IN THIS SECTION
Integrated Photonic Devices
1. Microstructured Waveguide Surface-Enhanced Raman Sensors
Surface enhanced Raman spectroscopy (SERS) exploits field enhancement at a nanostructured metal surface which allows single molecule detection and identification, through acquisition of a molecular “fingerprint”. The aim of this project is to study these phenomena in depth, and to realise novel integrated sensors exploiting them for a range of important applications such as identifying trace impurities for pollution monitoring, chemical safety systems, and clinical diagnostics. These SERS chips will be based around integrated optical waveguides which exploit the fabrication approaches of microelectronics to realise all-optical planar lightwave circuits. Raman spectroscopy no longer requires expensive lasers and spectrometers and the proposed SERS chips may bring closer the ideal of highly sensitive, highly specific, low-cost, portable sensing systems with no reagents.
We have successfully demonstrated integrated optical surface plasmon resonance (SPR) – based chemical and immunosensors and fluorescence-based immunosensors arrays, with detection limits for organic pollutants below 50ng/l and 1ng/l, respectively. These devices rely upon delicate specifically sensitized films and, usually, tagging of capture molecules, and are prone to cross-reactivity, giving poor selectivity within families of compounds. Integrated optical devices lend themselves to well-controlled “solid-state” evanescent interrogation of surfaces and surface films, and are suitable for mass-production and ready connection to instrumentation by optical fibre. The exploitation of SERS in an integrated optical format offers a generic solution to specific chemical and biochemical sensing without the use of immunochemistry, fluorescent tags, or special reagents. Three main questions arise: (i) how should a waveguide surface be structured to maximize the enhancement of excitation and collection of Raman spectra, (ii) can the study of microstructured waveguide devices shed further light on the physical contributions to the Raman enhancement and (iii) how do SERS and immunosensor chips compare in measurements in real situations. This project aims to resolve these questions and realise a new generation of advanced sensor.
2. Modelocked Ti:Sapphire Waveguide Lasers
Sapphire is an important platform for optoelectronic devices, and this project explores waveguide devices exploiting its unique material properties. This research will result in a new waveguide technology, and active and passive waveguide devices including tuneable and pulsed sapphire chip lasers. The unique features of sapphire such as its high transparency over a wide range of wavelengths and its great chemical resistivity, thermal conductivity and hardness, in combination with high quality micro-patterning methods will allow the development of a new generation of optical components and integrated optical devices. The major advances expected from this work include:
- Improved understanding of diffusion processes in sapphire.
- A new robust passive waveguide technology for application in extreme environments.
- Miniature low-power diode-pumpable sources of CW and pulsed light potentially tuneable between 660nm and 1050nm.
A key attribute of titanium-doped sapphire is its extremely broadband gain, which has resulted in bulk crystal based Ti:sapphire laser systems that emit ultra-short pulses in the 800nm wavelength region and are tuneable from 660nm to 1050nm. These laser sources have opened new frontiers in materials processing, tissue tomography, sensing and spectroscopy. Passive waveguide circuits in sapphire are expected to find widespread use in hostile chemical environments but the incorporation of gain in these circuits will massively enhance the designer’s toolbox and dramatically extend circuit applications. Waveguide Ti:sapphire sources may provide similar performance to that obtained from bulk optical systems while simultaneously offering low cost, compactness, robustness and portability. This will allow the implementation of Ti:sapphire waveguide lasers in portable scientific and analytical instruments, allowing access to enhanced ranges of performance and boosting potential applications.
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