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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.

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.

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.

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.

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.

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.

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.

© 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.

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.

A dual hollow-core anti-resonant fiber is proposed and numerically investigated. Two elliptical tubes are introduced to separate the core into two symmetrical cores; further nested tubes are adopted to achieve good single mode performance. Mode coupling takes place in the proposed fiber through an air gap between the two cores; the coupling strength can be controlled by adjusting fiber parameters. A broadband polarization splitter can be constructed by selecting a suitable fiber length. Numerical results show that a polarization splitter based on the proposed fiber has a length of 6.75 cm and a bandwidth of 310 nm, covering the wavelength range from 1.41 μm to 1.72 μm with an extinction ratio as low as −20 dB. The ratio of higher order mode to fundamental mode loss is great than 100, implying that the proposed polarization splitter also possesses effective single mode performance.

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 complex phenomenon including an asymmetric time varying Airy pulse and an asymmetric time varying bounded medium is considered. It is shown that this phenomenon is controlled by a generalised start parameter determined by the point of the source location and the moment of its initiation.

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.

A novel refractive index sensor based on a D-shaped photonic crystal fiber with a nanoscale gold belt is proposed. The nanoscale gold belt is deposited on the flat surface to produce surface plasmon resonance. Numerical results show that the refractive index sensor has a broad measurement range which is from 1.2 to 1.4 and the maximum sensitivity can reach to 3751.5 nm/RIU. The refractive index resolution of the sensor is under 1 × 10−5 RIU in the whole measuring range. A high adjusted R-squared, up to 0.99002, is acquired from the fitting curve of the resonance wavelength. The sensor is sensitive to the variation of the refractive index of analytes and can be applied to the fields of chemical and biological sensing field.

The incorporation of material losses within an unstructured transmission line Modeling electromagnetic field solver is presented. A theoretical and numerical development is complemented by a number of quantified canonical examples. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2218–2222, 2015

In this contribution we present the sensing capabilities of a novel N-path Mach–Zehnder interferometer (MZI) that relies on a multicore microstructured optical fibre (MC-MOF) connected between two sections of standard single mode fibre. The modal properties of the MC-MOF structure are analysed experimentally by measuring near field profiles. The dependence of the N-path MC-MOF MZI sensitivity on temperature, tensile strain and bending is investigated. The results suggest that such an interferometer is a good candidate for a tensile strain or bending sensor.

An approximating functions method for solving a nonlinear Volterra integral equation is presented. The equation form is the same for various media and it does not depend on the initial signal. Other key features of this approach are the natural description of non-stationary and nonlinear phenomena, the unified definition of inner and outer problems and the inclusion of initial and boundary conditions in the same equation. It permits universal modelling algorithms for a wide range of nonlinear electrodynamic problems. A computer model based on the algorithm is developed for 1D + 1T case and the transformation of an electromagnetic pulse in a nonlinear layer is investigated.

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 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.

The mid-infrared (MIR) emission behavior of Tb3+-doped Ge–As–Ga–Se bulk glasses (500, 1000, and 1500 ppmw Tb3+) and unstructured fiber (500 ppmw Tb3+) is investigated when pumping at 2.013 μm. A broad emission band is observed at 4.3–6.0 μm corresponding to F57→F67, with an observed emission lifetime of 12.9 ms at 4.7 μm. The F47 level is depopulated nonradiatively and so it is proposed that Tb3+-doped Ge–As–Ga–Se fiber may operate as a quasi-three-level MIR fiber laser. Underlying glass-impurity vibrational absorption bands are numerically removed to give the true Tb3+ absorption cross section, as required for Judd–Ofelt (J–O) analysis. Radiative transition rates calculated from J–O theory are compared with measured lifetimes. A numerical model of the three-level Tb3+-doped fiber laser is developed for Tb3+ doping of 8.25×1024 ions m−3 (i.e., 500 ppmw) and dependence of laser performance on fiber length, output coupler reflectivity, pump wavelength, signal wavelength, and fiber background loss is calculated. Results indicate the feasibility of an efficient three-level MIR fiber laser operating within 4.5–5.3 μm, pumped at either 2.013 or 2.95 μm.

Resonant frequency extraction from time signal simulations of optical resonators is often required to resolve closely spaced resonances in addition to estimating high Q factors. Traditional Fourier transform-based fitting methods thus require very long time signals, limiting their usage. Complex exponential fitting-based methods such as matrix pencil, modified Prony and harmonic inversion provide better accuracy, but each has its own advantages as well as disadvantages. In this study, it is shown that the matrix pencil method is limited by the number of time samples, but provides accurate results, whereas the harmonic inversion method provides less accurate results with high efficiency. The difference formulation of the modified Prony method implemented with multiple precision, while providing the best accuracy, is the least efficient approach and requires careful adjustment of its parameters to obtain a solution.

We present a study of mid-infrared photoluminescence in the wavelength range 3.5–5.5 μm emitted from Pr3+: GeAsGaSe core/GeAsGaSe cladding chalcogenide fiber. The Pr3+ doped fiber optic preform is fabricated using extrusion and is successfully drawn to low optical loss, step-index fiber. Broadband mid-infrared photoluminescence is observed from the fiber, both under 1.55 μm or 1.94 μm wavelength excitation. Absorption, and emission, spectra of bulk glass and fiber are presented. Luminescent lifetimes are measured for the fiber and the Judd–Ofelt parameters are calculated. The radiative transition rates calculated from Judd–Ofelt theory are compared with experimental lifetimes. The observed strong broadband emission suggests that this type of fiber is a good candidate for further development to realize both fiber lasers and amplified spontaneous emission fiber sources in the mid-infrared region.

Numerical modelling of a Pr3+-doped chalcogenide glass fibre laser is presented in this paper. The spectroscopic parameters are extracted from in-house prepared Pr3+ doped selenide-chalcogenide glass samples and used in the modelling. In this contribution, particular attention is paid to a novel resonant pumping scheme. The modelled laser performance is tested as a function of pump wavelength, fibre length, signal wavelength, fibre background loss and output coupler reflectivity. The modelling results show that the proposed resonant pumping scheme, which might be achieved in practice using a high power QCL pump, allows for a significant reduction in the laser threshold and an increase in the laser efficiency. A slope efficiency of 54% is calculated when the fibre losses are brought down to 1 dB/m.

A gain-switched Dy3+-doped ZBLAN fiber laser operating at 2.943 μm is experimentally reported for the first time to the best of our knowledge. The laser was pumped by a 1.1 μm Q-switched ytterbium (III) fiber laser constructed in-house. A stable pulse train is achieved with repetition rates spanning between 25 and 100 kHz. For the repetition rate of 50 kHz, stable 183 ns pulses with an energy of 0.72 μJ and peak power of 4 W are recorded. By using a longer length of Dy3+-doped ZBLAN fiber, gain-switched operation was achieved at a wavelength larger than 3 μm.

The omnidirectional transmission properties of photonic heterostructures composed of cascaded one-dimensional photonic crystals (1DPCs) with the same materials and different thickness ratios of the alternate high- and low-refractive index layers were studied theoretically. A criterion for designing omnidirectional reflectors with a maximum bandgap width is presented for heterostructures with an arbitrary number of cascaded 1DPCs. Omnidirectional reflectors based on two and three cascaded 1DPCs are designed according to the criterion.

The experimentally obtained luminescence characteristics of a praseodymium (Pr $$^{3+})$$ doped chalcogenide glass fiber are studied numerically using a rate equation approach. The numerical model includes both the radiative and non-radiative transition paths whilst it neglects the up-conversion processes. Photoluminescence spectra at mid-infrared wavelengths ranging from 3.5 to 6 $${\upmu }$$ m were obtained by using two pump wavelengths: 1.55 and 1.94 $${\upmu }$$ m. A good agreement between the experiment and theory is obtained for the photoluminescence decay profiles.

A novel method for obtaining a multimode optical coupler in chalcogenide glass fibre is described. The fibres used had a large $$\text{ Ge }_{17}\text{ As }_{18}\text{ Se }_{65}$$ core comprising about 74 % of the total cross-sectional area with an optical cladding of $$\text{ Ge }_{17}\text{ As }_{18}\text{ Se }_{62}\text{ S }_{3}$$ . A single arc-shaped U-groove was formed in each of two silicate glass blocks. A length of fibre was embedded into each groove and glued in place. The centre of each fibre length was subsequently side-polished. Finally two such embedded fibres were glued together in close contact to form the coupler, whilst monitoring the coupling ratio at the output.

Transmission-line modelling (TLM) is a valuable technique for numerical simulation of electromagnetic fields. Recently, investigations have been successfully carried out into the use of the TLM approach on unstructured meshes However, as the local characteristics of mesh geometry will clearly make an impact upon the fidelity of simulations, it is necessary to examine suitable techniques for mesh optimisation. Three different methods have been investigated here to find optimal meshes for subsequent TLM simulations: the centroidal Voronoi Tessellation method, the optimal Delaunay triangulation method and a spring relaxation method. These different techniques are assessed in terms of maximum efficiency of the subsequent TLM simulations and the computational cost that is incurred to identify them. Several different canonical examples of mesh are considered to determine the generality of the conclusions drawn.

Waveguide losses in all-solid photonic bandgap fibre are studied numerically using both vectorial mode solver and vectorial beam propagation methods. Confinement loss, including material losses, is comprehensively evaluated for defect modes of hexagonal lattice photonic bandgap fibre. The excitation of the index-guiding modes at the bandgap edges leads to a narrowing of the transmission bands. Submicron deformations of the transverse structure of the fibre lead to a significant reduction in the width of the transmission bands, yet the minimum value of the losses within these bandgaps remains practically unchanged. Longitudinal variation of the fibre profile increases the effective losses by up to tens of dB/m.

This paper presents a coupled electromagnetic-thermal model for modelling temperature evolution in nano-size plasmonic heat sources. Both electromagnetic and thermal models are based on the Transmission Line Modelling (TLM) method and are coupled through a nonlinear and dispersive plasma material model. The stability and accuracy of the coupled EM-thermal model is analysed in the context of a nano-tip plasmonic heat source example.

Scanning near-field infrared microscopy (SNIM) potentially enables subdiffraction, broadband mid-infrared (MIR:3–25-μm wavelength range) spectral-mapping of human cells and tissue for real-time molecular sensing, with prospective use in disease diagnosis. SNIM requires an MIR-transmitting tip of small aperture for photon collection. Here, chalcogenide-glass optical fibers are reproducibly tapered at one end to form a MIR transmitting tip for SNIM. A wet-etching method is used to form the tip. The tapering sides of the tip are Al-coated. These Al-coated tapered-tips exhibit near-field power-confinement when acting either as the launch-end or exit-end of the MIR optical fiber. We report first time optimal cleaving of the end of the tapered tip using focused ion beam milling. A flat aperture is produced at the end of the tip, which is orthogonal to the fiber-axis and of controlled diameter. A FIB-cleaved aperture is used to collect MIR spectra of cells mounted on a transflection plate, under illumination of a synchrotron- generated wideband MIR beam.

Time dependent electromagnetic pulses propagating with deceleration along the dominant propagation direction, and passing through a dielectric layer are investigated in the 1D + T case. This is achieved using an integral equation in the paraxial approximation obtained via the Green’s function symmetric with respect to the propagation direction.

An effective model of single and multilayered thin panels, including those formed using carbon fiber composite (CFC) materials, is incorporated into the Transmission Line Modeling (TLM) method. The thin panel model is a one-dimensional (1D) one based on analytical expansions of cotangent and cosecant functions that are used to describe the admittance matrix in the frequency domain; these are then converted into the time domain by using digital filter theory and an inverse Z transform. The model, which is extended to allow for material anisotropy, is executed within 1D TLM codes. And, for the first time, the two-dimensional (2D) thin surface model is embedded in unstructured three-dimensional (3D) TLM codes. The approach is validated by using it to study some canonical structures with analytic solutions, and against results taken from the literature. It is then used to investigate shielding effectiveness of carbon fiber composite materials in a practical curved aerospace-related structure., 8 pages; submitted to IEEE Transactions on Electromagnetic Compatibility

This paper considers the scattering of an H-polarized plane wave by a freestanding periodic grating that contains two circular cylinders on each period, one made of silver and the other of dielectric. If such a grating is made of deeply subwavelength wires, the reflection and transmission coefficients demonstrate both plasmon and grating resonances. To clarify them, we also discuss the scattering by similar gratings made of either silver or dielectric wires only. However, the main attention is paid to the associated lasing eigenvalue problem for the dielectric cylinders pumped to become quantum wires, i.e., to obtain a “negative-absorption” complex refractive index. The analysis is done using a meshless analytical-numerical method with guaranteed convergence. The computations show that, in this composite periodic cavity, material thresholds of lasing for the grating modes can be much lower than for the plasmon modes.

The thickness of the layers comprising optical structures is usually very thin. When modelling such thin features using a traditional numerical method, for instance the transmission-line modelling (TLM) method, a very small space step is often used to properly discretize the material geometry. This consequently results in large memory storage and longer run time. In this paper a new technique embedding thin structures between TLM nodes is investigated. The key features of this technique are the acquisition of the formulations in the frequency domain and the utilisation of digital filter theory and an inverse Z transform to change the formulations to the time domain. This technique has been successfully applied to calculate the reflection and transmission coefficients of optical structures incorporating thin layers, including antireflection coatings and fibre Bragg grating structures.

A polarization maintaining erbium-doped photonic crystal fiber laser (PM-Er-PCF), is presented. The laser operates in a ring cavity in the near infrared wavelength range. We believe that it is the first report of the successful realization of a polarization maintaining erbium-doped photonic crystal fiber laser. Single-wavelength and multiwavelength operation of the developed fibre laser was observed. Experimental results show that the laser operates with good output parameter stability over a period of one hour and exhibits a 37 dB signal-to-noise-ratio. We present a detailed description of the design process and of the experimental characterization and validation for the PM-Er-PCF. We also analyze the impact of the photonic crystal structure on the laser parameters.

Within the framework of the recently proposed approach to view the lasing in open microcavities as a linear eigenproblem for the Maxwell equations with exact boundary and radiation conditions, we study the correspondence between the modal thresholds and field overlap coefficients. Macroscopic gain is introduced into the cavity material within the active region via the “active” imaginary part of the refractive index. Each eigenvalue is constituted of two positive numbers, namely, the lasing wavenumber and the threshold value of material gain. This approach yields clear insight into the lasing thresholds of individual modes. The Optical Theorem, if applied to the lasing-mode field, puts the familiar “” condition on firm footing. It rigorously quantifies the role of the spatial overlap of the mode E-field with the active region, whose shape and location are efficient tools of the threshold manipulation. Here, the effective mode volume in open resonator is introduced from first principles. Examples are given for the 1-D cavities equipped with active layers and distributed Bragg reflectors and 2-D cavities with active disks and annular Bragg reflectors.

The properties of highly nonlinear glasses for photonic devices and the advantages of processing these materials using femtosecond laser pulses are discussed in a brief review. A novel approach is proposed for the optimization of the modification process that takes into account the dispersion of the nonlinear coefficients of refraction and absorption. Numerical modeling of the pulse energy deposition into a sample of chalcogenide glass shows that the shapes and dimensions of the modified regions depend on the nonlinear coefficients.

An alternating direction implicit (ADI), scheme for the wide-angle finite-difference beam propagation method (FD-BPM) based on the wide angled Pade multistep method is presented. The scheme incorporates an iterative technique for correction of the operator splitting error. The resulting equations are efficiently solved by the Thomas algorithm for tri-diagonal band matrices. The dispersion characteristics, accuracy and stability of the scheme is verified analytically and numerically for the cases of a plane wave propagating at fixed angle to the assumed propagation direction of the algorithm and the three dimensional angled propagation of a Gaussian beam. The computational requirements of the method are assessed against a standard wide-angle Pade multistep method that uses direct and iterative sparse matrix solvers.

This article presents an analytical approach to the 2D problem in which a circular whispering-gallery mode (WGM) resonator is subject to an abrupt temporal change in refractive index in a circular coaxial region or in a ring region near the rim.

Spectroscopic experiments were conducted to characterise commercial side emission optical fibres regarding their emission spectra and the intensity of emitted radiation in the spectral range from UV-A to visible blue. For fibres with silica core and scattering particles embedded in the cladding, the emission spectra are determined by the material of the scattering particles. While Al 2 O 3 particles allow emission of UV-A and visible blue light, ZnO filters most of the UV-A light up to wavelengths of 380 nm. The emitted intensity ideally decays exponentially along the fibre with a decay constant that is correlated to the particle concentration. The absolute values of the emitted intensity increase with increasing fibre radius. For fibres with PMMA core and surface perforation, relatively weak background emission of UV-A and blue light and additional local emission peaks due to the surface treatment were observed. The background emission can be explained by scattering due to the intrinsic non-uniformity of the PMMA core. The surface defects cause highly non-uniform and directional emission at a relatively high intensity. Compared to the silica core fibres, higher emission intensity in the UV-A and visible blue spectrum, albeit at a non-uniform distribution, was observed although the transmission along the fibre over longer distances is significantly lower for PMMA core fibres than for fibres with silica core.