Focal-ratio degradation (FRD) mitigation in a multimode fibre link using mode-selective photonic lanterns. Issue 2 (30th January 2021)

• Record Type: Journal Article
• Authors: Benoît, Aurélien; Yerolatsitis, Stephanos; Harrington, Kerrianne; Birks, Tim A; Thomson, Robert R
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 502:Issue 2(2021)
• Page Start: 2381
• Page End: 2388
• Publication Date: 2021-01-30
• Subjects: instrumentation: miscellaneous -- instrumentation: spectrograph -- methods: data analysis -- techniques: miscellaneous -- techniques: spectroscopic; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3904
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present a new way to mitigate focal-ratio degradation (FRD) when using optical fibres to transport multimode light. Our approach exploits a custom multicore fibre (MCF) with six dissimilar cores that are single-mode at ∼1550 nm wavelength and minimally coupled over 7 m. We fabricated adiabatic mode-selective photonic lanterns (PLs) at each end of the MCF to create a fibre link with multimode ports, the PLs coupling each spatial mode of the multimode ports to a specific core of the MCF and vice versa. The PL-MCF-PL link exhibits superior FRD behaviour compared to a conventional multimode fibre that also supports six modes, because it inhibits the transfer of light from lower order modes to higher order modes. These results open up a potential powerful new approach to mitigate FRD in multimode fibre links, with particular applications in astronomical instruments.