Astrophotonic Techniques for OH Emission Suppression
Summary
Ground-based infrared astronomy is fundamentally constrained by the bright and variable emission of hydroxyl (OH) molecules in the upper atmosphere. Astrophotonic techniques apply micro- and nano-fabricated optical devices to selectively filter or suppress these narrow spectral lines, thereby reducing sky background and enhancing sensitivity. Key approaches include aperiodic fibre Bragg gratings, which inscribe complex multi-notch reflection spectra directly in single-mode fibres; photonic ring resonators, which exploit high-Q resonances in chip-scale waveguides to notch out OH lines; and complex phase masks that enable precise inscription of multi-wavelength filters with high reproducibility. These devices can be integrated with conventional spectrographs via fibre-chip coupling or grafted onto existing fibre feeds, offering minimal footprint and thermal stability. Collectively, astrophotonic filters have demonstrated up to 94 per cent suppression of OH emission in targeted near-infrared windows and promise scalable solutions for extremely large telescopes. By lowering the infrared background, these technologies unlock deeper spectroscopic surveys of distant galaxies, exoplanet atmospheres and faint stellar populations.
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Astrophotonic Techniques for OH Emission Suppression publication trend
The graph below shows the total number of articles in astrophotonic techniques for oh emission suppression across all publications each year (not limited to Nature Index journals).
Technical terms
OH emission: Bright, narrowband spectral lines produced by hydroxyl molecules in the mesosphere, dominating ground-based near-infrared sky brightness.
Aperiodic fibre Bragg grating: A fibre-optic device with non-uniform refractive index modulation that reflects multiple, irregularly spaced wavelengths corresponding to atmospheric OH lines.
Ring resonator: A micro-scale waveguide loop that supports whispering-gallery modes, creating narrow spectral notches when critically coupled to an optical bus waveguide.
Complex phase mask: A patterned optical mask with discrete phase steps used to inscribe multi-notch Bragg gratings in fibre via a single-exposure lithographic process.
Notch filter: An optical component designed to attenuate specific, narrow wavelength bands while transmitting adjacent spectral regions with minimal loss.
References
- New approach to atmospheric OH suppression using an aperiodic fibre Bragg grating. Optics Express (2004).
- Photonic ring resonator filters for astronomical OH suppression.. Optics Express (2017).
- Complex phase masks for OH suppression filters in astronomy: part I: design.. Optics Express (2020).
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