Publications
See a list of publications below or visit the Photonics academic staff page and click on a particular member of staff to access their personal web page, which includes a list of their own publications.
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Journal articleAhmad H, Roslan NA, Zaini MKA, et al., 2023,
Generation of multiwavelength bismuth-doped fiber laser based on all-fiber Lyot filter
, Optical Fiber Technology, Vol: 81, ISSN: 1068-5200A stable multiwavelength fiber laser was proposed and demonstrated using a bismuth-doped fiber together with an all-fiber Lyot filter. The proposed multiwavelength bismuth-doped fiber laser (BDFL) spectrum can generate up to 21 output channels between 1309.88 nm and 1313.69 nm by carefully adjusting two polarization controllers (PCs). The multiwavelength BDFL shows good stability over time with a signal-to-noise ratio (SNR) of 48.69 dB, contributing to the average power fluctuations of 0.6 dB and wavelength drift of less than 0.1 nm in the laser output. In addition, the multiwavelength BDFL exhibits a free spectral range (FSR) of about 0.192 nm and a frequency bandwidth of 33.45 GHz. The characteristics of the multiwavelength BDFL can be observed by varying the pump power of the pump source, lasing output at different lengths of polarization maintaining fiber (PMF), and the generation in multiwavelengths using additional single mode-fiber (SMF).
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Journal articleRiemer K, Tan Q, Morse S, et al., 2023,
3D Acoustic Wave Sparsely Activated Localization Microscopy With Phase Change Contrast Agents.
, Invest RadiolOBJECTIVE: The aim of this study is to demonstrate 3-dimensional (3D) acoustic wave sparsely activated localization microscopy (AWSALM) of microvascular flow in vivo using phase change contrast agents (PCCAs). MATERIALS AND METHODS: Three-dimensional AWSALM using acoustically activable PCCAs was evaluated on a crossed tube microflow phantom, the kidney of New Zealand White rabbits, and the brain of C57BL/6J mice through intact skull. A mixture of C 3 F 8 and C 4 F 10 low-boiling-point fluorocarbon gas was used to generate PCCAs with an appropriate activation pressure. A multiplexed 8-MHz matrix array connected to a 256-channel ultrasound research platform was used for transmitting activation and imaging ultrasound pulses and recording echoes. The in vitro and in vivo echo data were subsequently beamformed and processed using a set of customized algorithms for generating 3D super-resolution ultrasound images through localizing and tracking activated contrast agents. RESULTS: With 3D AWSALM, the acoustic activation of PCCAs can be controlled both spatially and temporally, enabling contrast on demand and capable of revealing 3D microvascular connectivity. The spatial resolution of the 3D AWSALM images measured using Fourier shell correlation is 64 μm, presenting a 9-time improvement compared with the point spread function and 1.5 times compared with half the wavelength. Compared with the microbubble-based approach, more signals were localized in the microvasculature at similar concentrations while retaining sparsity and longer tracks in larger vessels. Transcranial imaging was demonstrated as a proof of principle of PCCA activation in the mouse brain with 3D AWSALM. CONCLUSIONS: Three-dimensional AWSALM generates volumetric ultrasound super-resolution microvascular images in vivo with spatiotemporal selectivity and enhanced microvascular penetration.
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Journal articleKoufidis SF, McCall MW, 2023,
Wavelength-independent Bragg-like reflection in uniaxial bi-anisotropic media
, Journal of the Optical Society of America B, Vol: 40, Pages: 2829-2829, ISSN: 0740-3224<jats:p>We have recently shown that a uniform birefringent medium exhibits a circular Bragg phenomenon that relies solely on resonant tuning of the medium’s parameters, rather than on a particular wavelength resonance, thus rendering its electromagnetic response arbitrarily broadband. The resonant condition, however, necessitated a chirality parameter equal to the average refractive index. Here, we demonstrate that non-axial wave propagation in an axially bi-anisotropic uniaxial medium also enacts such a response and, moreover, relaxes the severity of the tuning condition, offering a convenient platform for controlling both the location of the resonance and the corresponding bandwidth. Anomalous wave propagation at a singular point is additionally identified, in the vicinity of which a remarkably high and intrinsically broadband refractive index can be realized. Recent demonstrations of meta-media with giant and controllable chirality pave the path towards the realistic embodiment of a highly efficient optical modulator.</jats:p>
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Journal articleHong W, Sparks H, Dunsby C, 2023,
Alignment and characterisation of remote-refocusingsystems
, Applied Optics, Vol: 62, Pages: 7431-7440, ISSN: 1559-128XThe technique of remote refocusing is used in optical microscopy to provide rapid axial scanning without mechanically perturbing the sample and in techniques such as oblique plane microscopy that build on remote refocusing to image a tilted plane within the sample. The magnification between the pupils of the primary (O1) and secondary (O2) microscope objectives of the remote-refocusing system has been shown previously by Mohanan and Corbett [J. Microsc. 288, 95 (2022) [CrossRef] ] to be crucial in obtaining the broadest possible remote-refocusing range. In this work, we performed an initial alignment of a remote-refocusing system and then studied the effect of axial misalignments of O1 and O2, axial misalignment of the primary tube lens (TL1) relative to the secondary tube lens (TL2), lateral misalignments of TL2, and changes in the focal length of TL2. For each instance of the setup, we measured the mean point spread function FWHMxy of 100 nm fluorescent beads and the normalized bead integrated fluorescence signal, and we calculated the axial and lateral distortion of the system; all of these quantities were mapped over the remote-refocusing range and as a function of lateral image position. This allowed us to estimate the volume over which diffraction-limited performance is achieved and how this changes with the alignment of the system.
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Journal articleLightley J, Kumar S, Lim MQ, et al., 2023,
<i>openFrame</i>: A modular, sustainable, open microscopy platform with single-shot, dual-axis optical autofocus module providing high precision and long range of operation
, JOURNAL OF MICROSCOPY, ISSN: 0022-2720 -
Journal articleKoufidis SF, Koutserimpas TT, McCall MW, 2023,
Temporal analog of Bragg gratings
, Optics Letters, Vol: 48, Pages: 4500-4500, ISSN: 0146-9592<jats:p>Recently, scalar coupled-wave theory has been employed to analyze a medium with periodic time-varying permittivity, providing simple expressions and, consequently, straightforward insights into the parametric amplification mechanism. Here, we combine such an approach with the Möbius transformation method to investigate the dispersion and optical response of a finite “time-slab” of the aforementioned medium. We demonstrate the temporal analog of a Bragg grating, discuss the differences with its spatial counterpart, and examine nontrivial scenarios of the permittivity’s time-modulation, such as chirping and apodization. Furthermore, we propose a highly selective and, moreover, single-spatial-interface optical sensor, based on phase delineation.</jats:p>
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Journal articleTawy G, Davidson NP, Churchill G, et al., 2023,
Temperature-tunable UV generation using an Alexandrite laser and PPLN waveguides
, OPTICS EXPRESS, Vol: 31, Pages: 22757-22765, ISSN: 1094-4087 -
Journal articleTaylor JR, 2023,
Early optical soliton research at Imperial College London
, OPTICS COMMUNICATIONS, Vol: 536, ISSN: 0030-4018- Author Web Link
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- Citations: 3
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Journal articleSmith M, Sparks H, Almagro J, et al., 2023,
Active mesh and neural network pipeline for cell aggregate segmentation
, Biophysical Journal, Vol: 122, Pages: 1586-1599, ISSN: 0006-3495Segmenting cells within cellular aggregates in 3D is a growing challenge in cell biology due to improvements in capacity and accuracy of microscopy techniques. Here, we describe a pipeline to segment images of cell aggregates in 3D. The pipeline combines neural network segmentations with active meshes. We apply our segmentation method to cultured mouse mammary gland organoids imaged over 24 h with oblique plane microscopy, a high-throughput light-sheet fluorescence microscopy technique. We show that our method can also be applied to images of mouse embryonic stem cells imaged with a spinning disc microscope. We segment individual cells based on nuclei and cell membrane fluorescent markers, and track cells over time. We describe metrics to quantify the quality of the automated segmentation. Our segmentation pipeline involves a Fiji plugin that implements active mesh deformation and allows a user to create training data, automatically obtain segmentation meshes from original image data or neural network prediction, and manually curate segmentation data to identify and correct mistakes. Our active meshes-based approach facilitates segmentation postprocessing, correction, and integration with neural network prediction.
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Journal articleRiemer K, Toulemonde M, Yan J, et al., 2023,
Fast and selective super-resolution ultrasound in vivo with acoustically activated nanodroplets
, IEEE Transactions on Medical Imaging, Vol: 42, Pages: 1056-1067, ISSN: 0278-0062Perfusion by the microcirculation is key to the development, maintenance and pathology of tissue. Its measurement with high spatiotemporal resolution is consequently valuable but remains a challenge in deep tissue. Ultrasound Localization Microscopy (ULM) provides very high spatiotemporal resolution but the use of microbubbles requires low contrast agent concentrations, a long acquisition time, and gives little control over the spatial and temporal distribution of the microbubbles. The present study is the first to demonstrate Acoustic Wave Sparsely-Activated Localization Microscopy (AWSALM) and fast-AWSALM for in vivo super-resolution ultrasound imaging, offering contrast on demand and vascular selectivity. Three different formulations of acoustically activatable contrast agents were used. We demonstrate their use with ultrasound mechanical indices well within recommended safety limits to enable fast on-demand sparse activation and destruction at very high agent concentrations. We produce super-localization maps of the rabbit renal vasculature with acquisition times between 5.5 s and 0.25 s, and a 4-fold improvement in spatial resolution. We present the unique selectivity of AWSALM in visualizing specific vascular branches and downstream microvasculature, and we show super-localized kidney structures in systole (0.25 s) and diastole (0.25 s) with fast-AWSALM outdoing microbubble based ULM. In conclusion, we demonstrate the feasibility of fast and selective measurement of microvascular dynamics in vivo with subwavelength resolution using ultrasound and acoustically activatable nanodroplet contrast agents.
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Conference paperHong Y, Taengnoi N, Bottrill KRH, et al., 2023,
Experimental investigation of BDFA-based O-band direct-detection transmission using an optical recirculating loop.
, Pages: 10978-10990We implemented a bismuth-doped fiber amplifier (BDFA) based optical recirculating loop to investigate the performance of amplified O-band transmission over appreciable distances. Both single-wavelength and wavelength-division multiplexed (WDM) transmission were studied, with a variety of direct-detection modulation formats. We report on (a) transmission over lengths of up to 550 km in a single-channel 50-Gb/s system operating at wavelengths ranging from 1325 nm to 1350 nm, and (b) rate-reach products up to 57.6 Tb/s-km (after accounting for the forward error correction redundancy) in a 3-channel system.
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Journal articleGleneadie HJJ, Fernandez-Ruiz B, Sardini A, et al., 2023,
Endogenous bioluminescent reporters reveal a sustained increase in utrophin gene expression upon EZH2 and ERK1/2 inhibition
, COMMUNICATIONS BIOLOGY, Vol: 6 -
Journal articleMcCall MW, Koufidis SF, 2023,
Broadband Bragg phenomenon in a uniform birefringent medium
, OPTICS LETTERS, Vol: 48, Pages: 1096-1099, ISSN: 0146-9592 -
Journal articleTawy G, Minassian A, Damzen MJ, 2023,
Power-scaled CW Alexandrite lasers
, APPLIED PHYSICS B-LASERS AND OPTICS, Vol: 129, ISSN: 0946-2171 -
Journal articleDvinskikh L, Sparks H, Brito L, et al., 2023,
Remote-refocusing light-sheet fluorescence microscopy enables 3D imaging of electromechanical coupling of hiPSC-derived and adult cardiomyocytes in co-culture
, Scientific Reports, Vol: 13, Pages: 1-14, ISSN: 2045-2322Improving cardiac function through stem-cell regenerative therapy requires functional and structural integration of the transplanted cells with the host tissue. Visualizing the electromechanical interaction between native and graft cells necessitates 3D imaging with high spatio-temporal resolution and low photo-toxicity. A custom light-sheet fluorescence microscope was used for volumetric imaging of calcium dynamics in co-cultures of adult rat left ventricle cardiomyocytes and human induced pluripotent stem cell-derived cardiomyocytes. Aberration-free remote refocus of the detection plane synchronously to the scanning of the light sheet along the detection axis enabled fast dual-channel 3D imaging at subcellular resolution without mechanical sample disturbance at up to 8 Hz over a ∼300 µm × 40 µm × 50 µm volume. The two cell types were found to undergo electrically stimulated and spontaneous synchronized calcium transients and contraction. Electromechanical coupling improved with co-culture duration, with 50% of adult-CM coupled after 24 h of co-culture, compared to 19% after 4 h (p = 0.0305). Immobilization with para-nitroblebbistatin did not prevent calcium transient synchronization, with 35% and 36% adult-CM coupled in control and treated samples respectively (p = 0.91), indicating that electrical coupling can be maintained independently of mechanotransduction.
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Journal articleDvinskikh L, Sparks H, MacLeod K, et al., 2023,
High-speed 2D light-sheet fluorescence microscopy enables quantification of spatially varying calcium dynamics in ventricular cardiomyocytes
, Frontiers in Physiology, Vol: 14, Pages: 1-14, ISSN: 1664-042XIntroduction: Reduced synchrony of calcium release and t-tubule structure organization in individual cardiomyocytes has been linked to loss of contractile strength and arrhythmia. Compared to confocal scanning techniques widely used for imaging calcium dynamics in cardiac muscle cells, light-sheet fluorescence microscopy enables fast acquisition of a 2D plane in the sample with low phototoxicity.Methods: A custom light-sheet fluorescence microscope was used to achieve dual-channel 2D timelapse imaging of calcium and the sarcolemma, enabling calcium sparks and transients in left and right ventricle cardiomyocytes to be correlated with the cell microstructure. Imaging electrically stimulated dual-labelled cardiomyocytes immobilized with para-nitroblebbistatin, a non-phototoxic, low fluorescence contraction uncoupler, with sub-micron resolution at 395 fps over a 38 μm × 170 µm FOV allowed characterization of calcium spark morphology and 2D mapping of the calcium transient time-to-half-maximum across the cell.Results: Blinded analysis of the data revealed sparks with greater amplitude in left ventricle myocytes. The time for the calcium transient to reach half-maximum amplitude in the central part of the cell was found to be, on average, 2 ms shorter than at the cell ends. Sparks co-localized with t-tubules were found to have significantly longer duration, larger area and spark mass than those further away from t-tubules.Conclusion: The high spatiotemporal resolution of the microscope and automated image-analysis enabled detailed 2D mapping and quantification of calcium dynamics of n = 60 myocytes, with the findings demonstrating multi-level spatial variation of calcium dynamics across the cell, supporting the dependence of synchrony and characteristics of calcium release on the underlying t-tubule structure.
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Journal articleDamzen M, Xiao H, Jiang X, 2023,
Alexandrite lasers with blue-diode-pumping
, Optics Express, Vol: 31, Pages: 5832-5842, ISSN: 1094-4087The availability of high-power and high-brightness blue diode lasers makes them attractive as low-cost pump sources for broadly tunable Alexandrite lasers. In this paper we investigate the performance of an Alexandrite laser pumped by a high-power fiber-delivered blue diode module. Output power 1.84 W is achieved, the highest power from blue diode pumped Alexandrite to date. Excellent pump absorption is demonstrated of scrambled pump polarization on both a-axis and b-axis of Alexandrite crystal. Wavelength tuning and dual wavelength operation is produced using the self-birefringent filtering of the Brewster-cut Alexandrite crystal. An analysis is made of laser efficiency and mode formation including the creation of higher-order Laguerre-Gaussian vortex modes (LG01 and LG02). Performance is compared to red diode pumping and prospects for further optimization and power-scaling are discussed.
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Journal articleWang Y, Wang S, Halder A, et al., 2023,
(INVITED) Bi-doped optical fibers and fiber amplifiers
, Optical Materials: X, Vol: 17Bismuth (Bi)-doped aluminosilicate, phosphosilicate, germanosilicate and high (⩾50 mol%) germanosilicate fibers have shown luminescence around 1.15 μm, 1.3 μm, 1.45 μm and 1.7 μm, respectively. Bi-doped fibers have paved the way for developing optical amplifiers and fiber lasers in the wavelength region of 1150–1500 nm and 1600–1700 nm, where it can serve a wide range of applications in astronomy, imaging, medicine and advanced optical communications. However, spectroscopic study is required to understand the nature of near-infrared (NIR)-emitting Bi active centers (BACs) to improve the efficiency of Bi-doped fiber amplifiers and lasers. In this paper, we review the luminescence properties of Bi-doped glasses as well as Bi-doped fibers with aluminosilicate, phosphosilicate, and germanosilicate glass hosts. Absorption and emission cross-sections of Bi-doped phosphosilicate fibers are reported. In addition, we review the current state of the art of Bi-doped fiber amplifiers development in the second telecom window (O-band) and in the E-band and S-band for the next-generation high-capacity optical communications.
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Journal articleTaylor JR, 2023,
Fiber Laser Driven Three-Micron Source Development Based on Difference Frequency Generation
, OPTOELECTRONICS INSTRUMENTATION AND DATA PROCESSING, Vol: 59, Pages: 18-27, ISSN: 8756-6990 -
Journal articleDarling C, Davis SPX, Kumar S, et al., 2023,
Single-shot optical projection tomography for high-speed volumetric imaging of dynamic biological samples
, JOURNAL OF BIOPHOTONICS, Vol: 16, ISSN: 1864-063X -
Journal articleBattle RA, Chandran AM, Runcorn TH, et al., 2023,
Mid-infrared difference-frequency generation directly pumped by a fiber four-wave mixing source
, OPTICS LETTERS, Vol: 48, Pages: 387-390, ISSN: 0146-9592- Author Web Link
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- Citations: 1
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Conference paperLiang M, Minassian A, Damzen M, 2023,
Acousto-optic Q-switched Alexandrite Laser with Wavelength Tuning and Second Harmonic Generation
Alexandrite is an excellent solid-state laser medium for high-power Q-switched operation due to its high thermal conductivity (23 Wm−1K−1) and long upper-state lifetime (262 µs). Whilst electro-optically Q-switched (EO-QS) Alexandrite lasers with red diode-pumping have been demonstrated [1], this work presents results of the first ever Acousto-Optic Q-switched (AO-QS) Alexandrite laser. In addition, we present results of the conversion of the output of the wavelength-tuned AO-QS laser to tunable ultraviolet by second harmonic generation.
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Conference paperXiao H, Jiang X, Damzen MJ, 2023,
Alexandrite Lasers Operating with High-power Blue-diode-pumping
Alexandrite is a solid-state laser with excellent thermal properties for power scaling and together with its broad wavelength tunability (~720-820 nm) provides potential for applications in remote sensing, biophotonics, and quantum technologies. Until recently, diode pumping has been predominantly performed by red semiconductor lasers near 638nm, however, blue diodes operating near 445nm have higher emitter power, higher-brightness and low-cost ($/W) making them attractive as alternative pump sources for Alexandrite lasers. This work focuses on the investigation of Alexandrite lasers pumped by a high-power fibre-delivered blue diode module achieving record blue-pumped powers and provides in-depth laser performance characterisation.
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Conference paperTawy G, Davidson NP, Mennea PL, et al., 2023,
375-400nm UV Generation via an Alexandrite laser and Zn-indiffused MgO-doped PPLN Waveguides
Laser sources in the UV-blue region at around 350-400 nm are of increasing importance for applications including quantum technologies and material processing. To operate in a wide range of environments, these laser sources need to be compact, robust and have low-power and minimal cooling requirements. The work presented here looks at combining rapid progress in two areas of laser development for addressing these applications. Diode-pumped Alexandrite lasers have become a low-cost and simple approach to achieving multi-watt powers in the near-infrared at around 720-800 nm [1]. Zn-indiffused MgO-doped PPLN waveguides have recently demonstrated impressive second harmonic generation (SHG) conversion efficiencies in the near-infrared [2] as well as conversion into the UV with doubling to 390 nm recently reported [3].
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Conference paperKrawczyk B, Kudlinski A, Battle RA, et al., 2023,
Four-Wave Mixing Enhancement in a Yb-doped Photonic Crystal Fiber
Degenerate four-wave mixing (FWM) in photonic crystal fibers (PCFs) is an effective method for generating near-infrared coherent light across a wide range of wavelengths using compact, low-cost ytterbium or neodymium pump lasers [1]. For many applications, e.g. multiphoton microscopy, increasing the peak power of the short wavelength anti-Stokes sideband generated by FWM is advantageous. Several works have sought to scale the anti-Stokes peak power by optimizing the pump laser and PCF structure but the pump to anti-Stokes conversion efficiency remains limited by pump depletion [2]. By introducing Yb-doping into the core of a PCF designed for FWM, we propose to mitigate the effects of pump depletion by using stimulated emission to replenish the FWM pump energy that is transferred to the anti-Stokes (and Stokes) as it propagates down the fiber. Here we present a novel double-clad PCF with a Yb-doped core and demonstrate, for the first time to the best of our knowledge, that amplification of FWM pump pulses through stimulated emission increases the anti-Stokes power generated by FWM.
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Conference paperBattle RA, Simon D, Xiang Y, et al., 2023,
Cellular Level Resolution Ambient Mass Spectrometry Imaging using 3 µm Laser Ablation
Tissue can be rapidly ablated by lasers with wavelength around λ = 3 µm, which is strongly absorbed by water [1]. Mass spectrometry (MS) analysis of the ablated material can subsequently provide rich chemical data about the molecular content of the tissue. In mass spectrometry imaging (MSI), spatially resolved molecular data is obtained from a sample by collecting multiple mass spectra. From these individual spectra, the spatial distribution of molecules of interest can be mapped. In this work, we report a single-cell level resolution mass spectrometry imaging platform based on laser ablation using a parametric 3 µm laser source and Rapid Evaporative Ionization Mass Spectrometry (REIMS) [2]. The laser source is specifically developed to have high beam quality and sub-ns duration. This has allowed us to overcome previous ambient MSI spatial resolution limits, a key step to translating the benefits of MS analysis to clinical applications.
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Conference paperTaengnoi N, Bottrill KRH, Hong Y, et al., 2023,
Demonstration of 100-km Long O-band WDM Amplified Coherent Transmission
O-band WDM 100-Gb/s/λ dual-polarization quadrature phase shift keying transmission is demonstrated over a 100-km link, with gain provided by bismuth-doped fiber amplifiers. Two different channel spacings are studied: 0.6nm and 10nm.
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Conference paperTaengnoi N, Bottrill KRH, Hong Y, et al., 2023,
Coherent O-band Transmission of 4×25 GBd DP-16QAM Channels Over a 50 km BDFA-Equipped Link
The first WDM O-band coherent transmission experiment in a BDFA-amplified link is reported. Four 25 GBd DP16QAM channels (4×200 Gb/s) are transmitted over 50 km of fiber, occupying a bandwidth of 4.7 THz.
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Conference paperWang Y, Halder A, Richardson DJ, et al., 2023,
A highly temperature-insensitive Bi-doped fiber amplifier in the E+S-band with 20 dB flat gain from 1435-1475 nm
We report a bismuth-doped fiber amplifier operating in the E+S-band providing a 20.5±1dB flat gain with 5.5±2dB NF from 1435-1475nm for -10dBm input signal. The gain coefficient and temperature-dependent-gain coefficient are 0.065dB/mW and -0.005±0.001dB/, respectively.
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Conference paperBattle RA, Simon D, Xiang Y, et al., 2023,
High resolution mass spectrometry imaging using 3 micron laser ablation
, ISSN: 1605-7422We report a single-cell level resolution (≤10 µm), laser desorption-based mass spectrometry imaging platform. An optical parametric amplifier is used to generate ∼100 ps, 200 nJ pulses at around 3 µm with a maximum repetition rate of 500 kHz. The pulses are tightly focussed on to fresh frozen animal tissue samples with a thickness of 10 µm. Small volumes of tissue are readily ablated by the laser and are subsequently chemically analyzed using a Rapid Evaporative Ionization Mass Spectrometry (REIMS) source installed on a time of flight mass analyzer. Raster scanning the samples through the laser focus enables the acquisition of mass spectrometry data which can be processed into images with pixel size 10 µm without oversampling, corresponding to cellular level resolution.
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