cw three-wave mixing in single-mode optical fibers

TLDR

The study demonstrates that continuous three‑wave mixing in single‑mode fibers provides a simple, effective method for measuring silica’s nonlinearity and discusses its impact on Brillouin and Raman oscillators. The authors model two manifestations: (1) frequency mixing that generates new frequencies, and (2) multiple mixing that broadens a quasicontinuous spectrum, with a theoretical model for small broadening. Strong continuous three‑wave mixing of 514.5‑nm argon laser light in a single‑mode fiber produced new frequencies or a 4‑GHz‑wide quasicontinuous spectrum, achieving four‑fold broadening at lower intensities than required for stimulated Brillouin scattering, and the effect may constrain long‑haul fiber communication design.

Abstract

Strong continuous three-wave mixing of 514.5-nm argon laser light in a single-mode fiber is reported. The effect, due to the third-order nonlinearity of silica, has been observed for light whose frequency spectrum consists of either a few discrete monochromatic frequency components separated by ∼1 GHz or a quasicontinuous distribution of frequencies having a spectral envelope ∼4 GHz wide. We show that the effect provides a simple and effective method for measuring the nonlinearity of silica. In the first manifestation of the effect, the nonlinearity mixes the frequency components to produce new frequencies. In the second, multiple mixing occurs that broadens the quasicontinuous spectrum. This manifestation of the effect is large; broadening by a factor of 4 has been observed with lower intensity levels than are required to produce stimulated Brillouin scattering in the same fiber. A theoretical model is presented to describe spectral broadening by three-wave mixing for the case of small broadening. The effect of three-wave mixing on the operation of continuous stimulated Brillouin and Raman oscillators is also discussed. Finally, it is noted that the presence of this effect may constrain the design of long-haul single-mode fiber optical communication trunks.