Ceramics production: COld-cOntainer processing for Long-wavelength mid-infrared fibreoptics. (COOL)

We are making new types of optical fibre that transmit, and can emit, long-wavelength mid-infrared light. Why? Mid-infrared light-waves oscillate at frequencies within a range that matches the frequency-range of characteristic vibrations of molecular bonds. The molecular bond vibration increases in amplitude on (resonantly) absorbing mid-infrared light of the same frequency. For the first time, we made a record optical fibre that, on being laser pumped, emitted a record broad range of frequencies of mid-infrared light: 'a mid-infrared rainbow' called a mid-infrared supercontinuum (SC) of light [1]. Shining this broad SC of mid-infrared light onto a molecular sample, and collecting the light again after its interaction with the sample, reveals some mid-infrared frequencies are diminished in brightness, gone to stimulate particular molecular vibrations in the sample. This is called mid-infrared spectroscopy and it allows us to sense and image the molecular makeup of a molecular sample, including numerous molecular gases, liquids and solids as diverse as: greenhouse-gases, explosives, food and biological tissue.

To date, because mid-infrared light sources have been characteristically weak the source/sample/ detector have all had to be in close proximity. The new bright [1,2] mid-infrared fibre SC sources are a disruptive technology which will help establish a new paradigm in PORTABLE, REAL-TIME mid-infrared molecular sensing and imaging, opening up the mid-infrared spectral region for more general use. We are developing this new paradigm through focused development of portable fibre devices and systems which are robust, functionally designed, safe, compact and cost effective, and which are based on mid-infrared optical fibers. Hyper-pure optical fibres are required to increase the efficiency of the SC sources and to realise long-wavelength mid-infrared fibre lasers, and also for passive routeing of mid-infrared light to where it is needed.

Currently, making and purifying the long-wavelength mid-infrared optical fibres is rather intricate and takes about 8 man-weeks. This long-winded processing could be hugely cut, and hyper-purity improved, by applying the innovative processing methods to be developed in this Project.

Currently, resistive heating is used for glass-melting and purification but production times are exceedingly long. We demonstrated for the first time [3] that microwave-assisted heating can achieve high-speed glass-melting. In this Project, we will develop the microwave approach, optimise microwave-cavities and carry out rapid glass melting and follow-on rapid glass hyper-purification via microwave-heating.

Why is the microwave heating so fast? -because the microwaves directly couple to the mid-infrared glass melt and not to the container, which remains cold and uncompromised. Far higher glass-melting temperatures can be attained than normal which: (i) gives faster melt-homogenisation (0.5 h instead of 36 h) and (ii) facilitates high vapour pressures for fast multi-distillations of the glass-melt.

This Project aims to achieve novel cold-container processing to enable the unprecedented rapid manufacture of long-wavelength mid-infrared selenide and telluride chalcogenide glasses of new levels of hyper-purity needed to make new long-wavelength mid-infrared glass fibre-optic devices for disruptive portable, real-time molecular sensing and imaging.

In this Project we will demonstrate, by means of new rapid processing:

i. new hyper-pure fibres for conduiting long-wavelength mid-infrared light;
ii. new hyper-pure long-wavelength mid-infrared SC fibre sources for efficient portable molecular sensing and
iii. first time long-wavelength mid-infrared fibre lasers for pumping the fibre SC.


REFERENCES
1. Petersen, Tang, Benson, Seddon et al., NAT. PHOTON. 8 830(2014).
2. Yu et al., Opt. Lett., 40(6)1081(2015).
3. Prasad, Seddon et al., J. Non-Cryst. Solids, 356(41-42) 2134(2010).

IMPACT SUMMARY

1. INTRODUCTION

This Project will help to make a new generation of portable long-wavelength mid-infrared fibre-optic devices for molecular sensing and imaging. The technological impact of these new devices will be game-changing through diverse applications across many UK sectors such as healthcare, energy, security and manufacturing.

This Project aims to achieve novel cold-container processing to enable the unprecedented rapid manufacture of long-wavelength mid-infrared selenide and telluride glasses of new levels of hyper-purity. These are needed to make the new mid-infrared glass fibre-optic devices for the new disruptive paradigm of portable, real-time molecular sensing and imaging.

This Project will assist in "greener" materials' manufacture; the energy demands of the cold-container processing will be lower than the conventional processing it replaces.

The impact in UK science/engineering will be in aspects of generating new UK business and of trained people.

2. TECHNOLOGY IMPACT OF PORTABLE, REAL-TIME MID-INFRARED FIBRE-OPTIC SENSING AND IMAGING DEVICES ON UK SECTORS AND UK BUSINESS

Long-wavelength mid-infrared fibre supercontinuum sources and fibre lasers are disruptive technologies for real-time molecular sensing and imaging in: monitoring environmental quality (sensing pollutants e.g. exhaust gases from industrial plant, cars); energy-efficiency of fossil fuels (CO/CO2 balance); food security (authenticity/adulteration) and drink security (e.g. beer quality!); in agriculture (e.g. sensing ethylene gas in tomato ripening; monitoring leaf-hydration in farming); aquaculture (fish-farming: e.g. sensing bacterial contamination); real-time monitoring of manufacturing and chemical processing (e.g. distributed fibre-optic mid-infrared sensing enabling process control), including of oil fractionates/products; manufacturing pharmaceuticals and cosmetics and for medical diagnostics such as early skin cancer diagnosis through objective spectroscopic imaging of tissue in a primary-care setting.

Security and safety applications of mid-infrared fibre lasers include: mid-infrared ship-to-ship free-space communications, aircraft free-space counter-measures and collision-avoidance. Stand-off explosives' and narcotics' mid-infrared sensing, for instance at airports, will lead to better public safety.

New mid-infrared fibre lasers will exhibit better beam quality than currently available which will enable well-controlled laser cutting, machining and patterning of soft materials, like polymers and polymer-composites by analogy with currently emerging high-power near-infrared fibre lasers being exploited for laser cutting/welding of hard materials, like metals.

In the medical field, new wavelengths for laser surgery of human tissue will lead to more diverse and better matter/light interaction through resonance with protein/lipid absorption at newly available mid-infrared long-wavelengths, for better health outcomes.

Overall, portable long-wavelength mid-infrared fibre-based molecular sensing will allow greater control to be had in real-time, over many types of processes and procedures as well as being a new manufacturing tool. At a national level, National Health Service costs will be beneficially impacted, as well as patient comfort and convenience. There will be beneficial impact to UK industry, the UK energy sector, UK defence and security, UK agriculture and UK healthcare from this new technology.

3. IMPACT THROUGH PEOPLE TRAINING

During this Project, the Researcher will be equipped with skills in developing new manufacturing routes and trained in mid-infrared photonics. The future employment prospects are excellent in the 'people pipeline' in this new field. This includes the large PhD groups and undergraduate pools, of the Investigators, who will benefit directly by interacting with this major Project in new types of processing and in mid-infrared photonics.