AGILIS: Agile Guided Interferometer for Longbaseline Imaging Synthesis

Abstract

Context. In comparison to the radio and sub-millimetric domains, imaging with optical interferometry is still in its infancy. Due to the limited number of telescopes in existing arrays, image generation is a demanding process that relies on time-consuming reconfiguration of the interferometer array and super-synthesis. Aims. Using single mode optical fibres for the coherent transport of light from the collecting telescopes to the focal plane, a new generation of interferometers optimized for imaging can be designed. Methods. To support this claim, we report on the successful completion of the 'OHANA Iki project: an end-to-end, on-sky demonstration of a two-telescope interferometer, built around near-infrared single mode fibres, carried out as part of the 'OHANA project. Results. Having demonstrated that coherent transport by single-mode fibres is feasible, we explore the concepts, performances, and limitations of a new imaging facility with single mode fibres at its heart: Agile Guided Interferometer for Longbaseline Imaging Synthesis (AGILIS). Conclusions. AGILIS has the potential of becoming a next generation facility or a precursor to a much larger project like the Planet Formation Imager (PFI).

The GRAVITY fringe tracker

“…For an increasing number of telescopes, the detector noise therefore becomes ever stronger. However, in the case of a system without background and detector noise, the S/N on the eigenvalues no longer depends on N (Woillez et al 2017). The ultimate sensitivity of the fringe tracker can then be established at one photon per coherence time and per telescope, regardless of the number of telescopes.…”

2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments

“…The alternative use of fibers was first discussed by Froehly in 1981 [519], when it became apparent that SMFs could offer significant advantages for both beam transport and combination. In a ground-based fiber interferometer, starlight collected by the telescope passes through a corrective AO system before injection into SMFs [85,[520][521][522][523][524]. Fibers from each telescope transport light to the combiner laboratory, where path lengths are equalized using internal delays.…”

“…Ideally all delay equalization would be in-fiber, however gross km-scale delays are not easily implemented in traditional fiber because of strong material dispersion and so effective dispersion management needs to be realized [525][526][527][528][529][530]. Fine delay equalization, however, can be done in fiber by stretching fiber segments [525][526][527][528] prior to beam combination [520,523]. Alternatively, as is done today, gross and fine delay equalization can be in free-space using mirror arrangements and moving delay line carts [520,523,526,527], but this breaks the realization of an all fiber, all photonic interferometer.…”

“…Fine delay equalization, however, can be done in fiber by stretching fiber segments [525][526][527][528] prior to beam combination [520,523]. Alternatively, as is done today, gross and fine delay equalization can be in free-space using mirror arrangements and moving delay line carts [520,523,526,527], but this breaks the realization of an all fiber, all photonic interferometer.…”

Astrophotonics: astronomy and modern optics

“…Finally, first fringes in K band of 107 Her were measured connecting the two Keck telescopes with fluoride fibers but without active length stabilization . Subsequent experiments with 20 cm telescopes connected with a pair of 300 m-long silica fibers showed the possibility to obtain fringes on bright stars in J and H band, but pointed out the need for an active compensation system for the acoustic noise picked up by the fibers (Woillez et al 2017). More recently (Lehmann et al 2019), an actively stabilized 200?200 m fiber interferometer operating at telecom wavelength (1550 nm) was laid over the 160 m-long path outdoors between one of the CHARA telescopes and the beam-combination facility on Mt.…”