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

Abstract

Integrated photonic spectrographs offer an avenue to extreme miniaturization of astronomical instruments, which would greatly benefit extremely large telescopes and future space missions. These devices first require optimization for astronomical applications, which includes design, fabrication and field testing. Given the high costs of photonic fabrication, Multi-Project Wafer (MPW) SiN offerings, where a user purchases a portion of a wafer, provide a convenient and affordable avenue to develop this technology. In this work we study the potential of two commonly used SiN waveguide geometries by MPW foundries, i.e. square and rectangular profiles to determine how they affect the performance of mid-high resolution arrayed waveguide grating spectrometers around 1.5 μm. Specifically, we present results from detailed simulations on the mode sizes, shapes, and polarization properties, and on the impact of phase errors on the throughput and cross talk as well as some laboratory results of coupling and propagation losses. From the MPW-run tolerances and our phase-error study, we estimate that an AWG with R ∼ 10,000 can be developed with the MPW runs and even greater resolving power is achievable with more reliable, dedicated fabrication runs. Depending on the fabrication and design optimizations, it is possible to achieve throughputs ∼ 60% using the SiN platform. Thus, we show that SiN MPW offerings are highly promising and will play a key role in integrated photonic spectrograph developments for astronomy.

An on-chip astrophotonic spectrograph with a resolving power of 12,000

“…conclude that the phase errors are within limits (leq 120 deg 16 ), and hence do not degrade the AWG performance significantly. This indicates that the Ligentec platform is suitable and sufficiently stable for fabricating more realistic high-resolution AWGs (with larger FSRs) in the future.…”

“…An increase in the phase errors reduce the AWG throughput and increase the inter-channel crosstalk (which was studied in detail in our recent paper). 16 Given that the additional degradation in throughput is only 1.5 dB and the crosstalk is also within acceptable limits, we can The simulated AWG transmission profile in the 1575 -1585 nm range is shown here. Three spectral orders span this range, each with an FSR = 2.9 nm.…”

“…In our previous work, we simulated the high-resolution (R ∼ 10,000) AWGs in both of these MPW classes to examine the impact of phase errors on the AWG performance and thereby, provided fabrication tolerances to achieve high-efficiency and high spectral resolution. 16 In this paper, we present experimental results of a proof-of-concept AWG to test the suitability of the Ligentec 800-nm SiN platform for building high-resolution (R > 10,000) astronomical spectrographs. The key aspects that we measured here are on-chip and coupling efficiency, spectral resolution, and broadband operation.…”

Simulating the Study of Exoplanets Using Photonic Spectrographs

“…The first step is to characterize how the AWG transmits different wavelengths of light. Even if the AWG spectrograph is illuminated by a narrow emission line (much narrower than the spectral channel), multiple spectral channels will still receive the photons since each spectral channel has a finite non-zero response at each wavelength (due to the inherent properties of the spectrograph such as side lobes and phase errors 16 ). This 'scattering' is called the line spread function (LSF).…”

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

“…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].…”