Tunable optical nanocavity based on modulation of near-field coupling between subwavelength periodic nanostructures

We present the design and analysis of a tunable resonant optical filter based on modulation of the near-field coupling between two subwavelength periodic nanostructures embedded in a Fabry-Pe/spl acute/rot cavity. Due to the transverse localization of the optical field in the subwavelength gratings, their relative positioning strongly influences the near-field coupling between them and, thus, affects the resonance of the cavity. Rigorous electromagnetic analysis tools are applied to determine the optical characteristics of the filter with respect to the nanostructure lateral alignment, small variations in the shape of the nanostructures, and the physical separation of the nanostructures.     

测量溶液浓度的微波谐振腔优化设计

基于微波谐振腔微扰原理建立了应用于测量葡萄糖溶液浓度的谐振腔传感器模型。采用HFSS仿真软件对不同孔耦合结构尺寸的谐振腔进行仿真,通过比较耦合孔S11曲线得到谐振腔的最优化尺寸。仿真结果表明,该微波谐振腔耦合孔半径为3.5 mm,波导长30 mm时,微波谐振腔具有优越的电磁性能和很高的分辨率。以不同浓度的葡萄糖溶液为该谐振腔的加载样品,采用优化后的谐振腔模型进行仿真,结果表明不同浓度的葡萄糖溶液所引起的谐振频率变化显著,其变化幅度可以在S曲线上得出,通过检测频移的变化就可以得到葡萄糖溶液的浓度。     

Silicon Microtoroidal Resonators With Integrated MEMS Tunable Coupler

A single crystalline silicon microtoroidal resonator with integrated MEMS-actuated tunable optical coupler is demonstrated for the first time. It is fabricated by combining hydrogen annealing and wafer bonding processes. The device operates in all three coupling regimes: under-, critical, and over-coupling. We have also developed a comprehensive model based on time-domain coupling theory. The experimental and theoretical results agree very well. The quality factor (Q) is extracted by fitting the experimental curve with the model. The unloaded Q is as high as 110 000, and the loaded Q is continuously tunable from 110 000 to 5400. The extinction ratio of the transmittance is 22.4 dB. This device can be used as a building block of resonator-based reconfigurable photonic integrated circuits     

Photothermal imaging of nanoparticles and cells

This review summarizes the findings of recent applications of time-domain far-field photothermal (PT) technique to the detection and imaging of nanoscale absorbing particles. This two-beam (pump-probe) technique is based on time-resolved PT visualization of laser-induced thermal effects around nanoparticles. Imaging is accomplished, after an adjustable time delay after the pump laser pulse, with a second probe beam that senses the nanotarget. Using a tunable optical parametric oscillator laser (wavelength, 420 to 570 nm; energy, 0.1-300 /spl mu/J; pulse width, 8 ns) as the pump laser and a Raman shifter (639 nm, 10 nJ, 13 ns) as the probe laser, with a tunable delay of 0 to 5 000 ns of the probe pulse relative to the pump pulse, this approach has demonstrated the capability to visualize nanoscale gold particles (2 to 250 nm) alone and in cells, liposomes (30 to 90 nm), neutral red-stained particles (30 to 500 nm), and polystyrene beads. Different applications of the time-resolved PT technique are discussed, including imaging of absorbing cellular nanostructures and optimization of selective killing of cancer cells and bacteria.     

Single-mode distributed feedback and microlasers based on quantum-dot gain material

Quantum-dot gain material fabricated by self-organized epitaxial growth on GaAs substrates is used for the realization of 980-nm and 1.3-/spl mu/m single-mode distributed feedback (DFB) lasers and edge-emitting microlasers. Quantum-dot specific properties such as low-threshold current, broad gain spectrum, and low-temperature sensitivity could be demonstrated on ridge waveguide and DFB lasers in comparison to quantum-well-based devices. 980-nm DFB lasers exhibit stable single-mode behavior from 20/spl deg/C up to 214/spl deg/C with threshold currents < 15 mA (1-mm cavity length). Utilizing the low-bandgap absorption of quantum-dot material miniaturized monolithically integrable edge-emitting lasers could be realized by deeply etched Bragg mirrors with cavity lengths down to 12 /spl mu/m. A minimum threshold current of 1.2 mA and a continuous-wave (CW) output power of >1 mW was obtained for 30-/spl mu/m cavity length. Low-threshold currents of 4.4 mA could be obtained for 1.3-/spl mu/m emitting 400-/spl mu/m-long high-reflection coated ridge waveguide lasers. DFB lasers made from this material by laterally complex coupled feedback gratings show stable CW single-mode emission up to 80/spl deg/C with sidemode suppression ratios exceeding 40 dB.     

2.85GHz回旋波整流器高频系统的设计及优化

对2.85 GHz回旋波整流器的高频互作用区进行了研究与设计;运用CST分析了高频结构中耦合环结构的变化对高频系统S参数的影响,在此基础上对腔体结构做了优化;并用CST PIC对其进行了粒子模拟,优化解决了电子注的加入对谐振腔特性的影响。最后设计出了工作在2.85 GHz,具有较高能量转化效率的回旋波整流器高频互作用区。     

Resonant-cavity optoelectronic devices for fluorimetry

Vertical cavity, semiconductor optoelectronic devices have been designed specifically for applications in fluorescence spectroscopy. The devices emit and detect light in a direction normal to their surface and could be readily integrated into lab-on-a-chip formats with extremely close proximity coupling to the analyte. The emission is narrow band and centered at 645 nm, whereas the detection response is broadband extending from 645 to 870 nm. A resonant cavity structure has been used to independently control the emission and detection characteristics, and a comparison is given between structures with a cavity enhancement at either the emission or the detection wavelength. In both cases, an enhancement by a factor of greater than 15 is achieved due to the presence of the optical cavity. In emission, this provides micrometer-scale devices with power levels in the 50-/spl mu/W range. When the cavity is used to enhance detection, a minimum detection power level of 100 nW is achieved.     

Surface-plasmon quantum cascade microlasers with highly deformed resonators

We report the demonstration of surface-plasmon microcylinder quantum cascade lasers with circular and deformed resonators. An improved self-alignment fabrication technique was developed that allows the use of wet etching, necessary to achieve smooth and clean surfaces, in combination with the deposition of the surface-plasmon-carrying metal layer up to the very edge of the resonator, where the optical mode is mostly located. The diameter of the microcylinders ranges from 75 to 180 /spl mu/m while their deformation coefficient /spl epsiv/ ranges from /spl epsiv/=0 to /spl epsiv/=0.32. Circular microcylinder lasers show a reduction of /spl sim/50% of the threshold current density with respect to devices with standard ridge-waveguide resonators. On the other hand, highly deformed microcylinder lasers exhibit a complex mode structure, suggesting the onset of chaotic behavior.     

Reflection-Type Ferroelectric Phase Shifter With Defected Ground Structure

In order to obtain a low-loss ferroelectric phase shifter, we were designed and fabricated the reflection-type ferroelectric phase shifter with the defected ground structure (DGS) resonators. The ferroelectric phase shifter is consisted of a 3-dB 90° branch-line hybrid coupler and terminated reflective circuit with tunable ferroelectric DGS resonator which can provide a high Q resonator characteristic at high frequencies. The design parameters of equivalent circuit for the tunable DGS resonator are derived by circuit analysis method and three-dimensional full wave finite element method. At 13.5 GHz, the fabricated phase shifter exhibited an insertion loss of better than 3.4 dB.     

Fabrication technologies for vertically coupled microring resonator with multilevel crossing busline and ultracompact-ring radius

To eliminate the scattering loss at the crossing points of cross-grid busline waveguides, the multilevel crossing structure of the busline waveguides was introduced into a vertically coupled microring resonator (VCMRR) filter. To achieve this structure, two fabrication technologies were newly developed; one is a method to planarize perfectly the top surface of each buried waveguide, and the other is a method to fabricate microring waveguides with very smooth sidewalls. Using the latter method, an ultracompact VCMRR with a ring radius of 5 /spl mu/m was realized and a free spectral range of 37 nm was successfully demonstrated. Next, using the former method, single-ring and quadruple series-coupled ring resonators with multilevel crossing busline waveguides were fabricated. A clear filter response was obtained for the single-microring resonator, and a boxlike filter response was obtained for the quadruple series-coupled microring resonator with multilevel crossing busline waveguides.     

Relaxation of Critical Coupling Condition and Characterization of Coupling-Induced Frequency Shift in Two-Ring Structures

We present a systematic study of two-ring–one-bus (2R1B) and two-ring Mach–Zehnder interferometer (2RMZI). By exciting the cavity modes in certain ways, it is possible to shape the transmission spectrum that may be suitable for specific applications, such as relaxation of critical coupling for the case of 2R1B or finesse enhancement for the case of 2RMZI. The deteriorating effects of resonator self-coupling known as coupling-induced resonance frequency shift is quantized. The two-ring structures are demonstrated on a silicon-on-insulator platform where good agreement is obtained between the experiment and the theory.      

The impact of LOC structures on 670-nm (Al)GaInP high-power lasers

We investigate the potential of large optical cavity (LOC)-laser structures for AlGaInP high-power lasers. For that we study large series of broad area lasers with varying waveguide widths to obtain statistically relevant data. We study in detail I/sub th/, /spl alpha//sub i/, /spl eta//sub i/, and P/sub max/, and analyze above-threshold behavior including temperature stability and leakage current. We got as expected for LOC structures minimal /spl alpha//sub i//spl les/1 cm/sup -1/ resulting in /spl eta//sup d/=1.1 W/A for 64/spl times/2000 /spl mu/m/sup 2/ uncoated devices. We obtain total output powers /spl ges/3.2 W (qCW) and /spl ges/1.5 W (CW) at 20/spl deg/C.     

Design and Simulation of a Tunable Multilayer Lange Coupler

Full-wave electromagnetic simulators based in the method of moments (HP-EEsof Momentum) and in the finite difference time domain technique (Remcom's XFDTD) are ideal to analyze and study the effect of ferroelectric materials on the output response of microwave passive structures. The nonlinear electric field dependence of ferroelectric thin films has been used by the microwave research community to design tunable components. The fabrication of these structures is expensive and time consuming, hence, estimated results of the S-parameters using electromagnetic simulators are desirable previous to the fabrication process. In this work, BSTO ferroelectric thin film is used on MgO to simulate the output response of a K band multilayer Lange coupler. The S-parameters of the couplers are estimated for different bias conditions for the BSTO. Isolation, insertion loss, coupling, and return loss are computed for different bias conditions.     

Intracavity spectral shaping in external cavity mode-lockedsemiconductor diode lasers

Intracavity spectral shaping techniques have been employed to artificially shape and broaden the optical spectrum of external cavity mode-locked semiconductor lasers. Using an intracavity spectrometer and intensity Fourier-plane filtering, active mode-locked output spectra with a multiplicity of independently tunable wavelengths have been generated, while an adjustable intracavity etalon has been employed to generate an 18-nm spectral width. Furthermore, hybrid mode-locking with a multiple-quantum-well (MQW) saturable absorber combined with the intracavity etalon, followed by dispersion compensation has led to the generation of optical pulses of 330 fs in duration     

Integrated fluidic lenses and optic systems

Functionally integrated fluidic lenses and lens systems were demonstrated. Fluidic optic lenses can function as lenses with tunable focal distance, lens doublets with variable and convertible lens type, zoom lenses, and a lens system possessing both telephoto and reverse telephoto functions. High lens power and broad tuning range were achieved in a single 20-mm aperture device that can be tuned to have a convex or concave shape, with the respective tunable focal distance from 14.3 mm to infinity and from -6.1 mm to negative infinity. For fluidic adaptive zoom-lens-on-a-chip, a zoom ratio of 2.14 was achieved for 20-mm lens aperture, and a zoom ratio of 2.83 for 5-mm lens aperture. For the latter device, a tunable field-of-view from 10/spl deg/ to 80/spl deg/ was demonstrated, suggesting that the functions of telephoto and reverse telephoto systems can be achieved in a single zoom lens chip. Finally, the fluidic devices including the microfluidic pumps can be integrated with the lenses. All these integrated fluidic lenses and lens systems were microfabricated using a modified UV-LIGA process.     

High-Q tunable dielectric resonator filters

Tunable dielectric resonator filters can potentially address wireless and satellite applications that require very high Q values (4,000 and up) with a limited tuning range (less than 15%). Such high Q requirements cannot be met by any other known non-superconductor tunable filter technology at the present time. The intent of this paper is to provide newcomers and end users with the current status and prospective of using dielectric resonators for tunable filters. It is an enabling technology for high-Q tunable filter applications. A key challenge, however, is to increase the tuning range without degrading the Q value. While several techniques have been reported to demonstrate the feasibility of tuning dielectric resonators, the tunable dielectric resonator filter technology is still in its infancy. Very limited research effort has been dedicated to explore the potential for improving the tuning range. Most of the work reported thus far has focused on the use of TE_01delta modes and standard shape resonators demonstrating a narrow tuning range. We believe that the tuning range can be increased while maintaining reasonably high Q values by exploring the use of other modes and by the use of non-standard-shape dielectric resonators.     

Single-mode 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP quantum well vertical cavity surface emitting lasers

The 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current varies from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% from 0.17 to 0.11 mW/mA as the temperature is raised from room temperature to 75/spl deg/C. The VCSELs continuously operate up to 105/spl deg/C with a slope efficiency of 0.023 mW/mA. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is estimated to be 10.7 GHz with modulation current efficiency factor of /spl sim/5.25GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C. We also accumulated life test data up to 1000 h at 70/spl deg/C/10 mA.     

A series‐coupled LC quadrature oscillator using phase/amplitude calibration

In this paper, an analytic approach for the estimation of the phase and amplitude error in series coupled LC quadrature oscillator (SC‐QO) is proposed. The analysis results show that imbalances in source voltage of coupling transistor because of mismatches between LC tanks are the main source of the phase and amplitude error in this oscillator. For compensation of the phase and amplitude error, a phase and amplitude‐tunable series coupled quadrature oscillator is designed in this paper. A phase shift generation circuit, designed using an added coupling transistor, can control the coupling transistor source voltage. The phase and amplitude error can simply be controlled and removed by tuning the phase shifter, while this correction does not have undesirable impact on phase noise. In fact, the proposed SC‐QO generates a phase shift in the output current, which reduces the resonator phase shift (RPS) and improves phase noise. The phase and amplitude tunable SC‐QO is able to correct the phase error up to ±12°, while amplitude imbalances are reduced as well. To evaluate the proposed analysis, a 4.5‐GHz CMOS SC‐QO is simulated using the practical 0.18‐μm TSMC CMOS technology with a current consumption of 2 mA at 1.8‐V supply voltage. Copyright © 2016 John Wiley & Sons, Ltd.     

Theoretical studies of AlGaAs-GaAs multiple-quantum-well opticalcouplers defined by ion-implantation-induced intermixing

A simple and accurate model is presented for the analysis of ion-implanted AlGaAs-GaAs multiple-quantum-well (MQW) symmetric and asymmetric optical couplers. The modal propagation constants and field profiles of the guided modes of the couplers are solved numerically using a quasi-vector method based on the Galerkin's method. MQW optical couplers defined by ion-implantation-induced intermixing are shown to have similar optical properties as conventional dielectric rib optical couplers. They also provide a more flexible control over the waveguiding and coupling characteristics by changing parameters such as waveguide separation, mask width, ion implant energy, and diffusion time     

ANALYSIS OF A GRID DIPOLE ARRAY PLACED INSIDE A WAVEGUIDE CAVITY WITH A RECTANGULAR COUPLING APERTURE

The circuit and coupling properties of a dipole grid array placed inside a rectangular cross-section waveguide are analysed when also a rectangular aperture is used to couple the resonator energy into a semi-infinite waveguide. A Green function approach is employed to determine the current distribution on the dipole elements by solving an integral equation and taking into account the boundary conditions on the rectangular cavity walls. Both mutual and self-impedance terms are calculated for the dipole grid array, and the effects of the rectangular coupling aperture are also examined. © 1997 by John Wiley & Sons, Ltd.