Research And Design Of LCOS-based Tunable Optical Filter

The new generation of all optical network(AON) requires that the ROADM(Reconfigurable Optical Add/Drop Multiplexer) nodes can realize optical switching in wavelength granule. Bandpass tunable optical filter(TOF) and wavelength selective switch(WSS) are widely employed in this new type of ROADM nodes. This thesis explores TOF based on LCOS(Liquid Crystal on Silicon) technology. The main research work includes,The electro-optic effect of liquid crystal and phase modulation principle of LCOS are studied. The beam steering technology based on LCOS is discussed. Results based on phase difference analysis show that the diffraction characteristics of a LCOS dynamic phase grating depend on three factors: the diffraction of single pixel, the interference of the blazed grating and the interference of the echelon grating. The diffracted light concentrates on the +1 order and thus high diffraction efficiency is obtained. The beam steering angle is the diffraction angle of +1 order.A tunable filter array(TFA) with flat passband is designed based on free-space optics. The passband of the TFA is selected by proper pixel division and beam steering of the LCOS chip. The problems such as parameter matching of Gaussian beam and pixel division on the LCOS chip are analyzed extensively. Based on these, parameters of the components such as beam dispersing system, beam expanding components, polarization diversity optics, fiber array and micro-lens array are designed in detail. The whole optical system is finally simulated.WSS can be treated as a bandpass TOF with 1×K ports. Considering the application of LCOS in a WSS module, a simplified 2f optical model is built. The relationship between the diffraction of the LCOS dynamic phase grating and the specifications of the WSS module is analyzed based on Gaussian optics and Fourier optics. The conclusions are obtained as: the crosstalk of the WSS module is mostly affected by the fringing field effect of the LCOS pixels. In order to keep the crosstalk <-30 dB, the period of the LCOS grating is required as ?>23.75, which restricts the number of WSS ports. These results can be good reference for the optimization design of a WSS module.