This PDF file contains the editorial “Teaching Optical Engineering” for OE Vol. 47 Issue 05

We experimentally demonstrate a spectrum-efficient 80-Gbit/s differential phase-shift keying (DPSK) transmitter for a single wavelength channel using phase-interleaving technology without any optical-time or polarization-division multiplexing. Two cascaded independent 40-Gbit/s modulations were time-interleaved to generate an 80-Gbit/s DPSK signal with a compact spectrum. The proposed 80-Gbit/s DPSK transmitter consists of two independent 40-Gbit/s phase modulators only. No additional high-speed pre- or postcoder is required at the transmitter or receiver side. The proposed scheme is potentially cost-effective.

We propose a novel method of one-shot parallel complex Fourier-domain optical coherence tomography using a spatial carrier frequency for full range imaging. The spatial carrier frequency is introduced into the 2-D spectral interferogram in the lateral direction by using a tilted reference wavefront. This spatial-carrier-contained 2-D spectral interferogram is recorded with one shot of a 2-D CCD camera, and is Fourier-transformed in the lateral direction to obtain a 2-D complex spectral interferogram by a spatial-carrier technique. A full-range tomogram is reconstructed from the 2-D complex spectral interferogram. The principle of this method is confirmed by cross-sectional imaging of a glass slip object.

We optimize the layout of each light plane in a dual-view multistripe measurement system by employing spatial geometry analysis to avoid ambiguity. The imaging regions of every light plane can be labeled uniquely on two image planes within a certain measurement depth. Moreover, the flexible density of fringe patterns corresponding to the different measurement depths is immediately projected without the conventional coding procedure. Some experiments verify the effectiveness of the proposed method applied in high-resolution 3-D measurements.

Photons were generated possessing orbital angular momentum (OAM) in the form of Laguerre-Gaussian (LG) laser modes. Three Mach-Zehnder interferometer systems, with the use of Dove prisms, were constructed to sort and detect the LG modes based on their OAM state. Successful generating, sorting, and detecting of LG modes is the first step towards information encoding and decoding via lasers. It is possible to generate many LG modes, which can be orthogonally decoded. With many modes to encode information with it is possible to transfer more than one bit of information with a single photon using LG encoding. An experimental test of this concept was performed by demonstrating the generation and sorting of LG modes with attenuated intensities averaging below one photon passing through the system at a time. In summary, generating, sorting, and low-power detecting of specific LG modes were all demonstrated.

A challenge in the semiconductor industry is 3-D inspection of the miniaturized solder bumps grown on wafers for direct die-to-die bonding. An inspection mechanism proposed earlier requires the projection of a binary fringe grating to the inspected surface from an inclined angle. For high speed and accuracy of the mechanism, the projection optics has to meet these requirements: (1) it allows a tilt angle between the inspected surface and the projector's optical axis; (2) it has a high bandwidth to let high-spatial-frequency harmonics contained in the binary grating pass through the lens and be projected onto the inspected surface properly; (3) it has a high modulation transfer function; (4) it has a large field of view; and (5) it has an adequate depth of field that matches the depth range of the inspected surface. In this paper, we describe a projection optics design, consisting of a fringe grating and several pieces of spherical lens, that addresses the requirements. To reduce the lens aberrations, the grating is laid out with an angle chosen specifically to make the grating, the lens, and the average plane of the inspected surface intersect in the same line. Performance analysis and tolerance analysis are shown to demonstrate the feasibility of the design.

A keyframe selection algorithm is the process of selecting the essential image for 3-D reconstruction from among many uncalibrated images. Camera autocalibration between images is also essential for 3-D reconstruction. This paper proposes a keyframe selection algorithm that selects the best image to reduce reprojection error. The camera projection matrix in the selected keyframe arises from a full camera autocalibration process. From the camera projection matrix, which is assumed exact, the algorithm calculates the fundamental matrix using algebraic derivation. By this process, false matching is eliminated and finally a 3-D data set is obtained. In our experimental results, the proposed algorithm needs less time than other algorithms; it also has fewer errors in the reconstructed 3-D data. The fundamental matrix that is gained from algebraic derivation takes less time than other algorithms, and it has same average error as the others.

Bessel beams formed by an axicon are nondiffracting beams. Such beams are used in the field of laser machining because they have several desirable characteristics, including a micron-sized focal spot and a deep focal depth. Conical lenses are generally employed for producing Bessel beams. A binary diffractive axicon was made by electron beam fabrication; the first-order diffracted beam from this axicon has a similar optical field to that of a refracted beam from a conical lens. The characteristics of a laser beam spot focused by the axicon were investigated. We demonstrated theoretically and experimentally that the peak intensity on the optical axis oscillated with a larger amplitude as the spot size decreased when the beam spot was observed in the vicinity of the axicon. This phenomenon was well explained by taking higher-order diffraction into account. We also investigated the wavelength dependence of the spot size focused by the axicon, and found that the spot size was constant.

The miniaturization trend has enhanced the rapid development of small precision machines. The operational performance of a precision machine is mainly determined by its bearing clearance, the balancing quality of its shafts, and the actuation smoothness of the rotating shafts. In comparison with large shafts, small shafts are more susceptible to external interference and the loading effects of the measurement equipment. Accordingly, the inspection concepts for small shafts should be quite different from those for large shafts. This paper presents our approach to developing an economical optical measurement system with which the error motions of small rotating shafts can be inspected. The shadow method is applied as the measurement concept for the radial error motion. Two perpendicularly installed laser beams are partially shaded by the shaft, and the radial error motion is transformed into the alternations of light and shade on two photodiode arrays. For measuring the tilt error motion, a reflective method is realized to transform a tilt error motion into a 2-D movement of a reflective cross-hair pattern, which is detected by two photodiode arrays. To increase the measurement sensitivity, a novel bilateral configuration using offset pairs of photodiode detectors is developed; the signals of the detectors are processed by the differential principle. The shadow method shows better sensitivity and faster measuring speed than the reflective method because of its distinct projected beam.

The industry dealing with microchip inspection requires fast, flexible, repeatable, and stable 3-D measuring systems. The typical devices used for this purpose are coordinate measurement machines (CMMs). These systems have limitations such as high cost, low measurement speed, and small quantity of measured 3-D points. Now optical techniques are beginning to replace the typical touch probes because of their noncontact nature, their full-field measurement capability, their high measurement density, as well as their low cost and high measurement speed. However, typical properties of microchip devices, which include a strongly spatially varying reflectance, make impossible the direct use of the classical optical 3-D measurement techniques. We present a 3-D measurement technique capable of optically measuring these devices using a camera-projector system. The proposed method improves the dynamic range of the imaging system through the use of a set of gray-code (GC) and phase-shift (PS) measures with different CCD integration times. A set of extended-range GC and PS images are obtained and used to acquire a dense 3-D measure of the object. We measure the 3-D shape of an integrated circuit and obtained satisfactory results.

Specification of vibration modes, amplitudes, and damping coefficients of structures are crucial issues in civil and mechanical engineering. Several techniques have been used for this kind of studies, including holographic interferometry, speckle interferometry, and moiré technique. But, for a large-scale structure, the modal analysis technique is usually used. We use the time-averaged digital image of a sinusoidal pattern fixed on a vibrating 6-m iron I-beam to study in-plane vibration. The study includes specification of vibrating modes, amplitudes, and damping coefficients. Using a wide-angle high-resolution digital camera, successive images of the vibrating pattern are recorded in exposure times much longer than the vibration period and much shorter than the relaxation time. The visibility measurement along the images leads to the specification of the mentioned parameters.

System calibration is crucial for any 3-D shape measurement system. An accurate method is proposed to calibrate a 3-D shape measurement system based on a structured light technique. The projector is treated as a camera to unify the calibration procedures of a structured light system and a well-established stereo vision system. The key to realizing this method is to establish a highly accurate correspondence between camera pixels and projector pixels and generate digital micromirror device (DMD) image sets for projector calibration. A phase-shifting method is used to accomplish this task. A precalibrated lookup table and a linear interpolation algorithm are proposed to improve the accuracy of the generated DMD image, and accordingly improve the accuracy of the projector calibration and the 3-D measurement. Some experimental results are presented to demonstrate the performance of the system calibration.

A model of a mobile setup for shape reconstruction is presented. In this technique, the contouring is performed by laser scanning and image processing. The devices of this setup can be moved to examine occluded areas and small details. The modeling of the mobile setup is carried out by an approximation network, which produces an equation that computes the object dimensions from the deformation of a laser line and the camera position. Also, the geometric parameters of the optical system are deduced, based on the network and image processing. This model improves the performance and the accuracy of the reconstruction system, because all steps of the contouring are performed by computer algorithms. In this manner, the errors of the physical measurements are not passed to the reconstruction system. This procedure represents a contribution to the methods of contouring based on laser scanning. To describe the accuracy, a root mean square of error is calculated with respect to a contact method. This technique has been tested with real objects, and experimental results are presented. Also, the processing time is discussed.

While the uniform sampling method is quite popular for pointwise measurement of manufactured parts, we present three novel sampling strategies that emphasize 3D non-uniform inspection capability. They are direct and indirect adaptive sampling and local adjustment sampling. The adaptive sampling strategy is based on a recursive surface subdivision process that applies two different approaches. One uses the direct triangular patch subdivision while the other uses the indirect sectional adaptive approach. The direct adaptive sampling approach can distribute points more closely around edges, corners, and vertices as found on the class of machined products. The indirect adaptive sampling techniques extend optimum 2D sampling methods to 3D applications. The modified 2D adaptive sampling techniques are used sequentially twice; first, the critical cross sections are optimally selected, and then each section is optimally sampled to develop an accurate geometric description using a small number of sampling points. Beyond the practical application value of a technique to inspect curved surface objects, this kind of technique is also of value in understanding the principle of optimum sampling in a 3D sense. The local adjustment sampling strategy uses a set of predefined starting points and then finds the local optimum position of each nodal point. This method approximates the object by moving the points toward object edges and corners. The predefined starting points sets include uniform and non-uniform sampling distribution generated by the direct adaptive sampling approach. The results show that the initial point sets, when preprocessed by the adaptive sampling using triangular patches, are moved the shortest distance to edges and corners for global optimum approximation, again showing this method's superiority. (Partial Abstract)

Large-area concave refractive microlens arrays, or concave template structures, and then the non-refractive-index-gradient type of planar refractive microlens arrays in InP and quartz substrates, are fabricated utilizing the method consisting of conventional UV photolithography, thermal shaping of concave photoresist microlenses, etching with an argon ion beam of large diameter, and filling or growing optical medium structures onto the curved surfaces of preshaped concave templates. Several key conditions for fabricating concave and also planar microlenses are discussed in detail. The concave structures obtained are characterized by scanning electron microscope and surface profile measurements. The far-field optical characteristics of quartz/ZrO₂ planar refractive microlens arrays have been acquired experimentally.

The nematic liquid crystal variable retarder is a useful device for examining the polarization properties of optical components and material samples as well as for remote sensing applications. The response of the retarder to oblique ray angles is important in applications requiring a finite field of view such as imaging polarimetry. Mueller matrices that describe the response to incident angle are developed in two ways using an extended Jones matrix approach and through an alteration of a standard Stokes Mueller matrix for a retarder. Comparisons of the model results with lab measurements show good agreement, although with some differences due to varying assumptions in the models and nonideal aspects of the actual variable retarder. We provide analytical models that can be applied relatively easily to examine the effects of oblique angles in systems using liquid crystal variable retarders.

Using the ABCD matrix theory that takes into account the thermal lens effect of the gain medium and rate equations that consider the Gaussian spatial distributions of the intracavity photon density and pump beam, the pulse duration of a passively Q-switched laser is optimized by choosing the appropriate oscillating beam radius on the Q-switch wafer and pump beam radius in the gain medium, which provides a simple way to optimize the pulse duration. By changing the positions of the GaAs in the cavity or the pump beam focal plane in the gain medium in a diode-pumped passively Q-switched Nd:YVO₄ laser with a GaAs saturable absorber, the optimization of pulse duration is easily realized, which is in good agreement with the theoretical calculations.

Graded-index (GRIN) fiber lens arrays are fabricated from commercial GRIN fibers to collimate a high-power laser diode array. The beam divergence angles are reduced to 4.2 and 14.7 mrad in the fast and slow axes, respectively. The influences of smile and fluctuation in fiber length are discussed. Using an aspherical focal lens system, about 74% power can be launched into a fiber with a numerical aperture (NA) of 0.22 and a core diameter of 400 μm.

In the field of optical measurement, phase always represents the physical quantity to be measured. Thus, phase retrieval from a fringe pattern is a key step for quantitative measurement and evaluation. Much research work has been conducted to develop phase evaluation methods such as fringe tracking and fringe skeletons in earlier, and the more precise methods of phase-shifting and Fourier transform more recently. For phase evaluation, the phase-shifting method requires three or more phase-shifted speckle patterns at each deformed stage; thus, it is not suitable for measurement of continuous deformation. The Fourier transform, on the other hand, requires a high-frequency carrier for phase separation in the spectral domain, which places an additional requirement on experimental arrangement. Thus, it would be desirable to develop a convenient method that can retrieve the modulated phase from a single fringe pattern. We propose an approach that utilizes the phase-clustering property to extract phase information from a single interference specklegram. To explore the ability and limitation for the proposed technique, typical shearographic fringe patterns are used for phase evaluation. Results obtained are similar to those from the standard four-step phase-shifting method. Nonrepeatable continuous movement is also measured by the proposed method, and the results confirm the robustness and accuracy of the clustering method.

Recent experiments on optical damage by ultrashort laser pulses have demonstrated that the temporal pulse shape can dramatically influence plasma generation in fused silica. We use a modified 3+1D nonlinear Schrödinger equation for the pulse propagation coupled to a rate equation for the plasma density in the dielectric material to simulate pulse propagation and plasma formation in fused silica. We use these simulations to analyze the influence of pulse shape and beam geometry on the formation of the electron plasma and hence modification in the bulk material. In particular, we simulate the effect of pulses reconstructed from experimental data. It is expected that a better understanding of the dynamics of laser-induced plasma generation will enable the accurate simulation of optical damage in a variety of dielectrics, ultimately leading to an enhanced control of optical damage to real materials and optical devices.

We develop an in-line distributed optical fiber acoustic sensor array based on Sagnac interferometer use it to measure and locate leaks for the fluid-filled (or gas-filled) pipelines in real time. The advantage of the sensor array is that it can monitor two or many pipelines at the same time. The traditional loop Sagnac interferometer is changed into in-line structure by a Faraday rotator mirror. The representation of phase change caused by leakage is formulated for optic signal; the measuring principle and the leaking source location method for the sensor array are analyzed. An experiment is designed to detect and locate leaks. The results verify that the system can realize leak detection and locate leak accurately, and the error is less than 0.54%.

A highly compact laser-scanning device that can be used as an in situ detection and monitoring device for metal fatigue is described. A prototype is built on a Mica2 wireless sensor mote platform with TinyOS-based firmware. This device is shown to be capable of detecting fatigue-related changes in the surface bidirectional reflectance distribution (BRDF) of an aluminum test coupon, and detectable changes in BRDF are measured at a very early stage of fatigue development, when no cracks larger than 50 μm in length have yet developed at the monitored location. The system power requirements are compatible with standard sensor mote architectures such as the Mica and Telos series, enabling the potential for multiyear lifetimes without battery replacement. Such an in situ optical fatigue sensor could be used in a variety of structural health monitoring applications, including aerospace, rail transport, and civil structures.

A fiber optic sensor for liquid refractive index measurement based on a Fabry-Pérot interferometer is described. The interferometer is achieved between the reflection of a short fiber Bragg grating and the Fresnel reflection from the cleaved fiber end. This fiber end is then in contact with the liquid sample to provide refractive index measurements. The sensor is characterized by immersing the fiber tip in distilled water with different concentrations of ethylene glycol. A linear relation of the interferometer fringe visibility with refractive index variation is observed, and a resolution of ~10^-3 is obtained. It is also shown that the sensor operation is independent of temperature effects, other than the one related to temperature-induced change of the liquid refractive index.

An alternative type of multiport polarization-independent wavelength-interleaving bidirectional quasicirculator is proposed. It contains holographic spatial and polarization modules (HMs), a Lyot-Ohman filter (LOF), a quarterwave plate, and a mirror. Each HM contains a holographic spatial walk-off polarizer, a half-wave plate, and a glass plate. The LOF consists of three half-wave plates and three identical pairs of crystals. The functions of the HM and the LOF are described. Then, the operating principle and the performance of this quasicirculator are described and discussed. In this circulator, the signals in the even and odd channels can circulate with opposite handedness regardless of signal polarizations. It offers a high isolation level, polarization independence, low polarization-mode dispersion, parallel input/output ports and ease of increasing the number of ports.

A defocused transfer function of experimental microscopic bright-field images, closely connected with the evaluation of the relative refractive index profile of axially symmetric optical fibers, is presented. It is shown that with this function it is possible to obtain, with high precision, the defocused bright-field images of investigated fibers from their focus images and then to easily evaluate the relative refractive index profiles of the fibers.

We present an illustrative approach for significant simplification in the complexity of optimizing the scanning procedure of search and track systems. The optimization is done following a new phase space chart that is introduced and according to such parameters as probability of detection and false alarm rate. We compare two types of scanning of field of regard: continuous scan (push broom scan) and jump-scan (whisk broom scan). However, the presented approach enables more comprehensive investigation of any general scanning procedure of the search and track system.

We address the problem of foreground object detection through background subtraction. Although eigenbackground models are successful in many computer vision applications, background subtraction methods based on a conventional eigenbackground method may suffer from high false-alarm rates in the foreground detection due to possible absorption of foreground changes into the eigenbackground model. This paper introduces an improved eigenbackground modeling method for videos by recursively applying an error compensation process to reduce the influence of foreground moving objects on the eigenbackground model. An adaptive threshold method is also introduced for background subtraction, where the threshold is determined by combining a fixed global threshold and a variable local threshold. A fast algorithm is then given as an approximation to the proposed method by imposing and exploiting a constraint on motion consistency, leading to about 50% reduction in computations. Experiments have been performed on a range of videos with satisfactory results. Performance is evaluated using an objective criterion. Comparisons are made with two existing methods.

The usual methods of generating image mosaics suffer from abrupt color change where the color varies little in the source image, and from discontinuity of texture or shape where they are continuous in the source image. Our proposed method is based on wavelet transforms. It not only considers the similarity between a single tile and the corresponding original grid image, but also takes into account the match of surrounding tiles. The results of our experiments show that color changes are gentler in areas with similar colors originally, shapes are smoother, and textures are more refined in our image mosaics.

The robustness of a watermarking scheme based on the discrete fractional random transform has been investigated and demonstrated to be superior to those based on the discrete cosine transform, discrete fractional Fourier transform, and discrete Fourier transform. The spectrum distribution of the discrete fractional random transform is random and uniform, which guarantees good robustness. In addition, the discrete fractional random transform itself can serve as a secret key, and can provide high capacity while ensuring robustness in image hiding. Moreover, the feature of real output of the discrete fractional random transform with a half periodicity in its eigenvalues can save storage space of image data and is convenient for storage. Numerical simulations have confirmed our analysis and demonstrated the superiority of the discrete fractional random transform.

The inherent speckle noise in synthetic aperture radar (SAR) images severely degrades the image interpretation and affects the follow-up image-processing tasks. Thus, speckle suppression is a critical step in SAR image preprocessing. We propose a novel locally adaptive speckle reduction algorithm based on Bayesian maximum a posteriori (MAP) estimation in wavelet domain. First, the presented method performs logarithmical transform to original speckled SAR image and an undecimated wavelet transform (UWT). The Rayleigh distribution is used to model the statistics of the speckle wavelet coefficients, and the Laplacian distribution models the statistics of wavelet coefficients due to signal. A Bayesian estimator with a closed-form solution is derived from MAP criterion estimation, and the resulting formula is proved to be equivalent to soft thresholding in nature, which makes our algorithm very simple. Furthermore, the parameters of the Laplacian model are estimated from the coefficients in a neighboring window, thus making the presented method spatially adaptive in the wavelet domain. Theoretical analysis and simulation experiment results show that the proposed method is simple and effective. It significantly improves the visual quality of the SAR images and yields better performance than spatial filterings and traditional wavelet despeckling algorithms.

Dynamic speckle is a useful technique to show biological tissue activity and evolving processes in industry. There are several algorithms for quantitative and qualitative characterization of dynamic speckle. We use the statistical method receiver operating characteristic (ROC) to compare some speckle algorithms. We estimate the capacity of these descriptors to discriminate different activities and the smallest number of images necessary for a correct description of the phenomena. We also use the ROC curves to estimate the best conditions required by some activities. The results are verified using an activity image.

The snake model, which is well known in the domain of image segmentation, suffers from the problem that the result is heavily sensitive to the initialization, though many remedies (pressure force, gradient vector flow, etc.) have been proposed. In this paper, a new external force, called the adaptive pressure force, which can alternate adaptively between inflation and shrinkage according to the position of the contour, is presented. It can solve the problem of initialization very effectively. Besides, with the new external force, the problems of leakage of weak edges and poor convergence to concave boundaries can also be solved. Experiments demonstrate its effectiveness and robustness.

This paper presents an automatic superresolution method using multiviewpoint images. Viewpoints of objects in consecutive image frames often change in real video sequences. Hence, in order to adapt the conventional superresolution methods to multiviewpoint images, a geometric transformation of multiviewpoint images to a reference image plane should be performed. In this process, an accurate isoplane transformation is required. We propose a robust random sample consensus (RANSAC) criterion and a weighted homography estimation, which are important for accurate geometric transformation. Experiments were performed with several video sequences that simulate real surveillance systems. Multiviewpoint image sets were also used to verify the accuracy and stability of the proposed methods. The experimental results show that low-resolution images that are difficult to discern become recognizable high-resolution images using the proposed superresolution method.

This paper proposes a curvature-based corner detector that detects both fine and coarse features accurately at low computational cost. First, it extracts contours from a Canny edge map. Second, it computes the absolute value of curvature of each point on a contour at a low scale and regards local maxima of absolute curvature as initial corner candidates. Third, it uses an adaptive curvature threshold to remove round corners from the initial list. Finally, false corners due to quantization noise and trivial details are eliminated by evaluating the angles of corner candidates in a dynamic region of support. The proposed detector was compared with popular corner detectors on planar curves and gray-level images, respectively, in a subjective manner as well as with a feature correspondence test. Results reveal that the proposed detector performs extremely well in both fields.

In optical nondestructive testing, a novel solution is presented for fault detection based on the interpretation of fringe images. These images can be acquired using different optical methods, such as structured lighting or interferometry. We propose a set of eight special features adapted to the problem of surface inspection using structured illumination. These characteristics are combined with six further features specially developed for the classification of faults using interferometric images. We apply two kinds of decision rules: the Bayesian and the nearest neighbor classifiers. The proposed features are evaluated using a noisy and a noise-free image data set. All patterns were obtained by means of structured lighting. Concerning the noisy data set, we obtain better classification rates when all the 14 features are used in combination with a one-nearest-neighbor classifier. In case of a noise-free data set, we show that similar classification rates are obtained when the 14 features or only the 8 specific features are involved. The methods described are designed to address a broad range of optical nondestructive applications involving the interpretation and classification of fringe patterns.

We present a novel scheme for discarding wide-baseline mismatches. Based on a general two-frame wide-baseline matching model, the proposed algorithm first generates match clusters that are topologically invariable between frames, and then discards mismatches from clusters. Experimental results demonstrate that our algorithm can effectively extract high-precision scale-invariant feature transform (SIFT) matches from low-precision initial SIFT matches for wide-baseline image pairs. Furthermore, the algorithm always performs best or close to best in the comparison, indicating that it is more robust than other methods for discarding wide-baseline mismatches.

We propose a novel method for detecting scale-invariant keypoints. Our method first computes multiscale representations of an image for several different measures by scale-space filtering. Then we localize feature points in the image plane and determine the characteristic scales for these points using a saliency metric. Finally, some highly salient points are selected as keypoints. These points are invariant to scale and rotation. Experimental results show very satisfactory performance of the detector.

We present a novel diffractive optical element, the quantum dot array diffraction grating (QDADG), used in soft x-ray spectroscopy. Because of its sinusoidal transmission it effectively suppress higher order diffractions, which can improve the precision and SNR of soft x-ray spectroscopy in laser plasma diagnosis. There are, however, many difficulties in the fabrication of a soft x-ray spectroscopy QDADG because of its small dimensions and complex pattern. We propose a hybrid lithography to fabricate a QDADG, including electron-beam lithography and x-ray lithography. The diffraction property of the QDADG is also proved to be consistent with a theoretical prediction using experiments.

This paper presents a hybrid processor dedicated to the reconstruction algorithm in multislice spiral computed tomography. The described architecture focuses on the advanced single-slice rebinning algorithm, which is a basic 2-D-to-3-D rebinning method developed in 2000. The hybrid processor is composed of four cores (rebinning, filtering, backprojection, and interpolation), including an optical processor for the backprojection. The system is modeled with a multi-abstraction-level approach. The model permits one to evaluate the dependence of both the reconstruction quality and the computation time with different parameters (reconstruction parameters, device features, etc.). It is used in a substantial simulation process allowing the identification of predominant degradation sources and the evaluation of their impact, and leading to the specification of each subsystem. A prototype of each core has been realized. The optical core has been identified as the most critical element, although results are very encouraging. This study has underlined that a computational speedup of more than two orders of magnitude could be reached. This is expected to be very useful for future challenging applications in the field of image-guided computer-assisted surgery, where the reconstruction rate would become critical to ensuring acceptable responsiveness.