Potential of commercial SiN MPW platforms for developing mid/high-resolution integrated photonic spectrographs for astronomy
Pradip Gatkine, Nemanja Jovanovic, Christopher Hopgood, Simon Ellis, Ronald Broeke, Katarzyna Ławniczuk, Jeffrey Jewell, J. Kent Wallace, Dimitri Mawet
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) silicon nitride (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 (AWG) 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>10,000</mml:mn> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>60</mml:mn> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> 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.