This PDF file contains the editorial “Thanks” for OE Vol. 48 Issue 12

An integrated pulse shaper for femtosecond pulses was built and characterized. It uses far-field grating diffraction to generate the spectrum of an input pulse in the Fourier plane. The implementation of the system we present uses the concept of planar integration of free-space optical systems with a folded optical axis. The system is dispersion-free. Optical path-length differences are compensated for by using two cascaded 4f-imaging and filtering setups in the optical design. Material dispersion is avoided, since the light propagates in air and all optical elements in the system are implemented as reflective microoptical devices. Lenses were designed as concave mirrors and fabricated by ultraprecision micromachining. We present results regarding the design of the pulse shaper and its fabrication.

Light-emitting diode (LED) MR16 lamps, regarded as one typical general lighting product of LEDs, are being widely used in many applications. Light efficiency into a main beam and uniformity are two key issues for high quality illumination of LED MR16 lamps. In this study, a practical and precise nonimaging optical design method is presented, and two novel 90- and 120-deg free-form lenses for high illumination quality LED MR16 lamps are designed according to this method. Based on the Monte-Carlo ray-tracing method, numerical simulation results demonstrate that the light output efficiencies of these novel lenses reach as high as 98% and are 17% higher than that of traditional total internal reflection (TIR) MR16 lens. Moreover, more than 89% of light exiting from the surfaces of these novel lenses irradiate within the desired receive target, while only 60% irradiate for traditional TIR lens. The uniformities of illuminance distribution across the target of these novel MR16 lamps also are much higher. In addition, these novel lenses are both quite compact and no more than 1/5 of that of the TIR lens. Therefore, these LED MR16 lamps integrated by novel lenses provide an effective solution to high quality illumination.

We explore the effect of separation between the faces of a corner-cube reflector on its performance. This is important because, in several retroreflector applications, one (or more) face of the module is some type of modulator. The fabrication and assembly of these modules invariably results in, or requires, gaps between the faces. A two-dimensional aperture optical model is developed to analyze the effect of this separation on performance. A geometric optics approach is used to evaluate the consequence of the separation on the effective retroreflection area. Diffraction effects are then included to provide a complete model of the corner cube retroreflector (CCR). The results show that the separation-to-face length ratio (δ/L) is an important parameter in maximizing performance of the retroreflector module. We show that an increasing δ/L results in a rapid reduction in the retroreflected power. A CCR illuminated along the body-center direction, which yields the highest effective area, sees a 58% reduction in retroreflected power when δ/L=0.2. Consequently, the field of view of the retroreflector reduces significantly. On the basis of this work, we propose that an effective triface retromodulator could be a GaAs-on-Si modulator grown on a silicon precision corner-cube array, thus filling the entire surface with active material.

We describe the fabrication and characterization of a compressive-sampling multispectral imaging (CS-MSI) system that uses single-pixel detectors to capture multiple spectral images concurrently, without mechanical scanning. In particular, we pay special attention to the hardware/software characterization of the CS-MSI system, wherein we discuss the optical realization of the proposed system, measure the effective sensitivity range, and investigate the relationship between the digital micromirror device frame rate and the reconstruction quality. We also compare the imaging performance of the Hadamard-pace variable-density sampling method, which is the CS method implemented with our hardware architecture, with the conventional random sampling method. We propose a compressive-sampling modulation transfer function (CS-MTF) to measure the amplitude response of different spatial frequencies by using different CS methods.

Specifications of phase error, peak to valley (PV), and root mean square (rms) are not able to represent the properties of a wavefront reasonably because of their irresponsibility for spatial frequencies. Power spectral density is a parameter that is especially effective to indicate the frequency regime. However, it seems not convenient for opticians to implement. Parameters of phase gradient, PV gradient, and rms gradient are most correlated with a point-spread function of an imaging system, and they can provide clear instruction of manufacture. The algorithms of gradient parameters have been modified in order to represent the image quality better. In order to demonstrate the analyses, an experimental spherical mirror has been worked out. It is clear that imaging performances can be maintained while manufacture difficulties are decreased when a reasonable trade-off between specifications of phase error and phase gradient is made.

We focus on the capability and theoretical limits of a model-based scatterometry method to determine overlay using a single two-dimensional array target. We use our modeling capability to design an optimized test target for scatterometer-based overlay measurements in a range of semiconductor films. We propose a methodology to measure the overlay using a single two-dimensional array target designed with intentional offsets, Δx and Δy, between the top and bottom grid arrays along the X and Y directions. This method allows extraction of the two-dimensional overlays from first diffraction order measurements through bi-azimuth angle analysis (0 and 90 deg with respect to the incidence plane), and includes a simple linear response algorithm. Two critical issues are taken into account: correlation of Δx and Δy and lithography process errors. We have simulated the diffraction signatures of a two-dimensional target with a pitch of 400 nm and linewidth of 100 nm, and optimized the overlay target design to maximize the measurement sensitivity and minimize the correlation of two axial measurements. We also investigate the influence of parameter variations on overlay measurement error

A liquid-filled diaphragm (LFD) lens system that uses image feedback for automatic focus control has been designed and developed. The edge slope width (ESW) of the pixel intensity profile across a binary target was selected as the focus measure parameter. An algorithm was developed to achieve single- and dual-direction autofocus control. An improved autofocus method, which is based on the error between the expected ESW value for a focused image and the ESW value for the current (unfocused) image, was introduced to improve the performance of the system. An empirical equation of the focus measure error was used to predict the number of autofocus operation steps required to approach a near-focus region. A stepper motor was used for actuating a syringe-driven pump mechanism that injects or withdraws fluid into (or out of) the fluid lens chamber. The lens diaphragm was made of polydimethylsiloxane (PDMS) polymer that covers the fluid chamber. A monochrome CCD camera was attached to the LFD lens to capture live images of the target. The autofocus experiments carried out using the new differential error-based algorithm proved the viability of the algorithm in determining the near-focus region. A maximum reduction of time operation was also recorded to be 40 s in comparison with the normal autofocus algorithm.

We describe a phase-stepping and subsequent phase-unwrapping technique with tricolor images for the analysis of isochromatics and isoclinics using arbitrary retarded retarders. A retarder used in the proposed method is not necessarily a quarter-wave plate specified for the wavelength of the light used. Not only the isochromatic and isoclinic parameters but also the retardation of the input and output retarders are determined simultaneously by the proposed phase-stepping method. Thus, any wavelength of visible light can be used in a single polariscope requiring matching the wavelength of the quarter-wave plate. Utilizing the characteristics of the proposed method, phase-unwrapping and ambiguity correction can be performed with phase maps obtained for three different wavelengths.

An automatic technique for the 3-D vision of the foot sole is presented. This technique is performed by means of laser metrology and approximation networks. To retrieve the topography, the foot sole is scanned by a laser line through a glass window. The contouring of the foot sole is based on the behavior of the laser line. This 3-D modeling is performed by an approximation network. The structure of this network is built based on the line shift that is generated due to surface variation and the camera position. Also, the intrinsic and extrinsic parameters of the vision system are computed based on the network. In this manner, online setup modifications can be performed. Thus, the external measurements are not passed to the vision system. In this manner, the accuracy and the performance are improved because physical measurements are avoided. The approach of this vision system is to fit the shoe sole mold to the foot sole via contour curves. The results are evaluated by means of a root mean square of error using references from a contact method. Thus, a contribution in computer vision is achieved for profitable shoe design. The processing time is also described.

We propose a fuzzy scheme strategy for the generation of the diffuser dot patterns in the light guide of an edge-lit backlight. The fuzzy scheme strategy is based on fuzzy logic and rules, which are closely related to the physical luminance properties of the light guide. During the process of generating diffuser dot patterns, two inputs are the dot radius and the distance from dots to a light source, and one output is the luminance of the light guide panel. This strategy converts the linguistic strategy based on expert knowledge the optimal dot-generation strategy. Furthermore, this study includes the discussion of fuzzification and defuzzification strategies, the derivation of fuzzy logic rules, and the analysis of fuzzy reasoning mechanisms. Experiment results reveal that the proposed strategy can achieve an even luminance condition by establishing dot patterns. Compared to conventional methods, the fuzzy scheme strategy has two advantages. It effectively integrates the dot generation scheme into the subsequent optical design phase to make dot patterns more efficient and easy to control. Moreover, optimized dot patterns realize sufficient luminance uniformity.

We present a very simple and straightforward approach for the generation of broadband radiation in the visible region covering 397 to 529 nm by taking advantage of the angular dispersion of the broadband (0.8- to 1.6-μm) idler radiation of a Ti:sapphire second-harmonic (i.e., 395 nm)-pumped type I noncollinear optical parametric amplifier (NOPA). Type I broadband sum-frequency mixing (SFM) between the Ti:sapphire laser fundamental radiation (790 nm) and the octave-spanned carrier-envelope-phase (CEP)-locked idler radiation from a broadband NOPA is considered for generation of broadband radiation in several relatively recently developed borate crystals. Moreover, it is also shown that by applying simple SFM, it is possible to obtain a very large bandwidth in a 5-μm-thick crystal without requiring any angularly dispersed input radiation. Furthermore it is found that the performance of the most recently developed KBe₂BO₃F₂ crystal is the best among all the available borate group crystals.

A detailed theoretical analysis of stability in a quantum dash distributed Bragg reflector (DBR) laser is presented under the small-signal condition. The influence of p-type doping and inhomogeneous line broadening on the hysteresis width of the quantum dash DBR laser is studied using a rate equation model that includes all of the multidiscrete energy levels in the valence and conduction bands. Our calculations show that a large hysteresis width is obtained by detuning the laser by ~10 meV above the ground state energy and doping the dashes by acceptor concentration N_A=3.7×10¹⁷ cm^-3. Also we find that a large self-pulsation frequency is obtained by detuning the laser by -15 meV from the ground state energy and doping the dashes by N_A=2.5×10¹⁷ cm^-3. The laser hysteresis width can be greatly reduced by doping the dashes with N_A>1×10¹⁸ cm^-3.

Postwelding shift (PWS) is the dominant barrier to having high packaging yields. Previous investigation revealed that the PWS in butterfly laser diode module packaging could be mitigated by properly choosing weld process parameters such as welding sequence, clip design, pulse shape, and so on. We study the effect of the distance between the front (first) and the rear (second) welding spots numerically by the finite element method with a more realistic physics-based laser welding model. A novel PWS online measurement system based on the ultra-high-precision laser displacement meter is established to experimentally validate the effect of welding spot distance. Results from both methods are compared. Finally, we show that the influence of welding spot distance can be used to compensate PWS to some extent, if a proper welding spot distance is employed.

Using star tracker to perform space surveillance is a focal point of research in aerospace engineering. However, autonomous attitude determination with star trackers in missions is a challenging task, because of spacecraft attitude dynamics and false stars. We present a novel star pattern recognition algorithm to resolve these problems. The algorithm defines a star pattern, called a flower code, composed of angular distances and circular angles. Then, a three-step strategy is adopted to find the correspondence of the sensor pattern and the catalog pattern, including initial lookup table match, cyclic dynamic match, and validation. A number of experiments are carried out on simulated and real star images. The simulation results show that the proposed method provides improved performance, especially on robustness against false stars. Also, the results for real star images demonstrate the reliability of the method for ground-based measurements.

A low-power 2×2 multimode interference-Mach Zehnder interferometer thermo-optic switch is proposed and fabricated using a cross-linkable negative photoresist as core material. The waveguide can be easily fabricated by direct ultraviolet photolithography and wet etching processes. The experiment results show that the switch has a low switching power of 6.9 mW and a switching time of 0.4 ms.

We demonstrate a compact trench-based silicon-on-insulator (SOI) rib waveguide ring resonator comprised of trench-based bends and splitters. It has a perimeter of 50 μm and occupies an area of only 25×25 μm. The measured free spectral range (FSR) is 13.2 nm, which the largest reported for an SOI rib waveguide ring resonator. The measured FSR, full width at half maximum, and quality factor match reasonably well with analytical calculations. Further calculation shows that a FSR of 50.8 nm is achievable for an SOI rib waveguide ring resonator with a perimeter of 15 μm.

Optical properties of transparent polymer thin films, produced by spin-coating on silicon and constituted of polycarbonate (PC), poly(methyl methacrylate) (PMMA), and PC/PMMA, were investigated with regard to integrated thermo-optical (TO) device applications. Refractive index dependences on wavelength, temperature, and film composition were measured by spectroscopic ellipsometry with a dedicated autocontrolled heater setup, in the ranges of 400 to 800 nm, 25 to 85 °C and 0 to 100 wt % PC, respectively, with determination of Cauchy and Lorentz-Lorenz parameters. Within these intervals, thermomechanical compatibility and pronounced index contrast of around 0.12 between PC and PMMA, as well as their TO coefficients one order of magnitude higher than that of silica, allow convenient tailoring for specific TO requirements. In addition, wide-range fine-tuning of refractive index variation is found to be facilitated by the weak dependence of isothermal dispersion curves and TO coefficients on film composition.

Laser communication systems are highly preferred for broadband applications. This technology uses higher regions of the spectrum, and offers unsurpassed throughput, information security, reduced weight and size of the components, and power savings. Unfortunately, small beam divergence requires precise positioning, which becomes very critical at high data rates. Complex motion patterns of the communicating platforms, vibrations, and atmospheric effects cause significant signal losses due to the pointing errors, beam wander, and other higher order effects. Mitigation of those effects is achieved by fast tracking, which can be successfully combined with signal modulation. In this work, we focus on the application of acousto-optic technology and its effect on communication performance. We present experimental results for a laser communication link affected by pointing distortions. These distortions are generated to emulate specific operation environments with particular spectral characteristics. The acousto-optic technology is used to build an agile tracking system combined with signal modulation in the same device to assure maximum signal reception, in spite of the harsh operational conditions. The received communication signal is recorded and statistically analyzed to calculate the bit error rates. This work presents synthesis of a tracking system and experimental results characterizing the communication performance under uncompensated pointing disturbance and with tracking.

For the multilink failure problem of wavelength division multiplexing (WDM) optical networks, we establish a reliability analysis model of shared-path protection strategy based on the Bayesian network and correlated link failure probability and analyze the reliability of light paths assigned by two shared-path protection algorithms. The new reliability model makes the reliability calculation of path subject to multilink failures possible, greatly simplifying the calculation of probabilistic reasoning. In addition, based on the new Bayesian network reliability analysis model, a novel differentiated shared-path protection (DSPP) algorithm is proposed to protect against multilink failures in WDM optical networks. Simulation experiments show that, compared with the two previous shared-path protection algorithms, the DSPP algorithm not only can satisfy the specific requirements of users but also has better survivability for multilink failures.

The Michelson interferometer-based interleaver is widely used in wavelength-division multiplexing (WDM) systems. A performance comparison for a 10-gigabit/s WDM system with a Michelson interferometer-based interleaver of different designs is presented. The trade-off between the designs that improve the passband bandwidth and reduce chromatic dispersion is discussed. It is concluded that a comprehensive design, including analysis at both the component and system levels, is necessary.

We present a simple technique to determine the design parameters of an optical interconnect system that uses integral planar lenses. The technique is based on the ABCD transformation matrix method. This analysis technique is significantly simpler and more efficient than the previously published methods for finding the design parameters and predicting the coupling efficiency of the system. The proposed method is applied to compute the coupling efficiency of single- and two-level optical systems.

A high-fidelity numerical model is developed for the incoherent electro-optical imaging process in media where the inherent optical properties vary with range. Four contributions to the image data are considered: laser light reflected from the scene, volume backscatter of laser light, reflected solar light, and solar backscatter. The model implements rigorous mathematical formulations, incorporates adaptive error control, uses computationally efficient algorithms, and has been rigorously validated. The model is flexible enough to handle many different sensor configurations and sampling techniques, continuous-wave and pulsed laser sources, and range-dependent properties of the optical environment. The derivation of relevant mathematical models is reviewed and unified into a comprehensive and flexible system that can be tailored to fit the various incoherent electro-optical imaging systems currently in use or in development. The numerical implementations are described for each key component of the overall model, and a sampling of new verification and validation results is provided.

To transmit secret application data securely, error resiliently, and synchronously is an issue of great concern. On the basis of image sharing with the use of the JPEG2000-generated bit stream of wavelet transform coefficients and the modified Shamir's threshold scheme over a Galois field, we present a new method for image transmission. The scheme takes advantage of JPEG2000's features of having no error propagation and generating a compact and progressive bit stream. In addition, the algorithm embeds error control codes and synchronization marks into the generated shadow images. As a result, it is secure and error resilient and gives small shadow images and excellent rate-distortion performance for real-time progressive transmission and reconstruction over noisy channels. Experimental results demonstrated promising performance of the proposed method.

A fast coeff_token decoding method based on new memory architecture is proposed to implement an efficient context-based adaptive variable length-coding (CAVLC) decoder. The heavy memory access needed in CAVLC decoding is a significant issue in designing a real system, such as digital multimedia broadcasting players, portable media players, and mobile phones with video, because it results in high power consumption and delay in operations. Recently, a new coeff_token variable-length decoding method has been suggested to achieve memory access reduction. However, it still requires a large portion of the total memory access in CAVLC decoding. In this work, an effective memory architecture is designed through careful examination of codewords in variable-length code tables. In addition, a novel fast decoding method is proposed to further reduce the memory accesses required for reconstructing the coeff_token element. Only one memory access is used for reconstructing each coeff_token element in the proposed method.

DNA microarray image processing has vast potential in the measurement of mass gene expression. A common approach to processing microarrays consists of spot identification, spot segmentation, and information extraction. We are concerned with spot identification. We aim to tackle the problem of identifying spots in rotated and skewed arrays via an automated process. The method proposed is composed of three steps, namely, array orientation calculation based on the Hough transform, affine calculation and correction, and gridding. The method is able to correctly identify spots in a microarray that has been rotated or skewed at an angle between 0 and ±30 deg and corrupted by various types of noise such as high-intensity streaks, Gaussian noise, and salt-and-pepper noise.

A framework is suggested to segment the foreground in image sequences using background subtraction based on the reconstructed background image for each frame. First, the consecutive frames are taken as inputs for a motion estimation algorithm to calculate the motion vector between frames. Second, an incomplete background image can be achieved by cutting moving parts from origin images. Then, all the incomplete background images from the same sequence can be used to model the background by probabilistic principle component analysis with missing data. The background image can be estimated for each frame. Finally, a simple background subtraction can segment the foreground. The effectiveness of our method is demonstrated in different illumination conditions and compared to the commonly used Gaussian mixture models method.

We present an adaptive algorithm that finds the best block-matching results in a computationally constrained and varied environment. The conventional diamond search algorithm, though faster than most known algorithms, is not very robust for sequences with scene variations or significant global motion. To solve this issue, rather than only using one fast motion estimation algorithm, we devise a more adaptive selection of fast motion estimation algorithms. Our adaptive selection approach for fast block search (ASFBS) algorithm uses a diamond search and two new subalgorithms: a cross-three-step search algorithm for large moving images and an advanced cross-diamond search algorithm for small moving images. The proposed ASFBS adapts based on the length of the motion vector, the number of search points, and the matching criteria of the neighboring block. Experimental results show that ASFBS is much more robust; it is faster than other popular fast block-matching algorithms, with smaller distortions.

The vision-based vehicle detection in front of an ego-vehicle is regarded as promising for driver assistance as well as for autonomous vehicle guidance. The feasibility of vehicle detection in a passenger car requires accurate and robust sensing performance. A multivehicle detection system based on stereo vision has been developed for better accuracy and robustness. This system utilizes morphological filter, feature detector, template matching, and epipolar constraint techniques in order to detect the corresponding pairs of vehicles. After the initial detection, the system executes the tracking algorithm for the vehicles. The proposed system can detect front vehicles such as the leading vehicle and side-lane vehicles. The position parameters of the vehicles located in front are obtained based on the detection information. The proposed vehicle detection system is implemented on a passenger car, and its performance is verified experimentally.

Gaze-tracking technology is used to obtain the position of a user's viewpoint and a new gaze-tracking method is proposed based on a wearable goggle-type device, which includes an eye-tracking camera and a frontal viewing camera. The proposed method is novel in five ways compared to previous research. First, it can track the user's gazing position, allowing for the natural facial and eye movements by using frontal viewing and an eye-tracking camera. Second, an eye gaze position is calculated using a geometric transform, based on the mapping function among three rectangular regions. These are a rectangular region defined by the four pupil centers detected when a user gazes at the four corners of a monitor, a distorted monitor region observed by the frontal viewing camera, and an actual monitor region, respectively. Third, a facial gaze position is estimated based on the geometric center and the four internal angles of the monitor region detected by the frontal viewing camera. Fourth, a final gaze position is obtained by using the weighted summation of the eye and the facial gazing positions. Fifth, since a simple 2-D method is used to obtain the gazing position instead of a complicated 3-D method, the proposed method can be operated at real-time speeds. Experimental results show that the root mean square (rms) error of gaze estimation is less than 1 deg.

We propose an adaptive optics system for a lightweight remote sensing sensor. The phase diversity (PD) technique, in which known wavefronts (phase diversity) are applied to the optics and the inherent aberrations are estimated using the acquired images without a priori information, is a key to realizing the system. For the reduction of computing cost and the enhancement of the estimation accuracy of aberration, a spatial light modulator (SLM) is adopted not only for the wavefront compensator but also for the PD generator. The SLM produces arbitrary "aberration modes" that are each represented by a Zernike polynomial. Therefore, optimal phase diversities are applied to the optical system and particular modes are effectively obtained, which makes it possible to overcome the conventional PD generated by defocusing that describes only the quadratic form and lacks information of a particular mode. To solve the complex inverse problem of phase diversity with low computing cost, a general regression neural network (GRNN) is used. Moreover, principal component analysis compresses the input data for GRNN by extracting information from collected images in Fourier space, and reduces computation cost considerably without degrading estimation accuracy. The mathematical model is implemented and its performance is validated by numerical simulation.

This PDF file contains the errata for “OE Vol. 48 Issue 12 Paper OE ERR-DEC2009-1” for OE Vol. 48 Issue 12