High-Power Tunable GaAs Distributed Feedback Lasers

Photonics is a key enabling technology with far reaching applications. In this project we will realise a new generation of enhanced-functionality GaAs-based lasers for the 300 to 1300nm wavelength range. These devices, based on a new monolithic integration scheme, will impact upon existing applications in display, printing, absorption spectroscopy and telecoms, whilst enabling new applications in astrophotonics, sensing, biomedical imaging, photodynamic therapy, fluorescence spectroscopy, cosmetic and clinical surgery procedures, process control, agriculture, defence and security. Monolithic integration on GaAs has previously been impeded due to the requirement for overgrowth upon aluminium containing layers. We will capitalise on approaches demonstrated in the investigator's previous EPSRC feasibility study into advanced discrete GaAs components to investigate the potential for true monolithic integration. We will realise a distributed feedback (DFB) laser monolithically integrated with a power amplifier within a continuous buried waveguide. As an extra proof of flexibility, there will be a heater element adjacent to the DFB for both wavelength stabilisation and tuning. This disruptive new technology will enable low cost, highly efficient, high power, wavelength agile lasers, in the range from 600 to 1300nm. Additionally, inherent high power and spectral purity are favourable for frequency doubling to extend the range down to 300nm.
Specific objectives of this project will be a proof of concept demonstration of these integrated devices, backed up with reliability statistics at 760nm (based on quantum wells) and 1180nm (based on quantum dots), i.e. covering the short and long wavelength regions readily available in this technology.

Economical impacts are expected through IP creation and/or spin-out creation, incoming overseas contracts and knowledge transfer to British industry. High-power tunable lasers are expected to yield rapid impact in a range of markets, where new functionality and improved performance are anticipated, as well as size and cost reductions. Outputs from the research will feed directly into UK industry through systems integrators (e.g. spectroscopy systems) and enable basic research (e.g. bespoke devices for life sciences).
Measurement of spectral lines through laser spectroscopy determines energy levels in atomic/molecular systems, underpinning much of our scientific knowledge. Absorption and/or fluorescence spectroscopy are used in quality assurance, surface analysis, analysis of foodstuffs, pharmaceuticals, combustion products, astronomical spectroscopy, breath analysis, environmental sensing and agriculture. Spectroscopy of haemoglobin content and oxygenation in tissue is used to control photodynamic treatments of internal malignancies. Our technology will allow low cost, high power, tunable portable systems with the ability to probe short-lived reactions.
THz radiation has high chemical selectivity allowing identification of hidden objects, detection of trace gases having strong absorption lines in THz (particularly explosives and narcotics), quality control in pharmaceuticals, and analysis of packaged foodstuffs. An increasingly popular route to THz generation is via photomixing, where two wavelengths excite a photoconductor and produce current at their THz beat frequency. The proliferation of such sources is pending development of a suitable lasers such as those proposed here.
There is a drive for mobile phones, laptop computers, head-up and -mount displays to incorporate a projector to view large size images. Red and blue can be covered by existing laser diode technology, but a "green gap" exists in the diode laser spectrum. Photonics Spectra magazine forecast a green laser market of $500M by 2016. Frequency doubled 1180nm lasers can be used as portable sodium beacons (artificial stars), created by energizing a layer of sodium atoms that occur naturally at high altitude with a 589nm laser. The re-emitted laser light produces a glowing artificial star which is used for adaptive imaging. Fixed wavelength DFB lasers are presently supplied by two overseas companies: NanoPlus and Eagleyard. Low yield and costly production techniques result in very high (~£10k) cost per device. Our monolithically integrated solution would allow efficient, stable, high power portable devices to be sold for a fraction of this price, ensuring a competitive product and enabling wealth generation for the UK economy. Monolithic integration greatly reduces the number of optical packages and multiple costs incurred through component burn-in, assembly and cumulative loss at each fibre coupling.
Companies accessing a new integration platform capable of more complex integrations and cost efficiencies from a move to GaAs will increase their competitiveness, as will those companies in the potential supply chain, ensuring a swift response to present and emerging technological opportunities. Impacts are also anticipated for companies using products originating directly from this research and those companies integrating our designs into their systems for low cost and new functionality. Furthermore, spin-off impacts are possible in the cosmetic industry through hair and tattoo removal, as well as dermatology, with applications favoured at these GaAs accessible wavelengths.
Medium to longer term impacts are expected as 600 - 1500nm OEICs are enabled through development of a GaAs monolithic OEIC platform, enabling cost-down performance-up impacts in optical comms, where GaAs represents a feasible 6inch technology using readily available foundry facilities and an efficient material platform that could further integrate with high speed GaAs electronic ICs.