liquid crystal materials.The influence of different pixels in the phase grayscale image to the energy distribution of the diffracted light field of the liquid crystal was derived.The grayscale and phase response curves of the 4K resolution liquid crystal spatial light modulator were calibrated,and the diffraction efficiency of the beam deflection when using different period phase grayscale images was measured.4.According to the optical system structure requirements of WSS,the diffraction grating is designed by Modal Approach,and a variety of diffraction grating structures that satisfy the-1st order diffracted light blazing when TE/TM linearly polarized light is incident,and then Rigorous Coupled Wave Analysis is used to calculate the diffraction efficiency of the designed grating structure.The characteristics of the 1200 lines/mm grating with high incident angle tolerance are used to optimize the structure of the WSS optical path,which effectively improves the spectral tuning accuracy of the WSS.5.By redesigning and optimizing the optical structure of WSS,a 1×120 port wavelength selective switch is built.This WSS can output each frequency component of the input optical signal to any output port,and the insertion loss of 100 ports is 7.5?8.5d B.The channel passband and channel spacing can be adjusted flexibly by applying holograms onto an LCOS chip,the minimum channel bandwidth can achieve less than 10 GHz,the spectrum tuning accuracy can achieve sub-GHz.6.A three-step hybrid algorithm for WSS multicasting of input optical signals according to any energy ratio is proposed.The beam transformation model of the liquid crystal spatial light modulator in WSS is established,and a high-precision sampling method that satisfies the energy distribution within the 127?m size is proposed.On this basis,the traditional iterative Fourier algorithm,genetic algorithm and particle swarm algorithm are mixed and improved,a hybrid algorithm suitable for 256-level discontinuous phase is obtained.