3D Free-Form Optical Lens -- Miniaturised Fibre Couplers for Astrophotonics

TL;DR

This paper presents a novel miniaturised, monolithic micro-optics solution for efficient fibre coupling in astrophotonics, suitable for broad UV-IR spectral ranges on large telescopes like Keck.

Contribution

It introduces a unique micro-optics fibre coupler that replaces traditional solutions, enabling efficient broad-spectrum coupling in a compact, monolithic design for astronomical applications.

Findings

Demonstrated a micro-optics coupler compatible with UV-IR spectra

Achieved precise alignment within a monolithic glass/crystal structure

Suitable for integration with large telescope systems like Keck

Abstract

In astronomy, multi-object spectrographs employ fibre positioning robots to couple the light from multiple astronomy sources (stars or galaxies) into multiple multi-mode fibres, which are distributed across the focal plane of the telescope. These fibres transport the celestial light to the entrance slit of a spectrograph (or bank of spectrographs) for analysis. For any multi-object system mm-scale opto-mechanical solutions are required to couple the telescope light efficiently into the fibre. We demonstrate a unique micro-optics solution to replace current optical fibre couplers. Specifically, we target technology on board the Keck telescope's FOBOS - Fibre-Optic Broadband Optical Spectrograph - which operates at UV to IR spectral ranges. For spectrally broad UV-IR band operation we use glass and crystals: fused silica, crystalline quartz (transparency 0.16 - 2 micrometers), sapphire Al2O3 (0.2 - 5 micrometers), CaF2 (0.2-7 micrometers), and BaF2 (0.2-10 micrometers). The miniaturised micro-coupler is monolithic, with the entire light path contained within glass or crystal, seamlessly extending to the fibre entrance, which is laser-machined and precisely aligned with the optical axis.