Hollow antiresonant fibres for visible and ultraviolet beam delivery

Lead Research Organisation: University of Bath
Department Name: Physics

Abstract

Hollow core optical fibres guide light in a hollow (usually, gas-filled) core rather than in a solid glass core as in all conventional fibres. The use of a hollow core means that many of the constraints on optical fibre performance which are due to the properties of the core material are lifted (often by many orders of magnitude) and the fibres can by far outperform their more familiar conventional counterparts. There is a problem, however: how can you trap light in a hollow core? Substantial effort has been put into developing so-called photonic bandgap fibres over the last 20 years. These fibres rely on a complex cladding structure to trap light in the hollow core with low losses. They have been developed to a high degree but have been held back by some apparently insurmountable practical problems. These have especially constrained their performance at the short wavelengths which are important in many applications such as high precision laser machining and materials modification. The state-of-the-art laser systems can now deliver the necessary radiation for these applications: however, a truly flexible delivery system does not currently exist. This ability to deliver the pulsed laser light flexibly from the laser system to the point of application is a key advance required to develop practical and commercially viable applications.

Over the last eighteen months, researchers in this collaboration and at a couple of other laboratories across Europe have demonstrated that a much simpler fibre design can actually be far more effective than the bandgap fibres. This is especially true at long wavelengths (in the mid-infrared) and at short wavelengths (eg 1 micron wavelength and below.) Numerical simulations now suggest that these designs can be extended to offer the possibility of their outperforming any existing optical fibres at almost any optical wavelength.

This proposal is to demonstrate these fibres at a range of short wavelengths and to work with four UK-based companies to establish them as useful in manufacturing and clinical environments. This involves making fibres with several designs, verifying their performance, identifying the barriers to their use and overcoming them, and then working in the laboratories of our collaborators to establish them as useful on the factory floor and also in medical and engineering measurements.

Along the way, we aim to demonstrate the lowest-loss optical fibre ever (at a longer wavelength) and to investigate whether these designs can be extended to deliver laser beams with low beam quality.

Planned Impact

This project is designed around impact. That has been possible because work done over the last 12-18 months has reduced some of the key scientific risks in the project to the point where we and our collaborators have high confidence in the relevant fibre performance targets being met. This confidence has enabled us to take the following steps:

1. We have pulled our project partners right inside the research programme, rather than seeing them as eventual beneficiaries of the research. A significant part of the work programme (WP3 and WP4) consists of working directly with our partners, often in their laboratories, to integrate our fibres into their systems. This will enable improved technology transfer compared to other project models, and will focus attention on the "real issues" during the later parts of the work programme.

2. We have requested funding for fabrication and supply of stock fibres by a technician. Our intention is to develop specifications for 4-6 fibres during the first 12-18 months of the programme, and then fabricate long (minimum 1km) lengths of these fibres to be used in the subsequent stages. As well as ensuring that the applications development is not inhibited by a limited fibre supply, this will also enable us to investigate production/tolerance issues in our fabrication processes for these fibre types.

3. These stock fibres will also be made available through our more general industrial outreach programme, in which we will engage with a wider range of (UK-based) companies and businesses.

The impact which we expect this work to have is that we anticipate our fibres being incorporated into product lines, or made available as an option, by UK-based companies who require fibre delivery of intense or high-energy laser light at 1064nm, 532nm and into the ultraviolet. This will make those companies more competitive, enabling them to grow their business and employ more people in the UK.

In order to ensure that our impact plan is delivered effectively we have requested support for dedicated staff (Veronica Ferguson) at Heriot-Watt to coordinate the process. This will be further boosted by links with the EPSRC Centre for Innovative Manufacturing in Laser Based Production Processes (based at Heriot-Watt and led by the Heriot-Watt PI) that acts a national hub for activity and research into technologies well aligned with this programme. This will therefore provide a conduit for knowledge exchange and a natural pathway to impact.
 
Description "Negative curvature" hollow core fibres can be made low loss and single mode by appropriate cladding design.
Bend loss is directly related to similar characteristics and can be controlled to reasonable limits Hollow core fibres can be made with lower loss than any other type of optical fibre at both ultraviolet and mid infrared wavelengths. Mid-infrared fibres can be used to develop new forms of coherent light sources.Fibres will be useful in the field of laser cutting and marking.
Exploitation Route Fibres could be built into future generations of laser cutting and marking tool
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Energy,Healthcare,Manufacturing, including Industrial Biotechology

 
Description Demonstrator experiments at an industrial collaborator's labs have led them to enquire about commercial sources of fibre that could enable them to redesign their products
First Year Of Impact 2019
Sector Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Title Dataset for "Single-mode solarization-free hollow-core fiber for ultraviolet pulse delivery" 
Description The dataset includes all raw data and files to regenerate all figures in the paper, where we report novel anti-resonant silica hollow-core fibers (AR-HCFs) for solarization-free ultraviolet (UV) pulse transmission. We present a single fiber that guides over a part of the UV-C and the whole of the UV-A spectral regions and a second AR-HCF used for delivery of 17 nanosecond laser pulses at 266 nm at 30 kHz repetition rate. By direct comparison we demonstrate that the single-mode AR-HCF significantly outperforms commercially-available high-OH and solarization-resistant silica multimode fibers for pulsed light delivery in this spectral range. MATLAB scripts are also found which filter the straylight background in the raw data measured by UV spectrometer and generate the all attenuation curves in the paper. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
 
Title Dataset for ''Continuous-Wave Mid-Infrared Gas Fiber Lasers'' 
Description The dataset include all necessary data to generate figures 1, 4 (b), 4(c), 5-8 in the associated manuscript, "Continuous-Wave Mid-Infrared Gas Fiber Lasers". These data measure the properties of the lasers under different conditions, including different gas pressures and fiber lengths. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
 
Title Dataset for 'Mid-infrared 1 Watt continuous wave hollow-core fiber gas laser source' 
Description This dataset contains all data and program code underlying the results presented in the paper of 'Mid-infrared 1 Watt continuous wave hollow-core fiber gas laser source'. In the paper, we report the characteristics of a 1 Watt hollow-core fiber gas laser, emitting continuous-wave in the mid-infrared. Our system is based on an acetylene-filled hollow-core optical fiber, guiding with low losses at both the pump and laser wavelengths and operating in the single-pass ASE regime. By systematic characterization of the pump absorption and output power dependence on gas pressure, fiber length and pump intensity, we determine that the reduction of pump absorption at high pump flux and the degradation of gain performance at high gas pressure necessitate the use of increased gain fiber length for efficient lasing at higher powers. Low fiber attenuation is therefore key to efficient high-power laser operation. We demonstrate 1.1 Watt output power at 3.1 µm wavelength by using a high-power EDFA pump in a single-pass configuration, approximately 400 times higher CW output power than in the ring cavity previously reported. In the dataset, 1. Figure_1_original_absorption_intensity_strength_from_HITRAN.csv contains the orignal downloaded data from HITRAN database. MATLAB code is to convert the absorption intensity to the spectral transmittance per meter in fig.1. 2. Figure_2_b_EDFA_spectrum.csv contains the measured EDFA output spectrum at maximum amplification to generate fig.2 (b). 3. Figure_2_c_fiber_attenuation.csv contains the attenuations of fiber used in this paper, to generate fig.2 (c). 4. Figure_3_b_on_off_resonance_absorption_spectra.csv contains the transmission spectra across the whole pump spectrum, when on and off resonance measured by OSA at the end of fiber. The incident power is 40 dBm for both conditions. 5. Figure_3_c_side_scattering_slopes.csv contains the measure on and off absorption spectra, in unit of dB at various fiber length positions. 6. Figure_4_a_incident_power_laser_output.csv contains measured incident powers and output powers for various pressure in 15 m fiber length. 7. Figure_4_b_absorbed_power_laser_output.csv contains measured absorbed powers and output powers for various pressure in 15 m fiber length. 8. Figure_5_slope_efficiency_and_threshold.csv contains all data to generate fig.5 (a) and (b), including measured slope efficiencies, corresponding maximum absorbed pump power and absorbed pump threshold power for 15m and 6 m fiber lengths and various pressures. 9. The program to simulate the 1 meter transmission in acetylene gas of 1 mbar is included in the MATLAB script file theoretic_absorption.m. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Title Low-loss single-mode performance in anti resonant hollow-core fibers 
Description All data for the results of publication 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
 
Description Outreach activities 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact A range of outreach activities including stalls at University Open Days and recruitment days and participation in the annual "Bath Taps into Science" events both on and off campus
Year(s) Of Engagement Activity 2016,2017,2018
 
Description Royal Society Summer Science exhibit 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Exhibit titled "The 100m bubbles" at the Royal Society Summer Science fair. Lead Dr William Wadsworth.
Year(s) Of Engagement Activity 2016