Abstract

A lot of interest has been generated recently in stimulated Raman scattering (SRS) in a multimode fiber.^1-2 An interesting observation is that a multimode fiber essentially behaves like a single mode fiber for the purpose of SRS, i.e., the mode structure of SRS light is the same as that of the input light. We show here that the conclusion is no longer true in the presence of strong four photon mixing (FPM) in multimode fiber. Thus for a 7.9-μm core diameter step index multimode fiber, even for a true LP₀₁ mode of the input pump light at 532 nm, the mode structure of multiorder SRS shows a strong ringlike structure with concentric central spot, resembling LPQ2 mode (Fig. 1).

© 1994 Optical Society of America