Shaping the light transmission through a multimode optical fibre : complex transformation analysis and applications in biophotonics

Funding: UK Engineering and Physical Sciences Research Council and the University of St Andrews for funding.We present a powerful approach towards full understanding of laser light propagation through multimode optical fibres and control of the light at the fibre output. Transmission of light within a multimode fibre introduces randomization of laser beam amplitude, phase and polarization. We discuss the importance of each of these factors and introduce an experimental geometry allowing full analysis of the light transmission through the multimode fibre and subsequent beam-shaping using a single spatial light modulator. We show that using this approach one can generate an arbitrary output optical field within the accessible field of view and range of spatial frequencies given by fibre core diameter and numerical aperture, respectively, that contains over 80% of the total available power. We also show that this technology has applications in biophotonics. As an example, we demonstrate the manipulation of colloidal microparticles.Peer reviewe

Exploiting multimode waveguides for pure fibre-based imaging

We acknowledge support from the UK Engineering and Physical Science Research CouncilThere has been an immense drive in modern microscopy towards miniaturisation and fibre based technology. This has been necessitated by the need to access hostile or diffcult environments in-situ and in-vivo. Strategies to date have included the use of specialist fibres and miniaturised scanning systems accompanied by ingenious microfabricated lenses. We present a novel approach for this field by utilising disordered light within a standard multimode optical fibre for lensless microscopy and optical mode conversion. We demonstrate the modalities of bright-field and dark-field imaging and scanning fluorescence microscopy at acquisition rates allowing observation of dynamic processes such as Brownian motion of mesoscopic particles. Furthermore, we show how such control can realise a new form of mode converter and generate various types of advanced light fields such as propagation-invariant beams and optical vortices. These may be useful for future fibre based implementations of super-resolution or light sheet microscopy.Publisher PDFPeer reviewe

A material change for ultra-high precision force sensing

Funding: This research was supported by the Australian Research Council Centre of Excellence in Optical Microcombs for Breakthrough Science (project number CE230100006) and an Australian Research Council Laureate Fellowship (FL210100099).An original form of photonic force microscope has been developed. Operating with a trapped lanthanide-doped crystal of nanometric dimensions, a minimum detected force of the order of 110 aN and a force sensitivity down to 1.8 fN/Hz have been realised. This opens up new prospects for force sensing in the physical sciences.Peer reviewe

Selective and optimal illumination of nano-photonic structures using optical eigenmodes

Using optical eigenmodes defined by the interaction between the electromagnetic fields and photonic structures it is possible to determine the optimal illumination of these structures with respect to a specific measurable quantity. One such quantity considered here is the electric field intensity in the hotspot regions of an array of nano-antennas. This paper presents two possible methods, both based on optical eigenmodes, to determine the optimal and most efficient illumination that couples to a single hotspot on top of a single nano-antenna taken from an array of nano-antennas. The two methods are compared in terms of cross-talk and overall coupling efficiency.Comment: Paper presented at the TaCoNa-Photonics meeting October 2011, Bad Honnef, German

Widefield multiphoton imaging at depth with temporal focusing

Optical imaging has the potential to reveal high-resolution information with minimal photodamage. The recent renaissance of super-resolution, widefield, ultrafast, and computational imaging methods has broadened its horizons even further. However, a remaining grand challenge is imaging at depth over a widefield and with a high spatiotemporal resolution. This achievement would enable the observation of fast collective biological processes, particularly those underpinning neuroscience and developmental biology. Multiphoton imaging at depth, combining temporal focusing and single-pixel detection, is an emerging avenue to address this challenge. The novel physics and computational methods driving this approach offer great potential for future advances. This chapter articulates the theories of temporal focusing and single-pixel detection and details the specific approach of TempoRAl Focusing microscopy with single-pIXel detection (TRAFIX), with a particular focus on its current practical implementation and future prospects

Optical eigenmode imaging

We present an indirect imaging method that measures both amplitude and phase information from a transmissive target. Our method is based on an optical eigenmode decomposition of the light intensity and the first-order cross correlation between a target field and these eigenmodes. We demonstrate that such optical eigenmode imaging does not need any a priori knowledge of the imaging system and corresponds to a compressive full-field sampling leading to high image extraction efficiencies. Finally, we discuss the implications with respect to second-order correlation imaging

Is there an optimal basis to maximise optical information transfer?

We establish the concept of the density of the optical degrees of freedom that may be applied to any photonics based system. As a key example of this versatile approach we explore information transfer using optical communication. We demonstrate both experimentally, theoretically and numerically that the use of a basis set with fields containing optical vortices does not increase the telecommunication capacity of an optical system.Peer reviewe

Wavefront correction enables vibrational imaging of bacteria with multimode fibre probes

Raman spectroscopy is a valuable tool for non-invasive and label-free identification of sample chemical composition. Recently a few miniaturized optical probes emerged driven by the need to address areas of difficult access, such as in endoscopy. However, imaging modality is still out of reach for most of them. Separately, recent advances in wavefront shaping enabled different microscopies to be applied in various complex media including multimode fibers. Here we present the first and thinnest to date Raman fiber imaging probe based on wavefront shaping through a single multimode fiber without use of any additional optics. We image agglomerates of bacteria and pharmaceuticals to demonstrate the capability of our method. This work paves the way towards compact and flexible Raman endoscopy. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.Publisher PD

Raman imaging through a single multimode fibre

UK Engineering and Physical Sciences Research Council (EPSRC) (EP/J01771/X); European Union project FAMOS (FP7 ICT no. 317744); PreDiCT-TB consortium (IMI 115337); European Union’s Horizon 2020 Marie Sklodowska-Curie Actions (MSCA) (707084).Vibrational spectroscopy is a widespread, powerful method of recording the spectra of constituent molecules within a sample in a label-free manner. As an example, Raman spectroscopy has major applications in materials science, biomedical analysis and clinical studies. The need to access deep tissues and organs in vivo has triggered major advances in fibre Raman probes that are compatible with endoscopic settings. However, imaging in confined geometries still remains out of reach for the current state of art fibre Raman systems without compromising the compactness and flexibility. Here we demonstrate Raman spectroscopic imaging via complex correction in single multimode fibre without using any additional optics and filters in the probe design. Our approach retains the information content typical to traditional fibre bundle imaging, yet within an ultra-thin footprint of diameter 125 µm which is the thinnest Raman imaging probe realised to date. We are able to acquire Raman images, including for bacteria samples, with fields of view exceeding 200 µm in diameter.Publisher PDFPeer reviewe

Wide-field 3D optical imaging using temporal focusing for holographically trapped microparticles

Funding. Engineering and Physical Sciences Research Council (EPSRC) (EP/J01771X/1, EP/M000869/1).A contemporary challenge across the natural sciences is the simultaneous optical imaging or stimulation of small numbers of cells or colloidal particles organised into arbitrary geometries. We demonstrate the use of temporal focusing with holographic optical tweezers in order to achieve depth-resolved two-photon imaging of trapped objects arranged in arbitrary three dimensional geometries using a single objective. Trapping allows independent position control of multiple objects by holographic beam shaping. Temporal focusing of ultrashort pulses providesawide-field two-photon depth-selective activation of fluorescent samples. We demonstrate wide-field depth-resolved illumination of both trapped fluorescent beads and trapped HL60 cells in suspension with full 3D positioning control. These approaches are compatible with implementation through scattering media and can be beneficial for emergent studies in colloidal science and particularly optogenetics, offering targeted photoactivation over a wide area with µm depth control precision.PostprintPeer reviewe