Study of the atmospheric refraction in a single mode instrument - Application to AMBER/VLTI

International audienceThis paper presents a study of the atmospheric refraction and its effect on the light coupling efficiency in an instrument using single-mode optical fibers. We show the analytical approach which allowed us to assess the need to correct the refraction in J- and H-bands while observing with an 8-m Unit Telescope. We then developed numerical simulations to go further in calculations. The hypotheses on the instrumental characteristics are those of AMBER (Astronomical Multi BEam combineR), the near infrared focal beam combiner of the Very Large Telescope Interferometric mode (VLTI), but most of the conclusions can be generalized to other single-mode instruments. We used the software package caos (Code for Adaptive Optics Systems) to take into account the atmospheric turbulence effect after correction by the ESO system MACAO (Multi-Application Curvature Adaptive Optics). The opto-mechanical study and design of the system correcting the atmospheric refraction on AMBER is then detailed. We showed that the atmospheric refraction becomes predominant over the atmospheric turbulence for some zenith angles z and spectral conditions: for z larger than 30° in J-band for example. The study of the optical system showed that it allows to achieve the required instrumental performance in terms of throughput in J- and H-bands. First observations in J-band of a bright star, alpha Cir star, at more than 30° from zenith clearly showed the gain to control the atmospheric refraction in a single mode instrument, and validated the operating law

De l’optique dans les nanosatellites

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Near infrared spectro-interferometer usingfemtosecond laser written GLS embeddedwaveguides and nano-scatterers

International audienceGuided optics spectrometers can be essentially classified into two main families:based on Fourier transform or dispersion. In the first case, an interferogram generated insidean optical waveguide and containing the spectral information is sampled using spatiallydistributed nanodetectors. These scatter quasi-non-perturbingly light into the detector that isin contact with the waveguide, helping to reconstruct the stationary wave. A dedicated FFTprocessing is needed in order to recover the spectrum with high resolution but limited spectralrange. Another way is to directly disperse the different wavelengths to different pixels, eitherintroducing differential optical path in the same propagation plane (multiple Mach-Zehnderinterferometers or Arrayed Waveguides Gratings), or using a periodic structure toperpendicularly extract the optical signal confined in a waveguide (photonic crystals orsurface gratings), and by means of a relay optics, generate the spectrum on the Fourier planeof the lens, where the detector is placed. Following this second approach, we present a laserfabricatedhigh-resolution compact dispersive spectro-interferometer (R>2500, 30nm spectralrange at λ = 1560nm), using four parallel waveguides that can provide up to three nonredundantinterferometric combinations. The device is based on guided optics technologyembedded in bulk optical glass. Ultrafast laser photoinscription with 3D laser indexengineering in bulk chalcogenide Gallium Lanthanium Sulfide glass is utilized to fabricatelarge mode area waveguides in an evanescently-coupled hexagonal multicore arrayconfiguration, followed by subsequent realization of nanoscaled scattering centers via onedimensional nanovoids across the waveguide, written in a non-diffractive Besselconfiguration. A simple relay optics, with limited optical aberrations, reimages the diffractedsignal on the focal plane array, leading to a robust, easy to align instrument

All integrated Lithium Niobate Standing Wave Fourier Transform Spectrometer to improve sampling resolution

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A compact SWIFTS spectrograph with a leaky loop structure

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Large-mode-area infrared guiding in ultrafast laser written waveguides in Sulfur-based chalcogenide glasses

International audienceCurrent demands in astrophotonics impose advancing optical functions in infrared domains within embedded refractive index designs. We demonstrate concepts for large-mode-area guiding in ultrafast laser photowritten waveguides in bulk Sulfur-based chalcogenide glasses. If positive index contrasts are weak in As2S3, Ge doping increases the matrix rigidity and allows for high contrast (10−3) positive refractive index changes. Guiding with variable mode diameter and large-mode-area light transport is demonstrated up to 10μm spectral domain using transverse slit-shaped and evanescently-coupled multicore traces

Recent Progress in Mid Infrared Integrated Optics for Nulling Interferometry

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