WIDTH-TUNABLE SINGLE-FREQUENCY FIBRE LASER LIGHT SOURCE FOR COHERENT OPTICAL ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEM

摘要

A width-tunable single-frequency fibre laser light source for a coherent optical orthogonal frequency division multiplexing system, comprising a high-reflectivity chirped fibre Bragg grating (1), a high-gain fibre (2), a low-reflectivity chirped fibre Bragg grating (3), a single-mode semiconductor pump laser (5), an optical wavelength division multiplexer (4), an optical coupler (6), an optical circulator (8) and a tunable optical filter assembly (9). The low-reflectivity chirped fibre Bragg grating (3) and the high-reflectivity chirped fibre Bragg grating (1) together serve as front and back cavity mirrors of a resonant cavity so as to realize laser oscillation. Broad-spectrum laser output from the optical wavelength division multiplexer (4) is split by means of the optical coupler (6), and then, a part thereof enters the tunable optical filter assembly (9) by means of the optical circulator (8). A wavelength corresponding to any nominal centre frequency specified by ITU-T is selected by means of the tunable optical filter assembly (9), and the 3dB spectral width thereof is less than 0.1 nm. Then, the part of the laser returns back to and is injected into the resonant cavity by means of the optical circulator (8) and the optical coupler (6) to perform self-injection locking on the resonant cavity. In conjunction with a short linear resonant cavity structure and the tunable optical filter assembly (9) thereof, laser radiation of a narrow line width and single longitudinal mode is realized.