Simulations of a high-contrast single-mode fiber coronagraphic multiobject spectrograph for future space telescopes

Abstract

Directly imaging and characterizing Earth-like exoplanets is a tremendously difficult instrumental challenge. Present coronagraphic systems have yet to achieve the required 10 −10 broadband contrast in a laboratory environment, but promising progress towards this goal continues. A new approach to starlight suppression is the use of a single-mode fiber behind a coronagraph. By using deformable mirrors to create a mismatch between incoming starlight and the fiber mode, a single-mode fiber can be turned into an integral part of the starlight suppression system. In this paper, we present simulation results of a system with five single-mode fibers coupled to shaped pupil and vortex coronagraphs. We investigate the properties of the system, including its spectral bandwidth, throughput, and sensitivity to low-order aberrations. We also compare the performance of the single-mode fiber configuration with conventional imaging and multi-object modes, finding improved spectral bandwidth, raw contrast, background-limited SNR, and demonstrate a wavefront control algorithm which is robust to tip/tilt errors.

A multi-object spectrograph using single-mode fibers with a coronagraph: progress towards laboratory results on the high-contrast testbed for segmented telescopes

“…Simulations have shown that this has the potential to create large gains in contrast performance, 19 spectral bandwidth, and even improve the SNR in background-limited observations. 23 We seek to build on these results and replicate them in the lab, as described in the following sections.…”

“…We will first see how good our contrast is in narrowband light to verify that wavefront control is working, and then move on to the broadband portion of the experiment, where our goal is to realize as much of the performance gains shown in Ref. 23 as possible. The experiment itself is therefore simple: push the bandwidth as wide as possible while still maintaining better than 10 −8 contrast, which is the best that HCST has so far been able to achieve in narrowband light in imaging mode.…”

“…As with the simulations in Ref. 23, we used the FALCO 29 software package to perform the wavefront sensing and control. We approximated the true multicore fiber mode as individual single fibers overlaid atop one another, with the output electric fields treated as coherent and summed; as the crosstalk between the cores is so low (∼ −60 dB at 730 nm), this is a very close approximation of the electric field in the single-mode cores themselves.…”

“…Recent simulations and laboratory results [19][20][21][22] have shown that SMFs can be used as part of a wavefront control system while also offering improved spectral bandwidth and background-limited SNR. 23 However, like the coronagraphs themselves, they have so far not been demonstrated to achieve the simultaneous high contrasts and wide bandwidths that the simulations suggest are mathematically possible. We aim to change that, as well as demonstrate multi-fiber wavefront control at the same time.…”

Astronomical Applications of Multi-Core Fiber Technology

“…The intensity is clearly not zero but the phase shows a strong phase inversion at the location of the micro-lenses which strongly suppresses star light coupling into the fibers. Credit: Image reproduced from Coker et al (2019)[62].…”