# Modal analysis using photonic lanterns coupled to arrays of waveguides

## TL;DR

This paper introduces an integrated optical device using photonic lanterns and waveguide arrays to measure complex modal amplitudes in multimode fibers, enabling real-time modal analysis.

## Contribution

The paper presents a novel integrated optics component that can directly measure modal amplitudes and phases in multimode waveguides using a photonic lantern and waveguide array.

## Key findings

- Device can invert linear relations to derive modal amplitudes and phases.
- Potential application in real-time modal instability measurement in high power fiber lasers.
- Performance analysis shows feasibility of the proposed method.

## Abstract

We present a new concept of an integrated optics component capable of measuring the complex amplitudes of the modes at the tip of a multimode waveguide. The device uses a photonic lantern to split the optical power carried by an $N$-modes waveguide among a collection of single-mode waveguides that excite a periodic array of at least $N^2$ single-mode evanescently-coupled waveguides. The power detected at each output of the array is a linear combination of the products of the modal amplitudes-a relation that can, under suitable conditions, be inverted allowing the derivation of the amplitudes and relative phases of the modal mixture at the input. The expected performance of the device is discussed and its application to the real-time measurement of modal instability in high power fiber lasers is proposed.