Spontaneous Raman scattering in SDM fibers

Abstract

Spontaneous Raman scattering (SpRS) is a weak non-linear effect, particularly relevant to classical-quantum coexistence transmission and sensing applications. In classical transmission, the relevant Raman effect is stimulated Raman scattering (SRS), and recent studies have examined it in space-division multiplexing (SDM) fibers. An intrinsic relation between SpRS and SRS allows previous SRS results to inform SpRS models. In this work, we extend SpRS models derived for single-mode fibers (SMFs) to SDM fibers with multiple mode groups of degenerate modes, covering both Stokes and anti-Stokes bands. The proposed model is a useful, fiber-design-independent tool for evaluating scattered noise in optical links, and it is validated through experimental measurements in field-deployed multi-core fibers (MCFs) and multi-mode fiber (MMF), showing good agreement.

Figures (3)

• Figure 1: (a) Mode–group–averaged srs gain efficiency measured in the uc-mcf (solid line, circles), copropagating cc-mcf (dashed, squares), and counter-propagating cc-mcf (dotted, diamonds) configurations. Gain curves for the cc-mcf are extracted from di2025characterization. (b) Estimated sprs efficiency in the 4-core uc-mcf, obtained from copropagating noise (solid lines) and on–off gain (dashed lines) data, normalized by bandwidth. Shaded regions indicate the bandwidth of the unfiltered longitudinal laser modes. (c) Estimated sprs efficiency from experimental measurements in the 4-core uc-mcf (circles) and 4-core cc-mcf (squares: copropagating, diamonds: counter-propagating), obtained from noise (solid lines) and on-off gain (dashed lines) data. The labels "FW" and "BW" represent, respectively, co- and counter-propagating measurements.
• Figure 2: (a) Self- and cross-effective areas of mmf mode-groups. (c) Mode-group-averaged coupling coefficients and (c) mode-group-averaged frequency-dependent attenuation of the mmf.
• Figure 3: (a) Per-mode counter-propagating sprs noise in each mode group (distinguished by line styles) of the mmf, with the pump launched into the $1^{\mathrm{st}}$ and $5^{\mathrm{th}}$ mode groups. (b) Effective sprs efficiency estimated from measurements of each mode group with the pump in the fundamental mode. (c) Mode-group-averaged measurements for each pump configuration. (d) Effective sprs efficiency for the different sdm fiber types, where the mmf curve correspond to the average over all measurements.