Wide tuning of silicon-on-insulator ring resonators with a liquid crystal cladding

Wide electrical tuning of silicon-on-insulator ring resonators is demonstrated using a top cladding layer of nematic liquid crystals. A tuning range of 31?nm is demonstrated for ring resonators guiding the TM mode, covering nearly the entire C-band of optical communications. Ring resonators guiding the TE mode can be tuned over 4.5?nm. The combination of a liquid crystal director calculation and a fully anisotropic mode solver confirms the interpretation of these experimental results. The realization of broad and low-power tuning in silicon-on-insulator opens up new opportunities in the field of tunable lasers, filters, and detectors.     

Trimming of high-Q-factor silicon ring resonators by electron beam bleaching

We demonstrate a novel position-resolved resonance trimming strategy for silicon ring resonators. Ring resonators are covered with a chromophore-doped guest host polymer cladding. Illumination of the polymer cladding with high-energy electrons causes a bleaching of the chromophore molecules. Bleaching of the chromophores induces a reduction of the polymer refractive index, which can be used to trim the resonance frequency of the ring resonators. A maximum refractive index change of 0.06 and a TM polarization resonance shift of 16.4?nm have been measured. A Q factor of 20,000 before bleaching remains unaltered after the electron beam exposure process.     

Trimming of microring resonators by photooxidation of a plasma-polymerized organosilane cladding material

As the complexity of microphotonic devices grows, the ability to precisely trim microring resonators becomes increasingly important. Photo-oxidation trimming uses UV irradiation to oxidize a cladding layer composed of polymerized hexamethyldisilane (6M2S) deposited with plasma-enhanced chemical vapor deposition (PECVD). PECVD 6M2S has optical properties that are compatible with microring devices, and its high cross linking renders it insoluble. Photo-oxidation decreases the refractive index of PECVD 6M2S by nearly 4%, permitting large resonance shifts that are not feasible with thermal trimming techniques. Resonance shifts from single-mode, 100 microm diameter Si3N4 (n =2.2) rings were as large as 12.8 nm for the TE mode and 23.5 nm for the TM mode.     

QCM based sensor for detecting volumetric properties of liquids

We introduce a microacoustic sensor, which combines the quartz crystal microbalance, a liquid-filled cavity and an intermediate artificial layer with effective acoustic properties. Each of the three components fulfils a specific task. The quartz vibrates in its thickness shear mode and acts as source and detector of shear waves, which penetrate the intermediate artificial layer and excite a resonance in the liquid-filled cavity. Both the piezoelectric transducer and the liquid-filled cavity are high-Q resonators with well-adjusted resonance frequencies very close to each other. The intermediate artificial layer couples the two resonators in a distinct manner via control of the propagation of acoustic waves between the quartz crystal and the liquid-filled cavity layer. The origin of the sensor signal is a change of the resonance frequency of the liquid-filled cavity caused by variations of acoustic properties of the liquid analyte inside the cavity, first of all speed of sound. This resonance appears as second resonance peak in the admittance spectrum of the quartz crystal.     

Terahertz wave switch based on photonic crystal ring resonators

In this paper, we have presented a compact and integrated terahertz wave switch design based on photonic crystal ring resonators. The photonic crystal structure with square lattice is investigated and applied for design of ring resonators. The switching mechanism of this novel switch is based on the variation of the resonant frequency of the ring resonator inserted between two parallel waveguides. The refractive index of the holes of the structure filled with polyaniline electrorheological fluids are varied by applied external electric field, the result of which is the variation of the ring resonant frequency. The proposed device is analyzed by using finite difference time domain method. Numerical simulation results show that this switch has high extinction ratio, small size, low voltage and advantages of selectivity of coupling THz wave to different output ports.     

Athermal waveguides for optical communication wavelengths

We report on the design, fabrication, and characterization of temperature insensitive strip silicon-on-insulator racetrack resonators. The influence of various parameters, such as waveguide width, waveguide height, ring radius, coupling length, ring gap, and operating wavelength, on temperature-dependent wavelength shift is examined. A resonant wavelength shift of 0.2 pm/K at a 1550 nm wavelength is measured for 335 nm × 220 nm waveguides. A significant reduction of waveguide propagation losses, improved ring Q value, and higher extinction ratio are obtained after overlaying the silicon waveguides with a polymer cladding.     

Investigation of ring resonators in photonic crystal circuits

In this paper, we propose the implementation of waveguide-coupled ring resonators in photonic crystal integrated circuits. Using two-dimensional finite difference time domain (2D FDTD) method, we study the spectral characteristics of a waveguide-coupled ring carved in two-dimensional photonic crystal of square lattice (2D SLPC) and based on the results, we suitably modify the structure geometry to establish its performance as a ring resonator. We further investigate the effects of ring dimension and crystal parameters on the resonance properties of the ring resonator.     

Photonic engineering of surface‐emitting terahertz quantum cascade lasers

Various resonators for surface emission are reviewed that have recently been developed to improve radiative‐ and collection‐efficiencies of terahertz quantum cascade lasers (THz QCL). While the fabrication of waveguides for long wavelengths is challenging in terms of molecular beam epitaxy, long wavelengths also provide a wonderful testbed for new photonics structure concepts, since these can be easily produced by conventional optical lithography because of the typically large size of the required features. This led to novel geometries, like one‐ and two‐dimensional non‐periodic photonic crystals, or circular gratings for microdisk‐ and ring‐lasers, which are all implemented by simply patterning the top metal cladding of a metal‐metal waveguide. The modeling of such resonators with the finite element method is also described, highlighting the importance of this tool for the engineering of surface losses and far‐field patterns.     

Multi-channel drop filters using photonic crystal ring resonators

In this paper, we propose a photonic crystal multi-channel drop filter based on ring resonators and investigate its properties numerically by using the finite-difference time-domain (FDTD) method. This structure is constructed in a two-dimensional square lattice. Our multi-channel drop filter is composed of three waveguides and three ring resonators. These ring resonators are located in two different regions (heterostructure) which each region has specific dielectric constant. At resonance of each ring resonator, the power with certain wavelength transferred to one of the three drop waveguides is found to be more than 81%.     

In-line polarization controller that uses a hollow optical fiber filled with a liquid crystal

We demonstrate an in-line polarization controller based on a hollow optical fiber filled with a nematic liquid crystal by fabricating thin-film electrodes on the cladding of a fiber. The polarization controller consists of three control sections with fixed optic axes, which operate as phase retarders. The phase retardation in each section is controlled by the magnitude of the applied electric field. The full wave retardation voltage of the polarization controller is approximately 85 V.     

Fabrication of tapered fiber based ring resonator

Tapered fiber based ring resonators are fabricated and its optical characteristic is investigated in detail. The ring resonator is fabricated by coiling the tapered fiber, which is firstly made by heating and stretching a piece of optical fiber, after the polymer protective cladding has been removed The comb filter with a constant free spectral range (FSR) and the maximum extinction ratio of 4.2 dB is achieved by a single-mode fiber based ring resonator. The FSR of ring resonator can be adjusted by controlling the diameter of the ring. The extinction ratio is improved in the polarization maintaining fiber based ring resonator where the maximum extinction ratio of 14 dB is achieved at 1531 nm region.     

基于高折射率液体填充的花瓣形微结构光纤可调滤模特性

提出一种新型的可调滤模光纤结构,利用纤芯模式与微结构包层形成的超模群之间的耦合实现选择性滤模,采用花瓣形包层结构使包层中传输的模式更容易产生高的泄漏损耗;提出以液体填充包层介质柱,使包层形成的超模群有效折射率区间可以通过环境温度来调节,从而达到可调选择性滤模目的.利用液体柱的LP11模所形成的超模群,有效增大了其工作带宽和温度调谐范围.数值模拟结果表明,采用长度仅为71.4 mm的滤模光纤,可以使特定的抑制模式损耗达到20 dB以上,而其他模式损耗均在1 dB以下.提出的光纤可以在少模光纤传输系统中作为滤模器使用,以降低模式转换器、复用器/解复用器以及光开关和光路由等的模式串扰.     

A photonic crystal L-shaped bend based on ring resonators

We propose a new type of two-dimensional （2D） photonic crystal L-shaped bent waveguides based on ring resonators with an acceptable bandwidth. The proposed structure mechanism is based on coupling between a waveguide and a ring resonator. This structure is designed and verified by finite-difference time-domain （FDTD） computation. Our simulation using this method gets over 90% output.     

垂直入射条件下厚金属环结构的负磁导率与左手材料行为

用矩形波导法实验研究了微波垂直入射于具有一定厚度的金属铜圆环结构的微波电磁响应行为.结果表明,当金属铜环的厚度增加到一定值时,在中心频率为145GHz处出现透射禁带,并且相位在透射禁带处发生跃变.采用双各向异性媒质理论计算了铜圆环结构的磁导率随频率变化关系,在透射禁带处磁导率为负.对厚金属圆环与金属线一一对应组合的样品,微波沿环面垂直入射时测量到左手透射通带和相位超前,通带带宽达到15GHz,强度为-21dB. 关键词： 负磁导率 垂直入射     

Chirped area coupled resonator optical waveguide gyroscope

We study the transmission of an optical field through a rotating coupled resonator optical waveguide (CROW) in which the size of the ring resonators changes from one ring to the next. We focus on symmetric integer wavelength chirps of the circumference of the rings relative to the central ring in the array. The transfer matrix method is used to obtain the transmission as a function of the inertial rotation rate Ω resulting from the Sagnac effect. Chirping increases the slope of the oscillations in the transmission as a function of Ω, which can be exploited to further enhance the rotation sensitivity beyond that of a CROW with uniform resonators.     

Absorption Measurement Using a Leaky Waveguide Mode

We propose an optical waveguide sensor using a leaky mode for absorption measurement of liquid samples. This sensor uses a single coupling prism. A cladding layer and a waveguide layer are directly deposited on the reflecting surface of the prism. The intensity of the internally reflected beam at an appropriate incident angle is very sensitive to the imaginary part of the sample attached to the surface of the waveguide layer. The sensitivity of this sensor is controlled by the thicknesses of both cladding and waveguide layers. We studied the performance of the sensor by numerical calculation.     

Optical bistability in a single-bus InGaAs micro-ring resonator array

In this paper, we investigate the optical bistability induced by optical nonlinearity in a compact parallel array of micro-ring resonators with radius of 5 μm. Due to the nature of perfect light confinement in this structure, resonance and accumulation process in a ring resonator and optical nonlinear effects, are observable even at small optical power (a few milliwatts). Different optical applications such as all-optical switching, optical memory devices, logic gates and modulators are possible, due to optical bistability in a ring resonator. Using alternative semiconductor compounds, instead of silicon that have weak nonlinear optical properties, we improve the performance of ring-resonator based devices. Here we use a polymer cladding layer with negative thermo-optic coefficient. Using this structure we can eliminate the temperature created nonlinearity which is a very slow process. Therefore, the switching speed increases from a few MHz to several tens of GHz. By plotting the transfer function of the resonator, a hysteresis loop is observed in a few milliwatts. Although, using a ring resonator array the bandwidth reduces, however, the width of the hysteresis loop and resolution between both steady state increases.     

Photonic crystal based cross connect filters

We propose optical cross connect filters using photonic crystal ring resonators coupled waveguide crossings. We investigate the properties of this component numerically by using the finite-difference time-domain method. Our simulations reveal that the photonic crystal based cross connect filter has more than 92% normalized transmission. Extending our concept for cross connection applications, we demonstrate a 1 × 2 PC-based cross connect filter which utilizes a heterostructure. In this filter, at the resonance of each ring resonator, the normalized power transferred to the related waveguide of the two drop waveguides is found to be more than 91%.     

Simultaneous measurement of refractive-index and temperature with high sensitivity by combined use of long-period grating and defect cavity in photonic crystal fibers

A dual-parameter sensor for measuring refractive-index and temperature is designed based on a magnetic fluids infiltrated photonic crystal fiber. By inserting a defective cavity in the cladding layer and inscribing a long-period grating on the fiber core, the proposed sensing mechanism can be achieved directly. The mode coupling and the confinement loss of cladding modes are investigated, and a dual-parameter matrix method is utilized to solve the cross-sensitivity problem. In addition, the relationship between resonant wavelength and external magnetic-field has been studied, which can be used for measuring the magnetic field.     

可调谐光子晶体微环腔型光分叉复用器的设计

提出了一种基于二维光子晶体微环腔的新型光分叉复用器,并可以通过改变环区的硅介质柱的折射率实现波长调谐.运用经典的微环自由光谱范围FSR和微环半径R的关系,证实新型的光子晶体微环腔也满足该关系.利用二维时域有限差分法系统分析了下路信号波长及相应效率随折射率的变化关系.结果表明,只需改变环区折射率0.005,下路波长就可以漂移1 nm,而有效微环半径还不足1.4 μm.