Research And Design On A Tunable Optical Filter Array Based On LCOS

ROADM(Reconfigurable Optical Add/Drop Multiplexer)is an important equipment in the nodes of AON(All Optical Network),which can switch the light signals in wavelength granularity.TFA(Tunable Filter Array)is the core device in the download module of the ROADM node,which can drop any wavelength or any combination of wavelengths.This thesis presents the design of a new TFA structure based on LCOS(Liquid Crystal on Silicon)technology.The main work includes:The existing various approaches for TOF(Tunable Optical Filter)are analyzed in comparison.The optical properties of liquid crystals and the principle of beam deflection by LCOS are studied.The key components involved in the research are analyzed,including the dual-fiber collimator,the polarization conversion component,the beam expanding system and the diffraction grating.A TFA based on LCOS is presented.the input optical beam from each channel is first expanded in horizontal direction by a telescope system,which is composed of two cylindrical lenses.Then the beam is diffracted by a grating and dispersed on the LCOS horizontally.By controlling the phase delay generated by each pixel,the LCOS constructed a reflective phase grating.The wavelength corresponding to the passband is diffracted to the output port.The passband wavelength can be tuned by adjusting the period of the LCOS phase grating.The channels of the TFA are aligned vertically and share the beam expanding system and diffracting grating.The pixels on the LCOS are allocated for each channel in vertical direction.The parameters of the system are simulated and optimized based on software such as MATLAB and ZEMAX.Two verification experiments are designed,one for single channel and the other for multi-channel.Components for the two experiments are designed respectively and the experimental platforms are constructed.In the tuning wavelength range of 1530~1570nm,the 3dB and 20 dB bandwidths of the passband in the single channel experiment are 0.36 nm and 1.12 nm respectively.Different channels in the multi-channel experiment show good uniformity.The 3dB and 20 dB bandwidths are 0.38 nm and 1.04 nm respectively.The experimental results meet the simulation well.