John C. Brazas

Conformal grating electromechanical system (GEMS) for high-speed digital light modulation

A diffractive optical MEMS device for spatial and temporal light modulation is described that is capable of high-speed digital operation. The device contains electromechanical ribbons suspended flat above a silicon substrate by a periodic series of intermediate supports. When actuated electrostatically, the ribbons conform around the support substructure to produce a grating. The device has optical switching times of less than 50 nsec, sub-nanosecond jitter, high optical contrast and efficiency, and reliable actuation in contact mode. The fine gray levels needed for digital imaging systems are produced by pulse width modulation.

Analysis of input-grating couplers having finite lengths

Planar waveguide-grating couplers are analyzed to determine the effects of grating length, the incident beam size, and the coupling length of the grating on the input-coupling efficiency. The emphasis is to examine the effects of these finite lengths on the range of angles over which input coupling occurs and the shape of the efficiency curve. A general formula for normalized input-coupling efficiency is given to relate these lengths. When any one of these characteristic lengths is much smaller than the other two, both the angular width and angular dependence of the coupling efficiency for a scan of the incident beam angle will be mainly determined by that characteristic length. This is demonstrated experimentally for two cases: one has a relatively short grating length, and the other has a short coupling length.

High-Resolution Laser-Projection Display System Using a Grating Electromechanical System (GEMS)

Eastman Kodak Company has developed a diffractive-MEMS spatial-light modulator for use in printing and display applications, the grating electromechanical system (GEMS). This modulator contains a linear array of pixels capable of high-speed digital operation, high optical contrast, and good efficiency. The device operation is based on deflection of electromechanical ribbons suspended above a silicon substrate by a series of intermediate supports. When electrostatically actuated, the ribbons conform to the supporting substructure to produce a surface-relief phase grating over a wide active region. The device is designed to be binary, switching between a reflective mirror state having suspended ribbons and a diffractive grating state having ribbons in contact with substrate features. Switching times of less than 50 nanoseconds with sub-nanosecond jitter are made possible by reliable contact-mode operation. The GEMS device can be used as a high-speed digital-optical modulator for a laser-projection display system by collecting the diffracted orders and taking advantage of the low jitter. A color channel is created using a linear array of individually addressable GEMS pixels. A two-dimensional image is produced by sweeping the line image of the array, created by the projection optics, across the display screen. Gray levels in the image are formed using pulse-width modulation (PWM). A high-resolution projection display was developed using three 1080-pixel devices illuminated by red, green, and blue laser-color primaries. The result is an HDTV-format display capable of producing stunning still and motion images with very wide color gamut.

High-efficiency input coupling into optical waveguides using gratings with double-surface corrugation

Waveguide grating couplers that have surface corrugation on both boundaries of the waveguide were fabricated by the deposition of waveguide material at high-vacuum pressures onto a surface-relief grating etched into the substrate. A lateral shift between the two gratings along the direction of the common grating vector was created during the waveguide deposition when the substrate normal was tilted with respect to the direction of material deposition. A series of waveguide thicknesses having an identical angle of deposition were examined to observe the effect of the waveguide thickness, and corresponding lateral shift, on the branching ratio and input-coupling efficiency. Branching ratios of above 98% and input-coupling efficiencies near the theoretical limit for an incident Gaussian beam were obtained.

Mode-index waveguide lens with novel gradient boundaries developed for application to optical recording

A new type of mode-index waveguide lens is presented that has acircular gradient-index boundaries. These lenses have relatively large apertures and are fabricated by physical vapor deposition by using organic materials. A deposition mask that is accurately defined by using lithographic processing techniques was used to shape the lens boundaries during the addition of the lens to the waveguide. A comprehensive analysis of the lens system is presented. After adjusting the model to have aberrations that are comparable with those of the fabricated lens, spot size and sidelobe intensity values were nearly identical for the theoretical and experimental systems. The application of these lenses to optical recording technology is demonstrated by the generation of focus and tracking error signals.

Error signal processing with a mode-index waveguide lens

Passive integrated optical components have several advantages over conventional optical components including reduced size and weight, alignment as part of fabrication and integration with planar detectors and electronics. Waveguide lenses are recognized as key components for signal processing and source collimation in integrated optical systems. However, few papers have discussed their application to optical error signal processing for optical recording. Here we present a new type of mode-index waveguide lens used in a half aperture and dual-half aperture format for generating focus and tracking error signals in a test configuration.