Photonic generation of a microwave signal by employing a microfiber ring resonator

A novel approach to generate microwave signals is presented by employing a microfiber ring resonator. The microfiber ring resonator is assembled with a microfiber fabricated by heating and drawing standard single-mode fiber. By cascading microfiber ring resonator acted as a comb filter with a tunable bandpass filter, a wavelength-tunable dual-wavelength single longitudinal-mode laser is achieved. A microwave signal at 15.57 GHz with the linewidth of less than 21 kHz is demonstrated by beating the two wavelengths at a photodetector.     

A Microwave Photonic Notch Filter Using a Microfiber Ring Resonator

A novel tunable microwave photonic filter based on a microfiber ring resonator is proposed and experimentally demonstrated. A fiber ring laser based on the microfiber ring resonator is employed to generate two singlelongitudinal-mode carriers, then the dispersive element introduces the delay between two modulated carriers. By adjusting the diameter of the microfiber ring resonator, the proposed microwave photonic notch filter can be continuously and widely tuned. The measured notch rejection ratio is greater than 35 dB, and there is good agreement between the experimental result and the theoretical analysis.     

On‐demand photonic crystal resonators

Recent progress in the field of re‐locatable photonic crystal resonators is discussed with a particular emphasis on the flexible scheme that employs highly‐curved microfiber. In this scheme a spectrally‐tunable high‐quality‐factor resonator can be defined repeatedly by physically moving a curved microfiber to a new position. When a curved microfiber is placed on top of a photonic crystal waveguide (or photonic crystal), a photonic well is newly created in the vicinity of the contact point. Inside of this photonic well, high‐quality‐factor resonant modes are generated at frequencies below the cutoff edge of the guided mode. The tapered microfiber is an integral part of a single mode optical fiber and efficient out‐coupling is naturally obtained. The sub‐nanometer spectral tuning capability that is available by changing the curvature of the microfiber is also an important characteristic and discussed. This spectrally‐ and spatially‐reconfigurable photonic crystal resonator is expected to be a potential platform for photonic crystal based single photon sources, which enables accurate spatial overlap and spectral overlap with a single quantum dot, together with straightforward photon out‐coupling to the fiber with high efficiency.     

Photonic generation of millimeter-wave ultra-wideband signal using microfiber ring resonator

The photonic generation of millimeter-wave (MMW) ultra-wideband (UWB) signal using microfiber ring resonator (MRR) is proposed. The central frequency and 10-dB bandwidth of generated MMW-UWB signal varying with Q factor of MRR are analyzed. We successfully demonstrate a generation of 24-GHz MMW-UWB signal by utilizing a microfiber ring resonator with free spectrum range of 20 GHz and Q factor of 19,000. The generated MMW-UWB signal has a power spectrum density complying with Federal Communication Committee requirements.     

Tunable laser generation with erbium-doped microfiber knot resonator

A tunable laser is demonstrated using a microfiber knot resonator structure made by erbiumdoped fiber (EDF). The laser is made of a 2 m long EDF where 30 mm of its end section is tapered to construct a microfiber knot resonator (MKR). The combination of the EDF and MKR generates a stable single wavelength laser at 1555 nm wavelength with a signal to noise ratio (SNR) of 33.7 dB using a 63 mW of 980 nm pump power. The peak wavelength of the laser can be tuned by 340 pm as the MKR diameter reduces from 5.0 to 0.5 mm with an acceptable penalty in output power.     

全光纤型微环谐振器的研制

环形谐振器因体积小、功能强、结构简洁等优点长期以来一直在光无源、有源器件的设计和制作中发挥着重要的作用。对光纤的弯曲损耗特性进行了深入分析,指出只有采用微细光纤才能降低全光纤法所制作的环形谐振器的尺寸,加宽器件的自由光谱范围(FSR)获得更好的精细度和品质因子。然后,在改进熔融拉锥技术的同时,保持慢变、绝热条件拉制出在80 mm长度范围内具有良好均匀性、半径为5μm的高质量微细光纤,在此基础上采用自缠绕法研制出半径仅为500μm,谐振效果明显加强的全光纤型微环谐振器,从而很好地解决了集成型微环谐振器较高的弯曲损耗和连接损耗问题。     

Transmission characteristic of multi-turn microfiber coil resonator

A transmission characteristic of multi-turn microfiber coil resonator (MCR), which is assembled from an adiabatic microfiber, is demonstrated. A comb spectrum was obtained by wrapping a microfiber on a low refractive indexed rod. A resonance with a free spectral range of 0.8 nm was observed with a single turn on a 0.5 mm diameter low-indexed rod and the change in transmission spectrum of the MCR was evident as the number of turns increased. For every additional microfiber turn, there was an addition of an eigenmode to the system which could be observed from the addition of a new resonance for every fringe in the transmission spectrum. The FSR for every added eigenmode was measured to be close to 0.8 nm.     

Observation of a nonlinear microfiber resonator

Measurements of the intensity transfer function of a silica microfiber resonator are shown to follow a wide variety of hysteresis cycles, depending on the cavity detuning and the scanning frequency of the range of input powers. We attribute these observations to a nonlinear phase shift of thermal origin and provide a simple model that reproduces well our measurements. The response time is found to be around 0.6 ms.     

Anisotropic disk dielectric resonator with conducting end faces

Electrodynamic analysis of a disk dielectric resonator with finite-conductivity end faces that is excited at the whispering-gallery mode is carried out. The inverse problem of determining the components of the permittivity tensor of the anisotropic uniaxial crystal, loss tangent of the dielectric material, and surface resistance of the conductor is formulated and solved. The frequency spectra and energy characteristics of a Teflon disk resonator with copper-covered end faces are studied in the 8-mm wave range.     

A temperature sensor based on optical microfiber knot resonator

A type of compact temperature sensor based on microfiber knot resonator is proposed and demonstrated experimentally. The microfiber knot, which is assembled by two fiber probes, is placed on a plate glass substrate and coated with low-index polymer to keep the system robust. Sensitivities of this kind of temperature sensor as 0.27 nm/°C in heating process (when temperature ranges from 28 to 140 °C) and −0.28 nm/°C in cooling process (when temperature ranges from 135 to 25 °C) are obtained. Temperature resolution of 0.5 °C is demonstrated and higher resolution is predicted with a high-resolution spectrometer.     

微纳光纤镀铂金膜锁模光纤激光器

采用有限元法仿真了微纳光纤中模式在镀膜前后的能量、电场及有效折射率变化,分析了HE11、TE01、HE21和TM01模式在微纳光纤中的传输特性以及与铂金膜的相互作用原理。采用缓冲氧化物刻蚀液制作了微纳光纤并用离子喷溅法镀铂金膜,得到直径为13.2μm、铂金膜厚度为40 nm的微纳光纤器件,测试了其可饱和吸收特性,调制深度和饱和强度分别为0.57%和0.8 MW/cm²。制作了全光纤锁模激光器,锁模阈值为180 mW。锁模脉冲重复频率为17.93 MHz,脉冲宽度为103 ps,中心波长为1 031.6 nm,半高宽约为3.5 nm。     

Temperature compensation techniques for resonantly enhanced sensors and devices based on optical microcoil resonators

It is well known that environmental effects have a major influence on the optical stability of resonantly enhanced sensors and devices based on optical microfiber, namely in the configuration of a microcoil resonator. We propose a geometric design to reduce such effects by chirping the refractive index of successive paired turns in the microcoil resonator. The resistance to external effects such as temperature drifts can be considerably improved by optimizing the coupling coefficients and chirping profile, such that the wavelength span of the resonant condition is maximized without compensating its sensitivity to the desired measurand. We also demonstrate another technique based on resonant wavelength tuning using a compact piezoelectric ceramic disk measuring 3 mm in diameter and 1 mm in thickness, attaining tunability as high as 6.5 pm/100 V.     

Verification of surface WGM in radio frequency band

The ideas of generating surface whispering gallery mode (SWGM) through coating a microresonator with a layer of metamaterials is proposed in our previous work. In this paper, we verify the SWGM with a square resonator based on two-dimensional LC network in radio frequency band. The equivalent node voltage distribution matrix of this resonator is derived. Results show that node voltage can be amplified when the square resonator is covered with a layer of double negative metamaterials. The performance of the metamaterial resonator as a dielectric sensor with excellent sensitivity has been demonstrated. This work may put a great step toward the realization of SWGM sensors using metamaterials.     

Analysis of microring filter with two embedded microring

In this paper, a microring resonator with two embedded microring (MRTEM) has been presented and studied theoretically. Transfer matrix method (TMM) has been used to simulate MRTEM and analyze the relations between add/drop spectrum and embedded microring arrangements. Three kinds of embedded microring arrangements have been proposed and analyzed by TMM. The theoretical and simulation results show that the Q factor of our structure is higher than that of traditional microring structure and the spectrum of MRTEM is independent on embedded arrangements.     

温控太赫兹调制器多频带调制特性

基于开口谐振环结构设计了多频带太赫兹波调制器,并在谐振环的开口处及两侧均填充温敏介质锑化铟(InSb),研究了锑化铟的电磁性质随温度的变化、等效电感的组数对共振频带数目的影响以及锑化铟不同的填充方式对太赫兹波调制特性随温度的变化规律。研究结果表明,当环境温度从160 K上升到350 K时,锑化铟的载流子浓度和等离子体频率逐渐增大,然而等效介电常数却不断减小;每增加一组等效电感,太赫兹波调制器都会相应的增加一个共振频带;在调制器开口处和两侧均填充锑化铟时,当环境温度在160～350 K变化时,温度对太赫兹波的共振频率和共振幅度的调制效果比仅在开口处或者两侧填充锑化铟时更明显,且随着温度的升高,每个共振频带所对应的共振频率均明显增大。     

All-fiber add-drop filters based on microfiber knot resonators

We demonstrate an all-fiber add-drop filter composed of a microfiber knot (working as a resonator) and a fiber taper (working as a dropping fiber). The dropping taper can be either parallel or perpendicular to the input port of the filter. A quality factor (Q factor) of 13,000 is obtained from a parallel-coupling 308 microm diameter microknot add-drop filter with a free spectral range (FSR) of 1.8 nm. A Q factor of approximately 3300 is obtained from a cross-coupling 65 microm diameter microknot add-drop filter with a FSR of 8.1 nm. This device is particularly easy to fabricate and to connect to fiber systems.     

一种新型的水下低频共鸣器*

该文旨在宽开口的共鸣腔内嵌入聚氨酯泡沫来设计一种新型的水下低频共鸣器。首先通过水池实验测定聚氨酯泡沫板的声速。然后基于此建立镶嵌聚氨酯泡沫共鸣器的理论模型获得声阻抗率,通过与直口结构以及棒纵振动模型对比,验证理论模型的正确性,并建立集中参数系统,分析内嵌聚氨酯泡沫能够降低共鸣器共振频率的原因。最后通过有限元仿真软件进行计算,检验理论模型的正确性,与无聚氨酯泡沫镶嵌的共鸣器相比,镶嵌聚氨酯泡沫的共鸣器在维持较低品质因素的同时实现了共振频率大幅降低。     

Total Transformation of an Electromagnetic Wave Incident on a Corrugated Boundary between Transparent Dielectrics to a Transmitting Wave of the (-1)st-Order Harmonic

We present the results of a theoretical and experimental study of a new phenomenon of total transformation of an electromagnetic wave incident from a dielectric on a corrugated boundary between two transparent dielectrics to a transmitting wave of the (-1)st-order harmonic propagating in the other dielectric. The theoretical study is based on numerical solution of the full-wave equations for electromagnetic field. The experimental study is made using a Teflon prism with a corrugated surface located in a two-mirror resonator.     

Engineering Solution in Monitoring Nanoparticle-Fluid Flow During Nanocomposites Processing

New generation composites using nanoparticle-filled matrices have been significantly broadened to encompass a large variety of one-, two-, and three-dimensional systems made of distinctly dissimilar components mixed at the nanometer scale. Nevertheless, during the fabrication process of these novel composites, many problems potentially could arise. One such problem is the clogging of the channels of the microfiber matrix used due to strong interactions between the nanoparticle additives and the matrix walls. In this paper, a two-dimensional simulation model based on Lagrangian multiphase approach for nanoparticle-filled fluid, which flows around an aligned microfiber matrix, is introduced to investigate and predict the nanoparticles trajectories and their interactions with fluid flow and microfiber walls. An energy “imbalance” technique has been applied between the fluid and the microfiber walls to prevent any potential sticking of the nanoparticle additives on the microfiber walls. The trajectory of the nanoparticle has been predicted by integrating the force balance on it in a Lagrangian reference frame. The governing integral equations for the conservation of mass, momentum and energy have been solved in a segregated numerical fashion by a Control-Volume-Based Finite-Element Method.