Abstract
A comprehensive design of a folded-architecture arrayed-waveguide-grating (AWG)-device, targeted at applications as integrated photonic spectrographs (IPS) in near-infrared astronomy, is presented. The AWG structure is designed for the astronomical H-band (1500 nm–1800 nm) with a theoretical maximum resolving power R = 60,000 at 1630 nm. The geometry of the device is optimized for a compact structure with a footprint of 5.5 cm × 3.93 cm on SiO 2 platform. To evaluate the fabrication challenges of such high-resolution AWGs, effects of random perturbations of the effective refractive index (RI) distribution in the free propagation region (FPR), as well as small variations of the array waveguide optical lengths are numerically investigated. The results of the investigation show a dramatic degradation of the point spread function (PSF) for a random effective RI distribution with variance values above ∼ 10 - 4 for both the FPR and the waveguide array. Based on the results, requirements on the fabrication technology for high-resolution AWG-based spectrographs are given in the end.
Highlights
Arrayed-waveguide-grating (AWG) devices have been established as the most common wavelength division multiplexers (WDMs) in optical telecommunications [1,2,3]
integrated photonic spectrographs (IPS) devices have been shown to be no viable alternative to large conventional integral field spectrographs for extremely large telescopes, they can be useful in combination with small, diffraction-limited telescopes [9]
Input ports with the highest resolving power are located close to the central axis of the free propagation region (FPR) in order to minimize the off-axis degradation of the beam, while inputs with lower resolving powers reside on the periphery of the central waveguide group
Summary
Arrayed-waveguide-grating (AWG) devices have been established as the most common wavelength division multiplexers (WDMs) in optical telecommunications [1,2,3]. In the field of astrophotonics, the AWG technology received attention as a possible candidate for the realization of astronomical integrated photonic spectrographs (IPS) [7,8]. A further advantage is the possibility to combine the IPS with additional integrated photonic elements on a single compact chip (‘lab-on-a-chip’ concept), such as micro-ring resonators for wavelength calibration or sensors for chemical and biomedical analysis. Potential applications of an IPS include diffraction-limited single-object spectroscopy and low-resolution multiplexed spectroscopy. As such, they are not well suited for many scientific applications in astronomy, spectroscopy and sensing. High requirements on AWG device performance for spectroscopy and sensing create challenges in the design and fabrication previously not encountered in traditional telecom applications. This paper explores some of the most important challenges, in particular the influence of random effective RI variations across the wafer on the performance of large, high-resolution AWGs
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