Modeling lossy anisotropic dielectric waveguides with the method oflines

This paper presents a new formulation useful for modeling waveguides constructed from lossy inhomogeneous anisotropic media. Our approach is based on a pair of Sturm-Liouville type wave equations that have been derived to handle inhomogeneous, diagonalized complex permittivity and permeability tensors. The method of lines is then applied to these wave equations, and related field equations, creating an indirect eigenvalue problem that correctly models this class of structure. Some refinements to the method of lines are also proposed, particularly, regarding the construction of the modal matrices found in the eigenvalue problem. Using our approach, modal dispersion curves have been computed for millimeter-wave and optical structures. Comparisons made with results available from the literature validate our approach     

A comprehensive study of numerical anisotropy and dispersion in 3-DTLM meshes

This paper presents a comprehensive analysis of the numerical anisotropy and dispersion of 3-D TLM meshes constructed using several generalized symmetrical condensed TLM nodes. The dispersion analysis is performed in isotropic lossless, isotropic lossy and anisotropic lossless media and yields a comparison of the simulation accuracy for the different TLM nodes. The effect of mesh grading on the numerical dispersion is also determined. The results compare meshes constructed with Johns' symmetrical condensed node (SCN), two hybrid symmetrical condensed nodes (HSCN) and two frequency domain symmetrical condensed nodes (FDSCN). It has been found that under certain circumstances, the time domain nodes may introduce numerical anisotropy when modelling isotropic media     

Pulsed laser deposition and optical characterizations of the magnetic samarium orthoferrite

Pulsed Laser Deposition of magnetically ordered polycrystalline SmFeO₃ films has been optimized onto SiO₂ glass substrates as function of substrate temperature, oxygen pressure and pulsed laser fluency. Using a KrF excimer laser, crystallization temperature is found to be about 1048 K for a weak fluency of only 1.7 J cm^− 2. We show that this growth temperature can be reduced using higher fluency and that it is possible to obtain a film texturation along the c axis by reducing the oxygen pressure at given temperature and fluency. In a second part, we focus on the SmFeO₃ optical constants determined by in situ ellipsometry using a stacking model and the Cauchy dispersion relation for SmFeO₃ layer. We show a good correlation between the transmission and reflection calculated from these data and measured by ex situ spectrophotometry in the visible range.     

Theoretical performance of Bragg gratings based on long-range surface plasmon-polariton waveguides

A plasmon-polariton Bragg grating (PPBG) concept, based on the propagation of the long-range ss0b mode in structures comprising a thin metal film of finite width embedded in a homogeneous background dielectric, is discussed theoretically. The PPBGs are operated in an end-fire arrangement with access plasmon-polariton waveguides or optical fibers being directly butt-coupled to their input and output ports. A model for the PPBGs, which was recently proposed and validated experimentally for third order structures, is used to generate theoretical results describing their expected performance for various architectures. First order uniform periodic, interleaved, and apodized grating structures are considered and compared. Third order uniform periodic designs are also considered. The gratings investigated are based on a 20 nm thick Au film embedded in SiO2 and have a Bragg wavelength near 1550 nm. First order uniform periodic gratings provide the strongest reflection, with a maximum reflectance of about 97% being achievable over a length of a few millimeters and over a full width at half-maximum bandwidth of about 0.8 nm. The off-resonance insertion loss of the gratings can be as low as a few decibels. Specific Bragg wavelengths can easily be attained using interleaving without requiring extraordinary resolution from the fabrication process. Apodized designs providing low sidelobe levels are also investigated.     

Fabrication of surface plasmon waveguides and integrated components on Cytop

The fabrication and physical characterisation of waveguides and integrated components on Cytop are described. The waveguides consist of a thin narrow Au stripe, on an optically infinite layer of Cytop. The integrated components implemented with this waveguide consist of Y-junctions, Mach-Zehnder interferometers and couplers. The waveguides and components are dimensioned such that they propagate long-range surface plasmon-polariton waves when cladded with an index-matched fluid. The fabrication process flow and individual process steps are described in detail. Physical characterisation was conducted on structures having undergone intermediate process steps and on finished structures. The attenuation of waveguides measured through cut-back is in good agreement with theoretical expectations, and mode outputs observed via an infra-red camera are of very good quality. The waveguides and components are useful for (bio)chemical sensing in aqueous solutions.     

Characterization of chromatic dispersion and polarizationsensitivity in fiber gratings

Fiber gratings have already become key passive components in fiber optic communication systems. We have characterized gratings used in reflection for dispersion compensation and long period gratings used in transmission for gain flattening using a low-loss, low-noise experimental setup having a picometer optical wavelength resolution. Our measurements include reflection or transmission response, group delay and polarization dependent loss. We have scanned the spectrum of our devices using a very narrow linewidth tunable laser. A network analyzer is used for the chromatic dispersion measurements. Time delays corresponding to the design values have been measured within the useful bandwidth of the gratings for dispersion compensation and the devices have been found to have reasonably small ripples that increase in magnitude toward the shorter wavelength range. The long period gratings for gain flattening have very small group delays. Polarization dependent loss has been measured for the first time in these devices. A polarization analyzer was used and Jones matrix analysis was applied to obtain the measurements. The gratings for dispersion compensation have small a polarization dependent loss within their useful bandwidth, while the long period gratings exhibit higher values and a stronger wavelength dependency in the polarization dependent loss     

Characterization of wavelength-selective fiber-optic devices usinga modified phase-shift method

We present a novel measurement setup that can be used for the complete characterization of fiber Bragg gratings and wavelength selective fiber-optic devices. Our setup is based on the phase-shift method (PSM), which we have modified to include the measurement of polarization-induced effects such as polarization-dependant loss (PDL) and polarization-mode dispersion (PMD). We measure the spectral response of devices used in transmission and in reflection, the wavelength dependency of the group delays due to chromatic and polarization-mode dispersion, and the wavelength dependency of the polarization-dependent loss. Experimental results are presented and sources of error are discussed. Comparisons with the Jones matrix eigenanalysis method for the measurement of PDL and differential group delay due to PMD have been carried out     

Long-range surface plasmons on ultrathin membranes

A waveguide structure supporting long-range surface plasmon waves in any gaseous or liquid environment is described. The waveguide comprises a large area dielectric membrane of nanometric thickness upon which thin metal stripes and features are deposited. This structure allows the environment to surround the stripe thus ensuring that an essentially symmetric dielectric background is always present, as required to support the wave. The membrane perturbs the wave in a manner that significantly increases its surface sensitivity. The high surface sensitivity in concert with the ability to create long optical interaction length plasmonic structures leads to high sensitivity (bio)chemical sensors. Theoretical results describing the operation of the structure are given along with experimental results demonstrating the propagation of long-range surface plasmons in air and in liquid. The structure opens up a wealth of opportunities for research and application across many fields, including plasmonics, photonics, material science, surfaces, and solid-liquid interfaces.     

Design of microfluidic channels separated by an ultra-thin free-standing dielectric membrane

A microfluidic (MF) surface plasmon polariton sensor featuring a gold Mach–Zehnder interferometer on an ultra-thin (20–35 nm) dielectric membrane is described. While the presence of the membrane is required to maintain a near mirror symmetry of the dielectric properties of the medium on either side of the interferometer, it is a source of unique challenges in the MF system design. The pressure required to drive the fluid flow in microchannels causes deflection whose value depends on the membrane’s residual stress in the low pressure range and on its modulus at the higher pressure range. Depending on the empirical membrane strength which would meet the required equipment reliability, narrow fluidic channels may require tight dimensional tolerances to maintain the pressure difference across the membrane below a critical value. With wider channels (≥100 μm) dimensional tolerances are relaxed even with relatively weak membranes.     

A comparison of wavelength dependent polarization dependent lossmeasurements in fiber gratings

We have measured wavelength dependent Polarization Dependent Loss (PDL) in chirped fiber Bragg gratings for dispersion compensation, grating filters for wavelength add/drop multiplexing and long period gratings for EDFA gain flattening. The PDL is measured in devices used in reflection and in transmission by applying the Jones matrix method, the Mueller matrix method and the polarization scanning method. A comparison of the experimental results and an analysis of the sources of errors are presented