Direct Writing of 3D Integrated Photonic Circuits for Astrophotonics

By exploiting the interference of light coming from different telescopes it is possible to achieve high-resolution images of astronomical objects. Astrophotonics, namely the realization of stellar interferometry in integrated photonic circuits, represents a promising platform in this field, due to the intrinsic interferometric stability of the integrated devices with respect to bulk optics. However, since the celestial light is unpolarized, a fully polarization insensitive behaviour is required, and this can be very challenging to obtain in an integrated device, due to the intrinsic birefringence of waveguides. To obtain low-birefringence waveguides, it is possible to exploit femtosecond laser micromachining. With this technology, different layouts were proposed to achieve this result. Nevertheless, they place strict requirements on the geometry of the device, for example on the distance between the waveguides of a directional coupler. Moreover, these layouts may induce some polarization rotations.