Research on QPM and Its Cascaded Structure Applied in FOPA

Abstract

Abstract In the research of optical communication, Optical Parametric Amplification (OPA) has been an important point. As a Four Wave Mixing (FWM) effect based nonlinear process, OPA also requires Phase Matching (PM). Rigorous PM in practical research requires extremely harsh conditions. Quasi Phase Matching (QPM) and its cascaded structure can solve that problem, which would construct an overall phase matching. In the first part of this thesis, a QPM mechanism of segmented High NonLinear Fibre (HNLF) and inserted phase shifter for pumps, was proposed in application of FOPA. The phase shifters would “correct” the phase mismatching after every amplified signal by HNLF section. In this structure the phase matching was always kept in the vicinity of the initial matching value. The signal gain was flatter, and 6.4-9.5 dB higher than that of the non-QPM structure. In second part, a cascaded FWM+OPA structure was used to realize the copier-FOPA according to the cascaded QPM scheme. In the copier part, the information of signal wave was copied into the generated idler wave, before the signal light was amplified. Not only the copy, a 160 nm (Phase Insensitive, PI)/170 nm (Phase Sensitive, PS) gain bandwidth was obtained, which improved greatly comparing to that of the conventional. In FOPA part, the signal flatter gain decreases by approximately 14 dB (PI)/15 dB (PS), with fluctuation down to <0.1 dB (PI) / <0.2 dB (PS). The gain bandwidth decreases to 135 nm (PI) / 150 nm (PS), which is tens of nanometers wider than conventional FOPA.