低对称性光子晶体超宽带全角自准直传输的机理研究

提出了一种低对称性椭圆介质柱二维光子晶体结构, 利用平面波展开法研究了该结构在第一布里渊区的能带特性. 讨论了全角自准直效应的物理机制及椭圆柱结构参数对其带宽的影响, 明确给出了自准直传播模式的存在判据. 研究发现, 自准直模式几乎覆盖了TE偏振的整个第四能带, 而且该能带面上存在两个横跨第一布里渊区的超宽平坦区域. 时域有限差分法模拟结果表明, 利用超宽平坦区域的特性, 可同时实现带宽达187 nm (以1550 nm为中心波长)、准直入射角度几乎覆盖0°–90°的宽带全角自准直光传输.     

Broadband large-angle self-collimation in two-dimensional silicon photonic crystal

We report a two-dimensional silicon photonic crystal structure that supports the self-collimation effect with large incident angles over a broad wavelength range. We theoretically and experimentally show the propagation light in the designed and fabricated structure without diffraction. Broadband large-angle self-collimation is observed in infrared wavelength.     

Mesoscopic self-collimation and slow light in all-positive index layered photonic crystals

We demonstrate a mesoscopic self-collimation effect in photonic crystal superlattices consisting of a periodic set of all-positive index 2D photonic crystal and homogeneous layers. We develop an electromagnetic theory showing that diffraction-free beams are observed when the curvature of the optical dispersion relation is properly compensated for. This approach allows us to combine slow-light regime together with self-collimation in photonic crystal superlattices presenting an extremely low filling ratio in air.     

Self-collimation and beam splitting in low-index photonic crystals

We study self-collimation and beam splitting in low-refractive-index photonic crystals created within chalcogenide glass. We propose a beam splitter structure that allows direct experimental verification of photonic-crystal effects at optical wavelengths in a straightforward and definitive manner. The beam splitter provides angular separation of 90° using a highly compact spatial footprint, thus delivering direct application in highly integrated photonic devices.     

Wavelength-division-multiplexing system with photonic crystal self-collimation and co-directional coupling effect

A wavelength-division-multiplexing system with high compactness and extremely simple structures is designed and analyzed theoretically for optical communication wavelengths. The structure consists of a self-collimation region, a coupler, a coupling section, and two arbitrarily bent periodic dielectric waveguides (PDWGs). Operation principle of the devices is based on self-collimation and directional coupling mechanism. The equal-frequency contours (EFCs) are nearly flat from 0.17–0.22 (2πc/a), thus the self-collimation region acts as a multiplexer. Operation principle of the demultiplexer is based on directional coupling in two parallel periodic dielectric waveguides. The device performances have been evaluated by the finite-difference time-domain simulations coupled with perfectly matched layer (PML) boundary conditions.     

Experimental demonstration of self-collimation inside a three-dimensional photonic crystal

We present our experimental demonstration of self-collimation inside a three-dimensional (3D) simple cubic photonic crystal at microwave frequencies. The photonic crystal was designed with unique dispersion property and fabricated by a high precision computer-controlled machine. The self-collimation modes were excited by a grounded waveguide feeding and detected by a scanning monopole. Self-collimation of electromagnetic waves in the 3D photonic crystal was demonstrated by measuring the 3D field distribution, which was shown as a narrow collimated beam inside the 3D photonic crystal but a diverged beam in the absence of the photonic crystal.     

一维金属-介质周期结构的自准直特性和亚波长成像

计算了一维金属-介质周期结构(1DMD)的色散曲线，利用传输矩阵法模拟了该结构对入射高斯光束的自准直作用，着重讨论了金属层吸收的影响；对该结构在半波长厚度时近场成像特性进行了分析，单光源的成像分辨率为λ/8，达到亚波长分辨效果；分辨率随着光源逐渐远离近场范围而降低. 双狭缝的成像模拟进一步验证了1DMD结构的近场亚波长成像能力，分辨率达到λ/3.     

高对称型声子晶体自准直弯曲及分束

基于二维六方晶格声子晶体的高对称性, 通过裁剪声子晶体模型, 实现声波自准直束60°和120°全反射弯曲, 证实点源声波的准直弯曲和亚波长成像. 在六方晶格声子晶体中引入线缺陷, 实现自准直束的60°和120°弯曲及分裂, 详细分析了缺陷尺寸对入射准直束的60°(或120°)弯曲声束与透射声束能量分配的影响. 本文的工作可以使基于自准直效应的应用更加灵活.     

Enhanced beaming of light from a photonic crystal waveguide via a self-collimation photonic crystal

A simple method to control the light transmission from a photonic crystal waveguide (PCW) is proposed. The self-collimation (SC) effect in PC is utilized to depress the diffractive behavior of the light beam emitting out from the PCW. The finite difference in time domain (FDTD) simulation results show that choosing appropriate self-collimation frequency and the space between the PCW and the SC-PC can achieve a very good collimating beam in the outgoing side.     

Application of self-collimated beams to realization of all optical photonic crystal encoder

In this paper a 4×2 optical encoder is proposed by employing the self-collimation effect in 2D photonic crystals. The total structure of the proposed device is a combination of so called “beam splitters” and “mirrors”. The simulation result indicates that, this design can operate as 4×2 optical encoder, the footprint of structure is about 69 µm×55 µm and response time is about 1.4 ps.     

Polarization insensitive self-collimation waveguide in square lattice annular photonic crystals

The frequency bands for self-collimation at both TE and TM polarizations in square lattice annular photonic crystals are studied systematically by plane-wave expansion and finite difference time domain methods. By increasing the inner ring radius or reducing the outer ring radius, the self-collimation band will be moved to a lower frequency. Compared with the TM modes, TE ones have different frequency sensitivities to both the inner ring radius and outer ring radius tuning. Using these features, a polarization insensitive self-collimation waveguide in a high dielectric contrast system with bandwidth up to 102.9 nm is demonstrated as an example of the implementation of photonic integration circuits.     

基于图像处理的光学谐振腔自准直研究方法

针对我国氧碘化学激光器输出能量不断提高的情况下,主要限制光束质量的因素之一是出光过程中的光腔失调,提出了一种基于图像处理的光学谐振腔自准直研究方法。该研究方法利用氦氖穿腔光通过凹腔镜中心孔,并在凸腔镜后方放置工业相机,在屏幕上方形成一个干涉同心圆环。通过借助OpenCV库中二值化、霍夫圆检测等图像处理的方法,获得干涉同心圆环的圆心坐标,再通过以圆心为中心将图像分成上下左右四个部分,通过判断这四部分亮点像素的数量差值来预估干涉同心圆环的偏移状态,进而获得空腔条件下光学谐振腔发生变化的理论判据。实验结果表明,该方法可以获得相当精准的光学谐振腔失调判据,其失调判据选取左右亮点像素差值30 000,上下亮点像素差值45 000,为今后失调判据与步进电机自动调腔的结合做好充足的准备。

     

Millimeter-scale self-collimation in planar photonic crystals fabricated by CMOS technology

We report self-collimating demonstration in planar photonic crystals (PhCs) fabricated in silicon-on-insulator (SOI) wafers using 0.18 μm silicon complementary metal oxide semiconductor (CMOS) techniques. This process is original in the context of self-collimating PhC. Emphasis was on demonstrating self-collimation effect through the use of standard CMOS equipment and process development of an optical test chip using a high-volume manufacturing facility. The PhC were designed on 230 nm-top-Si layer using a square lattice of air-holes with 270 nm in diameter. The lattice constant of the PhC was 380 nm. The 1 mm self-collimation was observed at the wavelengths of 1620 nm.     

Dispersion-based optical routing in photonic crystals

We present and experimentally validate self-collimation in planar photonic crystals as a new means of achieving structureless confinement of light in optical devices. We demonstrate the ability to arbitrarily route light by exploiting the dispersive characteristics of the photonic crystal. Propagation loss as low as 2.17 dB/mm is observed, and proposed applications of these devices are presented.     

Photonic drop splitters based on self-collimation ring resonators in a silicon photonic crystal

We report here 1 × 3 and 1 × 2 photonic drop splitters (PDSs) with different splitting ratios based on self-collimation ring resonators (SCRRs) in an air-hole silicon photonic crystal. An 1 × 3 PDS consists of four beam splitters and an 1 × 2 PDS consists of three beam splitters and one mirror. Light propagates in the PDSs employing self-collimation effect. The theoretical transmission spectra at different drop ports in PDSs were analyzed with the multiple-beam interference theory. Then they were investigated with the finite-difference time-domain (FDTD) simulation technique. The simulation results agree well with the theoretical prediction. For the drop wavelength 1550 nm, the free spectral range of the PDSs is about 29 nm, which almost covers the whole optical communication C-band window. Because of small dimensions, air-hole structure and whole-silicon material, the proposed PDSs hold great potentials for applications in photonic integrated circuits.     

波状结构二维光子晶体的自准直特性及亚波长成像的研究

利用平面波展开方法计算了波状结构二维光子晶体(2DPC)的等频面，对等频面内矩形轮廓的等频线进行研究，提出了波状结构2DPC的自准直特性，运用时域有限差分(FDTD)方法模拟了波状结构2DPC在不同入射角情况下对所入射高斯光束的自准直作用.将波状结构2DPC的自准直特性运用到近场亚波长成像，模拟了波状结构2DPC的自准直亚波长成像效果，单光源的成像分辨率达到0.28λ，且随着光源逐渐远离近场范围而降低. 关键词： 光子晶体 自准直 等频面 亚波长成像     

二维光子晶体中与电磁波偏振态无关的自准直

利用有限时域差分法(FDTD)进行数值模拟，在二维光子晶体中实现了电磁波两种偏振态的自准直——全光自准直(full-light-self-collimation).研究表明，通过对光子晶体的结构做适当的调整，可以在较宽频率范围内实现横电波(TE波)和横磁波(TM波)沿着相同方向传播，同时保持较强的能流强度.全光自准直可以显著提高光源利用率和光波导的传播效率，在高密度集成光路中有非常重要的用途. 关键词： 光子晶体 偏振 自准直     

Polarization Beam Splitter Based on Self-Collimation Effect in Two-Dimensional Photonics Crystal

A photonic crystal polarization beam splitter based on the self-collimation effect is proposed. By means of the plane wave expansion method and the finite-difference time-domain method, we analyse the splitting mechanism in two alternative ways： performing a band gap structure analysis and simulating the field distribution. The results indicate that two beams of different polarizations can be split with an extinction ratio of nearly 20 dB in a wavelength range of POnm. The splitter may have practical applications in integrated photonic circuits.     

A tunable power splitter based on modes coupling and self-collimation effect in two-dimensional photonic crystals

A tunable power splitter is proposed in a two-dimensional photonic crystal with a line defect composed of two rows rods, whose refractive index can be controlled artificially. This device is working at a self-collimation frequency. The finite difference time domain (FDTD) simulations show that the beam splitting ratio is a function of the refractive index of line defect. If the index varies from 3.0 to 3.5, the beam intensity of one output port decreases from 87.2% (normalized by the input beam) to 0 while the intensity of the other output port increases from 8.98% to 100% monotonically. The coupling between the self-collimation mode and the defect mode is used to explain the working mechanism.