Inverse design and optimization of an aperiodic multi-notch fiber Bragg grating using neural networks.

Recent developments in the application of aperiodic fiber Bragg gratings (AFBGs) in astrophotonics, such as AFBG for astronomical near-infrared OH suppression and gas detection based on cross-correlation spectroscopy, have illuminated the problem that the optimization for AFBG with certain fabrication constraints has not been fully investigated and solved. Previous solutions will either sacrifice part of the spectral features or consume a significant amount of computation resources and time. Inspired by recently successful applications of artificial neural networks (ANNs) in photonics inverse design, we develop an AFBG optimization approach employing ANNs in conjunction with genetic algorithms (GAs) for the first time, to the best of our knowledge.

Photonic comb: a stabilized single-mode fiber etalon for wavelength calibration.

We present a low-cost alternative to more complex laser metrology systems that uses a single-mode fiber Fabry-Perot etalon to generate an emission spectrum of evenly spaced lines with similar intensities, ideal for calibrating spectrographs (both in terms of wavelength and image quality). The system uses the hyperfine transition lines of near 780.24 nm as an absolute reference.

A new gas detection technique through cross-correlation with a complex aperiodic FBG.

Optical cross-correlation is a technique that can achieve both high specificity and high sensitivity when deployed as the basis for a sensing technology. Offering significant gains in cost, size and complexity, it can also deliver significantly higher signal-to-noise ratios than traditional approaches such as absorption methodologies. In this paper, we present an optical cross-correlation technology constructed around a bespoke customised Fiber Bragg Grating (FBG).

Optimal broadband starlight injection into a single-mode fibre with integrated photonic wavefront sensing.

In astronomy and related fields there is a pressing need to efficiently inject light, transmitted through the atmosphere, into a single-mode fibre. However this is extremely difficult due to the large, rapidly changing aberrations imprinted on the light by the turbulent atmosphere. An adaptive optics system must be used, but its effectiveness is limited by non-common-path aberrations and insensitivity to certain crucial modes.

Seeking celestial positronium with an OH-suppressed diffraction-limited spectrograph.

Celestially, positronium (Ps) has been observed only through gamma-ray emission produced by its annihilation. However, in its triplet state, a Ps atom has a mean lifetime long enough for electronic transitions to occur between quantum states. This produces a recombination spectrum observable in principle at near IR wavelengths, where angular resolution greatly exceeding that of the gamma-ray observations is possible.