The potsdam arrayed waveguide spectrograph: A demonstrator of a cross‑dispersed integrated photonic spectrograph developed for the astronomical H‑band

The Potsdam Arrayed Waveguide Spectrograph (PAWS) is based on an integrated photonic spectrograph designed and developed by innoFSPEC to work in the astronomical H‑band. PAWS demonstrates how a traditional bulk optics spectrograph can be miniaturized and additionally serves as a tool for testing in‑house developed astrophotonical devices. The main element is a second‑generation Arrayed Waveguide Grating (AWG) with unprecedented performance in terms of spectral resolution and throughput that is fiber‑coupled and works as a first dispersive component. The pre‑dispersed light is fed into a free‑space optical system located in a cryostat, where the overlapping spectral orders are separated by cross‑dispersion. The resulting echellogram is recorded by a Teledyne 2k×2k H2RG near‑infrared array. Once the cryogenic cross‑dispersion optics inside the vacuum chamber were appropriately aligned to the AWG coupling optics outside of the chamber, different light sources were used to test the functionality of the complete system. A tunable laser source was used to create an echellogram through frame stacking. Additionally, the cross‑dispersed output of a supercontinuum source was recorded using different input waveguides of the AWG, and first light was achieved with laboratory measurements. PAWS represents a pioneering demonstration of an astronomy‑optimized AWG chip, exhibiting the advantageous capabilities of integrated photonic spectrographs, in particular in the context of space applications.