An Optimal Fiber Optics Solution for Potentially Detecting Earth-Like Planets Around Nearby Stars

Overview

The radial velocity (RV) method, otherwise known as Doppler spectroscopy, is an effective exoplanet detection technique that has been increasingly used in recent years, used to discover around 30% of all exoplanets discovered including Proxima B, the closest known exoplanet to the solar system. This technique detects irregularities in star movements potentially caused by the gravitational pull from orbiting planets. In order to discover Earth-like planets in the habitable zone (HZ) around solar-type stars, and to yield more credible and accurate results, more work must be done to achieve the ~0.1 m/s RV measurement uncertainty necessary. Optical fibers are used for light transmission and can significantly improve RV instrument stability. Since they connect the observation telescope and RV spectrograph, their light transmission properties will largely affect the quality of data being taken. Our team experimented with many different types of fibers (with differing diameter size and cross-section areas) to better understand optical fibers and to discover which fiber will produce the highest precision when implemented on our instruments. The fiber properties we tested were mode scrambling gain (MSG) and profile illumination ratio (PIR), a new concept our team developed. MSG characterizes the shift in the center of light that is not caused by the movement of the observed star, and PIR characterizes the uniformity of light distribution. We found that the 80 micron(μm) circular fiber, when coupled with a three-lens optical double scrambler, produced the highest MSG of ~3000 and the most stable PIR. It appears that this combination of the circular fiber with the optical double scrambler can produce smaller than 0.1 m/s RV measurement uncertainty if the stellar beam can be controlled to within 0.2 arcsec onto the fiber tip entrance, indicating Earth-like habitable planets can be detected around bright solar-type stars with this fiber optics system in combination with a highly stable and high resolution optical spectrograph.