SGER: Optimized Irregular Electromagnetic Field Transformation Elements

Purdue University, West Lafayette IN

Investigators

Abstract

0121317 Webb The investigation of a new class of diffractive structures having optimized irregular wavelength-scale elements is proposed. One interpretation of this class of structures is as a generalized photonic bandgap system, either within a waveguide or in unbounded media. While the characteristics of photonic bandgap structures, being based on classical periodic systems, is well known, the physical characteristics (attributes, limitations etc.) of irregular structures are essentially unknown. Webb introduced the concept of compact, wavelength-scale irregular field transformation elements in the context of a microwave mode converter, showed spectacular performance, a dramatic reduction in size, and increased functionality relative to traditional periodic (perturbation) approaches, and fabricated and tested an example. Generalized interpretations of this new class of diffractive structures offer tremendous application potential, such as revolutionary broad area vertical cavity surface emitting laser diode mode control and optical fiber wavelength division multiplexing elements, once the physics and synthesis approaches are taken from the current anecdotal stage to a more fundamental level of understanding. It is the purpose of this proposed research effort to do just that by addressing the following two objectives. o Physical Characteristics and Performance Metrics: The PI proposes to investigate the attributes of irregular, sub-wavelength diffractive structures, synthesized using a nonlinear optimization algorithm coupled to a forward numerical electromagnetic solver, in order to develop the phys-ical understanding necessary to exploit a variety of possible applications. He will study field control using wavelength-scale structures having conducting and/or refractive index variations in waveguide arid unbounded media systems that utilize evanescent field. Using a functional metric for the required field transformation, search algorithms will be developed and sensitivity analyses to degrees of freedom, wavelength and input field performed. o Synthesis: Nonlinear optimization techniques, while widely applied in areas such as imaging and signal processing, are not well developed for the synthesis of electromagnetic structures. The PI used a relatively simple multi-resolution algorithm in the design of irregular waveguide mode converters. He proposes the development of more rigorous and efficient synthesis tech-niques suitable for irregular diffractive structures by studying both continuous and discrete optimization approaches.