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A practical realization of a diode pumped actively Q-switched Er3+-doped fluoride fiber laser operating near 2.78 μm is reported. For the repetition rate of 100 Hz stable 26 ns pulses with an energy of 330 μJ and peak power of 12.7 kW are demonstrated. The laser performance is tested against variations in pump power, repetition rate and active fiber length.

Lightning diverter strips are commonly used to protect the antenna and sensitive equipment within an airborne radome. This article compares the impact of solid metallic and segmented diverter strips on the radiation properties of the enclosed antenna. Solid metallic and segmented diverter strips of different segment profiles, i.e., square, circular, and diamond, are considered. This article reports how the placement of diverters on the radome and their geometric detail affect the antenna parameters, namely reflection coefficient and far-field pattern. Furthermore, the surface electric field intensity on segmented diverter strips is analyzed for different shapes, sizes, and separations between the metallic segments.

In this letter, the effectiveness of a recently developed stretched coordinate (SC) perfectly matched layer (PML) formulation in the transmission line modeling (TLM) method is investigated for truncating the out-of-plane computational domain of different unit-cell-based frequency selective surface (FSS) simulations. Transmitted power is compared against various absorbing boundary conditions; the accuracy of each method is determined by benchmarking against results from method of moments (MoM) simulations. Good agreement with the MoM analysis is shown by the SC TLM-PML and, unlike the weakly stable split-field-based TLM-PML schemes, no instabilities are observed in the late time.

A novel implementation of the stretched coordinate perfectly matched layer (PML) is presented for the two-dimensional (2D) transmission line modelling (TLM) method. The formulation offers a unified approach and is based on the mapping of the TLM node to a complex stretched domain for which the resulting transformation of the constituent RLC transmission line components is elaborated. The transformation is shown to modify the TLM connect-scatter algorithm. The absorption performance is demonstrated by simulating a canonical waveguide test case. Unlike the existing split-field based TLM-PML implementations, which are better suited to lossless media, the numerical results obtained show the proposed PML formulation is effective in the termination of both lossy and lossless media.

Based on tapered Triple-Core Photonic Crystal Fiber (TCPCF), a high performance tunable Dual-Wavelength Erbium-Doped Fiber Laser (DW-EDFL) is proposed and experimentally demonstrated. The mode-coupling among three cores of TCPCF appears periodically and becomes further enhanced in tapered TCPCF, which are beneficial to form a filter to select lasing wavelength. A series of tapered TCPCFs with different taper lengths are fabricated and inserted into tunable DW-EDFL as filters. Multiple groups of tunable dual-wavelength lasing outputs are achieved by using the tapered TCPCF filter with a waist diameter of 126 μm. The maximum tunable range can reach up to 14.36 nm and the side mode suppression ratio of all lasing outputs are above 52 dB. In addition, the tunable single- and triple-wavelength lasers are also obtained. The tunable single-wavelength laser has an excellent linear response to strain and can be applied to realize a high-sensitivity strain sensor with the highest strain sensitivity of -13.1 pm/με.

An improved implementation of the perfectly matched layer (PML) is developed for the Transmission Line Modelling (TLM) method based on a mapping of the symmetrical condensed node (SCN) to an analytically extended geometric space. By mapping the TLM node, a medium - circuit equivalence is developed which maps transmission line parameters from real to complex domain. This consequently modifies the TLM scatter-connect process. The PML implementation is demonstrated for canonical cases where it is shown to have a comparable absorption performance and a significantly improved temporal stability relative to previously published TLM-PML formulations.

In this paper, a global multi-trace method for the scattering of time-harmonic waves by a structure that can contain, in addition to dielectric and perfectly conducting regions also perfectly conducting thin sheets, is presented. The method is direct in the sense that the unknowns are traces and jumps of the fields in the structure. The flexibility of the method and the correctness of the solution will be demonstrated by realistic examples.

This Letter, to the best of our knowledge, reports mid-infrared fiber lasing beyond 5 µm at room temperature for the first time, C e 3 + -doped, chalcogenide glass, step index fiber employed in-band pumping with a 4.15 µm quantum cascade laser. The lasing fiber is was 64 mm long, with a calculated numerical aperture of 0.48 at the lasing wavelengths. The core glass was G e 15 A s 21 G a 1 S e 63 atomic % (at. %), doped with 500 parts-per-million-by-weight Ce, with a 9 µm core diameter. The cladding glass was G e 21 S b 10 S e 69 at. % with a 190 µm outer diameter. As pump power increases continuous wave lasing corresponding to the 2 F 7 / 2 → 2 F 5 / 2 , transition in the C e 3 + ion occurs at 5.14 µm, 5.17 µm, and 5.28 µm.

A numerical model was developed to study the time dynamics of photoluminescence emitted by Tb3+ doped multimode chalcogenide-selenide glass fibers pumped by laser light at approximately 2 μm. The model consists of a set of partial differential equations (PDEs), which describe the temporal and spatial evolution of the photon density and level populations within the fiber. In order to solve numerically the PDEs a method of lines was applied. The modeling parameters were extracted from measurements and from data available in the literature. The numerical results obtained support experimental observations. In particular, the developed model reproduces the discrepancies that are observed between the photoluminescence decay curves obtained from different points along the fiber. The numerical analysis was also used to explain the source of these discrepancies.

This contribution reports on detailed experimental and numerical investigations of both near-infrared (NIR) and mid-infrared (MIR) photoluminescence obtained in praseodymium trivalent ion doped chalcogenide-selenide glass fiber. The experimental analysis allows for the identification of the radiative transitions within the praseodymium ion energy level structure to account for the photoluminescent behavior. Numerical analysis is carried out using the rate equations’ approach to calculate the level populations. The numerical analysis provides further insight into the nature of the radiative transitions in the Pr3+ ion doped chalcogenide-selenide glass and allows for the identification of the electronic transitions, which contribute to the observed photoluminescence. The numerical results agree well with the experimental results.

We study numerically a two-dimensional (2-D) elliptical microcavity laser, in the center of which a circular active region is located, modeling a focused pumped spot or an injection electrode. The object of the research is to study lasing spectra, gain-medium thresholds, and modal fields, found as solutions to a classical electromagnetic eigenvalue problem tailored to address the threshold conditions. The instrument of our study is the set of two coupled Muller boundary integral equations (BIE) on the boundaries of the cavity and the active region. These BIEs are discretized by the Nystrom technique that guarantees the convergence. Among the modes that co-exist in such a resonator, we demonstrate the whispering-gallery-like modes (WGM) and the bow-tie-like modes (BTM). We find that the threshold values of material gain of BTMs can become lower than those of nearby WGMs if the radius of the active region in the cavity center is getting sufficiently small.

This paper uses the unstructured transmission line modeling method to investigate near-field interactions between a broadband microwave antenna and a platform that arise as a result of antenna installation. The antenna, feed line, and the platform are represented by a common meshed model and simulated using a single time-domain numerical method. This paper aims to establish guidelines on how to achieve high accuracy when modeling both the near and far fields of an antenna while at the same time prioritizing computational resources. By isolating critical features such as the feed line and selected fine details of the antenna geometry, this paper assesses how accurately these fine features need to be described in the model and how they affect the return loss and far-field pattern of the antenna. The size of the platform is varied from small to medium size (up to 10 wavelengths) and its impact on the antenna performance is assessed. Finally, the conclusions of the study are applied to an example of an antenna installed in the leading edge of an aircraft wing, with and without, a protective radome cover.

Results from the electromagnetic modeling of the threshold conditions of hybrid plasmon modes of a laser based on a silver nanotube with an active core and covered with an active shell are presented. We study the modes of such a nanolaser that have their emission wavelengths in the visible-light range. Our analysis uses the mathematically grounded approach called the lasing eigenvalue problem (LEP) for the set of the Maxwell equations and the boundary and radiation conditions. As we study the modes exactly at the threshold, there is no need to invoke nonlinear and quantum models of lasing. Instead, we consider a laser as an open plasmonic resonator equipped with an active region. This allows us to assume that at threshold the natural-mode frequency is real-valued, according to the situation where the losses, in the metal and for the radiation, are exactly balanced with the gain in the active region. Then the emission wavelength and the associated threshold gain can be viewed as parts of two-component eigenvalues, each corresponding to a certain mode. In the configuration considered, potentially there are three types of modes that can lase: the hybrid localized surface plasmon (HLSP) modes of the metal tube, the core modes, and the shell modes. The latter two types can be kept off the visible range in thin enough configurations. Keeping this in mind, we focus on the HLSP modes and study how their threshold gain values change with variations in the geometrical parameters of the nanotube, the core, and the shell. It is found that essentially a single-mode laser can be designed on the difference-type HLSP mode of the azimuth order m = 1, shining in the orange or red spectral region. Furthermore, the threshold values of gain for similar HLSP modes of order m = 2 and 3 can be several times lower, with emission in the violet or blue parts of the spectrum.

In this contribution experimental investigation of acousto-optically Q-switched erbium-doped fluorozirconate fiber laser is presented. Under the repetition rate of 1 kHz laser produces pulses with the shortest duration of 20 ns and the maximum pulse energy of 180 μJ, corresponding to a maximum peak power of 9 kW.

We report a photonic implementation of the Reservoir Computer (PhRC) for sensing application. The kernel of the PhRC will be in the form of chaotic microcavity on a photonic crystal cavity platform designed to discriminate different analytes. The discrimination is achieved by recognising the unique temporal signal signature arising from the chaotic kernel in the presence of different analyte. The unique temporal signature is obtained exploiting the sensitive to the initial-condition response of a billiard shaped microcavity. This is noted that the new discrimination approach reported is performed directly on the temporal signal, in contrast to the conventional spectral fingerprinting.

Mid-infrared (MIR) direct fiber lasers beyond 4 μm wavelength will deliver optimum beam quality of bright, spatially and temporally coherent light, routeable in MIR fiber-optics. They are being developed for applications including narrow-band biomolecular sensing, medical laser surgery at new, long wavelengths and for pulsed seeding of long wavelength MIR-supercontinua in MIR glass fiber for all-fiber, compact systems for broad-band MIR medical sensing and hyperspectral imaging. Low phonon energy, selenide chalcogenide glasses are the optimum glass host for lanthanide ion doping for emission across the 3 to 10 μm wavelength MIR region. Here, we report our recent advances including: >1 mW incoherent emission in the 4-5 μm wavelength region and demonstration of gain beyond 4 μm in Pr3+ doped chalcogenide glass fiber, and proposed quasi three-level lasing beyond 4 μm in Tb3+ doped chalcogenide glass fibers. Encouragingly, since 2020, lasing in both Pr3+ and Tb3+ selenide chalcogenide bulk glasses has been reported. Our overall goal is for new portable, MIR spectroscopic systems based on chalcogenide optical fibers for in vivo sensing, imaging and treatment in healthcare, including for early diagnosis of disease.

Practical realization of gain-switched Dy3+-doped ZBLAN fiber laser operating at 2.94 µm is reported. The laser is pumped by a 1.1 µm Q-switched ytterbium (III) fiber laser, which was constructed in-house. The ZBLAN fiber laser generates a stable pulse train with repetition rates spanning the range from 25 to 100 kHz. At the repetition rate of 50 kHz, the pulse width is 183 ns while energy and peak power are 0.72 µJ and 4 W, respectively.

A diode-pumped Q-switched Er3+:ZBLAN double-clad, single-transverse mode fiber laser is practically realized. The Q-switched laser characteristics as a function of pump power, repetition rate, and fiber length are experimentally investigated. The results obtained show that the Q-switched operation with 46 µJ pulse energy, 56 ns long pulses, and 0.821 kW peak power is achieved at a pulse repetition rate of 10 kHz. To the best of our knowledge, this is the highest-ever demonstrated peak power emitted from an actively Q-switched, single-transverse mode Er3+:ZBLAN fiber laser operating near 2.8 µm.

In this contribution a discussion of design and practical realization of dysprosium ion doped, and erbium ion doped, fluoride glass fiber lasers is given. The specific operating wavelength range that is covered corresponds is near 3000 nm. The discussion is centered around the pulsed Q-switched operation of the fiber laser.

Mid-infrared (MIR) spectroscopy and imaging underpin many applications, ranging from industrial process monitoring to environmental analysis, and offer a new era in healthcare and clinical diagnostics. The spectral region from 1.5 to $12\ \mu \mathrm{m}$ is of interest since it contains strong characteristic absorption peaks associated with the vibrational transitions of many important molecules. A principal requirement for rapid measurement is bright, fibre-based, sources that, if possible, should also be robust and low cost. This paper describes our work to use sources based on the photoluminescence from Pr3+ and Dy3+ doped GeAsGaSe fibres to provide affordable carbon dioxide (CO 2 ) sensing in heritage buildings. Limitations to the Beer Lambert law, previously reported by others, were observed in the sensing system, and the sensors were consequently calibrated empirically. Simulation results show that the use of commercial filters provides a promising approach to realising more compact, real-time, sensing.

A very important problem in modern medicine is the identification of atherosclerotic lesions within human tubular vessels. Current methods such as OCT and intravascular ultrasonography are very expensive and do not provide conclusive information about the formation of atherosclerotic plaques, especially within the human thoracic aorta. This paper presents a new solution to the identification of atherosclerotic lesions based on a specially constructed endoscope that uses CCD cameras. The endoscope analyses the condition of the walls of the blood vessels (side analysis) and represents a step towards an in vivo investigation of part of the human body. The remaining problem is the exact identification of the places where changes occur in the human tubular vessels. Research using the fluorescence phenomenon gives a summary result from an area whose location can be determined with an accuracy of millimetres. For pipes with sufficiently large internal diameter CCD cameras can be used to produce images of the examined tissues. It is possible for doctors to use the images so obtained to identify diseased areas with high accuracy. An alternative approach for identifying atherosclerosis is to use a neural network method to analyse the received pictures. Popular methods such as Machine Learning and Deep Learning can also be used to identify features in medical images. Creating a ‘learning’ database of endoscopic images in which a doctor identifies regions of healthy and atherosclerotic tissue is time consuming. However, after creating the database, the image identification algorithm works much faster than known numerical methods. It can significantly contribute to improving the effectiveness of atherosclerosis diagnostics. This paper presents initial results that confirm the effectiveness of a Machine Learning approach in identifying atherosclerotic lesions from the analysis of endoscope images obtained with a black and white camera following fluorescence stimulation and with a colour CCD camera using white light illumination. These findings are important since histological tests are not possible in in vivo investigations.

1000 ppmw Sm

Many important molecules show strong characteristic vibrational transitions in the mid-infrared (MIR) part of the electromagnetic spectrum. This leads to applications in spectroscopy, chemical and bio-molecular sensing, security and industry, especially over the mid- and long- wave infrared atmospheric transmission windows of 3-5 μm and 8-13 μm. In this paper, we review some of our more recent experimental and simulation work aimed at developing new light sources based on chalcogenide glass optical fibres that can help us utilize this spectral region for biomedical applications. This includes the development of supercontinuum and bright luminescent sources and our progress towards fibre-based lasers. We place these developments in the context of MIR imaging and spectroscopy in order to show how they bring the promise a new era in healthcare and clinical diagnostics.

This paper investigates the impact of lightning segmented diverter strips on antenna performance. A fully coupled electromagnetic model is considered, where the antenna is enclosed by a realistic dielectric radome profile on which segmented diverter strips are placed. The geometric model of a radome with lightning diverter strips is generated by using a computer graphics method for seamlessly morphing two surfaces together. The antenna performance is characterised by both the S11 parameter and the far field profile.

We investigate the effects of switching the state of a PIN diode from insulating to conducting as a component within a Solid-State Receiver Protection (SSRP) system. The investigation follows a component adding process, ultimately arriving at a full configuration of a metallic post insulated from the waveguide by two dielectric blocks in the Off-state, which is then connected at one end in the On-state. The effects of the diameter of the post are also studied. The S-parameters of the system are calculated from the voltage and current transmission line observations sampled directly with a single time-domain numerical method based upon an unstructured mesh.

Tuneable all-optical signal processing has been the holy grail of information photonics; it has been pursued for many years but has proven to be very challenging. In this contribution, we present our recent work in developing an all-optical signal processing device called a photonic reservoir computer (PhRC) which can be tuned to perform a bespoke task. The PhRC is inspired by how the brain handles and process information. We demonstrate that a chaotic micro-resonator is a suitable platform for the optical implementation of such an artificial neural network.

This paper demonstrates the effectiveness of the recently introduced, stable, perfectly matched layer (PML) for the Transmission Line Modelling (TLM) method. The superiority of the new PML over the TLM matched boundary is demonstrated by application to electromagnetic scattering and radiation simulations.

Efficient continuous-wave laser operation at 2.982 $\mu \text{m}$ is achieved with a Dy3+:fluoride fiber pumped using an inhouse-built 1.1 $\mu \text{m}$ ytterbium (III) fiber laser. The laser output power reached is 554 mW, with a maximum slope efficiency of 18% with respect to the launched pump power. Additionally, the measured spontaneous luminescence within the visible wavelength range, under 1.1 $\mu \text{m}$ pumping, is presented and attributed to excited state absorption (ESA). The influence of the ESA on the laser performance is discussed. The results confirm that high output powers from Dy:fluoride fiber laser pumped at 1.1 $\mu \text{m}$ are possible.

A dual sakura hollow-core antiresonant fiber (DSHC-ARF) is proposed for developing an ultrawide-bandwidth polarization beam splitter (PBS). An air gap is introduced into the fiber between dual sakura hollow cores acting as a mode-coupling channel, which determines the implementation of a DSHC-ARF-based PBS. We demonstrate the wavelength dependence of coupling length can be reduced by introducing nested tubes and investigate their impact on single-mode operation further. Through optimizing the fiber, a high-performance PBS based on a 4.42 cm long DSHC-ARF can be obtained with an ultrawide bandwidth of 460 nm ranging from 1400 to 1860 nm, good single-mode operation with a higher-order mode extinction ratio above 100, and a low fundamental mode loss below 0.543 dB.

In this paper, a dual-wavelength interval tunable and multi-wavelength switchable fiber laser with high performance is proposed and experimentally demonstrated by using a four-leaf clover suspended core fiber (FLCSCF) filter. The filter, based on mode interference (MI), is fabricated by splicing a 10.5 cm long FLCSCF between two sections of single mode fiber (SMF). The FLCSCF has favorable mode confinement and low transmission loss, which is beneficial for forming a comb-like transmission spectrum with a high extinction ratio. By inserting the MI filter based on FLCSCF into a ring erbium-doped fiber laser (EDFL), switchable single- to six-wavelength lasing outputs are obtained; the optical signal to noise ratio (OSNR) of all lasing outputs is above 50 dB. Dual-wavelength lasing outputs with tunable wavelength intervals are achieved by applying strain on the filter and the maximum tunable range of dual-wavelength lasing outputs can reach up to 41 nm. In addition, six-wavelength lasing outputs exhibit good stability with the wavelength shift less than 0.04 nm and the peak power fluctuation lower than 1.5 dB. Such a multi-wavelength fiber laser (MWFL) with improved performance has great application potential in microwave communications and laser strain sensing.

We propose an As 2 Se 3 -based photonic quasi-crystal fiber (PQF) with high nonlinearity and birefringence. By optimizing the structure parameters, a nonlinear coefficient up to 2079 W −1 km −1 can be achieved at the wavelength of 2 μ m; the birefringence reaches up to the order of 10 −2 due to the introduction of large circular air holes in the cladding. Using an optical pulse with a peak power of 6 kW, a pulse width of 150 f s, and a central wavelength of 2.94 μ m as the pump pulse, a mid-infrared polarized supercontinuum is obtained by using a 15 mm long PQF. The spectral width for x - and y -polarizations covers 1 μ m–10.2 μ m and 1 μ m–12.5 μ m, respectively. The polarization state can be well maintained when the incident angle of the input pulse changes within ±2°. The proposed PQF, with high nonlinear coefficient and birefringence, has potential applications in mid-infrared polarization-maintaining supercontinuum generation.

For fiber-optic mid-infrared bio- and chemical-sensing, Ge-Sb-Se glass optical fibers are more attractive than Ge-As-Se because of: (i) lowered toxicity and (ii) lower phonon energy and hence transmission to longer wavelengths, with potential to reach the spectral ‘fingerprint region’ for molecular sensing. There is little previous work on Ge-Sb-Se fibers. Here, fibers are fabricated from two glass compositions in the GexSb10Se90-x atomic (at.) % series. Both glass compositions are of similar mean-coordination-number, lying in the overconstrained region, yet of different chemical composition: stoichiometric Ge25Sb10Se65 at. % and non-stoichiometric Ge20Sb10Se70 at. %. Thermal analysis on bulk glasses has previously shown that the former exhibited the maximum glass stability of the series. However, during fiber-drawing of Ge25Sb10Se65 at. %, the preform tip is found to undergo surface-devitrification to monoclinic GeSe2 alone, the primary phase, no matter if the preform is an annealed, as-melted rod or annealed, extruded rod. The heating rate of the preform-tip to the fiber-drawing temperature is estimated to be up to ~ 100 °C min−1 to ~ 490 °C. Lower heating rates of 10 °C min−1 using thermal analysis, in contrast, encourage crystallization of both Sb2Se3 and GeSe2. The non-stoichiometric: Ge20Sb10Se70 at. % composition drew successfully to low optical loss fiber, no matter whether the preform was an annealed, as-melted rod or annealed, extruded rod. This article is protected by copyright. All rights reserved.

Large-scale three-dimensional (3D) electromagnetic simulations are commonly used as design and investigation tools in a wide variety of technological fields. It is not uncommon for both excitations and observation quantities to be expressed in terms of particular field profiles of feed waveguides. These may then be used to evaluate, e.g. scattering parameters. These field profiles must be obtained as a pre-processing task before the main simulation. Use of a theoretical field profile as an excitation to a discretised structure will typically cause a non-physical reflection. It is therefore more desirable in practice to use a field profile that is consistent with both the discretisation of the geometry and the 3D method of simulation. The authors present an approach to extracting these 2D field profiles from large-scale 3D unstructured meshes which are to be simulated with the unstructured transmission line modelling method. Discretised slices from the 3D mesh are extracted and incrementally extruded into a form suitable for consistent pre-processing. The impacts of all the parameters of the approach are investigated. Benchmarking is undertaken on both coaxial cable and microstrip waveguide feed structures showing that good quality results can be obtained straightforwardly.

Selenide-chalcogenide glass, small-core, step-index fiber (SIF), core-doped with Pr3+: 9.51 × 1024 ions m−3 (500 ppmw) is fabricated for the first time with indium to help solubilize Pr3+. Core diameters of 20 or 40 μm are confirmed using scanning electron microscopy and near-field imaging; fibre numerical aperture is ∼0.4. Optical loss is ≥ 4.9 dB m−1 across the 3–9 μm mid-infrared (MIR) spectral range. On pumping at 1.55 μm or 2.013 μm, the SIFs give broad MIR emission across 3.5–6 μm assigned to 3H6 → 3H5 and 3H5 → 3H4. The Pr3+ emission-lifetime at 4.7 μm decreases from bulk-glass (10.1 ± 0.3 ms), to intermediately processed fiber (8.10 ± 0.5 ms) to SIF (7.1 ± 0.5 ms) induced by the processing. On end-pumping SIFs at 2.013 μm, the output pump-power and emission intensity at 4.7 μm became sub-linear and super-linear, respectively, suggesting MIR excited-state saturation is occurring.

An electromagnetic wavelength-scale analysis of the optical characteristics of multi-nanolayer photovoltaic (PV) structures: without an antireflection coating, with an antireflection coating on the top of the structure, and with both the antireflection coating on the top and a broadband non-periodic (chirped) distributed Bragg reflector (DBR) on the bottom of the structure is performed. All the PV structures studied are based on a Si p-i-n type absorber supported by a metallic layer (Cu) and SiO2 substrate. The top-to-bottom electromagnetic analysis is performed numerically by the method of single expression (MSE). Absorbing and reflecting characteristics of the multi-nanolayer PV structures are obtained. The influence of the thicknesses and permittivities of the layers of the PV structures on the absorbing characteristics of the structures is analyzed to reveal favourable configurations for enhancement of their absorption efficiency. The localizations of the electric component of the optical field and the power flow distribution within all the PV structures considered are obtained to confirm an enhancement of the absorption efficiency in the favorable configuration. The results of the electromagnetic wavelength-scale analysis undertaken will have scientific and practical importance for optimizing the operation of thin-filmmulti-nanolayer PV structures incorporating a chirped DBR reflector with regards to enhancing their efficiency.

A new method (FTIR continuous dn / dT method, n is refractive index and T temperature) for measuring the continuous thermo-optic coefficients of thin transparent films in the mid-infrared (MIR) spectral region is introduced. The technique is based on Fourier transform infrared (FTIR) transmission spectra measured at different temperatures. It is shown that this method can successfully determine the thermo-optic coefficient of chalcogenide glass thin films (of batch compositions Ge20Sb10Se70 at. % (atomic %) and Ge16As24Se15.5Te44.5 at. %) over the wavelength range from 2 to 25 µm. The measurement precision error is less than ± 11.5 ppm / °C over the wavelength range from 6 to 20 µm. The precision is much better than that provided by the prism minimum deviation method or an improved Swanepoel method.

We demonstrate a maximum gain of 4.6 dB at a signal wavelength of 5.28 μm in a 4.1 μm resonantly pumped Pr3+-doped selenide-based chalcogenide glass fibre amplifier of length 109 mm, as well as a new signal excited-stated absorption (ESA) at signal wavelengths around 5.5 μm. This work to the best of our knowledge is the first experimental demonstration of gain at mid-infrared (MIR) wavelengths in a Pr3+-doped chalcogenide fibre amplifier. The signal ESA of the fibre is attributed to the transition 3H6 → (3F4, 3F3) after the pump ESA (3H5 → 3H6) at a pump wavelength of 4.1 μm, which absorbs the MIR signal at wavelengths of 5.37, 5.51 and 5.57 μm, and so spoils the amplifier’s performance at these wavelengths. Thus, this signal ESA should be suppressed in a resonantly pumped Pr3+-doped selenide-based chalcogenide fibre amplifier.

In this contribution it is shown that broadband emission stretching from 2000 nm up to 6000 nm can be achieved when using selenide-chalcogenide glass. It is also shown experimentally that by appropriate selection of pumping wavelengths the shape of the output spectrum can be varied to suit a particular application.

This paper presents two methods for the segmentation of medical images based on evolutionary algorithms. Such image segmentation is a useful first step in the efficient and speedy analysis of medical images and provides a basis for the next stages of the image analysis process. In particular, the processing of images obtained from the inside of the human body allows for more effective diagnostics of lesions of human tissues. The first approach developed is based on evolutionary algorithms which divide the image into a given number of areas based on the intensity of RGB colours. The second segmentation method is based on the detection of edges in an image. An evolutionary algorithm was also used for this segmentation, based on the search for threshold values in the grey level in the image. We also compare the above segmentation methods with the numerical k-means segmentation method.

M-type fibers have the exceptional property that the higher-order LP0n modes are core-confined and easily excited, while the LP01 and other modes are confined to a high-index ring surrounding the core, so they are not easily excited. This has profound consequences for mid-infrared supercontinuum sources, where the high zero-dispersion wavelength of chalcogenide and ZBLAN fibers means that exotic pump sources have so far been necessary. We show here that in chalcogenide and ZBLAN M-type fibers the lower ZDW of the core-confined higher-order LP02 mode can be in the range of 2 to 3 µm (around 1.55 µm), while the fiber still has a large core diameter and thus supports high average power. This will allow established pump laser technology to be used in future high-power mid-infrared supercontinuum sources.

Due to lattice disorder, glassy semiconductors have energy levels in their bandgaps (gap states) that can be populated by sub-gap illumination or due to recombination of photo-excited carriers. The non-linear optical (NLO) response induced by high-intensity femtosecond (fs) laser pulses develops together with the gap states excitation. These effects in non-crystalline semiconductors have not yet been well studied. In this work, we use two realizations of the pump-probe method [1,2] to study the NLO response of chalcogenide glassy semiconductors of the systems As 40 S x Se 1-x and As 40 Se x Te 1-x with fs resolution in time upon illumination by fs laser pulses with the peak wavelengths λ p of 0.79 and 1.57 μm. By the partial replacement of S by Se in the As 40 S x Se 1-x system and of Se by Te in the As 40 Se x Te 1-x system, the bandgap energy Eg was varied so that the ratio R= hv/E g of the photon energy hv to the bandgap energy Eg was tailored in the range between 0.3 and 0.9. Magnitudes of the NLO coefficients of refraction n 2 and absorption β 2 have been obtained from measurements at each λ p with thin glass samples (thickness ∼1 mm) of each composition. Comparison of the data with the dispersion function G 2 (R) derived in the theory of NLO response of direct-gap crystalline semiconductors [3] (Fig.1a) allowed us to reveal that in the range 0.5 2 for a glass composition decreases with R in a similar way but it is always positive-valued. By solution of kinetic equations for densities of the photo-excited charge carriers, the dielectric constant e was evaluated by using the Drude-Lorentz model. We found that dynamics of the NLO response develop differently with or without a single-photon excitation of gap states [4,5]. In the range 0.3 2 increases with R (Fig.la). Here in the samples with R > 0.38, the two-photon excitation of gap states is possible; this is confirmed by Fig. 1b where the time-resolved NLO response of the samples is compared with the typical trace (inset) obtained in [2] for two-beam coupling signal from fused silica at the wavelength of 1.22 μm (R

Lightning strike protection is critical for aircraft made from carbon fiber composites that are less conductive than metals. In areas prone to initial lightning attachment, such as the wingtips and the nose radome, additional protection in the form of solid metallic or segmented diverter strips is typically required. However, generating a realistic model geometry of a wingtip or a radome nose with full lightning protection is a significant task in its own right as the diverter strips and the simulation mesh need to be aligned onto a non-developable surface. The paper explores the use of geometric techniques for the spatial manipulation of three-dimensional objects in order to generate realistic aircraft nose radome models incorporating lightning protection features. These models are then used to explore the effectiveness of a lightning protection scheme when high voltage is directly injected into the radome nose.

© 2019 Optical Society of America. A finite operator model is applied to the propagation of light in deformed step-index fibers. The distribution of the light captured by the fiber from an arbitrary initial excitation is illustrated in the phase space for each fiber boundary. The method proves to be promising in modeling the transmission of light in the presence of fiber asymmetries. Simulations are made of the captured power in the core in the presence of fiber deformations.

We demonstrate a maximum gain of 4.6 dB at a signal wavelength of 5.28 μm in a 4.1 μm resonantly pumped Pr3+-doped selenide-based chalcogenide glass fibre amplifier of length 109 mm, as well as a new signal excited-stated absorption (ESA) at signal wavelengths around 5.5 μm. This work to the best of our knowledge is the first experimental demonstration of gain at mid-infrared (MIR) wavelengths in a Pr3+-doped chalcogenide fibre amplifier. The signal ESA of the fibre is attributed to the transition 3H6 → (3F4, 3F3) after the pump ESA (3H5 → 3H6) at a pump wavelength of 4.1 μm, which absorbs the MIR signal at wavelengths of 5.37, 5.51 and 5.57 μm, and so spoils the amplifier’s performance at these wavelengths. Thus, this signal ESA should be suppressed in a resonantly pumped Pr3+-doped selenide-based chalcogenide fibre amplifier.

Lightning direct effects threats are a major concern for aircraft manufacturers. Of particular concern are fuel ignition threats caused by lightning current transfer between metallic fasteners and surrounding structures leading to voltage arcs, thermal sparks and pressurized gas effects. Although a large percentage of a modern aircraft structure is being replaced by carbon fibre reinforced plastic (CFRP), the main structural components remained joined by means of bolted joints. Although particular choices of fastener technologies are known to affect the current threshold for initiating arcs and sparks, the contributing effects of each design parameter of a structural joint are still not fully understood due to the fact that exploration of these parameters is primarily assessed using measurements. This paper reports a realistic model of a structural joint that includes the metallic bracket (representing a structural spar or rib) joined to the CFRP layer using a detailed model of a fastener (washer, nuts and bolts). The model is simulated using a robust broadband time-domain numerical model based on tetrahedral meshes. The design parameters of the structural joint are explored when high currents are directly injected into the fastener on a metallic bracket.