Dr. David Phillips
University of Exeter

I joined the department of Physics and Astronomy at the University of Exeter in June 2017 and established the 'Structured Light Group'. We are a team of 4 PhDs students and 2 postdoctoral researchers working on a range of projects spanning experimental optics and photonics, linked by their reliance on 'structured light' - precise shaping of the intensity, phase and polarisation (and also sometimes wavelength) of laser beams. Structured light fields find applications across many different areas of research. In particular, we use structured light to manipulate small particles in a microscope (optical tweezers), and to develop new types of imaging systems with capabilities beyond those of conventional cameras.


Abstract:
Untangling light for near-instantaneous imaging through multi-mode optical fibres

Multi-mode optical fibres (MMFs) are a promising candidate for minimally invasive micro-endoscopy, offering a large number of parallel information carrying channels packed into an ultra-thin geometry. Unfortunately, MMFs spatially scramble optical signals that propagates through them, thus preventing direct imaging and necessitating frame-rate limiting additional steps to recover images. We aim to eliminate this problem via the development a new tool - which we call an “optical inverter” - that physically unscrambles all light modes emanating from an MMF simultaneously. The realisation of this tool would allow MMFs to open a window into difficult to access environments, enabling, for example, the direct visualisation of cellular structure deep within living tissue. We base our optical inverter design on an emerging technology known as multi-plane light conversion, which efficiently transforms light using a cascade of inverse-designed diffractive planes separated by free space [1]. Here we present a first experimental prototype inverter capable of unscrambling up to 30 spatial modes that have propagated through a 1m long MMF [2]. We also show the future scalability of this concept through numerical simulations of reconfigurable optical inverters supporting up to 400 modes [3]. Figure 1 shows  the concept. Our methods pave the way towards near-instantaneous, single-shot, all-optical, incoherent imaging through MMFs, and may also find applications in the fields of optical communications, optical computing and quantum optics.

[1] Hlib Kupianskyi, Simon A. R. Horsley, and David B. Phillips. "High-dimensional spatial mode sorting and optical circuit design using multi-plane light conversion." APL Photonics 8, no. 2 (2023).
[2] Hlib Kupianskyi, Simon A. R. Horsley, and David B. Phillips. "All-optically untangling light propagation through multimode fibers." Optica 11, no. 1 (2024): 101-112.
[3] Unė G. Būtaitė, Hlib Kupianskyi, Tomáš Čižmár, and David B. Phillips. "How to Build the “Optical Inverse” of a Multimode Fibre." Intelligent Computing (2022).

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