Design considerations of photonic lanterns for diffraction-limited spectrometry

TL;DR

This paper explores the design of photonic lanterns to improve the coupling efficiency and stability of astronomical instruments, using numerical simulations to guide future diffraction-limited spectrometer development.

Contribution

It provides a detailed numerical analysis of photonic lantern performance considering geometry, wavelength, and wavefront error, including interactions with PIAA optics.

Findings

Photonic lanterns significantly improve coupling efficiency over direct SMF injection.

Design parameters like geometry and wavelength critically affect lantern performance.

Interactions between PLs and PIAA optics influence overall system stability and efficiency.

Abstract

The coupling of large telescopes to astronomical instruments has historically been challenging due to the tension between instrument throughput and stability. Light from the telescope can either be injected wholesale into the instrument, maintaining high throughput at the cost of point-spread function (PSF) stability, or the time-varying components of the light can be filtered out with single-mode fibers (SMFs), maintaining instrument stability at the cost of light loss. Today, the field of astrophotonics provides a potential resolution to the throughput-stability tension in the form of the photonic lantern (PL): a tapered waveguide which can couple a time-varying and aberrated PSF into multiple diffraction-limited beams at an efficiency that greatly surpasses direct SMF injection. As a result, lantern-fed instruments retain the stability of SMF-fed instruments while increasing their throughput. To this end, we present a series of numerical simulations characterizing PL performance as a function of lantern geometry, wavelength, and wavefront error (WFE), aimed at guiding the design of future diffraction-limited spectrometers. These characterizations include a first look at the interaction between PLs and phase-induced amplitude apodization (PIAA) optics.