Tapered Photonic Crystal Microcavities Embedded in Photonic Wire Waveguides With Large Resonance Quality-Factor and High Transmission

We present the design, fabrication, and characterization of a microcavity that exhibits simultaneously high transmission and large resonance quality-factor (Q-factor). This microcavity is formed by a single-row photonic crystal (PhC) embedded in a 500-nm-wide photonic wire waveguide - and is based on silicon-on-insulator. A normalized transmission of 85%, together with a Q-factor of 18 500, have been achieved experimentally through the use of carefully designed tapering on both sides of each of the hole-type PhC mirrors that form the microcavity. We have also demonstrated reasonably accurate control of the cavity resonance frequency. Simulation of the device using a three-dimensional finite-difference time-domain approach shows good agreement with the experimental results.     

Subminiature emitters based on a single (111) In(Ga)As quantum dot and hybrid microcavity

The results of numerical modeling and investigation of a hybrid microcavity based on a semiconductor Bragg reflector and a microlens selectively positioned above a single (111) In(Ga)As quantum dot are presented. Emitters based on the hybrid microcavity demonstrate the effective pumping of a single quantum dot and high emission output efficiency. The microcavity design can be used to implement emitters of polarization- entangled photon pairs based on single semiconductor quantum dots.     

High quantum efficiency, long wavelength InP/InGaAs microcavity photodiode

There is a inherent tradeoff between the quantum efficiency and bandwidth of conventional PIN photodiodes. In the case of devices based on III-V semiconductors, an absorption region thickness of approximately 2 mu m is required to achieve quantum efficiencies greater than 80%, although this limits the transit-time-limited bandwidth to less than 15 GHz. It has recently been shown that a microcavity photodiode can circumvent this performance tradeoff and achieve both high quantum efficiency and large bandwidths. The fabrication of a microcavity PIN photodiode with a high quantum efficiency near 1.55 mu m is described. An external quantum efficiency of 82% at 1480 nm has been achieved with an InGaAs absorption layer only 2000 AA thick embedded in a resonant cavity grown by metal organic vapor phase epitaxy (MOVPE).<>     

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.     

Room-temperature light emission from an airbridge double-heterostructure microcavity of Er-doped Si photonic crystal

We experimentally demonstrate an efficient enhancement of luminescence from two-dimensional (2D) hexagonal photonic crystal (PC) airbridge double-heterostructure microcavity with Er-doped silicon (Si) as light emitters on siliconon-insulator (SOI) wafer at room temperature. A single sharp resonant peak at 1 529.6 nm dominates the photoluminescence (PL) spectrum with the pumping power of 12.5 mW. The obvious red shift and the degraded quality factor (Q-factor) of resonant peak appear with the pumping power increasing, and the maximum measured Q-factor of 4 905 is achieved at the pumping power of 1.5 mW. The resonant peak is observed to shift depending on the structural parameters of PC, which indicates a possible method to control the wavelength of enhanced luminescence for Si-based light emitters based on PC microcavity.     

AlGaInP microcavity light-emitting diodes at 650 nm on Gesubstrates

We demonstrate microcavity light emitting diodes (MCLEDs) emitting at 650 nm on Ge substrates. Ge has the advantage of lower cost and higher strength compared to GaAs substrates. The multi-quantum well microcavity devices consisted of AlGaAs-based distributed Bragg reflector (DBR) mirrors, AlGaInP active material with an additional 5-μm p-Al_0.55Ga_0.45As current spreading layer on top of the p-DBR. A maximum external quantum efficiency of 4.35% and an optical power higher than 5 mW was obtained for a device with 200-μm diameter. The results indicate the potential use of MCLEDs on Ge for visible LEDs     

Dual Effect of ITO‐Interlayer on Inverted Top‐Illuminated Polymer Solar Cells: Wetting of Polyelectrolyte and Tuning of Cavity

Flexible inverted top‐illuminated polymer solar cells (IT‐PSCs) are fabricated by wetting of polyelectrolyte and designing a microcavity structure by laying an indium‐tin‐oxide (ITO) interlayer on top of an Ag reflector. The ITO‐coated Ag makes the surface hydrophilic, thereby improving wettability of polyethyleneimine (PEIE). This increased wettability of PEIE yields a reflective cathode with low work function of 3.73 eV. The ITO layer also tunes the light absorption spectrum in the active layer. Finite‐domain time‐difference simulation provides evidence that the ITO layer played a role in both the shift in resonant wavelength in the microcavity and confinement of the electric field to the active layer. Time‐dependent simulation suggests that the time to reach steady‐state light absorption is longer (6.6 fs) when a microcavity is present than when it is not present (3.8 fs); i.e., the microcavity increases light absorption in the active layer. The designed IT‐PSCs show a maximum photo‐conversion efficiency of 6.4% on plastic film and 6.1% on opaque copper foil; these are the highest values obtained by top‐illuminated PSCs on a metallic substrate. The IT‐PSCs have excellent mechanical flexibility and more stable in air than conventional normal structured devices.     

Fabrication of Microcavity Light-Emitting Diodes Using Highly Reflective AlN–GaN and Ta2O 5–SiO2 Distributed Bragg Mirrors

We report the fabrication of microcavity light-emitting diodes (MCLEDs) with high reflectivity and crack-free AlN-GaN distributed Bragg reflector (DBR). The 5lambda microcavity structure consists of an n-type GaN, ten pairs InGaN-GaN multiple quantum wells and p-type GaN sandwiched between the hybrid cavity mode of an AlN-GaN and a Ta₂O₅-SiO₂ DBR. The AlN-GaN DBR has 29 periods with insertion of six AlN-GaN superlattice layers showing a crack-free surface morphology and a high peak reflectivity of 99.4% with a stopband of 21 nm. The output power of MCLED is about 11 W at an injection current of 7 mA. The electroluminescence has a polarization property with a degree of polarization of about 51%.     

A methodology for implementing decimator FIR filters on FPGA

This paper presents a methodology which can be used to implement any decimator symmetric/antisymmetric (S/A) finite impulse response (FIR) filter. Two varieties are developed: a classic distributed arithmetic (CDA) based and a modified distributed arithmetic (MDA) based one. Both exploit the polyphase structure and the symmetry/antisymmetry of the filter and are evaluated in terms of area efficiency, speed and power consumption. The choice of the algorithm depends on the performance metrics targeted. The methodology has been applied to implement the filter bank CDF9/7 which constitutes a one dimensional (1D) and one level discrete wavelet transform (DWT). The filter bank also known as the bior4.4 biorthogonal wavelets is recommended by the JPEG2000 standard for lossy compression of images and video. The architecture has been implemented on an Altera field programmable gate array (FPGA) and the simulations run in Matlab, Modelsim and Altera Quartus II. The results prove the efficiency of the algorithms and show the tradeoff between the area occupied, the throughput and the power consumption.     

参数可线性重构的电流模式二阶带通滤波器

针对二阶通用带通滤波器存在特征参数不能线性重构的缺点,提出一种全新的特征参数可线性重构的电流模式二阶带通滤波器设计理论.该调谐滤波器通过调节反馈电流放大器的放大系数可线性重构二阶带通滤波器的截止频率、品质因素等参数,而滤波器的幅频特性保持不变.Spectre仿真结果表明,±1.5V电源电压下,滤波器的中心频率和品质因素在2 GHz内可线性重构.     

Optical Performance Improvement Mechanism of Multimode-Emitted White Resonant Cavity Organic Light-Emitting Diodes

A microcavity Fabry–Pérot resonator was constructed using a high reflective Al metal and SiO$_{2}$ –TiO$_{2}$ distributed Bragg reflector. Resonant cavity organic light-emitting diodes (RCOLEDs) were fabricated using the microcavity Fabry–Pérot resonator and the conventional organic light-emitting diodes. To improve the optical performances, four-mode emission of the RCOLEDs was resulted by using SiO$_{2}$ filler layer to extend the microcavity length. The improvement of the Commission Internationale d'Eclarirage and color-rendering index is attributed to the four-mode emission. The enhancement of brightness and luminance efficiency was attributed to the stimulated emission in the microcavity Fabry–Pérot resonator.      

A Dual-Mode Terahertz Filter Based on a Metallic Resonator Design

We present a metallic resonator fabricated on silicon capable of dual-mode operation at terahertz frequencies. The resonator exhibits a notch plus stop band filter response or a notch filter response depending on the orientation of the incident electric field with respect to the structure. The former results in two resonance features: one at 0.69 THz with a Q-factor of 3.7 and the other at 0.91 THz. The latter results in a resonance feature at 0.63 THz with a Q-factor of 5.7. Using 3D finite-difference time-domain simulations, the resonator is designed to operate between 0.1 and 1.4 THz. Experimental verification is performed using a free space terahertz time-domain spectroscopy system, and agreement with our simulations is realized.     

A 3.3 mW K-Band 0.18-μ m 1P6M CMOS Active Bandpass Filter Using Complementary Current-Reuse Pair

This letter presents a low-power active bandpass filter (BPF) at K-band fabricated by the standard 0.18 mum 1P6M CMOS technology. The proposed filter is evolved from the conventional half-wavelength resonator filter, using the complementary-conducting-strip transmission line (CCS TL) as the half-wavelength resonator. Furthermore, the complementary MOS cross-couple pair is proposed as a form of current-reuse scheme for achieving low-power consumption and high Q-factor simultaneously. The simulated results indicate that the Q-factor of the proposed half-wavelength resonator can be boosted from 9 to 513 at 25.65 GHz compared with the resonator enhanced by the nMOS cross-couple pair to Q-factor of merely 43 under the same power consumption. The proposed active BPF of order two occupies the chip area of 360 mum times 360 mum without contact pads. The measured results show that the center frequency of the active BPF is 22.70 GHz and a bandwidth of 1.68 GHz (7.39 %). The measured P_{1 dB} and noise figure at 22.70 GHz are -7.65 dBm and 14.05 dB, respectively. There is a 56.84 dB suppression between the fundamental tone and the second harmonic when the input power is -11.26 dBm. While showing 0 dB loss and some residual gain, the active BPF consumes 2.0 mA at 1.65 V supply voltage with maximum of 0.15 dB insertion loss and 9.96 dB return loss at pass band.     

High-isolation bonding pad design for silicon RFIC up to 20 GHz

A simple depletion-insulation (DI) bonding pad structure is presented for silicon radio frequency integrated circuits (RFIC). Experimental results show that DI bonding pads can achieve a 3 to 7 dB improvement in cross-talk isolation compared with an ordinary bonding pad at all measured frequencies. An improvement of up to 90% in the Q-factor is also achieved by the DI pad indicating a significantly reduced high-frequency substrate loss. When compared with a ground-shield (GS) bonding pad, the isolation and the Q-factor of the DI bonding pad is inferior. However, the DI pad has a 40% smaller pad capacitance compared with the GS pad. The DI structure can be used in interconnect optimization to achieve high cross-talk isolation and low substrate loss, with minimal increase in parasitic capacitance.     

A band-pass microwave photonic filter based on Lyot-Sagnac filter and cascaded optical structures

A band-pass microwave photonic filter（MPF）based on Lyot-Sagnac filter and two cascaded optical structures is demonstrated.In the experiment,a stabilized and tunable multi-wavelength optical source is obtained by slicing the broadband optical source（BOS）with a Lyot-Sagnac filter.A standard single-mode fiber（SMF）and a fiber ring resonator are cascaded to improve the mainlobe-to-sidelobe suppression ratio（MSSR）and Q-factor of the filter.The analysis shows that MSSR and Q-factor are improved by reducing the split ratio of the coupler or increasing the length of fiber in fiber ring resonator.The results have significant guidance for MPF design by choosing appropriate devices and parameters.Based on the analyses,a band-pass filter with MSSR of 53.54 dB and Q-factor of 4048 is achieved by choosing the split ratio of0.01,the length of SMF of 30 km and the length of fiber in fiber ring resonator of 152.27 cm.     

Spontaneous emission factor of a microcavity DBR surface-emittinglaser

The spontaneous emission factor (SEF) of a microcavity distributed Bragg reflector (DBR) surface-emitting laser has been obtained theoretically to investigate the possibility of the thresholdless lasing operation. Formulas expressing the spontaneous emission in a three-dimensional microcavity were obtained. By introducing the distribution of mode density in wavevector space, it is shown that the radiation pattern of spontaneous emission is deeply modified by the microcavity and is different from that in free space. Based on this result, the SEF and the emission lifetime are calculated as a function of emission spectral width and the size of the active region. It is found that the SEF exceeds 0.1, even though the spectral width is as large as 30 nm when the transverse size is smaller than 0.5 μm and the DBR reflectivity is larger than 90%     

一款应用于多频带的基于新型Cascode有源电感的高Q带通滤波器

设计了一款基于新型Cascode有源电感和有源负阻电路的二阶差分有源带通滤波器。新型有源电感和有源负阻电路的采用可实现在滤波器Q值不变的条件下对滤波器的中心频率进行调节。仿真结果表明,通过调节有源电感和有源负阻电路的偏置条件,可有效增大滤波器的Q值,且在保持Q值恒定在226的条件下中心频率的变化范围为0.2-3.7GHz。滤波器的以上特性使其能很好地应用于多频带的无线系统。     

Proposal for Q-Modulated Semiconductor Laser

A novel structure and mechanism for high-speed modulation of semiconductor lasers are proposed and analyzed. The modulator consists of an antiresonant cavity acting as a rear reflector of the laser. The change of the absorption coefficient in the modulator results in a change in the reflectivity of the rear reflector, and consequently the Q-factor, the lasing threshold, and the output power. An implementation structure and numerical results for a Q-modulated distributed feedback laser are presented. The monolithically integrated Q-modulated laser has potential advantages of high speed, low wavelength chirp, high extinction ratio, and high power efficiency     

Decoupling Efficiency of a Wideband Vivaldi Focal Plane Array Feeding a Reflector Antenna

A focal plane array (FPA) feeding a reflector can be used to achieve a large field of view (FOV) with overlapping simultaneous beams. In order to provide a continuous FOV over more than an octave bandwidth, the inter-element spacing in the FPA has to be electrically small over large parts of the band. This will inevitably result in strong mutual coupling effects between the array elements. On transmit, the total lost power due to mutual coupling can be quantified by the decoupling efficiency, a term recently introduced for antenna arrays. This paper presents measured decoupling efficiencies of a Vivaldi element FPA operating between 2.3 and 7 GHz. The radiation patterns of the FPA are calculated for two beam excitations by using measured embedded element patterns, and the corresponding decoupling efficiencies are evaluated by using measured $S$ -parameters between all element ports. The FPA is assumed to illuminate a deep reflector with $F/D=0.35$ , and the overall reflector aperture efficiencies are computed. The decoupling efficiencies are also determined through the measurements of the total radiation efficiencies in a reverberation chamber, which includes material absorption losses.      

Low threshold current density operation of GaInAsP-InP laser withmultiple reflector microcavities

We propose and demonstrate a new type of semiconductor laser having multiple reflector microcavities for the purpose of low threshold current operation. Very uniform multiple reflector microcavity structure was fabricated by electron beam (EB) lithography and selective wet chemical etching. Due to multiple reflection effect, threshold current density as low as 310 A/cm² (threshold current of 30 mA) was obtained at room temperature with the total cavity length of 64 μm and the cavity width of 200 μm