Beam focusing for field-emission flat-panel displays

A combination of finite element and finite difference techniques have been used to simulate the performance of micro-fabricated gated field emitters for flat-panel display applications. The computer model has been verified against both analytic models and experimental data for unfocused devices and then applied to the study of focused structures for which sufficient models and data are not yet available. Quantitative results include electrode current-voltage characteristics and electron beam widths as a function of distance from the cathode. Practical issues such as visual image quality, electrical stress and fabrication complexity are considered to identify a practical design for use in conjunction with existing high-efficiency cathode ray tube phosphors. It is found that the addition of an integrated aperture electrode to focus the emitted electrons increases the cathode-gate drive voltage by about 30% over the case of unfocused emitters. A concentric electrode design results in only 15% increase and promises simpler fabrication. Both approaches demonstrate electron beam widths of tens of microns at anode distances of several millimeters, allowing for full-color resolution in excess of 100 lines per inch with proven color phosphors     

气动激光窗口的光束传输特性

本文分析和实验研究了HAW型气动激光窗口所形成的小孔光阑效应和类透镜效应对光束传输的影响,阐明了在高功率气体激光器中使用气动激光窗口的优越性。     

Optically controlled characteristics in an ion-implanted silicon MESFET

OPFETs (optical FETs) are useful as compatible IC transducers in optical communication systems, although APDs (avalanche photo diodes) have higher multiplication gain and speed of response. Studies have been made on the optically controlled characteristics of an ion-implanted Si MESFET which show that drain-source current can be enhanced with increasing radiation flux intensity and lower wavelength of operation. Furthermore, the threshold voltage is found to be reduced under normally OFF conditions and increased under normally ON conditions for higher flux density and lower wavelength. The effect of radiation becomes predominant over the impurity concentration at flux densities greater than or equal to 10¹⁸/m² and wavelengths less than or equal to 0.78 μm.     

内含热薄透镜四镜环形腔的光束特性

二平二凹四镜8字型环形腔是色心激光、激光陀螺等研究经常采用的谐振腔。本文采用热薄透镜模型,运用等效腔方法,分析了四镜环形腔的光束特性。详细讨论了热效应对谐振腔基本特性的影响,给出了四镜环形腔的热不灵敏条件。这些结果对谐振腔的设计和应用具有一定的指导作用。     

Beam focusing using 60 GHz Fabry-Perot resonators with uniform and non-uniform metal grids

A new structure of millimetre-wave focusing antennas is presented. It consists of a plane-parallel Fabry-Perot resonator comprising two uniform and non-uniform inductive metal meshes excited by a horn antenna. The beam focusing is performed with the non-uniform mirror, the geometry of which is chosen so that it behaves as a spherical equiphase surface with a desired radius of curvature. The resulting radiation patterns are Gaussian; their directivity is controlled by the curvature of the synthesised wavefront. This concept is successfully validated in the 60 GHz band.     

Power focusing characteristics of ellipsoidal reflector

Power focusing characteristics of a prolate spheroidal reflector, the aperture of which is parallel to the line connecting the two focuses, are numerically studied. As a transmitting and a receiving antenna, linear wires with finite length are placed at or near the focuses of the reflector. Reflected near fields from the reflector are calculated by the physical optics technique, and transmitting and receiving antenna characteristics are obtained by the method of moments. Calculated results are given for the power focusing characteristics as a function of the eccentricity, the aperture size of the reflector, antenna directions, antenna lengths, and the receiving antenna displacement. Better power focusing characteristics are obtained when the transmitting antenna becomes less directive, or the size of the aperture becomes larger. Measured and calculated results agree very well.     

Analysis and perfomance characteristics of an intensified silicon vidicon tube

Typical performance characteristics for intensified silicon vidicon tubes are given. The tube can be operated at 5 × 10^-7_ fc faceplate illumination. A 40 percent modulation depth at 400 TV lines per raster height has been achieved at a 300-nA signal level. When operating at 200-nA signal, typical decay lag performance shows less than 20-nA signal 50 ms after the illumination is removed. Theoretical and experimental performance at low light levels are compared. The design of the electron optical system of the intensifier section is considered with respect to distortion and center and edge resolution. Two important target parameters, collection efficiency and resolution, are also considered theoretically and experimentally. A simple model for the collection efficiency is given; theory and experiment compare well. The effect on resolution of discrete diode spacing and target thickness is given and this is coupled with other modulation transfer parameters to predict the overall modulation transfer of the device. Critical performance characteristics are given for sample tubes.     

Kinetics of electroluminescence in an efficient silicon light-emitting diode with thermally stable spectral characteristics

The kinetics of the rise and decay of electroluminescence in an efficient silicon light-emitting diode that is formed by diffusion and features a high thermal stability of spectral parameters of electroluminescence in the region of band-to-band transitions is studied for various injection currents. The parameters of the electroluminescence kinetics are compared with effective lifetimes of minority charge carriers and characteristics of the current kinetics. It is found that the onset of a sharp rise in the electroluminescence intensity is delayed with respect to the instant when the voltage is applied to the diode; the results of measuring the emission distribution over the diode area are reported.     

Beam steering for wireless optical links based on an optical phased array in silicon

The ability to steer optical beams, crucial to the operation of high-speed optical wireless links may be achieved using optical phased array antennas which have significant potential in this application. The beam formed by the phased array antennas is steered by tuning the relative phase difference between the adjacent antenna elements which may be achieved nonmechanically. In this paper, the characteristics and behaviour of two dimensional optical phased arrays with a structure composed of 2?×?2, 4?×?4, and 16?×?16 antenna elements in beam steering are verified. The wavelength beam steering of ?0.16°/nm is measured along the θ direction with a required steering range (between main lobes) of 1.97° within a ?3 dB envelop of 5° extent in the θ direction and 7° extent in the Φ direction. To achieve two-dimensional beam steering, thermo-optic beam steering can be used in Φ direction. It is found that the thermo-optic phase tuning departs the expected quadratic dependence and is well characterised by a quartic dependence upon heater current or voltage.     

Pearcey光束的形成及其聚焦特性

设计一种简单的光学元件抛物缝孔径获得Pearcey光束,基于空间域中的广义惠更斯-菲涅耳衍射积分,导出该系统的Pearcey光束表达式。数值模拟和实验验证了Pearcey光束的产生。同时研究了Pearcey光束的自聚焦特性,讨论了抛物缝孔径焦准距对聚焦光斑的影响。实验所得自聚焦光斑大小与数值模拟相符,研究结果对Pearcey光束用于光学囚禁提供理论和实验依据。     

Efficient silicon light-emitting diode with temperature-stable spectral characteristics

The influence of temperature on the parameters of the band-to-band emission spectrum of a light-emitting diode based on single-crystal silicon was investigated; the unprecedentedly high stability against variations in temperature was observed for both the electroluminescence intensity at the peak of the spectral distribution (I _EL ^m ) and the wavelength corresponding to this peak (λ_m). The internal quantum efficiency of the light-emitting diode at room temperature is estimated as no lower than 0.1%. The value of I _EL ^m varies by no more than ～10% as the temperature is varied from 120 to 300 K. The value of λ_m remains virtually constant in the temperature range of 200–300 K. The unprecedentedly high stability of λ_m is related to interference effects in the oxide film through which the radiation of the light-emitting exits. It is shown that one of the important factors that govern the temperature stability of I _EL ^m is a decrease in the lifetime of the minority charge carriers with decreasing temperature.     

环形障碍物后的无衍射光重建产生局域空心光束

利用Hankel波理论和几何光学原理对无衍射光经环形障碍物的重建过程进行分析,结果表明轴棱锥产生的无衍射光是由从轴棱锥出射的两列Hankel波的叠加而形成的,并用Zemax软件对无衍射光经环形障碍物的过程进行光线仿真,模拟了环形障碍物后的轴上不同位置处的截面光强图,研究了局域空心光尺寸与环形障碍物参数之间的关系。并通过实验进行验证,实验中利用轴棱锥输出无衍射光,且在最大无衍射距离内放置环形障碍物,用CCD系统记录无衍射光经环形障碍物后的光强变化,实验和仿真结果基本吻合。仿真和实验结果均表明无衍射光束经环形障碍物后会重建并能产生中心光强为零的局域空心光束(Bottle beam),在光镊和光学微操作等方面具有潜在的应用价值。     

斜梁结构高温度稳定性MEMS自由梁谐振器设计

针对表面微加工MEMS谐振器由于温度改变引起的电气失效问题,采用一种高温度稳定性的斜梁支撑结构将温度变化引起的谐振器形变转化为水平位移,有效地避免了谐振梁与电极之间因材料热胀冷缩引起的电气失效和动态阻抗变化。在温度升高100°C的情况下,直梁支撑结构在垂直电极方向的位移为0.153μm,而文中所提出的斜梁支撑结构的位移为0.017μm;在提高温度稳定性的同时降低了由于电极间隙增大引起的谐振器动态阻抗变化,在0.3μm的初始间隙下,斜梁支撑结构的谐振器在温度升高100°C时的动态阻抗为直梁支撑谐振器的24%,损耗为-52dB,相比于传统直梁支撑结构的-61dB改善了9dB,有效地提升了MEMS谐振器的温度稳定性。     

伽里略非球面透镜扩束器

在激光系统中，伽里略球面透镜扩束器已得到广泛地应用，但是，它有许我乐足之处。本文中，研究了伽里略非球面透镜扩束器，给出了伽里略非球面透镜扩束器光学系统设计的方法和设计结果。我们得出的结论是：伽里略非球面秀镜扩束器比伽里略球面透镜扩束器好。     

涡旋光束经过轴棱锥后的聚焦特性

研究了涡旋光束通过轴棱锥聚焦后的聚焦特性。利用惠更斯-菲涅耳衍射积分理论推导了涡旋光束经过轴棱锥聚焦后所获得的聚焦光强分布。数值模拟结果表明,涡旋光束经过轴棱锥聚焦后可获得高阶贝塞尔光束。研究了不同锥角的轴棱锥对涡旋光束聚焦特性的影响以及不同拓扑电荷数对聚焦特性的影响。结果表明,在轴棱锥对应的最大准直距离内,所获得的高阶贝塞尔光束保持了原有的无衍射特性。     

Electrical characteristics of rectifying polycrystalline silicon/silicon carbide heterojunctions

This paper presents a study of the rectifying properties of heavily doped polycrystalline silicon (polysilicon) on 4H silicon carbide (4H-SiC). Current properties and barrier heights were found using analysis of the heterojunction. This revealed that Schottky analysis would be valid for the large barrier height devices. Isotype and an-isotype devices were fabricated on both p-type and n-type SiC and the electrical characteristics were investigated using capacitance vs voltage measurements, current vs voltage measurements (I-V), and temperature I-V measurements. Extraction of the barrier height, built-in potential, and Richardson constant were made and then compared to theoretical values for the heterojunction. Temperature I-V measurements demonstrated that the current transport mechanism is thermionic emission, confirming the validity of the Schottky diode model. The I-V characteristics show near ideal diode rectifying behavior and the capacitance-voltage characteristics show ideal junction space charge modulation for all polysilicon/SiC combinations. These experimental results match well with heterojunction band-offset estimated barrier heights and demonstrate that the barrier height of the polysilicon/4H SiC interface may be controlled by varying the polysilicon doping type.     

Emission characteristics of silicon vacuum triodes with fourdifferent gate geometries

Arrays of 10×10, 30×30, and 50×50 phosphorus-doped 0.005-0.025 Ω-cm, monocrystalline silicon field emitters have been fabricated with an emitter height of approximately 4.5 μm, a cone angle of 110°, and four gate openings ranging from 1.8 to 5.3 μm. The placement of the rims of the gates range from coplanar with the apexes of the emitters for the 1.8-μm devices to fully recessed for the 5.3-μm devices. The devices have been characterized in terms of geometry-dependent β factors, scaling of emission currents with array size, temperature dependency from room temperature to 48 K, pressure dependency from 2.5×10^-9 to 0.8×10^-5 torr, current fluctuations at room temperature and at 48 K, and image formation. All of the measurements have been performed by operating the devices in the gate-induced field emission mode     

Utilization of silicon detectors with “ideal-diode” current-voltage characteristics

The extremely low level of intrinsic noise attained in silicon detectors with “ideal-diode” current-voltage characteristics has made it possible to create measuring circuits capable of detecting currents as low as 10^?16 A and, at the same time, featuring a dynamic range as large as 10¹¹–10¹².     

Analytical electrostatic model of silicon conical field emitters.II. Extension to devices with focusing electrode

For pt. I see ibid., vol.48, no.1, p.134-43 (Jan. 2001). We extended the “bowling pin model” (BPM) presented in pt. I, to the case of double-gated conical field emitters. The model was used for trajectory calculations for both the single-gated and double-gated devices. Analysis also produced the governing relationship for the optimal operating voltages on the gate and focus electrodes of a double-gated emitter     

Emission characteristics of gated silicon wedges

Gated field emission wedges of varying lengths have been fabricated and tested. These wedges emit at 180-200 V from multiple emission sites that are approximately evenly distributed along the wedge. This results in emission currents that scale with the length of the wedge. The maximum emission current observed is about 0.1 μA/μm of wedge length, beyond which localized failure events occur. These localized failure events sometimes cause the wedge emitter to short to the gate, but frequently the emission characteristic of the wedge is not seriously affected as long as most of the wedge remains intact. A single wedge may undergo up to hundreds of individual failures and still emit