微弱光信号瞬态布里渊放大器的最佳工作点

Optimal working point of a Brillouin amplifier for a weak input signal in the transient regime

为提高瞬态布里渊放大器的工作性能,利用包含噪声的瞬态布里渊放大理论模型数值模拟了放大器的信噪比、灵敏度、能量转换效率及信号放大率随指数增益系数G的变化规律,获得了放大器的最佳工作点G_(opt.)采用倍频Nd:YAG脉冲激光器,以CS_2和FC-72为非线性介质进行了实验验证.结果表明,抽运光脉冲相对于信号光脉冲延迟脉冲宽度的一半进入放大器时,G_(opt)可设在介质受激布里渊散射阈值增益G_(th)之上.对于共线型布里渊放大结构,G_(opt)为Gth的1.1—1.3倍;对于非共线型结构,G_(opt)可超过G_(th)1.3倍,实现近饱和放大.

In order to improve the working performances of a transient Brillouin amplifier, the dependences of the signal-noise-ratio, sensi- tivity, energy extraction efficiency and signal amplification factor on exponential gain G are numerically studied based on the theoretical model of transient Brillouin amplification including distributed noise, and an optimal working point of a Brillouin amplifier is obtained. Experimental verifications are performed by choosing CS2 and FC-72 as nonlinear media. A frequency-doubled Nd ： YAG pulse laser is used. Results show that when the pump pulse lags behind the Stokes signal pulse by an amount of time equal to half the pulse width, Gopt can be set to be above the SBS threshold exponential gain Gth. For a collinear Brillouin amplifier, Gopt is 1.1--1.3 times Gth; while for a non-collinear structure, Gopt can be set to be over 1.3 times Gth. Nearly saturated amplification is achieved.