Derivation of General Formula for Coupling Loss of Single-mode Fiber Collimators with Gradient——index Rod Lenses

Gradient--index rod lens (GRIN--lens) whose pitch is ordinary value with bevel ferrule coupling system is analyzed, an equivalent method which can be used to analyze this system is put forward, and a general formula for determining the coupling loss with axes mismatch, radial mismatch, and angular mismatch is derived by use of the Gaussian field approximation and mode-field coupling theory. The experimental results are in good agreement with the theory prediction. It indicates that these formulas are suitable to analyze the gradient--index rod lens coupling system with pigtail fiber.     

Influence on Multimode Rectangular Optical Waveguide Propagation Loss by Surface Roughness

Optical scattering loss coefficient of muhimode rectangular waveguide is analyzed in this work. First, the effective refrac tive index and the mode field distribution of waveguide modes are obtained using the Marcatili method. The influence on scattering loss coefficient by waveguide surface roughness is then analyzed. Finally, the mode coupling efficiency for the SMFOpticalWaveguide （SOW） structure and MMFOptical Waveguide （MOW） structure are presented. The total scatter ing loss coefficient depends on modes scattering loss coeffi cients and the mode coupling efficiency between fiber and waveguide. The simulation results show that the total scatter ing loss coefficient for the MOW structure is affected more strongly by surface roughness than that for the SOW struc ture. The total scattering loss coefficient of waveguide decreas es from 3.97 x 10^-2 dB/cm to 2.96 x 10^-4 dB/cm for the SOW structure and from 5.24 - 10^-2 dB/cm to 4.7 x 10^-4 dB/ cm for the MOW structure when surface roughness is from 300nm to 20nm and waveguide length is 100cm.     

一种新型SiGe-OI脊形光波导的模式分析及结构参数优化

The mode of a novel SiGe-OI optical waveguide is analyzed, and its single-mode conditions are derived. The Ge content and structure parameters of SiGe-OI optical waveguides are respectively optimized. Under an operation wavelength of 1300 nm, the structures of SiGe-OI rib optical waveguides are built and analyzed with Optiwave software, and the optical field and transmission losses of the SiGe-OI rib optical waveguides are analyzed. The optimization results show that when the structure parameters H, h, W are respectively 500 nm, 250 nm, 500 nm and the Ge content is 5%, the total power loss of SiGe-OI rib waveguides is 0.3683 dB/cm considering the loss of radiation outside the waveguides and materials, which is less than the traditional value of 0.5 dB/cm. The analytical technique for SiGe-OI optical waveguides and structure parameters computed by this paper are proved to be accurate and computationally efficient compared with the beam propagation method （BPM） and the experimental results.     

Four-way radial waveguide power divider with high power-handling capacity

In this paper,a novel four-way radial waveguide power divider with low insertion loss and high power-handling capacity is proposed.This power divider consists of an input coaxial waveguide,a central probe,a radial waveguide,four equispaced identical coupling probes,four equispaced identical adjusting posts and four output coaxial waveguides.The novel coupling probes and the adjusting posts are used to realize favorable uniform power division.A power divider with the center frequency of 4.1 GHz is designed,fabricated and measured.Good agreement between simulation and experiment is noted.The measured 15 dB return-loss bandwidth of the power divider is about 600 MHz.The measured 0.5 dB insertion loss bandwidth is wider than 700 MHz.The differences and isolations between the output ports are also discussed.The power-handling capacity of the power divider is analyzed through simulation,and the result proves its usability in high power applications.     

Optimization of silicon-on-insulator based optical switch using tapered waveguides

Optimized 2×2 switches based on silicon-on-insulator (SOI) were demonstrated. In the design, single mode rib waveguidesand multimode interferences (MMIs) are connected by tapered waveguides to reduce the mode coupling loss between thetwo types of waveguides. The average insertion loss of the switches is about -16.9 dB and the excess loss of one is measuredof -1.3 dB. The worst crosstalk is larger than 25 dB. Experimental results indicate that some of the main characteristics ofoptical switches are improved in the modified design, which is according with theoretic analysis. The novel design can beused to improve the characteristics of optical switch matrixes based on 2×2 switch units.     

Non-polarization and high-coupling-efficiency coupler using multilevel grating structure

A multilevel grating coupler based on silicon-on-insulator (SOI) material structure is proposed to realize the coupling between waveguide and waveguide or waveguide and fiber. This coupler is compatible with the current fabrication facilities for complementary metal oxide semiconductor (CMOS) technology with vertical coupling. This structure can realize coupling when the beams with transverse electric (TE) polarization and transverse magnetic (TM) polarization are incident at the same time. The influences of the grating coupler parameters including wavelength, the thickness of waveguide layer, the thickness of SiO₂ layer and the number of steps on the TE mode and TM mode coupling efficiencies are discussed. Theory researches and simulation results indicate that the wavelength range is from 1533 nm to 1580 nm when the TE mode and TM mode coupling efficiencies are both more than 40% as the grating period is 0.99 μm. The coupling efficiencies of the incident TE and TM modes are 49.9% and 49.5% at the wavelength of 1565 nm, respectively, and the difference between them is only 0.4%.     

A simplified dispersion-compensation microstructure fiber with seven cores

In order to compensate the dispersion accumulated in a single mode fiber (SMF) for higher communication capacity, a simplified dispersion-compensation microstructure fiber (DC-MSF) with seven cores is proposed in this paper. The fiber’s cladding is made of pure silica without air holes, and its outer cores are composed of six germanium up-doped cylinders, which has the advantage of simple structure. The finite element method (FEM) and beam propagation method (BPM) are used to study the properties of the fiber, and the relationship between the structural parameters of the fiber and the dispersion, as well as the phase matching wavelength, is obtained. By optimizing the structural parameters of the fiber, the dispersion of the fiber can reach −5 291.47 ps.nm-1.km-1 at 1 550 nm, and the coupling loss to the conventional single-mode fiber is only 0.137 dB. Compared with the conventional dispersion-compensation fiber, the fiber has lots of advantages, such as single mode transmission, easy to fabricate and low coupling loss with traditional SMF, etc.     

Strip Waveguide Directional Coupling Modulator with Equivalent Refractive Index

The equivalent refractive index(ERI) method is employed to analyze the function of the strip waveguide directional coupling modulator(SWM). Through deducing the diagnostic equation of the Enm^x mode of the four--layer media film waveguide equivalent to the SWM,the transmission constant of the symmetrical mode of the positive phase and negative one and the coupling length of powerful transference are obtained. The veracity of ERI is validated with the example of Enm^x basal mode under the condition of comparing the three results of ERI,EIM and Marcatili.     

Ultra-small microring resonator based on sub-micrometer fiber

The transfer function of the microring resonator is deduced,and the effects of the normalized loss,coupling coefficient and surrounding media on the resonance performance are investigated thoroughly.Utilizing the improved fused tapering tech-nique and ingenious self-coiling coupling method,a high-quality microring resonator(radius of about 500μm)with larger extinction ratio(>10 dB)and sharper resonance is designed and fabricated by a segment of continuous sub-micrometer fiber.The microring resonator constructed in this way demonstrates extremely small connection loss with communication fiber in contrast to the planar waveguide technology.     

Analysis on Mode Field Distribution of Waveguide Grating Coupler by the Scalar FDTD

The scalar two--dimensional finite difference time domain (FDTD) method is applied to simulate the mode field distribution of TE0 of the waveguide grating coupler.Computer simulation shows that the same stable mode field distribution pattern is obtained through the different kinds of driving sources. It is found that the optical field mode is determined by waveguide structure and optical wavelength other than the driving source.According to the mode field distribution, the optimum coupling efficiency can be predicted.Compared with another numerical methods, the CPU- time and memory elements of computer used by FDTD are much less.     

Ranking Potential Reply-Providers in Community Question Answering System

Community Question Answering （CQA） websites have greatly facilitated users＇ lives, with an increasing number of people seeking help and exchanging ideas on the Internet. This newlymerged community features two characteristics： social relations and an ask-reply mechanism. As users＇ behaviours and social statuses play a more important role in CQA services than traditional answer retrieving websites, researchers＇ concerns have shifted from the need to passively find existing answers to actively seeking potential reply providers that may give answers in the near future. We analyse datasets derived from an online CQA system named ＂Quora＂, and observed that compared with traditional question answering services, users tend to contribute replies rather than questions for help in the CQA system. Inspired by the findings, we seek ways to evaluate the users＇ ability to offer prompt and reliable help, taking into account activity, authority and social reputation char- acteristics. We propose a hybrid method that is based on a Question-User network and social network using optimised PageRank algorithm. Experimental results show the efficiency of the proposed method for ranking potential answer-providers.     

一个全差分可编程的多通道神经信号记录芯片

A multi-channel,fully differential programmable chip for neural recording application is presented.The integrated circuit incorporates eight neural recording amplifiers with tunable bandwidth and gain,eight 4thorder Bessel switch capacitor filters,an 8-to-1 analog time-division multiplexer,a fully differential successive approximation register analog-to-digital converter(SAR ADC),and a serial peripheral interface for communication.The neural recording amplifier presents a programmable gain from 53 dB to 68 dB,a tunable low cut-off frequency from 0.1 Hz to 300 Hz,and 3.77 μVrms input-referred noise over a 5 kHz bandwidth.The SAR ADC digitizes signals at maximum sampling rate of 20 kS/s per channel and achieves an ENOB of 7.4.The integrated circuit is designed and fabricated in 0.18-μm CMOS mix-signal process.We successfully performed a multi-channel in-vivo recording experiment from a rat cortex using the neural recording chip.     

A power-efficient 12-bit analog-to-digital converter with a novel constant-resistance CMOS input sampling switch

Apower-efficient 12-bit40-MS/spipelineanalog-to-digitalconverter（ADC）implementedina0.13 μm CMOS technology is presented. A novel CMOS bootstrapping switch, which offers a constant on-resistance over the entire input signal range, is used at the sample-and-hold front-end to enhance the dynamic performance of the pipelined ADC. By implementing with 2.5-bit-per-stage and a simplified amplifier sharing architecture between two successive pipeline stages, a very competitive power consumption and small die area can be achieved. Meanwhile, the substrate-biasing-effect attenuated T-type switches are introduced to reduce the crosstalk between the two op- amp sharing successive stages. Moreover, a two-stage gain boosted recycling folded cascode （RFC） amplifier with hybrid frequency compensation is developed to further reduce the power consumption and maintain the ADC＇s performance simultaneously. The measured results imply that the ADC achieves a spurious-free dynamic range （SFDR） of 75.7 dB and a signal-to-noise-plus-distortion ratio （SNDR） of 62.74 dB with a 4.3 MHz input signal; the SNDR maintains over 58.25 dB for input signals up to 19.3MHz. The measured differential nonlinearity （DNL） and integral nonlinearity （INL） are -0.43 to ＋0.48 LSB and -1.62 to ＋ 1.89 LSB respectively. The prototype ADC consumes 28.4 mW under a 1.2-V nominal power supply and 40 MHz sampling rate, transferring to a figure- of-merit （FOM） of 0.63 pJ per conversion-step.     

Low power high gain gain-controlled LNA and mixer for GNSS receivers Wei Binbin(魏斌斌)1, Jiang Jinguang(江金光)1,2,3*

A low power high gain gain-controlled LNA ＋ mixer for GNSS receivers is reported. The high gain LNA is realized with a current source load. Its gain-controlled ability is achieved using a programmable bias circuit. Taking advantage of the high gain LNA, a high noise figure passive mixer is adopted. With the passive mixer, low power consumption and high voltage gain of the LNA ＋ mixer are achieved. To fully investigate the performance of this circuit, comparisons between a conventional LNA ＋ mixer, a previous low power LNA ＋ mixer, and the proposed LNA ＋ mixer are presented. The circuit is implemented in 0.18 #m mixed-signal CMOS technology. A 3.8 dB noise figure, an overall 45 dB converge gain and a 10 dB controlled gain range of the two stages are measured. The chip occupies 0.24 mm2 and consumes 2 mA current under 1.8 V supply.     

一种应用于GPS接收机的高线性度SiGe HBT低噪声放大器

A high linearity 1.575 GHz SiGe：HBT low noise amplifier （LNA） for global positioning system applications is described. The bipolar cascoded with an MOSFET LNA was fabricated in a commercial 0.18 μm SiGe BiCMOS process, A resistor bias feed circuit with a feedback resistor was designed for the LNA input transistor to improve its intermodulation and compression performance. The packaged chip tested on board has displayed a noise figure of 1. I 1 dB, a power gain of 18 dB, an output 1 dB compression point of ＋7.8 dBm and an input third-order intercept point of ＋1.8 dBm. The chip occupies a 500 × 560μm^2 area and consumes 3.6 mA from a 2.85 V power supply.     

用于U波段移动数字电视的宽带大动态范围高线性度射频前端

A wideband large dynamic range and high linearity U-band RF front-end for mobile DTV is introduced,and includes a noise-cancelling low-noise amplifier(LNA),an RF programmable gain amplifier(RFPGA) and a current communicating passive mixer.The noise/distortion cancelling structure and RC post-distortion compensation are employed to improve the linearity of the LNA.An RFPGA with five stages provides large dynamic range and fine gain resolution.A simple resistor voltage network in the passive mixer decreases the gate bias voltage of the mixing transistor,and optimum linearity and symmetrical mixing is obtained at the same time.The RF front-end is implemented in a 0.25 μm CMOS process.Tests show that it achieves an ⅡP3(third-order intercept point) of –17 dBm,a conversion gain of 39 dB,and a noise figure of 5.8 dB.The RFPGA achieves a dynamic range of –36.2 to 23.5 dB with a resolution of 0.32 dB.     

一种电流复用共栅低噪声放大器的低功耗433/915-MHz射频前端的设计

This paper presents a wideband RF front-end with novel current-reuse wide band low noise amplifier(LNA),current-reuse V –I converter,active double balanced mixer and transimpedance amplifier for short range device(SRD) applications.With the proposed current-reuse LNA,the DC consumption of the front-end reduces considerably while maintaining sufficient performance needed by SRD devices.The RF front-end was fabricated in 0.18 μm RFCMOS process and occupies a silicon area of just 0.11 mm2.Operating in 433 MHz band,the measurement results show the RF front-end achieves a conversion gain of 29.7 dB,a double side band noise figure of 9.7 dB,an input referenced third intercept point of –24.9 dBm with only 1.44 mA power consumption from 1.8 V supply.Compared to other reported front-ends,it has an advantage in power consumption.     

一种应用于GNSS接收机的低噪声和低杂散频率综合器

A low phase noise and low spur phase locked loop （PLL） frequency synthesizer for use in global navigation satellite system （GNSS） receivers is proposed. To get a low spur, the symmetrical structure of the phase frequency detector （PFD） produces four control signals, which can reach the charge pump （CP） simultaneously, and an improved CP is realized to minimize the charge sharing and the charge injection and make the current matched. Additionally, the delay is controllable owing to the programmable PFD, so the dead zone of the CP can be eliminated. The output frequency of the VCO can be adjusted continuously and precisely by using a programmable LC-TANK. The phase noise of the VCO is lowered by using appropriate MOS sizes. The proposed PLL frequency synthesizer is fabricated in a 0.18 μm mixed-signal CMOS process. The measured phase noise at 1 MHz offset from the center frequency is -127.65 dBc/Hz and the reference spur is -73.58 dBc.     

用于流水线ADC的频率自适应可编程MDAC电路

A programmable high precision multiplying DAC （MDAC） is proposed. The MDAC incorporates a frequency-current converter （FCC） to adjust the power versus sampling rate and a programmable operational am- plifier （POTA） to achieve the tradeoff between resolution and power of the MDAC, which makes the MDAC suitable for a 12 bit SHA-less pipelined ADC. The prototype of the proposed pipelined ADC is implemented in an SMIC CMOS 0.18 μm 1P6M process. Experimental results demonstrate that power of the proposed ADC varies from 15.4 mW （10 MHz） to 63 mW （100 MHz） while maintaining an SNDR of 60.5 to 63 dB at all sampling rates. The differential nonlinearity and integral nonlinearity without any calibration are no more than 2.2/-1 LSB and 1.6/-1.9 LSB, respectively.