Fibre Bragg Gratings

World leaders in fibre bragg technology, the groups research includes the design of Bragg gratings, demonstration of passive and active Bragg grating devices, single-frequency fibre lasers (DBR and DFB) and applications of these high-power laser configurations and telecommunication-systems.

The group has demonstrated broad range tuning of the wavelength of light generated through nonlinear optical processes in silica fibres - a world first in 2007.

The technology developed by the group has been used in many of the ORC’s projects within the telecommunications, sensors, short pulse and fibre laser areas.

 

Fibre Bragg Gratings Projects:

Supervisor: Dr Morten Ibsen

Bragg grating design, device fabrication and
tunable Bragg grating technologies

Fibre gratings provide powerful and flexible means of producing in-fibre mirrors with very specific reflectivity and accurately controlled amplitude and phase characteristics. The ORC has long been a world leader in this area and the technology is now being used in many of our application programs, including projects within the telecommunications, sensing, and fibre laser areas.

This project concerns the development of enhanced functionality of grating-based fibre devices with a specific emphasis on improving wavelength tunability, increasing phase and amplitude complexity, and providing ultra-fast performance. The combination of fibre gratings with photonic-crystal fibres and tapered fibre devices coated with carbon nanotubes (CNTs) and Graphene will also be investigated within the scope of this project, to exploit the exciting properties offered by these materials including their optical transparency, high nonlinearity and saturable absorption characteristics. This project involves substantial interactions between the Gratings Group and a number of the other application focused groups within the ORC.

 

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 provide almost ideal output performance in terms of efficiency, wavelength-stability, phase- and intensity-noise characteristics, mode-purity, and tunability. So far a number of single-frequency fibre laser configurations have been demonstrated, but one design that stands out for its low noise and frequency stability performance, is the distributed-feedback (DFB) fibre-grating laser.

This project will concentrate on developing efficient, low-noise single-frequency Bragg grating based fibre sources for operation in the 1150-1500nm and 1650-1750nm bands, using new host and gain materials. The work will include design, modelling, fabrication and characterisation of the sources, and tailoring of the output performance to meet set target specifications in gas sensing, medical application, and telecommunications. The project involves significant interactions with other groups within the ORC.

 

Femtosecond-writing of periodic structures
in optical fibres

The promise of femto-second technology for writing periodic index structures in non-silica materials is immense, and many areas are still largely unexplored. Refractive index-changes can be created in most glasses using fs-light (<400fs) without the need for germanium and hydrogen, which traditionally is being used to aid UV photosensitivity. This project will concentrate on exploring the possibilities of utilising fs-light to alter the optical properties of waveguides, and to make new functional all-optical components within fibres that are not nominally photosensitive to UV-light. The possibility of altering the optical characteristics of fibres and waveguides with fs-light also opens up a range of new opportunities for components in for example soft-glasses including phosphate, lead-silicate, chalcogenide and telluride. The work will focus on demonstrating new passive and active fibre devices and device concepts in these materials, and on testing them in optical systems.

 

Optical Coherence Tomography (OCT)
and biomedical imaging

New exciting 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 simultaneously achieve high-resolution tomographic images of static and moving constituents in highly scattering media. These new imaging techniques are now being used extensively in medicine to monitor for example blood flow and tissue compositions, and are currently being considered for use in for example in-situ therapeutic applications.

This project will focus on the development of new techniques and methods to achieve high data throughput and high resolution imaging. The work will concentrate on device aspects of OCT system technology, and will be making use of the extensive ORC fibre expertise. The project will be associated with certain aspects of the project on Bragg gratings for use in medical applications also offered within the Gratings Group. Some fibre development work will likely be required to facilitate wide bandwidth and rapidly tunable laser-sources, and therefore this project is a joint project between the Bragg Gratings group and the Silica Fibre group at the ORC. The project is mainly of an experimental nature, but will require some modelling of the designed sources as well. Good knowledge and strong interest in fibre optics and electronics would benefit the candidate.

 

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 tissue 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 through collaborative work will be carried out with our colleagues and partners at other UK universities. Certain aspects of the project will be closely involved with the OCT and biomedical imaging project also offered within the Bragg gratings group. This project represents a very good opportunity to be involved and make significant contributions to an aspect of fibre-optics that is still very much in its infancy.

 

Photonic fibre devices based on carbon
nanotubes (CNTs) and Graphene

Carbon nanotubes (CNTs) and Graphene have shown tremendous promise not only in electronics but also in photonics. These materials exhibit properties such as for example optical transparency that can be precisely controlled by managing the diameter and number of layers respectively. In this way it is possible to cover a broad range of wavelengths of interest in for example telecommunications, medicine and military applications. CNTs and Graphene have in the recent past not least been demonstrated as excellent saturable absorbers for applications in mode-locked fibre lasers, but their large nonlinear and exceptional thermal properties also lends them self well to many other potentially rewarding device-applications in photonics.

This project will investigate these opportunities and will include design, fabrication, characterisation, and testing of the designed devices in optical systems. Parts of the project will be involved with the Bragg grating design, device fabrication and tunable Bragg grating technologies project also offered within the Gratings Group.

 

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