Lynne A. Molter

Refractive index approximations from linear perturbation theory for planar MQW waveguides

The mode powers and propagation constants for planar multilayer waveguides formed with multiple quantum well (MQW) materials and with the MQW layers replaced by a single uniform layer are compared. By considering linear perturbations of the solutions of the wave equation, the optimal choice of average for the dielectric constant of the substituted single layer is determined. For the case of TE modes, minimal error in the propagation constant is predicted if a weighted average of the dielectric constants of the MQW materials is used. For the case of TM modes, using a weighted average of the reciprocal of the dielectric constants is predicted to yield the minimum error. Numerical results confirm these predictions. >

Evaluation of refractive index approximations used for mode determination in multiple quantum well slab waveguides

Approximations commonly used to determine the effective indexes of the guided modes of optical waveguides formed using multiple quantum well (MQW) materials are compared to the exact solutions in the slab waveguide model. Modeling the quantum well region as a single homogeneous layer with an average index of refraction is shown to produce results in close agreement with exact values of the effective index. A geometrically weighted average of the indexes provides the most accurate approximation for typical values of index and layer thickness of GaAs-Al/sub x/Ga/sub 1-x/As quantum well waveguides. >

Exact modal analysis and optimization of N/spl times/N/spl times/1 cascaded waveguide structures with multimode guiding sections

Cascaded multimode interference waveguide devices are analyzed to predict their switching properties. The results obtained using an exact modal analysis of an infinite slab model of these structures are compared to those found using simple approximations. Using this model, design parameters for both 2/spl times/2/spl times/1 and 8/spl times/8/spl times/1 switching structures are optimized; robustness of the numerical optimization algorithm is discussed. Sensitivity of device transmission performance to lengths and widths of each of the multimode regions, phase shifts in the interconnect regions, and wavelength are presented for the optimized devices. The deviations of the multimode region lengths found using simple approximations from those found by optimizing the model are also presented.

Design and modeling of passive optical switches and power dividers using non-planar coupled fiber arrays

Arrays of coupled waveguides such as the ubiquitous directional coupler are used extensively in optoelectronic devices, with demonstrated applications to optical communications networks, fiber interferometers, and optical homodyne receivers. In order to analyze the transmission characteristics of circular arrays of coupled optical fibers, we have developed a matrix representation of the coupled-mode formalism, allowing for varying fiber diameters and differing coupling strengths between the fibers in the array. The model is used to identify design criteria for application of such arrays as passive optical switches and power dividers.

Three-dimensional phase step profilometry with a multicore optical fiber

This paper demonstrates the feasibility of using phase stepping and a multicore optical fiber to calculate an objects depth profile. An interference pattern is projected by an optical fiber onto the object. The distorted interference pattern containing the object information is captured by a CCD camera and processed using a phase step interferometry method. The phase step method is less computationally intensive compared to two-dimensional Fourier transform profilometry and provides more accuracy when measuring objects of high frequency spatial variations.

The extinction ratio in optical two-guide coupler Delta beta switches

Two-guide Delta beta optical couplers that operate as on-off switches are reexamined using the exact eigenmodes of a slab waveguide model of the coupler. Two-section alternately detuned couplers, with the first section detuned by D and the second section by -D, are treated. The input/output configurations analyzed are case (1) where a single output guide is connected to the same guide of the coupler as the input guide, and case (2) where a single output guide is connected to the coupled guide. For both cases, ideal switching, i.e. complete extinction of the off state, can be obtained in the two-section Delta beta coupler over a wide range of coupler lengths. The results differ from those of conventional coupled-mode theory, however, in that complete extinction can be obtained when the two sections of the coupler have equal lengths only in a few special cases. Over most of the total coupler length range in which ideal switching is possible in both input/output configurations, the lengths of the two sections cannot be equal if complete extinction is to be obtained. >

Generalized switching properties of three-guide circular fiber arrays using coupled-mode analysis

A numerical method that utilizes coupled-mode theory to examine the switching properties of arrays formed by three fibers arranged in a circular configuration is developed. An error function that depends on the difference between the desired output conditions and those obtained for a given set of coupling and detuning coefficients is defined. To determine the values of these coefficients for a particular switching operation, the error function is minimized by varying the coupling and detuning coefficients. Results are presented for configurations that switch a signal from one fiber to another, equally split the power from a single input guide into two fibers at the output, and divide the power from a single input guide equally among all three output guides. >

Two Dimensional Force And Longitudinal Twisting Measurements With A Four-Core Optical Fiber Sensor

Shifts in 2-D interferograms of a four-core optical fiber are used to measure 2-D bending. Repeatable linear phase shifts versus 2-D force-induced deflection and the first simultaneous measurement of twisting and bending were demonstrated.

Analysis of N X M Waveguide Splitters and Couplers with Multimode Guiding Sections

Highly multimode waveguides in which multiple images of the input excitation are formed at different distances along the guide can be used for splitting and switching applications. These devices are often analyzed with a paraxial approximation. In the analysis presented here the actual shapes and propagation constants of the modes were considered. The analysis was performed on splitters with one input guide, centered on a multimode region, and N output guides; uniformity and sensitivity of the outputs to changes in the length and width of the multimode section for 1×2 and 1×8 splitters at a variety of positions along the multimode region were predicted. 2×2 couplers with off-centered inputs were also analyzed. A modification to the input/output guide positions of the couplers was made to reduce the length of the guide while achieving the same absolute sensitivity to variations in the length of the multimode region.

Generalized switching, splitting, and multiplexing operations using circular arrays of coupled waveguides

Nth-order coupled circular arrays of optical fibers can perform switching, splitting, and (de)multiplexing operations by adjusting the coupling between adjacent guides. A generalized 4-guide array to accomplish these operations is described, along with additional more specific results for higher-order systems.