This PDF file contains the editorial “Keeping Up-to-Date” for OE Vol. 47 Issue 09

Building on the argument that the change of motion states attracts more attention than the motion itself, this letter develops a novel method for key-frame extraction based on motion acceleration vectors. Different from the traditional methods using maximal or minimal motion energy, the proposed method uses the change of motion states, in magnitude and phase, of the main moving objects as the metric for key-frame extraction. Experimental results show that although similar objective performance is achieved by using the proposed method to that achieved with a widely used method based on motion energy, the key frames extracted by the proposed method are more consistent with human perception.

We improve the beam uniformity passing through multimode fibers using piezoelectric-based spatial mode scrambling. Both fiber squeezing and stretching techniques are applied and compared. A more than sixfold difference in the power intensity crossing the output beam profile without mode scrambling can be reduced to a <10% variation. The efficiency of collecting useful optical power for detection is also significantly improved. Such modules can find various applications in medical imaging, disease diagnosis, and local area networks.

The aspheric reflecting surface types studied by L. Mertz for correcting certain aberrations of a spherical primary telescope mirror are examined and some properties of these surfaces are presented. For the one-surface aspheric that corrects spherical aberration of all orders, a sixth-order equation for the surface shape is derived. For the set of two aspheric surfaces correcting spherical aberration and coma of all orders, a set of differential equations has been developed to describe the surface shapes. The off-axis imaging performance is derived from the on-axis imaging properties and compared with ray-trace results.

The multidimensional merit function space of complex optical systems contains a large number of local minima. We illustrate a method to find new local minima by constructing saddle points, with examples of deep and extreme UV objectives. The central idea of the method is that, at certain positions in a system with N surfaces that is a local minimum, a thin meniscus lens or two mirror surfaces can be introduced to construct a system with N+2 surfaces that is a saddle point. When optimization rolls down on the two sides of the saddle point, two minima are obtained. Often one of these two minima can also be reached from several other saddle points constructed in the same way. With saddle-point construction we can obtain new design shapes from existing ones in a simple, efficient, and systematic manner that is suitable for complex designs such as those for lithographic objectives.

Optical designers often insert or split lenses in existing designs. Here, we apply in the design of objectives for deep and extreme UV lithography an alternative method for adding new components that consists of constructing saddle points in the optical merit function landscape and obtaining new local minima from them. The design examples show that this remarkably simple method can be easily integrated with traditional design techniques. The new method has significantly improved our design productivity in all cases in which we have applied it so far. High-quality designs of lithographic objectives are obtained with this method.

The design of an aperture for the generation of laser speckle with a flat power spectrum covering a wide band of the measurement spatial-frequency range is presented. This aperture allows for the measurement of modulation transfer function (MTF) from zero to twice the Nyquist frequency of a two-dimensional detector array. This design mitigates many of the measurement problems inherent in other aperture designs. The MTF measurement of a CCD detector array is used to demonstrate the measurement technique and illustrate the advantages of the new aperture design.

This paper describes a simple optical range detector in the time-of-flight (TOF) category using a cw laser diode emitting at 1.55 μm. The principle of operation combines TOF with frequency-modulated cw methods. The main originality of this method consists in measuring the time delay between two signals without using the time variable. The forward current of the laser diode is modulated by a low-frequency triangular signal. The emitted and received signals are compared, and the amplitude difference gives a readout signal whose peak-to-peak amplitude is proportional to the TOF. An application to optical fiber length measurement is given.

A detailed description of an optical polarimetric scatterometer, its capabilities, and special application are presented. This instrument measures the 4×4 Mueller matrix elements as well as bidirectional reflective distribution functions (scatter cross sections) for light that is scattered from a target. Incident polarized light at wavelengths λ=0.6328 and λ=1.06 μm can be directed toward the target in an arbitrary direction. The receiver can be located anywhere in the solid angle 4π. Backscatter measurements, most commonly used in remote sensing, can also be obtained. The scatterometer has been used to validate different analytical/numerical solutions to a broad class of electromagnetic scattering problems, in controlled laboratory experiments. The optical constants of liquids and solids can be determined by relating the Mueller matrix elements to the ellipsometric parameters. Recently, the relationships between the Mueller matrix elements and the parameters related to the optical activity have been derived. Thus, the scatterometer has the potential to detect, identify, and characterize optical rotation and circular dichroism of biological and chemical materials that possess chiral properties. These relationships are based on depolarization of waves reflected and transmitted through optically active media. Only the eight quasi off-diagonal elements of the Mueller matrix are sensitive to optical activity.

We performed some laboratory experiments to evaluate a television camera system for sensing oil slicks. This system captures the marked differences in intensity of sunlight reflected from the surface of the sea and from the slick. We also proposed a novel method to compensate for the wavelength dependence of sunlight and the quantum efficiency of the CCD arrays, which has been ignored up to now. During laboratory experiments, a glass plate coated with an Al₂O₃ film has been employed instead of a real slick. The experimental results showed that detection probability depends on the sample thickness and, greatly, on the angle of incidence.

A dual-wavelength narrow-linewidth laser system, with ultranarrow wavelength spacing, is proposed and demonstrated. The operation principle of the laser system is based on the pump-induced thermal effects of the Er-Yb-doped fiber distributed Bragg reflector (DBR) laser. We designed and constructed a common Er-Yb-doped DBR fiber laser with proper parameters. With the pump power of the DBR laser increasing, the Bragg wavelengths and the bandwidths of the two gratings will change unequally. When the laser is pumped with 45 mW, we obtain stable dual-wavelength lasing with a 3-dB bandwidth of ≈0.014 nm and a wavelength spacing of ≈0.055 nm.

In this study, we described the scanning area limitation (SAL) speciality in laser flying marking and defined maximum markable time and maximum marking offset (MMO) for analyzing the effect of SAL on flying marking process. We presented maximum flying velocity (MFV) to evaluate the performance of a laser marking system and investigate the factors, including the the length of marking graphics in the moving direction and the marking order of graphics objects, which will impact the maximum flying velocity very much. Transverse and vertical directions of graphics entering into the scanning area and three object scanning path algorithms, the all-entered-marking, first-entering-first-marking (FEFM), and rowed-FEFM were analyzed and compared, and MMO and MFV were calculated using these algorithms. Experimental MFV results with different algorithms satisfied theoretical calculations very well, and it was shown that there is a best MFV performance when using the FEFM scanning path algorithm in the transverse moving direction.

Using the amplified spontaneous emission (ASE) from an erbium-doped fiber amplifier (EDFA) at zero signal condition, the shifting of resonant wavelengths in a mechanically induced long-period fiber grating (MLPFG), resulting from the intensity induced effects is demonstrated. The theoretical and experimental investigations on the ASE-induced effects in an MLPFG are presented. The developed theory is concise and is useful for differentiating the index changes due to Kerr and other intensity-dependent effects in a long-period fiber grating (LPFG). It is demonstrated that the induced index will be high for the LP₁₁ resonance near the third telecommunication window and is negligible for the LP₁₂ resonance. Because of the increase in microbend loss at each groove of the MLPFG, the thermally induced nonlinear effects lessen at higher values of applied pressures

A novel system for liquid-level detection is reported. The system uses two different wavelengths of light to detect the liquid level of medical samples in tubes that are covered by an unknown number of paper labels. By measuring the intensity of the transmitted light at two distinct wavelengths and computing their ratio, which is compared to a threshold value, a system was developed that is self-compensating for the number of tube labels and the type of medical sample to be analyzed. A laboratory prototype was built, and the test results were analyzed using different types of medical samples. Based on a series of experiments, the system was found to detect the liquid level of 0.4 mL with a maximum allowable tolerance of ±0.1 mL with better than 99.73% reliability and a total test time of 0.5 s. These results were achieved with test tubes that had up to six layers of labels attached to the outside of the tube, thereby making the tube completely opaque.

An analytical expression for the bandwidth of the reflection peak of a uniformly sampled fiber Bragg grating is achieved for the first time by expanding the index modulation into Fourier orders. The equivalent ac index change and duty cycle here are the two critical factors in determining the accuracy. The expression also well explains the asymmetric distribution of the reflective spectrum. Simulation results based on the transfer-matrix method agree well with the calculations.

We design a high-speed tunable electro-optical (EO) polymer-clad silicon over insulator (SOI) racetrack resonator with a 80-μm length and 5-µm radius that exhibits a switching speed of 100 GHz, a tuning voltage of 6.81 V, and an extinction ratio of 109.55 dB. This work employs high electro-optical coefficient polymers (r₃₃=1000 pm/V), which are currently under development, to implement very high speed switches.

We analyzed direct-sequence code-division multiple-access system using a successive interference cancellation (SIC) scheme. Modified prime-sequence codes are utilized as signature sequences, and the performance measure studied in this paper takes into account the the effect of imperfect interference cancellation. The basic principle of the SIC scheme is to subtract the strongest received signals from the original signal one by one till all users have been detected and demodulated. In this analysis we have compared optical code-division multiple-access systems with and without the cancellation scheme, and it is shown that the SIC scheme with −20-dBm effective power can suppress multiple-access interference better than the system without cancellation.

We propose and demonstrate a novel orthogonal optical labeling scheme based on 40-Gbit/s optical frequency-shift keying (FSK) payload and 2.5-Gbit/s intensity-modulated (IM) labeling. Using the technology of carrier-suppressed modulation and conversion of differential phase-shift keying to IM, only one light source is needed to generate the optical FSK signal. The system performance, including range of IM modulation depth, bit error ratio, and dispersion limitation, is carefully investigated by numerical simulation. With IM modulation depth of 0.4, the 40 Gbit/s FSK payload and 2.5-Gb/s IM label are transmitted over a 50-km standard single mode fiber (SMF) with 0.87 and 0.92 dB penalty and show immunity to input power range upto 11 and 15 dB, respectively. Optimal methods to improve the system performance are also proposed and discussed. After optimization, the IM modulation depth can be reduced to 0.2.

When bright moving objects are viewed with an electro-optical system at long range, they appear as small, slightly blurred moving points in the recorded image sequence. Typically, such point targets need to be detected in an early stage. However, in some scenarios the background of a scene may contain much structure, which makes it difficult to detect a point target. The novelty of this work is that superresolution reconstruction is used for suppression of the background. With superresolution reconstruction a high-resolution estimate of the background, without aliasing artifacts due to undersampling, is obtained. After applying a camera model and subtraction, this will result in difference images containing only the point target and temporal noise. In our experiments, based on realistic scenarios, the detection performance, after background suppression using superresolution reconstruction, is compared with the detection performance of a common background suppression method. It is shown that using the proposed method, for an equal detection-to-false-alarm ratio, the signal strength of a point target can be up to 4 times smaller. This implies that a point target can be detected at a longer range.

A new MPEG-2-to-H.264 video transcoding algorithm based on regions of interest (ROIs) is proposed. The whole transcoding scheme, including the ROI detection, is applied in the compressed domain to alleviate the computational load. The ROI detection uses the motion information from the partially decoded MPEG-2 bitstream. Then the ROIs that are likely to attract the viewer's attention are transcoded with drift compensation to provide better quality, while other regions are transcoded without drift compensation to save computational complexity. Experimental results show that our algorithm provides a better trade-off between computational complexity and picture quality. It achieves a speedup of 2 times over the closed-loop transcoding algorithm in the compressed domain, while giving comparable visual quality.

We propose a frame-rate conversion algorithm using hybrid-search-based motion estimation (ME) and adaptive motion-compensated interpolation (MCI). The ME method uses three search strategies: recursive search, three-step search with predictions, and single predicted search. One of them, which is best suited for the predicted motion type, is adaptively performed on a block basis. This adaptation process improves the accuracy of the estimated motion vectors without increasing the computational load. With the estimated motion vectors, the proposed MCI method reconstructs high-quality frames, without producing block artifacts, by considering multiple motion trajectories. The method utilizes pixel smoothness constraints besides motion-vector reliability when creating and combining the multiple motion-compensated results to remove block artifacts in regions with unreliable motion vectors. Experimental results show that the proposed ME method produces reliable motion vectors that are closer to true motions. Also, the proposed MCI method achieves better image quality than existing algorithms.

In flat-panel detector-based cone-beam computed-tomography breast imaging (CBCTBI) systems, scatter is an important factor that degrades image quality. It has been shown that despite the use of a large air gap, scatter still causes problems when imaging breast phantoms with our CBCTBI prototype. As a result, linear attenuation coefficient (LAC) distortion is obvious in the reconstruction; it appears as cupping artifacts and contrast loss. A simplified beam-stop array (BSA) algorithm is presented in this paper to solve this problem practically and efficiently. When the breast is positioned along the rotational axis, the scatter profiles from different views along a circular orbit are similar, and thus it is possible to use only one x-ray shot with the BSA in place for scatter pattern estimation, and this BSA image is used to generate a scatter pattern for all projections. The result of this scatter correction algorithm is compared with the reconstruction image over a small field of view, where scatter is assumed to be negligible, and the relative reconstruction error (RRE) is evaluated. The reconstruction is not sensitive to the estimation of scatter profile curvature, but is sensitive to the estimation of scatter intensity. It is shown as well that for any angular position where the BSA image is taken, the RRE is very small. The results show that the BSA algorithm works well for our CBCTBI prototype system with almost unchanged x-ray exposure.

Most previous spatial methods to deblur rotary motion blur raise an overregularization problem in the solution of deconvolution. We construct a frequency domain framework to formulate the rotary motion blur. The well-conditioned frequency components are protected so as to avoid the overregularization. Then, Wiener filtering is applied to yield the optimal estimation of original pixels under different noise levels. The identifications of rotary motion parameters are also presented. To detect the rotary center, we develop a zero-interval searching method that works on the degraded pixel spectrum. This method is robust to noise. For the blur angle, it is iteratively calibrated by a novel divide-and-conquer method, which possesses computational efficiency. Furthermore, this paper presents a shape-recognition and linear surface fitting method to interpolate missing pixels caused by circularly fetching. Experimental results illustrate the proposed algorithm outperforms spatial algorithms by up to 0.5–4 dB in the peak signal-to-noise ratio and the improvement of signal-to-noise ratio and prove the methods for missing pixel interpolation and parameter identifications effective.

We propose a framework for the stereoscopic visualization of urban environments. The framework uses occlusion and view-frustum culling (VFC) and utilizes graphics hardware to speed up the rendering process. The occlusion culling is based on a slice-wise storage scheme that represents buildings using axis-aligned slices. This provides a fast and a low-cost way to access the visible parts of the buildings. View-frustum culling for stereoscopic visualization is carried out once for both eyes by applying a transformation to the culling location. Rendering using graphics hardware is based on the slice-wise building representation. The representation facilitates fast access to data that are pushed into the graphics procesing unit (GPU) buffers. We present algorithms to access this GPU data. The stereoscopic visualization uses off-axis projection, which we found more suitable for the case of urban visualization. The framework is tested on large urban models containing 7.8 million and 23 million polygons. Performance experiments show that real-time stereoscopic visualization can be achieved for large models.

This paper proposes a novel shape descriptor, called the normalized weighted shape context (NWSC), for feature-based object matching. A shape context as a global characterization descriptor can represent the distribution of points in a set with scale and rotation invariance, but the current technology only provides invariance under translation, scale, and rotation transformations. This paper employs the inertia ellipse of a shape so that the proposed NWSC not only maintains good invariance under scale and rotation transformations but also obtains very robust and accurate matching results under affine transformations. Weights are assigned to each bin of the descriptor to measure its distinctiveness in the matching process. Moreover, a refining approach is proposed to eliminate mismatched features for self-calibration based on the NWSC. Practical experiments are carried out to evaluate its performance, and the results demonstrate that it significantly outperforms the standard shape context. The experiments show that the proposed approach enhances the matching accuracy to a great extent.

Iris recognition has received increasing attention in the field of biometrics due to its high performance in human identification. A challenge of iris recognition is to extract the small-size data with sufficient information from distinctive iris patterns. We propose a novel feature extraction algorithm for iris recognition, which utilizes a bank of Gabor filters and an effective encoding method. In image preprocessing, the lower portion of the iris is normalized and unwrapped into a rectangular block where the occluded area is masked out. Then multichannel Gabor filters are used to decompose the iris block. An iris code is generated by analyzing and encoding the horizontal variation of each filtered image. Finally, a feature selection scheme is adopted to remove redundant features to reduce the data size and improve the performance. Experimental results on public iris databases show that the proposed approach has a smaller code size and a lower equal error rate.

Structured-light illumination (SLI) means projecting a series of structured or striped patterns from a projector onto an object and then using a camera, placed at an angle from the projector, to record the target's 3-D shape. For multiplexing these structured patterns in time, traditional SLI systems require the target object to remain still during the scanning process. Thus, the technique of composite-pattern design was introduced as a means of combining multiple SLI patterns, using principles of frequency modulation, into a single pattern that can be continuously projected and from which 3-D surface can be reconstructed from a single image, thereby enabling the recording of 3-D video. But the associated process of modulation and demodulation is limited by the spatial bandwidth of the projector-camera pair, which introduces distortion near surface or albedo discontinuities. Therefore, this paper introduces a postprocessing step to refine the reconstructed depth surface. Simulated experiments show an 78% reduction in depth error.

We propose a novel optical pattern recognition system using multiple phase-shifted-reference fringe-adjusted joint transform correlation (MRFJTC) techniques. The MRFJTC algorithm can efficiently detect an object of interest in the input scene by producing a highly distinctive correlation peak while rejecting any and all nontarget objects in a complex background. The simple architecture of the proposed system can simultaneously recognize multiple targets of the reference class when present. The recognition performance is fast, automatic, and invariant to noise and distortions.

We present an efficient face tracking method that is robust, especially when the face is turned away from the frontal view to the side view (out-of-plane rotation). The proposed method, consisting of three steps, utilizes the horizontal and vertical projection histograms of a face region to model the visual appearance of the face. The vertical and horizontal positions of a face are sequentially determined. First, the horizontal projection histogram of each potential face region in the current frame near the corresponding face region in the previous frame is used as an input to a back-propagation neural network (BPNN) to reliably estimate the vertical position of the face, based on the observation that the distribution of the horizontal projection histogram of a face region is stable, even when the head is rotating about an axis parallel to the vertical axis of an image plane. Second, the vertical projection histogram of an eye region derived from the estimated vertical position of the face as well as output values from the BPNN is used to estimate the horizontal position of the face. Third, the detected face region is refined by head boundary detection. These three steps are repeatedly applied to track faces in each shot of an input video. Experimental results are provided to demonstrate the efficiency of the proposed method.

An optic-electronic hybrid certificate validation technique based on Fresnel encoding is proposed. A confirming experiment has been carried out. This technique consists of two processes: encoding and decoding. During the encoding process, an original image is encoded by a computer into an encoded image, which is subsequently printed on a certificate. During the decoding process, the encoded image is extracted from the certificate and decoded optically. The experimental result proves the validity and reveals some advantages of our method. Compared with some previous works, more useful original information can be encoded in our method. The security level of our method is also enhanced by importing the Fresnel diffraction range z as another key. This paper also explores practical application of this technique.