Infrared miniature spectrograph based on polymer waveguide array

Astrophotonics aims to apply photonic technology to manipulate light from a telescope and process it for astronomical research purposes in an efficient and cost-effective way. In particular, using planar dispersive device for astronomical spectroscopic research is a promising method, as the compact and lightweight device could replace at least some of the bulky parts in the modern spectrograph. However, the migration of arrayed waveguide gratings from optical communication to astronomy must go through new designs with tailored properties. In this work, we first demonstrate an arrayed waveguide grating with over 100-nm free spectral range and further propose a new design of an integrated photonic spectrograph without any free-space optics. The design merges the wavefront modulation of a conventional lens into the length/phase variation in the waveguide array, in addition to the required difference to form the grating effect. The end effect is that the output light from the facets of the arrayed waveguides is not only separated by wavelength, but also focused onto a camera at a fixed distance. Simulation shows this design can reach high resolving power (> 7,000) with more compact size and most importantly, it eliminates the need to add any conventional lens in the optical path, in the sense of a truly integrated photonic spectrograph.