This PDF file contains the editorial “Of Macs and Maps” for OE Vol. 48 Issue 05

The template updating problem of Kernel-based tracking (KBT) includes two aspects: target-scale update and target-model update. The proposed algorithm can update both tracking window's scale and target model by making use of continuous adaptive distribution. The ability of KBT can be complemented within its own framework with modest computation cost. The proposed tracking algorithm tries to get a balance between the stability of KBT and adaptability of CAMSHIFT for creating a robust tracker.

A new method and algorithm for measuring optical linear birefringence is proposed. The method allows the measurement of both the principal axis orientation angle and the retardation simultaneously by a three-step measurement. The average absolute error of the retardation of an achromatic quarter-wave plate (QWP) is found to be better than 10^-4 parts of the wavelength over the whole spectrum, and its principal axis system orientation is determined with accuracy better than 0.18 deg. In comparison to other methods, the current technique holds several advantages: wavelength independence, low cost, compact setup, ease of alignment, use of a simple algorithm, no polarization reflectance dependence, and possesses high accuracy. The method was applied also to the measurement of an arbitrary retardation of a sapphire plate and to the assessment of the dynamic retardation of a liquid crystal device.

We present a new algorithm for camera calibration using two concentric circles, which is a linear approach. In the calibration, a pinhole camera model is used. Different from previous methods, we take the projective equations of 3-D circles, which include the intrinsic parameter matrix of the camera, as the basis of our calibration approach. According to the special structure of the projective equations in algebra, we can get a linear equation system about the intrinsic parameters. After enough equations are constructed, the calibration can be easily finished. With at least three images of the two concentric circles, all five intrinsic parameters can be recovered. Experiments using computer simulated data and real data demonstrate the robustness and accuracy of our method.

Many robotic and industrial systems require 3-D range-sensing capabilities for mapping, localization, navigation, and obstacle avoidance. Laser-scanning systems that mechanically trace a range-sensing beam over a raster or similar pattern can produce highly accurate models but tend to be bulky and slow when acquiring a significant field of view at useful resolutions. Stereo cameras can provide video-rate range images over significant fields of view but tend to have difficulty with scenes containing low or confusing textures. A new generation of active light, time-of-flight range sensors use a 2-D array of sensor elements to produce a 3-D range image at video rates. These sensors pose unique calibration challenges, requiring both the usual calibration of lens distortion (intrinsic calibration) and calibration of the time-of-flight range measurement (3-D calibration). We present our application of a photogrammetric calibration approach using inexpensive printed optical targets and off-the-shelf software to solve both intrinsic and range calibrations for the MESA Imaging SwissRanger SR-3100 range imaging sensor. Specific calibration issues stemming from this sensor's correlation of reflectivity with measured range are identified. We further present the integration of this otherwise grayscale 3-D sensor with an optical camera, providing a full-color, video-rate 3-D sensing solution.

A novel optical system that combines a polarimetric current sensor based on the Faraday effect, and a voltage sensor based on the Pockels effect, is described. The proposed device uses polarizers that possess high polarization ratios in specific spectral ranges. This allows the simultaneous codification of current and voltage information in different spectral regions, which, in turn, enables independent measurements of both magnitudes. Validation experiments are presented.

A dual-driving polymer Mach-Zehnder interferometer (MZI) electro-optic switch is designed and optimized, which consists of a phase-generating coupler (PGC) and a 3-dB directional coupler. Structural schematics and principles of the PGC and the switch are described. Novel formulas of the switching time are presented. Under the central operation wavelength of 1550 nm, simulation for the designed device shows that the push-pull switching voltage is 2.445 V, the switching time is 18.1 ps, and the cross talk is less than -30 dB. By optimizing the PGC structure, the phase error resulting from the wavelength shift can be compensated effectively, and a wide spectrum about 110 nm can be achieved. The proposed analytical technique on waveguides and electrodes proves to be accurate and computationally efficient when compared with the beam propagation method (BPM) and the experimental results.

Optical notch filtering is essential for many engineering applications. Optical resonant filters represent a useful alternative to achieve optical notch filtering. Designing these filters with optimal performance is significant because they can be a key component of important systems, such as optical communications, biophotonics applications, and optical sensors. The design is based on choosing the filter structural parameters optimally to achieve the best filtering properties, which are decided by the application. The filter parameters were chosen as the waveguide thickness and gratings depth. A new merit function was defined to measure the filtering properties and contained a degree of importance that ranges from zero to unity as an additional parameter in order to meet specifications. The optimization was realized systematically after simple parameters' decoupling, which was based on practical considerations. A numerical example was considered, and simulations with results were presented for complete clarification of the work. Optimizing the performance of optical resonant filters to meet the system specifications is significant and useful because it contribute to a wide range of applications that depend on optical notch filtering.

Optical filters employing acousto-optic polarized mode conversion techniques are implemented to demonstrate the filtering, selection, and switching of packets of wavelength multiplexed optical channels in LiNbO₃ diffused optical waveguides. Geometrically tilted and chirped digital electrodes of the metallic interdigital transducer are used to excite acoustic surface waves for phase matching of the optical transverse electric (TE) and transverse magnetic (TM) guided modes, hence optical field coupling and transfer and filtering. By simultaneous launching of acoustics waves, the selection of wavelength channels can be made. A tuning range of >250 nm and that of the passband from <1 nm to >150 nm can be achieved with selectivity of optical channels of different wavelengths.

We present the interesting results of a tunable multisoliton pulse system, wherein the large bandwidth signals of the spatial soliton pulses can be generated after propagating within the nonlinear ring resonator system. A soliton pulse input with 50-ns pulse width, 1-W peak power, and center wavelength at 1550 nm is propagated into the nonlinear ring resonator system. By using the appropriate parameters relating to the practical device such as micro ring radii, coupling coefficients, linear and nonlinear refractive index, we found that the multisoliton pulses obtained have shown the potential of application for dense wavelength division multiplexing (DWDM). Soliton pulse width and free spectrum range of 10 pm and 0.6 nm are obtained, respectively, which can be used to increase the channel capacity in soliton communication. Furthermore, the soliton power obtained is available for system and link redundancy, where the output soliton power of 10 W is achieved.

A new scheme of a control-beam-driven nonlinear optical loop mirror (NOLM) with a birefringent twisted fiber and a symmetrical coupler designed for optical time division demultiplexing (OTDM) is analyzed. The theoretical model of the proposed NOLM scheme considers the evolution of polarization states of data and control beams and the mutual interactions of the data and control beams due to the cross-phase modulation (XPM). Attention is given to the optical switching commanded by the control-beam power and by the manipulation of nonlinear polarization rotation of the data and control beam. The simulations of NOLM transmissions demonstrate that the cross talk between demultiplexed and nondemultiplexed beams as an important parameter for optical switching by the presented NOLM can be significantly reduced. The results show that the device can be of interest for all-optical signal manipulations in optical communication networks.

We show, theoretically, that the combination of super-Gaussian filters and nonlinear gains can greatly control the self-frequency shift in ultrashort optical pulse. Typical examples are given for stabilizing the propagation of ultrashort optical pulse over a long distance. In particular, by comparing to the Gaussian filters, super-Gaussian filter is more effective in overcoming self-frequency shift in the presence of nonlinear gains.

The impulse and step responses as well as the pulse responses of a quadratic phase medium, the single-mode optical fiber, are presented. Analytical expressions of the fiber impulse and step responses are obtained, indicating the change of the phase of the lightwave carrier. Both coherent and incoherent detection schemes under the amplitude shift keying and continuous phase frequency shift keying (CPFSK) incorporating the maximum likelihood sequence estimation are examined with respect to the uncertainty depending on the number of bits of the sequence. The detection uncertainty shows that the coherent detection offers a high degree of discrimination as compared to its incoherent counterpart, especially for the case of CPFSK. The frequency discrimination detection of the CP FSK is correlated with the bandwidth-bit period product, the product between filter bandwidth and the bit period. Resilience to dispersion of ±9520 ps/nm can be achieved due to this minute uncertainty of this detection scheme.

The influence of microbends on a phase shift and attenuation in a classical Corning SMF-28 fiber and in a special microstructured single-mode fiber with a limited number of air-hole rings in the cladding has been investigated. The largest measured phase shift of 750 deg/mm was obtained for the classical fiber at displacement magnitude of 117 μm. This corresponds to 1.3×10^-3 change in the effective refractive index of the fundamental LP₀₁ mode in a microbent optical fiber section with length of 24 mm. The phase shift for the investigated microstructured fibers is in 3.9 times less. The cutoff of radiation intensity takes place at displacement magnitudes of 55 and 270 μm for the microstructured fiber and for the SMF-28 fiber, respectively. It is shown that the sensitivity of the microstructured fiber to the displacement magnitude is in about five times higher than that of the Corning SMF-28 fiber.

We present a novel all-optical quaternary shift keying (4-ASK) modulation technique based on the cross-gain modulation in a semiconductor optical amplifier (SOA) of a modulated probe with moderate extinction ratio. Experimental demonstrations are presented for 20-Gb/s non return to zero (NRZ) and return to zero (RZ) 4-ASK signals with different level distributions and extinction ratios. The dispersion tolerance limitations are investigated. RZ 4-ASK signals show better dispersion robustness (with accumulated dispersion range from -240 to 350 ps/nm) than NRZ 4-ASK signals due to their reduced frequency chirp.

We investigate the computer-generated cylindrical rainbow hologram. Since the general flat format hologram has a limited viewable area, we usually cannot see the other side of the reconstructed object. There are some holograms to solve this problem. A cylindrical-type hologram is well known as the 360-deg viewable hologram. There are two kinds of cylindrical holograms, a multiplex hologram and a laser reconstruction 360-deg hologram. Since the multiplex hologram consists of many 2-D pictures, the reconstructed image is not truly 3-D. In contrast, a laser reconstruction 360-deg hologram has a true 3-D effect. However, since the spatial resolution of the output device is not enough and the calculation amount is huge, there are few reports on computer-generated cylindrical holograms. In our previous study, the computer-generated cylindrical hologram was realized as a Fresnel hologram. The calculation amount was too huge and took about 44 h in total calculation time, though we had used several PCs. We now propose the rainbow-type computer-generated cylindrical hologram. To decrease the calculation amount, the rainbow hologram sacrifices the vertical parallax. Also, this hologram can reconstruct an image with white light. Compared with the previous study of the Fresnel type, the calculation speed becomes 165 times faster. After calculation, we print this hologram with a fringe printer, and evaluate reconstructed images.

Based on a truncated ellipse Gaussian model for localized distortion in transmission-type optical antenna, the receiver power penalty due to localized wavefront deformation is researched. It is shown that the receiver power depends on distortion deepness h, radii a and b, and position d, and changes regularly with them. Localized distortion has the greatest influence on receiver power at a depth of h ≈ 1.45λ, which does not depend on other deformation parameters. The maxima of the receiver power penalty for different distortion radii are given. To reduce the impact of localized distortion on the receiver power, the machining precision of lenses should be better than 1.45λ. We hope the results can be used in the design of intersatellite laser communication systems.

Successful implementation of extreme ultraviolet (EUV) lithography depends on minimizing collector optics degradation from intense plasma erosion and debris deposition. Thus, studying the surface of collector optics and its reflectivity degradation processes and then implementing innovative methods to enhance the surface chemistry causing the collector optics to suffer less damage or to be self-healing is crucial for this technology development. A high-quality Mo-Au Gibbsian segregation (GS) alloy is fabricated on silicon using a DC dual-magnetron co-sputtering system, and the subsequent effectiveness is investigated as a result of surface removal, bulk erosion, surface roughness, and reflectivity degradation after exposure in an EUV source. A thin Au segregating layer is maintained through segregation during exposure, even though overall erosion in the Mo-Au film is taking place in the bulk. The reflective material, Mo, underneath the segregating layer is protected by this sacrificial layer, which is lost due to preferential sputtering. The experimental results are presented on the effectiveness of the GS alloys to be used as the potential EUV collector optics material by comparing to the pure Ru and Mo films. The effect of the surface removal rate on the GS performance is also investigated.

Template matching is the process of determining the presence and the location of a reference image or an object inside a scene image under analysis by a spatial cross-correlation. Conventional cross-correlation type algorithms are computationally expensive. Furthermore, when the object in the image is rotated, the conventional algorithms cannot be used for practical purposes. An algorithm for a rotation-invariant template matching with subpixel accuracy is proposed based on the combination of the correlation and Fourier-Mellin transformation when the fluctuating scope of the rotation angle is [-20 deg, 20 deg]. The algorithm consists of two stages. In the first stage, the matching candidates are selected using a computationally low-cost improved correlation algorithm. The operation of AND is adopted to reduce the computational cost for this stage. In the second stage, rotation invariant template matching is performed only on the matching candidates using the cross-correlation algorithm after adjusting image with a Fourier-Mellin invariant (FMI) descriptor, and the matching precision is subpixel by the novel method using the Fermat point. Experimental results show that the proposed method is very robust to Gaussian noise and rotation, and it also achieves high matching accuracy and matching precision.

An image authentication and tampering localization technique based on a wavelet-based digital watermarking procedure [Opt. Express 3(12), 491-496 (1998)] is proposed. To determine whether a given watermarked image has been tampered with or not, the similarity between the extracted and embedded watermarks is measured. If the similarity is less than a threshold value, the proposed sequential watermark alignment based on a coefficient stamping (SWACS) scheme is used to determine the modified wavelet coefficients corresponding to the tampered region. Then, the morphological region growing and subband duplication (MRGSD) scheme are used to include neighboring wavelet coefficients and then duplicate the wavelet coefficients in other subbands. The experimental results show that the proposed SWACS and MRGSD schemes can efficiently identify different types of image tampering. Moreover, the detection performance of the proposed system on various sizes of the watermark and tampered region is also evaluated.

The H.264/AVC baseline profile is used in many applications, including digital multimedia broadcasting, Internet protocol television, and storage devices, while the MPEG-2 main profile is widely used in applications, such as high-definition television and digital versatile disks. The MPEG-2 main profile supports B pictures for bidirectional motion prediction. Therefore, transcoding the MPEG-2 main profile to the H.264/AVC baseline is necessary for universal multimedia access. In the cascaded pixel domain transcoder architecture, the calculation of the rate distortion cost as part of the mode decision process in the H.264/AVC encoder requires extremely complex computations. To reduce the complexity inherent in the implementation of a real-time transcoder, we propose a fast mode decision algorithm based on complexity information from the reference region that is used for motion compensation. In this study, an adaptive mode decision process was used based on the modes assigned to the reference regions. Simulation results indicated that a significant reduction in complexity was achieved without significant degradation of video quality.

In this paper, QR bar code and image processing techniques are used to construct a nested steganography scheme. There are two types of secret data (lossless and lossy) embedded into a cover image. The lossless data is text that is first encoded by the QR barcode; its data does not have any distortion when comparing with the extracted data and original data. The lossy data is a kind of image; the face image is suitable for our case. Because the extracted text is lossless, the error correction rate of QR encoding must be carefully designed. We found a 25% error correction rate is suitable for our goal. In image embedding, because it can sustain minor perceptible distortion, we thus adopted the lower nibble byte discard of the face image to reduce the secret data. When the image is extracted, we use a median filter to filter out the noise and obtain a smoother image quality. After simulation, it is evident that our scheme is robust to JPEG attacks. Compared to other steganography schemes, our proposed method has three advantages: (i) the nested scheme is an enhanced security system never previously developed; (ii) our scheme can conceal lossless and lossy secret data into a cover image simultaneously; and (iii) the QR barcode used as secret data can widely extend this method's application fields.

The technique of securing information display first proposed by Yamamoto, Hayasaki, and Nishida [Opt. Lett. 28, 1564-1566 (2003)] aims at protecting the displayed information by using a decoding mask with a limited viewing zone. Their encoding approaches were inherited from visual cryptography. We study several variants of securing information display for multiple secrets. By exploiting some primitive and informative features of binary images (instead of inheriting from visual cryptography), we design novel schemes to resolve these new problems. Our schemes extend the studies of securing information display and enrich the feasibility and flexibility of their applications.

Invariants are widely used in object recognition due to their good performance under circumstances such as changing viewpoints. Previous methods of calculating invariants from 3-D points and lines have limited success because of computational expense or hard constraints on spatial positions. To overcome these drawbacks, analyses have first been carried out of general situations where the 3-D projective invariants of points and lines can be computed from images. Then numbers of images required under possible situations are determined. Based on the analyses, a novel mathematical model has been extracted to compute 3-D point and line invariants in general positions. The validity of the model has been verified by experiments, where the invariants derived from five points and one line have been adapted. Simulation results on real images show that the invariants remain stable and accurate.

In traditional facial feature localization methods with active shape models, the explicit intensity characteristic of facial features is hardly employed to represent the local structures around them, since these susceptible intensity features are difficult to be extracted. In this work, a novel method is proposed to extract the intensity features based on the logarithmic total variation model. A simple scheme of incorporating the intensity information into the local appearance model is also proposed to validate the effectiveness of the intensity features in the facial feature localization task. Facial feature localization tests are conducted on a wide range of datasets. Experimental results demonstrate the reliability of the proposed method and indicate its superior location accuracy compared to the state of the art method.

We introduce a new approach for 3-D shape recovery based on discrete wavelet transform (DWT) and principal component analysis (PCA). A small 3-D neighborhood is considered to incorporate the effect of pixels from previous as well as next frames. The intensity values of the pixels in the neighborhood are then arranged into a vector. DWT is applied on each vector to decompose it into approximation and wavelet coefficients. PCA is then applied on modified energies of wavelet components. The first feature in the eigenspace, as it contains maximum variation, is employed to compute the depth. The performance of the proposed approach is tested and is compared with existing methods by using synthetic and real image sequences. The evaluation is gauged on the basis of unimodality and monotonicity of the focus curve. Resolution, accuracy, root mean square error (RMSE), and correlation metrics have been applied to evaluate the performance. Experimental results and comparative analysis demonstrate the effectiveness of the proposed method.

We present a new member of the biometrics family-i.e., nose pores-which uses particularly interesting properties of nose pores as a basis for noninvasive biometric assessment. The pore distribution on the nose is stable and easily inspected. More important, nose pore distribution features are distinguishable between different persons. Thus, these features can be used for personal identification. However, little work has been done on nose pores as a biometric identifier. We have developed an end-to-end recognition system based on nose pore features. We also made use of a database of nose pore images obtained over a long period to examine the performance of nose pores as a biometric identifier. This research showed that the nose pore is a promising candidate for biometric identification and deserves further research. The experimental results based on the unique nose pores database demonstrated that nose pores can give an 88.07% correct recognition rate for biometric identification, which showed this biometric identifier's feasibility and effectiveness.

The anomalous spectral behaviors of a chirped Gaussian pulsed beam diffracted by an annular aperture in the turbulent atmosphere are studied. On the basis of the extended Huygens-Fresnel principle and by introducing a hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression for the spectral intensity of chirped Gaussian pulses diffracted by an annular aperture in the turbulent atmosphere is derived. The corresponding expressions for a circular aperture, a circular black screen, and the unapertured case are given as special cases of the general results. The relative spectral shift of diffracted chirped Gaussian pulses in the turbulent atmosphere versus the different values of the radius of the annular aperture and the different values of the position parameter are also studied and illustrated with numerical calculations. The results of this work have potential applications in information encoding and transmission in a turbulent atmosphere.

We present a new formulation of the finite element method (FEM) dedicated to the rigorous solution of Maxwell's equations and adapted to the calculation of the scalar diffracted field in optoelectronic subwavelength periodic structures [for both transverse electric (TE) and transverse magnetic (TM) polarization cases]. The advantage of this method is that its implementation remains independent of the number of layers in the structure, the number of diffractive patterns, the geometry of the diffractive object, and the properties of materials. The spectral response of large test photodiodes that can legitimately be represented in 2-D has been measured on a dedicated optical bench and compared to the theory. The validity of the model as well as the possibility of conceiving in this way simple processible diffractive spectral filters are discussed.