Here we show our architectural approaches to nanophotonics to benefit from unique physical properties obtained by local interactions between nanometric elements, such as quantum dots, via optical near fields, that provide ultra high-density integration capability beyond the diffraction limit of light. We discuss a memory-based architecture and a simple hierarchical architecture. By using resonant energy levels between quantum dots and inter-dot interactions, nanometric data summation and broadcast architectures are demonstrated including their proof-of-principle experimental verifications using CuCl quantum dots. Through such architectural and physical insights, we are seeking nanophotonic information systems for solving the integration density limited by diffraction limit of light and providing ultra low-power operations as well as unique functionalities which are only achievable using optical near-field interactions.

Supercontinuum based sources and measurement techniques are developed, enabling optical ultra-broadband studies of nano-scale photonic crystal devices and integrated photonic circuits over 1.2 - 2.0 micron wavelength range. Experiments involving 1-D periodic photonic crystal microcavity waveguides and 3-D periodic photonic crystals with embedded point defects are described. Experimental findings are compared with rigorous electromagnetic simulations.

We present a set of modeling, sensitivity analysis, and design optimization methods for photonic crystal structures based on Wannier basis field expansion and efficient matrix analysis techniques. We develop the sensitivity analysis technique to analyze both refractive index perturbations and dielectric boundary shift perturbations. Our modeling method is ~1000X faster than FDTD for searching through a large number of similar device designs. We show that our optimization techniques, relying on the efficiency of the modeling and sensitivity analysis methods, enable systematic global and local optimizations of integrated optical components. We show that our design method can be controlled to favor designs without high-energy build-ups, potentially making them more fabrication-error tolerant. We present design examples and verify our designs with FDTD calculations.

The second order dispersion is proportional to the difference of time delays accumulated by waves of two adjacent wavelengths. This time delay difference can be obtained when the group velocity or the propagation distance is changing with wavelength. In both cases, a decrease of the smallest available group velocity leads to a proportional size reduction given a fixed dispersion value. In conventional waveguides the smallest group velocity is close to the speed of light in the core material, whereas in photonic crystal line-defect waveguides orders of magnitude smaller group velocities can be obtained within a certain bandwidth. Based on these waveguides, different concepts are proposed and evaluated. A large difference in group velocities for different wavelengths is obtained by anti-crossing of modes in single and coupled line-defect waveguides. Alternatively, in chirped photonic crystal waveguides the path difference, hence the group delay, is strongly varied for adjacent wavelengths. Positive and negative dispersion of approximately hundred ps/nm on millimeter scale over the bandwidth of a single WDM channel (0.8nm) are theoretically predicted and demonstrated using finite integration simulations.

Fiber delivery of intense laser radiation is important for a broad range of application sectors, from medicine through to industrial laser processing of materials, and offers many practical system design and usage benefits relative to free space solutions. Optical fibers for high power transmission applications need to offer low optical nonlinearity and high damage thresholds. Single-mode guidance is also often a fundamental requirement for the many applications in which good beam quality is critical. In recent years, microstructured fiber technology has revolutionized the dynamic field of optical fibers, bringing with them a wide range of novel optical properties. These fibers, in which the cladding region is peppered with many small air holes, are separated into two distinct categories, defined by the way in which they guide light: (1) index-guiding holey fibers (HFs), in which the core is solid and light is guided by a modified form of total internal reflection, and (2) photonic band-gap fibers (PBGFs) in which guidance in a hollow core can be achieved via photonic band-gap effects. Both of these microstructured fiber types offer attractive qualities for beam delivery applications. For example, using HF technology, large-mode-area, pure silica fibers with robust single-mode guidance over broad wavelength ranges can be routinely fabricated. In addition, the ability to guide light in an air-core within PBGFs presents obvious power handling advantages. In this paper we review the fundamentals and current status of high power, high brightness, beam delivery in HFs and PBGFs, and speculate as to future prospects.

We report Photonic Crystal (PhC) designs fabricated in silicon-on-insulator wafers (SOI) using 248 nm & 193 nm DUV lithography. Emphasis was on demonstrating unique PhC effects through the use of standard CMOS equpiment and process development of an optical test chip using a high-volume manufacturing facility. Most of the planar 2-D PhCs waveguides were designed using a triangular lattice of holes. An extensive range of test structures were also designed, including W1 and W3 waveguides in both triangular and square lattices. The use of optical proximity correction (OPC) and variations of pitch and hole dimensions allowed for a large design-of-experiment not practical using the more conventional e-beam direct-write approach. Smart Cut SOI wafers with a thin epitaxial Si layer on a 2μm buried SiO₂ layer were first processed and characterized using 248 nm lithography. Preliminary pitch/hole patterning requirements were 400nm/200nm. Resist was changed from high- to low-contrast resist to compensate for the high sensitivity of critical hole dimension to exposure dose. Optical characterization data of PhC test structures were used to map band structure calculations and more accurately determine the PhC effective index; results were used to model more accurate pitch/hole values. Successful processing results were also obtained using 193nm lithography to resolve PhC pitch/hole dimensions of ~280/180nm. Optical characterization data are being used to refine next-generation PhC designs.

We demonstrate experimentally an optical scanning technique for measuring the step heights of surface features without using conventional optical interferometers. This technique involves the deployment of the so-called photo-EMF sensors that are capable of sensing the presence of step-like features on an otherwise optically flat surface. Scanning of the target surface is achieved by rotating the object being investigated while keeping the laser beam stationary. Theoretical modeling and experimental data will be presented indicating the resolution of step-like features with merely 15 nm in height.

In this research effort, epitaxial lateral overgrowth (ELOG) of GaN on sapphire was performed by low-pressure metalorganic chemical vapor deposition (MOCVD) in a horizontal reactor. All ELOG growths were stopped prior to complete coalescence, and the resulting cross-sections were characterized by scanning electron microscopy (SEM). Both vertical {1120} and inclined sidewalls were observed. Inclined {112n}sidewalls of various angles (n ≈ 2-2.2) were found as previously reported in the literature¹. Both one-step and two-step ELOG processes were used to control the overgrowth geometry. It was confirmed that sidewall formation and growth rates are closely correlated with multiple parameters including temperature and V/III ratio¹. It was also found that substrate rotation greatly influences sidewall evolution and vertical growth rate. A conceptual model was begun to completely describe the ELOG process in a horizontal reactor. It is speculated that the different sidewalls observed as a function of substrate orientation result from variation in the local V/III ratio. Once developed, the final model will be used to control the sidewalls in the growth of ELOG structures for the fabrication of novel optoelectronic devices.

A robust and compact photonic proximity sensor is developed for optical fuze in munitions applications. The design of the optical fuze employed advanced optoelectronic technologies including high-power vertical-cavity surface-emitting lasers (VCSELs), the p-i-n or metal-semiconductor-metal (MSM) photodetectors, SiGe ASIC driver, and miniature optics. The development combines pioneering work and unique expertise at ARDEC, ARL, and Sandia National Laboratories and synergizes the key optoelectronic technologies in components and system designs. This compact sensor will replace conventional costly assemblies based on discrete lasers, photodetectors, and bulky optics and provide a new capability for direct fire applications. It will be mass manufacturable in low cost and simplicity. In addition to the specific applications for gun-fired munitions, numerous civilian uses can be realized by this proximity sensor in automotive, robotics, and aerospace applications. This technology is also applicable to robotic ladar and short-range 3-D imaging.

The need for alternative interconnect technologies that can efficiently deal with large bandwidths of information has led to the investigation of photonic devices suitable for integration into an optical interconnect platform. Active modulation of the optical properties of silicon-based photonic crystals provides the foundation for a variety of tunable components. One promising platform for active silicon photonics building blocks are porous silicon one-dimensional photonic bandgap microcavity structures infiltrated with optically active species. The porous silicon microcavities are fabricated by electrochemical etching, which allows flexibility in the design wavelength. As a first demonstration, electrical and thermal modulation of porous silicon microcavities is shown based on a change in the refractive index of liquid crystals infiltrated in the porous silicon matrix. Controllable tuning to both longer and shorter wavelengths is achieved based on the choice of liquid crystals. Extinction ratios greater than 10 dB have been demonstrated and larger attenuation can be realized by increasing the Q-factor of the microcavities. The porous silicon microcavities can also serve as a template for faster response time active devices based on the infiltration of quantum dots or electro-optic polymers. The relationships between microcavity Q-factor, extinction ratio, active species refractive index change, and device switching speed will be discussed.

We design broadband polarization mirrors for optical communications. The mirrors consist of multilayer subwavelength gratings that do not require lateral alignment with respect to one another. Flexible bandwidth control and wide angular response of reflectivity are demonstrated in several configurations with 2, 3, and 4 layers of gratings. Perspective applications to the polarization control of active devices in the telecommunication windows, including vertical cavity surface emitting lasers are presented.

Photonic crystal fiber is glass or polymer fiber with array of microscopic air holes running along length of the fiber. Waveguide properties of such fiber can be controlled by introducing additional materials into the air holes. Liquid crystals (LC) are very suitable for that purpose because its refractive index can be easily tuned by electric field or temperature. Alignment of LC in photonic holes determines mostly the optical properties of the fiber. In this paper, we have developed the technique of photo-configurable alignment of LC in glass micro-tubes and in photonic crystal fiber. The order parameter of LC has been obtained from FTIR spectroscopy data and has demonstrated good alignment quality. Presented technique can be used as non-contact method of LC alignment in complex photonic crystal structure.

Carrier lifetime measurements are a powerful tool to understand and quantify the recombination mechanisms in semiconductor lasers. In this work we report the results of carrier lifetime measurements performed on 1.3 μm p-doped InAs Quantum-Dot lasers at room temperature using the small-signal modulation technique. The carrier lifetime at a particular bias current is determined by fitting the measured optical frequency response curves to the calculated response derived from sub-threshold carrier and photon rate equations. Calculated optical response curves are dominated by a single pole regardless of whether a single or multiple carrier level rate equation analysis is used. We also measure a single pole optical response, throughout the entire range of bias currents, thus allowing us to extract the differential carrier lifetime. The recombination coefficients are extracted by simultaneously fitting the variation of differential carrier lifetime with bias current to equations relating the current and carrier lifetime to the recombination coefficients and carrier density. Specifically we find a cubic (or Auger) recombination coefficient of 1.2 x 10^-29 cm⁶/s and 5.6 x 10^-29 cm6/s in the single and multi carrier level rate equations respectively, while the bimolecular (radiative) coefficients are 1.8 x 10^-11 cm⁶/s and 6.5 x 10^-11 cm⁶/s, and the monomolecular (defect) coefficients are 2.9x10⁷ /s and 5.5x10⁷ /s. Regardless of the analysis used we find that the vast majority, approximately 80%, of the current at threshold is due to the cubic recombination process which is traditionally assumed to be Auger recombination.

L-Histidine is a naturally occurring essential amino acid. In addition it is biologically important in the dismutation of superoxide radical (O₂^-.) by superoxide dismutase (SOD). In this work, fluorescence and absorptiometric techniques are used to characterize the photo-phenomena of this compound in a simulated body fluid (SBF). In this medium L-histidine fluoresces at 458 nm when excited at 390 nm. Its wavelength of maximum absorbance, λ_max, was observed at 272 nm and a molar absorptivity, ε, of 1.50 x 10³/M-cm. This absorptiometric data suggest that L-histidine undergoes an n→π* electronic transition reaction in an SBF medium. The observed bimolecular quenching rate constant, k_q, of 1.68 x 10⁸/M-s, by hydrogen peroxide as quencher, suggests a non-diffusional quenching but rather an activation-controlled mechanism with a rate constant, ka, of 1.68 x 10⁸/M-s and an electron transfer rate constant of 3.65 x 10⁸/s. A quantum yield, Φ_f, of 0.09 and a fluorescence lifetime of 12.2 ns, respectively, were determined. The observed radiative and non-radiative rate constants, k_r and k_nr, of 7.38 x 10⁶/s and 7.46 x 10⁷/s, respectively, suggest that the deactivation of the thermally excited L-histidine is mainly through a non-radiative route rather than by normal fluorescence, which can account for the low quenching constant, KSV, of 2.13/M that was obtained. The solvent reorganization energy, λ_s, and the reaction free energy change, ΔG, of 1.48 eV and -2.47 eV, respectively, suggest that the electron transfer reaction in the L-histidine-H₂O₂ reaction in SBF medium is through a solvent separated mechanism.