High Quality-Factor 1-D-Suspended Photonic Crystal/Photonic Wire Silicon Waveguide Micro-Cavities

We have successfully fabricated and characterized suspended one-dimensional (1-D) photonic crystal/photonic wire (PhC/PhW) waveguide micro-cavities based on silicon-on-insulator (SOI). Our experiments have shown an enhancement of the resonance ${Q}$ -factor from 18 700 to approximately 24 000, with normalized optical transmission of 70%, after removing the silica cladding underneath the silicon waveguide. We have also demonstrated that, for this condition, the resonance peak wavelength can be controlled by varying the length of the micro-cavity. These results were obtained by removing the silica cladding below the silicon waveguide to produce a “hanging” wire waveguide. The three-dimensional (3-D) finite-difference time domain (FDTD) simulation approach used shows good agreement with measured results.      

Design of a photonic crystal microcavity for biosensing

We have designed an air-bridged PhC microcavity with high sensitivity and a high quality factor.The structure parameters of the microcavity are optimized by three-dimensional finite-difference time-domain method. We compare the performance of a silicon-on-insulator PhC microcavity and an air-bridged PhC microcavity,and analyze the effect of the thickness of the slab and the radius of the defect hole on the performance of the air-bridged PhC microcavity.For a thinner slab and a larger defect hole,the sensitivity is higher while the quality factor is lower.For the air-bridged photonic crystal slab,the sensitivity can reach 320-nm/RIU(refractive index unit) while the quality factor keeps a relatively high value of 120 by selecting the proper slab thickness and the defect hole radius,respectively,when the refractive index is 1.33.This is meaningful for low-detection-limit biosensing.     

3-D FEM Modeling and Fabrication of Circular Photonic Crystal Microcavity

In this paper, we study an unconventional kind of quasi-three-dimensional (3-D) photonic crystal (PhC) with circular lattice pattern: it consists of air holes in a GaAs material $({rm n}=3.408)$ along circular concentric lines. This particular PhC geometry has peculiar behavior if compared with the traditional square and triangular lattices, but it is difficult to model by using conventional numerical approaches such as wave expansion method. The resonance and the radiation aspects are analyzed by the 3-D finite-element method (FEM). The model, based on a scattering matrix approach, considers the cavity resonance frequency and evaluates the input–output relationship by enclosing the photonic crystal slab (PhCS) in a black box in order to define the responses at different input–output ports. The scattering matrix method gives important information about the frequency responses of the passive 3-D crystal in the 3-D spatial domain. A high sensitivity of the scattering parameters to the variation of the geometrical imperfection is also observed. The model is completed by the quality factor (Q-factor) estimation. We fabricated the designed circular photonic crystal over a slab membrane waveguide embedding InAs/GaAs quantum dots emitting around 1.28 $mu{hbox{m}}$. Good agreement between numerical and experimental results was found, thus validating the 3-D FEM full-wave investigation.      

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.      

Optical Bistable Operations in AlGaAs-Based Photonic Crystal Slab Microcavity at Telecommunication Wavelengths

We report on bistable operations in a microcavity formed on an AlGaAs-based photonic crystal slab at telecommunication wavelengths. We designed the cavity to achieve a high quality ($Q$)-factor, while maintaining a small mode volume; this was accomplished by removal of a single air hole. The fabricated microcavity exhibited a resonant peak with a$Q$-factor of 1900 at 1548 nm. In nonlinear transmission measurement, when the input power was increased, a bistable characteristic which was dependent on the detuned wavelength from the resonance was observed. The bistability was considered to originate from thermal nonlinearity due to two-photon absorption.     

A high quality factor photonic crystal channel-drop filter with a linear gradient microcavity

We design a channel-drop filter (CDF) with a linear gradient microcavity in a two-dimensional (2D) photonic crystal (PC). The model of three-port CDF with reflector is used to achieve high quality factor (Q-factor) and 100% channel-drop efficiency. The research indicates that adjusting the distance between reference plane and reflector can simultaneously influence the Q-factor due to coupling to a bus waveguide and the phase retardation occurring in the round trip between a microcavity and a reflector. The calculation results of 2D finite-difference time-domain (FDTD) method show that the designed filter can achieve the drop efficiency of 96.7% and ultra-high Q-factor with an ultra-small modal volume.     

Modeling and Experimental Verification of the Dynamic Interaction of an AFM-Tip With a Photonic Crystal Microcavity

We present a transmission model for estimating the effect of the atomic-force microscopy tapping tip height on a photonic crystal microcavity (MC). This model uses a fit of the measured tip-height-dependent transmission above a ldquohot spotrdquo in the MC. The predicted transmission versus average tapping height is in good agreement with the values obtained from tapping mode experiments. Furthermore, we show that for the existing, nonoptimized structure, the transmission coefficient can be tuned between 0.32 and 0.8 by varying the average tapping height from 26 to 265 nm. A transmission larger than that of the undisturbed cavity at resonance was observed at specific tip locations just outside the cavity-terminating holes.     

Low-Loss Slow Light Transmission in Photonic Crystal Waveguides Comprising of Liquid Crystal Infiltration

A low loss photonic crystal(PhC) waveguide having rectangular air holes in Si core is proposed having an average group index of 55 in the bandwidth of 1.2 THz.The possible propagation losses due to inefficient coupling are also investigated for proposed structure.It is found that high transmission is obtained for a broad bandwidth from the output of the finally designed heterogeneous waveguide consisting of a slow liquid crystal infiltrated PhC waveguide surrounded by fast PhC waveguides on both sides.     

基于光子晶体渐变型双异构微腔的掺铒硅光致发光研究

实验验证了室温下二维氧化物下包层非对称平板三角晶格光子晶体渐变型双异构微腔对绝缘体上硅(SOI)基片上铒氧共掺硅材料的显著发光增强作用.在波长为488 nm、功率为15 mW激光激发下,微腔的光致发光(PL)谱呈现出一个位于1 557.93 nm通信波长处的尖锐狭窄的发光峰,相比于无光子晶体区域,发光增强了约13倍.谐振峰随光泵浦功率增加,发生明显的红移,Q值逐渐下降,在1.5mW光泵浦功率下,Q值达6 655.微腔谐振波长与光子晶体晶格周期之间呈线性正比关系,通过调整晶格周期,实现了掺铒硅发光增强峰波长的灵活可控.     

Negative Uniaxial Crystal Behavior Of Circular Photonic Crystal

In this paper, we introduce an unconventional photonic crystal (PhC) geometry which defines two resonance frequencies. The presented circular PhC structure behaves as a negative uniaxial crystal and admits two preferred propagation directions defined by an extraordinary and an ordinary refractive index representing two field polarizations. The circular grating profile splits the electromagnetic field into a radial (extraordinary field) and a tangential (ordinary field) component, which represent two modes of the periodic structure. The total field in the PhC slab is generated by the superposition effect of the ordinary and extraordinary field produced in the 2-D periodic plane. This field configuration is obtained by the analogy with the dielectric multilayer structure. The presented PhC circular lattice pattern consists of air holes in a GaAs material $({n}=3.408)$ along circular concentric lines which have the same distance defined as the PhC a period. We validate the birefringence theory by the comparison between analytical and numerical results and then between the numerical and experimental ones.      

应用于生物传感的光子晶体微腔设计

We have designed an air-bridged PhC microcavity with high sensitivity and a high quality factor.The structure parameters of the microcavity are optimized by three-dimensional finite-difference time-domain method. We compare the performance of a silicon-on-insulator PhC microcavity and an air-bridged PhC microcavity,and analyze the effect of the thickness of the slab and the radius of the defect hole on the performance of the air-bridged PhC microcavity.For a thinner slab and a larger defect hole,the sens...     

八通道光子晶体滤波器的设计与仿真

设计了一种具有高隔离度的八通道光子晶体滤波器,并应用时域有限差分法分析计算了在晶格常数相同的条件下,点缺陷微腔局域频率与光子晶体介质柱半径之间的变化规律。在此基础上,对该八通道滤波器的传输特性进行了仿真。结果表明,晶格常数取540nm时,该滤波器各信道的中心频率在1 510～1 580nm,信道间隔小于9.5nm,信道间隔离度均大于35dB。     

二维介质圆柱光子晶体自准直迈克耳孙干涉仪

设计并模拟了一种基于光子晶体自准直效应的二维介质圆柱光子晶体迈克耳孙干涉仪。此结构包括一个分束器和两个反射器。利用有限时域差分法计算模拟发现, 在归一化频率范围0.192c/a～0.200c/a内, 光束保持自准直传输, 出口处透射谱成正弦形分布。固定短臂长度同时增大长臂的长度时发现透射谱峰值频率向低频方向移动, 而透射谱峰值的间距非线性下降。因为其等间距分开某一频率范围的特性, 此迈克耳孙干涉仪器可以用于波长信号分离器, 对于光通讯波长1550 nm, 整个干涉仪结构只有几十微米大小, 所以有可能将来用于光子晶体集成器件和全光通讯。     

Efficient Second Harmonic Generation Through Selective Photonic Crystal-Microcavity Coupling

In this paper, a new 2-D frequency converter based on second harmonic generation (SHG) in GaAs photonic crystal waveguides is proposed. The input waveguide, where the second order nonlinear process takes place, is coupled to a secondary waveguide that is designed to allow only SH propagation. A row of photonic crystal microcavity resonators is then placed parallel to the waveguides in order to assist the field coupling. By tuning the resonance of the microcavities at second harmonic wave, the waveguides-microcavities arrangement showed good enhancement of conversion efficiency and selectivity. The performance of the proposed frequency converter has been analyzed by using multiresolution time domain (MRTD) scheme developed for nonlinear problems in conjunction with uniaxial perfectly matched layer (UPML) boundary conditions that rigorously truncate the computational window.     

Low‐Power and High‐Contrast Nanoscale All‐Optical Diodes Via Nanocomposite Photonic Crystal Microcavities

A novel nanoscale integrated all‐optical diode is reported, realized by combining the strong plasmonic responses of gold nanoparticles with the all‐optical tunable properties of polymeric photonic crystal microcavities. Non‐reciprocal transmission properties are achieved based on the effect of surface‐plasmon resonance enhancing the optical non‐linearity and dynamic coupling of asymmetrical microcavity modes. An ultralow‐threshold photon intensity of 2.1 MW cm^?2 and an ultrahigh transmission contrast over 10⁴ are realized simultaneously. Compared with previously reported all‐optical diodes, the operating power is reduced by five orders of magnitude, while the transmission contrast is enlarged by three orders of magnitude.     

FEM Design and Modeling of $chi^{(2)} $ Second-Harmonic Enhancement in Circular Photonic Crystal

In this paper, we analyze the enhancement of $chi^{(2)} $ nonlinear process in membrane-type circular photonic crystal (PhC) based on GaAs. This unconventional kind of PhC is well suited for the generation of whispering gallery modes (WGMs) due to the circular symmetric periodic pattern. By using a laser Gaussian beam at 1.55 $ mu{hbox {m}}$ as pump signal, a WGM at 1.55 $ mu{hbox {m}}$ and a second-harmonic (SH) mode at 0.775 $ mu{hbox {m}}$ are obtained. The SH will be generated in the center of the missing-hole microcavity. The periodic pattern and the microcavity are tailored and optimized providing an SH efficiency conversion as high as 50%. We predict the resonances by an accurate 2-D time-domain model including $chi^{(2)}$ nonlinearity and by a 3-D finite-element method. Finally, by using a 3-D membrane configuration, we found a total quality factor of the SH mode of the order of 35 000.      

Modified Gain and Mode Characteristics in Two-Dimensional Photonic Crystal Waveguide With Microcavity Structure

Optical gain spectra of InGaAsP MQW for photonic crystal waveguide (PCWG) were simulated by the method with considering the variation of group velocity and the natural broadening synthetically. The dependence of the first mode's gain maximum on the width of PCWG was discussed. To improve the mode characteristics and the gain performances in the 2-D PCWG with relative large width, we proposed a new structure by combining a microcavity inside the 2-D PCWG. Mode characteristics in proposed structure were analyzed and the transmission performance was simulated by the FDTD method. The simulation results show that improved longitudinal mode characteristics can be obtained even in the W3 PCWG with relative wide waveguide width because of the additional frequency selecting mechanism provided by the microcavity.     

Silicon-Based Thermo-Optically Tunable Photonic Crystal Lens

We report an extremely compact (30 ?m × 7 ?m) silicon-based 2-D thermo-optically tunable photonic crystal (PhC) lens operated at around telecommunication wavelength (1.55 ?m ) with transverse-magnetic-like polarization light. A honeycomb lattice array of high index silicon rods with 340 nm in thickness, 234 nm in diameter, and 338 nm in lattice constant were embedded in 3-?m-thick low index silicon dioxide. A 150-nm-thick NiCr micro-heater was placed directly on top of the PhC structure to provide localized heating to the silicon rod array. The localized heating causes refractive index change in silicon due to thermo-optic effect which results in change of the focal length of the PhC lens. The device was characterized with a tunable laser light source in the wavelength range of 1500 ~ 1580 nm. Tuning of focal length in this device was experimentally demonstrated by applying different current through the heater. Such experimental results showed good agreement with the simulation results.     

Porous Hydrogel Encapsulated Photonic Barcodes for Multiplex MicroRNA Quantification

The development of a highly sensitive platform for multiplex circulating microRNAs (miRNAs) detection is important for clinical diagnosis. Here, a new type of porous hydrogel encapsulated photonic crystal (PhC) barcodes is presented with integrated rolling circle amplification (RCA) strategy for multiplex miRNA quantification. As the surrounding porous hydrogel shells of the PhC barcodes are interconnected inverse opal structure with hydrophilic scaffolds, they can provide homogeneous water surrounding for the miRNA targets reaction and RCA. The encapsulated PhC cores of the barcodes can offer stable diffraction peaks for encoding different miRNAs and their RCAs during the detection. By integrating the advantages of PhC barcodes and RCA, it is demonstrated that the technology shows acceptable accuracy and detection reproducibility for the rapid quantification of low‐abundance miRNAs, with the limits of detection of 20 fM. Thus, the proposed porous hydrogel encapsulated PhC barcodes provide a new platform for the multiplex quantification of low‐abundance targets for practical applications.     

Quantum Dot Photonic Crystal Light Sources

The control and manipulation of light on a planar IC similar to that achieved for electrons in semiconductor chips on submicrometer and nanometerscales is an area of very active research today. While electronic device miniaturization is close to reaching its maximum possible potential, photonic devices have unique properties that have yet to be exploited. With increasing advances in nanofabrication techniques and the understanding of optical properties of semiconductors, several optical devices such as lasers, detectors, interferometers,and waveguides have been constantly shrinking in size. We have achieved very high speed integrated optical devices at 10-100-/spl mu/m length scales. However, there is a need to further reduce the size of devices to make them competitive in size and cost to existing electronic devices and to utilize their potential and unique properties in a wide range of applications ranging from communications, displays to sensors. Photonic crystals have emerged as one of the best potential candidates that can achieve the goal of compact miniaturized photonic chips. In this paper, we describe the current efforts and advances made in the photonic crystal microcavity light sources and their future prospects.