In this paper, we propose a multilayer arrayed waveguide gratings (AWG) for spectro-interferometry applications which were fabricated using the femtosecond laser direct writing technique. Individually these devices consisted on an array of 19 single mode waveguides, were designed for operation at 633nm, and have a measured free spectral range of 28nm and a resolution of 4 nm. The aim of this work is to show the potential of arrayed waveguides gratings (AWG) stacked in a vertical layered structure, in order to simultaneously achieve spectral dispersion and multi-telescope interferometry for astrophotonic applications (visibility vs baseline as a function of wavelength). In particular, with the fabrication of three independent AWG, we can address closure phase studies, an important tool for exoplanet detection in astronomy.
Advances in 3D fabrication have afforded new freedoms in the design of custom optical elements. We explore a design space where the refractive index may vary freely with position in a material by considering applications in coherent beam shaping. First, we will describe experimental results where we have used femtosecond laser writing to fabricate custom GRIN waveguides in a planar geometry. We show a 2D device that converts a Gaussian beam to a flat top in one transverse direction, and is a single-mode waveguide in the other. Second, we describe a numerical method for designing 3D refractive index profiles. As an example, we will use the 3D method to design a device that transforms a circular beam with a Gaussian intensity profile into a square beam with a flat top.
Arrayed waveguide gratings (AWGs) are typically used by the telecommunications industry as (de)multiplexers. However, recently they have successfully been demonstrated as integrated sensors for applications such as biomedical and astronomical spectrographs. Unfortunately, advancement is generally stalled by development costs and time; or restricted to spectral regions covered by off-the-shelf lithographic produced AWGs. To broaden the potential applications of integrated spectrographs employing AWGs, we utilise the femtosecond laser direct write technique as a rapid-prototyping platform for fabricating AWGs. The AWGs fabricated operate at 633nm, have a free spectral range of 22.4nm, resolution of 1.35nm, resolving power of 468.7, a throughput of 11.47% across the 5 main orders, and 3.97% in the central 28th order. This mask-less process enables complete design freedom, takes approximately 2hours from completed design to finalized device, thus facilitating design feedback to easily fine tune the device specifications.
In some applications multimode fibres are used for efficient light collection, thus leading to large losses when coupling into single mode devices such as AWGs. A solution is to utilize a 3-dimensional photonic lantern. A photonic lantern converts multimode light into multiple single-mode waveguides that can then be individually launched into an AWG. While the AWG is only a 2-dimensional device the laser direct write technique enables 3-dimensional fabrication. Thus supporting the integration of a photonic lantern and AWG into a single monolithic chip, removing coupling losses while increasing the functionality of the AWG. Currently we have demonstrated the integration of a 3 port photonic lantern.