Stack, seal, evacuate, draw: A method for drawing hollow-core fiber stacks under positive and negative pressure

Raw images showing the stacks, canes and fibres that were manufactured using the novel fabrication techniques discussed in "Stack, seal, evacuate, draw: A method for drawing hollow-core fiber stacks under positive and negative pressure" Excel file containing measurements of the geometry of the IR fibre discussed in the paper.Images: SEM microscopy, optical microscopy, photography. Measurements of fibre geometry: measurements made using ImageJ software on SEM images of the fibre.Images are in TIFF or JPEG format. Optical microscopy performed using a Nikon eclipse ME600 microscope and captured/saved using IC measure 2.0.0.286 image software

Incoherent light in tapered graded-index fibre: a study of transmission and modal noise

© 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license, http://creativecommons.org/licenses/by/4.0/We investigated the impact of taper length on light transmission through tapered graded-index fibres. We tested commercial fibres from Thorlabs and a custom graded-index fibre using both coherent and incoherent light sources. Our experimental results show optimum performance for taper transition lengths of 25 mm, although our simulations suggest further improvement may be possible for even shorter transition lengths. We also measured the modal noise power fluctuations caused by bending the fibre. Here, we observe that the custom fibre tapers have the highest transmission but suffer from the most modal noise. Accordingly, we find that the commercial graded-index fibre tapers promise practical usage as a beam mode-field converter, as they have lower power fluctuations but retain relatively high transmission if compared to commercial small core step-index fibre.Peer reviewe

All-fibre wavefront sensor

We report on a tapered three-core optical fibre that can be used as a tip-tilt wavefront sensor. In this device, a coupled region of a few millimetres at the sensing tip of the fibre converts fragile phase information from an incoming wavefront into robust intensity information within each of the cores. The intensity information can be easily converted to linear wavefront error over small ranges, making it ideal for closed loop systems. The sensor uses minimal information to infer tip-tilt and is compatible with remote detector arrays. We explore its application within adaptive optics and present a validation case to show its applicability to astronomy.Comment: 7 pages, 6 figure

Birefringent Anti-Resonant Hollow-Core Fiber

Hollow-core fibers have demonstrated record performance in applications such as high-power pulse delivery, quantum computing, and sensing. However, their routine use is yet to become reality. A major obstacle is the ability to maintain the polarization state of light over a broad range of wavelengths, while also ensuring single-mode guidance and attenuation that is low enough for practical applications that require only a few meters of fiber length (&lt;1 dB/m). Here we simulated, fabricated, and characterized a single-mode birefringent anti-resonant hollow-core fiber. The birefringence was achieved by introducing capillary tubes of different thicknesses, thereby creating reduced symmetry in the structure. The measured group birefringence is in good agreement with the calculated group birefringence from simulations across the fiber guidance band within the telecommunications C-band. At 1550 nm, we measured a group birefringence of 4.4 × 10-5, which corresponds to a phase birefringence of 2.5 × 10-5. The measured loss of the fiber was 0.46 dB/m at 1550 nm. The measured polarization extinction ratio of the fiber at 1550 nm was 23.1 dB (25.7 dB) along the x-(y-) polarization axis, relating to an h-parameter of 9.8 × 10-4 (5.3 × 10-4).</p

Transmission properties of tapered optical fibres: Simulations and experimental measurements

© 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. https://creativecommons.org/licenses/by-nc-nd/4.0/We measured the transmission of tapered and untapered optical fibres as a function of input beam numerical aperture at 635 nm. The tapered fibres were fabricated with an adiabatic tapering process from graded and step-index fibres with 50 m core diameters to form a 100 mm long taper with 5:1 taper ratio. We tested tapered graded-index and step-index fibres fabricated from commercial Thorlabs products and a custom graded-index taper. The 5:1 tapered graded-index fibre can give a transmission greater than 0.4 for Thorlabs and 0.6 for the custom taper. We simulated the transmission of the tapered fibres and found reasonable agreement with the measured graded-index tapered fibre results across the numerical aperture range of interest. Experimentally, step-index tapered fibres performed relative poorly and considerably below modelling expectations. Based on our examinations this arises because the properties of step-index fibre were not robust to the tapering process. Suitably tapered graded-index fibres may offer a new route for efficient focal ratio reduction of fibre optic signals, e.g., in fibre-fed spectrographs, though we stress that our measurements have been limited to monochromatic light in this work.Peer reviewe

Mitigating Modal Noise in Multimode Circular Fibres by Optical Agitation using a Galvanometer

© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Modal noise appears due to the non-uniform and unstable distribution of light intensity among the finite number of modes in multimode fibres. It is an important limiting factor in measuring radial velocity precisely by fibre-fed high-resolution spectrographs. The problem can become particularly severe as the fibre's core become smaller and the number of modes that can propagate reduces. Thus, mitigating modal noise in relatively small core fibres still remains a challenge. We present here a novel technique to suppress modal noise. Two movable mirrors in the form of a galvanometer reimage the mode-pattern of an input fibre to an output fibre. The mixing of modes coupled to the output fibre can be controlled by the movement of mirrors applying two sinusoidal signals through a voltage generator. We test the technique for four multimode circular fibres: 10 and 50 micron step-index, 50 micron graded-index, and a combination of 50 micron graded-index and 5:1 tapered fibres (GI50t). We present the results of mode suppression both in terms of the direct image of the output fibre and spectrum of white light obtained with the high-resolution spectrograph. We found that the galvanometer mitigated modal noise in all the tested fibres, but was most useful for smaller core fibres. However, there is a trade-off between the modal noise reduction and light-loss. The GI50t provides the best result with about 60% mitigation of modal noise at a cost of about 5% output light-loss. Our solution is easy to use and can be implemented in fibre-fed spectrographs.Peer reviewe