This PDF file contains the editorial “Editorial: Rochester's Great Ice Storm of 1991” for OE Vol. 30 Issue 05

An optical transmitter for fiber optic interconnects that consists of an off-chip centralized laser in conjunction with on-chip multiple quantum well electroabsorption modulators is proposed and demonstrated, and its performance is discussed.

The excess signal loss in precision-wound optical fiber is measured as a function of the winding tension and the environmental temperature. Since the heat treatment of the wound fiber reduces the signal loss, the residual loss is attributed to the bending loss mechanism caused by the crossovers. A theoretical model is constructed to relate the distortion of the fiber to that of the buffer and is expressed in terms of the winding tension. Various mechanisms for the enhanced distortion at low temperature in current literature are examined along with the experimental data. The calculation is compared with the data with quantitative agreement.

We have characterized the performance of a series of fiber optic intensity sensors for temperature measurement. The method measures the change in absorption with temperature of light reflected from a thin silicon film deposited on the end of an optical fiber. Our single-ended sensing approach requires that the incident light intensity be reflected from both film surfaces and that these reflected signals reenter the fiber. Sensors fabricated with simplified methods have been shown to yield sensitivity comparable to that reported by other authors. Calibration data on sensors with different silicon film thicknesses are presented up to 400°C. Potential applications of the method are discussed.

Holography and optical processing often require coherent input beams with intensity distributions that are different from the usual Gaussian distribution of a laser. Aspherical lenses are used to perform general beam shaping in order to obtain the required intensity distributions. Computer-generated holograms (CGHs) can also be used for beam shaping. In this paper the computational procedure for CGHs, which implements a rotationally symmetric transformation, is supplied. The computational procedure consists of two steps. In the first step a transformation equation is computed from the two known intensity distributions by using an integral equation. This transformation equation will transform the available intensity distribution into the required intensity distribution. It is substituted into a differential equation from which a phase function is cornputed, and is then encoded as a CGH. Two CGHs are required to perform the transformation. The first one diffracts the light to form the desired intensity distribution at a given distance behind the CGH. At that position the second CGH is placed to cancel the diffraction in order to retain the desired intensity distribution. The resulting intensity distribution remains unchanged from then on except for the effect of the diffraction of the distribution itself. General intensity distributions have been implemented with CGHs produced with this technique, and the results are presented in this paper.

A two-element holographic optical system is described for converting an elliptically shaped Gaussian-profile laser beam into a rectangularly shaped beam that is uniform in amplitude and phase in the nearfield. Theoretical analysis, design considerations, and experimental results are presented for a compact converter system of less than 6 cm in length.

The full-frame image compression technique was developed at the University of California, Los Angeles, specifically for radiological applications. Because this method is very innovative and unique, no commercially available hardware is able to process the algorithm with any efficiency. We have developed a dedicated hardware module for this purpose based on the latest technology. Specifications were determined from clinical requirements. Various important technical challenges were overcome by customized system designs, including a key concept of using dual-bus architecture for direct memory access transfer. We report on the status of a functional prototype and some image quality evaluations.

We present a new image coding technique called hierarchical block truncation coding (HBTC). HBTC is a combination of the block truncation coding (BTC) technique and the quadtree segmentation method. Quadtree segmentation is used to decompose an image into homogeneous regions so that the BTC method can exploit the nonstationary characteristics of the image data. The resulting bit rate is lower than that of conventional BTC, depending on the characteristics and complexity of the digital image. We investigated the performance of the encoder on both still and moving images. A small reduction in the bit rate is achievable for still images, but false contours become apparent as the rate declines. The proposed method works well on difference images from a sequence since the moving areas are encoded with greater resolution than the stationary background. A significant bit rate reduction is seen for sequence transmission. The bit rate is reduced from the 1.625 bits per pixel (bpp) required for a conventional BTC implementation down to 1.19 bpp for the least detailed still image. A typical CCITT image sequence was encoded at an average rate of 1.21 bpp. The bit rate was further reduced to an average of 0.39 bpp with a small degradation in the quality of the reconstructed images by transmitting only the most varying portions of the sequence.

Target recognition systems have undergone a variety of changes over the past 20 years. Initial systems exploited signal processing techniques to detect ground-based targets based on one-dimensional signals. Limitations of these systems eventually led to the development of automated target recognizers (ATRs) that processed two-dimensional digital images to detect, classify, and identify targets. Though their performance exceeded that of signal processing systems, ATRs exhibited several deficiencies to which artificial intelligence (Al) offered numerous potential solutions. This paper reviews the evolution of target recognition systems with primary focus on Al applications. Deficiencies of Al approaches to target recognition are presented and complemented by a discussion of a blackboard-based ATR system currently being developed at Georgia Tech.

The resolution of a target-tracking optical novelty filter is discussed in terms of the response time of the nonlinear medium, the speed of the target, and the resolution of the input device. Optical novelty filters using a faster nonlinear medium may have a higher output resolution. This is particularly true in the case of tracking high-speed targets. The potential of implementing high-resolution optical novelty filters using photorefractive GaAs is investigated experimentally.

A theoretical model, developed by Wulich and Kopeika that gives the MTF for flow vibration frequency sinusoidal image motion applicable to reconnaissance, robotics, and computer vision, is evaluated experimentally to determine (1) accuracy of the MTF model and the validity of assumptions upon which it is based, (2) accuracy of "lucky shot" theoretical analysis to determine the number of independent images required to obtain at least one good quality image, and (3) accuracy of prediction for average blur radius. In most cases agreement between theory and experiment is quite good. Discrepancies are not too great and are attributed to problems with underlying theoretical assumptions where uniform linear motion cannot be assumed. The theory and experiment here are confined to low-frequency sinusoidal vibration where blur radius and spatial frequency content are random processes.

A "time dilation" push-broom imaging charge-coupled device (CCD) sensor is being considered for certification of landing and roving sites for the exploration of Mars. It will be used to certify several 10 x 10 km candidate sites and to identify rocks and holes of 1 m or larger at those sites, using an optical sensor with 0.25 m resolution. This will require a high-resolution large-aperture camera and a camera-pointing system designed for high accuracy and stability. To reduce the data rate and increase the exposure time, the imaging time will be stretched out by a factor of eight over the time required to fly directly over the imaged site. Six parallel data storage strings will be used to reduce the data acquisition rate, allowing each string to process a manageable 25 Mb/s.

A moving Ronchi ruling at the focal plane of a telescope has been employed to measure the relative motions of stars with great accuracy. The method has long-term stability and exceptional linearity over a relatively large field-of-view. This measurement technique may prove useful in other applications where such capabilities are required. This paper employs Fourier optics to describe the operation of the device, explore performance at very long and very short periods, and consider ruling profiles and other means of optimizing performance.

A new measurement technique for focal plane linearity was investigated experimentally. The spatial harmonic distortion test consists of projecting spatial sine waves of irradiance onto a focal plane by means of a Young's fringe technique. If the detectors in the array have a linear responsivity, a sinusoidal input waveform is mapped to a sinusoidal output. However, if the detectors in the array have a nonlinear responsivity (i.e., saturation), then the output waveform will exhibit harmonic distortion. When the Fourier transform of the array data is taken, the content at the second and third harmonics of the original sine-wave spatial frequency indicates the amount of nonlinearity in the aggregate array response. Measurement results are included for two focal planes: a vidicon tube camera and a solid-state charge-injection device (CID) camera. The minimum harmonic distortion measured was 3%. The sensitivity of this test is limited ultimately by the amount of spatial nonuniformity. Numerical and analytical models are given that indicate the minimum detectable harmonic distortion is in the range of a few percent. This test also allows measurement of the spatial-frequency dependence of the nonlinearity, a quantity that is not accessible with the usual flat-field techniques for linearity assessment.

Electrostatic lenses are used extensively to control charged-particle beams. In a particular application to ion beam lithography for microelectronics fabrication, it was necessary to perform extensive calculations of the focal properties of cylindrically symmetric ion lenses. We have found that the imaging properties of cylindrical electrostatic ion lenses can be modeled accurately and efficiently by a series of refractive optical lenses. This is a key step toward the use of mature optical design tools for the design of systems that focus charged particles.

The properties and development of low-loss (<1 dB/cm) graded-index (GRIN) polymer microstructure waveguides (PMSWs) on various substrates, including semiconductors, conductors, insulators, and Ceramics, are described. PMSW films can now be produced, uniformly, over substrate areas exceeding 400 cm². The polymer materials exhibit wide transmission bandwidths (0.3 to 2.7 μm) and thermal stability characteristics over a large dynamic temperature range ( —100°C to +180°C). Local sensitization techniques have been applied to PMSW films to produce planar, single and multiplexed, holographic gratings. Wavelength division demultiplexing devices and single-wavelength 1-to-N fanout optical interconnects have also been realized. The polymer technology reported is well suited for optical interconnection, signal processing, communication, and sensing applications.

We report our investigations of single- and multiple-beam optical limiter configurations using GaAs and Si as the nonlinear optical materials. Three distinct multiple-beam geometries are discussed. One of these, in which two beams interfere within the semiconductor to produce a grating, takes advantage oftransient energy transfer and photorefractive beam coupling to deplete the signal beam. The other two configurations exploit the whole-beam absorptive and refractive index changes induced in the semiconductor by a strong control beam that arrives at the sample before the signal. For one of the latter two configurations, nonlinear absorption and induced defocusing are used to attenuate the signal; in the other, nonlinear absorption and induced deflection are used. We discuss the relative merits of each configuration and compare them to singlebeam results obtained under identical experimental conditions.

New magnetic materials and x-ray mirrors have lead to the preparation of multilayered structures (MLS) with ultrathin periodic layers. However, physical limitations appear for periods below some tens of A. In particular, fabrication tolerances relative to these ultrathin layer thicknesses are critical for the realization of effective MLS. In sputtering, the deposition rate is easily reproducible and can be maintained at a constant and low value for several hours; for this reason we are able to perform a large number (more than 100) of periodic ultrathin layers by this system (3 to 1.5 nm period). High Resolution Transmission Electron Microscopy (HRTEM) and x-ray reflectivity measurements are used to compare interfaces and stacking regularities for different samples with 140 layers. The W/Si MLS present a better quality of interfaces and structures compared to the W/C MLS.

A precise expression for the diffraction pattern from a square aperture is derived. The field at the aperture is assumed to be a plane wavefront of constant intensity. The parameters involved are the wavelength λ of the incident light, the distance z_c between the aperture and the plane of interest, the dimension D of the square aperture, and the absorption coefficient a of the medium. The presented model is valid for all values of these parameters. It is also applicable to situations in which the Fresnel approximation does not provide an accurate solution anymore. It turns out that the intensity distribution is determined solely by the values of two dimensionless numbers: D²/(λz_c) and λ/z_c. Computational results are given for 200 nm ≤ λ ≤ 600 nm; 10^-3 μm ≤ z_c ≤ 100 μm; and 1 μm ≤ D ≤ 100 μm.

This article reviews our laboratory's experience in the field of vascular welding using the milliwatt CO₂ laser to repair 4-mm to 9-mm canine vessels. Previous work in arterial anastomosis and intraluminal welding is presented. A preliminary study in the area of venous laser-assisted anastomosis is presented in detail. A limited discussion of the field will emphasize what we know and what still must be learned.

Laser-induced morphological and electrical changes to silicon CCD imaging devices were studied. The devices were polysilicon gate time delay integrating CCD arrays of 2048x96 elements. The laser source for these experiments was a Q-switched Nd:YAG laser at 1.06 μm with 10-ns pulses at a 10-Hz repetition rate focused to an approximate 400-μm spot radius. Single pulse and multiple pulse damage behavior were studied. Both CCD arrays and diagnostic structures from the wafer periphery were tested. The additional diagnostic structures included polysilicon resistors and metallic oxide semiconductor field-effect transistor (MOSFET) gates. of the measurements made, leakage current between polysilicon clock lines, drain-to-substrate and drain-to-source leakage currents, and transconductance in MOSFETs were found to be the most sensitive parameters to laser-induced change. The onset of electrical parameter changes was observed at laser fluences as low as 0.2 J/cm². Severe electrical parameter changes began at 0.5 J/cm² and continued up to the onset of severe morphological damage at 1.0 J/cm². Above this fluence, both polysilicon and aluminum interconnect lines melted and broke.

This PDF file contains the editorial “Book Rvw: Lens Design," by Milton Laikin for OE Vol. 30 Issue 05