Tunable dual-polarization photonic ring resonator filters for OH-supressed ground-based astronomy

We seek to advance the capabilities of photonic technologies in support of ground-based infrared astronomy. Currently, observations in the wavelength range 1.0μm < λ < 2.5μm suffer from an irreducible background generated by emission from OH (hydroxyl) molecules in the upper atmosphere. Placing instruments in space is one solution, but these are significantly more expensive and much harder (and more dangerous) to maintain and upgrade. Meanwhile, narrow-band notch filters incorporated into the optical path of ground-based astronomical instruments can suppress this background with very little accompanying loss of signal from the astronomical sources of interest. Micron-scale ring resonators are one technology that provides a promising method of generating such notch filters. Building on our previous efforts in astrophotonic technology development, our current goals are 1) to optimize the design of ring resonators so that the notch filters they create provide greatest suppression at the wavelengths of the most prominent OH lines, and 2) to optimize the coupling of the resonator-equipped silicon devices with the input fibers (from the sky) and output fibers (to the spectrograph and detector) such that the throughput losses do not completely eliminate the signal-to-noise improvement gained from the OH suppression. To accomplish the former, we introduce heaters that can actively change the wavelength of the notch filters to match the OH emission lines, as well as mechanisms for polarization-dependent and -independent suppression. To accomplish the latter, we incorporate post-fabrication packaging of fibers to ensure optimal alignment.