Coherent control of light through laser written photonic lanterns

This is the author accepted manuscript. The final version is available from IEEE via the link in this recordWe demonstrate coherent control of light through bespoke laser written photonic lanterns. This enables imaging in a variety of new situations, with potential applications to micro-endoscopy, chip-based LIDAR, and microfluidic imaging.Chinese Scholarship CouncilEngineering and Physical Sciences Research Council (EPSRC)Royal Academy of Engineering,European Research Council (ERC

NV center emission in a substrate free low index environment

With in-built advantages (high quantum efficiency and room temperature photostability1) for deployment in quantum technologies as a bright on-demand source of single photons, the nitrogen vacancy (NV) center is the most widely studied optical defect in diamond. Despite significant success in controlling its spontaneous emission2, the fundamental understanding of its photo-physics in various environments and host material remains incomplete. Studying NV photoemission from nanodiamonds on a glass substrate, we recently pointed out a disparity between the measured and calculated decay rates (assuming near unity quantum efficiency)3. This indicates the presence of some strong nonradiative influences from factors most likely intrinsic to nanodiamond itself. To obtain a clearer picture of the NV emission, here we remove the substrate contributions to the decay rates by embedding our nanodiamonds inside silica aerogel, a substrate-free environment of effective index n ∼ 1.05. Nanodiamond doped aerogel samples were fabricated using the two-step process4. Time-resolved fluorescence measurement on ∼20 centers for both coverslip and aerogel configurations, showed an increase in the mean lifetime (∼37%) and narrowing of the distribution width (∼40%) in the aerogel environment, which we associate with the absence of a air/cover-glass interface near the radiating dipoles3. Finite difference time domain (FDTD) calculations showed the strong influence of the irregular nanodiamond geometry on the remaining distribution width. Finally a comparison between measurements and calculations provides an estimate of the quantum efficiency of the nanodiamond NV emitters as ∼0.7. This value is apparently consistent with recent reports concerning the oscillation of the NV center between negative and neutral charge states5. © 2013 SPIE

Relations between assemblages of carpological remains and modern vegetation in a shallow reservoir in southern Poland

This paper explores relations between assemblages of carpological remains and vegetation in and around a small, shallow reservoir in southern Poland. The study was conducted from 2006 to 2008. Quantity and distribution of species in the reservoir were recorded annually during the growing season. In October 2008, 40 samples of surface sediment (top 2 cm) were collected along transects at 10 m intervals. Samples of 100 cm3 were prepared for analysis of plant macroremains. Assemblages of carpological remains generally reflect local vegetation well. In some cases, however, even analysis of numerous samples failed to fully capture the species composition or reflect plant ratios in the parent phytocenosis. Reasons for this include factors that affect seed production, transport and fossilization, which differ among species. Among the best-represented macroremains were plants of the rush phytocenosis. In analysed samples, macroremains of 68.8 % of extant rushes were identified. Sixty percent of submerged and floating-leaf taxa were found in carpological samples, whereas 26.7 % of the trees and bushes were represented in sediment deposits. Species composition of phytocenoses in the reservoir and in surrounding areas was best reflected by macroremains from the nearby reed bed. Numbers of diaspores of Mentha aquatica, Hippuris vulgaris and Carex reflected well their relative abundance in phytocenoses. Chara sp., Juncus inflexus and Eupatorium cannabinum were overrepresented, whereas Typha latifolia and Sparganium minimum were poorly represented in relation to contemporary plant cover. There were no diaspores of Phragmites australis, which dominates the contemporary reed bed. Besides the shape of a reservoir, the key factor influencing diaspore numbers is distribution of plant cover. In many cases, single diaspores (Potentilla erecta, Myosotis scorpioides, Lythrum salicaria, Scutellaria galericulata), or higher concentrations (Hippuris vulgaris, Mentha aquatica, Eleocharis palustris, Schoenoplectus tabernaemontani, Chara sp.) reflected well the location of parent vegetation. The findings indicate that carpological remains in sediments can be an important source of information about plants in and around lakes. They generally reflect well local vegetation and in some cases may be used to identify taxa that dominated in the past

Computational optical imaging with a photonic lantern

[EN] The thin and flexible nature of optical fibres often makes them the ideal technology to view biological processes in-vivo, but current microendoscopic approaches are limited in spatial resolution. Here, we demonstrate a route to high resolution microendoscopy using a multicore fibre (MCF) with an adiabatic multimode-to-single-mode "photonic lantern" transition formed at the distal end by tapering. We show that distinct multimode patterns of light can be projected from the output of the lantern by individually exciting the single-mode MCF cores, and that these patterns are highly stable to fibre movement. This capability is then exploited to demonstrate a form of single-pixel imaging, where a single pixel detector is used to detect the fraction of light transmitted through the object for each multimode pattern. A custom computational imaging algorithm we call SARA-COIL is used to reconstruct the object using only the pre-measured multimode patterns themselves and the detector signals.This work was funded through the "Proteus" Engineering and Physical Sciences Research Council (EPSRC) Interdisciplinary Research Collaboration (IRC) (EP/K03197X/1), by the Science and Technology Facilities Council (STFC) through STFC-CLASP grants ST/K006509/1 and ST/K006460/1, STFC Consortium grants ST/N000625/1 and ST/N000544/1. S.L. acknowledges support from the National Natural Science Foundation of China under Grant no. 61705073. DBP acknowledges support from the Royal Academy of Engineering, and the European Research Council (PhotUntangle, 804626). The authors thank Philip Emanuel for the use of his confocal image of A549 cells and Eckhardt Optics for their image of the USAF 1951 target. The authors sincerely thank the anonymous reviewers of this paper for their detailed and considered feedback which helped us to improve the quality of this paper significantly.Choudhury, D.; Mcnicholl, DK.; Repetti, A.; Gris-Sánchez, I.; Li, S.; Phillips, DB.; Whyte, G.... (2020). Computational optical imaging with a photonic lantern. Nature Communications. 11(1):1-9. https://doi.org/10.1038/s41467-020-18818-6S19111Wood, H. A. C., Harrington, K., Birks, T. A., Knight, J. C. & Stone, J. M. High-resolution air-clad imaging fibers. Opt. Lett. 43, 5311–5314 (2018).Akram, A. R. et al. In situ identification of Gram-negative bacteria in human lungs using a topical fluorescent peptide targeting lipid A. Sci. Transl. Med. 10, eaal0033 (2018).Shin, J., Bosworth, B. T. & Foster, M. A. Compressive fluorescence imaging using a multi-core fiber and spatially dependent scattering. Opt. Lett. 42, 109–112 (2017).Papadopoulos, I. N., Farahi, S., Moser, C. & Psaltis, D. Focusing and scanning light through a multimode optical fiber using digital phase conjugation. Opt. Express 20, 10583–10590 (2012).Čižmár, T. & Dholakia, K. Exploiting multimode waveguides for pure fibre-based imaging. Nat. Commun. 3, 1027 (2012).Plöschner, M., Tyc, T. & Čižmár, T. Seeing through chaos in multimode fibres. Nat. Photon. 9, 529–535 (2015).Birks, T. A., Gris-Sánchez, I., Yerolatsitis, S., Leon-Saval, S. G. & Thomson, R. R. The photonic lantern. Adv. Opt. Photon. 7, 107–167 (2015).Birks, T. A., Mangan, B. J., Díez, A., Cruz, J. L. & Murphy, D. F. Photonic lantern’ spectral filters in multi-core fiber. Opt. Express 20, 13996–14008 (2012).Edgar, M. P., Gibson, G. M. & Padgett, M. J. Principles and prospects for single-pixel imaging. Nat. Photon. 13, 13–20 (2019).Mahalati, R. N., Yu, Gu. R. & Kahn, J. M. Resolution limits for imaging through multi-mode fiber. Opt. Express 21, 1656–1668 (2013).Amitonova, L. V. & de Boer, J. F. Compressive imaging through a multimode fiber. Opt. Lett. 43, 5427–5430 (2018).Mallat, S. A Wavelet Tour of Signal Processing 2nd edn (Academic Press, Burlington, MA, 2009).Lustig, M., Donoho, D. & Pauly, J. M. Sparse MRI: the application of compressed sensing for rapid MR imaging. Magn. Reson. Med. 58, 1182–1195 (2007).Davies, M., Puy, G., Vandergheynst, P. & Wiaux, Y. A compressed sensing framework for magnetic resonance fingerprinting. SIAM J. Imaging Sci. 7, 2623–2656 (2014).Wiaux, Y., Puy, G., Scaife, A. M. M. & Vandergheynst, P. Compressed sensing imaging techniques in radio interferometry. Mon. Not. R. Astron. Soc. 395, 1733–1742 (2009).Carrillo, R. E., McEwen, J. D. & Wiaux, Y. Sparsity averaging reweighted analysis (SARA): a novel algorithm for radio-interferometric imaging. Mon. Not. R. Astron. Soc. 426, 1223–1234 (2012).Katz, O., Bromberg, Y. & Silberberg, Y. Compressive ghost imaging. Appl. Phys. Lett. 95, 131110 (2009).Sun, B., Welsh, S. S., Edgar, M. P., Shapiro, J. H. & Padgett, M. J. Normalized ghost imaging. Opt. Express 20, 16892–16901 (2012).Kim, M., Park, C., Rodriguez, C., Park, Y. & Cho, Y.-H. Superresolution imaging with optical fluctuation using speckle patterns illumination. Sci. Rep. 5, 16525 (2015).Combettes, P. L. & Pesquet, J. -C. in Fixed-Point Algorithms for Inverse Problems in Science and Engineering (Springer, New York, 2011).Komodakis, N. & Pesquet, J.-C. Playing with duality: an overview of recent primal dual approaches for solving large-scale optimization problems. IEEE Signal Proc. Mag. 32, 31–54 (2015).Chandrasekharan, H. K. et al. Multiplexed single-mode wavelength-to-time mapping of multimode light. Nat. Commun. 8, 14080 (2017).Wadsworth, W. J. et al. Very high numerical aperture fibers. Photon. Technol. Lett. 16, 843–845 (2004).Pesquet, J.-C. & Repetti, A. A class of randomized primal-dual algorithms for distributed optimization. J. Nonlinear Convex Anal. 16, 2353–2490 (2015).Chambolle, A., Ehrhardt, M. J., Richtárik, P. & Schönlieb, C.-B. Stochastic primal-dual hybrid gradient algorithm with arbitrary sampling and imaging applications. SIAM J. Optim. 28, 2783–2808 (2018).Bolte, J., Sabach, S. & Teboulle, M. Proximal alternating linearized minimization for nonconvex and nonsmooth problems. Math. Program. 146, 459–494 (2014).Chouzenoux, E., Pesquet, J.-C. & Repetti, A. A block coordinate variable metric forward-backward algorithm. J. Glob. Optim. 66, 457–485 (2016).Flusberg, B. A. et al. Fiber-optic fluorescence imaging. Nat. Methods 2, 941–950 (2005).Tsvirkun, V. et al. Bending-induced inter-core group delays in multicore fibers. Opt. Express 25, 31863–31875 (2017).Candès, E. J., Wakin, M. B. & Boyd, S. Enhancing sparsity by reweighted l1 minimization. J. Fourier Anal. Appl. 14, 877–905 (2008).Condat, L. A primal–dual splitting method for convex optimization involving lipschitzian, proximable and linear composite terms. J. Optim. Theory Appl. 158, 460–479 (2013).Vu, B. C. A splitting algorithm for dual monotone inclusions involving cocoercive operators. Adv. Comp. Math. 38, 667–681 (2013)

Development of Photonic Crystal Fiber Based Gas/ Chemical Sensors

The development of highly-sensitive and miniaturized sensors that capable of real-time analytes detection is highly desirable. Nowadays, toxic or colorless gas detection, air pollution monitoring, harmful chemical, pressure, strain, humidity, and temperature sensors based on photonic crystal fiber (PCF) are increasing rapidly due to its compact structure, fast response and efficient light controlling capabilities. The propagating light through the PCF can be controlled by varying the structural parameters and core-cladding materials, as a result, evanescent field can be enhanced significantly which is the main component of the PCF based gas/chemical sensors. The aim of this chapter is to (1) describe the principle operation of PCF based gas/ chemical sensors, (2) discuss the important PCF properties for optical sensors, (3) extensively discuss the different types of microstructured optical fiber based gas/ chemical sensors, (4) study the effects of different core-cladding shapes, and fiber background materials on sensing performance, and (5) highlight the main challenges of PCF based gas/ chemical sensors and possible solutions

Microscopic optical buffering in a harmonic potential

In the early days of quantum mechanics, Schrödinger noticed that oscillations of a wave packet in a one-dimensional harmonic potential well are periodic and, in contrast to those in anharmonic potential wells, do not experience distortion over time. This original idea did not find applications up to now since an exact one-dimensional harmonic resonator does not exist in nature and has not been created artificially. However, an optical pulse propagating in a bottle microresonator (a dielectric cylinder with a nanoscale-high bump of the effective radius) can exactly imitate a quantum wave packet in the harmonic potential. Here, we propose a tuneable microresonator that can trap an optical pulse completely, hold it as long as the material losses permit, and release it without distortion. This result suggests the solution of the long standing problem of creating a microscopic optical buffer, the key element of the future optical signal processing devices

Revealing the nature of morphological changes in carbon nanotube-polymer saturable absorber under high-power laser irradiation

Composites of single-walled carbon nanotubes (SWNTs) and water-soluble polymers (WSP) are the focus of significant worldwide research due to a number of applications in biotechnology and photonics, particularly for ultrashort pulse generation. Despite the unique possibility of constructing non-linear optical SWNT-WSP composites with controlled optical properties, their thermal degradation threshold and limit of operational power remain unexplored. In this study, we discover the nature of the SWNT-polyvinyl alcohol (PVA) film thermal degradation and evaluate the modification of the composite properties under continuous high-power ultrashort pulse laser operation. Using high-precision optical microscopy and micro-Raman spectroscopy, we have examined SWNT-PVA films before and after continuous laser radiation exposure (up to 40 hours) with a maximum optical fluence of 2.3 mJ·cm−2. We demonstrate that high-intensity laser radiation results in measurable changes in the composition and morphology of the SWNT-PVA film due to efficient heat transfer from SWNTs to the polymer matrix. The saturable absorber modification does not affect the laser operational performance. We anticipate our work to be a starting point for more sophisticated research aimed at the enhancement of SWNT-PVA films fabrication for their operation as reliable saturable absorbers in high-power ultrafast lasers

Overcoming degradation in spatial multiplexing systems with stochastic nonlinear impairments

Single-mode optical fibres now underpin telecommunication systems and have allowed continuous increases in traffic volume and bandwidth demand whilst simultaneously reducing cost- and energy-per-bit over the last 40 years. However, it is now recognised that such systems are rapidly approaching the limits imposed by the nonlinear Kerr effect. To address this, recent research has been carried out into mitigating Kerr nonlinearities to increase the nonlinear threshold and into spatial multiplexing to offer additional spatial pathways. However, given the complexity associated with nonlinear transmission in spatial multiplexed systems subject to random inter-spatial-path nonlinearities it is widely believed that these technologies are mutually exclusive. By investigating the linear and nonlinear crosstalk in few-mode fibres based optical communications, we numerically demonstrate, for the first time, that even in the presence of significant random mixing of signals, substantial performance benefits are possible. To achieve this, the impact of linear mixing on the Kerr nonlinearities should be taken into account using different compensation strategies for different linear mixing regimes. For the optical communication systems studied, we demonstrate that the performance may be more than doubled with the appropriate selection of compensation method for fibre characteristics which match those presented in the literature

Strain-induced pseudomagnetic field and Landau levels in photonic structures

Magnetic effects at optical frequencies are notoriously weak. This is evidenced by the fact that the magnetic permeability of nearly all materials is unity in the optical frequency range, and that magneto-optical devices (such as Faraday isolators) must be large in order to allow for a sufficiently strong effect. In graphene, however, it has been shown that inhomogeneous strains can induce 'pseudomagnetic fields' that behave very similarly to real fields. Here, we show experimentally and theoretically that, by properly structuring a dielectric lattice, it is possible to induce a pseudomagnetic field at optical frequencies in a photonic lattice, where the propagation dynamics is equivalent to the evolution of an electronic wavepacket in graphene. To our knowledge, this is the first realization of a pseudomagnetic field in optics. The induced field gives rise to multiple photonic Landau levels (singularities in the density of states) separated by band gaps. We show experimentally and numerically that the gaps between these Landau levels give rise to transverse confinement of the optical modes. The use of strain allows for the exploration of magnetic effects in a non-resonant way that would be otherwise inaccessible in optics. Employing inhomogeneous strain to induce pseudomagnetism suggests the possibility that aperiodic photonic crystal structures can achieve greater field-enhancement and slow-light effects than periodic structures via the high density-of-states at Landau levels. Generalizing these concepts to other systems beyond optics, for example with matter waves in optical potentials, offers new intriguing physics that is fundamentally different from that in purely periodic structures.Comment: 24 pages including supplementary information section, 4 figure