This PDF file contains the editorial “Editorial: Authors, Members, and Readers” for OE Vol. 33 Issue 11

This PDF file contains the editorial “Guest Editorial: Micro-Optics” for OE Vol. 33 Issue 11

Micro-optical devices such as diffractive and refractive microlenses fabricated using integrated circuit technology have been highlighted during the past five years. This scientific breakthrough has created a revolution in optical technology. Miniaturizing devices using microoptics promise to revolutionize many electrooptical systems-from video cameras, video phones, and compact disk data storage to robotic vision, optical scanners, and high-definition projection displays. The supporting technologies for these micro-optical systems, such as binary optics and plastic micro-replication, are built on existing or adapted integrated circuit technologies that have been developed over the past five years. In parallel with this optical technology revolution, researchers have also developed another frontier technology called micro-electro-mechanical (MEM). MEM technology has found applications in automotive, machine tools, airbag actuators, and many generic microsensors. Merging microoptics, microelectronics, and micromechanics creates a new and broader class of micro-opto-electro-mechanical (MOEM) devices, which may attract additional industrial demonstrations of commercial devices such as torsional mirrors, laser scanners, optical shutters, and dynamic micromirror displays. Both constituent technologies of MOEM devices have the potential of batch processing and embossed replication, which, again, makes them highly attractive for low-cost commercial applications. Other more complex microsystems that use MOEM devices such as microspectrometers, microinterferometers, and miniature on-machine-inspection subsystems are being investigated. This new technology enables high-performance devices for microsensor systems that are lighter, easier to produce, more efficient, and less expensive than conventional components.

The finite element method (FEM) is introduced to numerically model near-field diffraction devices using Maxwell's equations. This method is commonly used in the antenna and microwave communities to analyze scattering and waveguiding problems, but is not yet popular in the optics community. Its advantages are the rigorous modeling using Maxwell's equations, the ease of implementation, the sparsity of the resulting system matrix, and the possibility to include complex material structures. The FEM can be used for perlormance evaluation of given devices and as a helpful tool in the design process for new devices. The FEM is reviewed, its numerical implementation is discussed, and some example structures are considered.

Binary and multilevel diffractive lenses with submicrometer feature sizes are realized on silicon and galliumphosphide wafers using CAD methods, direct write e-beam lithography, reactive ion etching, antireflection coating, and wafer dicing. Measurements prove aberration-free imaging and maximum diftraction efficiencies of 70% for lenses with high numerical aperture (NA) of 0.5. Comparisons to other miniature and micro-optical elements are carried out with respect to laser-to-single-mode-fiber coupling and show the competitive performance of the diffractive lenses. Arrays for 18-channel parallel receiver modules are fabricated in on-axis and off-axis versions. Optical crosstalk is estimated.

The use of thin-film deposition in the fabrication of antireflection-coated diffractive optical elements is discussed. The antireflection coatings for these diffractive elements are optimized on the basis of an angular spectrum approach and the method of characteristic matrices. A minimum reflectivity as low as 1 x 10^-4 is realized using in situ controlled multilayers of TiO₂ and SiO₂. The blazed profile of the diftractive optical elements is approximated by a stepped profile with up to 32 phase levels. The highest measured diffraction efficiency for 32-level Fresnel zone lenses was 97%.

Coherent arrays of refractive micro-optics are fabricated in the surface of silicon using a combination of lithographic and reactive-ion etching (RIE) techniques. The aspheric profile can be approximated in a stepwise manner by iterative steps of photolithography and RIE (binary optics technology), by direct etching of a preshaped polymer microlens etch mask into the substrate, or by analog etching of a lens profile directly into the substrate through a pinhole mask.

Refractive microlenses are fabricated by the preshaped photoresist refractive optics by melting (P²ROM) process. A polar coordinate HeCd laser beam lithography system (laser writer) is used to directly expose a continuous spheroidal profile into photoresist to fabricate 200-μm-diam microlenses with speeds between f/1.5 and f/5. Interferometric surlace measurements, used to determine the optical quality of the preshaped microlenses, indicate reduced spherical aberration in slow lenses fabricated by the P²ROM method.

A laser writing system for the fabrication of continuous-relief micro-optical elements in photoresist is described. The technology enables a wide range of planar micro-optical elements to be fabricated and replicated into polymer film using Ni shims electroformed from the photo-resist originals. The advantages and limitations of laser writing technology for micro-optics fabrication are discussed. Examples of fabricated micro-optical elements include Fresnel microlenses and microlens arrays, kinoforms, and other continuous-relief phase elements.

The possibility of micro-optical component (MOC) fabrication by laser action onto optical glasses and glass-like material (GLM) is based on the local heating-cooling cycle. The results of such action are certain to be defined by physical processes that accompany local heating and fast cooling of glass and GLM. It is possible to classify these laser action processes on the optical materials in three main groups in terms of temperature, heating and cooling rates, and the size of residual stresses. The presented facts suggest that during laser heating, the processes of changing the structure and properties of glasses and GLM differ by speed and temperature from processes that occur at heating in a furnace.

Change of optical properties for glasses and glass ceramics of the SiO₂, A1₂O₃, CaO, MgO, and TiO₂ type resulting from structural phase transformations under the local influence of laser radiation is discussed. A CO₂ laser with wavelength 10.6 .μm and output power up to 60 W is used in the experiments. It is shown that the change of the ratio between crystalline and amorphous phases induced in this manner in the chosen materials can be used to form micro-optical elements in optical information transfer and processing systems. The change of optical properties in titanium-keeping glass films is also considered when their thermal instability in crystallization is stimulated by local heating with laser radiation.

Micromirrors having diameters from a few micrometers to several millimeters have been produced on (100) silicon by wet-chemical etching in KOH:H2O. The f/#'s range from about 2.5 to at least 10. The microroughness of an etched mirror with diameter 550 μm and 9.6-μm sagitta is less than 5 nm and its surface figure is within 0.5 μm of a perfect sphere. Data over a wide range of diameters are presented and a semiempirical model is developed to explain the behavior. The concordance of the normalized etched profiles for all diameter mirrors demonstrates that the etching is dominated by surface reaction rather than diffusion limitation. Design and fabrication schemes are presented for making a wide range of mirror diameters and focal lengths, for both single micromirrors and arrays. The etched depressions can be used as templates for microlenses and as substrates for geodesic waveguide lenses and arrays. Chem-mechanical polishing on the etched structures reduces the edge curvature and produces oblate spheroidal surfaces, both of which should improve geodesic lens behavior. The etched structures can also be used as variable crystal orientation substrates for epitaxial nucleation and various surface analysis studies.

A superimposed grating comprising a diffraction grating and a high-frequency grating, whose aim is to achieve alignment-free and multifunctional integrated optical elements, is demonstrated for the first time. Then a lightweight and compact magneto-optical disk head that uses this superimposed grating is proposed. The superimposed grating, which simultaneously operates a polarizing beamsplitter and an off-axis cylindrical lens, has three functions required for optical heads: focusing error detection, tracking error detection, and signal detection. Measured focusing and polarizing characteristics suggest that the superimposed grating has the desirable error detection and signal detection for magneto-optical disk heads. A detailed investigation of this grating with an emphasis on clarifying both its basic principles and its use with magneto-optical disk heads is presented.

The use of the diffraction phenomenon in pattern recognition is a well-established area in optical information processing. Typically the generation of a correlation peak by suitable filters is used to recognize a pattern. We introduce a symmetry measure for pattern recognition. It can be used for a wide class of filters, which we call phase-matched filters. Encoding techniques of diffractive optics allow its implementation as amplitude- or phase-encoded filters.

An exact, analytic model for binary chirped gratings is presented together with a rigorous solution applicable in the electromagnetic regime. The solution employs a multiple scattering matrix formulation and boundary value problem techniques to determine the scattering coefficients of the diffracted fields in the fast polarization case, which in turn leads to an iterative algorithm for wavefront shaping and grating parameter design. Numerical examples on the design of a binary grating lens operating in the near field are presented with computer simulations. These show that under oblique plane wave illumination more than 90% of the diffracted power can be focused into a narrow beam of one wavelength of beamwidth over the image plane, which is located only 12 wavelengths away from the grating plane.

A method to compute diffractive elements focusing in a set of scaled lines located in different focal planes along the optical axis is considered. A phase nonlinearity is applied to the phase function of a focusator in a line. It is proved that the selection of the nonlinearity is reduced to the problem of the phase diffraction grating with preset energy distribution in the orders. Multifocal elements to focus in a set of scaled lines in a single plane are considered as well.

Optical beam scanners are critical components for airborne and space-based laser radar, on-machine-inspection systems, factory automation systems, and optical communication systems. We describe here a laser beam steering system based on dithering two complementary (positive and negative) microlens arrays. When the two microlens arrays are translated relative to one another in the plane parallel to their surfaces, the transmitted light beam is scanned in two directions. We have demonstrated scanning speeds up to 300 Hz with a pair of 6-mm-aperture microlens arrays designed for input from a HeNe laser. The output beam covers a discrete 16 x 16 spot scan pattern with about 3.6 mrad separation and only 400 μrad of beam divergence, in close agreement with design predictions. This demo system is relatively compact; less than 2 in. on a side. We also describe several near-term applications, some critical design trade-offs, and important fabrication and design issues.

Efficient large-aperture lens elements are required for 3-D integral imaging and display systems. A systematic evaluation of the spatial resolution capabilities of microlens optical combinations and the synthesis of a large-aperture objective lens by a segmented lens form is reported. It is shown that by employing an optical combination comprising macrolens arrays in conjunction with microlens focusing screens a suitable transmission element, which retains the required angular and lateral resolution, can be constructed. The advantage of using segmented lenses is their capacity to produce spatially inverted, scaled images suitable for direct orthoscopic capture. The analysis of spatial resolution presented by various authors is examined and evaluated by comparison with collated evidence.

A micromachined chopper has demonstrated modulation of coherent and incoherent light. The chopper uses an electrostatically driven lateral micromotor to actuate a shutter plate across a through-substrate window. Test devices have been fabricated and exhibit operating frequencies ranging from 1 to 31 kHz and have stable deflection amplitudes of 400 μm. Further optimizations of the design are discussed.

A phase-only spatial light modulator is a highly efficient component for the filter plane of a real-time correlator. Implementation using flexure-beam micromechanical devices offers many advantages, such as high reflectivity and a high frame rate. However, extra effort is required to ensure high optical efficiency and low parasitic noise. This paper reports on the Texas Instruments implementation of a limited-addressability flexure-beam device that has a fill factor up to 74.3% and provides a dc shield for the analog signal on the mirror. It requires 30 V to modulate the 2π phase modulation of a 633-nm wavelength using an optical-bench setup. The rise and fall times are approximately 3.5 and 2.5 μs, respectively, at π modulation of 546 nm using an interlerometric microscope.

Optical systems of compound eyes are of great interest in the study of micro-optics. We propose an artificial visual sensor in a model of the apposition eye of an insect. As a key component unit of the visual sensor, a sensor array consisting of 16 x 16 individual optical sensors each with a small view field is fabricated and examined. To achieve both the practical assembly and the compact size of the sensor array, a photodiode array, a glass substrate with a pinhole array, and a group of rod-type gradient-index microlenses are stacked. The optical thickness of the sensor array is 2.9 mm. Because of the low intensity of light received by the photodiode the photocurrent is amplified 10⁷ times in current-to-voltage conversion efficiency. The fabricated sensor array produces a mosaic image with 16 x 16 pixels and eight shades of gray scale. By arranging several of these sensor arrays along a circumference, a wide-field-angle visual sensor similar to a compound eye could be realized.

Compact and low-cost laser-diode collimating light sources that employ a thin and mass-producible diffractive micro-Fresnel lens have been developed for optical information-processing equipment such as laser-beam printers. For the compensation of the defocusing of an output beam caused by temperature dependence of the laser-diode wavelength, engineering plastics with different thermal expansion coefficients are adopted for the components. The fabricated light source emits stably up to 60°C. The present laser light sources exhibit allowable optical characteristics for optical information-processing equipment as well as cost-efficient mass production.

Low-cost, efficient, and compact high-power laser diodes (LDs) will make desktop laser manufacturing (rapid prototyping, sintering, drilling, marking, etc.) a reality soon. Laser processing of materials requires not only high average power, from tens of watts to kilowatts, but also high incident beam intensity or power density, from 10³ to 10⁸ W/cm². Current commercial high-power LDs do emit 10⁸ W/cm²; however, they are microscopic in size, and an individual diode emits ~ 1 W (cw) in a highly divergent (~30 x 10 deg) multimode structure. Gathering high power from a large number of such microscopic incoherent diodes into a small spot of high intensity requires micro-optic component and complex system design. Several difterent design approaches for high-intensity laser-diode systems are presented. Some of these are commercial, others will be soon, and still others will need technological developments. Possible applications and some preliminary results of direct diode-laser sintering and transformation hardening of stainless-steel ribbons are also presented.

The conical scanning horizon sensors on the IRS-l B spacecraft have provided results on the outgoing atmospheric 14- to l6-μm carbon dioxide radiance. These radiance values are presented and discussed for the periods January to August 1992. The sensors detect the horizon radiance in the 14- to l6-μm band of carbon dioxide, which is uniformly mixed in the atmosphere. The sensors' narrow field of view cuts the horizon twice in each conical scan, generating a space-to-earth and an earth-to-space crossing. The telemetered counts from the sensor are converted into radiances at various latitude-longitude points. This is the first time that radiance contour plots have been obtained as a function of latitude and longitude. The plots show a hitherto unreported variation of 30% with respect to longitude, which is correlated in some cases with increased stratospheric (10-mbar) temperature.

Many remote sensing instruments employ diffuse targets for calibration. These targets usually consist of diftusers with high Lambertian characteristics illuminated by a calibrated irradiance source. There is increasing interest in conducting in-orbit radiance calibration checks of remote sensing instruments using sunlight reflected off a diffuser. We report on the effects of space flight on the reflectance properties of polytetrafluoroethylene (PTFE) and aluminum diffuser samples flown on three Space Shuttle flights. These experiments showed good stability of both diffuser types in the visible and near infrared but experienced measurable degradation in the ultraviolet. Degradation varied from flight to flight and seemed to be related to different levels of contamination experienced on the three flights.

We have fabricated 1.8-in., 86,400-pixel poly-Si thin-film-transistor (TFT) LCDs with a novel TFT structure and a storage-capacitance (C_st) arrangement. The TFTs have a self-aligned offset structure that is made by a simple process without using an additional mask. With this structure, we have reduced the OFF current, and hence attained a high ON/OFF current ratio of 10⁷. A novel C_st line arrangement called "modified on C_st gate" was adopted. Gate lines and C_st lines are arranged alternately, and the (n - 1)'th C_st line is connected to the n'th gate line at the line's end. The C_st line works as backup for the gate line. Consequently, we have obtained TFT arrays with no line defects (240 gate lines). By using these techniques, we have succeeded in fabricating a high-performance 1.8-in. poly-Si TFT-LCD panel for a projection TV.

We propose a head-tracking autostereoscopic display system based on magnetic-sensor tracking of the viewer's side-to-side location, and optical slewing of a stereoscopic image-pair array projected onto a lenticular screen so as to keep the images received by the viewer's eyes distinct. Viewer distance changes are accommodated by slight magnification changes of the projected image array. A high-definition-TV LCD projector is used with a 178-cm (70-in.) lenticular sheet (diagonal measurement) to provide impressive computer-generated 3-D images over a particularly wide viewing zone. The system finds application in a virtual-space teleconferencing system that requires a large-scale stereoscopic display without the use of special viewing glasses.

A new method is used to diagnose plasma density space-profiles that involves phase conjugate reflection of four-wave mixing. Theoretical calculations for plasma parameters in the HT-6M tokamak show that two pump-wave beams (HCN laser), with a power of 1 W together with a signal beam (D₂O or CH₃F laser) of 0.1 W, can create a reflection of 0.1 to 0.43 mW with a phase conjugate to the signal where the cross section of all external beams is 1 cm². This means that the reflective ratio of four-wave mixing is two orders larger than the ratio of laser superheating scatter. The lower power laser, therefore, can be used to diagnose plasmas.

We describe the use of data validation routines within the context of a tiled phase unwrapping algorithm used in fringe analysis. A review of current and past techniques for phase unwrapping is included and the relative advantages of the tiled strategy are discussed. In all, four validation methods are presented, although we point out that any user would probably have to select their own set of tests based on the particular optical arrangement employed and the physics of the experiment. An example unwrap is included along with some discussion of the merits of using the tests in the light of the processing requirements.

The interference fringes obtained by optical methods such as holographic interterometry and Twyman-Green interferometry are analyzed using image processing. To perform accurate and automated analysis, phase analysis methods have been recently developed. The Fourer transform moire and grid methods (FTMGM) and the phase-stepping method (PSM) are popular techniques to analyze phase distribution. However the FTMGM has noticeable error at the edges of the image if the data at both edges are not continuous. The PSM has large error if the brightness has noise. A new phase analysis method is proposed to erase these errors. This method can be performed using 3-D image processing. A 3-D (x,y,α) image is formed of many sequential phase-shifted 2-D (x,y) images, where a is the shifted phase value. By performing the a-directional Fourier transform on this 3-D image, the accurate phase distribution of the fringe pattern is obtained. An example applied to Twyman-Green interferometry is shown.

Rayleigh's quarter wavelength rule and Maréchal's condition are used to establish allowable spherical aberration in in-line Fraunhofer holography with collimated beams. Allowable minimum object diameter by both these approaches is described and compared.

A novel optically based magnetic field sensing technique is developed that uses a thin magnetic film as the sensing element and the longitudinal and transverse magneto-optic Kerr effects in an optical read technique. The linear system response is tested for small magnetic fields using a simple free-space ellipsometry measurement system. Measurements taken at 8 mHz showed a magnetic field sensitivity of 4 x 10^-3 Oe, with a system dynamic range of over 60 dB. The noise spectrum was dominated by 1/f noise. Calculations for a shot-noise-limited measurement system indicate that a magnetic field sensitivity of 10^-6 Oe/Hz^1/2 may be possible through enhancement of the sensing element parameters and 100-mW light sources.

The purpose is to evaluate the effectiveness of a retroreflector when employed in a moiré deflectometric telescope. A moiré deflectometric telescope using a retroreflector is designed based on the standard moiré deflectometer combining a retroreflector as invented by the authors. A density variation in a piece of glass (phase object) is considered. Moiré deflectograms are obtained using the standard setup for a moiré deflectometer as well as with the setup employing a retroreflector. The setup of a moiré deflectometric telescope and the newly designed moiré deflectometric telescope using a retroreflector are tested.

Based on the binary image algebra algorithm for a hit-or-miss transform of mathematical morphology, a new optoelectronic system with two parallel channels is set up for real-time multiple-object recognition. Two Dammann gratings are used for convolutions in morphological operations. The relation of rotation-recognizing sensitivity to the threshold values is discussed.

Morphological image processing is an important tool for a broad range of problems in image processing. A 512-entry table lookup method is used for real-time implementation. But it is not efficient to transfer this method directly into software. The author proposes a fast software implementation technique, in which a 256-entry lookup table containing neighborhood information is built and a dynamic table lookup process is applied to reduce the number of logical matching operations and the number of accesses of the neighboring pixels. In this proposed method only the foreground pixels, which are pixels on the object, are processed. Among the foreground pixels, only at the starting pixel of each "run" of l's is it necessary to read the eight neighboring pixels. For the other pixels, it is necessary to read only three neighbors. This method shows a significant improvement in timesaving. In addition, for systems supporting fast access to consecutive address memory, the author proposes another implementation, which treats the image as a contiguous block of memory. Thus advantage is taken of RAM technology.

The Hopfield neural network has been widely applied in many areas. Is highly interconnected structure of neurons is not only very effective in computational complexity but also very fault tolerant. Such neural networks have been used as analog computational networks for solving optimization problems. The low-level image processing of edge detection can also be regarded as an optimization problem. This paper presents an edge detection algorithm using a Hopfield neural network. This algorithm utilizes a concept that is different from conventional differentiation operators, such as the Sobel and Laplacian. In this algorithm, an image is mapped to a Hopfield neural network, which is completely depicted by an energy function. In other words, an image is described by a set of interconnected neurons. Every pixel in the image is represented by a neuron, which is connected to all other neurons but not to itself. The weight of connection between two neurons is described as a function of the contrast of gray-level values and the distance between the two pixels. The initial state of each neuron represents the normalized gray-level value of the corresponding pixel in the original image. As a result of Hopfield-network analysis, neuron states are modified till convergence. Even though the neuron states are analog, they are close to 1.0 in all regions except edges, where the corresponding neurons have near-0.0 state values. A robust threshold on the output level of the converged network can be easily set up at 0.5 to extract edges.

Expressions for the probability density function (pdf) of optical signal intensity in an optical communication channel impaired by motion-induced beam jitter and turbulence are derived. It is assumed that the optical beam possesses a Gaussian profile, generated by a pulsed laser, and that the beam scintillation is governed by either log-normal distribution for weak turbulence or K distribution for moderate to strong turbulence in the saturation region. For extreme propagation distances or very strong turbulence, a negative exponential pdf is used to model turbulence. For the aforementioned beam scintillation statistics, approximate pdf's for the signal intensity are also obtained and the conditions for which these approximations seem to be valid are also discussed.

What is, to our knowledge, a new kind of laser free space communication system is reported. In this system, a laser diode is locked and tracked at the transmission peak of a Faraday anamolous dispersion optical filter (FADOF) so as to obtain a stabilized lasing. A Zeeman absorption FADOF (FADOF/Zeeman) was employed as a stabilized receiver. The bandwidth of the FADOF/Zeeman is about 1 GHz, which is three times less than that of the FADOF. The tuning capability is about 1 GHz/0.01 T. We successfully conducted the audio and visual telephone optical communication experiment by means of this system in a strong solar background and compared the systematic property of the FADOF/Zeeman receiver and the interference filter (IF) receiver. The results show that the sensibility of the FADOF/Zeeman receiver is about 25 times higher than that of the IF.

Extinction of laser rangefinder (LRF) pulses by the atmosphere depends on the laser wavelength, weather conditions, and the aerosol concentration along the optical path. The total atmospheric extinction α is the sum of the molecular and aerosol contributions α_m and α_a. We present simple expressions for α_m and α_a for wavelengths near 1.44, 1.54, 2.1, and 10.6 μm, which are eyesafe for most LRF applications. Also included are results for 1.06 μm, which although not an eyesafe wavelength is used extensively for LRF applications. The expressions allow the extinction coefficient to be estimated as a function of standard meteorological parameters, assuming horizontal beam propagation at sea level and a homogeneous atmosphere. Measurements of the signal-to-noise ratio of LRF returns from a calibrated target are presented for various weather conditions and wavelengths.

A digital control has been developed for a galvanometer scanner used in a confocal scanning laser microscope. The galvanometer scanner utilizes a microprocessor-controlled scan control unit, able to produce repetitive analog waveforms and digital control signals, and to record analog and digital signals. The scan control unit outputs a sawtooth waveform to the galvanometer, records the position signal from the position sensor in the galvanometer, and uses this information to calculate the timing needed to trigger the reading of 1024 x 1024 equally spaced pixels in the specimen. The galvanometer may be statically positioned at an arbitrarily chosen pixel, thereby allowing recording of data from a point within the microscope specimen for an arbitrary length of time. This makes it possible to record spectral information or to measure fluorescent lifetimes at a single point.

A portable shortwave infrared (SWIR) spectrometer has been developed that covers the range from 1.05 to 2.45 μm. The spectral sampling interval is 1.37 nm, and the spectral resolution can be varied from about 5 nm to more than 100 nm. A single spectrum can be acquired in as little as 1 s. The signal-to-noise ratio (SNR) for a single 1-s scan is about 100 at a wavelength of 2.2 μm for a lambertian surface of 100% reflectance illuminated by the sun at normal incidence with 14-nm spectral resolution. The SNR at 1.25 μm is about 900 for the same conditions. The estimated 1o uncertainty in the absolute radiometric calibration of the instrument is 2% to 3%. Field-of-view defining optics are coupled by a flexible fiber optic bundle to the spectrometer, which consists of a nonscanning concave holographic diffraction grating with a flat focal field imaged onto a 1024-element liquid nitrogen cooled PtSi linear array detector. The primary use for the instrument is the collection of ground reflectance and radiance data for the radiometric calibration of operational and proposed high spectral resolution remote sensing systems.

A recovering technique of an elevation map by stereo modeling of the real aerial image sequence is presented. An area-based stereo matching method is proposed and parameter values are experimentally chosen. In a depth extraction step, the depth is determined by solving a vector equation suitable for stereo modeling of aerial images that do not satisfy the epipolar constraint. Also, the performance of the conventional feature-based method is compared via computer simulations. Finally, techniques analyzing the accuracy of the recovered elevation map (REM) are discussed. The experimental results based on error performance show the efficiency of the proposed method.

There has been an increase in attempts to quantitatively measure clutter in the background of visual and infrared scenes; this parameter is crucial for determining the probability of detection of military targets in actual battlefield conditions. We analyze several clutter metrics by comparing the location of fixation points with the spatial distribution of the areas of high clutter. We determine that a strong correlation does exist.

The resolution achieved by an optical imaging system in the presence of the random effects of the atmosphere is severely degraded from the theoretical diffraction limit. Techniques exist for recovering near diffraction-limited performance of an imaging system in the presence of atmospheric turbulence. These image enhancement techniques include speckle imaging, deconvolution, and adaptive optics. A turbulence chamber has been designed and built for laboratory testing of current and future adaptive optics and image enhancement techniques. The turbulence is produced within a chamber consisting of two small fans and a heating element. The effects of the generated turbulence on optical propagation are directly measured by sensing the perturbed wavefront phase. The wavefront phases are measured using a shearing interferometer. The statistical properties of the turbulence are then characterized by means of estimating the phase structure function from the wavefront phase measurements. We found that the estimate of the phase structure function depends only on the magnitude of the separation between two points on the optical wavefront and follows the Kolmogorov 5/3 power law.

The theory of incoherent image formation has been applied to study the black-target method for veiling-glare measurements. Theoretical analysis and experiments show that as the black-target size increases and/or as the detection aperture decreases, the measured veiling-glare index decreases.

This PDF contains the communication on "Etalon effects in laser mirrors."

This PDF file contains the letter “Letter: Comment on the paper” for OE Vol. 33 Issue 11

This PDF file contains the editorial “Book Rvw: Diode Laser Arrays," edited by Dan Botez and Don R. Scifres for OE Vol. 33 Issue 11