47,320 research outputs found
Adaptive Kerr-assisted transverse mode selection in multimode fibers
Multimode optical fibers (MMFs) have recently regained interest because of the degrees of freedom associated with their different eigenmodes. In the nonlinear propagation regime in particular, new phenomena have been unveiled in graded-index (GRIN) MMFs such as geometric parametric instabilities and Kerr beam self-cleaning [1, 2]. The speckled pattern observed at the output of the MMF at low powers, is transformed at high powers into a bell-shaped beam close to the fundamental mode. Recent work has also demonstrated that Kerr beam self-cleaning can lead to a low-order spatial mode, different from a bell-shape, by adjusting the laser beam in-coupling conditions [3]. An attractive way to systematically control the spatial excitation conditions at the fiber input is provided by the use of a spatial light modulator (SLM) which permits to profile the beam wavefront entering the MMF. In most cases, experiments involving adaptive optics consider linear propagation through scattering plates or MMFs [4]. So far, few works have dealt with the nonlinear propagation regime[5, 6]
Few-mode fibers and AO-assisted high resolution spectroscopy: coupling efficiency and modal noise mitigation
NIRPS (Near Infra-Red Planet Searcher) is an AO-assisted and fiber-fed
spectrograph for high precision radial velocity measurements that will operate
in the YJH-bands. While using an AO system in such instrument is generally
considered to feed a single-mode fiber, NIRPS is following a different path by
using a small multi-mode fiber (more specifically called "few-mode fiber").
This choice offers an excellent trade-off by allowing to design a compact
cryogenic spectrograph, while maintaining a high coupling efficiency under bad
seeing conditions and for faint stars. The main drawback resides in a much more
important modal-noise, a problem that has to be tackled for allowing 1m/s
precision radial velocity measurements. We study the impact of using an AO
system to couple light into few-mode fibers. We focus on two aspects: the
coupling efficiency into few-mode fibers and the question of modal noise and
scrambling. We show first that NIRPS can reach coupling >= 50% up to magnitude
I=12, and offer a gain of 1-2 magnitudes over a single-mode solution. We
finally show that the best strategy to mitigate modal noise with the AO system
is among the simplest: a continuous tip-tilt scanning of the fiber core.Comment: 10 pages, 5 figures. Proceeding of the AO4ELT5 conferenc
Astronomical photonics in the context of infrared interferometry and high-resolution spectroscopy
We review the potential of Astrophotonics, a relatively young field at the
interface between photonics and astronomical instrumentation, for
spectro-interferometry. We review some fundamental aspects of photonic science
that drove the emer- gence of astrophotonics, and highlight the achievements in
observational astrophysics. We analyze the prospects for further technological
development also considering the potential synergies with other fields of
physics (e.g. non-linear optics in condensed matter physics). We also stress
the central role of fiber optics in routing and transporting light, delivering
complex filters, or interfacing instruments and telescopes, more specifically
in the context of a growing usage of adaptive optics.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2016, 21 pages, 10 Figure
MYSTIC: Michigan Young STar Imager at CHARA
We present the design for MYSTIC, the Michigan Young STar Imager at CHARA.
MYSTIC will be a K-band, cryogenic, 6-beam combiner for the Georgia State
University CHARA telescope array. The design follows the image-plane
combination scheme of the MIRC instrument where single-mode fibers bring
starlight into a non-redundant fringe pattern to feed a spectrograph. Beams
will be injected in polarization-maintaining fibers outside the cryogenic dewar
and then be transported through a vacuum feedthrough into the ~220K cold volume
where combination is achieved and the light is dispersed. We will use a C-RED
One camera (First Light Imaging) based on the eAPD SAPHIRA detector to allow
for near-photon-counting performance. We also intend to support a 4-telescope
mode using a leftover integrated optics component designed for the VLTI-GRAVITY
experiment, allowing better sensitivity for the faintest targets. Our primary
science driver motivation is to image disks around young stars in order to
better understand planet formation and how forming planets might influence disk
structures.Comment: Presented at the 2018 SPIE Astronomical Telescopes + Instrumentation,
Austin, Texas, US
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