Micro-lens arrays as tip-tilt sensor for single mode fiber coupling

Abstract

We introduce a design for a tip-tilt sensor with integrated single-mode fiber coupling for use with the front-end prototype of the iLocater spectrograph at the Large Binocular Telescope to detect vibrations that occur within the optical train. This sensor is made up of a micro-lens array printed on top of a fiber bundle consisting of a central single-mode fiber and six surrounding multi-mode fibers. The design in based on a previous prototype that utilized a multi-core fiber with seven single-mode fibers. 1 With this updated design, we are able to achieve a better sensing throughput. We report on the modeled performance: if the beam is perfectly aligned, 69% light is coupled into the central single-mode fiber feeding the scientific instrument. When the beam is not aligned, some of the light will be coupled into the outer sensing fibers, providing the position of the beam for tip-tilt correction. For this design we show that there is a linear response in the sensing fibers when the beam is subject to tip-tilt movement. Furthermore we introduce an adaptive optics testbed, which we call the Koenigstuhl Observatory Opto-mechatronics Laboratory (KOOL), this testbed currently simulates vibrations at the Large Binocular Telescope, and in collaboration we have extended it to allow single-mode fiber coupling tests.

Characterization of Single-mode Fiber Coupling at the Large Binocular Telescope

“…These test runs will include the use of a fast tip-tilt mirror and IR quadcell photodiode. Beam stabilization with a quadcell will also be compared to tip-tilt correction using a prototype photonic device described in Hottinger et al (2018).…”

“…The small core diameter enables high-spatial resolution filtering of the input field, a particularly important feature for high dispersion coronagraphy, exoplanet atmospheric characterization, and fiber-nulling Wang et al 2017). In addition, single-mode devices are an integral part of the emerging astro-photonics field, including fiber-based wavefront sensing and photonic reformatters (Bland-Hawthorn et al 2010;Hottinger et al 2018;Harris et al 2018).…”

Astronomical Applications of Multi-Core Fiber Technology

“…The IFU consists of 9 SMFs in a square geometry attached to individual microlenses. The plan is to replace the IFU with a MCF in future and a 3D printed MLA on the front of fiber as demonstrated by Hottinger et al [48], improving overall system efficiency. This instrument will be used to study and map the surfaces of giant resolved stars and disks.…”

Experimental Research on Automatic Alignment and Control Algorithm of Spatial Light-Fiber Coupling

“…e experimental results show that the system response rate using this method was 40 Hz. In 2018, Tottinger et al [8] proposed an optical fiber position sensor method. e sensor consists of a microlens array printed on an optical fiber bundle.…”