An efficient, compact, and versatile fiber double scrambler for high precision radial velocity instruments

Abstract

We present the design and test results of a compact optical fiber double-scrambler for high-resolution Doppler radial velocity instruments. This device consists of a single optic: a high-index $n$$\sim$2 ball lens that exchanges the near and far fields between two fibers. When used in conjunction with octagonal fibers, this device yields very high scrambling gains and greatly desensitizes the fiber output from any input illumination variations, thereby stabilizing the instrument profile of the spectrograph and improving the Doppler measurement precision. The system is also highly insensitive to input pupil variations, isolating the spectrograph from telescope illumination variations and seeing changes. By selecting the appropriate glass and lens diameter the highest efficiency is achieved when the fibers are practically in contact with the lens surface, greatly simplifying the alignment process when compared to classical double-scrambler systems. This prototype double-scrambler has demonstrated significant performance gains over previous systems, achieving scrambling gains in excess of 10,000 with a throughput of $\sim$87% using uncoated Polymicro octagonal fibers. Adding a circular fiber to the fiber train further increases the scrambling gain to $>$20,000, limited by laboratory measurement error. While this fiber system is designed for the Habitable-zone Planet Finder spectrograph, it is more generally applicable to other instruments in the visible and near-infrared. Given the simplicity and low cost, this fiber scrambler could also easily be multiplexed for large multi-object instruments.

10 pages, 13 figures, accepted in ApJ

References in corpus (6)

• SOPHIE+: First results of an octagonal-section fiber for high-precision radial velocity measurements
• Instrumentation for the detection and characterization of exoplanets
• Suppression of Fiber Modal Noise Induced Radial Velocity Errors for Bright Emission-Line Calibration Sources
• Optical fiber modal noise in the 0.8 to 1.5 micron region and implications for near infrared precision radial velocity measurements
• Fiber scrambling for high-resolution spectrographs. I. Lick Observatory
• The Habitable-zone Planet Finder Calibration System

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• Precision velocimetry planet hunting with PARAS: Current performance and lessons to inform future extreme precision radial velocity instruments
• Fiber mode scrambler for the Subaru infrared Doppler instrument (IRD)
• A Harsh Test of Far-Field Scrambling with the Habitable Zone Planet Finder and the Hobby Eberly Telescope
• Modal noise characterisation of a hybrid reformatter
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