Search

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.

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.

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.

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.

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.

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.

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.

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.

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.

© 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.

A new framework for the development of the perfectly matched layer (PML) in the Transmission Line Modelling (TLM) method is demonstrated. The formulation is based on the stretched coordinate PML and involves the mapping of the TLM node to an analytically extended geometric domain. The implementation demonstrates the more stable second order discretization of the PML equations in TLM. The validity of the PML formulation is demonstrated on a canonical case of a metal waveguide and compared with an existing PML TLM scheme.

This work reports on the fabrication and subsequent supercontinuum generation in a Ge-As-Se-Te/Ge-As-Se core/clad chalcogenide step-index fiber with an elliptical-core and an ultra-high numerical aperture of 1.88 ± 0.02 from 2.5 - 15 µm wavelength. The fiber has very low transmission loss of < 2 dB/m from 5-11 µm and a minimum loss of 0.72 ± 0.04 dB/m at 8.56 µm. Supercontinuum spanning from 2.1 µm to 11.5 µm with an average power of ∼6.5 mW was achieved by pumping a ∼16 cm fiber with a minor/major axis core diameter of 4.2/5.2 µm with 250 fs pulses at 4.65 µm wavelength and a repetition rate of 20.88 MHz. The effect of the elliptical-core was investigated by means of mechanical rotation of the fiber relative to the linear pump polarization, and it was found to cause a shift in the supercontinuum spectral edges by several hundred nanometers.

We report on the internal examination of mid-infrared chalcogenide glasses using near-infrared light to reveal light-scattering defects. The technique is demonstrated on imperfectly made chalcogenide glass rods and fiber. This simple, non-destructive technique enables assessment of the interior of glasses and convenient detection of regions containing defects hidden due to the glass opacity to visible light. This method will reveal the presence of unwanted light-scattering defects including nucleated crystals, dust, striae, and bubbles. Hence, this method will help to optimize both chalcogenide glass chemical formulations, against devitrification, and process design to manufacture glass rods and fiber with minimized light scattering defects.

This work reports on process-induced impurities in rare-earth ion: Dy3+-doped selenide chalcogenide glasses, which are significant materials for active photonic devices in the mid-infrared region. In particular, the effect of contamination from the silica glass ampoule containment used in chalcogenide glass synthesis is studied. Heat-treating Dy-foil-only, and DyCl3-only, separately, within evacuated silica glass ampoules gives direct evidence of silica ampoule corrosion by the rare-earth additives. The presence of [Ga2Se3] associated with [Dy] on the silica glass ampoule that has been contact with the chalcogenide glass during glass melting, is reported for the first time. Studies of 0–3000 ppmw Dy3+-doped Ge16.5As9Ga10Se64.5 glasses show that Dy-foil is better than DyCl3 as the Dy3+ additive in Ge-As-Ga-Se glass in aspects of avoiding bulk crystallization, improving glass surface quality and lowering optical loss. However, some limited Dy/Si/O related contamination is observed on the surfaces of Dy-foil-doped chalcogenide glasses, as found for DyCl3-doped chalcogenide glasses, reported in our previous work. The surface contamination indicates the production of Dy2O3 and/or [≡Si-O-Dy=]-containing particles during chalcogenide glass melting, which are potential light-scattering centers in chalcogenide bulk glass and heterogeneous nucleation agents for α-Ga2Se3 crystals.

In this contribution the diode pumped high-power Er:ZBLAN laser operating at around 2.8 µm is reported. The laser produces 2 W output power with the slope efficiency of 24 % measured with respect to the incident pump power. Full Text: PDF References S. D. Jackson, "Towards high-power mid-infrared emission from a fibre laser", Nature Photonics 6, 423 (2012). CrossRef V. Portosi, D. Laneve, C. M. Falconi, and F. Prudenzano, "Advances on Photonic Crystal Fiber Sensors and Applications", Sensors 19, (2019). CrossRef M. C. Falconi, D. Laneve, and F. Prudenzano, "Advances in Mid-IR Fiber Lasers: Tellurite, Fluoride and Chalcogenide", Fibers 5, 23 (2017). CrossRef M. Michalska, P. Grześ, J. Świderski, "High power, 100 W-class, thulium-doped all-fiber lasers", Phot. Lett. Poland, 11, 109 (2019). CrossRef Y. O. Aydin, V. Fortin, R. Vallee, and M. Bernier, "Towards power scaling of 2.8 μm fiber lasers", Opt. Lett. 43, 4542 (2018). CrossRef S. Crawford, D. D. Hudson, and S. D. Jackson, "High-Power Broadly Tunable 3- μm Fiber Laser for the Measurement of Optical Fiber Loss", IEEE Photonics Journal 7, 1 (2015). CrossRef V. Fortin, F. Jobin, M. Larose, M. Bernier, and R. Vallee, "10-W-level monolithic dysprosium-doped fiber laser at 3.24 μm", Opt. Lett. 44, 491 (2019). CrossRef L. Sojka, et al., "Experimental Investigation of Mid-Infrared Laser Action From Dy 3+ Doped Fluorozirconate Fiber", IEEE Photon. Technol. Lett. 30, 1083 (2018). CrossRef M. Pollnan and S. D. Jackson, "Erbium 3 /spl mu/m fiber lasers", IEEE J. Sel. Top. in Quantum Electron., 7, 30 (2001). CrossRef Y. O. Aydin, F. Maes, V. Fortin, S. T. Bah, R. Vallee, and M. Bernier, "Endcapping of high-power 3 µm fiber lasers", Opt. Express 27, 20659 (2019). CrossRef C. A. Schafer, "Fluoride-fiber-based side-pump coupler for high-power fiber lasers at 2.8 μm", et al., Opt. Lett. 43, 2340 (2018). CrossRef O. Henderson-Sapir, J. Munch, and D. J. Ottaway, "New energy-transfer upconversion process in Er 3+ :ZBLAN mid-infrared fiber lasers", Opt. Express 24, 6869 (2016). CrossRef F. Maes, V. Fortin, S. Poulain, M. Poulain, J.-Y. Carree, M. Bernier, and R. Vallee, "Room-temperature fiber laser at 3.92 μm", Optica 5, 761 (2018). CrossRef R. I. Woodward, M. R. Majewski, D. D. Hudson, and S. D. Jackson, "Swept-wavelength mid-infrared fiber laser for real-time ammonia gas sensing", APL Photonics 4, 020801 (2019). CrossRef M. Kochanowicz, et al., "Near-IR and mid-IR luminescence and energy transfer in fluoroindate glasses co-doped with Er 3+ /Tm 3+ ", Opt. Mater. Express 9, 4772 (2019). CrossRef M. Kochanowicz, et al., "Sensitization of Ho 3+ - doped fluoroindate glasses for near and mid-infrared emission", Optical Materials 101, 109707 (2020). CrossRef J. Wang, X. Zhu, M. Mollaee, J. Zong, and N. Peyhambarian, "Efficient energy transfer from Er 3+ to Ho 3+ and Dy 3+ in ZBLAN glass", Opt. Express 28, 5189 (2020). CrossRef M. C. Falconi, D. Laneve, V. Portosi, S. Taccheo, and F. Prudenzano, "Design of a Multi-Wavelength Fiber Laser Based on Tm:Er:Yb:Ho Co-Doped Germanate Glass", J Lightwave Technol 1 (2020). CrossRef K. Anders, A. Jusza, P. Komorowski, P. Andrejuk, and R. Piramidowicz, "Short wavelength up-converted emission studies in Er 3+ and Yb 3+ doped ZBLAN glasses", J. Lumin. 201, 427 (2018). CrossRef P. Komorowski ,K. Anders ,U. Zdulska,R. Piramidowicz R. "Erbium doped ZBLAN fiber laser operating in the visible - feasibility study", Photonics Lett Pol 9, 85 (2017). CrossRef J. Swiderski, M. Michalska, and P. Grzes, "Broadband and top-flat mid-infrared supercontinuum generation with 3.52 W time-averaged power in a ZBLAN fiber directly pumped by a 2-µm mode-locked fiber laser and amplifier", Applied Physics B 124, 152 (2018). CrossRef V. Fortin, M. Bernier, S. T. Bah, and R. Vallee, "30 W fluoride glass all-fiber laser at 2.94 μm", Opt. Lett. 40, 2882 (2015). CrossRef

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.

1000 ppmw Sm3+-doped Ge19.4Sb9.7Se67.9Ga3 atomic % chalcogenide bulk glass and unstructured fiber are prepared. Near- and mid-infrared absorption spectra of the bulk glass reveal Sm3+ electronic absorption bands, and extrinsic vibrational absorption bands, due to host impurities. Fiber photoluminescence, centred at 3.75 µm and 7.25 µm, is measured when pumping at either 1300 or 1470 nm. Pumping at 1470 nm enables the photoluminescent lifetime at 7.3 µm to be measured for the first time which was ∼100 µs. This is the longest to date, experimentally observed lifetime in the 6.5-9 µm wavelength-range of a lanthanide-doped chalcogenide glass fiber.

The modeling and design of fiber lasers facilitate the process of their practical realization. Of particular interest during the last few years is the development of lanthanide ion-doped fiber lasers that operate at wavelengths exceeding 2000 nm. There are two main host glass materials considered for this purpose, namely fluoride and chalcogenide glasses. Therefore, this study concerned comparative modeling of fiber lasers operating within the infrared wavelength region beyond 2000 nm. In particular, the convergence properties of selected algorithms, implemented within various software environments, were studied with a specific focus on the central processing unit (CPU) time and calculation residual. Two representative fiber laser cavities were considered: One was based on a chalcogenide&ndash, selenide glass step-index fiber doped with trivalent dysprosium ions, whereas the other was a fluoride step-index fiber doped with trivalent erbium ions. The practical calculation accuracy was also assessed by comparing directly the results obtained from the different models.

In this paper, the Unstructured Transmission Line Modelling (UTLM) method based on a tetrahedral mesh is applied to model the electromagnetic coupling into wire looms and bundles with multiple cores that are typical of an aircraft system, when they are exposed to plane wave illuminations. The impact on the electromagnetic coupling into wires of both bundle configuration and the positioning of the bundle relative to simple structures are investigated using the UTLM method with explicit meshing of the wires. The work not only confirms that UTLM method as a powerful tool for dealing with wire looms and bundles but provides invaluable information on the margins to be expected in key experimental waveform parameters such as peak amplitude and frequency response.

A time-resolved pump-probe method is used for the evaluation of non-linear optical coefficients of chalcogenide glasses from the As-S-Se and Ge-Se systems near their fundamental absorption band edges. The results are analyzed via comparison with the spectral dependencies of the non-linear optical coefficients of crystalline semiconductors; the role of electron transitions through the gap states of chalcogenide glasses is discussed.

In this contribution we use a numerical model to study the photoluminescence emitted by Tb3+ doped chalcogenide-selenide glass fibers pumped by laser light at approximately 3 µm. The model consists of the set of ordinary differential equations (ODEs), which describe the spatial evolution of the pump laser and MIR photoluminescence light within the fiber. The ODEs are coupled with the rate equations that describe the energy level populations. A self-consistent solution of the equation system yields the pump light, MIR photoluminescence and level population distribution within the fiber. Using the developed model we numerically calculate results and discuss the dependence of the output photoluminescence MIR power on the fiber optical loss, fiber length and pump wavelength.

We develop a model of a terbium (111) ion doped selenide chalcogenide glass fibre source that provides spontaneous emission within the mid-infrared (MIR) wavelength range. We use two numerical algorithms to calculate the solution and compare their properties.

The spectral behaviour and the real-time operation of Parity-Time (\(\mathcal {PT}\)) symmetric coupled resonators are investigated. A Boundary Integral Equation (BIE) model is developed to study these structures in the frequency domain. The impact of realistic gain/loss material properties on the operation of the \(\mathcal {PT}\)-symmetric coupled resonators is also investigated using the time-domain Transmission-Line Modelling (TLM) method. The BIE method is also used to study the behaviour of an array of PT-microresonator photonic molecules.

The RWG basis widely used in the discretisation of the EFIE is traditionally defined over interior edges of the structure's mesh when modelling charge-neutral scattering problems. In this paper, a careful extension to the RWG function space that allows for flow of current in and out of a structure via its boundary edges while maintaining current conservation is constructed. This space is appropriate for the computation of capacitance, where (i) a constant voltage difference is maintained between two components making up the device, and (ii) the total current is conserved. Using this basis implicitly enforces a constant potential difference between the metal plates (cf. natural boundary conditions), and explicitly places a restriction on the current (cf. essential boundary conditions). It improves upon the classic delta gap excitation of capacitive structures in that it is asymptotically independent of the triangulation used to describe the device's geometry.

A ray dynamical approach is developed for the study of large-core asymmetric step index fibres (SIF), especially those made from chalcogenide glasses (ChGs) which can exhibit very high refractive index, large numerical aperture, and which are transparent at mid-infrared wavelengths. The model allows for deformations of the SIF away from concentric circular structures, and for the light rays captured by the fibre to behave chaotically within the asymmetric boundaries of the fibre. Chaotic and periodic rays can be classified by the Poincare surface of sections (SOSs). In the model, the ray dynamics in the SIF are approximated by dividing the SOSs into pixels; the construction of a transfer matrix stores all the mapping probabilities. The light intensity distribution in the SOSs is efficiently propagated using the constructed transfer matrix, providing a viable alternative to propagating all the rays in the SIF by brute force ray tracing. The model enables the rapid calculation of the power accumulated in the fibre core following an arbitrary excitation.

The well-known method presented by Swanepoel can be used to determine the refractive index dispersion of thin films in the near-infrared region from wavelength values at maxima and minima, only, of the transmission interference fringes. In order to extend this method into the mid-infrared (MIR) spectral region (our measurements are over the wavelength range from 2 to 25 μm), the method is improved by using a two-term Sellmeier model instead of the Cauchy model as the dispersive equation. Chalcogenide thin films of nominal batch composition As40Se60 (atomic %) and Ge16As24Se15.5Te44.5 (atomic %) are prepared by a hot-pressing technique. The refractive index dispersion of the chalcogenide thin films is determined by the improved method with a standard deviation of less than 0.0027. The accuracy of the method is shown to be better than 0.4% at a wavelength of 3.1 μm by comparison with a benchmark refractive index value obtained from prism measurements on Ge16As24Se15.5Te44.5 material taken from the same batch.