Fiber Optic Communications Using Liquid-Crystal-Based Fourier Optical Spectrum Analyzer without Moving Parts

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We propose and demonstrate a liquid-crystal (LC)-based Fourier optical spectrum analyzer (FOSA). The FOSA consists of a birefringent filter array with an embedded LC phase modulator. The LC phase modulator is used to control the phase difference between two orthogonally polarized beams to avoid mechanical movement in conventional Fourier transform spectrometers. The detailed operation principle of this FOSA is described. A single-LC-based 6-stage FOSA is experimentally demonstrated, and the results obtained using such a FOSA show good agreement with the results measured using a reference spectrometer. We propose a liquid crystal (LC)-based cost-effective Fourier optical spectrum analyzer (FOSA) without moving parts. Unlike normal spectrometers, the LC FOSA retrieves the spectrum's Fourier coefficients instead of the direct spectrum measurement by changing different LC states in a number of stages. Besides the common applications, the LC FOSA can precisely read and recover the envelope of a dense wavelength-division-multiplexing spectrum to act as a spectral monitor and then work with a gain-flattening device to control the optical network instantly and dynamically.

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