用位相光栅进行图象相减

置一位相光栅于相干光学处理系统频谱平面,利用其零级与一级衍射光的相干迭加实现图象相减.通过控制光栅的位相调制量使零级与一级衍射光强相等,调节光栅位置获得π位相差.选择适当的光栅,还可同时得到图象的相加和相减信号.     

利用Mach-Zehnder干涉仪实现黑白图象密度假彩色编码

本文提出一种黑白图象密度但彩色编码的新方法。它必Mach-Zehnder干涉仪作为输入装置，并用两个光栅分别对位相型输入图象和参考白光束加必调制，然后在频率域施行小孔滤波，所获得的编码图象其颜色与密度的对应关系连续可调。     

位相调制图像密度假彩色编码的处理方法

介绍了位相调制图像密度假彩色编码的原理及实验方法，并就实验过程中应注意的一些问题作出了较详细的说明     

用傅科刀口实现位相物体的假彩色编码

本文提出了用傅科刀口法实现位相物体的假彩色化，对方法进行了理论分析，并给出了实现结果。此法与以往的假彩色编码方法相比，结构简单，操作方便，效果良好。     

组合屏大型电视图象显示器的数字系统

本文介绍了一种组合屏幕电视图象显示器(电视墙)的数字信号处理系统,并着重讨论了隔行扫描—逐行扫描的转换技术和行内插技术在系统中的应用。     

分形插值和分形图象压缩编码相结合进行图象数据压缩

本文首先研究了分形图象压缩编码和分形插值图象压缩方法。这两种方法在压缩比很高时图象效果均不是很理想,为此我们提出了综合利用分形插值和分形图象编码方法进行图象数据高效压缩的思想。实验结果验证了这种思想的正确性和可行性。新的方法在恢复图象信噪比为28.5dB时,压缩倍数可高达76倍,速度也大大提高。     

用维纳滤波改善零树编码图象的质量

基于零 树小波编码的图象在高压缩比时会产生振铃失真。本文分析了失真的原因,提出采用边沿增强与一维维纳滤波相结合的方法减少失真。实验结果表明,这种方法简单有效,能够提高图象的主观质量与客观指标ＰＳＮＲ。     

局域傅立叶变换实现三色光栅黑白编码图象的彩色恢复

本文提出一种从编码黑白胶片恢复真彩图象的数字局域解码技术和方法，首次实现了用计算机设备作编码片的解码。从离散数字抽样角度解释了黑白胶片光栅编码彩色图象记录技术，分析了光栅编码方法，根据局域变换思想建立起局域傅立叶变换带通滤波算子，实现从黑白编码胶片还原由Ｒ、Ｇ、Ｂ构成的原彩色像。该方法不需要傅里叶逆变换，只需一次傅里叶变换就可完成彩色恢复的任务。     

Ronchi光栅误差的数值仿真

为了解决光栅制造误差影响莫尔计量精度的问题,运用傅里叶光学理论和坐标变换方法给出了完整的莫尔条纹透光函数表达式,并用线性系统叠加理论对光栅误差函数进行模拟,再用得到的莫尔条纹模型对光栅误差进行仿真,获得了短周期误差和长周期误差的莫尔条纹波形,最后对误差仿真结果进行了分析和验证.结果表明,光栅短周期误差造成莫尔条纹信号波形出现高次谐波干扰,但数字滤波能有效消除其对计量精度的影响,而光栅长周期误差会严重影响光栅检测系统输出精度.     

Wavelength-switchable fiber ring laser using cascaded fiber Bragg gratings combined with amplitude modulator

The wavelength-switchable fiber laser has been studied in this paper. A wavelength-switchable erbium-doped fiber ring laser constructed using cascaded five fiber Bragg gratings (FBGs) incorporated with amplitude modulator is achieved and switching over 5 separate wavelengths has been demonstrated. The output power is about −4 dB m, the 3-dB linewidth is less than 0.02 nm, and the side mode suppression ratio is more than 45 dB. The transit process of the wavelength switching from one wavelength to another is studied and the lasing competition is also investigated.     

Gain-flattening filter using long-period fiber gratings

We propose a novel structure for a gain-flattening filter, in which a conventional long-period fiber grating (LPFG) and a phase-shifted LPFG are written closely. The transmission characteristics are investigated in the case of a closely arranged configuration. For the fabrication of a phase-shifted LPFG, a UV-trimming method to control the amount of the phase shift is examined theoretically and experimentally. Finally, a 67-mm-long LPFG gain-flattening filter designed for an erbium-doped fiber amplifier is fabricated and the measured spectrum is shown     

In-line polarimeter using blazed fiber gratings

We fabricate highly blazed, polarization-sensitive fiber grating taps and show how these may be used in combination with a UV-induced fiber waveplate to form a compact, in-fiber polarimeter. We show how the polarimeter may be employed as a feedback element to control polarization and use the feedback loop to demonstrate the stable, broadband (>70 nm) operation of the fiber polarimeter.     

Optical mode conversion using chirped gratings

A design is presented for a 3 dB TE0-TE1 optical waveguide mode convertor using a chirped grating. Devices were fabricated in Ti in-diffused lithium niobate by ion beam etching the grating pattern into the waveguide surface. TE0-TE1 mode coupling was observed experimentally with an insertion loss of 1.5 dB.     

In-fiber spectrometer using tilted fiber gratings

We demonstrate a compact in-fiber low-resolution spectrometer. Wavelength resolution of 7 nm was achieved using the core radiation-mode coupling of a tilted grating in an optical fiber with a photosensitive cladding. We applied the device to measure the powers of a multiwavelength Raman pump source.     

光栅大小对琅奇光栅泰伯效应的影响分析

基于菲涅耳衍射的传递函数理论推导了单色平面波入射有限尺寸琅奇光栅的菲涅耳衍射光强分布,分析了为获得泰伯像,光栅尺寸必须满足的关系式.仿真结果表明:光栅尺寸的大小影响泰伯像的形成,在一定衍射距离的观察区域内要获得泰伯像,光栅尺寸必须满足一定大小;光栅大小决定于衍射距离、观察区域大小和光栅周期等.光栅沿狭缝周期性变化方向尺寸的大小对泰伯像获取的影响较大:观察屏与光栅在泰伯距离上的偏移使衍射图像偏离泰伯像,但这种影响随着光栅常数的减小而减小.     

A STUDY ON THE PSEUDOCOLOR ENCODING DISPLAY OF SOUND HOLOSPECTROGRAM

In this paper, a new pseudocolor method to display sound holospectrogram is proposed and studied. On the picture of such a four-dimensional spectrogram, the horizontal axis refers to time, the vertical axis to frequency, the color to phase, and the brightness to magnitude. An example of display is given by employing the realized system.     

Compact all-fiber add-drop-multiplexer using fiber Bragg gratings

A novel compact all-single-mode fiber add-drop-multiplexer for dense wavelength-division-multiplexing systems is demonstrated. The device consists of a polished fiber coupler with identical Bragg gratings within the interactive length. The multiplexer operation has been theoretically analyzed and calculated transmission and reflection spectra are given. A fabricated prototype device shows good performance, but suffers from a high-insertion loss of 7 dB, which is due to the long but imperfect coupling region and can be drastically reduced in principle. A return loss >30 dB, coupling efficiency=99%, and bandwidth at FWHM /spl Delta//spl lambda/=1.2 mn was measured.     

Nonlinear pulse switching using long-period fiber gratings

We show that the intensity required to achieve all-optical switching in long-period fiber gratings can be reduced by orders of magnitude through the use of uniform phase-shifting regions between gratings. Predicted switching intensities are of the order 100 MW/cm² compared to 10 GW/cm² for normal device configuration