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Center for Organic Photonics and Electronics

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Concurrent three-dimensional characterization of the refractive-index and residual-stress distributions in optical fibers

(Georgia Institute of Technology, 2012-08) Hutsel, Michael R. ; Gaylord, Thomas K.

A three-dimensional index-stress distribution (3DISD) measurement method for determining concurrently the refractive-index distributions (RIDs) and residual-stress distributions (RSDs) in optical fibers is presented. The method combines the quantitative-phase microscopy technique, the Brace–Köhler compensator technique, and computed tomography principles. These techniques are implemented on a common apparatus to enable concurrent characterization of the RID and the RSD. Measurements are performed on Corning SMF-28 fiber in an unperturbed section and in a section exposed to CO₂ laser radiation. The concurrent measurements allow for the first accurate comparison of the collocated RID and RSD. The resolutions of the refractive index and stress are estimated to be 2.34×10⁻⁵and 0.35 MPa, respectively.
Compact silicon diffractive sensor: design, fabrication, and prototype

(Georgia Institute of Technology, 2012-07) Maikisch, Jonathan S. ; Gaylord, Thomas K.

An in-plane constant-efficiency variable-diffraction-angle grating and an in-plane high-angular-selectivity grating are combined to enable a new compact silicon diffractive sensor. This sensor is fabricated in silicon-on-insulator and uses telecommunications wavelengths. A single sensor element has a micron-scale device size and uses intensity-based (as opposed to spectral-based) detection for increased integrability. In-plane diffraction gratings provide an intrinsic splitting mechanism to enable a two-dimensional sensor array. Detection of the relative values of diffracted and transmitted intensities is independent of attenuation and is thus robust. The sensor prototype measures refractive index changes of 10 ⁻⁴ . Simulations indicate that this sensor configuration may be capable of measuring refractive index changes three or four orders of magnitude smaller. The characteristics of this sensor type make it promising for lab-on-a-chip applications
Pattern-integrated interference lithography: single-exposure fabrication of photonic-crystal structures

(Georgia Institute of Technology, 2012-06) Burrow, Guy M. ; Leibovici, Matthieu C. R. ; Gaylord, Thomas K.

Multibeam interference represents an approach for producing one-, two-, and three-dimensional periodic optical-intensity distributions with submicrometer features and periodicities. Accordingly, interference lithography (IL) has been used in a wide variety of applications, typically requiring additional lithographic steps to modify the periodic interference pattern and create integrated functional elements. In the present work, pattern-integrated interference lithography (PIIL) is introduced. PIIL is the integration of superposed pattern imaging with IL. Then a pattern-integrated interference exposure system (PIIES) is presented that implements PIIL by incorporating a projection imaging capability in a novel three-beam interference configuration. The purpose of this system is to fabricate, in a single-exposure step, a two-dimensional periodic photonic-crystal lattice with nonperiodic functional elements integrated into the periodic pattern. The design of the basic system is presented along with a model that simulates the resulting optical-intensity distribution at the system sample plane where the three beams simultaneously interfere and integrate a superposed image of the projected mask pattern. Appropriate performance metrics are defined in order to quantify the characteristics of the resulting photonic-crystal structure. These intensity and lattice-vector metrics differ markedly from the metrics used to evaluate traditional photolithographic imaging systems. Simulation and experimental results are presented that demonstrate the fabrication of example photonic-crystal structures in a single-exposure step. Example well-defined photonic-crystal structures exhibiting favorable intensity and lattice-vector metrics demonstrate the potential of PIIL for fabricating dense integrated optical circuits
Pattern-integrated interference lithography instrumentation

(Georgia Institute of Technology, 2012-06) Burrow, Guy M. ; Leibovici, Matthieu C. R. ; Kummer, J. W. ; Gaylord, Thomas K.

Multi-beam interference (MBI) provides the ability to form a wide range of sub-micron periodic optical-intensity distributions with applications to a variety of areas, including photonic crystals (PCs), nanoelectronics, biomedical structures, optical trapping, metamaterials, and numerous subwavelength structures. Recently, pattern-integrated interference lithography (PIIL) was presented as a new lithographic method that integrates superposed pattern imaging with interference lithography in a single-exposure step. In the present work, the basic design and systematic implementation of a pattern-integrated interference exposure system (PIIES) is presented to realize PIIL by incorporating a projection imaging capability in a novel three-beam interference configuration. A fundamental optimization methodology is presented to model the system and predict MBI-patterning performance. To demonstrate the PIIL method, a prototype PIIES experimental configuration is presented, including detailed alignment techniques and experimental procedures. Examples of well-defined PC structures, fabricated with a PIIES prototype, are presented to demonstrate the potential of PIIL for fabricating dense integrated optical circuits, as well as numerous other subwavelength structures.
Multimode metal-insulator-metal waveguides: Analysis and experimental characterization

(Georgia Institute of Technology, 2012-02) Lin, Chien-I ; Gaylord, Thomas K.

The analysis and experimental characterization of the propagation constants and attenuation coefficients of surface plasmon (SP) modes in planar multimode metal-insulator-metal (MIM) waveguides are presented. The experimental characterization is based on determining the width of the reflection angular spectrum in the attenuated total reflection (ATR) configuration. Due to its transverse character, the ATR configuration provides a more straightforward and simpler way to determine the propagation constants and attenuation coefficients of plasmonic modes in MIM structures, compared to using tapered end-couplers with multiple waveguide samples or near-field scanning optical microscopy (NSOM). In this paper, the propagation constants and attenuation coefficients of multimode MIM structures are investigated, and MIM waveguide structures with 730 and 1460 nm SiO2 cores and Au claddings are fabricated and experimentally characterized. The measurement results indicate that the absorption of Au is responsible for the high attenuation in MIM plasmonic modes, while scattering loss is another source of attenuation for higher-order modes (smaller zigzag angles). To the best of the authors\' knowledge, the present work represents the first time the attenuation coefficient and propagation constant of each mode in a multimode MIM waveguide have been individually measured.
Three-beam interference lithography methodology

(Georgia Institute of Technology, 2011-02) Stay, Justin L. ; Burrow, Guy M. ; Gaylord, Thomas K.

Three-beam interference lithography represents a technology capable of producing two-dimensional periodic structures for applications such as micro- and nanoelectronics, photonic crystal devices, metamaterial devices, biomedical structures, and subwavelength optical elements. In the present work, a systematic methodology for implementing optimized three-beam interference lithography is presented. To demonstrate this methodology, specific design and alignment parameters, along with the range of experimentally feasible lattice constants, are quantified for both hexagonal and square periodic lattice patterns. Using this information, example photonic crystal rodlike structures and hole-like structures are fabricated by appropriately controlling the recording wavevector configuration along with the individual beam amplitudes and polarizations, and by changing between positive- or negative-type photoresists.
Loss measurement of plasmonic modes in planar metal-insulator-metal waveguides by an attenuated total reflection method

(Georgia Institute of Technology, 2010-11) Lin, Chien-I ; Gaylord, Thomas K.

We report experimental excitation and characterization of surface plasmon modes in planar metal–insulator–metal (MIM) waveguides. Our approach is based on determining the width of the reflection angular spectrum in the attenuated total reflection (ATR) configuration. Owing to its transverse character, the ATR configuration provides a more straightforward and simpler way to determine the loss of plasmonic modes in MIM structures, compared to using tapered end couplers with multiple waveguide samples or scanning near-field optical microscopy. In this Letter, two waveguide structures with Au claddings and 50/200nm SiO ₂ cores are investigated. The propagation lengths measured at λ=1.55μm are 5.7 and 18μm , respectively, in agreement with the theoretical predictions.
Characterization of the loss of plasmonic modes in planar metal-insulator-metal waveguides by a coupling-simulation approach

(Georgia Institute of Technology, 2010-02) Lin, Chien-I ; Gaylord, Thomas K.

Metal–insulator–metal (MIM) structures have been the subject of great interest as nanoscale plasmonic waveguides. The modeling and measurement of the loss in these waveguides is one of the critical issues in realizing the plasmon-based nanocircuitry. Due to the subwavelength size of the structure, the light injection and the measurement of the loss in MIM structures typically require tapered fibers or waveguides, as well as multiple waveguide structures with various length scales [8, 9] or scanning near-field optical microscopy. The transverse transmission/reflection (TTR) method is presented for determining the loss of plasmonic modes in MIM waveguides. The approach is based on determining the width of the reflection angular spectrum in the attenuated total reflection configuration. Owing to its transverse character, the TTR method potentially provides a more straightforward and simpler way to determine the loss of plasmonic modes in MIM structures.
Accurate cross-sectional stress profiling of optical fibers

(Georgia Institute of Technology, 2009-09) Hutsel, Michael R. ; Ingle, Reeve ; Gaylord, Thomas K.

A novel technique for determining two-dimensional, cross-sectional stress distributions in optical fibers and fiber-based devices is presented. Use of the Brace-Kohler compensator technique and a polarization microscope for the measurement of retardation
Conditions for primitive-lattice-vector-direction equal contrasts in four-beam-interference lithography

(Georgia Institute of Technology, 2009-08) Stay, Justin L. ; Gaylord, Thomas K.

Four distinct conditions for primitive-lattice-vector-direction equal contrasts in four-beam interference are introduced and described. By maximizing the absolute contrast subject to an equal contrast condition, lithographically useful interference patterns are found. Each condition is described in terms of the corresponding constraints on the plane wave wave vectors, polarizations, and intensities. The resulting locations of global intensity maxima, minima, and saddle points are presented. Subordinate conditions for unity absolute contrast are also developed. Three lattices are treated for each condition: simple cubic, face-centered cubic, and body-centered cubic.