Optimum design of n+-n-n+InP devices in the millimeter-range frequency limitation—RF performances

Systematic simulations of n⁺-n-n⁺InP millimeter-wave transferred-electron devices have been performed in order to define the frequency limitation of the fundamental accumulation transmit mode, as well as the maximum RF performance of these devices. The simulations indicate that the use of n⁺-n-n⁺InP devices yields significant net output powers and efficiencies up to 160 GHz, according to the present state of technology.     

Mode Cooperation in a Submillimeter Wave FU Series Gyrotron

At certain gyrotron operating conditions, mode cooperation instead of mode competition takes place between a fundamental and a second harmonic mode. This means the phase bunching of a gyrating electron beam under the second harmonic operation reduces the starting current for the fundamental operation and increases total output power as well as beam efficiency. Such mode cooperation is observed in experiments and confirmed by computer simulations for submillimeter wave Gyrotron FU II.     

Numerical optimization of the single fundamental mode output from asurface modified vertical-cavity surface-emitting laser

The effects of etching a shallow surface relief in the top mirror of an oxide confined vertical-cavity surface-emitting laser, for the purpose of selecting the fundamental mode, have been investigated by numerical simulations. A quasi-3-D model has been implemented which self-consistently accounts for optical, electrical, and thermal effects. The design has been optimized for maximum single fundamental mode output and the limiting mechanisms have been studied. The results are also compared with experimental values and the effects of limitations in fabrication precision are investigated     

A 98/196 GHz Low Phase Noise Voltage Controlled Oscillator With a Mode Selector Using a 90 nm CMOS Process

A 98/196 GHz low phase noise voltage controlled oscillator (VCO) with a fundamental/push-push mode selector using a 90 nm CMOS process is presented in this letter. An innovative concept of the VCO with the mode selector is proposed to switch the fundamental or second harmonic to the RF output. The VCO demonstrates a fundamental frequency of up to 98 GHz with an output power of greater than $-8~{rm dBm}$. The phase noise of the VCO is better than $-100.8~{rm dBc}/{rm Hz}$ at 1 MHz offset frequency, and its figure-of-merit is better than $-186~{rm dBc}/{rm Hz}$. Moreover, the output frequency of the work is up to 196 GHz with a fundamental suppression of greater than $-30~{rm dBc}$ as the VCO is operated in push-push mode.      

Design of a Quasi-Optical Mode Converter for a Frequency Step-Tunable Gyrotron

The quasi-optical mode converter for a frequency step-tunable gyrotron which consists of a dimpled-wall antenna (Denisov-type launcher) and a beam-forming mirror system has been optimized for 9 modes from TE_17,6 at 105 GHz to TE_23,8 at 143 GHz. The first mirror is a large quasi-elliptical focusing one; the second and third are phase-correcting mirrors with a non-quadratic shape of the surface. The results of calculations show that for these modes the Denisov-type launcher has a well-focused beam with low diffraction losses, and the radiation pattern presents an almost identical field shape for all modes considered. A multi-mode optimization of the phase-correcting mirrors with two different methods has been tested. The simulations show that the phase-correcting mirrors can be used for broadband operation in the frequency range from 105 GHz up to 143 GHz in the various design modes. This quasi-optical mode converter can achieve efficiencies of 94%-98% for converting the rotating high-order cylindrical cavity modes into the usable fundamental Gaussian mode.     

Photoconductive Terahertz antenna with radial symmetry

It has been demonstrated recently that it is possible to guide broadband Terahertz pulses utilising a novel coaxial waveguide. This technique is hindered by the difficulty in exciting the radially polarised fundamental mode of the waveguide. To optimise mode matching, a novel radially symmetric photoconductive Terahertz antenna is proposed. Using finite element method simulations and analytical calculations, it is shown that this antenna can generate the desired radial polarisation.     

TE21模回旋返波振荡的起振分析

该文基于回旋行波放大器的线性理论,对TE₂₁模回旋返波振荡起振长度和起振频率随导引中心半径、电压、速度比、注电流及工作磁场等参数的变化进行了详细的数值模拟,并给出了相应的物理解释,分析了TE₂₁模基波和二次谐波回旋返波振荡特点,研究了分布损耗对回旋返波振荡的抑制效果。所得结果对回旋行波放大器和回旋返波振荡器的设计有参考意义。     

Robust slot-fed dielectric resonator antenna using an intermediatesubstrate

A new slot-fed rectangular dielectric resonator antenna design is presented. An intermediate substrate is introduced between the slot and the resonator, resulting in a correct excitation of the fundamental mode and a particularly robust structure to adhesive thickness. Comparisons between finite difference time-domain simulations and measurements confirm the good properties of the proposed design     

Anomaly of modal field in side-tunnel single-polarisation fibre

A noticeable anomaly of modal field in side-tunnel single-polarisation optical fibres is observed for some cross-sectional shapes. Accordingly, as hollow tunnels encroach on a core region, the field of the fundamental mode breaks up into a double peak. As a result of this transition, it closely resembles that of a higher-order mode.     

Calculating the Characteristic Impedance of Finlines by Transverse Resonance Method

The characteristic impedance of finlines with up to three slots is calculated by a rigorous hybrid-mode analysis which includes the finite metallization thickness and finite depth of the mounting grooves. The transverse resonance principle utilized reduces considerably the order of the involved matrix eigenvalue problem. The propagation constants for the fundamental HE/sub 1/ mode (and EH/sub 0/ mode at related structures), as well as for the higher order modes (up to HE/sub 7/), and the characteristic impedances for the fundamental modes are computed as a function of frequency for the bilateral and unilateral finline, as well as for the unilateral finline with two coupled slots, and an additional slot on the opposite side of the substrate surface. The finite metallization thickness and mounting groove depth considered show significant influence on the behavior of the characteristic impedance.     

Monolithically integrated 780-nm-band high-power and 650-nm-bandlaser diodes with real refractive index guided self-aligned structure

780-nm-band high-power and 650-nm-band laser diodes (LDs) with real refractive index guided self-aligned (RISA) structures are monolithically integrated for the first time. High-power and fundamental transverse mode operation at an output power of 100-mW continuous wave (CW) up to 80°C is attained for the 780-nm-band LD. For the 650-nm-band LD, high temperature and fundamental transverse mode operation at an output power of 10-mW CW up to 80°C is obtained     

A broad-band waveguide grating coupler with a subwavelength grating mirror

A new diffractive device for light coupling between a planar optical waveguide and free space is proposed. The device utilizes a second-order waveguide grating to diffract the fundamental waveguide mode into two free propagating beams and a subwavelength grating (SWG) mirror to combine the two free propagating beams into a single beam. The finite-difference time-domain (FDTD) simulations show that the SWG mirror improves the coupling efficiency of the waveguide fundamental mode into the single out-coupled beam from about 30% to 92%. A high efficiency (>90%) is predicted for a broad wavelength range of 1520-1580nm. The proposed device is compact (/spl sim/80 /spl mu/m in length) and it eliminates the need for blazing the waveguide grating.     

220GHz高功率同轴谐振腔回旋管

介绍了220 GHz同轴腔回旋管的设计,工作模式为TE04圆电模式.采用自洽非线性理论对谐振腔的工作参数进行了参数优化,选取工作电压50 k V,工作电流10 A,工作磁场8.4 Tesla.设计的同轴型双阳极磁控注入式电子枪,电子注速度横纵比1.5,速度零散5.2%.并采用粒子模拟方法进行了整管仿真.理论计算与粒子模拟结果表明,设计的220 GHz同轴腔回旋管有望获得200 k W以上的输出功率与40%以上的互作用效率.     

Multiple Diodes Quasi-Optical Oscillater

This paper presents quasi-optics techniques, millimeter techniques and a global optimization method etc techniques. It is a structure of quasi-optics power combiner, that includes a spherical reflection, that the radius of the curvature is R and another one is a hybrid reflector that is called input reflector. The space of the both reflectors is LL. The monolithic source-array is made up of 25 Gunn diodes that are mounted of parallel brass bars that have low thermal resistance. And the bars are fixed on the inner plane surface of the hybrid reflector. The hybrid reflector made up of a plane and a spherical, that the radius of the curvature are R. It is designed that higher fundamental mode power, larger fractional power of fundamental mode power and more combining efficiency of the quasi-optics power combiner. This paper describes an algorithm, which can determine the global optima of the power combiner of solid-state millimeter wave resonator. The global optimization method can determine a neighborhood of the global optima of an objective function and an estimation of the global optima. In the quasi-optical resonator, the objective functions are the fundamental mode power, the fractional power of fundamental mode and the combining efficiency respectively.     

Polarisation control in VCSELs by elliptic surface etching

850 nm-wavelength vertical-cavity surface-emitting lasers (VCSELs) with an elliptical shallow surface relief having various aspect ratios and orientations have been fabricated. Using appropriate etch dimensions, VCSELs of up to 12.5 μm active diameter are forced to operate on the fundamental mode for a certain current range. By aligning the longer axis of the etched ellipse with the [011] or [011¯] crystal axis, the polarisation of the fundamental mode is pinned accordingly with a polarisation suppression ratio of ~30 dB     

Control of vertical-cavity laser polarization with anisotropictransverse cavity geometries

We show the two-fold polarization degeneracy of etched air-post vertical-cavity surface emitting laser diodes can be lifted and a dominant polarization state selected through use of anisotropic transverse laser cavity geometries. For lasers with rhombus-shaped cavities, fundamental mode lasing emission linearly polarized along one specified crystal axis is obtained up to twice the threshold current. For dumbbell-shaped lasers, fundamental mode lasing emission linearly polarized along one specified crystal axis is maintained over the entire operating range of the device producing a maximum orthogonal polarization suppression ratio of 14 dB     

Neutral-point-clamped inverter with improved voltage waveform andcontrol range

A hysteresis controller-based PWM method for neutral point clamped (NPC) inverters is proposed. The closed-loop system uses the two-axis components of the transformed line-to-line voltage vectors as the control variables. In its linear control range, the PWM method includes two operating modes, namely, low and high references. At high references' mode, the output voltage is generated by switching among four vectors instead of three to improve the waveform generation. The proposed system has a linear control range 15.5% wider than conventional phase control methods. Furthermore, the control range can be easily expanded beyond the higher linear controllable range up to the square waveforms without suddenly increasing the waveform distortion. Therefore, the fundamental component of the output voltage can be smoothly and continuously controlled from zero up to square waveforms. The control circuit includes a hysteresis controller that is capable of stabilizing the neutral point potential variations within fixed limits during steady and transient states. The control method also offers high performance and fast response. Computer simulations and experimental results on a laboratory-tested motor drive are given to validate the proposed control scheme     

Nonlinear propagation and self-switching of ultrashort opticalpulses in fiber nonlinear directional couplers: the normal dispersionregime

The propagation of short optical pulses in a nonlinear directional coupler operating in the normal dispersion regime is investigated. The specific example of a birefringent periodically rocked fiber filter where coupling occurs between the two orthogonally polarized modes that are aligned with the birefringence axes of the fiber is considered. In the simulations, a bell-shaped input pulse is injected into one polarization mode: for different input peak powers, the energy present in the same mode at the output of a coupler, which is one or two coupling lengths long, is calculated. The nonlinear temporal broadening, due to the combined effect of group velocity dispersion and self-phase modulation, sets a fundamental lower limit to the time width of the input pulses. When pulses shorter than this critical value are used, the power-dependent energy switching characteristics of a device one coupling length long gets substantially spoiled. Effects related to the finite spectral bandwidth of the fiber filter are discussed. Numerical simulations are compared to recent experimental results on the self-switching of picosecond pulses in the visible (615 nm) with a birefringent rocking fiber     

Spatially singlemode broad-area semiconductor laser with planar external cavity

A broad-area laser diode combined with a planar external waveguide cavity operates in the fundamental mode and reshapes the output emission into a circular 15/spl deg/ beam. A 500 /spl mu/m-long by 40 /spl mu/m-wide laser diode with uncoated facets coupled with the uncoated ModeReShaper (MRS) planar chip has a coupling efficiency of /spl sim/40% and stabilised the fundamental mode at drive currents up to three-times threshold.     

Effective area limit of large-mode-area solid-core photonic bandgap fibers for fiber laser applications

We investigate the bending characteristics of solid-core photonic bandgap fibers (SC-PBGFs) aiming to achieve large mode area (LMA) and effectively single-mode operation with a practically allowable bending radius for high-power Yb-doped fiber lasers and amplifiers. Through detailed numerical simulations based on the finite element method (FEM), we evaluate the impacts of the order of photonic bandgap on the bending performance and point out the limits of core size enlargement in the SC-PBGFs with a 1-cell core structure due to the increment of bending loss. In addition, under practical constraints, we find that the SC-PBGFs having a 7-cell core can achieve sufficient differential bending loss between the fundamental mode and the higher-order modes and a much larger effective area limit as compared with previously-reported index-guiding LMA fibers.