Polarization-Insensitive Four-Wave-Mixing-Based Wavelength Conversion in Few-Mode Optical Fibers

Abstract

We report theoretical and experimental results on a wavelength converter based on intermodal phase-matching in a graded index three-mode elliptical-core fiber. Here, two copolarized pump waves propagate in one spatial mode whereas a signal and the corresponding generated idler propagate in another mode. We demonstrate that the idler power is independent of the signal polarization in both a 1 km and a 50 m long fiber. We attribute this polarization insensitivity to the fast random birefringence of the fiber under investigation in combination with the co-polarized pump configuration.

Multiple modal and wavelength conversion process of a 10-Gbit/s signal in a 6-LP-mode fiber

“…We can also notice that the wavelength range of the phase matching process increases with higher-order modes, while the CE drops to −18 dB for LP 31 . This behavior is attributed to the increasing number of degenerate modes in these groups and their associated random couplings, for which the slight differences in the phase matching condition enlarge the resulting bandwidth at the expense of the conversion efficiency [20,21]. It could be also related to the core-radius fluctuations, which randomly changes the propagation constants of all the modes along the fiber length [22].This issue is quite similar to the case of parametric processes in single mode fibers for which the random fluctuations of the dispersion properties along the fiber length, especially the zero-dispersion wavelength, induce a decrease of the conversion efficiency [23].…”

Bandwidth enhancement of inter-modal four wave mixing Bragg scattering by means of dispersion engineering

“…Inter-modal FWM BS processes have recently been demonstrated both in fibers 15 and in silicon waveguides. 16 Specifically, we have theoretically and experimentally studied phase-matching, uni-directionality of conversion, and insensitivity to pump polarization in IM FWM processes in randomly birefringent fibers guiding a small number of modes.…”

“…16 Specifically, we have theoretically and experimentally studied phase-matching, uni-directionality of conversion, and insensitivity to pump polarization in IM FWM processes in randomly birefringent fibers guiding a small number of modes. 11,14,15 In Ref. 15, we focused on the IM FWM BS process in an elliptical core three-mode graded-index fiber, achieving phase matching for only the BSr idler with ∆λ ps of about 25 nm (40 nm) for the LP 01 − LP 11a (LP 01 − LP 11b ) pump-signal mode groups.…”

“…11,14,15 In Ref. 15, we focused on the IM FWM BS process in an elliptical core three-mode graded-index fiber, achieving phase matching for only the BSr idler with ∆λ ps of about 25 nm (40 nm) for the LP 01 − LP 11a (LP 01 − LP 11b ) pump-signal mode groups. Using 50 m of that fibre, we demonstrated ∆λ pp bandwidths of up to 3 nm.…”

“…Using 50 m of that fibre, we demonstrated ∆λ pp bandwidths of up to 3 nm. 15 In this paper, we report on the design, fabrication, and characterization of several 100 m long gradedindex (GI) MMFs to specifically demonstrate the bandwidth enhancement for the IM FWM BS process through dispersion engineering, reporting ∆λ pp bandwidths of up to 7 nm. This length was chosen to provide balance between idler gain and conversion efficiency (CE) bandwidth, given that the bandwidth decreases with length, whereas gain increases.…”