Elimination of cross talk in waveguide intersections

We present general criteria for crossing perpendicular waveguides with nearly 100% throughput and 0% cross talk. Our design applies even when the waveguide width is of the order of the wavelength. The theoretical basis for this phenomenon is explained in terms of symmetry considerations and resonant tunneling and is then illustrated with numerical simulations for both a two-dimensional photonic crystal and a conventional high-index-contrast waveguide crossing. Cross-talk reduction by up to 8 orders of magnitude is achieved relative to unmodified crossings.     

Broadband and lossless lithium niobate valley photonic crystal waveguide

We investigate the influences of structure parameters and interface shapes on the bandwidth of the edge state of lithium niobate valley photonic crystals.By inc...     

Broadband super-collimation with low-symmetric photonic crystal

We investigate dispersive properties of two dimensional photonic crystal (PC) called star-shaped PC (STAR-PC) in order to succeed super-collimation over a broad bandwidth. Both time- and frequency-domain numerical methods are conducted. Due to introduced low-symmetry in the primitive cell, flat contours are observed at the fifth band for transverse magnetic mode. The proposed structure supports a super-collimation effect over a broad wavelength range between 1443 nm and 1701 nm with a bandwidth of Δω = 16.42%. The intrinsic characteristic of STAR-PC provides in-plane beam propagation with a limited diffraction length of 120a, where a is the lattice constant. By means of STAR-PC, one may realize super-collimation based single-mode optical devices with a low insertion loss, reduced dispersion and wide bandwidth.     

Broadband and lossless lithium niobate valley photonic crystal waveguide [Invited]

We investigate the influences of structure parameters and interface shapes on the bandwidth of the edge state of lithium niobate valley photonic crystals. By increasing the size difference of two air holes in the same unit cell, we find that the bandwidth of the lossless nontrivial edge state possesses a peak value of 0.0201(a/λ), which can be used to construct broadband valley photonic crystal waveguides. Mode field distributions verify that the waveguide is robust against sharp bends and exhibits chirality. When the unit cell is arranged in a bearded interface with the top and bottom components showing negative and positive valley Chern numbers, respectively, we find that the lithium niobate valley photonic crystal is more likely to exhibit a lossless edge state, which is difficult to be realized in valley waveguides with low refractive index materials. This work can provide guidance on the design of the high-performance topological waveguide.     

Reconfigurable photonic crystal circuits

We describe progress in the field of tuning, (re)configuration of Photonic crystal (PhC) based devices with a particular emphasis on our recent concepts and techniques that we have developed to tune and/or reconfigure the properties of photonic crystal nanocavities. We show how our hybrid approach based on photosensitive material and tapered silica fiber can tune the (Q, λ) properties of preexisting Photonic crystal cavities. We describe our alternative techniques to create ‘a posteriori’ spatially (re)configurable high‐Q cavities in a PhC platform. We show that optofluidics – the fusion of microfluidics with photonic devices – offers an unquestionable added value to the quest of a truly versatile, (re)configurable photonic crystal based photonic chip.     

Wideband and low dispersion slow light in slotted photonic crystal waveguide

We present a procedure to generate wideband and low dispersion slow light in slotted photonic crystal waveguide. By shifting the first and second rows of air holes of slotted photonic crystal waveguide, the bandwidth of slow light can be increased, with small group velocity dispersion. Using 2D plane wave expansion method, we numerically demonstrate slow light with the nearly constant group indices of 23, 42, and 54 over 17.6 nm, 6.7 nm and 3.3 nm bandwidth, respectively. The maximal normalized delay-bandwidth product is 0.26. From the fabrication's point of review, shifting the position of holes is easier to be controlled technically than changing the diameters of air holes. In addition, our simulations suggest this design is tolerant to deviation for positions of the first two rows of air holes. Therefore, the proposed approach decreases the dependence on the fabrication accuracy.     

Efficient parametric interactions in a low loss GaInP photonic crystal waveguide

We describe time domain characterizations of dynamic four-wave mixing in a low loss modified W1 GaInP photonic crystal waveguide. Using 32 ps wide pump pulses with peak powers of up to 1.1 W we achieved a very large conversion efficiency of -6.8 dB as well as a 1.3 dB parametric gain experienced by a weak CW probe signal. Time domain simulations confirm quantitatively all the measured results.     

宽带光子晶体插分滤波器

 通过使用正方格介质柱二维光子晶体设计了带有环形谐振器的一种插分滤波器ADF(add drop filter)结构,该结构具有1个输入端口和2个输出端口,采用时域有限差分法研究了带有1个环形谐振器和2个环形谐振器的ADF结构传输性能。结果表明：该ADF结构在第三通信窗口具有优良的滤波作用,能够根据需要将电磁波信号沿着波导向前后上下4个方向传输,ADF结构还具有可调性开关波长、宽频带、高传输率等特点,在光子晶体集成化、光器件制作等方面具有潜在价值。     

Broadband single-polarization photonic crystal fiber

We demonstrate a single-mode photonic crystal fiber that supports only one polarization state in a 220-nm-broad spectral region centered at 727 nm. The fiber has a mode-field diameter of 15.5 microm and background losses of < 15 dB/km in the single-polarization region. To our knowledge, these are the broadest bandwidth and the largest mode size yet reported for a single-polarization fiber.     

Broadband dispersion-compensating photonic crystal fiber

We present a modified dual-core photonic crystal fiber, based on pure silica, with special grapefruit holes in the inner cladding. The fiber has large, broadband negative dispersion, and the dispersion value varies linearly from -380 t o-420 ps/(nm km) in the C band. To decrease the fabrication difficulty, large air holes are adopted. Furthermore, the chromatic dispersion of the fiber is not sensitive to the structure parameters. So the proposed fiber structure can greatly facilitate fiber drawing and can be used for broadband dispersion compensation.     

Design and analysis of a wideband photonic crystal waveguide with low group-velocity and low dispersion

The slow light propagation in a line waveguide in the two-dimensional triangular photonic crystal has been numerically studied, based on which a wideband photonic crystal waveguide with low group-velocity and low dispersion is proposed. The numerical simulation analysis shows that it is possible to maximize the group index and minimize the group-velocity dispersion in wide bandwidth by increasing the radius of the basic air hole and changing the position of the first two rows of air holes in photonic crysta...     

利用耦合波导列提高光子晶体波导辐射

将耦合波导列应用于光子晶体单模波导,提出一种提高光辐射的光子晶体结构. 基于时域有限差分方法的理论研究表明,当将耦合波导列附加到单模光子晶体波导出口端的适当位置,使出射光分成若干强弱不一的光束,这些光束在传播空间通过干涉形成一定程度的汇聚,大大提高了光子晶体波导在水平方向的光辐射效率. 另外,当耦合波导列的行数大于某固定值(2N=8)时,辐射质量基本保持不变,由此可获得最紧凑的器件结构. 这种类型光子晶体在近场光学和集成光学等诸多方面有潜在的应用价值. 关键词： 光子晶体波导 光辐射 波导列 耦合波导     

Interference grating structures in photonic crystal circuits

Photonic Crystal Circuits have been widely investigated for various optoelectronics device applications. And the gratings in photonics devices are indispensable tool, which is very common for light manipulation. In this study, an interference grating structure formed by Gaussian beam interferences in photonic crystal waveguide such that having Kerr type nonlinearity is proposed and its transmission characteristics are investigated. Finite-Difference Time-Domain method is used to analyze the device characteristics. According to simulation results, the interference grating has shown special transmission characteristics that can bring tunability for photonic crystal devices. This can be an effective method for controlling optical signals in the photonic crystal for all optical switching/routing applications as a part of add/drop multiplexing.     

High sensitivity photonic crystal waveguide sensors

A theoretical investigation of the sensitivity of an optical liquid sensor, based on photonic crystal waveguide, is carried out. The sensing principle is based on the variation of the effective index of the waveguide induced by analyte refractive index change. The sensor modelling is carried out by using the 3D finite element method. The influence of geometrical parameters on the sensor sensitivity has been investigated. The results show that the sensitivity can be optimized by an appropriate choice of the geometrical parameters and a sensitivity superior to 20 has been achieved, near the cut-off in the slow light region, which is several times higher than that can be achieved with conventional waveguides.     

Intrinsic localized modes in photonic crystal circuits

A discussion of intrinsic localized modes (ILMs) in photonic crystals is given. Emphasis is placed on ILMs in photonic crystal waveguides formed from Kerr nonlinear materials and photonic crystal circuits formed by joining nonlinear photonic crystal waveguides into networks. Work on stationary and propagating ILMs in nonlinear waveguides and waveguide junctions is reviewed. In addition, some discussion is given on the optical bistability of the barrier and junction geometries and on recent results on two-dimensional ILMs in Kerr nonlinear photonic crystals.     

Nanofluidic tuning of photonic crystal circuits

By integrating soft-lithography-based nanofluidics with silicon nanophotonics, we demonstrate dynamic, liquid-based addressing and high deltan/n (approximately 0.1) refractive index modulation of individual features within photonic structures at subwavelength length scales. We show ultracompact tunable spectral filtering through nanofluidic targeting of a single row of holes within a planar photonic crystal. We accomplished this with an optofluidic integration architecture comprising a nanophotonic layer, a nanofluidic delivery structure, and a microfluidic control engine. Variants of this technique could enable dynamic reconfiguration of photonic circuits, selective introduction of optical nonlinearities, or delivery of single molecules into resonant cavities for biodetection.     

高透射率慢光速的光子晶体耦合腔波导的研究

将二维三角晶格光子晶体波导和微腔结构结合,优化设计了一种二维三角晶格光子晶体共振耦合腔波导,运用时域有限差分法(FDTD)模拟共振耦合腔波导TE偏振光的透射谱,通过透射谱得到传输光的透射率和群速度。结果表明,合适参数的二维三角晶格共振耦合腔波导在波长1.551μm处的群速度为c/130、透射率为20.1%,在波长1.502μm处的群速度为c/50、透射率为29.2%。运用平面波展开法(PWE)计算的该波导的能带结构对慢光特性进行了分析。这种慢光特性的光子晶体波导将在光存储、光延迟及光子集成等方面有潜在的应用价值。     

Nonlinear Fabry-Perot resonator with a silicon photonic crystal waveguide

We derive an equation that describes the nonlinear operation of a Fabry-Perot resonator with a large group index waveguide. Specifically, a silicon photonic crystal microcavity with two-photon-excited free carrier nonlinearity and Kerr nonlinearity is assumed. The equation clearly explains the bistability of the device and the reduction of the required pump energy for a specific nonlinear phase shift at an appropriate phase detuning from the resonance. We present a simple procedure to predict the required optical pump energy for the modulation and the resulting modulation depth by use of the equation and the device parameters.     

Broadband single-polarization guidance in hybrid photonic crystal fibers

We present hybrid photonic crystal fibers that provide broadband single-polarization guidance based on two different propagation mechanisms, namely, total internal reflection and the photonic bandgap effect. Experimental results demonstrate polarization dependent loss as high as 26.7 dB and the bandwidth of single-polarization behavior over 225 nm.     

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.