H. John Caulfield

Very thick holographic nonspatial filtering of laser beams

Philip Hemmer, MEMBER SPIE Rome Laboratory RL/EROP, 63 Scott Road Hanscom Air Force Base, Massachusetts 01731 Abstract. A novel device, the nonspatial filter, is described for laser beam cleanup. It is based on the Bragg selectivity of thick holograms. Unlike pinhole and fiber spatial filters, which employ lenses and apertures in the transform plane, nonspatial filters operate directly on the laser beam. This eliminates the need for laser beam focusing, which is the source of many of the material and alignment instabilities and laser power limitations of spatial filters. Standard holographic materials are not suitable for this application because differential shrinkage during processing limits the maximum Bragg angle selectivity attainable, and because they are generally too thin. New technologies that eliminate the problem of differential shrinkage are described. These technologies are based either on the use of a rigid porous substrate material, such as porous glass, filled with a light-sensitive material, such as holographic photopolymers or dichromated gelatin, or on the use of a thick photopolymer with diffusion amplification (PDA). We report results of holographic nonspatial filtering of a laser beam in one dimension, with an angular selectivity of better than 1 mrad.

Switched holograms for reconfigurable optical interconnection: demonstration of a prototype device

We report the construction of a device intended for programmable optical interconnection of multiple processors in a highly parallel computer. This device, the Holoswitch, is based on an array of optical switches (liquid crystal polarization switches and polarizing beam splitters), which direct a set of optical beams toward any of a selection of holograms. Each hologram, when selected, deflects the input beams toward an output array with any desired prerecorded permutation. The prototype device has nine different interconnection patterns recorded on a single 10-x12.7-cm DCG hologram. We have recorded permutation patterns with up to 64 optical channels in an area of 4 cm(2).

Associative mappings by optical holography

Abstract Algebra-based content addressable memories have been constructed recently using optical methods. We show here that holography can accomplish the same tasks on much larger vectors.

Achieving stabilization in interferometric logic operations

Interferometric systems with amplitude beam splitters can implement reversible operations that, on detection, become Boolean operators. Being passive, they consume no energy, do not limit the operating bandwidth, and have negligible latency. Unfortunately, conventional interferometric systems are notoriously sensitive to uncontrolled disturbances. Here the use of polarization in a common-path interferometric logic gate with and without polarization beam splitters is explored as an attractive alternative to overcome those difficulties. Two of three device configurations considered offer significant stability and lower drive modulator voltage as advantages over the previous systems. The first experimental tests of such a system are reported. Common-path interferometry lends itself to even more stability and robustness by compatibility with no-air-gap, solid optics.

Optical High-Performance Computing: introduction to the JOSA A and Applied Optics feature

The feature issues in both Applied Optics and the Journal of the Optical Society of America A focus on topics of immediate relevance to the community working in the area of optical high-performance computing.

Position-sensing detector for logical operations using incoherent light

The application of a position-sensing detector to optical logic operations has been introduced and experimentally demonstrated for the first time. We describe some possible architectures for all 16 two-input Boolean gates as well as for multi-input gates.

The Alvarez-Lohmann lens as a do-nothing machine

Abstract A do-nothing machine uses complex methods to convert an input pattern or function into an identical output pattern or function. They are of great interest because a selective modification somewhere within that machine can often accomplish useful results. Here, we start with the simplest possible optical system—a piece of glass split between the top and bottom by some simple or complex cut and rejoined perfectly. To light passing through, the cut does nothing. But, if we displace the top and bottom parts by some small amount, the combined system can serve as a variable thickness plate, a variable deflection angle prism, a variable focal length lens, etc. as first shown independently by Alvarez and Lohmann. This appears to be the first explanation of Alvarez–Lohmann lenses in such a simple way and it leads to the possibility of new structures not contemplated by either of the inventors.

Templates for invention in the mathematical and physical sciences with applications to optics

Some of the greatest mathematicians and scientists in history have made their most important contributions by applying unsystematically one of three general patterns or templates for inventions. Here, for the first time to my knowledge, these templates are stated explicitly and illustrated with examples from optics. I call them The Do- Nothing Machine, The Continuous Extension, The Up-Down Paradigm, and The Reversal of Fortune.

Interference fringe analysis based on centroid detection

Phase measurement of interference fringes is an integral part of several fields in optics. Using simple straight sinusoidal fringe patterns, we describe the relationship between fringe position or phase to the centroid position when these fringes are incident on a position sensitive detector. With detailed descriptions and some experimental results, we show that a phenomenal sensitivity is possible in principle with what we believe is a new approach of phase measurement, and excellent sensitivity is readily achieved.

What can we do with a linear optical logic gate

In an earlier paper [H.J. Caulfield, J. Westphal, The logic of optics and the optics of logic, Information Sciences 162 (2004) 21-33], we considered a simple interferometer (initially conceived as Mach-Zehnder) with two uniform intensity mutually coherent inputs. By encoding those inputs with phases 0 and @p representing Boolean 0 and 1 and identifying the detected values of the outputs as logical Boolean values, we found that the outputs could be identified as the Boolean operations XOR and COINC (sometimes called XNOR). Here, we show that this seemingly simple interferometer can perform many additional functions if we use phases to interpret its outputs. But the XOR/COINC are the only non-trivial logic gate we can get no matter how we cascade Mach-Zehnder interferometers. We also generalize those operations upwards (to three or four arguments). We show that the three argument interferometer or four-argument interferometer cannot produce a Fredkin gate or its variation.