Virginie Collomb

MAFL experiment: development of photonic devices for a space-based multiaperture fiber-linked interferometer.

We present a three-telescope space-based interferometer prototype dedicated to high-resolution imaging. This project, named multiaperture fiber-linked interferometer (MAFL), was founded by the European Space Agency. The aim of the MAFL project is to propose, design, and implement for the first time to the best of our knowledge all the optical functions required for the global instrument on the same integrated optics (IO) component for controlling a three-arm interferometer and to obtain reliable science data. The coherent transport from telescopes to the IO component is achieved by means of highly birefringent optical fiber. The laboratory bench is presented, and the results are reported allowing us to validate the optical potentiality of the IO component in this frame. The validation measurements consist of the throughput of this optical device, the performances of metrological servoloop, and the instrumental contrasts and phase closure of the science fringes.

Use of selectively buried ion-exchange waveguides for the realization of Bragg grating filters

Ion exchange on glass substrates has proved to be an efficient low cost and high performance technology to realise integrated optic devices. Among structures developed thanks to this technology, those presenting both surface and buried waveguides are of great interest. In this paper, we first describe a fabrication process of selectively buried ion exchange waveguides. Its principle is based on a two step ion exchange process. First a surface waveguide is realised by a thermal exchange of Ag\+-Na\+. Then a mask is deposited on the back side of the optical wafer perpendicularly to the axis of the waveguide. Finally a second step assisted by an external electric field is performed. Then we report the performances of this method through the measurement of the burying depth evolution. When the mask is wide enough, the burying depth varies from 2 μm above the middle of the mask to 12 μm in the unmasked region. The transition is 3 mm long and therefore avoid any excess losses. For this structure, no deformation of the fundamental mode has been observed. Finally, the first results of use of these selectively buried waveguides to realize Bragg filters with a surface grating is presented through a comparison of measured reflexion spectra.

Integrated optics interferometer for high precision displacement measurement

We present the design and fabrication aspects of an integrated optics interferometer used in the optical head of a compact and lightweight displacement sensor developed for spatial applications. The process for fabricating the waveguides of the optical chip is a double thermal ion exchange of silver and sodium in a silicate glass. This two step process is adapted for the fabrication of high numerical aperture buried waveguides having negligible losses for bending radius as low as 10 mm. The optical head of the sensor is composed of a reference arm, a sensing arm and an interferometer which generates a one dimensional fringe pattern allowing a multiphase detection. Four waveguides placed at the output of the interferometer deliver four ideally 90° phase shifted signals.

Spectral behavior of integrated optics asymmetric y-junction used for optimizing a planar optics telescope beam combiner

Astronomical aperture synthesis requires to combine beams coming from telescopes, with constraints on mechanical and thermal stability, accuracy on the measurement of the interferences visibility. One adapted way for solving the problem is integrated planar optics. A first two telescope beam combiner made by ion exchange technique on glass substrate and build with symmetric Y-junction provides laboratory white light interferograms simultaneously with photometric calibration. In order to increase the interferometric signal without loss of photometric output, we propose to replace symmetric Y-junctions by asymmetric ones. In this paper, we report the conception, the manufacturing and the characterization of asymmetric Y-junction realized by ion exchange on glass substrate. The specific application of astronomical interferometry required the characterization of such component in term of spectral behavior, so we report the simulation and the measurement of asymmetric Y-junction response versus wavelength.