Modal noise mitigation in a photonic lantern fed near-IR spectrograph

Fraser A. Pike; Aurélien Benoit; David G. MacLachlan; Robert J. Harris; Itandehui Gris-Sánchez; David Lee; Timothy A. Birks; Robert R. Thomson

doi:10.1117/12.2561644

13 December 2020 Modal noise mitigation in a photonic lantern fed near-IR spectrograph

Fraser A. Pike, Aurélien Benoit, David G. MacLachlan, Robert J. Harris, Itandehui Gris-Sánchez, David Lee, Timothy A. Birks, Robert R. Thomson

Author Affiliations +

Proceedings Volume 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV; 114510E (2020) https://doi.org/10.1117/12.2561644
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Abstract

Recently, we have demonstrated the potential of a hybrid astrophotonic device, consisting of a multi-core fiber photonic lantern and a 3D waveguide reformatting component, to efficiently reformat the multimode point spread function of a telescope to a diffracted limited pseudo-slit. Here, we report on an investigation into the potential of this device to mitigate modal noise - one of the main hurdles of multi-mode fiber-fed spectrographs. The modal noise performance of the photonic reformatter and other fiber feeds was assessed using a bench-top spectrograph based on an echelle grating. In a first method of modal noise quantification, we used broadband light as the input, and assessed the modal noise performance based on the variations in the normalized spectrum as the input coupling to the fiber feed is varied. In a second method, we passed the broadband light through an etalon to generate a source with spectrally narrow peaks. We then used the spectral stability of these peaks as the input coupling to the fiber feed was varied as a proxy for the modal noise. Using both of these approaches we found that the photonic reformatter could significantly reduce modal noise compared to the multi-mode fiber feed, demonstrating the potential of photonic reformatters to mitigate modal noise for applications such as near-IR radial velocity measurements of M-dwarf stars.

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Fraser A. Pike, Aurélien Benoit, David G. MacLachlan, Robert J. Harris, Itandehui Gris-Sánchez, David Lee, Timothy A. Birks, and Robert R. Thomson "Modal noise mitigation in a photonic lantern fed near-IR spectrograph", Proc. SPIE 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV, 114510E (13 December 2020); https://doi.org/10.1117/12.2561644

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