The motion of the contracting heart has made it impossible to study coronary arteries after venous injection of a contrast medium using digital subtraction angiography (DSA), even with cardiac gating. The motion of the heart, as well as that of surrounding bone and tissue, produces artifacts in the difference image that often overlie the contrast-enhanced vessel images. Because the vessels are small and the contrast medium inherent in a venous injection is dilute, the intensity of a vessel image is weak. The motion artifacts typically are strong enough to obscure the vessel images, rendering the images diagnostically useless. A technique for removing motion artifacts is presented that permits removal of motion between a pair of images acquired during mask-mode DSA by geometrically transforming one image so that it is regis-tered with the other. The transformations can handle three-dimensional motion. Genetic optimization algorithms are employed to determine the optimum transformation. A series of phantom images are used to demonstrate the ability of the technique to remove three-dimensional motion.
An iterative method is proposed for the sharpening of programmable filters in a 4-f optical correlator. Continuously variable spatial light modulators (SLMs) permit the fine adjustment of optical processing filters so as to compensate for the departures from ideal behavior of a real optical system. Although motivated by the development of continuously variable phase-only SLMs, the proposed sharpening method is also applicable to amplitude modulators and, with appropriate adjustments, to binary modulators as well. A computer simulation is presented that illustrates the potential effectiveness of the method: an image is placed on the input to the correlator, and its corresponding phase-only filter is adjusted (allowed to relax) so as to produce a progressively brighter and more centralized peak in the correlation plane. The technique is highly robust against the form of the system's departure from ideal behavior.
The cost effectiveness of using aspheric surfaces in infrared systems is reviewed. In particular, two design studies are described, the first of a Maksutov-type objective and the second of a high numerical aperture pyroelectric vidicon objective. In the first case, the use of first one and then two aspheric surfaces results in an increasing ability to satisfy all of the aberration and dimension requirements of its specification. In addition, a size versus raw material trade-off becomes possible. In the second case, a four-element spherical design is compared with a two-element aspheric design over a large range of numerical apertures. The analysis demonstrates that the improved transmission and reduced materials costs that result from the use of aspheric surfaces outweigh the cost of aspheric manufacture. The paper concludes that in the cases examined, aspherics are highly cost effective, provided that a facility for diamond machining to an optical finish, without subsequent polishing, is available.
The measurement of longitudinal strain of optical fibers using several optical techniques is discussed. A review of the optical principles used to design each measurement system is included. Mathematical expressions for strain due to tensile stress, thermal stress, and hydrostatic pressure are provided. Each technique is based upon directly or indirectly measuring the change in the transit time of an optical signal injected into the test fiber. Equations are provided that relate the strain to the change in fiber transit time. Examples of calibration results and cable tests are given.
Fourier spectra of images with zero-one transmission characteristics are analyzed, assuming their boundaries to be described by random functions. The effect on recognition using different correlation functions and correlation coefficients to characterize the boundaries is presented. In one case a closed-form solution is found.
Digitally sampled in-line holograms may be linearly filtered to reconstruct a representation of the original object distribution, thereby decoding the information contained in the hologram. The decoding process is performed by digital computation rather than optically. Substitution of digital for optical decoding has several advantages, including selective suppression of the twin-image artifact, elimination of the far-field requirement, and automation of the data reduction and analysis process. The proposed filter is a truncated series expansion of the inverse of that operator that maps object opacity function to hologram intensity. The first term of the expansion is shown to be equivalent to conventional (optical) reconstruction, with successive terms increasingly sup-pressing the twin image. The algorithm is computationally efficient, requiring only a single fast Fourier transform pair.
Recording of holographic optical elements often entails the use of complex aspheric elements or computer-generated holograms for obtaining the necessary recording wavefronts. Since the production of these aspheric elements and computer holograms is difficult, we developed recursive design techniques for obtaining the recording wavefronts from relatively simple intermediate holograms. These techniques are based on changing the geometries and/or the wavelengths between recording and readout of these intermediate holograms. The design techniques are presented, along with a specific illustration of a holographic Fourier transform lens. Both the calculated and experimental results demonstrate the possibility of achieving much lower aberrations and better resolution than can be obtained with comparable spherical holographic lenses.
To shorten the access time of optical disk equipment, a small optical head and an eccentricity correction circuit are required. This paper describes both a small optical head with a combined prism and a roof-shaped prism and an eccentricity correction method with synchronized sine wave. Two newly developed prisms make it possible to form the optical head by using only six optical parts. Eccentricity correction is performed by moving the actuator according to the synchronized sinusoidal correction signal. The amplitude and phase of the correction signal are matched to those of the track movement by a microcomputer. This eccentricity correction can reduce a 200 µm eccentricity to 10 µm , improve tracking ability, and shorten the random access time.
Turbulence, atmospheric background, and aerosol forward scattering modulation transfer functions (MTFs) are analyzed with regard to both low elevation remotely piloted vehicles and high elevation reconnaissance applications. Turbulence is seen to limit image quality only at very high spatial frequencies, where degradation is likely to take place anyway as a result of vibration and diffraction. Background and aerosol MTFs limit low spatial frequency contrast as well. However, this can be overcome somewhat by proper selection of the imaging wavelength and of operation timing. This analysis can aid in sensor selection for system design from the standpoints of both wavelength selection and sensor resolution. Because this analysis includes the effects of weather changes on image propagation through the atmosphere, it also can aid in selecting operation timing on the basis of weather forecasts, with a view toward optimizing expected resolution.
Infrared (8 to 12 µm) sky radiance measurements over the ocean near San Diego are compared with those calculated by LOWTRAN 6 using the Navy maritime aerosol model with simultaneously measured (radiosonde) meteorological parameters and atmospheric radon concentrations. For a low wind speed condition, the measured and calculated radiances agreed within 2% at the optical horizon. However, during moderate wind speed conditions, the current wind speed component of the aerosol model had to be lowered by factors near 0.05 for the calculated and measured radiances to agree. The adjusted model is then found to agree closely with published results of large particle size distribution measurements in the North Atlantic.
The design, fabrication, and testing of an acousto-optic-based binary data recorder are described. The data to be recorded are applied to an acousto-optic (AO) Bragg cell illuminated by a pulsed laser diode, and the bit sequence present in the cell is imaged onto a linear detector array. Emphasis was placed on incorporating the optical system and the linear detector array with its control board into a rugged module of modest size capable of recording non-return-to-zero data at rates of 200 Mbits/s or greater. The design specifications of the AO cell and the pulsed laser were based on earlier analysis and proof-of-principle experiments. An in-house-built TI3AsS4 AO cell with a bandwidth of 260 MHz centered at 400 MHz gave 11% diffraction efficiency at the 810 nm wavelength used in the system. When used with a laser pulse of 4 ns full-width at half-maximum, this system had a maximum operating rate of 240 Mbits/s. The same optical system used with an AO cell with 500 MHz bandwidth and a 1.7 ns laser pulse had a maximum rate of 500 Mbits/s. The quality of the optical imaging did not appear to limit the performance, suggesting the possibility of either further increasing the data rate or reducing the size. Possible modifications to explore these options are discussed.
An optical systolic finite impulse response (FIR) filter (or convolution operation) implementation using barrel shifters and a modified signed digit (MSD) adder is discussed. The computational element used in systolic FIR filters in electronics consists of a multiplier and an accumulator. A speedup in the throughput data rate along with a high degree of regularity and concurrency can be achieved by replacing the multiplier with barrel shifters and accumulators. The optical implementation of this architecture offers reconfigurability together with the inherent speed and massive parallelism of optics. It is shown that an FIR filter of order eight can be implemented by using one liquid crystal light valve (LCLV) and one optical MSD adder. All barrel shifters in the architecture are implemented using different areas in the same LCLV structure. The MSD adder is implemented using symbolic substitution logic (SSL), and the input operands in the various cells are arranged on the same input data plane to give all required summation terms.
Three methods of monitoring nonquarterwave stacks are investi-gated: the turning value method, the inflection point method, and the second-harmonic method. The advantages of these methods are that they are monochromatic and that they do not rely on any absolute measurements of transmittance during monitoring. Computer simulations of the deposition process are performed for different nonquarterwave stacks to check the accuracy of the three methods, and we investigate whether these methods can compensate for errors in thickness occurring during deposition.
This nice book has 19 chapters, four short appendixes, a glossary, and an index in 315 pages, plus the preface and table of contents. The chapters are each about 15 pages long; they are intellectually bite-size. The book is divided into three parts: Figures of Merit and Feasibility Study, Detailed Design and Appendixes, and Glossary and Index. There is no clear reason for this division, but it does no harm either. The book itself is well bound and easy to read, having been nicely printed out on good paper and with a good type font.
A few months ago, Ken Leib wrote a nice letter to me commenting on the editorial in which I paid tribute to George Reynolds (Optical Engineering, April 1987). Ken then went on to suggest that we should consider including one personal or historical type article in each issue of the journal. He expressed some concern about acceptance of such articles by the membership at large, but indicated that he personally would like to see us publish biographies of some of the "giants" of SPIE or articles related to the history of the society. That is an interesting idea, and I would like to hear from others concerning this suggestion.