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  • Conference paper
    Thipparapu NK, Alam S, Wang Y, Shankar P, Richardson DJ, Sahu JKet al., 2021,

    Tunable Actively Mode-locked Bi-doped O-band Fibre Laser

    Widely tunable pulsed fibre laser sources in the O-band (1260-1360nm) are of interest in a variety of fields including spectroscopy, optical communication, time-resolved measurements, and optical system diagnostics [1]. Furthermore, major constituents of biological tissues such as water, oxyhemoglobin, and melanin exhibit minimum optical loss windows in the 1300nm band pointing to applications in medicine [2]. Bi-doped phoshosilicate fibres (BPSFs) have recently been investigated as a promising medium to develop new wavelength lasers and amplifiers in the O-band [3]. They exhibit broad emission spectra which is an important characteristic for developing widely tunable pulsed laser sources [4]. However, to the best of our knowledge, there are no reports of tunable pulsed Bi-doped fibre lasers around 1300nm. Here, we demonstrate an actively tunable mode-locked Bi-doped fibre laser (ML-BDFL) operating in the wavelength region from 1300-1370nm.

  • Conference paper
    Hong Y, Bottrill KRH, Wang Y, Thipparapu NK, Sahu JK, Petropoulos P, Richardson DJet al., 2021,

    O+E-band Transmission over 50-km SMF using A Broadband Bismuth Doped Fibre Amplifier

    Ultra-wideband (UWB) transmission over single-mode fibres (SMFs) is an attractive route in optical transmission, since it allows the available low-loss bandwidth offered in conventional silica SMFs to be utilised more efficiently [1] - [3]. However, data transmission beyond a single span over wavelengths outside the erbium gain band remains challenging, primarily because of the lack of suitable optical amplifiers. Recently, the emergence of bismuth-doped fibre amplifiers (BDFAs) has shown considerable potential for amplified high-speed data communications outside the C+L-bands [4] - [8]. An exciting recent work has reported the development of a BDFA exhibiting a 115nm gain bandwidth, covering the range 1345-1460nm [8]. In this paper, we demonstrate the first data transmission experiment utilising this BDFA as a booster amplifier, and we study its performance across this entire gain band.

  • Conference paper
    Wang Y, Thipparapu NK, Richardson DJ, Sahu JKet al., 2021,

    High Gain Bi-Doped Fiber Amplifier Operating in the E-band with a 3-dB Bandwidth of 40nm

    We report a double-pass bismuth-doped fiber amplifier operating in the E-band providing 38dB gain with 6dB NF for -23dBm input signal at 1430nm. The amplifier 3-dB bandwidth and temperature-dependent-gain coefficient are 40nm and -0.006dB/, respectively.

  • Journal article
    Gratus J, Kinsler P, McCall MW, 2021,

    Temporary Singularities and Axions: An Analytic Solution that Challenges Charge Conservation

    , ANNALEN DER PHYSIK, Vol: 533, ISSN: 0003-3804
  • Journal article
    Hong Y, Bottrill KRH, Taengnoi N, Thipparapu NK, Wang Y, Sahu JK, Richardson DJ, Petropoulos Pet al., 2021,

    Numerical and experimental study on the impact of chromatic dispersion on O-band direct-detection transmission.

    , Appl Opt, Vol: 60, Pages: 4383-4390

    The recent emergence of efficient O-band amplification technologies has enabled the consideration of O-band transmission beyond short reach. Despite the O-band being a low chromatic dispersion (CD) window, the impact of CD will become increasingly significant when extending the reach of direct-detection (DD) systems. In this work, we first numerically investigate the 3-dB bandwidth of single-mode fibers (SMF) and the CD-restricted transmission reach in intensity-modulation DD systems, confirming the significant difference between low- and high-dispersion O-band wavelengths. We then carry out experimental transmission studies over SMF for distances of up to 70 km at two different wavelengths, the low-dispersion 1320 nm and the more dispersive 1360 nm, enabled by the use of an O-band bismuth-doped fiber amplifier as a preamplifier at the receiver. We compare three 50-Gb/s optical DD formats, namely, Nyquist on-off keying (OOK), Nyquist 4-ary pulse amplitude modulation (PAM4) and Kramers-Kronig detection-assisted single-sideband quadrature phase shift keying (KK-QPSK) half-cycle subcarrier modulation. Our results show that at both wavelengths, OOK and QPSK exhibit better bit error rate performance than PAM4. When transmitting over 70-km of SMF at the less dispersive wavelength of 1320 nm, 50-Gb/s OOK modulation offers more than 1.5-dB optical power sensitivity improvement at the photodiode (PD) compared to 50-Gb/s QPSK. Conversely, at 1360 nm, the required optical power to the PD can be reduced by more than 3 dB by using QPSK instead of OOK.

  • Journal article
    Cannon T, Lagarto J, Dyer B, Garcia Castano E, Kelly D, Peters N, Lyon A, French P, Dunsby Cet al., 2021,

    Characterisation of NADH fluorescence properties under one-photon excitation with respect to temperature, pH and binding to lactate dehydrogenase

    , Optical Society of America Continuum, Vol: 4, Pages: 1610-1625

    Reduced nicotinamide adenine dinucleotide (NADH) is the principal electron donor in glycolysis and oxidative metabolism and is thus recognized as a key biomarker for probing metabolic state. While the fluorescence characteristics of NADH have been investigated extensively, there are discrepancies in the published data due to diverse experimental conditions, instrumentation and microenvironmental parameters that can affect NADH fluorescence. Using a cuvette-based time-resolved spectrofluorimeter employing one-photon excitation at 375 nm, we characterized the fluorescence intensity, lifetime, spectral response, anisotropy and time-resolved anisotropy of NADH in aqueous solution under varying microenvironmental conditions, namely temperature, pH, and binding to lactate dehydrogenase (LDH). Our results demonstrate how temperature, pH, and binding partners each impact the fluorescence signature of NADH and highlight the complexity of the fluorescence data when different parameters produce competing effects. We hope that the data presented in this study will provide a reference for potential sources of variation in experiments measuring NADH fluorescence.

  • Journal article
    Taengnoi N, Bottrill KRH, Hong Y, Wang Y, Thipparapu NK, Sahu JK, Petropoulos P, Richardson DJet al., 2021,

    Experimental characterization of an o-band bismuth-doped fiber amplifier.

    , Opt Express, Vol: 29, Pages: 15345-15355

    The recent emergence of bismuth-doped fiber amplifiers (BDFAs) offers the potential to transmit high-speed WDM signals over long distances in the O-band spectral region, thereby greatly enhancing the scope of systems utilizing these wavelengths. In this paper, we present a comprehensive experimental study on several basic characteristics of an O-band BDFA based on a phosphosilicate optical fiber, including the frequency-dependent noise figure, gain tilt (static and dynamic), transient response, and polarization dependent gain. We discuss our findings and their implications on the use of BDFA technology in high bit-rate multichannel systems.

  • Journal article
    Murray RT, Chandran AM, Battle RA, Runcorn TH, Schunemann PG, Zawilski KT, Guha S, Taylor JRet al., 2021,

    Seeded optical parametric generation in CdSiP2 pumped by a Raman fiber amplifier at 124  µm

    , Optics Letters, Vol: 46, Pages: 2039-2039, ISSN: 0146-9592

    We report a seeded optical parametric generator (OPG) producing tunable radiation from 4.2–4.6 µm. The seeded OPG employs a 13 mm long CdSiP2 (CSP) crystal cut for non-critical phase-matching, pumped by a nanosecond-pulsed, MHz repetition rate Raman fiber amplifier system at 1.24 µm. A filtered, continuous-wave fiber supercontinuum source at 1.72 µm is used as the seed. The source generates up to 0.25 W of mid-infrared (MIR) idler power with a total pump conversion of 42% (combined signal and idler).

  • Conference paper
    Hong Y, Deligiannidis S, Taengnoi N, Bottrill KRH, Thipparapu NK, Wang Y, Sahu JK, Richardson DJ, Mesaritakis C, Bogris A, Petropoulos Pet al., 2021,

    Performance-enhanced Amplified O-band WDM Transmission using Machine Learning based Equalization

    We investigate the performance of a machine learning-based equalization in an amplified 4×50-Gb/s O-band WDM system. The results show that the scheme offers significant receiver sensitivity improvements over decision-feedback equalization, especially at more dispersive wavelengths.

  • Journal article
    Kerridge-Johns WR, Jaillot J-B, Damzen MJ, 2021,

    Sampling a vortex from a Gaussian beam using a wedge-plate shearing interferometer

    , Applied Optics, Vol: 60, Pages: 3510-3510, ISSN: 1559-128X

    Many vortex-generation techniques have been developed to address a range of potential applications, exploiting their unique amplitude and phase profiles and their possession of orbital angular momentum. In this work, we present what may be the simplest method of vortex beam generation, requiring only a wedged optic: the wedge-plate shearing interferometer (WPSI). We show that the WPSI can reflect a first order Laguerre–Gaussian vortex beam (LG01) with a theoretical purity of >99% from an input fundamental Gaussian beam, with 98% LG01 purity experimentally demonstrated. We demonstrate 1% power conversion with a route to 14%. The monolithic WPSI is a simple, compact, and highly stable device, which can operate at any wavelength that the material is transparent to. We anticipate that it will be useful where sampling a robust, high-purity vortex beam from a Gaussian laser beam is required, including low-cost vortex generation for metrology or education.

  • Conference paper
    Dvinskikh L, Harding S, Sparks H, Gorelik J, MacLeod K, Dunsby Cet al., 2021,

    High speed imaging of calcium dynamics in cardiomyocytes with a flexible light-sheet fluorescence microscope

    , Biophotonics Congress 2021
  • Journal article
    Collart C, Ciccarelli A, Ivanovitch K, Rosewell I, Kumar S, Kelly G, Edwards A, Smith JCet al., 2021,

    The migratory pathways of the cells that form the endocardium, dorsal aortae, and head vasculature in the mouse embryo

    , BMC DEVELOPMENTAL BIOLOGY, Vol: 21, ISSN: 1471-213X
  • Journal article
    Ahmad H, Aidit SN, Ooi SI, Samion MZ, Wang S, Wang Y, Sahu JK, Zamzuri AKet al., 2021,

    1.3 µm dissipative soliton resonance generation in Bismuth doped fiber laser.

    , Sci Rep, Vol: 11

    In this work, a Figure-9 (F9) bismuth-doped fiber laser (BiDFL) operating in the dissipative soliton resonance (DSR) regime is presented. The 1338 nm laser used a BiDF as the active gain medium, while a nonlinear amplifying loop mirror (NALM) in an F9 configuration was employed to obtain high energy mode-locked pulses. The wave breaking-free rectangular pulse widened significantly in the time domain with the increase of the pump power while maintaining an almost constant peak power of 0.6 W. At the maximum pump power, the mode-locked laser delivered a rectangular-shaped pulse with a duration of 48 ns, repetition rate of 362 kHz and a radio-frequency signal-to-noise ratio of more than 60 dB. The maximum output power was recorded at around 11 mW with a corresponding pulse energy of 30 nJ. This is, to the best of the author's knowledge, the highest mode-locked pulse energy obtained at 1.3 μm as well as the demonstration of an NALM BiDFL in a F9 configuration.

  • Conference paper
    Murray RT, Chandran AM, Battle RA, Runcorn TH, Schunemann PG, Zawilski KT, Guha S, Taylor JRet al., 2021,

    Seeded optical parametric generation in CdSiP2 pumped by a nanosecond pulsed, MHz repetition rate Raman fiber amplifier at 1.24 µm

    , Nonlinear Frequency Generation and Conversion: Materials and Devices XX, Publisher: SPIE, Pages: 1-10

    We report a CdSiP2 (CSP) based seeded optical parametric generator (OPG), emitting sub-nanosecond duration, 3 MHz repetition rate, wavelength tunable mid-infrared (MIR) light at 4.2-4.6 μm. We generate up to 0.25 W at 4.2 μm with a total pump conversion efficiency of 42%. The OPG is pumped by a 1.24 μm Raman fiber amplifier system. This is the first demonstration of pumping CSP with a Raman fiber source in this region, and we show that Raman fiber sources in the near-infrared (NIR) are ideal pump sources for non-critically phasematched (NCPM) CSP devices. Pumping CSP at 1.24 μm permits the use of NCPM whilst decreasing the negative effects of both two-photon absorption and linear absorption losses, when compared to conventional 1 μm pumping. This offers a potential advantage for MIR power scaling of CSP parametric devices due to a reduced thermal load in the crystal from residual pump absorption. The OPG is seeded with a continuous-wave fiber supercontinuum source emitting radiation in the 1.7 μm region, to lower the threshold pump intensity required for efficient conversion. NCPM and temperature tuning of the crystal allow for simple wavelength tuning of the idler radiation. We report on laser damage induced by elevated crystal temperatures, which we propose is linked to the decrease in CSP bandgap energy with increasing temperature.

  • Journal article
    Kondo H, Ratcliffe CDH, Hooper S, Ellis J, MacRae J, Hennequart M, Dunsby CW, Anderson K, Sahai Eet al., 2021,

    Single-cell resolved imaging reveals intra-tumor heterogeneity in glycolysis, transitions between metabolic states, and their regulatory mechanisms

    , CELL REPORTS, Vol: 34, ISSN: 2211-1247
  • Journal article
    Wang Y, Thipparapu NK, Richardson DJ, Sahu JKet al., 2021,

    Ultra-Broadband Bismuth-Doped Fiber Amplifier Covering a 115-nm Bandwidth in the O and e Bands

    , Journal of Lightwave Technology, Vol: 39, Pages: 795-800, ISSN: 0733-8724

    In this article, we experimentally demonstrate an all-fiber optical amplifier using Bi-doped phosphosilicate fiber (BPSF) operating in both the O-band and the E-band, providing >20 dB gain from 1345 to 1460 nm for an input signal power of -23 dBm. A maximum gain of 31 dB with a noise figure (NF) of 4.8 dB was achieved at 1420 nm for -23 dBm input signal, whereas for an input signal power of -10 dBm it was 26 dB with a NF of 5.3 dB. The in-band OSNR of the proposed Bi-doped fiber amplifier (BDFA) was >22 dB from 1345 to 1460 nm for a -23 dBm input signal. The gain coefficient was found to be 0.04 dB/mW for a -23 dBm input signal. Also, the temperature dependent gain and NF performance of the BDFA within -40 to +60 °C were characterized. The temperature-dependent-gain (TDG) coefficient for a -23 dBm input signal was found to be -0.015 dB/°C at a signal wavelength of 1420 nm where the BDFA gain is maximum, while for an input signal power of -10 dBm it was -0.01 dB/°C at 1420 nm. The TDG coefficient of the proposed BDFA from 1350-1460 nm was in the range from -0.079 to -0.008 dB/°C. The BDFA gain and NF performance were also measured and compared using BPSFs with different unsaturable loss (UL) characteristics.

  • Journal article
    Jones DC, Alexandrov Y, Curry N, Kumar S, Lanigan PMP, McGuinness CD, Dale MW, Twitchen DJ, Fisher D, Neil MAA, Dunsby C, French PMWet al., 2021,

    Multidimensional spectroscopy and imaging of defects in synthetic diamond: excitation-emission-lifetime luminescence measurements with multiexponential fitting and phasor analysis

    , Journal of Physics D: Applied Physics, Vol: 54, Pages: 1-13, ISSN: 0022-3727

    We report the application of phasor analysis and nonlinear iterative fitting to complex spatial and spectroscopic luminescence decay data obtained from multidimensional microscopy of a CVD diamond grown on a HPHT substrate. This spectral and lifetime-resolved analysis enabled spatial mapping of variations in concentrations of nitrogen vacancy (NV) defects in both charge states and the quenching of NV− defects, as well as the identification of SiV− luminescence. These imaging and spectroscopic modalities may be important for reliable fabrication of quantum devices based on such defects in diamond, which will require well-defined and characterised quantum electronic properties.

  • Conference paper
    Tawy G, Minassian A, Damzen MJ, 2021,

    8.5W linear and 3.6W Ring TEM<inf>00</inf> diode-pumped alexandrite lasers

  • Conference paper
    Berk J, Paterson C, Foreman MR, 2021,

    Tracking using surface plasmon leakage radiation speckle

    An approach capable of label-free sensing and tracking of single nanoscale particles using interference between light scattered from the particle and a plasmon leakage radiation speckle field is introduced. Simulations show nanometre level tracking accuracy.

  • Conference paper
    Darling C, Davis SPX, Kumar S, French PMW, McGinty Jet al., 2021,

    Single-Shot Volumetric Imaging Using Optical Projection Tomography

    , ISSN: 1605-7422

    We present a single-shot volumetric imaging method, utilising optical projection tomography. We record projections simultaneously, implementing compressive sensing and machine learning to record up to 70 (camera limited) 1x1x1.9mm volumes/second.

  • Conference paper
    Lightley J, Görlitz F, Kumar S, Kalita R, Kolbeinsson A, Garcia E, Alexandrov Y, Bousgouni V, Wysoczanski R, Barnes P, Donelly L, Bakal C, Dunsby C, Neil MAA, Flaxman S, French PMWet al., 2021,

    ROBUST OPTICAL AUTOFOCUS SYSTEM UTILIZING NEURAL NETWORKS APPLIED TO AUTOMATED MULTIWELL PLATE STORM MICROSCOPY

    , ISSN: 1605-7422

    We present a robust, low-cost neural network-based optical autofocus system that can operate over a range of ±100µm with submicron precision, enabling automated high-content super-resolved imaging with a 1.3 NA objective lens.

  • Conference paper
    Kalita R, Lightley J, Kumar S, Alexandrov Y, Garcia E, Flanagan W, Neil MAA, Dunsby C, French PMWet al., 2021,

    Single-shot quantitative phase contrast using polarisation-resolved differential phase microscopy

    , ISSN: 1605-7422

    We present a robust, low-cost single-shot implementation of differential phase microscopy utilising a polarisation-sensitive camera to simultaneously acquire 4 images from which the phase gradients and quantitative phase image can be calculated.

  • Conference paper
    Chandran AM, Battle RA, Murray RT, Runcorn TH, Taylor JRet al., 2021,

    743 nm Source by SHG of a Cascaded Phosphosilicate Raman Fiber Amplifier

    We demonstrate a nanosecond-pulsed 743 nm source by second harmonic generation of a cascaded phosphosilicate Raman fiber amplifier operating at 1485 nm. The source emits >1 W of 743 nm average power at a 5 MHz repetition rate.

  • Conference paper
    Geberbauer JWT, Kerridge-Johns WR, Damzen MJ, 2021,

    &gt;30 W vortex laser using vortex output coupler

  • Conference paper
    Tawy G, Minassian A, Damzen MJ, 2021,

    8.5W linear and 3.6W Ring TEM<inf>00</inf> diode-pumped alexandrite lasers

  • Conference paper
    Thipparapu NK, Alam S, Wang Y, Shankar P, Richardson DJ, Sahu JKet al., 2021,

    Tunable actively mode-locked bi-doped O-band fibre laser

  • Conference paper
    Wang Y, Thipparapu NK, Richardson DJ, Sahu JKet al., 2021,

    High gain Bi-doped fiber amplifier operating in the E-band with a 3-dB bandwidth of 40nm

    We report a double-pass bismuth-doped fiber amplifier operating in the E-band providing 38dB gain with 6dB NF for -23dBm input signal at 1430nm. The amplifier 3-dB bandwidth and temperature-dependent-gain coefficient are 40nm and -0.006dB/?, respectively.

  • Conference paper
    Hong Y, Taengnoi N, Bottrill KRH, Thipparapu NK, Wang Y, Sahu JK, Richardson DJ, Petropoulos Pet al., 2021,

    Experimental Demonstration of 50-Gb/s/λ O-band CWDM Direct-Detection Transmission over 100-km SMF

    , ISSN: 2162-108X

    We demonstrate the first single-sideband 50-Gb/s/λ coarse WDM direct-detection transmission in the O-band. It is shown that the Kramers-Kronig-detection assisted single-sideband transmission exhibits significant OSNR sensitivity improvements over double-sideband transmission, enabling up to 100-km reach.

  • Conference paper
    Wang Y, Thipparapu NK, Richardson DJ, Sahu Jet al., 2021,

    Bi-doped fiber amplifiers for ultra-wideband optical communication systems

    , ISSN: 1099-4742

    Bismuth (Bi)-doped fibers provide great potential for developing optical amplifiers in the low-loss transmission window, 1250-1650nm, of silica fibers. In this paper, we review recent progress of Bi-doped fiber amplifiers (BDFAs) covering 1345-1460nm spectral region. We also present the BDFA performance at different ambient temperatures.

  • Conference paper
    Hong Y, Bottrill KRH, Taengnoi N, Thipparapu NK, Wang Y, Sahu JK, Richardson DJ, Petropoulos Pet al., 2021,

    Amplified O-band direct-detection transmission using bismuth-doped fiber amplifiers

    , ISSN: 0277-786X

    The recent emergence of bismuth-doped fiber amplifiers (BDFAs) enables the reach extension of high-speed O-band communication links. In this work, our recent efforts on amplified O-band direct-detection (DD) transmission using BDFAs are reviewed. We first present the performance of a four-channel O-band coarse wavelength-division multiplexed (CWDM) transmission over 50-km length of single-mode fiber (SMF), showing that the chromatic dispersion (CD) which has long been neglected in O-band transmission, will degrade the transmission performance of dispersive O-band channels. In this context, we quantify the relative benefits of different DD formats at 50 Gb/s over up to 70-km length of SMF in a BDFA pre-amplified O-band system. The considered formats include Nyquist on-off keying (OOK), Nyquist 4-ary pulse amplitude modulation (PAM4), and Kramers-Kronig (KK) detection assisted subcarrier modulation using quadrature phase-shift keying (QPSK), and they are evaluated over both the low CD 1320-nm wavelength and the more dispersive 1360-nm wavelength. It is demonstrated that OOK exhibits the best receiver sensitivity over all distances up to 70 km at the 1320-nm channel, whereas KK-QPSK achieves the optimal transmission performance at the 1360-nm wavelength when the reach is extended beyond 50 km. We consider that our results provide useful insights into possible future implementations of longer-reach O-band WDM systems.

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