# Super- and Anti-Principal Modes in Multi-Mode Waveguides

## TL;DR

This paper introduces super- and anti-principal modes in multimode waveguides, which exhibit enhanced or reduced spectral correlations, outperforming traditional principal modes in stability and sensitivity, with potential applications in communication and imaging.

## Contribution

The study presents a new class of states in multimode fibers that outperform principal modes in spectral stability and sensitivity, including the experimental generation and analysis of these states.

## Key findings

- Super-principal modes have enhanced spectral stability.
- Anti-principal modes are highly sensitive to frequency changes.
- Modes are orthogonal even with mode-dependent loss.

## Abstract

We introduce a new type of states for light in multimode waveguides featuring strongly enhanced or reduced spectral correlations. Based on the experimentally measured multi-spectral transmission matrix of a multimode fiber, we generate a set of states that outperform the established "principal modes" in terms of the spectral stability of their output spatial field profiles. Inverting this concept also allows us to create states with a minimal spectral correlation width, whose output profiles are considerably more sensitive to a frequency change than typical input wavefronts. The resulting "super-" and "anti-principal" modes are made orthogonal to each other even in the presence of mode-dependent loss. By decomposing them in the principal mode basis, we show that the super-principal modes are formed via interference of principal modes with closeby delay times, whereas the anti-principal modes are a superposition of principal modes with the most different delay times available in the fiber. Such novel states are expected to have broad applications in fiber communication, imaging, and spectroscopy.