Fibre Bragg Gratings

1. Bragg grating design, device fabrication and tunable Bragg grating technologies

Fibre gratings provided a powerful and flexible means to produce in-fibre mirrors with ultra-high reflectivity and with accurately controlled amplitude and phase characteristics. The ORC has long been a world leader in this area of technology and which is used in many of our application programs within the ORC- including projects within the telecommunications, sensors, short pulse and fibre laser areas.

This project concerns the development of new techniques with which to improve both the quality and functionality of grating based devices with an emphasis on improved tunability, increased grating complexity and active devices based on gratings in rare earth doped fibres. The combination of gratings and both holey fibres and tapered fibre devices is also to be considered. This project is likely to involve significant interactions between the gratings group and the various application groups around the ORC.

2. Design and applications of low-noise, high-power, single-frequency Bragg grating all-fibre lasers for new wavelength regimes

 Single frequency fibre lasers have attracted much attention for a number of reasons. They can provide almost ideal output performance when efficiency, stability, noise-characteristics, mode-purity, and tunability are considered. So far a number of single-frequency fibre laser configurations have been demonstrated, but one design that stands out when seeking the above mentioned parameters is the distributed feedback (DFB) fibre-grating laser. From this, wavelength operation ranging from 980nm over 1200nm to 1550nm and 1836nm depending on the chosen host and gain-material have been demonstrated with powers in the 1-100mW range. This level can without much degradation to the key performance parameters be increased significantly by employing external amplification of the source-output. For some applications, for example LIDAR, operation outside the band most conventionally used by silica fibre transmission is of interest, covering regions on both the short wavelength and long wavelength side of this band.

This project will concentrate on the development of low-noise single-frequency Bragg grating based sources for operation outside the traditional wavelength bands discussed above using new host and gain materials. The work will include design, modelling, fabrication and characterisation of the sources and tailoring of the output performance of these to meet set specifications and will involve significant interactions with other applications and laser groups within the ORC.

3. Femtosecond-writing of periodic structures in new materials (in collaboration with the Physical Optics Group)

This project will concentrate on exploring the possibilities of using femto-second (fs) (<200fs) light to alter the optical properties of glass waveguides and to make new all-optical components within these. The promise of fs technology is immense, and much is still largely unexplored. Refractive index-changes can be introduced in glasses and materials using fs-light without the need for sensitisation with for example germanium and hydrogen, which traditionally are used to aid photosensitivity. This possibility of altering the optical characteristics of fibres and waveguides, simply through exposure to high-energy light, opens up for a whole host of new opportunities for components (e.g. enhanced temperature-stability of these). After initial characterisation of the effects of the high-energy pulses on the waveguide properties (e.g. loss, index-change, temperature-stability and non-linearity), the work will focus on demonstrating new fibre device concepts and on using these devices in systems and system-configurations such as for example all-optical frequency-conversion, frequency-modulation and fibre lasers.

4. Optical Coherence Tomography (OCT) and biomedical imaging

New and exiting opportunities and possibilities are emerging in the areas of in-vivo and in-situ imaging such as Optical Coherence Tomography (OCT) and Optical Doppler Tomography (ODT) to achieve high-resolution tomographic images of static and moving constituents simultaneously in highly scattering media. These new imaging techniques are now being used to monitor for example blood flow and tissue compositions and are currently being considered for use in for example in-situ therapeutic applications.

This work will focus on development of new techniques and methods to achieve simple and high-resolution imaging using our vast range of in-house technologies such as specialty high-bandwidth light-sources, tunable laser-sources and specialty fibres. The work will concentrate on the device aspects of the setup, but will also involve use of the designed apparatus in real world applications and will be closely associated with certain aspects of the project on Bragg gratings for use in medical applications.

5. Bragg gratings for use in medical applications

This project will focus on exploring applications of Bragg gratings in medical imaging and medicine. Bragg gratings are finding more and more applications in medicine because of their inherent fibre compatibility and small size. Small size implies that they may be inserted into for example blood vessels and tumours to monitor temperature, flow and pressure.

The work in this project will include Bragg grating design, fabrication and testing in-house at the ORC. Characterisation of the fabricated devices and testing of these, though collaborative work will be carried out with our partners at University hospitals within the UK. Certain aspects of this project will be closely involved with the imaging project also offered within the Bragg gratings group. This project therefore represents a very good opportunity to get involved and make significant contributions to an aspect of fibre-optics that is still very much in its infancy but has a massive potential for commercial recognition and success.

Click here for a full list of PhD projects available at the ORC