Optical fiber modal noise in the 0.8 to 1.5 micron region and implications for near infrared precision radial velocity measurements

TL;DR

This paper investigates modal noise in optical fibers within 0.8 to 1.5 microns, highlighting its impact on near-infrared radial velocity measurements and testing mitigation techniques for high-precision spectrographs.

Contribution

It provides experimental characterization of modal noise in the near-infrared and evaluates the effectiveness of mechanical scramblers for mitigation.

Findings

Modal noise increases with wavelength, affecting NIR spectrograph performance.

Mechanical scramblers can improve modal scrambling in fibers.

Results inform design of the Habitable Zone Planet Finder.

Abstract

Modal noise in fibers has been shown to limit the signal-to-noise ratio achievable in fiber-coupled, high-resolution spectrographs if it is not mitigated via modal scrambling techniques. Modal noise become significantly more important as the wavelength increases and presents a risk to the new generation of near-infrared precision radial spectrographs under construction or being proposed to search for planets around cool M-dwarf stars, which emit most of their light in the NIR. We present experimental results of tests at Penn State University characterizing modal noise in the far visible out to 1.5 microns and the degree of modal scrambling we obtained using mechanical scramblers. These efforts are part of a risk mitigation effort for the Habitable Zone Planet Finder spectrograph currently under development at Penn State University.