Hybrid sol-gel technology for fast prototyping in astronomical interferometry

Hybrid sol-gel technology was used for fabrication of prototypes of coaxial two, three and four telescopes beam combiners for astronomical applications. These devices were designed for the astronomical J-band and have been characterized using an optical source with emission centered at 1265 nm and with a spectral FWHM of 50 nm. Interferometric characterization of the two, three and four beam combiners, showed average contrasts respectively higher than 98%, 96% and 95%. Interferometric spectral analysis of the beam combiners revealed that the chromatic differential dispersion is the main contributor to the observed contrast decay in the latter cases. The laser direct writing technique was used for fabrication of a coaxial two beam combiner on sol-gel material; it showed a contrast of 95%. The measured high contrast fringes confirm that the procedures used lead to performant IO beam combiners. These results demonstrate the capabilities of the hybrid sol-gel technology for fast prototyping of complex chip designs for astronomical applications.