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A goal for the validation of computational electromagnetics (CEM) is to provide the community with a simple computational method that can be used to predict the assessment of electromagnetic compatibility (EMC) data as it would be undertaken by individuals or teams of engineers. The benefits of being able to do this include quantifying the comparison of data that has hitherto only been assessed qualitatively, to provide the ability to track differences between model iterations, and to provide a means of capturing the variability and range of opinions of groups and teams of workers. The feature selective validation (FSV) technique shows great promise for achieving this goal. This paper presents a detailed analysis of the FSV method, setting it firmly in the context of previous comparison techniques; it suggests the relationship between validation of graphically presented data and the psychology of visual perception. A set of applicability tests to judge the effectiveness of computer-based CEM validation techniques is also proposed. This paper is followed by a detailed comparison with visual assessment, which is presented in Part II.

For the first time embossing of ribs, from 1 to 10 μm wide and ∼10 mm long, has been carried out in chalcogenide glass layers sputtered onto semiconductor wafer substrates, with potential to act as monomode waveguides; these features have been similarly embossed in the surface of bulk chalcogenide glasses. The embossing shows very good replication of the GaAs mould patterning to 1 μm definition, with evidence also for sub-micron replication. For the embossing, thin coatings of the chalcogenide glasses were sputtered onto wafer substrates as follows: (i) a 6 μm layer of Ge17As18Se65 (at.%) onto porous Si-on-Si wafer substrates and (ii) a 4 μm layer of Ge15As15Se17Te53 onto uncoated GaAs substrates. The Ge17As18Se65 sputtered glass layer on porous Si-on-Si was demonstrated to slab waveguide at 1.55 μm wavelength; it was designed to achieve monomode waveguiding at 1.55 μm after embossing, for the 5 μm wide rib. The series of ribs, 1–10 μm wide, were successfully embossed in the Ge17As18Se65 glass sputtered layer on porous Si-on-Si, but cracking of the glass layer occurred during the embossing process. Successful embossing of ribs without the glass layer cracking was achieved for the Ge15As15Se17Te53 sputtered glass layer on uncoated GaAs. Due to its relative simplicity, it is likely that hot embossing of this type of glass-based matrix offers an extremely promising route for producing high-resolution, guided-wave optical components and circuitry at low-cost, high-volume, and for a wide wavelength range.

Two practically important effects in magnetooptic photonic bandgap (MO PBG) structures are investigated for the first time, namely 1) oblique incidence and 2) diffractive effects caused by incident beams of finite width. A rigorous solution of the full three-dimensional wave equation in a MO medium is derived and used to evaluate the effect of beam spot size on the transmission properties of MO PBG structures. It is shown that the properties of MO PBG structures are highly sensitive to the angle of incidence and, furthermore, that in the case of a small beam size, plane-wave analysis significantly overestimates the transmission and isolation properties of MO PBGs.

In some recent publications, formulations of a time-domain beam propagation method (TD-BPM) were developed to incorporate dispersive media with complex permittivity described by a single first-order pole or a modified version thereof. However, for many emerging optical applications, procedures are needed for general linear dispersive media with dispersions described by rational functions, such as a combination of multiple second-order poles. The authors present an efficient frequency-dependent full-band TD-BPM formulation for the analysis of general linear dispersive media. In this method, the complex time-domain convolution of the dispersive media is evaluated efficiently via a Z-transform. The formulation is validated by simulating dispersive media with complex permittivity described by single and multiple second-order poles at microwave and optical frequencies. It is shown that the proposed formulation can accurately simulate broadband electromagnetic responses using a much larger time-step size than those required by other conventional numerical techniques. Extension of this formulation to the treatment of any general material, such as dispersive non-linear material, is straightforward.

The lasing characteristics of a photonic molecule in the form of two optically coupled semiconductor microdisks are investigated. Electromagnetic analysis of the lasing spectra and linear thresholds of the coupled whispering-gallery (WG) modes of four different symmetry classes is presented. Here, Maxwell's equations and accurate boundary and radiation conditions are considered as a specific "cold-cavity-with-gain" eigenvalue problem. Each eigenvalue is a pair of real-valued parameters -frequency and threshold material gain. In the two-dimensional (2-D) approximation, based on the introduction of an effective refractive index, this problem is reduced to a determinant equation with favorable features. A secant-type method is further used to calculate thresholds and lasing frequencies numerically. Results obtained show that optical coupling may lead to a further reduction of the ultralow thresholds of the WG modes, although the opposite, i.e., threshold spoiling, is more common.

This paper considers the switching effects on whispering gallery modes in circular dielectric resonators when their material is subject to abrupt time changes in permittivity. Both the transient response and the new steady-state regime are described in detail by means of an analytical approach.

An electromagnetic analysis of thin-disk semiconductor resonators with uniform and nonuniform gain regions is presented. A "cold-cavity-with-gain" Maxwellian formulation, including accurate boundary and radiation conditions, is considered as an eigenvalue problem, for the real-valued parameters of frequency and threshold material gain. Although the well-known approximate effective-index method is used to reduce a three-dimensional (3-D) field problem to a two-dimensional (2-D) one, a rigorous formulation of the latter is retained. A quasi-3-D feature is provided through full account of the multiple-wave nature and dispersion of the effective index. Results obtained quantify the ultralow thresholds of the whispering-gallery modes and show the advantage of a ring-shaped gain region.

This paper presents a transmission-line modeling (TLM) algorithm, which is based upon unstructured tetrahedral meshes. In comparison with the conventional, usually Cartesian, scheme, the use of such meshes provides a significant enhancement in the flexibility and accuracy of the TLM simulations, permitting both smooth boundary approximations and the use of diversely sized elements in multiscale problems. A full theoretical development of the unstructured algorithm is presented for the first time and canonical problems are used to demonstrate the computational advantages available. Particular consideration is given to practical meshing constraints and the merging of adjacent tetrahedra into larger cells used to avoid the use of undesirably small time steps.

Transformation of the whispering-gallery (WG)-modes in imperfect two-dimensional square and triangular microcavities with various degrees of deformation is studied by means of the Muller boundary integral equation technique. Continuous transformation of a circular microcavity, which supports double-degenerate WG-modes, toward a square or a triangle removes the degeneracy of certain WG-modes. The spectrum of the modes that split depends on the symmetry of the emerging microcavity: WG/sub 2m,n/-modes in case of a C/sub 4v/ symmetry (square) or WG/sub 3m,n/-modes in the case of C/sub 3v/ symmetry (triangle). In both cases, the modes with the highest Q-factors are nondegenerate modes with antisymmetrical field patterns. We estimate mode frequencies, quality factors and field distributions of practically achievable rather than "ideal" square and triangular microcavities, and compare the effect of various types of fabrication imperfections (corner sharpness, sidewall curvature and surface roughness) on their characteristics. Accurate study of the modal spectra enables us to confirm and explain previous observations, such as: 1) co-existence of the WG-like and volume modes in square microcavities; 2) the separation of the high-Q WG-like modes being twice that determined by the cavity length; and 3) much lower Q-factors of realistic concave-wall triangular microcavities than those of their ideal counterparts.

An accurate laser simulator is developed to investigate the influences of various device parameters on modal discrimination and beam quality to optimize the brightness of semiconductor lasers. Previous work using the Prony method is extended, both by using a more robust laser simulator to solve for the optical fields and by extending the Prony method to operating conditions above threshold. The semiconductor laser model is used to investigate the effects of various device parameters on the characteristics of a gain-guided 980-nm Al-free stripe geometry laser. The device parameters investigated are the device geometry, the thickness and doping level of the waveguiding layer and the front facet reflectivity. Together with practical and economic considerations, the device parameters of a wide emitter gain-guided laser are optimized. The optimized gain-guided laser is predicted to operate in the fundamental mode up to 1.15 W. At this maximum fundamental mode power, the slow axis beam divergence at 1/e/sup 2/ points is 5.4/spl deg/, the beam quality factor M/sup 2/ is 1.62, the astigmatism is 27 /spl mu/m, and the brightness is 61 MW/cm/sup 2/sr.

The paper investigates and compares a range of different models currently used for modelling nonlinear optical phenomena. The models are implemented in the numerical time domain Transmission Line Modelling (TLM) method and include a Kerr model and different formulations of the Duffing model. The models are used to simulate an all-optical limiter for a CW input and results compared with ones available in the literature. This enables a comparison to be made between the different models, from which it is concluded that the Duffing model has some advantages, when modelling materials and phenomena involving more than one frequency, arising from its ability to describe dispersive effects. These conclusions are further supported by the simulation results obtained for a pulse input.

The computationally efficient DuFort-Frankel beam-propagation method (BPM) is ideally suited to parallel computing. Although the scheme is conditionally stable for structures with lossless materials, in the presence of material loss it can become unstable. It is shown that the use of perfectly matched layer (PML) boundary conditions can also cause instability, especially in the three-dimensional (3-D) case. These instabilities are characterized and a stabilized DuFort-Frankel scheme is presented that extends the scope of this powerful method to cover these practically important scenarios.

The use of optimization methods to automatically synthesize novel structures is attractive for optoelectronic design. However, the application of such methods to practical components is hindered by the long run times required to evaluate the performance of each particular trial design. This paper investigates, for the first time, how systematically adapting the accuracy of the simulations during the optimization process can be used to speed up the synthesis of effective designs. Adaptive accuracy variation is achieved in two ways: altering the acceptable error demanded of a particular simulation method and using a hierarchy of different methods. This novel method of synthesis is applied to quickly obtain optimal rib waveguide structures for two practical problems, namely modal degeneracy and low-loss fiber coupling.

To date, the transmission line modelling method has been applied to structured, usually Cartesian, meshes. The flexibility offered by using 2D and 3D unstructured meshes, which is invaluable for practical simulation tasks, is now combined with the transmission line modelling algorithm to yield a powerful tool for computational electromagnetics.

The structure-related (SR) finite-difference beam-propagation method is applied to integrated optical couplers employing curved waveguide sections. A general nonorthogonal coordinate system is introduced that matches the local structure geometry, yielding a more accurate analysis with coarser meshes than standard schemes, thus providing significant computational resource savings. Furthermore, the algorithm is easily interfaced with conventional schemes. Examples of curved two-dimensional and three-dimensional directional waveguide couplers are examined to show the advantages and generality of SR schemes as well as to explore the role of the extra degrees of freedom offered by nonorthogonal meshing.

We study the influence of a patterned contact design on the beam properties of high-brightness tapered lasers. A simple approach to simulate patterned injection has been developed and introduced into a quasi-three-dimensional tapered laser model. The method is applied to tapered lasers, whose performance is limited by two different mechanisms: self-focusing and poor modal filtering. The results show an improvement in beam quality in comparison to standard devices.

Results from detailed numerical analyses of the modal characteristics of large-cross-section silicon-on-insulator-based rib waveguides are presented. They highlight for the first time that satisfying widely used design criteria is not sufficient to ensure single-mode behavior. In particular, the geometries that the design formulas predict should be single-mode are shown to support higher order vertical modes that do not couple (leak) into the outer slab region and are thus low loss in nature. Fortunately, a wide range of practical rib geometries still remains for which the leakage loss of modes other than those of EH/sub 00/ and HE/sub 00/ is sufficiently high to make the waveguides effectively single mode for each polarization.

The plane wave and localized function expansion methods are established for bandgap and modal calculations of holey fibres. The calculations rely on evaluating the Fourier transform coefficients of the dielectric constant profile. In this paper we derive a generalized formula for determining these coefficients for holey fibres with holes of arbitrary polygonal shape. The accuracy of the Fourier representation is studied for different hole shapes rotated at various angles to the lattice. We combine the approach with the localized function method to study the modal properties of some holey fibres, reporting new numerical results on the influence of the hole shape on the modal and group velocity dispersion of microstructured fibres with rhombic holes aligned along radial lines.

Transmission-line modeling (TLM) is an established numerical simulation method for electromagnetics that has been employed in a wide variety of application areas. To date, TLM has been formulated primarily for structured (usually Cartesian) meshes. This paper presents and illustrates the application of a new TLM algorithm suitable for use with unstructured two-dimensional meshes based upon triangular elements.

Time-domain Volterra integral equations are obtained for the electromagnetic fields in longitudinal uniform dielectric waveguides with time-varying media in their core. Resolvent operators are constructed for the case when the core permittivity changes abruptly in time and new features are observed in the consequent field transients in comparison with those occurring in a simple unbounded space.

We present a simulation tool useful to optimize the design of semiconductor tapered lasers and to study the physical processes inside of them. This is achieved by using a state-of-the-art quasi-three-dimensional (quasi-3-D) electrical and thermal model, coupled to a two-dimensional (2-D) wide-angle beam propagation method optical model. A calibration procedure of model parameters is proposed to contribute to the development of reliable simulation tools. Different laser diodes with a tapered gain section, emitting at 735 and 975 nm, are used to validate the model through the extensive comparison of experimental and simulated results. The suitability of 2-D and 3-D electrical, thermal, and optical models is discussed in terms accuracy and computational effort.

The behavior of a 2D model of an extended hemielliptic silicon lens of a size typical for THz applications is accurately studied for the case of a plane E-wave illumination. The full-wave analysis of the scattering problem is based on the Muller's boundary integral-equations (MBIE) that are uniquely solvable. A Galerkin discretization scheme with a trigonometric basis leads to a very efficient numerical algorithm. The numerical results related to the focusability of the lens versus its rear-side extension and the angle of the plane-wave incidence, as well as near-field profiles, demonstrate strong resonances. Such effects can change the principles of optimal design of lens-based receivers. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 515–518, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20520

An improved three-point finite-difference scheme is presented, which deals correctly with all terms up to 2nd order in the expansion of the derivative, regardless of the existence of multiple dielectric interfaces between sample points. The improved differencing scheme is implemented into a 1D slab-mode solver for validation of accuracy and a 2D mode solver. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 95–101, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20558

A combined analytic-numerical approach is presented for investigations of electromagnetic signal propagation in dielectric waveguides containing a non-linear medium. The approach is based on the resolvent method for the Volterra integral equation describing an electromagnetic process. The proposed algorithm uses the exact expression for the solution to the integral equation for the electromagnetic field in the planar waveguide with time jump changing of the medium properties. In the case of a non-linear dielectric as the waveguide core the continuous change of the medium parameters is replaced by jump changes of the latter. This is the only approximation made in the algorithm. The resolvents that are constructed give the exact solution on each jump step. The results from some example numerical calculations are presented.

A full vector, semi-analytical, yet accurate, analysis of coated optical fibre facets is presented, based upon the free space radiation mode method. This yields a simple final expression for the modal reflectivity. A highly efficient algorithm has been developed to implement this analysis. Example results for the reflectivity of the fundamental HE11 mode supported by typical single-mode fibres are given, which are compared to those obtained from an equivalent scalar investigation. Results show that correct modelling of the low reflectivities of coated facets requires a full vector analysis.

High-Q semiconductor microdisk resonators laterally coupled to optical waveguides serve as compact and robust components in wavelength-division-multiplexing systems. We present an efficient algorithm for the two-dimensional design of wavelength-selective filters based on waveguide-coupled whispering-gallery-mode (WGM) microresonators of arbitrary cross-sectional shape. A full-wave integral equation formulation enables us to accurately account for the coupling between the resonator and bus waveguide as well as for radiation and material losses. Furthermore, we apply this approach to the analysis of elliptic-resonator filters. Filter tuning by changing the resonator shape from circular to elliptic reduces the dependence of the coupling efficiency on the width of the air gap. Two alternative coupling designs are suggested for monolithic and hybrid integration technologies. One is based on increasing the coupling length, while the other exploits the field concentration at the increased-curvature portion of the deformed WGM resonator.

The properties of a tapered semiconductor laser cavity, which can be used to generate a high-brightness optical beam, are studied. The cavity consists of a narrow straight waveguide section and a tapered power amplifier section. The influence of the input waveguide width and length, as well as of the length and taper angle of the power amplifier section, on the overall performance of the cavity are discussed. Finally, the application of beam spoilers is studied. In order to solve the wave equation, the wide-angle-beam propagation method incorporating a higher-order finite-difference scheme is applied.

The ability to optimise the performance of today's opto-electronic circuits over a range of operational parameters and fabrication tolerances is foremost in the designer's mind. The ability to investigate the effects of tolerancing and integration upon device performance over a range of wavelengths is highly desirable for their successful exploitation. The spectral index (SI) method is a well-established method traditionally used for the analysis of the modal properties of semiconductor rib waveguides. In this paper the efficiency and accuracy of the SI method is exploited for the first time in a scattering-matrix approach to the analysis of complex integrated optical circuits. The SI approach yields highly accurate results with minimal computational effort. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 68–73, 2003

The nonlinear phenomena accompanying the process of light generation in high-power tapered semiconductor lasers are studied using a combination of simulation and experiment. Optical pumping, electrical overpumping, filamentation, and spatial hole burning are shown to be the key nonlinear phenomena influencing the operation of tapered lasers at high output powers. In the particular tapered laser studied, the optical pumping effect is found to have the largest impact on the output beam quality. The simulation model used in this study employs the wide-angle finite-difference beam propagation method for the analysis of the optical propagation within the cavity. Quasi-three-dimensional (3-D) thermal and electrical models are used for the calculation of the 3-D distributions of the temperature, electrons, holes, and electrical potential. The simulation results reproduce key features and the experimental trends.

We present an accurate, reliable and versatile method for studying the effect of deformations on the characteristics of the high-Q whispering gallery (WG) modes supported by two-dimensional dielectric resonators (DR). An eigenvalue problem is formulated in terms of contour integral equations and further discretised with the method of analytical regularisation. Such a procedure significantly reduces the number of unknowns whilst providing high and controllable accuracy. Natural frequencies, Q-factors and field patterns of elliptical, flower- and egg-shaped DRs are calculated. Methods to enhance the Q-factors, provide directional light output, and parasitic mode suppression are discussed. The identification of WG modes is simplified by the symmetrical/asymmetrical mode separation included into the formulation of the problem and solution algorithm.

Designs for 980 nm AlxGa1−xAs/In0.2Ga0.8As/GaAs high-power, high-brightness semiconductor lasers/amplifiers with distributed phase correction and short-cavity lengths (i.e. cavity lengths 560–1040 μm) are presented. The proposed lasers/amplifiers employ a single mode feed waveguide coupled to a power amplifier with a laterally graded effective refractive index (GRIN) profile to control the lateral mode shape and phase. The lateral index of the power amplifier has a hyperbolic secant (HYSEC) profile, which can be approximately realised by tailoring the effective refractive index of the amplifier using a series of discrete etches. The epitaxial and structure designs of the laterally discretised GRIN lasers/amplifiers are presented. Finally, a method for improving the effective refractive index discretisation is described.

The application of the Volterra integral equation method for investigations of the interaction of electromagnetic fields with a one-dimensional time-varying dielectric layer is considered. The medium permittivity inside the layer may change in time owing to a nonlinearity as well as to extrinsic sources. Original software for the computer modeling of such an interaction is developed. Numerical results are presented and a comparison made between the accuracy and stability of integral equation method and the finite-difference time-domain (FDTD) method.

A full-vectorial contour integral equation analysis of the natural modes of dielectric waveguides (DW) of arbitrary cross section is presented. The Galerkin method, together with the Analytical Regularization procedure, is applied to discretizing and solving the eigenvalue problem. This ensures the fast convergence and superior accuracy of the numerical algorithms. The waveguide cross section is characterized by a parametrical curve defining its contour, with a limited curvature at each point. This avoids the singularity points at corner regions and provides accurate results, even for waveguides with virtually sharp corners. Both fundamental and higher order mode propagation characteristics are studied in the bound, leaky, and complex regimes. Numerical results consistent with other theories and experimental data are presented for a wide range of practical dielectric waveguides that demonstrate the efficiency, accuracy, and versatility of the method developed. Finally, the technique is applied to model a fused fiber coupler.

An efficient hybrid method has been developed to analyze, for the first time, the three-dimensional problem of fiber-to-chip coupling. The method employs the numerical finite difference beam propagation method to model the fields in the planar chip guide and the semi-analytical free space radiation mode method to model the fields in the fiber guide. The two methods are linked via an iterative algorithm. The results for the transmission, backreflection, and radiation losses are presented for the case of direct butt-coupling and coupling via an antireflection coating. Finally, the effect of the vertical misalignment is analyzed and results are compared with the ones obtained experimentally.

An efficient and accurate algorithm based on the combination of the Green's function method and an analytical regularization technique is applied to study the complex natural frequencies and Q factors of two-dimensional (2-D) dielectric resonators (DRs) in a layered environment. Frequency shift and degeneracy splitting of the whispering-gallery modes (WGMs) of circular-cylindrical and tubular DRs immersed into layered dielectric media are computed and analyzed.

A wide-band finite-difference–time-domain beam propagation method (FD TD-BPM) based on Pade approximants is introduced to improve the bandwidth of the conventional TD-BPM. Numerical dispersion relations for the TD-BPM are derived to demonstrate the increase in bandwidth of the wide-band TD-BPM. The effects of the spatial and time step sizes on the numerical dispersion are also investigated. It is shown that the wide-band TD-BPM is less sensitive to the choice of spatial step size and allows a larger time step size to be used compared to the finite-difference time-domain (FD-TD) method. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 243–247, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10428

A novel finite-difference beam-propagation method (FD-BPM) algorithm for the analysis of photonics structures with sloped sides in the transverse plane is presented. By introducing nonorthogonal coordinate systems in the transverse plane, the staircasing effects inherent when one is modeling with a rectangular mesh are eliminated, and accuracy is substantially improved. The algorithm is tested in the analysis of sloped rib waveguides. The results obtained confirm the accuracy and high efficiency of the new algorithm. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 401–407, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10335

We present numerical modeling of mid-infrared (MIR) supercontinuum generation (SCG) in dispersion-optimized chalcogenide (CHALC) step-index fibres (SIFs) with exceptionally high numerical aperture (NA) around one, pumped with mode-locked praseodymium-doped (Pr3+) chalcogenide fibre lasers. The 4.5um laser is assumed to have a repetition rate of 4MHz with 50ps long pulses having a peak power of 4.7kW. A thorough fibre design optimisation was conducted using measured material dispersion (As-Se/Ge-As-Se) and measured fibre loss obtained in fabricated fibre of the same materials. The loss was below 2.5dB/m in the 3.3-9.4μ m region. Fibres with 8 and 10μm core diameters generated an SC out to 12.5 and 10.7μm in less than 2m of fibre when pumped with 0.75 and 1kW, respectively. Larger core fibres with 20μm core diameters for potential higher power handling generated an SC out to 10.6μm for the highest NA considered but required pumping at 4.7kW as well as up to 3m of fibre to compensate for the lower nonlinearities. The amount of power converted into the 8-10 μm band was 7.5 and 8.8mW for the 8 and 10μm fibres, respectively. For the 20μm core fibres up to 46mW was converted.

We discuss the modelling and design of mid-infrared fibre lasers for realisation in a chalcogenide glass host doped with lanthanide ions. Three lanthanide dopant ions are considered: terbium, dysprosium and praseodymium. The laser configuration exploits the advantages of a cascade lasing scheme, which allows for a reduction in both the side effects of the long lifetime of the lower lying state and heat generation within the laser structure.

The environment of Dy3+ is investigated when it is added as DyCl3 or Dy foil into two base glasses, Ge16.5As19−xGaxSe64.5, where x = 3 or 10 at%, at doping levels between 0 and 3000 parts per million by weight (ppmw) Dy3+. Extended X-ray Absorption Fine Structure demonstrates the glasses doped with Dy foil, or less than 1000 ppmw Dy3+ as DyCl3, contain Dy ions that are fully incorporated into the glass network and are coordinated by 7–8 Se atoms. However, when the DyCl3 dopant is present in concentrations ≥1000 ppmw Dy3+ the environment is dominated by Dy–Cl bonds. Furthermore, these Dy–Cl environments are nanocrystalline, retaining chemical order beyond the first coordination shell. By comparison with XRD and FTIR results, we report that the presence of α-Ga2Se3 crystallites in the glass, and the increased optical scattering in the fibres, are both related to the presence of DyCl3 crystallites.

Lanthanide ion doped glass materials find many applications in photonics. In recent years a particular attention has been drawn to lanthanide ion doped low phonon energy glasses and their potential application as amplifiers and lasers delivering mid-infrared coherent light. We present a comprehensive study of the photoluminescence measured from chalcogenide glass samples doped with praseodymium ions. The study includes Judd-Ofelt analysis and simulations performed consistently on the basis of the rate equations approach. The results allow for estimating the actual efficiency of the particular radiative transitions and also for extracting the parameters characterising the non-radiative processes.

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 the standard single mode fibre. The modal properties of the MC-MOF structure are analyzed 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 interferometer is a good candidate for a tensile strain or bending sensor.

Chalcogenide glasses are promising materials for mid-infrared (MIR) fibre optic applications i.e. 3-25 μm wavelength. Their low phonon energy is attractive not only for passive mid-IR transmission fibre-conduits but also for active fibre. For the latter, rare earth (RE-)-ion doped chalcogenide glasses have been investigated, as direct emission mid-IR fibre lasers. The quality of the chalcogenide glass fibre is key to this application. RE-ion addition to the chalcogenide glasses can lead to devitrification. Gallium has been identified as a useful additive to help successfully solubilise the RE-ions and it is thought that gallium complexes the RE-ions in the glass matrix. We investigate here replacing gallium with indium. Indium shares Group 13 of the New Periodic Table with gallium and so exhibits similar chemical behaviour. Indium is heavier than gallium, potentially promoting lower phonon energy locally at the RE-ion. We have found enhanced fluorescence behaviour of the RE-ion in bulk glasses formulated with indium rather than gallium. Here, drawing of step index fibre (SIF) based on ~ 500 ppmw (parts per million by weight) Pr 3+ -doped Ge-As-(In or Ga)-Se chalcogenide glasses is successfully carried out. MIR fibre loss of the Pr 3+ -doped SIFs is measured as well as fibre photoluminescence in the range 3-6 μm.

Scattering of a normally incident plane wave by a dielectric slab with air-filled periodic inclusions of circular cylinder form is investigated. Comparison with the related homogeneous slab problem shows the presence of modes associated with the periodic inclusions. The corresponding resonances are sharp. Lasing threshold and the real-valued lasing frequency are then sought by introducing a negative imaginary part into the slab refractive index to develop a laser eigenvalue problem (LEP). The dependencies of lasing threshold and frequency on geometrical parameters are found, and indicate that the periodic modes have high lasing efficiency.

Compact devices are important for the realization of terahertz communications systems. This article proposes a novel photonic crystal-based device for realizing microminiature, high-selectivity high Q band-pass filters (BPF) and the design of a dual-mode square lattice photonic crystal BPF that utilizes the degenerated modes of a point defect microcavity is presented. To design a high Q microcavity, the photonic band-gap is initially calculated using the plane wave expansion method. Second, the eigenfrequencies and modal fields of a point defect microcavity that generates localized states in the band-gap are calculated by a supercell method. Finally, the characteristics of mode splitting and the proposed dual-mode BPFs are numerically studied by a full-wave time-domain method. © 2014 The Authors. Microwave and Optical Technology Letters Published by Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:792–797, 2014

We theoretically demonstrate a novel approach for generating Mid-InfraRed SuperContinuum (MIR SC) by using concatenated fluoride and chalcogenide glass fibers pumped with a standard pulsed Thulium (Tm) laser (TFWHM=3.5ps, P0=20kW, νR=30MHz, and Pavg=2W). The fluoride fiber SC is generated in 10m of ZBLAN spanning the 0.9–4.1μm SC at the −30dB level. The ZBLAN fiber SC is then coupled into 10cm of As2Se3 chalcogenide Microstructured Optical Fiber (MOF) designed to have a zero-dispersion wavelength (λZDW) significantly below the 4.1μm InfraRed (IR) edge of the ZBLAN fiber SC, here 3.55μm. This allows the MIR solitons in the ZBLAN fiber SC to couple into anomalous dispersion in the chalcogenide fiber and further redshift out to the fiber loss edge at around 9μm. The final 0.9–9μm SC covers over 3 octaves in the MIR with around 15mW of power converted into the 6–9μm range.

Chalcogenide glasses are promising materials for mid-infrared (IR) fiber lasers (i.e. 3 - 25 μm wavelength range). These glasses exhibit low phonon energies, together with large refractive indices, rare earth (RE-) ion solubility and sufficient mechanical and chemical robustness. Optical quality of the fiber is key. Gallium is known to promote RE-ion solubility in chalcogenide glasses, probably forming a [Pr(III)] - Se - [Ga(III)] associated type complex. Here, indium is investigated as an alternative additive to gallium in Pr3+-doped Ge-As-Se chalcogenide glasses. Indium has the same outer electronic structure as gallium. Moreover, indium has the advantage of being heavier than gallium, potentially promoting a lower phonon-energy, local environment of the RE-dopant. Zero to ~2000 ppmw (nominal parts per million by weight) Pr3+- doped Ge-As-In-Se bulk glasses are prepared using the melt-quench method. ~500 ppmw Pr3+- doped Ge-As-In-Se, optically-clad fiber is realized via fiber-drawing of extruded fiberoptic preforms. Fiber absorption and emission spectra are collected and compared with those of the bulk glasses.

In the 21st century, cancer has become a common and feared illness. Early detection is crucial for delivering the most effective treatment of patients, yet current diagnostic tests depend upon the skill of a consultant clinician and histologist for recognition of the cancerous cells. Therefore it is necessary to develop a medical diagnostic system which can analyze and image tissue instantly, removing the margin of human error and with the additional benefit of being minimally invasive. The molecular fingerprint of biological tissue lies within the mid-infrared (IR) region of the electromagnetic spectrum, 3-25μm wavelength. This can be used to determine a tissue spectral map and provide information about the absence or existence of disease, potentially in real-time and in vivo. However, current mid-IR broadband sources are not bright enough to achieve this. One alternative is to develop broadband, mid-IR, supercontinuum generation (SCG). Chalcogenide glass optical fibers have the potential to provide such mid-IR SC light. A popular chalcogenide glass fiber type is based on Ge-As-Se. For biomedical applications it is prudent to avoid the use of arsenic, on account of its toxicity. This paper investigates replacing arsenic with antimony, towards Ge-Sb-Se smallcore optical fibers for SCG. Physical properties of candidate glass pairs are investigated for glass stability via differential thermal analysis etc. and fiber optical loss measurements of associated fibers are assessed. These results are compared to analogous arsenic-containing chalcogenide glasses and optical fibers, and conclusions are drawn focusing on whether there is potential for antimony chalcogenide glass to be used for SCG for mid-infrared medical diagnostics.

A hollow circular cylinder composed of thin carbon fibre composite materials is modelled using the numerical Transmission Line Modelling (TLM) method. This is used as a canonical example of an object whose perimeter intersects the mesh at a variety of angles and inter sample positions. In this model, the thin cylinder wall is linearized and then embedded within the relatively coarse mesh. The embedded model eliminates the need for fine discretisation thus reducing the time step and memory requirements for the numerical method. To verify the accuracy of the embedded model the resonant frequencies of the CFC cylinder are compared with the analytical results of the equivalent metal cylinder. The scattering of the plane wave of the CFC cylinder is also analysed.

We report on the impact of realistic gain and loss models on the bistable operation of nonlinear parity-time Bragg gratings. In our model we include both dispersive and saturable gain and show that levels of gain/loss saturation can have significant impact on the bistable operation of a nonlinear PT Bragg grating based on GaAs material. The hysteresis of the nonlinear PT Bragg grating is analyzed for different levels of gain and loss and different saturation levels. We show that high saturation levels can improve the nonlinear operation by reducing the intensity at which the bistability occurs. However when the saturation intensity is low, saturation inhibits the PT characteristics of the grating., 5 pages, 5 figures, submitted to Optics letters