Tuneable Gigahertz Mode Spaced Frequency Combs

Lead Research Organisation: University of Dundee
Department Name: Physics


I propose to demonstrate the first optical frequency comb systems where the tooth spacing is tuneable by many free spectral ranges, and use this to introduce novel spectroscopic techniques and applications in selected areas of metrology, spectroscopy and medicine, creating both significant scientific and commercial impact.

The proposed comb system combines repetition frequency tuneable femtosecond pulse surface emitting semiconductor lasers with ytterbium fibre amplifier systems (YDFAs) and photonic crystal fibre (PCF) to enable this novel comb capability. The physical properties of the comb system, from the noise characteristics of the semiconductor laser at its centre, to that of the complete system will be investigated and compared to the current state of art systems.

A tuneable gigahertz repetition frequency source will enable the study of vibrational modes in nano-scale objects. For example PCF has radial vibrational modes in the GHz range, as do the protein shells of viruses. We will study these resonances by developing new spectroscopic techniques enabled by the tuneable comb system. We will study the enhancement and suppression of nonlinearities in PCF by resonantly exciting vibrational modes. We will also study the inactivation of viruses by resonantly exciting vibrations in their shells, causing them to break up.

The classic frequency comb has followed a development path similar to the laser; at its inception no one could imagine the vast range of applications it has enabled. The novel capabilities of this comb system will similarly enable many future applications and measurement techniques which will only be envisaged as the capability and international exposure of this system increases.

A key to the continuing success of the research theme started beyond this proposal will be strong national and international collaborations. I have established a strong and broad ranging network of collaborators and will continue to build this network throughout the proposal to enable this research to set the agenda and lead this new field into the future.

Planned Impact

The proposed research will generate a wide range of societal and economic impacts.
In terms of societal impacts, the knowledge developed during this project will represent a unique spectroscopy and metrology capability in the UK. It will enable new experimental techniques, gaining a deeper insight into the physical properties of nano-scale objects. The proposed research has potential to stimulate cross-field research in massively multiplexed computing and ultra-low noise microwave generation, which could have many applications from metrology to next generation supercomputers to radar. Further to this there is potential for healthcare impact. The investigation of resonant inactivation of blood borne viruses could have profound impacts in society.
Economically, during the proposal we aim to generate IP and to exploit this in UK based spin-out companies over the course of the proposal. The comb system and developed spectroscopic techniques have potential commercial value as measurement tools for scientific applications, whilst the economic impact of the laser driven inactivation of drug resistant viruses could be profound. The proposal will train future scientists and develop strong interdisciplinary collaborations to increase the productivity of research undertaken in the UK.
Academically the proposal will generate impact including studies of the fundamental noise characteristics of the femtosecond semiconductor laser; new frequency comb capabilities; development of applications; new spectroscopic techniques; medical applications and the potential for selective laser driven virus inactivation and identification. The proposal creates impact within a number of areas of the ICT theme and also across discipline boundaries into medicine as well as potentially chemistry and nanotechnology.
The project will benefit several PhD and Masters research students, who will receive research training and development opportunities within my group. The proposed work will also benefit the broad range of academic and commercial collaborators who are involved in the project through access to the sources we are developing and the ongoing exploitation of it in applications and scientific studies. Further to these existing collaborators we will build new collaborations during the course of the fellowship, specifically engaging with academics in interdisciplinary fields in medicine and chemistry and areas of ICT such as the RF and microwave community on top of the photonics community.


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Related Projects

Project Reference Relationship Related To Start End Award Value
EP/J017043/1 01/09/2012 30/09/2013 £597,062
EP/J017043/2 Transfer EP/J017043/1 01/10/2013 28/02/2018 £445,555
Description Gigahertz repetition rate femtosecond pulse optically pumped semiconductor lasers are an advanced and flexible type of laser which combines the wavelength flexibility and customisable design of semiconductor structures with the reliability, excellent beam quality and advanced laser performance of solid state lasers. Over the course of this grant we have uncovered several key findings. We developed spectral broadening and pulse compression from the output of VECSELs and fibre amplified VECSELs using highly nonlinear fibre, allowing high average powers and sub-100-fs pulse duration to be achieved. We have studied nonlinear lensing in VECSEL gain structures to shed light on the possible mechanisms for self mode-locking which has recently been observed. We identified potential mechanisms, characterised the strength of the lensing and developed models to predict stable operating regimes. We have also developed DBR mirror free VECSELs which can be used in transmission and have reached record output powers in continuous wave as well as developed a DBR-free semiconductor saturable absorber to enable mode-locking. This DBR-free technology is opening up new research directions, enabling different design rules to be used and freeing up many of the technical constraints which limit normal VECSEL perfomance.
Exploitation Route Our findings are being taken forwards through academic research on the DBR-free VECSELs as well as by transfer of knowledge to industry through joint projects such as a KTP project with Coherent Scotland. The knowledge gained on nonlinear lensing could allow for advanced mode-locked sources to be developed, again through academic and industrial joint projects. Finally this research, along with other advances in the field are showing promising signs in biophotonics imaging techniques, with a particular focus on multi-photon microscopy.
Sectors Healthcare,Manufacturing, including Industrial Biotechology,Other

Description To date, or findings have been used by other research groups internationally, as part of the mode-locked VECSEL community. We have undertaken a KTP project with Coherent Scotland aiming to commercialize some of the technology developed during the past 5 years but to date we are still some way off commercialization.
First Year Of Impact 2015
Sector Pharmaceuticals and Medical Biotechnology,Other
Impact Types Economic

Description Innovate UK KTP
Amount £175,000 (GBP)
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 07/2015 
End 06/2017
Description Royal Society Research Grant
Amount £15,000 (GBP)
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 03/2015 
End 02/2016
Title Figures in support of 27.5 W/m2 collection efficiency solar laser using a diffuse scattering cooling liquid 
Description This is the recorded data corresponding to the graphs provided in the published paper "27.5 W/m2 collection efficiency solar laser using a diffuse scattering cooling liquid". Figure 2A: The absorption as a function of ray incident angle for 98% and 0% diffuse reflectivity. Figure 2B: Modelled solar absorption in Nd:YAG rod as a function of reflectivity of diffuse scatterer in contact with the side wall of the rod. Figure 4: Modelled laser output power as a function of solar power entering the 20 mm long, 3 mm diameter Nd:YAG rod for 98% reflectivity scatterer and 0% diffuse scatterer. Figure 6: Laser output power vs total solar power hitting the front surface of the Fresnel lens for both water and water-paint cooling liquids. Figure 7: Modelled and experimental laser power as a function of power entering the laser rod. Table of losses: experimentally measured loss from each component in the sunlight collection path. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes