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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.

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.

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 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.

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.

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.

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.

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.

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 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.

We present the optical properties such as the linear refractive index ( n ), the absorption coefficient ( α ), the energy band gap ( E g ) and the nonlinear refractive index ( n 2 ) measured by spectroscopy and degenerate four wave mixing methods for Er 3+ -doped oxyfluoride glasses and nano-glass-ceramics. The n 2 of the Er 3+ -doped oxyfluoride nano-glass-ceramic is almost twice that of the Er 3+ -doped parent oxyfluoride glass and undoped oxyfluoride glass. The n 2 values of the Er 3+ -doped oxyfluoride glass and non-Er 3+ -doped oxyfluoride glass are almost the same.

The established time domain Transmission-Line Modelling (TLM) numerical method is extended to include models of (i) saturable dispersive gain and (ii) non-linear dielectric material. The method is used to simulate a photonic memory device based on a nonlinear Parity-Time (PT) structure.

Two time-resolved experimental methods have been used for characterization of the non-linear optical response of chalcogenide glasses of the system As-S-Se-Te in IR and THz ranges upon excitation by femtosecond laser pulses at 800 nm wavelength. Photoinduced conductivity and refractivity were studied by using a rate equation model.

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.

We perform a numerical analysis of mid-infrared photoluminescence emitted by praseodymium (III) doped chalcogenide selenide glass pumped at near-infrared wavelengths. The results obtained show that an effective inversion of level populations can be achieved using both 1480 nm and 1595 nm laser diodes. The rate of the spontaneous emission achieved when pumping at 1480 nm and 1595 nm is comparable to this achieved using the standard pumping wavelength of 2040 nm., 7 pages, 8 figures

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.

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.

Using the recently developed method based on the rigorous theory of singular and hypersingular integral equations (IEs) and Nystrom-type discretization, a paraboloidal reflector assisted with a conical shield is investigated. To decrease the computation time we propose a new method of calculation of the Modal Green's Functions in the quasi-optical range. The far and near fields of the studied reflector are analyzed in the transmission and reception cases, and reveal fine features that escape asymptotic analysis. Elementary numerical optimization of the shield-assisted paraboloidal antenna is performed.

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.

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.

Broadband terahertz time domain spectroscopy (THz-TDS) and time resolved terahertz spectroscopy (TRTS) were performed on a 54 μm thick chalcogenide glass (As 30 Se 30 Te 40 ) sample using a two-color laser induced air plasma THz system in transmission and reflection configurations, respectively. Two absorption modes were observed at 2–3 THz and 5–8 THz. The photo-induced conductivity can be well described by the Drude-Smith conductivity model, which shows significant carrier localization effects. A fast refractive index change was observed 100 fs before the conductivity reached its maximum with two orders of magnitude larger amplitude than expected for the optically induced THz Kerr effect, indicating that the free carriers are responsible for the transient index change.

In this contribution a multiwavelength erbium ring laser is presented. The multiwavelength operation isachievedby using a novel in-line Mach-Zehnder (MZ) fibre interferometer based on multicore microstructured fibre (MC-MOF).The MZ interferometer acts as a periodic spectral filter. The modal properties of the MC-MOF are analysed using the finite difference method. Dual wavelength operation is demonstrated with an optical signal-to-noise ratio (OSNR) of 35 dB and a peak separation of 2 nm.

The mid-infrared (MIR) spans the 3 – 25 µm wavelength range. Rare-earth-ion doped selenide-chalcogenide glasses are being developed for direct-emission MIR fibre lasers. The true Pr3+ absorption cross-section in the 3.5 – 6 µm wavelength region of a Pr3+-doped (500 ppmw of Pr3+ i.e. 9.47×1019 Pr3+ ions cm−3) GeAsGaSe host-glass is presented, after numerically removing the underlying, extrinsic vibrational absorption due to [H-Se-] contamination of the host-glass.

We discuss the numerical modelling of lanthanide-ion doped chalcogenide glass fibre lasers for operation in the mid-infrared wavelength region. We extract the modelling parameters from emission and absorption measurements using Judd-Ofelt and McCumber theory. Numerical algorithms are developed based on the experimentally extracted fibre parameters. The simulation results predict lasing with slope efficiency of at least 20 % provided, that the fibre loss can be kept at the level of 1 dB/m or less.

Much effort has been devoted to the study of glasses that contain the chalcogen elements (sulfur, selenium and tellurium) for photonics' applications out to MIR wavelengths. In this paper we describe some techniques for determining the refractive index dispersion characteristics of these glasses. Knowledge of material dispersion is critical in delivering step-index fibres including with high numerical aperture for mid-infrared supercontinuum generation.

An interferometric pump-probe method with the femtosecond resolution in time is used to study the third-order non-linear optical response and photosensitivity of a variety of chalcogenide glasses of the system As-S-Se.

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.

Novel chalcogenide glass-based fiber opens up the mid-infrared (MIR) range for real-time monitoring and control in medical diagnostics and chemical processing. Fibers with long wavelength cut-off are of interest here. Sulfide, selenide and telluride based chalcogenide glass are candidates, but there are differences in their glass forming region, thermal stability and in the short and long wavelength cut-off positions. In general sulfide and selenide glasses have greater glass stability, but shorter long-wavelength cut-off edge, compared to telluride glasses; selenide-telluride glasses are a good compromise. Low optical loss selenide-telluride based long wavelength fibers could play a substantial role in improving medical diagnostic systems, chemical sensing, and processing, and in security and agriculture. For biological tissue, the molecular finger print lies between ~3-15 μm wavelengths in the MIR region. Using MIR spectral mapping, information about diseased tissue may be obtained with improved accuracy and in vivo using bright broadband MIR super-continuum generation (SCG) fiber sources and low optical loss fiber for routing. The Ge-As-Se-Te chalcogenide glass system is a potential candidate for both MIR SCG and passive-routing fiber, with good thermal stability, wide intrinsic transparency from ~1.5 to 20 μm and low phonon energy. This paper investigates Ge-As-Se-Te glass system pairs for developing high numerical aperture (NA) small-core, step-index optical fiber for MIR SCG and low NA passive step-index optical fiber for an in vivo fiber probe. Control of fiber geometry of small-core optical fiber and methods of producing the glass material are also included in this paper.

In the UK, it is now recognised that 1 in 2 people born after 1960 will develop some form of cancer during their lifetime. Diagnosing patients whilst in the early stages drastically improves their chances of survival but up until now the gold standard for cancer detection is via a lengthy excision biopsy procedure, which relies on the skill of a histopathologist. Evidently, the need for a faster solution is paramount. The mid-infrared (MIR) spectral region covers the wavelengths 3-25 μm and characteristic vibrational spectra unique to each molecular type. Subtle changes in the specific spectral response within this region are indicative of changes within the cells relative to normal cells, signifying the presence or absence of a disease. Our goal is to carry out disease diagnosis in vivo. Reaching these wavelengths has previously presented difficulties as conventional MIR blackbody light sources are weak and optical fibers for transmitting MIR light to/from tissue in vivo can be limited by strong material absorption such as silica glass >2.4 μm and tellurite, and heavy metal fluoride, >4.75 μm. However, chalcogenide glasses have been shown to transmit MIR light out to 25 μm. This paper reports on a glass composition in the Ge-Sb-Se system and its suitability as an optical fiber for the transmission of MIR to and from tissue samples, enabling in vivo mapping for an immediate diagnostic response- a technique termed ‘optical biopsy’.

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.

We demonstrate an M-type fiber suitable for launching higher-order-modes (such as LP 02 LP 03 ) as core-confined-modes, while guiding LP 01 and other lower-order-modes in a ring. The M-type fiber can shift the zero-dispersion-wavelength of bulk-material by several 1000 nanometers.

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.

Recently, particular attention has been given to metallic waveguides supporting surface plasmons as promising components for integrated optical devices. However, the use of conventional numerical optimization tools for their design is hindered by the intensive computational effort associated with meshing down to the resolution of the thin metallic layer. In this study, the previous three-point second order accurate finite-difference formula suitable for correctly placing thin dielectric layers within coarse grids is extended to fourth order accuracy by using the generalized Douglas scheme, including the case when thin metallic layers supporting surface plasmons lie wholly between sample points. The improved formulation, combined with an imaginary distance procedure, is used to analyze the eigenmodes of both 2D and 3D thin metal films located upon dielectric substrates. Accurate calculation with coarser meshes than those required by the other standard differencing schemes is demonstrated, thus providing both a significant saving in computational resource and an extra degree of freedom in meshing such structures.

Research into microdisk lasers demonstrates new achievements both in the technology and in the associated physical effects and applications. Melting and rounding of the disk edge boosts the Q-factors due to improved surface smoothness. In-plane cavity shape is widely used as a design instrument. Optimal shaping of pumped area lowers the threshold power. Photonic molecules made of several microdisks as "photonic atoms" show lasing at several closely spaced frequencies. A microdisk with a single quantum dot as an active region is considered as the most promising system for realisation of a single photon emitter necessary for quantum computing. These new effects and devices can be simulated with accurate numerical techniques, developed recently for "warm-cavity" linear modelling, that are able to bring a new vision of the physics of lasing.

The resolvent method approach is proposed for analytically solving the time domain Volterra integral equation (TDVIE) which describes the electromagnetic fields in 2-D cylindrical structures with time changes in the permittivity. It is shown that the approach allows investigation of the electromagnetic field transformation due to an abrupt time change in dielectric permittivity inside a circular cylinder as well as the construction of the Green’s function for an initial-boundary value problem. Key mechanisms of electromagnetic field transformation are investigated and a qualitative distinction of the processes is shown that depends on an initial field configuration.

The propagation of a non-stationary light beam through a linear/non-linear discontinuity in a planar waveguide is considered by using an approximate approach based on the Generalised Non-Linear Schrodinger Equation (GNLSE) and the rigorous Transmission Line Modelling (TLM) Method. The objective is to compare the different theoretical approaches that can be used for the design of guiding structures with pulse shaping and signal processing functionality. Reflection and transmission of the light beam propagating through the junction of linear and non-linear waveguides are studied with respect to a dimensionless parameter that defines the increase of the refractive index induced by high-intensity radiation. In conclusion, the routes to efficient modelling are discussed.