Application of atmospheric OH suppression technology to ground-based infrared astronomy

We seek to advance the capabilities of photonic technologies in support of ground-based infrared astronomy. Currently, observers in this field suffer from an irreducible background generated by emission from OH (hydroxyl) molecules in the upper atmosphere. However, if narrow-band notch filters could be incorporated into the optical path of astronomical instruments prior to any optical elements that would spectrally broaden such emission lines, then this background could be effectively suppressed 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. Theoretical estimates show that suppression (by 20-40dB) of the most prominent OH lines improves the signal to noise of near-IR observations by a factor of 5 or more - this is similar in effect to turning a telescope with a 1m aperture into a telescope with a 5m aperture!