Photonic ring resonator filters for astronomical OH suppression

Area of Science:

• Photonics and Optical Engineering
• Astronomy and Astrophysics Instrumentation
• Materials Science for Optics

Background:

• Ring resonators are optical devices capable of filtering specific wavelengths from light.
• Atmospheric OH emission lines present a significant challenge in astronomical spectroscopy, obscuring faint celestial signals.
• Existing filtering methods may lack the efficiency or specificity required for effective OH line suppression.

Purpose of the Study:

• To investigate the design requirements for ring resonators as notch filters for suppressing atmospheric OH emission lines in astronomical spectra.
• To evaluate the feasibility of using ring resonators in astronomical instruments for improved spectral clarity.

Main Methods:

• Theoretical derivation of design parameters for OH suppression using ring resonators.
• Finite difference time domain (FDTD) simulations to model resonator performance.
• Analysis of factors such as radius, material, coupling, and Q factor.

Main Results:

• Small radius ring resonators (< 10 μm) are necessary for achieving an adequate free spectral range.
• High index contrast materials like Silicon (Si) and Silicon Nitride (Si3N4) are suitable for fabricating these resonators.
• Critically coupled rings with high self-coupling coefficients offer potential for high Q factors and deep suppression, but necessitate post-inscription tuning.

Conclusions:

• Ring resonators are a promising technology for OH emission line suppression in astronomical spectroscopy.
• Achieving efficient OH suppression requires careful design, including small radii and high index contrast materials.
• Further advancements in post-inscription tuning and fiber-chip coupling are crucial for practical implementation in astronomical instruments.