Measurements of differential chromatic dispersion and contrasts in a hectometric silica fiber interferometer in the frame of the 'OHANA Project

Abstract

In the frame of 'OHANA project (phase II), IRCOM institute is in charge of the 300-meters-long silica fibres devoted to link the Canada France Hawaii Telescope and the GEMINI telescope over J and H-band. In this paper, we report a method to compensate the differential chromatic dispersion between two 300m-long silica polarization maintaining fibres. It consists in adding short fibre length (from 0 to 3 m) on the less dispersive arm. We experimentally demonstrate that the chromatic differential dispersion is different for the two neutral axis of the polarization-maintaining fibre and that a tradeoff between order 2 and 3 of the chromatic dispersion is necessary to reach the best results. Moreover, thanks to a channeled spectrum analysis and using a Taylor series expansion, the spectral phase is analyzed around a mean frequency. Using these data, it is possible to foresee the evolution of the fringes contrast as a function of the additional fibre length. These simulations fit properly the measurements of the fringes contrasts demonstrating the good modeling. At least, we simulate the variation of the contrast as a function of wavelength and spectral resolution over a given spectral window. Consequently, we are able to adjust the fibre lengths in order to perform a coherent linkage maximizing the contrast over J and H-band. The work reported in this paper is part of a global work on fibers in the 'OHANA project. In another paper, Kotani et al. describe the results achieved on fluoride glass fibers devoted the astronomical K-band.