Diffused Channel Waveguides Research Articles

Utilizing the Shift-or-Shrink Algorithm to Optimize the Direct Coupling from Laser Diodes to Diffused Channel Waveguides

Several formulae for computing the direct coupling efficiencies from laser diodes to diffused channel waveguides, based on mathematic models for approximating the corresponding laser beams and the waveguiding modes, have been derived in this paper. Then, the authors utilize a simple shift-or-shrink (SOS) algorithm to seek their optimal coupling conditions, including the incident positions of the laser beams and the corresponding horizontal and vertical beam widths. The simulation results are presented and compared.

Analytical electric field intensity profile in diffused channel waveguides

A novel analytic solution to field distribution is used to calculate the intensity distribution for channel waveguides with a two-dimensional diffusion-type refractive index profile. Composition profiles for the waveguides are obtained by applying the two-dimensional diffusion theory to treat the case of isotropic sideways diffusion. The dependence of the field distributions on the width/depth ratio is studied as an aid to the design of modulators and switches for integrated optics.

Investigation of a polarization controller in Ti:LiNbO3 near 1530 nm wavelength

The results of analytical and experimental investigations for an electro-optic polarization controller are reported. A device configuration composed of two polarization converters with a phase shifter centered between them and all integrated over a single Ti diffused channel waveguide on LiNbO3 is used. Polarization control is achieved by applying voltages on the three integrated elements independently to adjust the phase difference between orthogonal TE and TM components of a guided optical wave as well as their relative strength. Experimental results agree with analytical predictions. For arbitrary incident polarization, endless polarization transformation can be realized at the output.

Photonic Circuits for Generating Modal, Spectral, and Polarization Entanglement

We consider the design of photonic circuits that make use of Ti:LiNbO$_{3}$ diffused channel waveguides for generating photons with various combinations of modal, spectral, and polarization entanglement. Down-converted photon pairs are generated via spontaneous optical parametric down-conversion (SPDC) in a two-mode waveguide. We study a class of photonic circuits comprising: 1) a nonlinear periodically poled two-mode waveguide structure, 2) a set of single-mode and two-mode waveguide-based couplers arranged in such a way that they suitably separate the three photons comprising the SPDC process, and, for some applications, 3) a holographic Bragg grating that acts as a dichroic reflector. The first circuit produces frequency-degenerate down-converted photons, each with even spatial parity, in two separate single-mode waveguides. Changing the parameters of the elements allows this same circuit to produce two nondegenerate down-converted photons that are entangled in frequency or simultaneously entangled in frequency and polarization. The second photonic circuit is designed to produce modal entanglement by distinguishing the photons on the basis of their frequencies. A modified version of this circuit can be used to generate photons that are doubly entangled in mode number and polarization. The third photonic circuit is designed to manage dispersion by converting modal, spectral, and polarization entanglement into path entanglement.

Power exchange in strongly coupled diffused channel waveguide arrays: an analyticalapproach

We present the modified scalar coupled mode analysis for an array ofN diffused channel waveguides. The study simulates the lateral evanescent field coupling inthe graded index channel waveguide array. In a two-step procedure, the propagationcharacteristics of individual waveguides are obtained first by the completely analytical,closed-form expressions obtained from the variational method. Consequent upon obtainingthe individual waveguide characteristics, the complete scalar coupled mode theory has beendeveloped that includes the non-orthogonality of the individual waveguide modes forstrongly coupled waveguides. The coupled mode equations are solved to obtain thesupermodes corresponding to the coupled waveguide configuration. Further to this, powerexchange in the graded index multi-waveguide systems has been studied. Complete powertransfer between the outside guides of the symmetric three-waveguide graded indexcoupler is reported when the condition of equispaced effective indices is met.

Er-LiNbO_3 waveguide: field approximation for simplified gain calculations in DWDM application

The coupled differential equations, which govern the evolution of pump and signal power in the gain characterization of Er-doped diffused channel waveguides, involve integrals that depend explicitly on the modal fields at the pump and all signal wavelengths. We use an analytical form of the modal field as an appropriately chosen buried asymmetric Gaussian function centered at the field maximum; this leads to analytical forms of coupled differential equations with no integrals for the calculation of gain characteristics of the amplifying waveguide. Thus, computations are simplified and computation time is also significantly reduced.

Empirical relations for the propagation characteristics of diffused channel waveguides

Empirical relations for the propagation constant and the field profile parameters of integrated optical diffused channel waveguides have been developed. The field profile used is the evanescent secant-hyperbolic field, which has been shown earlier to be a very good approximation for diffused channel-waveguide modes. Least-square fitting has been used to obtain the empirical relations. The results show that the error in empirical relations for the propagation constant is within 2% for a broad range of waveguide parameters. The obtained empirical relations for the field profile and the propagation constant have been used, as an example, to calculate the coupling length of diffused channel-waveguide-based directional couplers.

Method of integral equation in the theory of weak-guiding inhomogeneous optical waveguides

A method of integral equation is stated and applied in the analysis of the characteristic and noncharacteristic modes in 3D weak-guiding inhomogeneous optical waveguides. The dispersion curves for the modes of diffused channel waveguides are studied near the critical conditions in absorbing media. The accuracy of recovering the permittivity profile in a channel waveguide from the far-field radiation of the fundamental mode is estimated.

Zn-vapor diffused Er:Yb:LiNbO 3 channel waveguides fabricated by means of SiO 2 electron cyclotron resonance plasma deposition

We report here the fabrication method and operation of Zinc-vapor diffused channel waveguides on Erbium/Ytterbium (Er/Yb)-doped Lithium Niobate (LiNbO 3). electron cyclotron resonance (ECR) plasma deposition technique, UV photolithography and Reactive Ion Etching (RIE) are used to define an SiO 2 mask for pattern transfer. The whole process is performed at low temperatures eliminating typical LiO 2 out-diffusion problems and achieving low surface damage. The flexibility of the fabrication technology has been shown to be potentially applicable to integrated optics. EDAX measurements reveal good confinement and homogeneity of the diffused regions. Atomic Force Microscopy (AFM) surface characterization shows the swelling of the diffused areas, consistent with the topoepitaxial growth of a Zn x Li y Nb z O w layer.

WAVELENGTH CONVERSION OF AN INFRARED SIGNAL THROUGH CASCADED SECOND-ORDER NONLINEARITY IN A LITHIUM-NIOBATE CHANNEL WAVEGUIDE

We describe a wavelength conversion experiment (generation of a pulse at the wavelength λp - Δλ from a signal at λp+Δλ under the action of a pump at λp) performed through cascaded second-order process in a lithium niobate channel waveguide. With a 58-mm-long Ti diffused channel waveguide, λp=1.1 μ m (the wavelength of phase matching for the first step of sh generation), Δλ of several nanometers and 20 ps pulse duration, wavelength conversion with unit efficiency is obtained with a pump pulse energy of the order of 102 pJ. The experimental results are successfully interpreted by making use of modal analysis and solving the appropriate nonlinear equations.

Closed-form variational effective-index analysis for diffused optical channel waveguides

We present an application of simple closed-form expressions based on a variational approach for field parameters and effective indices for a closed-form analysis of diffused planar single-mode optical waveguides to obtain the characteristics of diffused channel waveguides by a combination of the variational and effective-index methods.

Leaky modes of channel waveguides with uniaxial anisotropy

An exact numerical method for analyzing the propagation properties of leaky modes of inhomogeneous channel optical waveguides with a complex uniaxial diagonal permittivity tensor is developed. The method is based on solving the system of integro-differential equations formulated with respect to transversal components of the magnetic field and the longitudinal component of the electric field. Some results of investigation of leaky modes of diffused channel waveguides in LiNbO3 and LiTaO3 crystals are given.

Modal analysis of anisotropic diffused-channel waveguide by a scalar finite element method

A procedure to model optical diffused-channel waveguides is presented in this work. The dielectric waveguides present anisotropic refractive indexes which are calculated from the proton concentration. The proton concentration inside the channel is calculated by the anisotropic 2D-linear diffusion equation and converted to the refractive indexes using mathematical relations obtained from experimental data. The arbitrary refractive index profile is modeled by a nodal expansion in the base functions. The TE and TM-like propagation properties (effective index) and the electromagnetic fields for well-annealed proton-exchanged (APE) LiNbO/sub 3/ waveguides are computed by the finite element method.

Simplified universal dispersion curves for channel waveguides

Simplified universal dispersion curves for graded-index diffused channel waveguides have been obtained with the new normalized WKB equation using the effective index method. It is shown that, similarly to planar guides, the propagation constant of all the guided modes of a particular channel can be obtained by two parameters, called the normalized mode orders. The dispersion relations between the propagation constant and the normalized mode order of the channel have been obtained for a number of profile shapes and waveguide dimensions.

Channel waveguide mode beat interferometer

In this paper we demonstrate the successful use of an integrated optical diffused channel waveguide as transducer element in a mode beat (difference or polarimetric) interferometer as a first step towards an integrated multianalyte sensor. This type of evanescent-field sensor is based on the different responses of the two fundamental modes in a monomode birefringent waveguide to changes in the refractive index of the sample in the vicinity of the sensor surface. The sensor has been tested and characterized as a differential microrefractometer for aqueous samples and as an optical thin-film monitor for biochemical affinity reactions using the well-known biotin-avidin system as a test system. The experimental results are in good agreement with the behaviour predicted by model calculations.

Design of the spot size for single-mode Ti/Mg:LiNbO3, channel waveguide for optimum coupling with fibers

Abstract To improve the coupling effciency between fibers and conventional Ti:LiNbO3 diffused channel waveguides, it is feasible that the elliptical mode pattern of the channel waveguide can be modified by the Ti/Mg double diffusion method. By means of the three-dimensional beam propagation method, we successfully show that the mode size of the waveguide fabricated by this method is well matched to that of the fiber for TE and TM polarizations separately.

An approximate method for computing mode-dispersion parameters in two-dimensional diffused-channel waveguides

We develop an approximate analysis based on the effective-index method to obtain the universal chart of the normalized parameters describing the mode dispersion of a two-dimensional diffused-channel wave-guide with an erfc-Gaussian index profile. We have shown that the Gaussian can well be approximated by an hyperbolic-secant-squared profile and we have compared our results with those obtained by using the effective-index method.

The fabrication and assessment of optical waveguides in poly (p-phenylenevinylene/poly (2,5-dimethoxy-p-phenylenevinylene) copolymer

Optical waveguides have been fabricated using a copolymer of poly( p-phenylenevinylene) PPV and poly(2,5-dimethoxy- p-phenylenevinylene) PDMeOPV via a precursor route. Controlled conversion of the precursor copolymer can give partially conjugated higher band gap or fully conjugated lower band gap regions, and the difference in refractive index is used to define diffused-channel waveguides. The spatial resolution of the process is limited only by the diffusion of acid around the capping layer, and by the lithography. We have made lines in 0.15μm thick films as narrow as 1μm and have demonstrated optical waveguiding in 4μm wide lines. Slab waveguides and diffused-channel waveguides have been assessed by prism and end-fire coupling at 633nm and 780nm. The anisotropy in the refractive index, and optical propagation losses have been measured.

A physical optics analysis for general bends in a 3D diffused channel waveguide using an equivalent 2D model

An accurate and very fast physical optics method for the analysis of bends in 3D diffused channel waveguides is described. The method is based upon the construction of an equivalent 2D slab waveguide bend having the same essential propagation characteristics as those of the original structure. To evaluate its accuracy, we analyze the radiation loss of a specific S-bend in a diffused channel waveguide periodically loaded with micro-prisms. It is shown to agree well with the measured performance. This agreement indicates that physical optics can indeed be used to analyze and to give design insights to general structures containing 3D junctions, with and without micro-prisms.

A simple variational analysis of diffused channel waveguides

The variational analysis of Ti:LiNbO3 strip waveguides is resolved into two related one-dimension problems, which provides a new iterative approach for the calculation of the mode parameters and the propagation constant. The analytical expressions of the local effective index profiles can be obtained from the variational analysis. The parameters of four trial solutions for the fundamental mode in a diffused-channel waveguide have been determined by using the present method. Comparison with results using the effective method shows that these four approximate expressions are accurate enough. It is also shown that this method converges very quickly and is suitable for both diffused channel waveguides and optical waveguides with rectangular cross-section.