# Exploring the Capabilities of Astrophotonics for the Precise Alignment of Segmented Telescopes

## TL;DR

This paper explores the use of photonic lanterns as innovative wavefront sensors to detect segment misalignments in large segmented telescopes, combining simulations and experiments to demonstrate their effectiveness.

## Contribution

It introduces the novel application of photonic lanterns for sensing segment piston offsets, including simulation, neural network reconstruction, and experimental validation.

## Key findings

- Photonic lanterns can measure segment pistons with linear accuracy.
- Neural networks extend measurement capabilities beyond linear regimes.
- Experimental validation confirms potential for future telescope applications.

## Abstract

The next generation of large telescopes for direct imaging of exoplanets will require segmented primary mirrors. Over both long and short timescales, these telescopes experience segment misalignments which degrade the final science image. Adaptive optics (AO) systems can be used to correct these aberrations in real time. AO systems require wavefront sensors (WFSs) that measure the phase of the incoming light in order to reconstruct optical aberrations. However, most WFSs used for sensing atmospheric turbulence cannot correctly detect aberrations induced by misalignments in segmented telescopes, as they show poor sensitivity to phase discontinuities. We investigate the potential of photonic lanterns (PLs), which are waveguides that allow for the low-loss transmission from multi-mode to multiple single-mode optical signals, for sensing segment misalignments at the focal plane. We assess the ability of PLs to measure piston offsets in segmented mirrors through both simulations and laboratory experiments. We simulate the photonic lantern and demonstrate linear reconstruction on segment pistons. Further, we train a neural network to reconstruct aberrations outside of the linear regime. We experimentally validate reconstruction of segment piston offsets on the Miniature Infrared SEAL (muirSEAL) testbed, which includes a segmented deformable mirror, a PSF imaging branch, and a PL. This work demonstrates the potential of the PL as a compact WFS for future space- and ground-based segmented-mirror telescopes.