Performance limits of astronomical arrayed waveguide gratings on a silica platform

Abstract

We present a numerical and experimental study of the impact of phase errors on the performance of large, high-resolution Arrayed Waveguide Gratings (AWG) for applications in astronomy. We use a scalar diffraction model to study the transmission spectrum of an AWG under random variations of the optical waveguide lengths. We simulate phase error correction by numerically trimming the lengths of the optical waveguides to the nearest integer multiple of the central wavelength. The optical length error distribution of a custom-fabricated silica AWG is measured using frequency-domain interferometry and Monte-Carlo fitting of interferogram intensities. In the end, we give an estimate for the phase-error limited size of a waveguide array manufactured using state-of-the-art technology. We show that post-processing eliminates phase errors as a performance limiting factor for astronomical spectroscopy in the H-band.

Potential of commercial SiN MPW platforms for developing mid/high-resolution integrated photonic spectrographs for astronomy

“…Phase errors in the array could arise from side wall imperfections, defects, thickness variations in the deposition processes, stitching errors in case of e-beam lithography or if using multiple reticles for a single device in case of stepper lithography, and so on [43]. To simulate the impact of these imperfections, we added phase errors to our simulations.…”

Astrophotonics: Processing starlight

“…innoFSPEC is building a miniaturised spectrograph on-a-chip for astronomy based on an arrayed waveguide grating (AWG), a technology originating in the telecommunication industry. Scientists at innoFSPEC have optimised the design specifically for astronomy [7], by which they achieved extraordinarily high resolution (up to 30,000) and throughput (insertion loss of 2 dB). These fiber-fed devices could potentially replace free-space prism or grating optics.…”

Design, simulation and characterization of integrated photonic spectrographs for Astronomy I: Generation-I AWG devices based on canonical layouts

“…The pre-calculated far field and effective index data was then used to set up the scalar diffraction model. In the second stage, the wavelength-dependent transmission from input waveguides 𝑗 to output waveguide 𝑘 was calculated according to [10,16]…”

“…The fabrication of functional high-resolution AWGs poses significant challenges in terms of fabrication accuracy. High-resolution AWGs with hundreds of waveguides and optical propagation lengths on the order of cm are very susceptible to phase error induced image degradation, leading to fabrication tolerance limited performance [16,17]. In earlier publications, we have studied the potential and technical limitations of silica-platform AWG, with a focus on the effects of fabrication tolerance related phase errors and the necessity of AWG post-processing by means of UV trimming [16,18].…”

“…High-resolution AWGs with hundreds of waveguides and optical propagation lengths on the order of cm are very susceptible to phase error induced image degradation, leading to fabrication tolerance limited performance [16,17]. In earlier publications, we have studied the potential and technical limitations of silica-platform AWG, with a focus on the effects of fabrication tolerance related phase errors and the necessity of AWG post-processing by means of UV trimming [16,18]. In this work, we experimentally study several different AWG designs of varying resolving power on a silica-on-silicon platform.…”