Specification of spectral line shape and multiplex dispersion by self-imaging and moiré technique

Due to finite width of a spectral line, the visibility of the moiré fringes formed by a grating and the self-image of another similar grating reduces by the increase of the self-image order. This effect is exploited to specify the spectral line shape by evaluating the Fourier transform of a function related to the visibility. Even, by using in-expensive optics, the technique can provide the spectral line shapes of rather broad widths—of the order of nanometer and more—by precisions that are comparable by those obtained by expensive Fourier transform spectrometers.Besides, it is shown that by comparing the line shapes obtained with and without a dispersive medium between the gratings, one can specify the dispersion function of the medium in the wavelength range covered by the spectrum.     

Self-imaging with curved gratings

We analyze the near field behavior of binary amplitude gratings which present a curved profile. This configuration has an important application in rotary optical encoders. This kind of encoders is used to measure the angular displacement between two different parts of the devices. To our knowledge, its behavior in the near field has not been analyzed yet. We have found that Talbot effect is produced but the period of the self-images and Talbot distances change as we separate from the grating. We have fabricated a curved grating and have performed the experiment to corroborate the behavior theoretically found. This fact could be useful in systems that use Talbot effect to measure displacements, since the mechanical tolerances grow.     

基于全内反射光子晶体多模波导偏振无关型光分束器

研究了全内反射在光子晶体多模波导中的作用,利用常规的耦合模理论对对称入射时的多模干涉行为和自映射现象进行了讨论和分析.研究表明,输入光场依然能沿着多模导光区高效的传输,这种结构中的光场传输是由全内反射和布喇格反射的联合作用而决定的.设计了一种全内反射偏振无关型光分束器,这种分束器在集成光学中具有重大的潜在应用价值.     

自成像共焦腔相干合成空间滤波器设计

理论分析了利用自成像共焦腔实现激光列阵相干合成的物理模型,对自成像共焦腔的一维相干合成和二维相干合成进行了模拟仿真计算,得到腔内场的强度分布图样.在此基础上,研究了空间滤波器在相干合成中实现模式选择的机理,并讨论滤波器的设计对相干合成及模式选择的影响,分别对一维相干合成和二维相干合成的情况,仿真计算了输出功率与滤波器位置和宽度的关系,为实验提供了理论依据.     

Flexible coherent diffraction lithography by tunable phase arrays in lithium niobate crystals

Flexible coherent diffraction lithography is proposed and preliminarily tested by means of an optical phase mask. The phase mask consisted of a two-dimensional hexagonal lattice of reversed ferroelectric domains engineered in a z-cut lithium niobate substrate and was electro-optically tunable. Appropriate phase shift values across adjacent reversed domains were induced by the application of an external electric field along the z-axis of the crystal via transparent electrodes. Photolithographic exposures of the self-imaging near-field diffraction intensity patterns, at various planes corresponding to the Talbot distances, were performed by using different values of the driving electric field signal.     

Talbot experiment re-examined: demonstration of an achromatic and continuous self-imaging regime

In the original Talbot experiment, a grating made of thin slits was illuminated in polychromatic light. Reconstituting this simple experiment, we have observed that at a certain distance from the grating, achromatic lines are formed whose transverse-resolution remains unaffected over a wide propagation-distance range. To our knowledge, this phenomenon has never been reported before. A theoretical explanation of this achromatic and continuous self-imaging regime is given and experimental results are reported.     

Array illuminator based on self-imaging in white light

An array illuminator is a device/optical system that splits an incoming beam of light into an array of many light spots/beams. It is useful in logic systems and in optical digital computing or in switching systems to energize arrays of components such as logic gates, optically bistable devices and electro-optic modulators. Array illuminators working in white light are interesting because they do not suffer from coherent noise and yield better signal-to-noise ratio. We propose configurations for array illuminator based on Fresnel diffraction and working under white light illumination conditions. Performance evaluation of the illuminators is also undertaken and the results of investigation are reported.     

Selective modes excitation in multimode photonic crystal waveguides

We investigate modes excitation with the input field of different positions in two-dimensional multimode photonic crystal waveguides. Odd modes can be selectively excited by the input field of odd symmetry. The input field with different positions can excite different modes due to the field intensity distribution of modes. When the input field locates at the position of the zero field, intensity of waveguide modes is zero and the modes are not excited. The finite-difference time-domain method is used to obtain the excited field distributions.     

Experimental study of phase-locking of two photonic crystal fiber lasers

Two photonic crystal fiber (PCF) lasers are phase-locked by using self-imaging resonator techniques. Obvious and steady interference strips are observed even without using spatial filter in high power operation, which demonstrates the advantages of pure single-mode PCF lasers in coherent beam combining. The maximum coherent output power of 95.8 W is obtained with coupling efficiency of 90.2%.