Tuneable edge enhancement filters for optical correlation

Difference of Gaussian (DOG) filters, a form of wavelet filter, are an extremely useful preprocessing tool for the enhancement of image edge data. The DOG filter is highly tuneable by control of the standard deviations of its constituent Gaussian distributions. These can be used in the frequency plane of optical correlators and implemented in the form of a static non-updateable filter. This article reports on a simple optical technique using photorefractive materials whereby a filter, updateable in real time and very similar to the DOG filter, is implemented by tuning the intensity of the hologram reference wave to give enhanced modulation in a selectable frequency band. This is called a tuneable photorefractive (TPR) filter. The results of the DOG and TPR filters are compared with those of the phase-only filter and classical matched spatial filter with respect to the criteria of signal-to-noise ratio, Horner efficiency and discrimination capability.     

Approximate bandpass and frequency response models of the difference of Gaussian filter

The Difference of Gaussian (DOG) filter is widely used in optics and image processing as, among other things, an edge detection and correlation filter. It has important biological applications and appears to be part of the mammalian vision system. In this paper we analyse the filter and provide details of the full width half maximum, bandwidth and frequency response in order to aid the full characterisation of its performance.     

Advanced glossmeters for industrial applications

In this paper, we present three new types of diffractive-optical-element (DOE)-based glossmeters (DOGs) that have been developed for both laboratory and online local specular gloss measurements of objects in industrial processes. The three are denoted as the handheld wireless glossmeter, μDOG two-dimensional (2D) and μDOG one-dimensional (1D), respectively. These glossmeters are designed to operate under conditions where gloss measurement with conventional glossmeters is impossible or difficult, or when fine structures of the gloss over a surface are an issue. Here, we show the applicability of the handheld glossmeter and μDOG 2D in the inspection of gloss from rough stainless steel plates finished by different machining methods. We also briefly introduce the concept of online gauge μDOG 1D for gloss assessment in industrial measurement environments.     

Wavelength-dependence of double optical gating for attosecond pulse generation

Both polarization gating （PG） and double optical gating （DOG） are productive methods to generate single attosecond （as） pulses. In this paper, considering the ground-state depletion effect, we investigate the wavelength-dependence of the DOG method in order to optimize the generation of single attosecond pulses for the future application. By calculating the ionization probabilities of the leading edge of the pulse at different driving laser wavelengths, we obtain the upper limit of duration for the driving laser pulse for the DOG setup. We find that the upper limit duration increases with the increase of laser wavelength. We further describe the technical method of choosing and calculating the thickness values of optical components for the DOG setup.     

用子波变换模拟视觉信息提取过程

利用逆变换研究了ＤＯＧ子波变换在提取输入信号时的特性，指出了尺度逐次变化的子波变换表现出的由粗到精的信息提取性质和局域特性与人类视觉系统对光学图像信息的提取过程的某些方面有相似性．本文认为ＤＯＧ于波变换将是研究人类视觉系统信息处理机制的重要工具．     

Inhomogeneous Double Optical Gating of High-Intensity Isolated Attosecond Pulse Generation in Crossed Metal Nanostructures

We propose and investigate an effective method for obtaining high-energy and high-intensity isolated attosecond pulses (IAPs) using the inhomogeneous double optical gating (DOG) technology in specifically designed metal nanostructures. First, using the homogeneous mid-infrared DOG technology modulated by a linearly near-infrared field, we obtain a harmonic yield of 2.5 orders of magnitudes higher than that from the single polarization gating (PG) technology. Further, introducing the crossed metal nanostructures along the driven and gating components, we can extend not only the harmonic cutoff but also enhance the harmonic yield attributed to the plasmonic field enhancement near the vicinity of metal nanostructures. As a result, we find a single harmonic plateau with smaller modulations. The supercontinuum is not very sensitive to the pulse duration of the near-infrared field, and the harmonic yields can be further enhanced with increase in the pulse intensity of the near-infrared field, showing a 108 eV supercontinuum with an intensity enhancement of 4 orders of magnitudes. Finally, by superposing the selected harmonics from the inhomogeneous DOG scheme, we obtain a 33 as SAP with an intensity increase of 4 orders of magnitudes.     

利用子波变换模拟人眼视觉信息提取过程的研究

由于人类视觉系统在对图象信息进行初级加工过程中表现出由粗到细且能使其局域化的特性,而子波变换恰恰正好具有这样的特性.本文提出了利用DOG函数作为子波基函数,模拟人眼视觉信息提取过程,并给出了两维模拟计算的结果.提出了基于子波变换理论的视觉信息提取通道模型.在文中讨论了这一模型的特点和潜在的应用前景.     

Studying the energy dependence of intrinsic conversion efficiency of single crystal scintillators under X-ray excitation

Single crystal scintilators are used in various radiation detectors applications. The efficiency of the crystal can be determined by the Detector Optical Gain (DOG) defined as the ratio of the emitted optical photon flux over the incident radiation photons flux. A parameter affecting DOG is the intrinsic conversion efficiency (n _C ) giving the percentage of the X-ray photon power converted to optical photon power. n _C is considered a constant value for X-ray energies in the order of keV although a non-proportional behavior has been reported. In this work an analytical model, has been utilized to single crystals scintillators GSO:Ce, LSO:Ce and LYSO:Ce to examine whether the intrinsic conversion efficiency shows non proportional behavior under X-ray excitation. DOG was theoretically calculated as a function of the incident X-ray spectrum, the X-ray absorption efficiency, the energy of the produced optical photons and the light transmission efficiency. The theoretical DOG values were compared with experimental data obtained by irradiating the crystals with X-rays at tube voltages from 50 to 140 kV and by measuring the light energy flux emitted from the irradiated screen. An initial value for n _C (calculated from literature data) was assumed for the X-ray tube voltage of 50 kV. For higher X-ray tube voltages the optical photon propagation phenomena was assumed constant and any deviations between experimental and theoretical data were associated with changes in the intrinsic conversion efficiency. The experimental errors were below 7% for each experimental setup. The behavior of n _C values for LSO:Ce and LYSO:Ce were found very similar, i.e., ranging with values from 0.089 at 50 kV to 0.015 at 140 kV, while for GSO:Ce, n _C demonstrated a peak at 80 kV.     

Jitter Characterization in Optical Preamplifier Direct Detection System

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激光溅射法在射频离子阱中产生和囚禁低能多电荷离子

Timing jitter performance in binary optical preamplifier direct detection system is investigated through both the analytical method and computer simulation method. The presented analytical method is based on the moment generating function (MGF) and has taken into account the influence of optical filter on the optical pulse shape. It can be used to optimize the timing jitter performance for linear clock extraction scheme for any type of optical filter and narrow bandpass electrical filter. The presented computer simulation method is capable of dealing with any nonlinear clock extraction scheme and also the impact of laser phase noise on timing jitter performance.     

Perceptual contrast enhancement with dynamic range adjustment

Recent years, although great efforts have been made to improve its performance, few Histogram equalization (HE) methods take human visual perception (HVP) into account explicitly. The human visual system (HVS) is more sensitive to edges than brightness. This paper proposes to take use of this nature intuitively and develops a perceptual contrast enhancement approach with dynamic range adjustment through histogram modification. The use of perceptual contrast connects the image enhancement problem with the HVS. To pre-condition the input image before the HE procedure is implemented, a perceptual contrast map (PCM) is constructed based on the modified Difference of Gaussian (DOG) algorithm. As a result, the contrast of the image is sharpened and high frequency noise is suppressed. A modified Clipped Histogram Equalization (CHE) is also developed which improves visual quality by automatically detecting the dynamic range of the image with improved perceptual contrast. Experimental results show that the new HE algorithm outperforms several state-of-the-art algorithms in improving perceptual contrast and enhancing details. In addition, the new algorithm is simple to implement, making it suitable for real-time applications.     

Denoising 3D MR images by the enhanced non-local means filter for Rician noise

The non-local means (NLM) filter removes noise by calculating the weighted average of the pixels in the global area and shows superiority over existing local filter methods that only consider local neighbor pixels. This filter has been successfully extended from 2D images to 3D images and has been applied to denoising 3D magnetic resonance (MR) images. In this article, a novel filter based on the NLM filter is proposed to improve the denoising effect. Considering the characteristics of Rician noise in the MR images, denoising by the NLM filter is first performed on the squared magnitude images. Then, unbiased correcting is carried out to eliminate the biased deviation. When performing the NLM filter, the weight is calculated based on the Gaussian-filtered image to reduce the disturbance of the noise. The performance of this filter is evaluated by carrying out a qualitative and quantitative comparison of this method with three other filters, namely, the original NLM filter, the unbiased NLM (UNLM) filter and the Rician NLM (RNLM) filter. Experimental results demonstrate that the proposed filter achieves better denoising performance over the other filters being compared.     

Design of a Label Recognition Filter for Crosstalk Suppression in a Label Recognition Unit using Optical Correlation Assuming the Assistance of Optical Time-Gating

To suppress crosstalk caused by matched filtering in label recognition based on optical correlation, we propose the novel design method of a label recognition filter to improve the discrimination performance. Assuming the assistance of optical time-gating, the label recognition filter is designed by a technique of a multiple-object discriminant filter (MODF) so that the crosstalk can be suppressed only at the center of correlation signals. This method can reduce the requirement for the performance of an optical thresholder. Simulation results show that the designed label recognition filter can successfully suppress the crosstalk.     

Impact of a Post-OTDM-Demultiplexing Optical Filter on Dense OOK OTDM-WDM Transmission

The impact of a post-OTDM-demultiplexing optical filter on the performance of dense on-off keying (OOK) optical time division multiplexing (OTDM)—wavelength division multiplexing (WDM) systems was studied. For return-to-zero (RZ) modulation, it was found that the additional filter working in a double-tier filter configuration did not offer any significant improvements to performance when the signal pulse width is optimized. Improvements generally increase only when the signal pulse width deviates from its optimal value and only for low spectral densities. For ideal non-return-to-zero (NRZ) modulation, however, significant improvements of around 1 dB are obtained using the double-tier configuration over a large range of spectral densities.     

Discrete continuous-phase superresolving filters

A new type of phase-only superresolving pupil filter with a discrete continuous-phase profile is presented that is a combination of discrete multilevel-phase modulation and continuous-phase modulation. This type of filter can achieve better superresolution performance than the continuous-phase filters reported in Opt. Lett. 28, 607 (2003). Therefore, with regard to the superresolution effect, this type of filter deserves study for practical applications. More importantly, the diffraction performance of this type of filter can explain the effect of a discrete-phase filter illuminated with a continuous wave front, whose superresolving performance cannot be analyzed with previous superresolution methods.     

Infrared dim and small target detecting and tracking method inspired by Human Visual System

Detecting and tracking dim and small target in infrared images and videos is one of the most important techniques in many computer vision applications, such as video surveillance and infrared imaging precise guidance. Recently, more and more algorithms based on Human Visual System (HVS) have been proposed to detect and track the infrared dim and small target. In general, HVS concerns at least three mechanisms including contrast mechanism, visual attention and eye movement. However, most of the existing algorithms simulate only a single one of the HVS mechanisms, resulting in many drawbacks of these algorithms. A novel method which combines the three mechanisms of HVS is proposed in this paper. First, a group of Difference of Gaussians (DOG) filters which simulate the contrast mechanism are used to filter the input image. Second, a visual attention, which is simulated by a Gaussian window, is added at a point near the target in order to further enhance the dim small target. This point is named as the attention point. Eventually, the Proportional-Integral-Derivative (PID) algorithm is first introduced to predict the attention point of the next frame of an image which simulates the eye movement of human being. Experimental results of infrared images with different types of backgrounds demonstrate the high efficiency and accuracy of the proposed method to detect and track the dim and small targets.     

Characterization of Fluorescence Induced by Side Illumination of Rhodamine B Doped Plastic Optical Fibers

The impact of a post-OTDM-demultiplexing optical filter on the performance of dense on-off keying (OOK) optical time division multiplexing (OTDM)—wavelength division multiplexing (WDM) systems was studied. For return-to-zero (RZ) modulation, it was found that the additional filter working in a double-tier filter configuration did not offer any significant improvements to performance when the signal pulse width is optimized. Improvements generally increase only when the signal pulse width deviates from its optimal value and only for low spectral densities. For ideal non-return-to-zero (NRZ) modulation, however, significant improvements of around 1 dB are obtained using the double-tier configuration over a large range of spectral densities.     

VHF波段超窄带超导滤波器的设计及其时域调谐

低频超窄带滤波器要求谐振器间的耦合极弱,设计受到薄膜面积限制,其性能对基片介电常数的均匀性极为敏感且受制作和封装精度的限制.这些因素将导致的滤波器中心频率偏移和带内性能恶化.对此,时域调谐提供了很好的解决途径.我们采用嵌套双螺旋型谐振器,在37mm×12mm的MgO基片上设计制作了4节超导滤波器,中心频率为166.9 MHz,相对带宽仅为0.29%.由于基片厚度或介电常数的偏差及不均匀性会导致滤波器中各谐振的谐振频率偏移,使通带性能受到很大影响.我们提出了将机械调谐与时域分析相结合的方法,通过机械调谐纠正各谐振器的谐振频率,改善滤波器性能.同时为了解决多信道滤波器系统中,各滤波器工作于同一温度下,系统频率一致性问题,通过时域调谐获得频率可调范围信息.对上述0.5 MHz带宽的VHF波段滤波器应用时域调谐方法,得到的可调范围为0.7 MHz,测试结果表明该滤波器具有优异性能,带内插损小于0.4 dB,反射损耗达到14.8 dB,带外抑制大于-70 dB.     

Design of sextuple-mode triple-ring HTS UWB filter using two-round interpolation

A single-stage ring resonator capable of introducing six modes within the ultra-wideband (UWB) passband is presented. The sextuple-mode resonator consists of three rings and three sets of stepped-impedance open stubs. Based on this sextuple-mode resonator, a UWB filter fed by the interdigital-coupling line (ICL) is designed. And we propose a two-round interpolation method to obtain the filter's initial dimensions. The designed filter is fabricated on a double-sided YBCO/MgO/YBCO high-temperature superconducting (HTS) thin film for demonstration. The experimental results show that this UWB filter produces eight resonances in the passband eventually, which effectively improves the in-band reflection and the band-edge steepness. Moreover, the upper stopband performance is enhanced due to the transmission zeros (TZs) generated by the stepped-impedance open stubs and the ICL structure. The measured good performance verifies the practicability of the two-round interpolation approach, which can also be extended to other odd-even-mode filter designs.     

S波段窄带带通体声波滤波器设计

针对无人机测控应用设计了一种S波段窄带带通体声波(BAW)滤波器,其技术指标为:中心频率2.46 GHz,带宽41 MHz,带内插损大于-3 dB,带内纹波小于1 dB,带外抑制小于-40 dB@2.385 GHz和2.506 GHz。采用Mason模型设计了BAW滤波器中各薄膜体声波谐振器(FBAR)的叠层结构;使用变迹法设计了各FBAR(电极)的形状;采用一种自行开发的自动布局方法得到紧凑的BAW滤波器布局;建立了BAW滤波器的声-电磁协同仿真模型,通过这种高保真的多物理场仿真方法对设计结果进行了性能验证。该设计流程是通用的,并且有两个特点:采用声-电磁协同仿真方法对设计阶段的BAW滤波器进行最终性能检验,可以及早发现并拒绝1D Mason模型过于乐观的设计;滤波器布局设计中采用了一种新的自动化布局方法,大大简化了在此阶段的反复尝试工作,也为声-电磁协同仿真模型输出了必需的面内结构信息。