Postgraduate research projects

1. Pulsed high power fibre lasers and amplifiers (in conjunction with Dr Andy Malinowski)

Fibre laser technology offers tremendous prospects for the development of compact, robust pulse sources capable of operating over an enormous range of pulse parameters spanning from the nanosecond down to the femtosecond regime. This project concerns the development of high power pulsed laser and amplifier systems based on diode–pumped, dual-clad rare-earth doped optical fibres. Semiconductor seed lasers with pulse durations ranging from nanosecond to picosecond will be used. We will also investigate application of the amplifier technology developed within this project to amplification of our femtosecond fibre lasers. This project aims to develop techniques to power scale the output from pulsed fibre laser systems to several hundred watts of average power, and to investigate means to convert the output wavelength to anywhere from the UV out to the far IR using fibre and/or crystal nonlinearities. The project will involve the development of new fibre types, the development of new short pulse oscillator and amplifier configurations and concepts and the extension of nonlinear frequency techniques to ultrahigh average power levels. Applications of the technology are also to be explored and elements of the work are likely to be performed in conjunction with industrial partners.

2. Nonlinear optics in multimode fibres: Modelling (in conjunction with Dr Peter Horak)

The propagation of laser pulses in optical fibres can lead to some interesting and useful phenomena. In recent experiments, we have observed some unusual and exciting effects in multi-mode holey fibres, such as the generation of white light from a green laser source. This is a largely unexplored area with potential applications from medical imaging by optical coherence tomography to high-power illumination. We are looking for a student with a strong interest in modelling of optics phenomena to investigate these nonlinear effects. The work will be mainly theoretical/numerical, but will be performed in close interaction with ongoing experiments. Potential project goals are:

• Investigation of nonlinear effects in multi-mode holey fibres
• Supercontinuum generation in multimode standard optical fibres
• Optimisation of fibre design for the generation of specific light spectra.

3. Nonlinear optics in multimode fibres: Experiments (in conjunction with Drs Andy Malinowski/Jonathan Price)

A wide variety of nonlinear optical effects have been observed in optical fibres including the Kerr, Raman and Brillouin effects. To date the majority of nonlinear fibre optics research has focused on the manifestation and use of nonlinear effects in single mode fibres. This has been due largely to the fact that this reduces the complexity of the nonlinear interactions making them more readily usable for applications, and partly to the fact that this reduces the power requirements. However, the output powers achievable using fibre technology have increased to the kW level for continuous wave lasers and to the 10MW level for pulsed systems. These power levels open up the possibility of generating and using nonlinear effects in multi-mode fibres.

In this exciting new project we propose to investigate the nonlinear optics of MM fibre focusing in particular on:

• Pulse propagation in highly MM fibres using self-focusing and soliton propagation to balance the effects of diffraction and dispersion in space and time respectively in order to preserve spatial/temporal signal quality. 
• Maintaining mode quality in high power MM fibre lasers and amplifiers 
• Frequency conversion
• Optical switching

The project will require a mixture of both experimental and theoretical work and will involve collaboration with research teams working on waveguide theory, high power lasers, optical communication systems and fibre fabrication.

4. Optical processing and transmission in future optical networks (in conjunction with Dr Periklis Petropoulos)

Future, high capacity (multi-Terabit) optical networks will require as much of the data generation, routing and control to be performed in the optical domain - moving electrons around in electronic circuits is simply too slow. This project will focus on exploring new concepts in optical switching and processing and applying these to increasing optical network functionality and capacity. The project builds upon existing in-house research programs. Specific topics of research will concern optical regeneration of signals, optical header recognition and routing and bit-rate transmission and signal monitoring.

5. Optical code division multiple access network technology (in conjunction with Dr Periklis Petropoulos)

Code division multiple access is a spread spectrum communications technique that has been applied with a great deal of success to the mobile communication industry. CDMA allows many separate users of a network to independently share the same bandwidth with low cross-talk, low noise and high efficiency. This project concerns applying these same concepts and techniques within the optical domain to facilitate new functions and improved security within all-optical networks.

6. The fabrication and applications of holey/microstructured fibres

Holey optical fibres which comprise of a microscopic array of air holes in the centre of an otherwise solid fibre present exciting new possibilities for a whole new generation of both active and passive optical fibre devices. This new form of fibre can possess optical properties that simply cannot be realised with conventional fibre types and looks set to play an important role in application areas as diverse as telecommunications, lasers, aerospace and fundamental physics. This project is concerned with the development of new fabrication techniques for this radically new form of fibre with a view to extending the range of possible fibre geometries (and hence the range of optical properties), improving the loss and precision with which these fibres can be made, and the development of new characterisation techniques. The project is also likely to require a significant element of device work in conjunction with the specialist individual groups who use these fibres within their immediate device/systems research programs. Specific ongoing research topics include the development of holey fibres: for nonlinear optical switching in high bit rate communication systems, high power laser delivery for machining and aerospace application, high power (>100W) lasers, and femtosecond pulse generation and compression.

7. Optical fibre nanowires and nanowire device (in conjunction with Dr Gilberto Brambilla)

Optical fibre nanowires are submicrometric structures fabricated by adiabatically stretching optical fibres, thus preserve the original dimensions of the optical fibre at their input and output. Optical fibre nanowires are of interest for a range of emerging fibre optic applications since they offer a number of enabling optical and mechanical properties, including large evanescent fields (a considerable fraction of the transmitted power can propagate in the evanescent field outside of a nanowire), high nonlinearity (light can be confined to a very small area over long device lengths allowing the ready observation of nonlinear interactions) and extreme flexibility (bend radii of the order of a few microns can be readily achieved). This project concerns the fabrication of optical fibre nanowires from silica and compound glass fibres. Different manufacturing methods will be investigated to optimise the nanowire properties. Devices exploiting the unique mechanical and optical properties are also to be explored and elements of the work are likely to be performed in conjunction with other research groups. These include applications for optics, sensing, biology and chemistry.

8. Nonlinear manipulation of ultra short pulses (supervised by Dr Neil Broderick)

Recent years have seen the development of compact affordable femtosecond pulse sources which has opened up a wide range of applications that were previously restricted to a few specialised labs. However much work remains in controlling, changing and measuring these femtosecond pulses. One promising technique is to use second order nonlinear effects in a cascaded geometry so that it mimics the effects of a third order nonlinearity. This allows many familiar nonlinear effects to be seen at lower powers as well as opening the door to new nonlinear effects. Initially this work will look at pulse compression, and the role of self-steepening before moving on to controlling the nonlinearity through balancing the competing effects. This work will also look at optical shock formation where new analytic techniques must be used to analyse the propagation of pulses in matter. This work will be done in collaboration with Prof. Richardson's group and will find important applications in the X-ray generation project within the ORC.

9. The design and fabrication of microstructured fibres (supervised by Dr Neil Broderick)

The ORC is a world leader in the design and fabrication of microstructured fibres and is building a world class fabrication facility to ensure that this continues. The mircostructred fibre group at the ORC is one of the larger groups and we are looking for new students to play an active role. The students should have a strong interest in the modelling and fabrication of novel fibres and be willing to design, fabricate and test them. This project will start with looking at new designs for optical fibres for a range of applications such as nonlinear optics, astro-photonics, optical sensors, etc and the student will learn how to fabricate the resulting fibres before testing them. This integrated process will ensure that the student leaves familiar with all aspects of fibre technology and will allow the student to concentrate on the aspect that they prefer.

10. Slow light in Periodic Media (supervised by Dr Neil Broderick)

Recent advances in telecommunications have increased the need for the storage of optical pulses for extended periods of time. One of the proposed ways to do this is to exploit the large group velocity dispersion of photonic crystals near the edge of the photonic band gap. When combined with a Kerr nonlinearity optical pulses can propagate at arbitrary speeds through the media allowing controllable optical pulse delay. This project will explore this effect in periodic media, starting with fibre Bragg gratings and builds on the world leading research into nonlinear Bragg gratings that has been done here recently. In addition to looking at slow light effects, other nonlinear effects in Bragg gratings will be examined such as optical bistability, Raman DFB lasers, optical logic, enhanced four wave mixing. 

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