Fourier modal methods for modeling optical dielectric waveguides

This work contains new materials relative to the use of Fourier expansion techniques, also called plane-wave expansion techniques, for modelling normal modes of optical waveguides. Two rigorous fully vectorial methods are presented and benchmarked for a classical rib waveguide geometry well studied in the literature. The first method relies on a pole extraction and on a one-dimensional expansion scheme. A four-digit accuracy for the normalized propagation constant B is obtained for the dominant TE and TM modes of the benchmark problem and for a small number of retained Fourier harmonics. Better accuracy is anticipated for larger truncation ranks. The second method relies on a two-dimensional expansion scheme in Fourier space and provides a three-digit accuracy for the normalized propagation constant.     

On the scalar modal analysis of optical waveguides using approximate methods

We have discussed the approximate methods which are used for obtaining scalar guided modes of optical waveguides. The methods include the perturbation method, the variational method including the Rayleigh-Ritz method, and the Galerkin and the collocation method. The main purpose of this paper is to discuss the inter-relationships and equivalences of these methods, and to bring out the fact that these relationships have, in fact, not been recognized in the guided wave optics literature, although in the numerical electromagnetics and applied mathematics literature some of these relationships are well known. We have also pointed out specific examples where, due to this lack of recognition of relationships, there are repetitions in the literature. In particular, we have noted that the Rayleigh-Ritz method and the Galerkin method have been used using the same set of basis functions for the same kind of waveguides without recognizing the existing literature. We have also reported for the first time an explicit relationship between the Galerkin method and the collocation method. This relationship also points out in which cases one method is more accurate and/or numerically efficient than the other. Another interesting relationship explored is that between the perturbation method and the variational method.     

Complex FEM modal solver of optical waveguides with PML boundary conditions

A full-wave modal analysis of two-dimensional, lossy and anisotropic optical waveguides using the finite element method (FEM) is presented. In order to describe the behavior of radiating fields, anisotropic perfectly matched layer boundary conditions are applied for the first time in modal solvers. The approach has been implemented using high order edge elements. The resulting sparse eigenvalue algebraic problem is solved through the Arnoldi method. Application to an antiresonant reflecting optical waveguide is reported.     

Review of numerical and approximate methods for the modal analysis of general optical dielectric waveguides

AbstactAbstact This paper reviews numerical and approximate methods for the modal analysis of general optical dielectric waveguides with emphasis on recent developments. Six groups of methods are reviewed, covering (1) the finite-element method, (2) the finite-difference method, (3) the integral-equation method, (4) methods based on series expansion, (5) approximate methods based on separation of variables, and (6) methods that do not fit into the above groups, ranging from the specialized ones for analysing restricted classes of waveguides to the most general ones for analysing inhomogeneous, arbitrarily-shaped, anisotropic waveguides. Some suggestions with regard to the selection of methods for particular applications are given.     

Engineering transverse Bragg resonance waveguides for large modal volume lasers

We recently analyzed a new class of laser amplifier based on transverse Bragg reflection. We show that the unique properties of Bragg confinement make it possible through modal loss discrimination to achieve single-transverse-mode operation with transverse modal size that is an order of magnitude larger than in lasers that depend on total internal reflection for transverse confinement.     

Athermal waveguides for optical communication wavelengths

We report on the design, fabrication, and characterization of temperature insensitive strip silicon-on-insulator racetrack resonators. The influence of various parameters, such as waveguide width, waveguide height, ring radius, coupling length, ring gap, and operating wavelength, on temperature-dependent wavelength shift is examined. A resonant wavelength shift of 0.2 pm/K at a 1550 nm wavelength is measured for 335 nm × 220 nm waveguides. A significant reduction of waveguide propagation losses, improved ring Q value, and higher extinction ratio are obtained after overlaying the silicon waveguides with a polymer cladding.     

Zero-birefringence photosensitive polyimides for optical waveguides

Zero-birefringence (delta n < 1 x 10(-6)) photosensitive fluorinated polyimides are synthesized for use in polymer optical waveguides. To obtain zero birefringence, the UV exposure time and copolymer content of photosensitive polyimides are controlled. Zero birefringence combined with photoprocessing of the material has excellent potential for applications in high-performance wavelength division multiplexing components such as polarization-independent arrayed waveguide gratings and Bragg wavelength filters.     

Theory of optical waveguides

This report summarizes the activities at the 3rd International Workshop on Optical Waveguide Theory, held at the Scuola Superiore Guglielmo Reiss Romoli, L'Aquila, Italy, on 9–11 September, 1978.     

Complex coupled-mode theory for tapered optical waveguides

A coupled-mode formulation based on complex local modes is developed for tapered and longitudinally varying optical waveguides. Different from the conventional coupled-mode theory that requires integration over the entire spectrum of radiation modes, the new formulation treats the radiation fields via discrete complex modes similarly to the guided modes. Accuracy, convergence, and scope of validity for the solutions of the complex coupled-mode equations are investigated in detail for a typical single-mode waveguide taper. It is demonstrated that the complex coupled-mode theory has overcome the difficulties of the conventional theory in simulation of radiation field effects while preserving the simplicity and intuitiveness of this popular method.     

CdTe epilayers for uses in optical waveguides

CdTe epilayers have been grown by vapor phase epitaxy (VPE) on glass, MgO, sapphire, LiNbO₃ and mica substrates. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies show the good structural quality of the epilayers. In these epilayers, a few optical modes were excited with a 1.33-μm laser. The measured propagation losses were in the range between 5 dB/cm and less than 0.5 dB/cm. From dark-mode m-lines, the epilayer thickness was found to be in the 1–3 μm range, in good accord with that obtained by SEM measurements. The refractive index obtained from the fitting is also in good accord with that of bulk CdTe. Received: 7 October 1999 / Accepted: 13 March 2000 / Published online: 5 July 2000     

Organic crystals growth for optical channel waveguides

Optical channel waveguides of meta-nitroaniline (m-NA) crystal, which has potential applications to nonlinear optical devices, have been fabricated on glass substrates having fine grooves. The crystal growth was performed by zone-melting, scanning a CO₂ laser beam along the grooves filled with the polycrystal m-NA. Optical and X-ray observations showed that zone-melting changed the polycrystalline state to a single crystalline state with the 〈001〉 direction along the groove. The scattering loss for a 5 mm-long m-NA crystal waveguide (100 μm both in width and in depth) was found to decrease from 50 dB to 2.5 dB with this process.     

Numerical analyses of optical couplers for planar waveguides

The paper presents the results of numerical analyses of optical structures realized in the form of planar waveguides made of materials with high values of the refractive index n ??1.85. The analysed structures consist of a waveguide and input-output systems. Input-output couplers are realized in the form of prisms as well as Bragg??s grating couplers. Numerical investigations were carried out by applying the finite difference time domain (FDTD) method.     

Nonlinear planar asymmetrical optical waveguides for sensing applications

This paper provides a theoretical analysis for TE polarized waves guided by a linear film surrounded by two asymmetrical nonlinear media for sensing applications. The sensitivity of the proposed sensor is derived. The conditions required for the sensor to exhibit its maximum sensitivity are presented. This analysis covers the case when the measurand is homogeneously distributed in the covering medium. We show that nonlinear sensors have sensitivities higher than those of linear sensors. The authors believe that optical sensing can be improved by introducing nonlinear waveguides.     

New method for loss measurements in optical waveguides

A new three-prism method for measuring losses of optical waveguides is presented. It has a high accuracy and is comparatively simple, both in construction and during the measurement process. The method can be applied to all kinds of planar waveguides and enables one to obtain results which are independent of the coupling efficiencies of the middle movable prism and laser radiation fluctuations.     

Coupled magnetic resonator optical waveguides

Optical resonators are important devices that control the properties of light and manipulate light–matter interaction. Various optical resonators are designed and fabricated using different techniques. For example, in coupled resonator optical waveguides, light energy is transported to other resonators through near‐field coupling. In recent years, magnetic optical resonators based on LC resonance have been realized in several metallic microstructures. Such devices possess stronger local resonance and lower radiation loss compared with electric optical resonators. This study provides an overall introduction on the latest progress in coupled magnetic resonator optical waveguide (CMROW). Various waveguides composed of different magnetic resonators are presented and Lagrangian formalism is used to describe the CMROW. Moreover, several interesting properties of CMROWs, such as abnormal dispersions and slow‐light effects, are discussed and CMROW applications in nonlinear and quantum optics are shown. Future novel nanophotonic devices can be developed using CMROWs.     

Dispersion modified slot optical waveguides

Advent of slot waveguide structures had opened a new era where light can be confined in low index slot guarded by high index slabs. Already in use SOI slot waveguides (contrast ratio is 2.42) have two distinct properties over the conventional waveguides, i.e. high E-field amplitude, optical power, optical intensity in low index materials, and strong E-field confinement localized to nanometer-size low index regions. We hereby propose a low refractive index contrast ratio slot waveguide structure (ratio is 1.18) comprising of commercially available glass material. Novelty lies in showing high E-field amplitude, optical power, optical intensity, and strong E-field confinement in low index slot regions despite of lowest ever reported contrast ratio. A systematic numerical study on the higher order dispersion characteristics of the widely studied SOI-based slot structure and of our proposed low refractive index contrast slot structure is carried out. It has been demonstrated that low refractive index contrast ratio slot optical waveguide GVD properties are quite different than SOI slot optical waveguide. The less normal dispersion existing in this kind of waveguide could have an impact on their applications in various nonlinear or linear applications.