Investigation of Infrared Photonic Crystal Slab with Defect Waveguides

This paper deals with the two dimensional (2-D) infrared photonic crystal slab with an air-bridge structure featuring defect waveguides in which the optical propagation properties were obtained by measurements of transmission spectra. 3-D finite-difference time-domain (FDTD) simulations have revealed the appearance of four defect propagation modes for the band structure and transmission spectra in the air-bridge slab. These defect modes were experimentally identified in the measured transmission spectra.     

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     

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。     

Fabrication and characterization of photonic crystal-based symmetric Mach-Zehnder (PC-SMZ) structures based on GaAs membrane slab waveguides

We have experimentally demonstrated two- dimensional (2-D) photonic crystal (PC) waveguides (WGs) such as straight, bent, Y-branch, directional coupler (DC), and quantum dots (QDs)-based nonlinear optical (NLO) WGs using a GaAs air-bridge membrane with triangular-lattice line-defect WGs. These WGs are necessary for a 2-D PC-based symmetric Mach-Zehnder (PC-SMZ) type ultrafast all-optical switch. Experimental results on the clear observation of the optical interference at the Y-junction DC, nonlinearity-induced phase shift at the NLO waveguide, and transmission spectra in the total PC-SMZ WG configuration will be addressed, as well as measured results on each WG element.     

Out-of-plane losses of line-defect photonic crystal waveguides

A numerical model is presented for computing the out-of-plane losses of a general class of two-dimensional photonic crystals superimposed. onto a slab confinement structure. The usefulness of this model is demonstrated by calculating the propagation loss of a single-row-defect waveguide composed of hexagonal air holes etched into two different slab structures. The results are interpreted in terms of a simple coupled-mode-theory picture in which loss is due to resonant coupling between the fundamental and certain radiative slab modes. These calculations show that low-loss photonic crystal waveguides should be possible by carefully designing the slab waveguide     

Design of Taper Structure for Highly Efficient Coupling Between 1-D Photonic Crystal Coupled Resonator Optical Waveguide and Straight Waveguide

This paper presents a design method of a taper structure for highly efficient coupling between 1-D photonic crystal coupled resonator optical waveguides (1-D PC-CROWs) and input straight waveguides. We propose a new taper structure where not only air hole radius but also waveguide width are varied linearly in order to adjust the dispersion curves shift. By using the proposed tapered structure, we can connect each waveguide with high transmission over wide bandwidth. Our numerical simulation results show that a transmission of 98% around 1550 nm wavelength in a 6.6 $mu$m long taper can be obtained with a 42 nm bandwidth.      

Efficient light transmission through InP-based photonic crystalwaveguides

Very efficient light transmission over a length of several millimetres through linear photonic crystal slab waveguides, patterned into an InGaAlAs waveguiding layer on InP substrate, is demonstrated. Quantitative evaluation of the light propagation in these waveguides, using the Fabry-Perot resonance method, yields a minimum loss of 1.6 dB/mm, for a waveguide with seven missing rows at 1550 nm wavelength     

Design and fabrication of silicon photonic crystal optical waveguides

We have designed and fabricated waveguides that incorporate two-dimensional (2-D) photonic crystal geometry for lateral confinement of light, and total internal reflection for vertical confinement. Both square and triangular photonic crystal lattices were analyzed. A three-dimensional (3-D) finite-difference time-domain (FDTD) analysis was used to find design parameters of the photonic crystal and to calculate dispersion relations for the guided modes in the waveguide structure. We have developed a new fabrication technique to define these waveguides into silicon-on-insulator material. The waveguides are suspended in air in order to improve confinement in the vertical direction and symmetry properties of the structure. High-resolution fabrication allowed us to include different types of bends and optical cavities within the waveguides.     

Photonic Crystal Slab Waveguides Based on Antiresonant Reflecting Optical Waveguide Structures

A novel two-dimensional photonic crystal slab waveguide based on an antiresonant reflecting optical waveguide (ARROW) structure is proposed and designed. Lightwaves propagating in this waveguide are confined by antiresonance reflection vertically and the photonic band gap laterally. In order to obtain the characteristics of the ARROW-based photonic crystal waveguides, the three-dimensional finite-difference time-domain simulations are performed. With a lateral adiabatic taper, a coupling efficiency of 80.3% from a single-mode fiber to the ARROW-based photonic crystal waveguide of a single-line defect is obtained. In addition, propagation losses less than 10 dB/mm and bend losses of 0.23 and 0.39 dB/bend for the designed 60$^{circ}$ and 120$^{circ}$ bends are achieved at an operating wavelength of $1.55~mu{hbox {m}}$.      

Measurement of photonic mode dispersion and linewidths in silicon-on-insulator photonic crystal slabs

The dispersion of photonic modes in one-dimensional (1-D) and two-dimensional (2-D) patterned silicon-on-insulator (SOI) waveguides, also containing line defects, is fully investigated both above and below the light line. Quasi-guided (radiative), as well as truly guided modes are probed by means of angle- and polarization-resolved microreflectance and attenuated total reflectance measurements. For the 1-D case, the sharp resonances observed in reflectance spectra are analyzed in terms of the Airy-Fano model, and the measured linewidths are shown to be very close to theoretical predictions. In the 2-D lattices containing W1 line defects the presence of a supercell repetition leads to the simultaneous excitation of defect and bulk modes which are folded in a reduced Brillouin zone. The measured dispersion is in very good agreement with full three-dimensional calculations based on expansion on the waveguide modes, indicating that a deep understanding of the propagation properties of patterned SOI waveguides is achieved.     

Channel drop filter using a single defect in a 2-D photonic crystal slab waveguide

This paper describes a theoretical and experimental analysis of the channel drop filter using a single defect formed near the two-dimensional (2-D) photonic crystal slab waveguide. First, we calculate the transmission spectrum of a 2-D photonic crystal waveguide and show that high transmittance for a wide wavelength range (/spl sim/60 nm) is obtained in the 1.55-/spl mu/m region. We also show that a defect state having a wavelength within the high transmission wavelength range can be formed in the photonic bandgap by introducing a single defect of appropriate radius. Next, we fabricate several devices and show that the emission wavelength from each defect can be tuned by changing the defect radius. The measured tuning characteristics coincide well with the calculated results. From the near-field pattern of the device, we estimate the emission efficiency of the present device at almost a few tens percent. We clarify the structural condition in order to obtain the maximum output efficiency and show that tuning of emission wavelength while maintaining high output efficiency is possible by selecting appropriate defect radius and position. Based on these results, we propose an ultrasmall channel drop filter for a wavelength-division-multiplex optical communication system.     

Two-Dimensional Ferroelectric Photonic Crystal Waveguides: Simulation, Fabrication, and Optical Characterization

The optical properties of two dimensional photonic crystal (PhC) waveguides were investigated using ferroelectric barium titanate (BTO) thin films as the optical medium. The photonic band structure was calculated using a 2-D finite difference time domain (FDTD) method; a broad band gap is observed that results from the high refractive index contrast. The simulated transmission spectra indicate the stop band of PhC is mainly determined by three parameters: lattice constant, refractive index contrast, and waveguide mode order. From transmission measurements the PhC with a lattice constant ${a}=420$ nm shows a strong light dispersion and the other PhC with ${a}=450$ nm shows a 120-nm broad stop band. Strong localization of visible light within the PhC cavities is demonstrated from the light scattering images. The observed strong light confinement and its spatial intensity profile due to resonance agree with the calculated profiles. From polarized optical microscopy we discovered the scattered light wavelength was highly sensitive to magnitude of the lattice constant. The optical scattering properties indicate BTO PhC can potentially serve as micrometer size electro-optically tunable switches and color filters.      

光子晶体齿状波导的滤波特性研究

为了设计基于光子晶体波导的高性能滤波器件,在2维正方格子光子晶体波导结构中引入一系列齿状缺陷,采用有限元法对齿状光子晶体波导的传输特性进行了数值仿真和理论分析。结果表明,对于单个齿状缺陷,缺陷产生的共振频率使得在光子晶体波导通频域带出现带隙结构,可以实现良好的窄带滤波,并且通过改变齿状缺陷深度可以有效地控制缺陷的共振频率;引入多个齿状缺陷,缺陷之间会经过耦合作用形成一系列缺陷态,使得在光子晶体波导导通频域中出现宽带的带隙结构,可以实现宽带滤波。该光子晶体波导滤波器对窄/宽带滤波可根据波导结构中引入的齿状缺陷进行简单灵活调节。此研究在设计基于光子晶体波导的光子滤波器件方面具有潜在的应用价值。     

多掺杂一维各向异性光子晶体的缺陷特性

为了研究多掺杂一维各向异性光子晶体的光学特性,采用传输矩阵法计算了光波通过多掺杂一维各向异性光子晶体的透射率。经数值模拟得到:光通过该结构光子晶体后,TE波和TM波的透射谱中随掺杂层个数的变化出现了单、双及多缺陷模,禁带中缺陷模的个数随掺杂层数的增大而增多,缺陷模的位置随掺杂层光学厚度的变化向短波方向移动,TE波和TM波的缺陷模能完全分开,透射谱的这一特点为设计制作单、双通道滤波器提供了理论依据。     

含双缺陷的一维准周期光子晶体的缺陷模特性

利用传输矩阵法,计算了含双缺陷的一维准周期光子晶体的透射谱,并侧重分析了缺陷模的特征。结果表明:当两缺陷层间距较小时,两缺陷模分裂的距离较大,对应的透射率较小;而当两缺陷层间的光学距离变大,两缺陷模的间距变小,缺陷膜的透射率增加。两缺陷模间的关联系数随两缺陷层间的光学厚度的增加而减少。缺陷层光学厚度增加时,缺陷模向长波方向平移,反之向短波方向移动。缺陷层光学厚度的变化对缺陷模的透射率几乎没有影响。     

Lasing at bend, branch and intersection of photonic crystal waveguides

The authors report room temperature lasing by pulsed photopumping at line and point composite defects, i.e. a 60/spl deg/-bend, a Y-branch and an intersection of single line defect waveguides, in a GaInAsP photonic crystal slab. The lasing wavelength was different from the simple line defect lasing mode. This indicates that such waveguide components act as microcavities with localised modes.     

A rib optical waveguide with cutoff mesa isolation

A rib optical waveguide using the concept of optical cutoff to provide isolation between adjacent waveguides in a photonic integrated circuit is disclosed. Due to the evanescent nature of light propagation in cutoff waveguides, this cutoff mesa rib waveguide permits fabrication of single-moded rib waveguides with minimal self-interference and crosstalk by means of light guided in a remaining slab waveguide. Design rules are given and operation of a single-moded cut-off mesa rib waveguide and an MZI using this waveguide are demonstrated     

A compact two-dimensional grating coupler used as a polarization splitter

We demonstrate a novel polarization splitter based on a two-dimensional grating etched in a silicon-on-insulator waveguide. The device couples orthogonal modes from a single-mode optical fiber into identical modes of two planar ridge waveguides. The extinction ratio is better than 18 dB in the wavelength range of 1530-1560 nm and the coupling efficiency is approximately 20%. The device is very compact and couples light only to transverse-electric modes of the planar waveguides. Therefore, it may be used in a polarization diversity configuration to implement a polarization insensitive photonic integrated circuit based on photonic crystal waveguides.     

材料色散对1维光子晶体缺陷模影响的研究

为了分析材料色散对缺陷模的影响,对色散材料采用洛伦兹振子模型,利用传输矩阵法计算了含缺陷1维光子晶体的透射谱,分析了各层的色散对该结构1维光子晶体缺陷模的影响。结果表明,无论是高、低折射率介质还是缺陷层的色散都可以引起缺陷模的频移或分裂;缺陷模的频移方向与考虑色散后光学厚度的变化有关,如果光学厚度增大,则发生红移,反之则发生蓝移;低折射率介质的色散使缺陷模频移的效果最显著。这一结果对光子晶体的设计和研究有一定的参考价值。     

Transmission properties of a two-dimensional photonic crystal slabwith an excitonic resonance

The transmission properties of a 2-D photonic crystal slab with an exciton resonance are investigated experimentally and theoretically. Good agreement between experiment and scattering matrix based theory is obtained. The photonic crystal slab is composed of a square lattice of etched square holes in a quartz substrate, filled by an inorganic-organic semiconductor and covered by a polystyrene guiding film. We demonstrate that the transmissivity of the structure shows pronounced dips, which originate from the excitation of quasi-guided modes in the photonic crystal slab. The measured and calculated angular dependence of the energy of these dips and their optical activity allow us to identify the physical properties of the quasi-guided modes, such as their symmetry and distribution of electromagnetic field