Approach to wavelet multiresolution analysis using Coiflets and a two-wave mixing arrangement

An approach to the wavelet multiresolution analysis is realized using Coiflet wavelets and a two-wave mixing arrangement via transmission gratings in a bismuth silicon oxide (BSO) crystal. A Coiflet filter acts not only as a band-pass filter but as a high-pass or low-pass filter. 2-D wavelet bases are generated by a tensorial product of the 1-D Coiflet bases and are separable in x and y. Therefore, the 1-D band-pass property produces direction ability in the 2-D tensorial products. In this way, unlike the Mexican hat-based filters, the Coiflet-based filters allow selecting horizontal, vertical or diagonals details of an original image. The decomposition of a signal in two levels of multiresolution is experimentally demonstrated in this scheme. The original image is discomposed in an average image and several detail images depending on the level of multiresolution. Coif12 wavelets are used to achieve the multiresolution analysis. The photorefractive implementation of the wavelet analysis is numerically simulated and experimentally performed. An agreement between numerical and experimental results is obtained.     

Multiple bistability in an optical fibre double-ring resonator by using degenerate two-wave mixing

A theoretical study is presented of multiple bistability in a single-mode optical fibre double-ring resonator using an all-fibre scheme involving degenerate two-wave mixing. Two successive bistable hysteresis loops (one is a normal type and another an inverting type) are formed in the input-output transmission curve. The dependence of the multiple bistability on major parameters of the fibres and the couplers is investigated.     

中皮秒二波耦合及其应用

本文报道在InP:Fe中皮秒二波耦合的实验研究.文中测量了瞬态二波耦合增益随泵浦光与探测光相对延迟时间改变而变化的曲线,分析了瞬态二波耦合中各种过程的特性,最后还利用皮秒二波耦合实现了低开启光强、高信噪比,透过率达17%的皮秒光开关.     

Remote photoacoustic imaging on solid material using a two-wave mixing interferometer

We report on remote and contactless photoacoustic imaging (PAI) for the inspection of solid materials using a two-wave mixing interferometer. In this Letter, a semitransparent sample was excited with picosecond laser pulses. The local absorption of the electromagnetic radiation led to generation of broadband ultrasonic waves inside the sample. Ultrasonic waves arriving at the sample surface were detected utilizing a two-wave mixing interferometer. After data acquisition, the initial pressure distribution was reconstructed using a Fourier space synthetic aperture technique algorithm. We show the potential of PAI for the inspection of semitransparent solid materials.     

Detection of small phase modulation using two-wave mixing in photorefractive crystals

Two-wave mixing of phase-modulated beams in photorefractive crystals under a dc electric field is studied both theoretically and experimentally. Based on the vectorial theory of light diffraction in crystals of cubic symmetry, we derived an analytical expression that describes the phase demodulation in crystals with an arbitrarily oriented electric field. The phase-demodulation technique was used for estimation of the space-charge field created in photorefractive crystals. It is shown that the space-charge-field grating created in GaP and Bi₁₂TiO₂₀ crystals is much smaller than that predicted from the one-level band-transport model of the photorefractive effect. Received: 12 December 2000 / Revised version: 8 February 2001 / Published online: 27 April 2001     

Fidelities of output coherent images produced by photorefractive two-wave mixing

We study theoretically the fidelities of output coherent images in incoherent-to-coherent conversion based on photorefractive two-wave mixing in the presence of an incoherent image-bearing beam. A vector version of the whole beam split step method is developed. The dependencies of the fidelities of output coherent images on geometric and physical parameters such as the incident direction of the beams, the intensity ratios between the beams, and coupling coefficients are investigated in detail. PACS 42.65.Hw     

Tomographic imaging by two-wave mixing with a wavelength-scanning laser diode

A method of tomographic imaging is proposed in which two-wave mixing in a photorefractive crystal is used with wavelength scanning of a laser diode and phase modulation of the pump beam. This method provides full optical processing and is effective for weak light from objects because of the use of two-wave mixing. The depth resolution of the method was ~1 cm when the wavelength-scanning width was ~0.02 nm .     

Signal-beam amplification by two-wave mixing in a liquid-crystal light valve

A new two-wave-mixing interaction with gain through a Bi(12)SiO(20) liquid-crystal light valve is presented. We show that the diffraction of a pump beam in the direction of a weak signal leads to a net amplification of the signal beam, with no need for a phase shift between the interference pattern and the induced index grating. A two-wave-mixing gain of 10 and a 150-ms response time are obtained with a 8.8-microm -thick liquid-crystal layer, a total intensity of the interacting beams of only 200 muW/cm(2), and an ac external voltage of +/-6 V . Image amplification is also demonstrated.     

光折变晶体LiNbO3：Fe简并两波混频在干涉测量中的应用

本文从理论上深入地分析光折变晶体中简并两波混频的动态特性。通过有关公式的推导,阐明动态两波混频在实时干涉测量中应用的原理。文中还提出利用LiNbO_3:Fe晶体的测量光路,给出其实测结果。并对测量精度作出分析。     

利用螺旋型波带片进行边缘增强成像

为了提高对等离子体内界面区域的诊断精度,研究了利用螺旋型波带片实现边缘增强成像的技术。制作了用于可见光波段的一阶螺旋型波带片,最外环宽度3μm。利用螺旋型波带片对振幅式物体进行了边缘增强成像,实验获得了成像物体内边界区域的清晰图像,界面区域的成像强度得到很大增强。通过实验测量发现,当物距在菲涅耳衍射区域内时,螺旋型波带片也能够获取较好的成像质量,表明螺旋型波带片具有较大的视场角,能够对大尺度物体进行边缘成像。基于螺旋型波带片的边缘增强成像可以弥补传统成像方式对界面区域成像的不足,提高对等离子体内界面区域的诊断能力。     

利用螺旋型波带片进行边缘增强成像

为了提高对等离子体内界面区域的诊断精度,研究了利用螺旋型波带片实现边缘增强成像的技术。制作了用于可见光波段的一阶螺旋型波带片,最外环宽度3 μm。利用螺旋型波带片对振幅式物体进行了边缘增强成像,实验获得了成像物体内边界区域的清晰图像,界面区域的成像强度得到很大增强。通过实验测量发现,当物距在菲涅耳衍射区域内时,螺旋型波带片也能够获取较好的成像质量,表明螺旋型波带片具有较大的视场角,能够对大尺度物体进行边缘成像。基于螺旋型波带片的边缘增强成像可以弥补传统成像方式对界面区域成像的不足,提高对等离子体内界面区域的诊断能力。     

New biochemical material laser emission in microdroplets using ribo-flavin and its enhancement by mixing highly scattering intralipid medium

New laser emission from a biochemical material, ribo-flavin (vitamin B₂), at 570 nm was observed for the first time in liquid microdroplets pumped at 475 nm using a pulsed optical parametric oscillator. Laser emission spectra from microdroplets containing ribo-flavin in water and glycerol solution exhibit periodic mode structures depending on the microdroplet diameter demonstrating the morphology-dependent resonances. Magnitude enhancement of lasing emission is confirmed experimentally from liquid microdroplets of ribo-flavin solution with appropriate mixture of the fat emulsion Intralipid-10% suspension as highly scattering medium. We believe that such biochemical-soft multiple light scatterer systems may allow a wide range lasing of other bio-materials and even lead to the discovery of some novel species as well as highly sensitive analysis and diagnosis for future applications.     

用计算全息（CGH）制作的楔环探测器（WRD）及其在模式识别中的应用

提出用计算机制全息图配合CCD器件制成具有楔环探测器功能的CGH/WRD系统.它将取样、探测功能相分离,充分利用CGH的灵活性,亦可适用于其他形状的探测.文中详述了系统的设计思想及实现方法并给出了其用于模式识别的实验结果.     

Hybrid pattern recognition using the Fraunhofer diffraction pattern

A hybrid pattern-recognition method is proposed. The Fraunhofer diffraction pattern of an object was obtained in a coherent optical system and then it was processed by a digital image-processing system. The shift- and rotation-invariant characteristic values of the diffraction pattern was calculated and the classification of the object was carried out by using those values. The proposed method was tested in a simple experimental system by using some components of an electromagnetic relay as the sample objects to be recognized.     

Giant momentary readout produced by switching electric fields during two-wave mixing in sillenites

We show theoretically and experimentally that switching an applied square-wave field produces strong and short pulses of the outgoing signal during two-wave mixing in sillenite crystals. These pulses originate from the strong effect of the field on the optical eigenmodes and can be used in new optical schemes based on time-separated recording and readout processes.     

Intensity dependence of the transient two-wave mixing by population grating in Er-doped fiber

Theoretical analysis of the transient two-wave mixing (TWM) of two continuous waves with rectangular phase modulation counter-propagating through the Er-doped optical fiber is presented. Approximate analytic solutions obtained for undepleted interacting waves of low power (neglecting large-scale saturation of the fiber optical absorption) and of high power (with significant spatially uniform large-scale absorption saturation) are complemented by numerical simulation for a broad region of the recording light power. The experimental dependence of the TWM efficiency on the recording power obtained for a single-mode fiber with ?640 ppm erbium concentration and with initial optical density ≈8.4 at λ = 1526 nm demonstrated the initial, growing and decaying parts predicted theoretically. The maximum experimentally observed relative TWM signal amplitude proved to be approximately 3 times lower than expected.     

Voltage reduction for photorefractive two-wave mixing in InP:Fe by optical gap control

We report a method to increase the photorefractive two-wave mixing gain coefficient in semiconductors by using additional incident laser radiation. Two auxiliary beams are used to optimize the spatial distribution of an applied electrical field via modulation of the photoconductivity of the sample. By applying a voltage of 3.5 kV on a 4.3 mm thick InP:Fe crystal we obtain a two-wave mixing gain of 9 cm^–1. This is about 50% larger than that obtained without auxiliary beams.     

彩色图像边缘检测及其在图像融合中的应用

提出了一种新的基于小波变换的彩色图像边缘检测方法,运用噪声和微弱边缘的识别以及动态双域值的选取,使得检测出来的边缘定位精度高,抑制噪声性能好。利用基于区域特征的信息融合策略,比较待融合图像的边缘点的值和区域能量特征值,选择特征突出者对应的原始图像区域组成融合结果。实验结果表明,该算法可以良好地保留两幅图像的细节信息,得到高质量的融合图像。