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Abstract: A novel numerical simulation method for the shaping of an excimer laser beam by an acoustic grating is proposed. Partially coherent theory and extended Huygens–Fresnel principle are used to analyze the light intensity diffraction pattern. Fast Fourier transform function FFT in the Matlab is used to calculate the numerical integral, which makes the integral operation simple and efficient. It is shown by a numerical simulation that the output intensity distribution is closely related to the coherence width, Raman–Nath comprehensive parameter, diffraction distance and ultrasonic wave frequency. The simulation results show that a flat top beam can be obtained by controlling these parameters. On the other hand, the results are used as an effective analytic tool for the determination of the design parameters of acousto-optic modulator. [Copyright &y& Elsevier]

Abstract: An asymmetric cryptosystem is proposed in this paper for color image hiding and extracting using phase truncated fractional Fourier transforms (FrFTs) and phase retrieval iterative algorithm. The secret image are decomposed into R, G and B channels, and permuted by Arnold transforms (ARTs). The R channel is self-encoded in the manner that the other two channels are separated into three phase masks (PMs) as encryption keys in the following three phase truncated FrFT operations while phase keys for decryption are generated and retained. A phase retrieval iterative algorithm in fractional Fourier domain is employed to hide the self-encoded result in one color channel of host image. The phase keys for decryption are different from those for encryption, which indicates the asymmetry of the proposed method and higher security. Numerical simulations are given to show the validity and robustness of our system. [Copyright &y& Elsevier]

Abstract: In this paper, we present a spectral joint fractional Fourier transform correlation (SJFRTC) for detecting and identifying very small target with only a few pixels using reflectance spectral information in the hyperspectral imagery. In this technique, fractional correlation (FC) between input spectral signature and known reference spectral signature is performed digitally or optically. Binary differential technique is utilized to enhance the performance of the SJFRTC, resulting in delta-function-like correlation peaks without dc interference. Distinctive and distinguishable correlation performance is obtained using peak-to-clutter ratio (PCR) instead of absolute correlation peak value, which makes the proposed technique independent from the intensity variation of the spectral signature. Simulation results using real-life hyperspectral images show that the binary SJFRTC can detect both single or/and multiple targets successfully with excellent detection capability, as compared to the other traditional hyperspectral detection algorithms. [Copyright &y& Elsevier]

Abstract: A composite nonlinear correlation is proposed to perform invariant recognition for the input image with continuous-scale distortions. The proposed correlation can be considered as a summation of many composite wavelet matched filters. Every matched filter consists of a linear combination of binary slices that are generated from threshold decomposition of the training images, and an adaptive wavelet filter. The adaptive wavelet is optimized to produce the sparse image features. Computer simulations are carried out to prove the scale-invariance and noise robustness of the new scheme. [Copyright &y& Elsevier]

Abstract: A wavelet-based rotation invariant morphological correlation (WBRIMC) is proposed as a new architecture to improve the properties of the classical rotation invariant morphological correlation (RIMC). For the WBRIMC, the JPS of the RIMC is filtered by an appropriately dilated power spectrum function of wavelet. Simulation results confirm that the WBRIMC has higher discrimination capability with sharp and intense correlation signals, and is more tolerant to the salt-and-pepper noise and white additive Gaussian noise than is the Circular harmonic filter (CHF), the phase only CHF (POCHF) and the RIMC. [Copyright &y& Elsevier]

Abstract: A Laplace filtering based morphological correlation (LBMC) is proposed as a modified approach to improve the properties of the classical morphological correlation (MC). For the LBMC, power spectrum of Laplace operator is introduced to filter the joint power spectrum (JPS) of the MC before final inverse Fourier transform. Computer simulation results show that, as compared with the linear correlation (LC) and the conventional MC, LBMC provides better discrimination capability with sharp and unmistakable correlation signal and its performance metrics are more stable when input scene is corrupted by outlier noise (salt-and-pepper noise) and additive white Gaussian noise. Although the LBMC is not illumination invariant when multiplication illumination factor is larger than unity, considerable discrimination capability is still obtained. [ABSTRACT FROM AUTHOR]

Truly knitted textiles based supercapacitors (SCs) are receiving great attention owing to their inherent flexibility and electrochemical performance. Here, the one-pot knitted conductive 3D spacer fabric (3DSF) was, for the first time, used as the frame supporting the highly pseudocapacitive materials. MnO 2 and the electrochemically reduced graphene oxide (ErGO) are grown on the top and bottom layer of the 3DSF respectively, realizing a 3D all-textile asymmetric SC (3DAS) with a functional and structural integrity. Both water-proof and wear-resistant properties are readily rendered after encapsulating with the flexible multifunctional polyurethane (PU) film. A high specific capacitance of 1.02 F cm−2 (36.59 F g−1) is achieved at the current density of 7.5 mA cm−2 (0.275 A g−1), and the maximum areal energy density is nearly 1.02 mWh·cm−2 at a power density of 5.27 mW cm−2. The approach of coupling the advanced computerized technology with the chemical synthesis opens new avenues for the development of the truly flexible and wearable energy storage devices. Image 1 • One-step knitted conductive 3D spacer fabric fits the flexible supercapacitor. • Conductive nickel coated silver-plated nylon fibers serve as the current collector. • Manganese dioxide is electrodeposited on top layer as the positive electrode. • Reduced graphene oxide is electrodeposited on bottom layer as negative electrode. • PU film encapsulation enables the water proof and wear resistant properties. [ABSTRACT FROM AUTHOR]

Glare reduction is the focus of much attention in the field of optical engineering owing to its vital role in high-quality image acquisition in photoelectric visual inspection technology. Based on Fresnel reflection theory, we have derived a polarization factor related to the glare intensity distribution and have obtained theoretical results showing that the factor plays a leading role in reducing glare. Based on the image detection model, we have derived a displacement factor which determines the position and the size of the glare area, and have obtained theoretical results showing that the factor plays a supporting role in reducing glare. The image gray-scale transformation curve is obtained by sampling image data under the different polarization and positions. And these image data are measured from certain object in the equivalent environment while the different conditions. Then the theories above have been justified and the whole theory of the polarization-based glare elimination method has been interpreted completely via actual experiments in glare elimination. As a result, reducing the intensity contrast between the glare area and its neighboring area is proved to be the essence of glare elimination. Furthermore, the glare can be nearly eliminated perfectly by adjusting the polarization factor and the displacement factor. [ABSTRACT FROM AUTHOR]

Abstract: A diffractive polarizing beam splitter (PBS) of two-layer grating is described for operation in reflection. The novel PBS grating includes two dielectric layers and a metal slab on the substrate. The reflective efficiency is widely simulated and optimized by using rigorous coupled-wave analysis. With the optimized grating parameters, efficiency of 96.46% for TE polarization of the two-layer reflective PBS grating is much more than 88.52% of the single layer PBS grating and 93.07% of the sandwiched PBS grating. The analysis shows that efficiencies more than 90% can be achieved for 394nm spectral bandwidths within the incident wavelength range of 1480–1874nm, which are much broader than the bandwidths of 67nm spectral bandwidths of the reported single layer grating. The novel PBS for operation in reflection can have merits of high efficiency, broad bandwidth for incident wavelength range and high extinction ratio in the –1st order with wide angular range. [Copyright &y& Elsevier]

Abstract: We present an optical method for double image encryption by using linear exchanging operation and double random phase encoding (DRPE) in the gyrator transform (GT) domain. In the linear exchanging operation, two primitive images are linearly recombined via a random orthogonal transform matrix. The resultant blended images are employed to constitute a complex-valued image, which is then encoded into a noise-like encrypted image by a DRPE structure in the GT domain. One can recover the primitive images exactly with all decryption keys correctly applied, including the transform orders, the random phase masks and random angle function used for linear exchanging operation. Computer simulations have been given to demonstrate that the proposed scheme eliminates the difference in key spaces between the phase-based image and the amplitude-based image encountered in the previous schemes. Moreover, our scheme has considerably high security level and certain robustness against data loss and noise disturbance. [Copyright &y& Elsevier]

Abstract: We describe a novel reflective dual-function beam splitter by a deep-etched high-spatial-frequency metal-based sandwiched grating. For TE polarization, the presented grating can show high efficiency in the reflective −1st order. And for TM polarization, two-port output can be obtained with good uniformity in the reflective 0th and the −1st orders. Physical analysis of modal method and numerical calculation of rigorous coupled-wave analysis (RCWA) are utilized to optimize such a dual-function beam splitter grating. Grating duty cycle is chosen properly for the grating period by the effective indices difference of excited modes in the grating region based on modal method. And grating depth and covering layer thickness are optimized using simulation of RCWA. The presented dual-function beam splitter grating can have advantages of the special incident angle of 45°, high efficiency and uniformity, and wide incident angular bandwidth, which should be a useful element for various optical systems. [Copyright &y& Elsevier]

Abstract: We describe a novel reflection polarizing beam splitter (PBS) by a fused-silica metal-based sandwiched grating. The grating period is given with the incident Bragg angle of 45° for simple operation in practice. A special duty cycle of 0.22 is chosen according to the modal method by a two-beam interference of the excited modes in the grating region. And the grating depth and covering layer thickness are numerically optimized using rigorous coupled-wave analysis. The fabrication tolerance around the optimized grating parameters is discussed. Moreover, a more wide tolerance for etched depth is achieved for easy and mass production. The presented PBS of a fused-silica metal-based sandwiched grating can show high efficiency with wideband property for incident wavelength for TE polarization and very high extinction ratio with broad incident angular bandwidth in the –1st order. [Copyright &y& Elsevier]

Abstract: We describe a novel transmission grating with a connecting layer to achieve high efficiency diffraction with polarization-independence. The grating duty cycle and period are optimized by modal method. Accurate grating depth and connecting layer thickness are optimized using rigorous coupled-wave analysis. High efficiencies of 99.21% for TE polarization and 99.12% for TM polarization can be achieved with the optimized grating parameters. Furthermore, the grating with a connecting layer can show efficiencies larger than 97% for both TE and TM polarizations within the given range of grating depth and connecting layer thickness, which will be significant for practical applications of such a high-efficiency polarization-independent grating with a connecting layer. [Copyright &y& Elsevier]

Abstract: We describe a novel polarizing beam splitter (PBS) of transmission connecting-layer-based grating, which can show high efficiency for TE polarization in the −1st order and TM polarization in the 0th order. According to the modal method, grating duty cycle and period are prescribed to obtain high efficiency for TM polarization. Using the rigorous coupled-wave analysis, grating depth and thickness of the connecting layer are optimized to achieve high efficiency for TE polarization. The presented PBS has advantages of wideband properties for incident wavelength and angle. Most importantly, the efficiency is improved greatly for TE polarization compared with the reported PBS based on fused-silica grating. [Copyright &y& Elsevier]

Abstract: A shift- and scale-invariant version of morphological fringe-adjusted joint transform correlation (MFJTC) is proposed in this paper, which we call shift- and scale-invariant MFJTC (SIMFJTC). SIMFJTC is combination of MFJTC and conventional radial harmonic filter (RHF). Using computer simulation, we compare the output results of SIMFJTC with those of morphological radial harmonic correlation (MRHC) and SDF-based FPFJTC when input scene is corrupted by salt-and-pepper noise and cluttered background. Our results show that SIMFJTC has higher discriminability and displays better stability against salt-and-pepper noise and cluttered background. Moreover, scale-invariance of SIMFJTC is much stricter than MRHC and SDF-based FPFJTC. [Copyright &y& Elsevier]

A polarization-independent ultra-broadband T-type absorber with doped silicon in the terahertz band is proposed, which consists of T-shaped Si/SiO 2 arrays. The results show that the absorption is more than 95% at 1.0–5.3 THz. Such an absorber can have a center frequency and relative bandwidth ratio of 3.15 THz and 137%. In addition, the absorption of 90% can be achieved at 1.0–5.3 THz with the incident angle of 0–44°. The energy distribution of the electromagnetic field at the peak of the ultra-broadband absorber is clearly explained by finite element method. Furthermore, compared with the proposed reference planar absorber and the reported broadband absorber, the T-type absorber in this work has better absorption bandwidth, center frequency, and relative bandwidth ratio. The impedance of T-type terahertz absorber is demonstrated well by impedance matching theory. It is believed that the ultra-wideband terahertz absorber with silicon doped based on periodic T-shaped arrays has great potential in the wideband terahertz absorber field and can be applied in the biomedical field. [ABSTRACT FROM AUTHOR]

An enhanced newly high-efficiency dual-function beam splitter of the grating is described in this paper. The proposed grating can realize newly dual-function at infrared wavelength under second Bragg incidence, which can function as high-efficiency component for TE polarization. Moreover, under TM polarization, the grating is different from the other traditional dual-function grating, which can achieve a three-port output with high efficiency and good uniformity. By using the finite element method, an optimum grating structure can be presented with the efficiency of three diffraction orders (0th, −1st, −2nd) for TM polarization greater than 30%. As for TE polarization, the efficiency of −2nd order will be better than 95% with a wide bandwidth. Therefore, the proposed grating can be well applied in variety optical fields. [ABSTRACT FROM AUTHOR]

A polarization-selective beam splitter is presented based on a reflective surface-relief two-layer grating with a metal slab. The grating is composed of two dielectric layers and a metal slab on the substrate. For TE polarization, efficiencies of 97.58% can be diffracted into the reflective −1st order. For TM polarization, two-port output of 47.55% and 47.11% can be split into the 0th order and the −1st order, respectively. Such a polarization-selective beam splitter can be fulfilled by one grating in reflection. The grating depths of two layers are optimized by using rigorous coupled-wave analysis with the given duty cycle of 0.6 and period of 1100 nm. The performance for different incident conditions is investigated when the incident wavelength and angle deviate from the central wavelength and the Bragg angle, respectively. For TM polarization, good uniformity can still be achieved within the given incident wavelength and angle regions. For TE polarization, the reflective polarization-selective beam splitter can have merits of wideband for different incident wavelengths. [ABSTRACT FROM AUTHOR]

Abstract: A novel reflective two-layer grating is proposed to obtain broad incident wavelength and angular bandwidths with the polarization-independent property. Although the conventional reflective single-layer grating can diffract high efficiency into the—1st order based on the mixed metal dielectric structure, deviations of the incident wavelength and angle will introduce much influence on the efficiency. By the reflective two-layer grating, the incident bandwidth can be improved greatly with high efficiency. The reflective two-layer grating can diffract efficiencies more than 90% into the—1st order within the incident wavelength range of 1376–1675nm or the incident angular bandwidth of 33.05–51.21°. The presented reflective two-layer grating can have advantages of high efficiency and improved bandwidths. The given quite moderate fabrication tolerance should be significant for practical applications of such a reflective two-layer grating. [Copyright &y& Elsevier]

We developed an ultrabroadband two-layer hybrid grating for polarizer. The efficiencies and extinction ratios of the two-layer polarizer were characterized for different grating geometrical parameters including periods, duty cycles and dielectric layer thicknesses. In order to obtain the suitable grating geometric parameters, the diffraction was numerically simulated by using rigorous coupled-wave approach in the near infrared incident regions. Based on the simulation results, reflection efficiency of TE-polarized light and transmission efficiency of TM-polarized light more than 96 % can be obtained within the incident wavelength rang of 1220−1940 nm and incident angle range of 4.2–58.8°. Furthermore, the extinction ratio of the grating can reach 28.09 dB for the polarizer. [ABSTRACT FROM AUTHOR]

Embedded double-layer transmission grating beam splitter under the second Bragg incidence is presented in this paper. With a given duty cycle of 0.5 and a period of 940 nm, we use rigorous coupled-wave analysis method to investigate this beam splitter. The grating parameters are optimized for high-efficiency output. Each efficiency of the three orders under polarizations of TE and TM is close to 33.3 % respectively. Compared with the single-layer fused-silica grating, the three-port double-layer grating is flexible with complex structure and stable in performance. The field distribution modal method are given, which can well explain the propagation process and coupling mechanism. [ABSTRACT FROM AUTHOR]

• Efficiency of 97.04 % is diffracted in the -1st order for TE polarization. • Efficiencies of 49.64 %/49.80 % are split in two orders for TM polarization. • Performance of the novel grating is improved compared with surface-relief grating. The subwavelength three-layer embedded grating is described under Littrow mounting for dual-function splitting. At the incident 800 nm wavelength, diffraction efficiency of TE polarization is 97.04 % for the optimized profiles. For TM polarization, diffraction efficiencies corresponding to 49.64 % and 49.80 % are obtained in two ports. The diffraction efficiency of the new embedded grating is higher than that of the previously reported surface-relief three-layer grating-based dual-function splitting. Moreover, the new grating can exhibit large deviation using angle. [ABSTRACT FROM AUTHOR]