Speciality optical fibres for astronomy

Abstract

Astrophotonics is a rapidly developing area of research which applies photonic technology to astronomical instrumentation. Such technology has the capability of significantly improving the sensitivity, calibration and stability of astronomical instruments, or indeed providing novel capabilities which are not possible using classical optics. We review the development and application of speciality fibres for astronomy, including multi-mode to single-mode converters, notch filters and frequency combs.In particular we focus on our development of instruments designed to filter atmospheric emission lines to enable much deeper spectroscopic observations in the near-infrared. These instruments employ two novel photonic technologies. First, we have developed complex aperiodic fibre Bragg gratings which filter over 100 irregularly spaced wavelengths in a single device, covering a bandwidth of over 200 nm. However, astronomical instruments require highly multi-mode fibres to enable sufficient coupling into the fibre, since atmospheric turbulence heavily distorts the wavefront. But photonic technologies such as fibre Bragg gratings, require single mode fibres. This problem is solved by the photonic lantern, which enables efficient coupling from a multi-mode fibre to an array of single-mode fibres and vice versa.We present the results of laboratory tests of these technologies and of on-sky experiments made using the first instruments to deploy these technologies on a telescope. These tests show that the fibre Bragg gratings suppress the night sky background by a factor of 9. Current instruments are limited by thermal and detector emission. Planned instruments should improved the background suppression even further, by optimising the design of the spectrograph for the properties of the photonic components.Finally we review ongoing research in astrophotonics, including multi-moded multicore fibre Bragg gratings, which enable multiple gratings to be written into the same device simultaneously, femtosecond direct-write photonic lanterns and Bragg gratings, and complex notch filters and frequency combs using microring resonators, and plans for future astrophotonic instrumentation.

Astrophotonic solutions for spectral cross-correlation techniques

“…Fibre Bragg gratings (FBGs) have been a well-established photonic solution for OH skyglow removal in the near-infrared. 7 This involves the creation of custom FBGs that target specific airglow lines that suppress them to improve the sensitivity of low resolution near-infrared spectroscopy. Recent work has also shown similar Bragg gratings can be made in silicon photonics.…”

“…Astrophotonic devices offer new approaches to transitional astronomical instrumentation. These include miniature spectrometers, 5,6 customizable notch filters, 7,8 multi-mode to single mode converters 9 (photonic lanterns). Due to the scale of these astrophotonic instruments, they are much more compact and cheaper than one-of-a-kind traditional instruments that use bulk optics.…”

Predicting and Discovering True Muonium (μ+μ−)

“…In the past, many production channels have been discussed: πp → (µ + µ − )n [35], γZ → (µ + µ − )Z [35], eZ → e(µ + µ − )Z [36,37], µ + µ − → (µ + µ − ) [16], e + e − → (µ + µ − ) [29,38,39], e + e − → (µ + µ − )γ [29], η → (µ + µ − )γ [40,41], [43], and q + q − → (µ + µ − )g in a quark plasma [44]. Some of the more novel methods of utilizing these production channels considered include: fixed target experiments [45], Fool's Intersection Storage Rings [29], and even from astrophysical sources [46,47].…”