Time refraction in integrated photonics

Time refraction is an ultrafast dynamic phenomenon where the refractive index of a material is changed as light is flying through it. Time refraction is incredibly difficult to see because light must be trapped within a material while the material’s refractive index is changed. Hero experiments have been performed using free-carriers injected optically, but these demonstrations are limited by the small index changes available (< 0.1%) and the free-carrier losses.

For years, proposals have been made to use the Kerr effect* to make the ultrafast refractive index changes without optical losses, but the refractive index changes have always been tiny (< 0.01%). Now, new research on the Kerr effect in epsilon-near-zero materials indicates that materials with much larger index changes will be available in the future, with > 6% already demonstrated. This greater index change will open new possibilities in time refraction for dynamic on-chip photonic functions and devices. Time refraction is an understudied problem, and this theoretical project aims to move towards the manufacturing of integrated devices that use time-refraction by using simulations to benchmark new device designs and determine the best compound semiconductors** and their trade-offs. We will aim to design and simulate a new set of integrated photonics devices to demonstrate time refraction and related phenomena such as adiabatic frequency conversion, optical isolation, all-optical delay, and the stopping of light.

*The Kerr effect is a third order nonlinearity that makes the refractive index a function of the instantaneous electric field. By using an ultrafast pump-pulse that is not absorbed, the intense electric fields will change the refractive index of the material during the pump’s duration.

**A promising way to achieve epsilon near zero materials is to use doped compound semiconductors – it’s the collective motion of free carriers at the plasma frequency that produces the effect. Multilayers or metamaterials can also be used as effective media with epsilon near zero properties.

How to apply:

Applicants should apply to the Doctor of Philosophy in Physics and Astronomy with a start date of 1st January 2025. 

Applicants should submit an application for postgraduate study via the Cardiff University webpages (https://www.cardiff.ac.uk/study/postgraduate/research/programmes/programme/physics-and-astronomy) including: 

• your academic CV 

• Your degree certificates and transcripts to date including certified translations if these are not in English 

• two references, at least one of which should be academic. Your references can be emailed by the referee to [email protected]  

Please note: We are do not contact referees directly for references for each applicant due to the volume of applications we receive.  

 • personal statement (as part of the university application form, or as a separate attachment, if you prefer. It has to provide a clear explanation of your research interest, preparation undertaken, and an understanding of the project. 

Your personal statement should be no more than 500 words, and address the following questions:

1. What are your scientific research interests and ambition? 

2. How has your academic and/or professional journey prepared you for PhD study? (for instance, give examples of work you particularly enjoyed, of challenges you overcame, of connecting with others about your work or ideas, of showing inventiveness, of developing new skills and knowledge)

3. Why do you think this project is important?”

The typical academic requirement is a minimum of a 2:1 physics and astronomy or a relevant discipline. 

Applicants whose first language is not English are normally expected to meet the minimum University requirements (e.g. IELTS 6.5 Overall with 5.5 minimum in sub-scores) (https://www.cardiff.ac.uk/study/international/english-language-requirements) 

In the “Research Proposal” section of your application, please specify the project title and supervisors of this project.

In the funding section, please select that you will not be self-funding and write that the source of funding will be EPSRC. 

Once the deadline for applications has passed, we will review your application and advise you within a few weeks if you have been shortlisted for an interview. 

Eligibility :

EPSRC DTP studentships are available to home and international students. Up to 30% of our cohort can comprise international students, once the limit has been reached we are unable to make offers to international students. International students will not be charged the fee difference between the UK and international rate. Applicants should satisfy the UKRI eligibility requirements.

For more information, or if there are any questions, please contact Physics and Astronomy PGR Student Support team at [email protected]

Please also check the following link: https://www.cardiff.ac.uk/study/postgraduate/funding/research-councils/epsrc-studentships