Professor Radan Slavik

• In recent years, there have been significant developments in lightwave technologies enabling wide exploitation of optical phase, as exemplified in particular by the dawn of Coherent Optical Communications - the key enabler for the growth in the capacity of the Internet. This is due to many key breakthroughs in laser technology (low-noise low-cost and compact lasers), new revolutionary concepts that have recently  been introduced (e.g., the Optical Frequency Comb, the significance of which was demonstrated by the award of a Nobel Prize in 2005), and significant advances in electronics that, thanks to the increased speeds now possible, can accommodate the processing of very complicated coherent (amplitude + phase) signals.
• Another exciting field is Hollow Core Optical fibres, which guides ligth in a central hole surrounded by a microstructure that prevents light escaping from the core. Although known for over 20 years, only very recently their fabrication enabled them to use their full potential. 

Hollow Core fibres with low or zero sensitivity to environmental variation

Background: Hollow core fibres are new emerging types of fibres in which the light is not guided through the glass (like in most fibres used today, e.g., for transmitting data over Internet). Instead, it is guided through a hole that is surrounded by an engineered structure that prevents the light from escaping from the central hole. As there is no glass in the light path, the light-glass interaction (which is responsible for most limitations in standard fibres) is strongly suppressed, making these fibres an ultimate candidate for next generation fibre optics.

My research: One of the key (but not obvious) properties of hollow core fibres is their insensitivity to environmental changes (e.g. temperature). I have introduced this topic in my Department in 2013 and I have been dealing with it ever since. Currently, it forms a flagship topic of my research. Currently, it consists of four distinct research streams:

1. Fundamental Fibre properties: In collaboration with our Fibre Design group, I investigate novel fibre designs that lead to improved thermal stability.
2. New approaches to low or zero thermal sensitivity: I look for alternative methods, e.g., change of glass composition, engineering of fibre coating, etc.
3. Demonstration of low thermal sensitivity applications: In collaboration with many external partners, I demonstrate advantages of using hollow core fibres, potentially enabling new emerging technologies, e.g., laser stabilization for seismic sensing which I am working on with the National Physical Laboratory, laser calibration for LIDARs (used, e.g., as ‘eyes’ for self-driven cars) which I am working on with API Sensors Ltd., or optically-switched Data Centre networks (in collaboration with the University College London).
4. Gas dynamics in gas-filled Hollow Core Fibres:  We use precise measurement techniques that we have developed for characterization of very low thermal changes in hollow core fibres to measure other important phenomena in these fibres. This includes the dynamics of filling these fibres with gases, which is relevant for sensors (e.g., for breath analysis) and reference gas cells (for metrology). This is in collaboration with Dr. Natalie Wheeler from the ORC.

Ultra-stable laser oscillators

This is a collaboration with the National Physical Laboratory in London. The aim of this activity is research into ultra-stable optical oscillators and how to use them , e.g., on satellites to achieve improved-accuracy GPS positioning and timing, which is essential for a host of new emerging applications (self-driven vehicles, Industry 4.0, relativistic geodesy, etc.). 

Our approach is to phase-lock lasers to ultra-stable fibre interferometers. We use standard as well as Hollow Core fibres. Unlike competing systems, our devices will be portable and light-weight.

Radio Frequency photonics (RF Photonics)

Background: In electronics, high-frequency signals (>20 GHz) that are of interest in radar or emerging 5G mobile networks can be transmitted only over very limited distances (<10 m) due to the cable loss. This can be mitigated by sending these signals over optical fibres (forming an RF photonics link), extending the reach to kilometres and beyond. Besides transmission, photonics can be also used for high-frequency signals processing, e.g., signal up-conversion and multiplication. Although classical optical fibres enable RF photonics, system performance could be often significantly improved when using Hollow Core optical fibres.

My research covers all these topics, specifically:

1. RF Photonics link
2. Compact frequency combs
3. RF photonics with Hollow Core Fibres