Evaluation methods and requirements for the stimulated Brillouin scattering threshold in a single-mode fiber

This paper presents an experimental discussion of methods for evaluating the input power limitation caused by stimulated Brillouin scattering (SBS) in a single-mode fiber, and known as the SBS threshold. We consider five different evaluation methods including the traditional approach, which considers the input power at which the reflected power is the same as transmitted power. We show that two evaluation methods, which consider the second derivative of the reflected power and the change in the transmitted power characteristics, well describe analogue transmission characteristics by taking account of the input power dependence of the carrier-to-noise ratio (CNR). We also show that the SBS threshold can be evaluated practically by considering a 4% level change in the reflected power against the input power in terms of harmonization with the CNR. We also discuss the evaluation conditions required for an accurate SBS threshold measurement. We clarify the requirements for both the uncertainty in the reflected power and the input power interval in data acquisition.