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  • 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.

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

    >30 W vortex laser using vortex output coupler

  • Journal article
    Himabindu DD, Kumar SP, 2021,

    A Survey on Computer Vision Architectures for Large Scale Image Classification using Deep Learning

    , International Journal of Advanced Computer Science and Applications, Vol: 12, Pages: 105-120, ISSN: 2158-107X

    The advancement in deep learning is increasing day-by-day from image classification to language understanding tasks. In particular, the convolution neural networks are revived and shown their performance in multiple fields such as natural language understanding, signal processing, and computer vision. The property of translational invariance for convolutions has made a huge advantage in the field of computer vision to extract feature invariances appropriately. When these convolutions trained using back-propagation tend to prove their results ability to outperform existing machine vision techniques by overcoming the various hand-engineered machine vision models. Hence, a clear understanding of current deep learning methods is crucial. These convolution neural networks have proven to show their performance by attaining state-of-the-art performance in computer vision over years when applied on humongous data. Hence in this survey, we detail a set of state-of-the-art models in image classification evolved from the birth of convolutions to present ongoing research. Each state-of-the-art model evolved in the successive year is illustrated with architecture schema, implementation details, parametric tuning and their performance. It is observed that the neural architecture construction i.e. a supervised approach for an image classification problem is evolved as data construction with cautious augmentations i.e., a self-supervised approach. A detailed evolution from neural architecture construction to augmentation construction is illustrated by provided appropriate suggestions to improve the performance. Additionally, the implementation details and the appropriate source for the execution and reproducibility of results are tabulated.

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

    CdSiP<inf>2</inf> based mid-infrared optical parametric sources pumped with Raman fiber amplifiers

    CdSiP2 (CSP) is a nonlinear optical semiconductor which can phasematch pump wavelengths throughout the near-infrared (NIR) to generate mid-infrared (MIR) light through parametric three-wave mixing. In this work, we investigate the unique combination of NIR Raman fiber amplifiers around 1.24 µm and non-critical phasematching in CSP, to demonstrate tunable sources in the 4-5 µm MIR region.

  • Conference paper
    Sparks H, Almagro J, Behrens A, Salbreux G, Dunsby Cet al., 2021,

    Dual-view oblique plane microscopy

    Dual-view Oblique Plane Microscopy (dOPM) enables single-objective multi-view light-sheet fluorescence microscopy. This talk introduces the dOPM concept and demonstrates optical resolution performance with exemplar 3D datasets of fluorescence bead samples and fixed multicellular spheroids.

  • 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

  • Journal article
    Kumar S, Bhuyan MK, Iwahori Y, 2021,

    Multi-level uncorrelated discriminative shared Gaussian process for multi-view facial expression recognition

    , Visual Computer, Vol: 37, Pages: 143-159, ISSN: 0178-2789

    In multi-view facial expression recognition, discriminative shared Gaussian process latent variable model (DS-GPLVM) gives better performance than that of linear and nonlinear multi-view learning-based methods. However, Laplacian-based prior used in DS-GPLVM only captures topological structure of data space without considering the inter-class separability of the data, and hence the obtained latent space is suboptimal. So, we propose a multi-level uncorrelated DS-GPLVM (ML-UDSGPLVM) model which searches a common uncorrelated discriminative latent space learned from multiple observable spaces. A novel prior is proposed, which not only depends on the topological structure of the intra-class data, but also on the local-between-class-scatter-matrix of the data onto the latent manifold. The proposed approach employs an hierarchical framework, in which, expressions are first divided into three sub-categories. Subsequently, each of the sub-categories are further classified to identify the constituent basic expressions. Experimental results show that the proposed method outperforms state-of-the-art methods in many instances.

  • Conference paper
    Deepak MD, Karthik P, Kumar SS, Deepak NAet al., 2021,

    Comparative Study of Feature Extraction Using Different Transform Techniques in Frequency Domain

    , Pages: 2835-2846, ISSN: 1876-1100

    The compressed sensing is a mathematical approach of reconstructing a signal that is acquired from the dimensionally reduced data coefficients/less number of samples, i.e., less than the Niquist rate. The data coefficients are high-frequency components and low-frequency components. The high-frequency components are due to the rapid changes in the images (edges) and low-frequency correspond are due to slow varying information (continuous surface). The idea is to retain only low-frequency components, i.e., the significant components that constitute the compressed signal. This compressed signal is the sparse signal which is so helpful during medical scenario. During the Medical Resonance Imaging (MRI) scans, the patient undergoes many kinds difficulties like uncomfortness, patients are afraid of the scanning devices, he/she cannot be stable or changing his body positions slightly. Due to all these reasons, there can be a chance of acquiring only the less number of samples during the process of MRI scan. Even though the numbers of samples is less than the Nyquist rate, the reconstruction is possible by using the compressed sensing technique. The work has been carried out in the frequency domain to achieve the sparsity. The comparative study is done on percentage of different levels of sparsity of the signal. This can be verified by using peak signal-to-noise ratio (PSNR), root mean square error (RMSE), and structural similarity (SSIM) methods which are calculated between the reference image and the reconstructed image.

  • Conference paper
    Lightley J, Gorlitz 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

    , European Conferences on Biomedical Optics - Advances in Microscopic Imaging III, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
  • Journal article
    Jones B, McGlone ER, Fang Z, Pickford P, Corrêa IR, Oishi A, Jockers R, Inoue A, Kumar S, Görlitz F, Dunsby C, French PMW, Rutter GA, Tan TM, Tomas A, Bloom SRet al., 2021,

    Genetic and biased agonist-mediated reductions in β-arrestin recruitment prolong cAMP signalling at glucagon family receptors

    , Journal of Biological Chemistry, Vol: 296, Pages: 1-15, ISSN: 0021-9258

    Receptors for the peptide hormones glucagon-like peptide-1 (GLP-1R), glucose-dependent insulinotropic polypeptide (GIPR) and glucagon (GCGR) are important regulators of insulin secretion and energy metabolism. GLP-1R agonists have been successfully deployed for the treatment of type 2 diabetes, but it has been suggested that their efficacy is limited by target receptor desensitisation and downregulation due to recruitment of β-arrestins. Indeed, recently described GLP-1R agonists with reduced β-arrestin-2 recruitment have delivered promising results in preclinical and clinical studies. We therefore aimed to determine if the same phenomenon could apply to the closely related GIPR and GCGR. In HEK293 cells depleted of both β-arrestin isoforms the duration of G protein-dependent cAMP/PKA signalling was increased in response to the endogenous ligand for each receptor. Moreover, in wild-type cells, “biased” GLP-1, GCG and GIP analogues with selective reductions in β-arrestin-2 recruitment led to reduced receptor endocytosis and increased insulin secretion over a prolonged stimulation period, although the latter effect was only seen at high agonist concentrations. Biased GCG analogues increased the duration of cAMP signalling, but this did not lead to increased glucose output from hepatocytes. Our study provides a rationale for development of GLP-1R, GIPR and GCGR agonists with reduced β-arrestin recruitment, but further work is needed to maximally exploit this strategy for therapeutic purposes.

  • Journal article
    Coney A, Damzen M, 2021,

    High-energy diode-pumped alexandrite amplifier development with applications in satellite-based lidar

    , Journal of the Optical Society of America B: Optical Physics, Vol: 38, Pages: 209-219, ISSN: 0740-3224

    Efficient, wavelength-tunable diode-pumped alexandrite laser systems offer the potential for a more versatile, satellite-based lidar source compared to fixed wavelength Nd:YAG systems and non-space compliant lamp-pumped alexandrite. In this paper, we develop a strategy to enable the high-energy operation required for atmospheric lidar based on an efficient diode-pumped Master-Oscillator Power-Amplifier (MOPA) system design. A novel multi-pass ‘diamond’ slab amplifier geometry is introduced alongside the experimental results of the world’s first diode-pumped alexandrite amplifier producing a gain of 2.13 in a demonstration system. A diode-pumped Q-switched alexandrite oscillator is presented with a record-highest pulse energy of 3.80 mJ. Detailed optimisation of a two-stage amplifier design is studied numerically and maximised with temperature, wavelength and pump pulse duration to produce 50 mJ pulse energy. This forms part of an optimised alexandrite MOPA design capable of high pulse energy, showing the future potential of diode pumped alexandrite for satellite-based atmospheric lidar.

  • 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

    , European Conferences on Biomedical Optics - Advances in Microscopic Imaging III, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
  • Conference paper
    Tawy G, Minassian A, Damzen MJ, 2021,

    8.5W Linear and 3.6W Ring TEM<sub>00</sub> Diode-Pumped Alexandrite Lasers

    , Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
  • Conference paper
    Darling C, Davis SPX, Kumar S, French PMW, McGinty Jet al., 2021,

    Single-Shot Volumetric Imaging Using Optical Projection Tomography

    , European Conferences on Biomedical Optics - Advances in Microscopic Imaging III, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
  • Conference paper
    Geberbauer JWT, Kerridge-Johns WR, Damzen MJ, 2021,

    &gt;30 W Vortex Laser Using Vortex Output Coupler

    , Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
  • Journal article
    Ahmad H, Samion MZ, Kamely AA, Wang S, Wang Y, Sahu JKet al., 2020,

    Multiwavelength Brillouin Generation in Bismuth-Doped Fiber Laser with Single- And Double-Frequency Spacing

    , Journal of Lightwave Technology, Vol: 38, Pages: 6886-6896, ISSN: 0733-8724

    Multiwavelength fiber lasers operating in the 1.3 μm wavelength region are of great interest as they complement existing systems in the conventional optical communication band of 1.55 μm. In this work, a multiwavelength Brillouin fiber laser with single- and double-Brillouin frequency spacings operating in 1.3 μm is proposed and demonstrated using a dispersion compensating fiber (DCF) as the Brillouin gain medium. A bismuth-doped fiber serves as the laser gain medium. At the maximum pump power of 1021 mW and with the Brillouin pump set at 11 dBm, up to 7 Brillouin Stokes lines with a wavelength spacing of 0.074 nm are obtained in the single-spaced configuration. In the case of the double-spaced configuration, 14 Stokes lines are generated with a wavelength spacing of 0.15 nm between the even Stokes lines. By tuning the central wavelength of the Brillouin pump, both laser configurations are wavelength-tunable with a range of 93 nm and 19 nm for the single-spaced and double-spaced Brillouin lasers respectively. This is, to the best of the author's knowledge, the first demonstration of a multiwavelength/Brillouin laser using a bismuth-doped fiber as the laser gain medium.

  • Software
    Gong H, Wenjun G, Neil M, 2020,

    HexSimProcessor

    This repository is for the publication: "GPU-accelerated real-time reconstruction in Python of three-dimensional datasets from structured illumination microscopy with hexagonal patterns". It includes: raw data from experiments and simulations, the code for generating the simulated data, and the code for post-processing the raw data.

  • Conference paper
    Tewari S, Agrawal U, Verma S, Kumar S, Jeevaraj Set al., 2020,

    Ensemble model for COVID-19 detection from chest X-ray scans using image segmentation, fuzzy color and stacking approaches

    Coronavirus is a virus of RNA-type that can infect both humans and animal and causes a wide variety of respiratory infections. In humans, it also causes pneumonia. Since coronavirus has been declared a pandemic, Reverse Transcription Polymerase Chain Reaction (RT-PCR) has been the standard method for detection but is a time consuming operation and due to sudden surge in demand it has a high cost. In this study, coronavirus was detected from X-ray scans of chest using a deep learning model consisting of fuzzy image enhancement, offline data augmentation, image segmentation and classification through Convolutional Neural Network. For training and classification, an ensembeled model consisting of the features of VGG-16, ResNet-50 and MobileNetV2 was built and optimized with bayesian optimization. The proposed model achieved an overall accuracy of 96.34%. The precision, recall and F1-Score for COVID-19 class was 100%, 96% and 98% respectively.

  • Journal article
    Sparks H, Dent L, Bakal C, Behrens A, Salbreux G, Dunsby Cet al., 2020,

    Dual-view oblique plane microscopy (dOPM)

    , Biomedical Optics Express, Vol: 11, Pages: 7204-7220, ISSN: 2156-7085

    We present a new folded dual-view oblique plane microscopy (OPM) techniquetermed dOPM that enables two orthogonal views of the sample to be obtained by translating apair of tilted mirrors in refocussing space. Using a water immersion 40× 1.15 NA primaryobjective, deconvolved image volumes of 200 nm beads were measured to have full width athalf maxima (FWHM) of 0.35±0.04 μm and 0.39±0.02 μm laterally and 0.81±0.07 μm axially.The measured z-sectioning value was 1.33±0.45 μm using light-sheet FWHM in the frames ofthe two views of 4.99±0.58 μm and 4.89±0.63 μm. To qualitatively demonstrate that the systemcan reduce shadow artefacts while providing a more isotropic resolution, a multi-cellularspheroid approximately 100 μm in diameter was imaged.

  • Journal article
    Wang S, Wang Y, Thipparapu NK, Ibsen M, Richardson DJ, Sahu JKet al., 2020,

    Tunable CW Bi-Doped Fiber Laser System from 1320 to 1370 nm Using a Fiber Bragg Grating

    , IEEE Photonics Technology Letters, Vol: 32, Pages: 1443-1446, ISSN: 1041-1135

    Here we present a fully fiberized Bi-doped ring laser incorporating a fiber Bragg grating (FBG) operating at a wavelength of 1340nm, which provides 172mW of continuous-wave output power with a slope efficiency of 35%. In addition, we demonstrate a wavelength-tunable version of the laser, which can be tuned from 1320nm to 1370nm by employing a home-made mechanically tunable FBG. Within the whole 50nm tuning band the laser maintains the output power of more than 100mW and the slope efficiency of more than 25%. A maximum output power of 165mW is achieved over the wavelength range of 1330-1340nm. The linewidth of tunable laser is 0.04nm.

  • Conference paper
    Gouveia RM, Lepert G, Gupta S, Mohan RR, Paterson C, Connon CJet al., 2020,

    Biomechanical Modulation Therapy: Stem Cell Therapy Without the Stem Cells for the Treatment of Severe Ocular Burns

    , Trans-Agency Scientific Meeting on Developing Medical Countermeasures to Treat the Acute and Chronic Effects of Ocular Chemical Toxicity, Publisher: ELSEVIER IRELAND LTD, Pages: S8-S8, ISSN: 0378-4274
  • Conference paper
    Kerridge-Johns WR, Jaillot J-B, Damzen MJ, 2020,

    Shear plate Interferometer for complex angular momentum field generation

    , Frontiers in Optics, Publisher: OSA, Pages: 1-1

    We show that a shear plate interferometer can generate high purity complex angular momentum states and is simple, cheap, compact, and could operate in wavelength regions where optics for conventional techniques are not available.

  • Conference paper
    Wysoczanski R, Baker JR, Fenwick P, Garcia E, Kumar S, Neil MAA, Dunsby C, French PMW, Barnes PJ, Donnelly LEet al., 2020,

    Analysis of defective phagocytosis in COPD using super-resolution microscopy and automated bacterial quantification

    , Publisher: EUROPEAN RESPIRATORY SOC JOURNALS LTD, ISSN: 0903-1936
  • Journal article
    Quicke P, Howe CL, Song P, Jadan HV, Song C, Knöpfel T, Neil M, Dragotti PL, Schultz SR, Foust AJet al., 2020,

    Subcellular resolution three-dimensional light-field imaging with genetically encoded voltage indicators

    , Neurophotonics, Vol: 7, ISSN: 2329-4248

    Significance: Light-field microscopy (LFM) enables high signal-to-noise ratio (SNR) and light efficient volume imaging at fast frame rates. Voltage imaging with genetically encoded voltage indicators (GEVIs) stands to particularly benefit from LFM's volumetric imaging capability due to high required sampling rates and limited probe brightness and functional sensitivity. Aim: We demonstrate subcellular resolution GEVI light-field imaging in acute mouse brain slices resolving dendritic voltage signals in three spatial dimensions. Approach: We imaged action potential-induced fluorescence transients in mouse brain slices sparsely expressing the GEVI VSFP-Butterfly 1.2 in wide-field microscopy (WFM) and LFM modes. We compared functional signal SNR and localization between different LFM reconstruction approaches and between LFM and WFM. Results: LFM enabled three-dimensional (3-D) localization of action potential-induced fluorescence transients in neuronal somata and dendrites. Nonregularized deconvolution decreased SNR with increased iteration number compared to synthetic refocusing but increased axial and lateral signal localization. SNR was unaffected for LFM compared to WFM. Conclusions: LFM enables 3-D localization of fluorescence transients, therefore eliminating the need for structures to lie in a single focal plane. These results demonstrate LFM's potential for studying dendritic integration and action potential propagation in three spatial dimensions.

  • Journal article
    Quicke P, Howe CL, Song P, Jadan HV, Song C, Knöpfel T, Neil M, Dragotti PL, Schultz SR, Foust AJet al., 2020,

    Subcellular resolution 3D light field imaging with genetically encoded voltage indicators

    , Neurophotonics, Vol: 7, ISSN: 2329-4248

    Significance: Light-field microscopy (LFM) enables high signal-to-noise ratio (SNR) and light efficient volume imaging at fast frame rates. Voltage imaging with genetically encoded voltage indicators (GEVIs) stands to particularly benefit from LFM’s volumetric imaging capability due to high required sampling rates and limited probe brightness and functional sensitivity.Aim: We demonstrate subcellular resolution GEVI light-field imaging in acute mouse brain slices resolving dendritic voltage signals in three spatial dimensions.Approach: We imaged action potential-induced fluorescence transients in mouse brain slices sparsely expressing the GEVI VSFP-Butterfly 1.2 in wide-field microscopy (WFM) and LFM modes. We compared functional signal SNR and localization between different LFM reconstruction approaches and between LFM and WFM.Results: LFM enabled three-dimensional (3-D) localization of action potential-induced fluorescence transients in neuronal somata and dendrites. Nonregularized deconvolution decreased SNR with increased iteration number compared to synthetic refocusing but increased axial and lateral signal localization. SNR was unaffected for LFM compared to WFM.Conclusions: LFM enables 3-D localization of fluorescence transients, therefore eliminating the need for structures to lie in a single focal plane. These results demonstrate LFM’s potential for studying dendritic integration and action potential propagation in three spatial dimensions.

  • Conference paper
    Sathian J, Abadi MM, Damzen MJ, Ghassemlooy Zet al., 2020,

    Communication characteristics of high-brightness light sources based on luminescence concentration

    Communication characteristics of high-brightness solid-state light sources based on luminescence concentration generated using blue emitting InGaN light emitting diode arrays are demonstrated here for the first time. The proposed device is used as a transmitter in visible light communications, and its performance is evaluated.

  • Journal article
    Damzen M, Sathian J, Tawy G, Sheng X, Minassian Aet al., 2020,

    Non-astigmatic Alexandrite ring laser design with wavelength-tunable single-longitudinal-mode operation

    , Journal of the Optical Society of America B: Optical Physics, Vol: 37, Pages: 2185-2192, ISSN: 0740-3224

    This work presents a study of a fully nonastigmatic design of a single-longitudinal-mode, wavelength-tunable, unidirectional alexandrite ring laser cavity and assessment of its performance compared to more complex laser design requiring astigmatism compensation. A “displaced mode” nonastigmatic laser cavity design eliminating astigmatic cavity elements is developed around an alexandrite crystal end-pumped by a low-brightness, high-power red diode laser pump system. Single-longitudinal-mode, continuous-wave operation is demonstrated with output power of 700 mW with an excellent TEM00 mode (M2<1.1) across a wide pump power range. Wavelength tuning from 748–773 nm is produced using a birefringent filter plate. The nonastigmatic alexandrite laser design achieves better spatial quality and resilience to maintain TEM00 operation across wide variation in pump-induced lensing compared to the astigmatic design. To the best of our knowledge, this is the first wavelength-tunable, single-longitudinal-mode operation of a unidirectional alexandrite ring system in a fully nonastigmatic cavity regime.

  • Journal article
    Tawy G, Minassian A, Damzen M, 2020,

    High-power 7.4W TEM00 and wavelength-tunable Alexandrite laser with novel cavity design and efficient fibre-coupled diode-pumping

    , OSA Continuum, Vol: 3, Pages: 1638-1649, ISSN: 2578-7519

    We report significant improvement in the performance of TEM00 alexandrite laser operation by employing high power fibre-coupled red diode pumping, novel cavity design, and active direct Shack-Hartmann wavefront sensor measurement of pump-induced lensing. We demonstrate 12.7 W of laser power in low-order (𝑀2∼5) mode operation from a compact double-end-pumped cavity, and with novel cavity design, a record power of 7.4 W in TEM00 operation with excellent beam quality (𝑀2≤1.1). With single-end pumping, laser power of 4.7 W (𝑀2∼1.3) was achieved with slope efficiencies as high as 54.9 %; a record efficiency for red-diode-pumped alexandrite. Using a birefringent filter, continuous laser wavelength tuning from 725-808 nm is achieved in diffraction-limited TEM00 mode, with laser power of 4.7 W at 765 nm, and >1 W across 730-805 nm, which is a higher tunable power than any other directly diode-pumped vibronic laser, to the best of our knowledge.

  • Journal article
    Sparks H, Dvinskikh L, Firth J, Francis A, Harding S, Paterson C, MacLeod K, Dunsby Cet al., 2020,

    Development a flexible light-sheet fluorescence microscope for high-speed 3D imaging of calcium dynamics and 3D imaging of cellular microstructure

    , Journal of Biophotonics, Vol: 13, ISSN: 1864-063X

    We report a flexible light‐sheet fluorescence microscope (LSFM) designed for studying dynamic events in cardiac tissue at high speed in 3D and the correlation of these events to cell microstructure. The system employs two illumination‐detection modes: the first uses angle‐dithering of a Gaussian light sheet combined with remote refocusing of the detection plane for video‐rate volumetric imaging; the second combines digitally‐scanned light‐sheet illumination with an axially‐swept light‐sheet waist and stage‐scanned acquisition for improved axial resolution compared to the first mode. We present a characterisation of the spatial resolution of the system in both modes. The first illumination‐detection mode achieves dual spectral‐channel imaging at 25 volumes per second with 1024 × 200 × 50 voxel volumes and is demonstrated by time‐lapse imaging of calcium dynamics in a live cardiomyocyte. The second illumination‐detection mode is demonstrated through the acquisition of a higher spatial resolution structural map of the t‐tubule network in a fixed cardiomyocyte cell.

  • Journal article
    Hong Y, Sakr H, Taengnoi N, Bottrill KRH, Bradley TD, Hayes JR, Jasion GT, Kim H, Thipparapu NK, Wang Y, Umnikov AA, Sahu JK, Poletti F, Petropoulos P, Richardson DJet al., 2020,

    Multi-Band Direct-Detection Transmission over an Ultrawide Bandwidth Hollow-Core NANF

    , Journal of Lightwave Technology, Vol: 38, Pages: 2848-2856, ISSN: 0733-8724

    In this article, we report high-speed multi-band direct-detection (DD) transmission over a hollow-core nested antiresonant nodeless fiber (NANF). Thanks to the ultrawide bandwidth of the NANF, we demonstrate dual-band transmission across the O- and C-bands over a ∼1-km length of a hollow-core fiber for the first time. Eight wavelength-division multiplexed (WDM) channels were transmitted using 100-Gb/s/λ Nyquist 4-ary pulse-amplitude modulation (PAM4) signals, which to the best of our knowledge, is the highest aggregate capacity ever transmitted in a DD hollow-core fiber-based transmission system. Optical pre-amplification was adopted for signal reception in both bands, achieved using an in-house built bismuth-doped optical fibre amplifier (BDFA) and a commercial erbium-doped fiber amplifier (EDFA) in the O- and C-band, respectively. We further demonstrate beyond 100-Gb/s/λ adaptively-loaded discrete multitone (DMT) transmission over the S+C+L-bands using the same NANF, without the use of optical amplification. Our experiments show that apart from fiber loss, the use of the NANF did not introduce any additional transmission penalties. The demonstrated results validate the ultrawide bandwidth and excellent modal purity of the fabricated NANF, which allow beyond 100-Gb/s/λ penalty-free transmission over multiple bands, highlighting the potential of this fiber technology for high-speed short- to intermediate-reach applications.

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