# Aperiodic phase masks for inscribing complex multi-notch OH-emission filters for astronomy

## TL;DR

This paper introduces a novel aperiodic phase mask (APM) technique for creating complex fiber Bragg gratings that can suppress multiple OH emission lines in the near-infrared, enhancing astronomical observations.

## Contribution

The paper presents the first implementation of an aperiodic phase mask for fabricating multi-channel aperiodic fiber Bragg gratings with complex filtering capabilities.

## Key findings

- Successfully fabricated multi-notch filters for OH emission suppression.
- Enhanced ground-based telescope sensitivity in the near-infrared.
- Demonstrated compatibility with standard phase mask fabrication setups.

## Abstract

We demonstrate for the first time, a new type of aperiodic phase mask (APM) for fabricating multi-channel aperiodic fiber Bragg gratings. The mask is made of individual diffraction phase gratings with discrete unequal phase-steps incorporated at periodic locations. The diffraction at the discrete phase-steps in the phase mask produces corresponding half phase-steps at periodic locations along the fiber. The accumulated phase, along with index modulation, generates the desired multinotch reflection spectrum. Complex fiber Bragg grating filters fabricated using APM, in a standard phase mask based fabrication setup, can be used to simultaneously suppress multiple aperiodic OH emission wavelengths in near infrared (NIR) existing in upper atmosphere, and increase the sensitivity of ground based telescopes.