It is with great personal pleasure that I am able to announce that Dr. Donald C. O’Shea will become the next editor of Optical Engineering on January 1, 1998. Congratulations, Donald, on this appointment and thanks to the society for choosing such an excellent candidate. Editors feel somewhat parental about the journals they edit and so passing the journal to a new editor is somewhat like seeing one of your children getting married.

Over the past decade, a new interdisciplinary field of research called ‘‘smart structures’’ has emerged. A smart structure can be generally described as a nonbiological structure that has a definite designed-in purpose and the ‘‘will’’ and means to actively try to achieve that purpose. In some sense, a smart structure would be a nonbiological analog of a living structure such as a tree.

The Large Millimeter-wave Telescope/Gran Telescopio Milime ´ trico (LMT/GTM), is a 50-m diameter radio telescope designed to operate at 1-mm wavelengths. To achieve its surface accuracy requirements, the telescope relies on an actively controlled primary surface. The active primary enables active correction of errors in the reflecting surface caused by thermal and gravitational deformations of the supporting backstructure. In addition to these slowly varying loads, there are higher frequency disturbances caused by some observation techniques. In a conventional telescope, the observer must wait for the vibration to decay naturally before continuing an observation. However, for an active surface telescope (such as the LMT/GTM), the mass of the surface and the large number of actuators can be used to add damping to the support structure. The use of active surfaces in vibrational damping of their support structures is investigated. A method is presented that enables decoupling of the vibrational modes in such a way that the surface figure can be controlled simultaneously.

Experience with adaptive optical systems has highlighted the fact that these systems are often designed without adequate attention to the wavefront control system. One example is the ‘‘mode visibility’’ problem, in which the wavefront sensor design results in aberrations that can be introduced into the optical system by the actuators but cannot be sensed adequately by the wavefront sensor and therefore cannot be corrected by the closed-loop wavefront control system. To prevent such problems, the overall system design must include control system issues at an appropriate level. For purposes of control system design, an adaptive optical system can be modeled as mappings among three vector spaces: the space containing the actuator command, the space containing the wavefront error of the system, and the space containing the wavefront sensor output. The singular value decompositions of these mappings enable analysis of the controllability and observability properties of the system. In particular, the condition number of the mapping from actuator space to sensor space is a measure of the combined controllability and observability of the system, and the minimization of this condition number results in a system with good controllability and observability properties.

The problem of determining sensor subaperture locations for a shearing interferometer wavefront sensor that maximize controllability and observability is examined and shown to be an intractable optimization problem. A practical algorithm, the sequential backward selection algorithm, is used to determine a suboptimal sensor configuration. Monte Carlo studies show that the algorithm determines a nearly optimal and entirely acceptable configuration in a reasonable time.

We demonstrate that temperature- and strain-insensitive long-period gratings can be fabricated in conventional optical fibers. The former is employed to measure strain with resolution of 20 µ? under thermal fluctuations in the surroundings, while the latter is used to detect temperature variations as small as 0.8°C in the presence of axial strain.

A wavelet-transform-based technique to enhance defect detection in a carbon fiber composite plate interrogated using ultrasonic Lamb waves and incorporating an optical fiber receiver is described. Fundamental symmetric (S0) Lamb waves were introduced into the sample plates using a conventional piezoelectric transducer operating at a frequency of around 250 kHz. Coupling into the plates was achieved using a perspex phase-matching wedge. The propagating acoustic pulses were monitored using a simple embedded or surface-mounted singlemode optical fiber forming the signal arm of an optical fiber Mach- Zehnder interferometer. The direct Lamb wave reflections from delaminations in the sample plates were of low amplitude, although a degree of defect visibility enhancement was achieved by correlating the received signals with the outgoing ultrasonic pulse. A considerable improvement in the defect visibility over the latter technique was found by using a wavelet-transform-based novelty technique to identify the defective plate zones. Using an orthogonal wavelet transform to compress the data, important structurally related features were extracted by setting appropriate threshold levels on the wavelet coefficients. The reconstructed (uncompressed) data from defect-free portions of the plate were used to construct a template representing a normal condition. Defect location was achieved by analysis of the departure of signals arising from defective plate regions from the no-fault condition template.

A new method is proposed for measuring interstory drift, the shifting of floors relative to one another when a building undergoes wind or earthquake loading. A free-space crosshair beam is projected from ceiling to floor onto a square of four position-sensitive photodetectors. Every lateral position and torsional angle gives a unique set of voltages at the photodetector outputs; thus, as the floors shift with respect to one another under load, detector voltages vary, the new beam axis location is determined, and the 2-D interstory drift is obtained. The theory of operation and a quasi-static verification of the method using micropositioning stages to provide input displacements are reported. Lateral positions, including translational and rotational components, are calculated from the photodetector outputs, and show excellent agreement with input displacements. The overall performance of the sensor system is extremely linear and predictable, and appears robust enough for field deployment. It is envisioned that some day it could serve as the input to an active control system used to stabilize smart buildings experiencing earthquake and wind loads.

Fiber optic grating systems are described that have been used to measure strain in cylindrical structures. The applications of these systems to a composite utility pole and to a composite missile body are described. Composite utility poles have significant advantages with respect to wooden utility poles that include superior strength and uniformity; light weight for ease of deployment; the ability to be recycled, reducing hazardous waste associated with chemically treated wooden poles; and compatibility with embedded fiber optic sensors, allowing structural loads to be monitored. Tests conducted of fiber optic grating sensors in combination with an overcoupled coupler demodulation system to support structural testing of a 22-ft composite pole are reported. Monitoring strain in composite missile bodies has the potential to improve the quality of manufactured parts, support performance testing, and enhance safety during long periods of storage. Strain measurements made with fiber optic grating and electrical strain gauges are described.

Radiation-induced changes to the polarization states of light propagating in various photonic devices are observed. The nature of the polarization changes is reported for one particular photonic device—the acousto optic Bragg cell. A short description of the detection methodology used to quantify transient changes to the polarization states and to the degree of polarization in tellurium dioxide and gallium phosphide Bragg cells are presented. A discussion of the Stokes parameter analysis used to interpret the data is also presented.

Computer simulations are used to demonstrate the feasibility of operating a low-order adaptive optics system for observation of bright low-earth orbiting satellites during daylight hours. The system considered includes speckle postprocessing of partially compensated focal plane images to produce reconstructions with resolution near the diffraction limit of the telescope.

The correlation performance of four different types of joint transform correlators (JTCs) is investigated in a noncooperative situation when the target image is cluttered with scene noise and present under poor illumination condition. Computer simulation and experimental results are provided. Although the binary JTCs based on spatialfrequency- dependent threshold (SFDT), sliding-window local-median threshold (SWLMT) offer good correlation performance in poor target image illumination conditions their performance is affected in the presence of background noise in the target image. The JTC based on modified-fringe-adjusted filter (MFAF) performs better in such a combined situation.

A reformulation of the asymptotic solution of the coupledmode equations with a periodic variation of the refractive index along the propagation length is presented. A first-order correction using the asymptotic solution and Piccard’s method are also determined. It is found that the first-order solution compares very well with the numerical solution throughout a wide range of coupling parameters. The key differences between the method presented here and elsewhere reside in the derivation of the asymptotic solution as well as in the carefull derivation of the higher order corrections.

Cranz-Schardin cameras are low-cost, high-speed cameras. Although developed over 70 yr ago and available commercially, the design principles are not found in standard texts. Geometric optics are used to develop the design of a Cranz-Schardin camera. The design reveals the tight coupling between the light sources and the rest of the optics. The design of a light power gathering system is also described. The implementation of the design principles is illustrated by an actual camera capable of capturing four frames at a maximum rate of 1,000,000/s.

A test method for the evaluation of the in-plane shear modulus of composite laminates is presented. The method is essentially a resonance test on a cantilevered rectangular orthotropic laminate using laser holographic interferometry. Based on Rayleigh’s quotient, a simple formula is derived to determine the in-plane shear modulus using the resonance frequency of the first torsional vibration. An appropriate value of the length-to-width (aspect) ratio of the specimen is suggested to evaluate the in-plane shear modulus accurately. The results show that the measured in-plane shear moduli by the present method agree well with the modulus obtained by a ±45-deg off-axis tensile test.

In different fiberization processes, glass fibers are drawn out in a turbulent flame. High-speed in-line holography is applied to visualize glass fibers. However, the random spatial distribution of temperature induces strong local variations of the refraction index. Consequently, the reconstructed images are altered. The direct analysis of the diffraction patterns recorded by the holographic plate can offer an alternative solution. The diffraction process can be interpreted as a convolution with a wavelet family of functions. The scale parameter a is related to the distance between the object and the plane of observation. The 3-D location of a fiber element and its orientation ? are estimated by searching for the parameters a and ?, which yield a maximum modulus of the wavelet transform. The results are compared with those obtained from a conventional optical reconstruction. The application of the wavelet transform improves the SNR in the image and enables the 3-D fiber location to be determined more accurately (±50 µm for the axial coordinate estimation).

A large number of electro-optical (EO) and IR sensors are used on military platforms such as ground vehicles, low-altitude air vehicles, high-altitude air vehicles, and satellite systems. Ground vehicle and low-altitude air vehicle (rotary and fixed-wing aircraft) sensors typically use the probabilities of discrimination (detection, recognition, and identification) as design requirements and system performance indicators. High-altitude air vehicles and satellite sensors have traditionally used national imagery interpretation rating system (NIIRS) performance measures for guidance in design and measures of system performance. Data from the high-altitude air vehicle and satellite sensors are now being made available to the warfighter for many applications including surveillance and targeting. National imagery offices are being merged and restructured to support the warfighters and connectivities to high-altitude air vehicle sensors more effectively. It is becoming more apparent that the gap between the NIIRS approach and the probabilities of discrimination approach must be addressed. Users, engineers, and analysts must have a comparative basis for assessing the image quality between the two classes of sensors. The two approaches are described and compared.

An effective design structure for 2-D analysis/synthesis filter banks with high computational efficiency are proposed. The system involves a 2-D single-sideband (SSB) system, which is developed in terms of a 2-D separable weighted overlap-add (OLA) method of analysis/ synthesis and enables overlap between adjacent spatial domain windows. This implies that spatial domain aliasing introduced in the analysis is canceled in the synthesis process and provides perfect reconstruction. Achieving perfect reconstruction, each individual analysis/synthesis filter bank with SSB modulation is satisfied to be a cosine modulated version of a common baseband filter. Since a cosine-modulated structure is imposed in the design procedure, the system can reduce the number of parameters required to achieve the best computational efficiency. It can be shown that the resulting cosine-modulated filters are very efficient in terms of computational complexity and are relatively easy to design. Moreover, this design approach can be imposed on the system with relatively low reconstruction delays.

A new gray-level threshold selection method for image segmentation is presented. It is based on minimizing the difference between entropies of the object and the background distributions of the gray-level histogram. The proposed method is similar to the maximum entropy method proposed by Kapur et al. (1985), however, the new method provided a good threshold value in many instances where the previous method did not. The effectiveness of our method is demonstrated by its performance on videomicroscopic images of the rat lung. Extension of the method to higher order probability density functions is described.

A flexible microscope is configured, evaluated, and employed in the noninvasive investigation of fluid transport in a tissuelike model or porous, fibrous matrix. A simple optical configuration that employs microendoscopic probes, an objective lens, and a commercial CCD for detection, produces resolution performance in the range of 25 to 40 line pairs/mm (lp/mm). Remote, time-sequenced imaging is shown to be possible using this moderate resolution flexible microscope. The microendoscopes employed are 1 to 3 m in length and range in outer diameter from 1.5 to 2.5 mm; some contain a working lumen for the introduction of a tool or a fluid at the site of investigation. Target lighting is accomplished by an integral fiber bundle built into the endoscope and supplied from an external xenon discharge lamp. This instrumentation is combined with specialized image processing for quantitative, time-sequenced imaging of marker dye transport on a tissuelike model substrate. Quantitative absorbance imaging is accomplished by calibrating response for marker dye standards on the test substrate and correlating camera pixel grayscale values to solute concentration. The quantitative mapping (concentration versus time and position) of fluid transport is used to evaluate convective versus diffusive flow.

In fractal decoding procedures, the reconstructed image is obtained by means of a predefined number of iterations with an arbitrary initial image. A novel fast decoding algorithm with convergence criteria is proposed. It is composed of a selective decoding of range blocks with a block convergence criterion (BCC), estimation of an initial image, and one-buffer decoding. In the proposed algorithm, continuation of the decoding process is judged by an image convergence criterion (ICC), not by the predefined number of iterations. Without redundant iterations and loss of quality, the reconstructed image is obtained by the amount of calculations corresponding to only three to four iterations of the general decoding procedure.

An improved and efficient method to estimate quadric parameters of imaged objects using structured light is presented. In contrast with our previous work Busboom and Schalkoff (1996) and Sorgel and Schalkoff (1997), the algorithm employs a closed-form solution and therefore iteration is unnecessary. This is possible due to the development of the line-to-curve mapping (LCM) algorithm. The algorithm relies on the fitting of a 2-D, second order curve to a passive ‘‘stripe’’ image resulting from the projection of structured light. The capabilities and shortcomings of the method are illustrated by a series of simulations and experiments. Improvements of the critical second order curve fit in the passive image are introduced and the performance of the enhanced algorithm is analyzed.

A novel implementation of the method for obtaining the partial derivatives of in-plane and out-of-plane displacement fields in the inplane electronic speckle pattern shearing interferometry (ESPSI) configuration is described. Lateral shear interferograms of object image fields generated by individual symmetrical illuminating beams are recorded independently. The phases are calculated using the temporal phase-stepping method and their digital subtraction/addition gives required in-plane/out-of-plane displacement derivatives, respectively. Phase stepping is readily performed in the setup using fiber optics and modulated laser diode illumination without any mechanical movement of the components.

If a flat wavefront illuminates a lens and we measure the curvature of the refracted wavefront, the focal length of this lens can be determined. Different alternatives to measure the convergence or divergence power of a wavefront using fringes projected by a Ronchi ruling placed in contact with the lens are described. The Talbot autoimaging phenomenon is used to optimize the contrast of the projected fringes as much as possible. The different manners in which the fringes can be formed as well as the different manners in which these fringes can be analyzed and their spatial frequencies measured, are described using Talbot interferometry with a second ruling on the plane of observation. The two rulings have a small angle between them. The curvature of the wavefront illuminating the rulings is measured by the inclination of the moire´ fringes formed by the two ruling. Using the method described here, an instrument could be constructed to measure the power of ophthalmic lenses.

The modified phase locked loop (PLL) technique applied to the analysis of 2-D carrier-frequency fringe patterns is presented. It uses two images with a projected grating shifted in phase by half of its period. The proposed technique was tested for the mannequin shape determination with good results obtained with two iterations only. Due to the properties of the PLL technique there is no problem with phase unwrapping and very short calculation time is needed.

Lasers based on Nd:Cr:GSGG low-energy oscillator/highenergy multiple-pass amplifiers produced 1.7 J pulses in a M2?2 divergence beam at 2.4% electrical efficiency. Thermal lensing and birefringence correction were major factors driving the amplifier design. Essential components in achieving a moderate average power output were an intra-amplifier telescope to correct for lowest order thermal focusing, a phase conjugate mirror to correct for higher order thermal lensing aberrations, and a linear optics derived polarization conjugator to correct for birefringence.

Broad-area semiconductor lasers with stripe patterns formed on their front mirrors and the properties of such lasers are described. The stripes are of alternately different reflectivity and therefore the pattern acts as a low frequency grating. Such a grating significantly affects the shape of the laser output beam. The envelope of its intensity profile becomes almost Gaussian and the beam cross section is much closer to a circle than in the case of standard lasers.

A Rayleigh/Mie lidar system deployed at the Sondrestrom Atmospheric Research Facility located on the west coast of Greenland near the town of Kangerlussuaq (67.0 deg N, 50.9 deg W) has been in operation since 1993 making unique observations of the arctic middle atmosphere. The vertically directed lidar samples the elastically backscattered laser energy from molecules (Rayleigh) and aerosols (Mie) over the altitude range from 15 to 90 km at high spatial resolution. The limited amount of arctic observations of the middle atmosphere currently available emphasizes the importance and utility of a permanent Rayleigh lidar system in Greenland. The lidar system consists of a frequencydoubled, 17-W Nd:YAG laser at 532 nm, a 92 cm Newtonian telescope, and a two-channel photon counting receiver. The principal objective of the lidar project is to contribute to studies concerned with the climatology and phenomenology of the arctic middle atmosphere. To this end, we describe the lidar system in detail, evaluate system performance, describe data analysis, and discuss the system capabilities in determining the density, temperature, and the presence of aerosols in the arctic middle atmosphere. Particular emphasis is placed on the derivation of temperature from the lidar measurement and on the impact of signalinduced noise on this analysis. Also, we develop a statistical filter based on a Bayesian approach to optimally smooth the lidar profile in range. This filter preserves the short-term fluctuations in the low-altitude data consisting of relatively high SNR, whereas more smoothing is applied to the high-altitude data as the SNR decreases.

A simple technique is devised to measure the angles of a pentagon and a hexagon without using expensive spectrometers, autocollimators, and angle gauges. A general technique for measuring the angles of polygons with sides ranging from 5 to 12 is proposed. The technique can be used for carrying out measurements with an autocollimator, when a suitable angle-gauge combination is not available. The method can also be used for both glass and hardened steel polygons with moderate polish.

We describe a new optical inspection method based on the analysis of the combined space-frequency representation of the scattered field. Samples of the sliding window spectrum are measured optically and then the surface features are reconstructed by numerical methods. The methods investigated include reconstruction from the Gabor expansion coefficients, using the Zak transform, and phase recovery from amplitude only data, using projection onto constraint sets algorithm. Computer simulations and experimental results show that this method can reconstruct accurately shallow phase objects, even when their dimensions are smaller than the diffraction limit of the optical setup.

A liquid crystal neuron array for carrying out optical subtraction and thresholding operations is proposed. It consists of 32 X 32 smart pixels, which can be used as artificial neurons. The device operates in parallel, that is, all the pixels are processed together simultaneously. All these functions are completed by the physics features of liquid crystal and silicon rather than by computing and controlling in a very large scale integrate circuit (VLSI). The principle of operation and the fundamental characteristics of the neuron array are described in detail.

A mutually pumped phase conjugator is realized using a bridge configuration with a novel crystal of copper-doped potassium sodium strontium barium niobate. Phase conjugation reflectivity reaches 218%. The buildup times of phase conjugation outputs are measured, and a curve fit of the times is made. A self-curving coupling channel is observed. We use the theory developed by Lyubomudrov and Shkunov to model the coupling channels. The curved beam trajectory depending on the incident position and the incident angle is also calculated. With the results we show that one, two, three, and more four-wave mixing interaction regions exist in photorefractive bridge mutually pumped phase conjugators. Additionally, the simultaneous phase conjugation outputs of four incident beams are also demonstrated experimentally with the crystal.

A theory of phase-detecting algorithms based on Fourier theory was described by Freischlad and Koliopoulos (1990). We present an application of this theory to a discrete sampling. It is shown that Greivenkamp (1984) results for a least-squares fitting of the sampling points can be obtained from this Fourier theory. We also present a new graphical vector description of the conditions required by the sampling weights in synchronous phase detection algorithms. Some applications of this graphical representation are presented.

For many reasons smaller spacecraft are becoming more appealing. Because of their lower inertias, these spacecraft are more sensitive to disturbances and likely to have more attitude jitter than the larger units. These jitter levels are unacceptable for some scientific instruments and need to be compensated. In the case of line-of-sight type instruments, the attitude jitter can be mitigated by incorporating a fast steering mirror into the system. To take full advantage of these devices, the spacecraft attitude must be measured at sufficiently high bandwidth, well beyond what is commonly provided by inertial reference units. Various ways to obtain higher bandwidth attitude measurements for the purpose of jitter control are explored and a practical solution to the problem is proposed.

We investigate the distortion of demodulated output signal in a fiber optic Michelson interferometric sensor in relationship to the imperfect properties of its 3 X 3 coupler. A general guide rule in choosing a 3 X 3 coupler and its connection type in the interferometer to reduce this kind of signal distortion is also suggested.

Some considerations of the spectroscopic performance of a soft x-ray Fabry-Pe´ rot e´ talon (XFPE) are presented. A whole study of the phase change on reflection of a soft x ray multilayer interferential mirror (MIM) has been necessary to evaluate the theoretical behavior of the order of interference of an XFPE. For grazing incidence angles, there is a linear dependence between the latter parameter and the grazing angle in the range of the diffraction Bragg peak. This property has enabled us to obtain local expressions for the finesse and the resolving power of an XFPE. Numerical simulations emphasize the interest of such a structure in x-ray spectroscopy.

The role of holography in characterization of small objects in a dynamic volume is well established.1–3 There is significant current interest in applications and refinement of the technique.4–18 The size accuracy or resolution is one of the most important parameters and aberration3,19–31 is one of the critical governing aspect. To establish the aberrationrelated resolution, Rayleigh quarter wavelength rule and Mare´chal’s condition are two important32 approaches.

The author begins the book with the statement, ‘‘Getting started is often the most difficult part of a new task, and it is always the first thing to do.’’ His purpose in writing the book is to help the reader to be successful in the design and production of optical thin films. The seven chapters cover the essential elements of optical coatings.