Multimode interference-based photonic crystal waveguide power splitter

A compact power splitter based on the multimode interference (MMI) effect in photonic crystal waveguides is designed and analyzed. The device size reduction compared with the conventional MMI power splitter can be attributed to the large dispersion of the photonic crystal waveguides. The Massachusetts Institute of Technology Photonic-Bands code is used to calculate the band structures of photonic crystal waveguides. The finite-difference time-domain method is adopted to simulate the relevant structures.     

基于厄米-高斯函数法研究1维光子晶体波导

为了对折射率型1维光子晶体缺陷波导中的光传输进行有效数值模拟,采用此类型波导的厄米-高斯函数展开方法进行了研究。首先给出了计算方法的详细理论推导,然后利用该方法计算了偏振态不同、结构参量不同的情况下波导本征模式的色散关系、模场空间分布、能量控制因子及等效折射率。结果表明,1维光子晶体缺陷波导与阶跃平面光波导主要差别在于高阶模式,且可通过调节1维光子晶体的结构参量来有效调控高阶模式的传输。     

Negative refraction in a Si-polymer photonic Crystal membrane

We have observed negative refraction in a photonic crystal (PC) membrane structure at near-infrared wavelengths. The device is fabricated on a silicon-on-insulator substrate and consists of a silicon rod matrix suspended in a polymer where optical energy is delivered by ridge waveguides with various incident angles. The propagation direction inside the PC shows extraordinary refraction with an angle consistent with our two-dimensional numerical simulations. To our knowledge, this is the first experimental observation of isotropic negative refraction in a Si-based planar PC structure at optical frequencies. The realization of negative refraction in a planar Si-based system enables applications in negative index imaging to be integrated into compact optical circuits.     

SOI纳米线波导和相关器件研究进展

SOI纳米线波导具有对光场限制作用强、传输损耗低、弯曲半径小、集成度高、与传统CMOS工艺兼容等优点,采用SOI纳米线波导能够大大缩小光子器件的长度和面积,提高器件工作速度和效率,降低器件功耗.介绍了SOI纳米线波导在模式、损耗、偏振等方面与传统大尺寸硅基波导所表现出来的不同特性,评述了当前关于SOI纳米线波导和基于SOI纳米线波导光子器件的最新研究进展.     

Short Polarization Filter in Pillar-Based Photonic Crystals

The strong polarization dependence of two- dimensional photonic crystals is exploited for polarization filtering. The device with a length of 3.9 mum is integrated in a photonic integrated circuit based on InP waveguide technology. The average transmissions in the wavelength range from 1530 to 1570 nm are -8.7 dB for transverse-magnetic polarization and -26.5 dB for transverse-electric polarization.     

On the Theory of Corrugated Optical Disk Waveguides

The corrugated disk dielectric waveguide is investigated by considering a linear combination of orthogonal wavefunctions of the uncorrugated device. It is shown that, just as in the case of corrugated planar slab waveguides, codirectional as well as contradirectional coupling of guided modes is possible. Some potential applications of the device are discussed and device parameters are investigated for specific waveguide materials.     

Fabrication of LiTaO3 optical waveguides by Ni diffusionbelow the Curie temperature

Using Ni diffusion into LiTaO₃ below the Curie temperature for the fabrication of optical waveguides was presented for the first lime. Ordinary and extraordinary polarization waveguide modes were obtained. The index distribution profiles of both modes were measured by a prism coupler. Loss in planar waveguides at 0.6328 μm is 0.7±0.1 dB/cm for the ordinary mode and 1.3±0.2 dB/cm for the extraordinary mode. Moreover, a Mach-Zehnder interferometer was fabricated by this method for electrooptic characterization. The measured half-wave voltage is 5.5 V and the extinction ratio is greater than 29 dB     

Modal propagation within MQW waveguides

The propagation of TE modes and TM modes within planar multiquantum waveguides with large numbers of wells and barriers is shown to exhibit markedly different behavior for the two polarization states. The solutions for these two modes are developed for an arbitrary number of N barriers, and zero- and first-order approximations in powers of 1/N are calculated for quantities of physical interest. A very high geometric birefringence is demonstrated     

Birefringent properties of GaAlAs multiple quantum well planaroptical waveguides

Planar GaAlAs optical waveguides in which the waveguide core region is composed of multiple quantum wells are considered. Calculations of optical waveguide dispersion are performed to determine variations in effective refractive indexes for TE and TM modes and in the mode birefringence for large ranges of total waveguide thickness, number, and refractive index of well and barrier layers, and the ratio of well and barrier layer thickness. Ranges of these parameters which yield optical waveguides having unusually high birefringence and optical waveguides supporting single polarization planar propagation only are identified     

A novel polarization splitter based on the photonic crystal fiber with nonidentical dual cores

A novel polarization splitter based on photonic crystal fibers (PCFs) with two nonidentical cores is proposed. The two highly birefringent cores are vertically arranged to obtain polarization selective coupling. The horizontal polarization exchanges its energy between the two cores. However, the vertical polarization shows little coupling between the two cores. This is achieved in single-material glass waveguides for the first time to our knowledge. The PCF-based polarization splitter exhibits many advantages such as shorter length, high extinction ratio, and wide bandwidth over its counterparts.     

负胶-玻璃复合平面光波导传播特性的研究

本文报导了负胶-玻璃复合平面光波导传播特性的实验研究。测量并归纳了负胶介质薄层对银离子交换玻璃平面波导传播特性影响的实验趋势。介绍了弯曲条载波导的实验研究。     

Grating-assisted coupling of light between semiconductor and glasswaveguides

Floquet-Bloch theory is used to calculate the electromagnetic fields in a leaky-mode grating-assisted directional coupler (LM-GADC) fabricated with semiconductor and glass materials. One waveguide is made from semiconductor materials (refractive index ≈3.2) while the second is made from glass (refractive index ≈1.45). The coupling of light between the two waveguides is assisted by a grating fabricated at the interface of the glass and semiconductor materials. Unlike typical GADC structures where power is exchanged between two waveguides using bound modes, this semiconductor/glass combination couples power between two waveguides using a bound mode (confined to the semiconductor) and a leaky mode (associated with the glass). The characteristics of the LM-GADC are discussed. Such LM-GADC couplers are expected to have numerous applications in areas such as laser-fiber coupling, photonic integrated circuits, and on-chip optical clock distribution. Analyses indicate that simple LM-GADC's can couple over 40% of the optical power from one waveguide to another in distances less than 1.25 mm     

硅基片上偏振分束器研究进展

硅基集成光波导具有很高的折射率对比度,能将光场限制在纳米尺度,是制备结构紧凑、高效的纳米光子器件的关键。但是,高折射率对比度也会引起波导双折射效应。因此,几乎所有纳米光子器件都是偏振相关的。偏振分束器是偏振分集光子集成电路中克服硅纳米器件强偏振依赖性的重要组成部分,在片上相干通信、传感与环境检测等领域具有广阔的应用前景。目前报道的基于亚波长光栅波导结构的偏振分束器,工作带宽在200 nm以上,消光比也超过了20 dB。文章简述了各种类型偏振分束器的工作原理,对其尺寸、消光比、带宽等方面的性能进行了比较,分析了各类偏振分束器的优劣势,最后总结了其主要应用场景并展望了未来发展方向。     

Light propagation characteristics of straight single-line-defectwaveguides in photonic crystal slabs fabricated into asilicon-on-insulator substrate

Straight single-line defect optical waveguides in photonic crystal slabs are designed by the finite difference time-domain method and fabricated into a silicon-on-insulator (SOI) wafer. By employing an airbridge structure, clear light propagation for both polarizations is observed without any leakage along the waveguide. This experimental result is well explained by photonic bands of pure guided modes. Minimum propagation loss is estimated to be 11 dB/mm. This value is lower than that reported so far for three-line-defect waveguides with an SOI slab structure and almost comparable to that for an index confinement waveguide with a rectangular Si core. This propagation loss is dominated by the scattering loss by some irregularities. However, photonic crystal waveguides have the possibility of an essential lower scattering loss than in the index confinement waveguide because of the inhibition of radiation modes by the photonic bandgap     

Cascaded photonic crystal guides and cavities: spectral studies andtheir impact on integrated optics design

We report on the investigation of cavities coupled to channel waveguides defined in a triangular-lattice photonic crystal etched into a GaAs/AlGaAs heterostructure waveguide. We make use of the internal probe technique by selectively exciting the photoluminescence of InAs dots embedded in the planar waveguide. We collect at the nearby cleaved edge the fundamental mode transmitted through the channel waveguides. From the study of a number of basic cases, we exemplify how one may deduce the main guideline design rules for given cavity-guide interaction mechanisms and then for the implementations of functions such as bending and filtering. In particular, the role of the so-called ministopband (MSB) feature of the waveguide and the nature of the cavity modes involved are outlined     

Performance of an array of circular waveguides with strip-loadeddielectric hard walls

An infinite planar periodic antenna array of radiating open-ended circular waveguides is considered. The conducting waveguide walls are covered with dielectric layers loaded with longitudinal conducting strips for providing the hard wall boundary condition. Analysis of the array is carried out by the mode-matching method. The waveguide modes involved in the method are calculated by using the asymptotic strip boundary condition. It is shown that they are split into an independent subsystem of TE modes for the whole cross section and two independent subsystems of TM modes: one is for the central region and another is for the layer region. The calculations show that the operation of the hard waveguides in an array with small element spacing is similar to that of the multimode smooth wall waveguides completely filled with dielectric. For large diameters and element spacing, the hard waveguides have significant advantages over the smooth ones. It is shown that unlike an individual hard waveguide, the aperture efficiency of such a waveguide in the array has a nonmonotonic dependence on the waveguide radius. The results characterizing the behavior of the aperture efficiency and cross-polarization level in a frequency band as well as the contribution of certain waveguide modes in the reflected power are presented and discussed. The examples of the element patterns corresponding to minimal cross polarization are also given     

Characterization of vapor diffused Zn:LiTaO3 opticalwaveguides

Diffusion and optical properties of planar waveguides produced in LiTaO₃ by a recently developed technique that utilizes Zn diffusion from vapor phase are presented. The waveguides are obtained by 6-h diffusion at temperatures as low as 800°C. The results indicate that Zn is a fast diffusant in LiTaO₃ and has activation energies that are slightly less than those for Ti diffusion into LiTaO ₃. The diffusion temperatures for Zn are much lower than the 1150-1200°C require for Ti metal indiffusion. The diffusion coefficient of Zn at 800°C, is comparable to that of Ti at 1200°C. The resulting waveguides support both ordinary and extraordinary modes of polarization. The low temperature diffusion slows out diffusion and has been shown to be advantageous for making low-loss optical waveguides in LiTaO₃     

Wavelength switching by mode interference between longitudinally coupled photonic crystal channel waveguides

A wavelength switching mechanism of two longitudinally coupled and independently contacted photonic crystal channel waveguides is reported. The waveguides are coupled by a photonic crystal section of one period in /spl Gamma/-M orientation. The cavity lengths are chosen such that the cavity modes exhibit slightly different mode spacings and allow for a wavelength switching by mode interference between the two cavities.     

Proposal for a Compact Resonant-Coupling-Type Polarization Splitter Based on Photonic Crystal Waveguide With Absolute Photonic Bandgap

We propose a resonant-coupling-type polarization splitter based on a photonic crystal structure with absolute photonic bandgap. The scalar finite-element method was used to calculate resonant frequencies of the cavity and frequency dependences of the polarization splitter. This device supports single-mode operation for both transverse-electric and transverse-magnetic waves. We show that miniaturization of the proposed polarization splitter can be realized by utilizing resonant coupling.     

Local field analysis of bent graded-index planar waveguides

A local field analysis is proposed for bent planar waveguides with arbitrary refractive index profiles. Exact vector wave equations that include the gradient index, or polarization correction, term are derived for both transverse electric and transverse magnetic modes from Maxwell's equations in a local bent coordinate system. The approximate local field and correction to the propagation constants are obtained by perturbation analysis. As an example of the method, an infinitely extended parabolic index profile is studied