Mark Lasher

Photonic computing using the modified signed-digit number representation

Improving the precision of optically performed computations is a critical aspect of photonic computing. One possible method for improving precision is through the use of modified signed-digit (MSD) arithmetic. Optical implementation of MSD arithmetic offers several important advantages over other optical techniques such as the digital multiplication by analog convolution (DMAC) algorithm or the use of residue arithmetic. These advantages include the parallel pipeline flow of digits due to carry-free addition and subtraction, fixed-point as well as floating-point capability, and the potential for performing divisions. We present a brief description of the modified signed-digit number system and suggest one optical architecture for implementing MSD fixed-point addition, subtraction, and multiplication.

Effects of underwater turbulence on laser beam propagation and coupling into single-mode optical fiber

We characterize and compare the effects of turbulence on underwater laser propagation with theory. Measurements of the coupling efficiency of the focused beam into a single-mode fiber are reported. A simple tip-tilt control system, based on the position of the image centroid in the focal plane, was shown to maintain good coupling efficiency for a beam radius equal to the transverse coherence length, r(0). These results are relevant to high bandwidth communication technology that requires good spatial mode quality.

Laser Projected 3D Volumetric Displays

A 3D volumetric display system utilizing a rotating helical surface is described. The rotating helix system permits images to be displayed in a 3D format that can be observed without the use of special glasses. Its rotating helical screen sweeps out a cylindrical envelope, providing a volumetric display medium through which scanned laser pulses are projected. The light scatters from the surface of the helix so that each voxel appears to emanate from specific points in space. Each point has x-y-coordinates determined by the laser scanner and a z- coordinate determined by the intersection of the laser beam and the helix surface. Display images are created by synchronizing the interaction of the laser pulses and the moving screen to address a full 3D volume that gives the viewer true depth cues (binocular parallax, accommodation, convergence) without the need for any special viewing aids. We describe recent work on the development of mechanical, optical, electronic, and software engineering for a display system based on a 36-inch diameter helix using high speed, multichannel, random access laser scanners. Color images are created using red, green and blue laser sources. The system is capable of displaying 800,000 voxels per second, per color. A portable, 12-inch diameter, translucent helix system is also presented.

Fluorescent volumetric display excited by a single infrared beam

A volumetric display technique that uses fluorescence excited by a single infrared beam is proposed. A convergent laser beam is used to activate ions locally around the focal point. Three-dimensional scanning by the focal point is achieved by moving an inclined image plane in the direction perpendicular to an optical axis. Preliminary experimental results of three-dimensional image generation in an Er(3+)-doped fluoride glass excited by a laser beam of 810 nm wavelength are presented.

PLZT-based dynamic diffractive optical element for high-speed random-access beam steering

A novel type of electro-optic diffractive element is presented which can satisfy the requirements for a high space-time bandwidth deflector while providing for two-dimensional random access beam steering control. The basic device consists of a multichannel array of phase modulators fabricated using Lanthanum-modified lead zirconate titanate (PLZT) operating as a programmable diffractive optical element. Two-dimensional deflection control can be readily obtained by crossing two one-dimensional arrays. This device is useful for wavelengths in the visible to mid-IR range and is based on PLZT ceramic materials which can be readily mass-produced. It possesses the versatility and multifunctionality of liquid crystal based optical phased array systems while allowing for very fast switching speeds with good thermal stability. We present a brief comparison of this novel deflector with other scanning technologies and outline the benefits and trade-offs of the PLZT-based device. Experiments on 16- and 32-channel arrays with full wave voltages less than 400 volts demonstrate continuous lateral beam steering control of a HeNe laser beam. We also demonstrate full deflection control with a minimum number of control lines using a modified deflector arrangement. And we present measurements showing sub- microsecond switching speeds from such PLZT-based phase modulators. Mature versions of this type of scanner will find use in a wide variety of applications including 2-D and 3-D laser displays, laser communications, and LIDAR systems.

Laser-projected 3D volumetric displays

A 3D volumetric display system utilizing a rotating helical surface is described. The rotating helix system permits images to b e displayed in a 3D format that can be observed without the use of special glasses. Its rotating helical screen sweeps out a cylindrical envelope, providing a volumetric display medium through which scanned laser pulses are projected. The light scatters from the surface of the helix so that each voxel appears to emanate from specific points in space. Each point has x-y-coordinates determined by the laser scanner and a z-coordinate determined by the intersection of the laser beam and the helix surface. Display images are created by synchronizing the interaction of the laser pulses and the moving screen to address a full 3D volume that gives the viewer true depth cues without the need for any special viewing aids. We describe recent work on the development of mechanical, optical, electronic, and software engineering for a display system based on a 36-inch diameter helix using high speed, multichannel, random access laser scanners. Color images are created using red, green and blue laser sources. The system is capable of displaying 800,000 voxels per second, per color. A portable, 12-inch diameter, translucent helix system is also presented.

Encoding Schemes For A Digital Optical Multiplier Using The Modified Signed-Digit Number Representation

The modified signed-digit (MSD) number representation offers full parallel, carry-free addition. A MSD adder has been described by the authors. This paper describes how the adder can be used in a tree structure to implement an optical multiply algorithm. Three different optical schemes, involving position, polarization, and intensity encoding, are proposed for realizing the trinary logic system. When configured in the generic multiplier architecture, these schemes yield the combinatorial logic necessary to carry out the multiplication algorithm. The optical systems are essentially three dimensional arrangements composed of modular units. Of course, this modularity is important for design considerations, while the parallelism and noninterfering communication channels of optical systems are important from the standpoint of reduced complexity. The authors have also designed electronic hardware to demonstrate and model the combinatorial logic required to carry out the algorithm. The electronic and proposed optical systems will be compared in terms of complexity and speed.

Laser propagation at 1.56 μ m and 3.60 μ m in maritime environments

We report results from field experiments that have compared laser propagation at 1.565 μm and 3.603 μm in a variety of atmospheric conditions in a low-altitude maritime environment in order to quantify the relative effects of turbulence under realistic conditions. Intensity scintillation and normalized focused spot sizes were found to be significantly less affected by turbulence at the longer wavelength, in general agreement with theoretical predictions. Also, the longer wavelength beam was noticeably less degraded by aberrations in the transceiver optical components. These advantages should be considered when evaluating the wavelength trade-offs in laser communication systems.

Coherent laser radar at 3.6 µm

Coherent laser radar systems in the mid-IR wavelength region can have advantages in low-altitude environments because they are less sensitive to scattering, turbulence, and humidity, which can affect shorter- or longer-wavelength systems. We describe a coherent laser radar at 3.6 µm based on a single-frequency optical parametric oscillator and demonstrate the system over short ranges outdoors. The system was used to make micro-Doppler measurements from idling trucks that were processed to give surface vibration spectra.

Laser-Based Display Technology Development at the Naval Ocean Systems Center (NOSC)

For several years, the Naval Ocean Systems Center (NOSC) has been working on the development of laser-based display systems with the goal of upgrading the image quality and ruggedness of shipboard displays. In this paper the authors report work on the major task of developing a full-color laser-addressed liquid crystal light valve (LCLV) projection system.