PhD project opportunities

Below is a list of potential PhD projects available within our research group. Please get in touch with the relevant project supervisor to discuss.

Monolithically integrated GaN high-frequency surface acoustic wave filters (SAW) for future 5G networks

Supervisor: Professor Krishna Balram

A modern smartphone requires on the order of 10-15 RF filters to enable communications using different frequency bands (for ex: cellular, WiFi, Bluetooth, GPS). Currently, the RF filtering is done using multiple discrete filters put together in a packaging marvel (for ex: Qualcomm’s RF 360 platform). While this might work in the near term, as 5G kicks in and the filtering requirements become more cumbersome (more bands, higher frequencies), we would like to explore a monolithic solution to the problem.

Our approach involves integrating high frequency surface acoustic wave (SAW) filters with low noise GaN amplifiers. GaN is widely deployed for building the power amplifiers in smartphones and given its strong piezoelectric coefficient, is ideal for building SAW filters. Using the state-of-the-art Raith ebeam lithography system at the University of Bristol, we would like to demonstrate SAW filters integrated with LNAs in the 3-6 GHz range for future 5G communication systems. Using integrated heaters and a circuitry for filter multiplexing, our goal is to demonstrate a single chip solution for smartphone communications.

Contact: Professor Krishna Balram


Piezoelectric acousto-optic devices for radio frequency (RF) signal processing

Supervisor: Professor Krishna Balram

As the spectacular success of LIGO has shown, optical cavity interferometry provides unparalleled sensitivity and is usually the method of choice for detecting weak signals. By designing efficient transducer platforms, a given perturbation can be mapped onto an optical cavity and measured close to fundamental detection limits. This project aims to develop novel receivers for very weak RF signals (such as encountered in MRI, radio astronomy, radar and even cell phone reception in indoor environments) based on integrated piezo-electric platforms (such as GaAs and GaN). The piezo-electric effect allows us to efficiently excite a localized mechanical mode of an opto-mechanical cavity. By engineering the cavity to support an optical mode which is strongly coupled to the mechanics, we can use the optical mode to pick up the displacement induced perturbation and thus the RF signal. Our goal is to understand the fundamental limits of conversion efficiency in RF to optical signal transducers (optical modulators) and detection efficiency in these RF-optical receivers.

Contact: Professor Krishna Balram


Design Centering for Nanophotonics

Supervisor : Professor Martin Cryan

Solar thermal energy, where sunlight is used to heat surfaces and liquids is one of the most efficient types of solar energy conversion. This PhD will explore the use of nanostructured surfaces to improve the performance of these devices.

This project will use Finite Difference Time Domain modelling to develop novel structures based on nanostructured surfaces based low cost patterning techniques such as laser etching and nanoimprint lithography. It will then characterise fabricated surfaces for use in solar thermal cells. We have developed a high temperature vacuum sealed system such that temperature of >600 deg C can be obtained

Contact: Professor Martin Cryan


Nanostructured Surfaces for Solar Thermal Applications

Supervisor : Professor Martin Cryan

Solar thermal energy, where sunlight is used to heat surfaces and liquids is one of the most efficient types of solar energy conversion. This PhD will explore the use of nanostructured surfaces to improve the performance of these devices.

This project will use Finite Difference Time Domain modelling to develop novel structures based on nanostructured surfaces based low cost patterning techniques such as laser etching and nanoimprint lithography. It will then characterise fabricated surfaces for use in solar thermal cells. We have developed a high temperature vacuum sealed system such that temperature of >600 deg C can be obtained

Contact: Professor Martin Cryan


Nanoantennas for enhancing fluorescence biosensing

Supervisor : Professor Martin Cryan

Nanoantennas are a new field of engineering and science that apply traditional RF antenna concepts to light at the nanoscale. These types of devices can produce very high electromagnetic field strengths in very small volumes which can result in increased light emission from fluorophores. This has application in many areas such as sensing and imaging.

This project will use Finite Difference Time Domain codes to design and optimise such structures. Various processes will be used to fabricate the structures include electron beam lithography, Nanoimprint lithography and Displacement Talbot lithography. This work is currently being sponsored by www.ABB.com and opportunities exist for collaboration with them.

Contact: Professor Martin Cryan


Single photon sources in photonic structures

Supervisor (Staff member): Professor John Rarity, Professor Krishna Balram

There are various sources in solid state systems that show atom like properties in that they emit photons one at a time. Here we are looking to couple light efficiently from single photon sources into waveguides to make single photons. By nanostructuring the waveguides we can enhance the coupling intopreferred modes. At this time, we are looking at nanodiamonds containing Nitrogen vacancy defect centres as our single photon source coupling these to silicon nitride waveguides. Once the technology is demonstrated it could be applied to a wide variety of sources including defects in 2D materials (Graphene, Tungsten Selenide, hexagonal Boron Nitride H-BN). We are particularly interested in developing efficient coupling to atom like systems that have ground state spin to investigate applications to quantum memory and quantum communication. PhD students will study fluorescence spectroscopy using confocal microscopes, waveguide fabrication techniques and on-chip microelectronics schemes to control source and manipulate single spins

Contact: Professor John Rarity Professor Krishna Balram


Cubesat optical communications

Supervisor (Staff member): Professor John Rarity

In this project the student will work in (a small team) on the testing and development of a CUBESAT optical communications system for quantum key distribution. Key goals will be the development of an active pointing and tracking control system with an accuracy down to microradian precision using a closed loop tracking system, development of compact optical telecope for sender and receiver stations. Integration of photon sources and photon counting detectors into the system building on previous (10 years) of work on free space communications within the group. The end goal will be to develop a single photon communication system to demonstrate quantum key distribution from a low cost cubesat to ground. This would reduce the cost of developing quantum communications in space by many orders of magnitude.

https://en.wikipedia.org/wiki/Quantum_Experiments_at_Space_Scale

Contact: Professor John Rarity


Fibre-coupled single photon sources based on quantum dots

Supervisor: Dr Edmund Harbord

Single photon sources (SPS) are a key component for the future quantum internet. This project will engineer a high brightness, on demand source of indistinguishable single photons direct to a fibre. Finite Difference Time Domain codes will be used to design a high efficiency photonic structure to extract the photons into a well defined optical mode. You will fabricate structures using the state-of-the-art cleanroom techniques including e-beam lithography, and develop optical coupling techniques to attach the fibre to the photonic nanostructure. This PhD project is linked to the EPSRC project SPIN SPACE (EP/M024237/1).

Contact: Dr Edmund Harbord


Spintronic lasers for telecommunications and RF-to-optical conversion

Supervisor: Dr Edmund Harbord

"Artificial atoms" or "quantum dots" are nanoscale inclusions of one semiconductor embedded in another. They are an important component of semiconductor lasers, especially "spin lasers" – spintronic devices which enable polarization switching and rapid modulation of light, vital if we are to defeat the "capacity crunch" that will affect optical fibre communications in the 2020s.

In this project, the student will develop radio- and microwave antennas, and use them to irradiate spin lasers.

Radio-to- optical conversion To use NMR pulses to manipulate the ensemble of nuclear spins in a spin laser. By optically pulping the laser, we can achieve spin lasing. This will be disrupted by the radio frequency signal, switching lasing on-and- off. Effectively, we will be using a spin laser as a nano-antenna – detecting radio-frequency signals (wavelength ~m) with a micron-scale device.

Further, as we will be detecting radio-frequency signals with optical photons, we will effectively amplify the signal by a factor of 104. The frequency of the detection can be tuned by an electrical bias applied to the spin laser. New techniques will be developed to demonstrate all-optical switching and spin logic in a semiconductor. This PhD project is linked to the EPSRC project SPIN SPACE (EP/M024237/1).

Contact: Dr Edmund Harbord


Tammtronics - future photonics exploiting novel photonic states for lasers and microwave electronics

Supervisor: Dr Edmund Harbord

Tamm Optical States – sometimes called “Tamm plasmons” - are a novel way of confining light in a semiconductor device. They are the photonic equivalent of the Tamm electronic states that occur at the termination of a crystal lattice, and offer a route to a highly manufacturable lasers and to create fast optical-microwave switches. 

In this project, you will design, fabricate, and measure telecommunicationswavelength devices based on Tamm plasmons. Depending on the evolution of the project, this could include a Tamm laser, Tamm photodetector, and / or a microwave switch.  

 

Contact: Dr Edmund Harbord


Quantum memory using a quantum dot

Supervisor: Prof Ruth Oulton

To build the future quantum internet, we need a "quantum memories" – devices that preserve the full state of single photons in a semiconductor. An obstacle to preserving the information for long times is the randomly fluctuating nuclear spins in the semiconductor. We seek to understand and engineer this nuclear spin environment. Radio-frequency pulses (RF) can be used to control nuclear spins: in this project, RF pulse sequences will be delivered to a semiconductor at cryogenic temperatures. The student will design and build a novel system that can efficiently send broadband pulses into this environment.

Contact: Prof Ruth Oulton


Efficient single photon sources using Tamm plasmons

Supervisor: Prof Ruth Oulton

Quantum dots - nanoscale inclusions of InAs embedded in GaAs - are efficient sources of single photons, necessary for the next generation of quantum technologies. However, although the QDs have high internal quantum efficiency, the external quantum efficiency of the semiconductor nanostructures is extremely low, >1%. In this project, new sources of single photons will be developed with high external efficiency, using a new type of optical photoni structure - the Tamm plasmon These topological structures confine light in a small volume and have extremely high quantum efficiency.

Contact: Prof Ruth Oulton


Real Time Low Cost Multi-Coincidence Counter

Supervisor: Professor Naim Dahnoun

Coincidence counter is a correlation tool used for counting the combinations of simultaneously occurring time events in a certain time interval over multiple number of channels. Coincidence counters are commonly used in many different applications including quantum entanglement experiments, positron emission tomography and time of flight measurements. Due to advance in engineering and science, low cost, flexible, high resolution coincidence counting is possible. However, present instrument cannot achieve low pico-second range measurements while keeping the dead time (time between measurements) and at low cost. In this research, state of the art components such as CPU, GPU, FPGA, CMOS, ASIC and so on should be investigated to achieve desired solution.

Contact: Professor Naim Dahnoun


1ps Time-to-Digital Converter utilising reconfigurable switch matrices

Supervisor: Dr Naim Dahnoun

Time to Digital Converters (TDCs) are devices which convert the time between two events, heralded by electrical pulses, into a digital number. They are important instruments in the fields of metrology, quantum photonics and autonomous vehicles, with the goal of obtaining high accuracy, high count-rate TDCs at a low cost being vital to the commoditisation of these technologies. However, obtaining high resolutions is not easy as we have issues with systematic delays, random delays, clock jitter, limited switching speed, limited slew rates and device mismatch. In http://ieeexplore.ieee.org/abstract/document/5738332/, the author demonstrates the possibility of creating selectable delay elements with a minimum delay of tens of picoseconds, but an inter-delay minimum difference of 1 picosecond. The aim of this project is to verify the feasibility of achieving these results on modern hardware and applying the Vernier method to this idea to achieve a TDC with 1 picosecond resolution.

Contact: Dr Naim Dahnoun


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