Tin M. Aye

Enhanced optical modulation using azo-dye polymers

The performance of the conventional azo-dye polymer modulation system is compared with that of the recently developed attenuated-total-reflection (ATR) dye-polymer modulation techniques. Experiments based on Fabry-Perot resonance shifting in ATR geometry indicate that the modulation parameters, namely, speed, contrast, and efficiency, are enhanced. Although the dye-polymer response still remains fairly slow, ATR methods provide substantial improvement over the existing system. An all-optic long-range surface-plasmon azo-dye polymer modulation system is also proposed. Computer simulation of the reflectance and the photoinduced resonance shifting suggest that the proposed system can be used effectively for all-optic modulation. Some of the limitations of both systems and a pratical application of the ATR modulation methods are discussed.

Compact HMD optics based on multiplexed aberration-compensated holographic optical elements

Head and helmet mounted displays (HMDs) can benefit greatly from new wide field-of-view, compact visor optics to project very high resolution (e.g., 5k X 4k) imagery. Physical Optics Corporation (POC) is developing novel, compact, lightweight wide field-of-view optics based on three-color multiplexed aberration-compensated holographic optical elements (MAC-HOEs). Taking advantage of the flexibility of holography, the HMD optics can be made compact using waveguide projection through the curved visor substrate, so that the see-through visor can have a wide field-of-view without large, bulky optical components. Using narrowband red-green-blue hologram multiplexing, MAC-HOEs can significantly reduce the chromatic and geometrical aberration introduced by conventional HOEs and refractive optics. In the initial phase of development, POC demonstrated the feasibility of the HMD optics through computer design and analysis, and by fabricating and demonstrating a MAC-HOE component.

Mutual injection locking: a new architecture for high-power solid-state laser arrays

In this paper, bidirectional (mutual) injection locking is demonstrated with solid-state lasers, producing significant improvements over traditional single-direction injection locking. Each laser element shares part of its output with other elements in bidirectional locking, distinct from single-direction (traditional) injection locking where one master laser provides the locking signal for a number of slaves. In a phase-locked array, the individual laser outputs add coherently, and the brightness of the entire array scales with the square of the number of elements, as if the active material diameter were increasing. Benefits of bidirectional locking, when compared to traditional injection locking, include reduced laser threshold, better output beam quality, and improved scaling capability. Experiments using two Nd:YVO/sub 4/ lasers confirmed that mutual injection locking reduced lasing threshold by a factor of at least two and increased the output beam quality significantly. The injection-locking effects began with 0.03% coupling between lasers and full-phase locking for coupling exceeding 0.5%. The 0.5% requirement for full-phase locking is significantly lower than the requirement for traditional injection locking. The large coupling requirement limits traditional injection-locked arrays to fewer than 20 elements, whereas mutually injection-locked arrays have no such limit. Mutual injection locking of an array of lasers can lead to a new architecture for high-power laser systems.

Tunable holographic Fabry–Perot étalon fabricated from poor-quality glass substrates

A novel holographic recording method has been demonstrated for fabricating highly reflectant mirror coatings on a glass substrate of poor surface quality. Electro-optically tunable characteristic fringes of a high-finesse Fabry-Perot étalon have been observed from a cavity consisting of a thin nematic liquid-crystal layer and coated with holographic mirrors. Good agreement has been found between measured values and values predicted by coupledwave theory.

Submicrometer lithography using lensless high-efficiency holographic systems

A hologram recording geometry that was total internal reflection of the reference and reconstruction beams from a photosensitive material surface is used to achieve 0.5-microm resolution at lambda = 457 nm in the readout of a reconstructed image on a photoresist. Such a geometry has demonstrated stable image quality for parallel displacement within the illuminated area and diffraction efficiency tolerance within a +/-2 degrees tilt about the axis of the reconstruction beam. The total-internal-reflection recording system provides double-fringe sets for each plane component inside the volume hologram; therefore, a diffraction efficiency as high as 80% was observed. The result is applicable to highvolume submicrometer lithography and can be expanded to a 20-cm (8-in.) semiconductor submicrometer pattern. The use of a large-aperture, well-collimated laser beam provides us with much higher throughput than that of existing lithography machines.

Second-order radiometric ray tracing

Conventional ray-tracing methods fail for non-Lambertian sources. To address this deficiency, we introduce a radiometric ray-tracing (R2T) method, applicable to quasi-homogeneous sources of arbitrary spatial coherence. Based on Fourier optics, applied to physical radiometry in the radiance transfer function second-order approximation, the R2T method retains the standard ray-tracing codes but modifies them to include phase-space weighting factors attached to conventional geometric rays.

Image tiling for a high-resolution helmet-mounted display

Head-mounted or helmet-mounted displays (HMDs) have long proven invaluable for many military applications. Integrated with head position, orientation, and/or eye-tracking sensors, HMDs can be powerful tools for training. For such training applications as flight simulation, HMDs need to be lightweight and compact with good center-of-gravity characteristics, and must display realistic full-color imagery with eye-limited resolution and large field-of-view (FOV) so that the pilot sees a truly realistic out-the-window scene. Under bright illumination, the resolution of the eye is ~300 μr (1 arc-min), setting the minimum HMD resolution. There are several methods of achieving this resolution, including increasing the number of individual pixels on a CRT or LCD display, thereby increasing the size, weight, and complexity of the HMD; dithering the image to provide an apparent resolution increase at the cost of reduced frame rate; and tiling normal resolution subimages into a single, larger high-resolution image. Physical Optics Corporation (POC) is developing a 5120 × 4096 pixel HMD covering 1500 × 1200 mr with resolution of 300 μr by tiling 20 subimages, each of which has a resolution of 1024 × 1024 pixels, in a 5 × 4 array. We present theory and results of our preliminary development of this HMD, resulting in a 4k × 1k image tiled from 16 subimages, each with resolution 512 × 512, in an 8 × 2 array.

Direct-view autostereoscopic monitor without goggles

Physical Optics Corporation has developed an autostereoscopic 3D display system that does not require viewers to wear goggles. This system is based on a stationary holographic projection diffuser fabricated using volume multiphase holographic optical elements. Design and development of the prototype are also described.

Efficient hybrid electric and thermal energy generation

We demonstrate a novel hybrid solar photovoltaic electrical and thermal energy cogeneration system with high efficiency, at potentially reduced overall weight and size compared with current solar energy systems. The new system is based on highly efficient photovoltaic solar cells and tubular water thermal receivers, incorporating holographic spectral beam light guide concentrators resulting in a more cost-effective solution. Details of fabrication and preliminary experimental testing results are presented.

Reflection shearography for nondestructive evaluation

Conventional nondestructive evaluation (NDE) techniques include visual inspection, eddy current scanning, ultrasonics, and fluorescent dye penetration. These techniques are limited to local evaluation, often miss small buried defects, and are useful only on polished surfaces. Advanced NDE techniques include laser ultrasonics, holographic interferometry, structural integrity monitoring, shearography, and thermography. A variation of shearography, employing reflective shearographic interferometry, has been developed. This new shearographic interferometer is discussed, together with models to optimize its performance and experiments demonstrating its use in NDE.