一种高效高功率倏逝波耦合型光电探测器的研究

The effects of the multimode diluted waveguide on quantum efficiency and saturation behavior of the evanescently coupled uni-traveling carrier （UTC） photodiode structures are reported. Two kinds of evanescently coupled uni-traveling carrier photodiodes （EC-UTC-PD） were designed and characterized： one is a conventional EC-UTC-PD structure with a multimode diluted waveguide integrated with a UTC-PD; and the other is a compact EC-UTC-PD structure which fused the multimode diluted waveguide and the UTC-PD structure together. The effect of the absorption behavior of the photodiodes on the efficiency and saturation characteristics of the EC-UTC-PDs is analyzed using 3-D beam propagation method, and the results indicate that both the responsivity and saturation power of the compact EC-UTC-PD structures can be further improved by incorporating an optimized compact multimode diluted waveguide.     

基于GaAs基大功率激光器的热分析

The thermal characteristics of 808 nm Al Ga As/Ga As laser diodes(LDs) are analyzed via electrical transient measurements and infrared thermography. The temperature rise and thermal resistance are measured at various input currents and powers. From the electrical transient measurements, it is found that there is a significant reduction in thermal resistance with increasing power because of the device power conversion efficiency. The component thermal resistance that was obtained from the structure function showed that the total thermal resistance is mainly composed of the thermal resistance of the sub-mount rather than that of the LD chip, and the thermal resistance of the sub-mount decreases with increasing current. The temperature rise values are also measured by infrared thermography and are calibrated based on a reference image, with results that are lower than those determined by electrical transient measurements. The difference in the results is caused by the limited spatial resolution of the measurements and by the signal being captured from the facet rather than from the junction of the laser diode.     

聚光作用下光伏电池阵列性能分析

Performance of concentrating photovoltaic/thermal system is researched by experiment and simulation calculation. The results show that the I-V curve of the GaAs cell array is better than that of crystal silicon solar cell arrays and the exergy produced by 9.51% electrical efficiency of the GaAs solar cell array can reach 68.93% of the photovoltaic/thermal system. So improving the efficiency of solar cell arrays can introduce more exergy and the system value can be upgraded. At the same time, affecting factors of solar cell arrays such as series resistance, temperature and solar irradiance also have been analyzed. The output performance of a solar cell array with lower series resistance is better and the working temperature has a negative impact on the voltage in concentrating light intensity. The output power has a -20 W/V coefficient and so cooling fluid must be used. Both heat energy and electrical power are then obtained with a solar trough concentrating photovoltaic/thermal system.     

1.06 μm high-power InGaAs/GaAsP quantum well lasers

The high power and low internal loss 1.06 μm InGaAs/GaAsP quantum well lasers with asymmetric waveguide structure were designed and fabricated. For a 4000 μm cavity length and 100 μm stripe width device, the maximum output power and conversion efficiency of the device are 7.13 W and 56.4%, respectively. The cavity length dependence of the threshold current density and conversion efficiency have been investigated theoretically and experimentally; the laser diode with 4000 μm cavity length shows better characteristics than that with 3000 and 4500 μm cavity length:the threshold current density is 132.5 A/cm², the slope efficiency of 1.00 W/A and the junction temperature of 15.62 K were achieved.     

Design of violet InGaN light-emitting diode with staggered quantum well structure

The staggered InGaN quantum well （QW） structure and the conventional InGaN QW structure for the emission at a particular wavelength of 400 nm are designed and theoretically investigated, including the distribution of the carders＇ concentration, the radiative recombination rate, the Shockley-Read-Hall （SRH） recombination rate as well as the output performance and the internal quantum efficiency. The theoretical result indicates that the staggered QW structure offers significant improve- ment of carriers＇ concentration in the QW, especially the hole concentration. The output power and the internal quantum efficiency also show 32.6 % and 32.5 % enhancement, respectively, in comparison with that of the conventional InGaN QW structure. The reduction of the electron overflow can be the main factor for the improvement of the optical performance for novel staggered InGaN QW structure.     

Design of violet InGaN light-emitting diode with staggered quantum well structure

The staggered InGaN quantum well (QW) structure and the conventional InGaN QW structure for the emission at a particu-lar wavelength of 400 nm are designed and theoretically investigated,including the distribution of the carriers’ concentration,the radiative recombination rate,the Shockley-Read-Hall (SRH) recombination rate as well as the output performance and the internal quantum efficiency. The theoretical result indicates that the staggered QW structure offers significant improve-ment of carriers’ concentration in the QW,especially the hole concentration. The output power and the internal quantum efficiency also show 32.6 % and 32.5 % enhancement,respectively,in comparison with that of the conventional InGaN QW structure. The reduction of the electron overflow can be the main factor for the improvement of the optical perfor-mance for novel staggered InGaN QW structure.     

Ultralow internal optical loss in separate-confinement quantum-well laser heterostructures

Internal optical loss in separate-confinement laser heterostructures with an ultrawide (>1 smm) waveguide has been studied theoretically and experimentally. It is found that an asymmetric position of the active region in an ultrawide waveguide reduces the optical confinement factor for higher-order modes and raises the threshold electron density for these modes by 10–20%. It is shown that broadening the waveguide to above 1 μm results in a reduction of the internal optical loss only in asymmetric separate-confinement laser heterostructures. The calculated internal optical loss reaches ∼0.2 cm⁻¹ (for λ≈1.08 μm) in an asymmetric waveguide 4 μm thick. The minimum internal optical loss has a fundamental limitation, which is determined by the loss from scattering on free carriers at the transparency carrier density in the active region. An internal optical loss of 0.34 cm⁻¹ was attained in asymmetric separate-confinement laser heterostructures with an ultrawide (1.7 μm) waveguide, produced by MOCVD. Lasing in the fundamental transverse mode has been obtained owing to the significant difference in the threshold densities for the fundamental mode and higher-order modes. The record-breaking CW output optical power of 16 W and wallplug efficiency of 72% is obtained in 100-μm aperture lasers with a Fabry-Perot cavity length of ∼3 mm on the basis of the heterostructures produced. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 12, 2004, pp. 1477–1486. Original Russian Text Copyright ? 2004 by Slipchenko, Vinokurov, Pikhtin, Sokolova, Stankevich, Tarasov, Alferov.     

Bending efficiency analysis of horizontal single- and multiple-slot waveguide microrings

The bending efficiencies of three-dimensional(3D) horizontal single-and multiple-slot waveguide microrings are analyzed using the effective index and modified transfer matrix methods.The effects of waveguide parameters,low-index material,high-index material,asymmetric structure,and asymmetric slots on the bending loss are studied.The results show that the bending efficiency can be enhanced by applying asymmetric structures and asymmetric slots.In addition,it is demonstrated that the bending loss increases with the increase of the number of slots.However,by using proper thicknesses for different high-index layers of the horizontal multiple-slot waveguide,it is possible that the horizontal multiple-slot waveguide can provide a lower bending loss than the single-slot one.     

A common-gate bootstrapped CMOS rectifier for VHF isolated DC-DC converter

A common-gate bootstrapped CMOS rectifier dedicated for VHF (very high frequency) isolated DC-DC converter is proposed.It uses common-gate bootstrapped technique to compensate the power loss due to the threshold voltage,and to solve the reflux problem in the conventional rectifier circuit.As a result,it improves the power conversion efficiency (PCE) and voltage conversion ratio (VCR).The design saves almost 90% of the area compared to a previously reported double capacitor structure.In addition,we compare the previous rectifier with the proposed common-gate bootstrapped rectifier in the case of the same area;simulation results show that the PCE and VCR of the proposed structure are superior to other structures.The proposed common-gate bootstrapped rectifier was fabricated by using CSMC 0.5 μm BCD process.The measured maximum PCE is 86% and VCR achieves 77% at the operating frequency of 20 MHz.The average PCE is about 79% and average VCR achieves 71% in the frequency range of 30-70 MHz.Measured PCE and VCR have been improved compared to previous results.     

High efficiency, high power 808nm laser array and stacked arrays optimized for elevated temperature operation

Operation of 808-nm laser diode pumping at elevated temperature is crucial to many applications. Reliable operation at high power is limited by high thermal load and low catastrophic optical mirror damage (COMD) threshold at elevated temperature range. We demonstrated high efficiency and high power operation at elevated temperature with high COMD power. These results were achieved through device design optimization such as growth conditions, doping profile, and materials composition of the quantum-well and other layers. Electrical-to-optical efficiency as high as 62% was obtained through lowered threshold current, lowered series resistance and increased slope efficiency. The performance of single broad-area laser diodes scales to that of high power single bars on water-cooled copper micro-channel heatsinks or eonductively-cooled CS heatsinks. No reduction in bar performance or significant spectral broadening is seen when these micro-channel coolers are assembled into 6-bar and 18-bar CW stacks for the h     

原子层沉积氧化铝薄膜对多晶太阳能电池表面钝化的影响

A stack of Al2O3/SiNx dual layer was applied for the back side surface passivation of p-type multi-crystalline silicon solar cells, with laser-opened line metal contacts, forming a local aluminum back surface field （local Al-BSF） structure. A slight amount of Al2O3, wrapping around to the front side of the wafer during the thermal atomic layer deposition process, was found to have a negative influence on cell performance. The different process flow was found to lead to a different cell performance, because of the Al2O3 wrapping around the front surface. The best cell performance, with an absolute efficiency gain of about 0.6% compared with the normal full Al-BSF structure solar cell, was achieved when the Al2O3 layer was deposited after the front surface of the wafer had been covered by a SiNx layer. We discuss the possible reasons for this phenomenon, and propose three explanations as the Ag paste, being hindered from firing through the front passivation layer, degraded the SiNx passivation effect and the Al2O3 induced an inversion effect on the front surface. Characterization methods like internal quantum efficiency and contact resistance scanning were used to assist our understanding of the underlying mechanisms.     

Evaluation of the drain-source voltage effect on AIGaAs/InGaAs PHEMTs thermal resistance by the structure function method

The effect of drain-source voltage on A1GaAs/InGaAs PHEMTs thermal resistance is studied by experimental measuring and simulation. The result shows that A1GaAs/InGaAs PHEMTs thermal resistance presents a downward trend under the same power dissipation when the drain-source voltage （VDs） is decreased. Moreover, the relatively low VDS and large drain-source current （IDs） result in a lower thermal resistance. The chip-level and package-level thermal resistance have been extracted by the structure function method. The simulation result indicated that the high electric field occurs at the gate contact where the temperature rise occurs. A relatively low VDS leads to a relatively low electric field, which leads to the decline of the thermal resistance.     

Design and Optimization of a novel structure for efficient side-coupling of high power double-cladding fiber lasers

A novel structure for efficient side-coupling of high power double-cladding fiber lasers is presented. The maximum cou- pling efficiency of this structure is more than 90% for TM-polarization in the 1 and -1 order but is only 40% for TE- polarization. Thus, a multi-layer stair-structure is introduced and optimized by combining transmission algorithm and genetic algorithm to obtain higher coupling efficiencyηfor TE-polarization and the maximum coupling efficiency almost reaches to 70%.     

表面增透结构AlGaInP LED的研究

A kind of AlGaInP light emitting diode （LED） with surface anti-reflecting structure has been introduced to solve the problems of low light efficiency and restricted luminous intensity. The new structure can be demonstrated theoretically and experimentally, and LEDs with the new structure have higher on-axis luminous intensity and larger saturation current than conventional LEDs and LEDs with ITO film only, which is caused by higher external quantum efficiency and also higher internal quantum efficiency. The new LEDs are especially suitable for working at large injected currents.     

Enhancement of Crystalline Quality of Strained Straind InAs／InP Quantum Well Structures by Rapid Thermal Annealing

The effect of rapid thermal annealing of the optical properties of a strained InAs/InP single quantum well structrure has investigated in this paper.The luminescence intensity of the quantum well at 8K was increased by a factor of 4 and 1.55meV blue shoft of the quantum well photoluminescence peak was observed af-ter annealing at the optimal condition of 700℃ for 5s.Furthermoer,we found that the luminescence efficiency of the deep radiative levels in the samples was also affected by rapid thermal annealing.Our experimental results have demonstrated that Rapid thermal annealing significantly improves the erystalline quality of strained quantum well struc-tures after growth and is an important way for enhancement of the performance of the laser device.     

Optimization of electrode shape for high power GaN-based light-emitting diodes

Because the polarization effect influences the distribution of the carriers in the multiple quantum wells of the light-emitting diodes （LEDs）, the light-emitting efficiency is also affected. The influence of the polarization effect on GaN-based LEDs＇ performance is simulated. By simulating four different types of electrode shapes, it＇s found that the electrode shape influences not only the photoelectric characteristics but also the optical absorption by the semiconductor. Through the optimization of the electrode shape, the I-V characteristic is improved, and the series resistance is lowered. The optical absorption by the semiconductor is decreased and then the heat generated in the LEDs is lowered. As a result, both the photoelectric conversion efficiency and the stability are improved.     

Optimal design of a low-loss 2-bit electrooptic analog-to-digital converter

The structure of the optical waveguide of 2-bit electrooptic A/D converter with proton-exchange micro prisms is optimized by the finite-difference beam propagation method （FD-BPM） The electrode parameters of the converter are optimized by conformal mapping. The optimal parameters are a half- wave voltage of Vπ = 4.5 V and a bandwidth of △f = 1.4 GHz. A normalized transmitted power of 69.75% is obtained by FD-BMP and the output waveguide gap is 300 μm.     

A high-drop hole-type photonic crystal add-drop filter

Based on the effect of total internal reflection（TIR）and photonic band gap,a new type of hexagonal-lattice hole-type silicon photonic crystal add-drop filter is proposed with a large circular hole as inner ring.The single mode operation is realized by compressing the two rows of photonic crystal above and below the line defect waveguide.Two-dimensional（2D）finite-difference time-domain（FDTD）method is then applied to investigate the impacts of side length of inner ring and coupling strength on its drop efficiency.It is also fairly compared with the traditional inner ring structure composed of hexagonal-lattice holes.The results show that the proposed structure can offer higher spectral selectivity than the traditional one.Two channel wavelengths of 1.425μm and 1.45μm can be simultaneously dropped at corresponding ports with drop efficiency of more than 90%and quality factor of 900 in the proposed configuration when the width of bus waveguide,the side length of inner ring and the coupling strength are 0.8 3 a,4a and 0,respectively,where a is the lattice constant.     

Generation and detection of squeezed state

Soliton amplitude squeezed state is obtained and dctected by using asymmetric Sagnac interferometer and balanced homodyne detecting system. An improved photo detector circuit for quantum state detection is introduced. The circuit has a bandwidth of 10MHz and the saturation power is about 19 mW. A maximum photocurrent noise reduction of 1.1 dB below the shot noise is achieved. Taking the detection efficiency into account, the squeezing will be about 1.5 dB.     

A novel polarizer based on directional coupler and surface plasmon polaritons

A novel polarizer with a silver nanoribbon added into a traditional waveguide directional coupler is designed to realize the polarized output of TE mode. A high extinction ratio can be obtained because of the selectivity of surface plasmon polaritons （SPPs） on polarization. The effects of the polarizer parameters on coupling efficiency and extinction ratio are discussed. Simulation results indicate that the coupling efficiency for TE mode can reach about 95%, but only 3% for TM mode, with the extinction ratio of TE mode about 15 dB when the light wavelength is 1550 nm, The polarizer may have potential applications in photonic integrated circuits and quantum information technology.