New approach to atmospheric OH suppression using an aperiodic fibre Bragg grating

At near infrared wavelengths, the night sky background seen from the Earth’s surface is almost completely dominated by bright spectral lines due to hydroxyl in the upper atmosphere. In the wavelength range 1–2µm, more than 100 intrinsically narrow spectral lines account for about 98% of the sky background. Now that the performance of infrared detectors is comparable to CCDs at optical wavelengths, the bright infrared sky is the last remaining hurdle to ground-based infrared telescopes reaching sensitivity levels associated with optical telescopes. We demonstrate an aperiodic fibre Bragg grating (AFBG) which performs 94% suppression of OH emission in the 1.50-1.57µm window at a resolving power of R=10,000. This is a working prototype for a device which will allow comparable levels of OH suppression at R=50,000 across the entire near infrared (1.0–2.0µm) spectrum.