Gregory R. Kilby

Design and analysis of a diffractive optical filter for use in an optoelectronic error-diffusion neural network.

The design, fabrication, experimental characterization, and system-performance analysis of a diffractive optical implementation of an error-diffusion filter for use in digital image halftoning is reported. A diffractive optical filter was fabricated as an eight-level phase element that diffuses the quantization error nonuniformly in both the weighting and the spatial dimensions, according to a prescribed algorithm. Ten identical diffractive elements were fabricated on ten different wafers and subsequently characterized experimentally. A detailed error analysis including both fabrication and instrumentation errors was carried out to quantify the performance of the fabrication process as well as the expected system performance of the filters. Halftone system performance was evaluated by use of the experimental filters performance and both quantitative and qualitative performance metrics. The results of this analysis demonstrate that multiple identical copies of a diffractive optical filter can be produced with sufficient accuracy that no loss in the halftoning system performance results.

Optical single-angle plane-wave transmittances/reflectances from Schwarzschild objective variable-angle measurements

Photonic crystal structures and other nanoscale and microscale optical structures are centrally important to future device technology. The fundamental infrared single-angle plane-wave experimental characterization of these structures is needed to evaluate the analysis, design, and fabrication progress on these devices. The very small sizes of these devices necessitates focusing the infrared probe light typically with a Schwarzschild reflecting objective. The small spot size inherently requires the large range of incident angles associated with the objective. In this work, a variable-angle measurement method is presented for obtaining the optical single-angle plane-wave transmittances/reflectances. The primary steps in this method are (1) calculating the reference sample single-angle plane-wave transmittance/reflectance, (2) measuring the composite transmittances/reflectances of a reference sample over a range of objective angles of incidence, (3) calculating the intensity-angular-weighting coefficients fo...

Fourier transform infrared transmission microspectroscopy of photonic crystal structures

The detailed microscopic characterization of photonic crystal (PC) structures is challenging due to their small sizes. Generally, only the gross macroscopic behavior can be determined. This leaves in question the performance at the basic structure level. The single-incident-angle plane-wave transmittances of one-dimensional photonic crystal (PC) structures are extracted from multiple-incident-angle, focused-beam measurements. In the experimental apparatus, an infrared beam is focused by a reflecting microscope objective to produce an incident beam. This beam can be modeled as multiple, variable-intensity plane waves incident on the PC structure. The transmittance of the structure in response to a multiple-incident-angle composite beam is measured. The composite beam measurement is repeated at various incident angle orientations with respect to the sample normal so that, at each angular orientation, the included set of single-angle plane-wave components is unique. A set of measurements recorded over a range of angular orientations results in an underspecified matrix algebra problem. Regularization techniques can be applied to the problem to extract the single-angle plane-wave response of the structure from the composite measurements. Experimental results show very good agreement between the measured and theoretical single-angle plane-wave transmittances.

Experimental characterization of a diffractive optical filter for use in an optoelectronic analog-to-digital converter

The first experimental characterization of an eight-level, phase-only diffractive optical implementation of an error diffusion filter for use in digital image halftoning is reported. Ten identical elements were fabricated through a DARPA-sponsored workshop and subsequently experimentally characterized. A detailed statistical error analysis including both fabrication and instrumentation errors was performed to quantify the performance of the fabrication process as well as the expected system performance of the filters. Over the 10-sample ensemble, an average diffraction efficiency of 83.7% was measured with an RMS error between the designed and experimental coefficients of 0.2411%, producing nearly diffraction limited performance.

Measurement Noise Tolerance of a Single-Angle Plane-Wave Photonic Crystal Characterization Method

A method to measure the single-angle plane-wave transmittance/reflectance of photonic crystal structures has been developed. The method employs an inverse matrix computation susceptible to measurement noise. The noise tolerance of the characterization method is identified.

Characterization of scaled-up photonic crystal structures using a discretely tunable carbon-dioxide laser

Micron-scale, photonic crystal devices fabricated using standard microelectronics technology can be used as a step in the development of sub-micron-scale devices. A discretely tunable CO2 laser beam is focused onto the sample and transmission data are collected. Regularization methods are used to calculate the single-angle plane-wave response of the device.