Dual-core optical fibers for efficient mid-infrared generation via third-order frequency mixing and coupling-length phase matching

Abstract

Appropriately designed dual-core fibers using coupling-length phase matching (CLPM) allow for phase-matched frequency downconversion over wide frequency intervals using the third-order optical nonlinearity of glass. By tuning the distance between the two cores, CLPM allows continuously tunable phase matching for widely different wavelengths for the process in which a pump wave at a frequency ω 2 generates or amplifies two waves with frequencies ω 3 > ω 2 and ω 1 = 2 ω 2 − ω 3 . The intensity-dependent correction that accounts for nonlinear phase modulation is derived in general. In addition, a specific CLPM configuration is found to be insensitive to phase modulation, and can achieve 100% theoretical quantum yield for pump wave injection in one core. Fiber-based frequency converters can thus be designed for large differences between pump wavelengths and generated wavelengths, with the phase-matched interaction enabling the use of meter-long fibers to compensate for low third-order susceptibilities. Examples of fiber designs for pump wavelengths at 1.3 and 1.55 µ m , to generate radiation with wavelengths longer than 2 µ m , are discussed for silica and fluoride fibers.