# Modal Group Velocity Mismatch Induced Intermodal Modulation Instability in Step-index Fiber

## TL;DR

This paper investigates noise-seeded intermodal modulation instability in step-index fibers, highlighting how large group velocity mismatch due to refractive index contrast leads to efficient spectral peak generation, supported by experimental and theoretical analysis.

## Contribution

It provides a detailed experimental and theoretical study of intermodal modulation instability caused by group velocity mismatch in step-index fibers, which was not thoroughly explored before.

## Key findings

- Efficient IM-MI observed with multiple spectral peaks.
- Spectrum evolution depends on pump power and fiber length.
- Theoretical model aligns well with experimental results.

## Abstract

We present detailed experimental study on noise-seeded intermodal modulation instability (IM-MI) in normal dispersion region of a conventional step-index fiber. The sharp refractive index contrast between core and cladding leads to large group velocity mismatch between the spatial modes, coaxing to efficient IM-MI and generation of multiple spectral peaks along with Raman peaks. Evolution of the spectrum with pump powers and fiber lengths are observed. Experimental findings are well supported with the theoretical framework based on bimodal-MI model considering the distinct dispersion parameters of the participating modes.