Theory of double-chirped mirrors

A theory of double-chirped mirrors (DCMs) for dispersion compensation in ultrashort pulse laser sources is presented. We describe the multilayer interference coating by exact coupled-mode equations. They show that the analysis and synthesis of a coating with a slowly varying chirp in the layer thicknesses can be mapped onto a weakly inhomogeneous transmission line problem. Solutions of the transmission line equations are given using the WKB-method. Analytic expressions for reflectivity and group delay are derived. The solutions show that the main problem in chirped mirror design is the avoidance of spurious reflections, that lead to Gires-Tournois-like interference effects responsible for the oscillations in the group delay. These oscillations are due to an impedance matching problem of the equivalent transmission line. The impedance matching can be achieved by simultaneously chirping the strength of the coupling coefficient and the Bragg wavenumber of the mirror. An adiabatic increase in the coupling coefficient removes the typical oscillations in the group delay and results in broad-band mirrors with a controlled dispersion. Finally, the mirror is matched to air with a broadband antireflection coating. We discuss a complete design of a laser mirror with a reflectivity larger than 99.8% and a controlled dispersion over 300-nm bandwidth. Using such mirrors in a Ti:sapphire laser, we have demonstrated ≈30-fs pulses, tunable over 300 nm, as well as 8-fs pulses from the same setup. A different design resulted in 6.5-fs pulses     

射频微机电系统开关软磁悬臂梁微电镀工艺

研究了一种电磁型射频（RF）微机电系统（MEMS）开关的软磁悬臂梁的制备工艺。为了得到适合MEMS器件应用的镍铁合金磁性薄膜,展开微电镀工艺分析,采用振动样品磁强计测量镍铁合金薄膜的磁参量。实验结果：最大相对磁导率约为460,薄膜矫顽力约为490A／m,饱和磁感应强度约为0．9T,剩磁感应强度为0．03～0．06T。此结果为开关结构设计优化提供了依据。     

Optical raster-scanning displays based on surface-micromachinedpolysilicon mirrors

We demonstrate high-resolution, raster-scanning display systems based on pairs of orthogonally scanning, surface-micromachined mirrors. The first mirror of the raster-scanning pair determines the line-scan rate of the display and is driven at its resonant frequency which is on the order of 4.7 kHz. The second mirror, driven at a frequency below its resonance and scanning orthogonally to the first mirror, determines the image refresh rate. Both mirrors have a maximum optical scanning angle of 15°. Single-chip and two-chip scanners are demonstrated. The resolution of the single-chip display, based on average pixel size, is 102×119 pixels. The curvature of the mirror surfaces are characterized and optically compensated to achieve this resolution     

Surface micromachined segmented mirrors for adaptive optics

This paper presents recent results for aberration correction and beam steering experiments using polysilicon surface micromachined piston micromirror arrays. Microfabricated deformable mirrors offer a substantial cost reduction for adaptive optic systems. In addition to the reduced mirror cost, microfabricated mirrors typically require low control voltages (less than 30 V), thus eliminating high-voltage amplifiers. The greatly reduced cost per channel of adaptive optic systems employing microfabricated deformable mirrors promise high-order aberration correction at low cost. Arrays of piston micromirrors with 128 active elements were tested. Mirror elements are on a 203-μm 12×12 square grid (with 16 inactive elements, four in each corner of the array). The overall array size is 2.4 mm square. The arrays were fabricated in a commercially available surface micromachining process. The cost per mirror array in this prototyping process is less than $200. Experimental results are presented for a hybrid correcting element comprised of a lenslet array and piston micromirror array, and for a piston micromirror array only. Also presented is a novel digital deflection micromirror that requires no digital to analog converters, further reducing the cost of adaptive optics systems     

Low-dropout regulator with dual cross-coupled current mirrors

A low-dropout regulator (LDO) based on dual cross-coupled current mirrors is reported in this paper. The proposed dual cross-coupled current mirrors boost output signal current such that the loop gain of LDO is significantly enhanced, and the error amplifier in LDO retains single-pole property within the loop bandwidth of LDO. Designed in a 65-nm CMOS process and operating at a minimum of 1-V supply, the proposed LDO provides a 0.8-V output and delivers a maximum of 50 mA. The figure-of-merit of the proposed LDO is 8.9 ps.     

Analytical transient response of MOS current mirrors

The analytical transient response of MOS current mirrors is derived for the case when the input current is a saturating ramp. The closed form solution obtained for the voltages and currents in the circuit is expressed using Airy's functions. The settling time is then calculated using the closed‐form current equation. For the case when the settling time is greater than the transition time of the input current, a closed form solution is obtained. When the settling time is less than the input transition time, a very simple fitting function is found to accurately model the dependence of the settling time on the various parameters in the circuit, including the transition time of the input current. Simulations show excellent agreement of the estimates of the settling time macromodel with LEVEL‐1 SPICE results. For LEVEL‐3 MOSFET models, the error in the macromodel is within 20% of detailed circuit simulation. Copyright © 2003 John Wiley & Sons, Ltd.     

Tunable microcavity based on InP-air Bragg mirrors

A tunable Fabry-Perot filter based on InP-air Bragg mirrors has been studied. The filter experimental performances are a resonance line width of 0.6 nm and a tuning range of 62 nm for 14 V. The full-width at half-maximum is kept below 1 nm over a 40-nm tuning range. The relation between the bending of the suspended layers during the actuation and the optical properties of the filter are analyzed     

New CMOS current mirrors with improved high-frequency response

A new CMOS current mirror is presented which has the static characteristic of the cascode current mirror and a high-frequency performance equivalent to or better than that of the simple current mirror. Moreover, the circuit proposed does not present the instability problem of the improved cascode utilized to increase the high-frequency response. The circuit is designed using CMOS 2 μm technology with various aspect ratios and simulated with the SPICE programme.     

Channel equalization and blocking filter utilizing microelectromechanical mirrors

This paper describes the design and performance of a 64-channel equalization and blocking filter. It utilizes a free space lens and grating multiplexer with micromechanical tilt mirrors providing variable attenuation. The module achieves a 5-dB insertion loss with a 3-dB passband of 87 GHz for 100-GHz spaced channels. The attenuation range achieved is in excess of 35 dB, making it suitable for wavelength blocking in switching applications. The device has been demonstrated to be compatible with 10- and 40-Gb/s transmission.     

Spot optical measurements on micromachined mirrors for photonic switching

This paper describes and compares three optical methods for performing spot measurements on micromachined mirrors, designed for photonic switching in fiberoptic networks. For static characterization, two spot-position detection systems, one based on a vidicon camera and the other based on a bidimensional silicon position sensitive detector (PSD), are illustrated, tested, and compared. Moreover, the dynamic behavior has been monitored with the PSD-based detection arrangement and with a semiconductor laser feedback interferometer. Advantages and drawbacks of these methods are highlighted. Testing is reported on torsional, silicon micromachined mirrors, with a single degree of freedom. High dc voltage for static measurements, and sinusoidal or white-noise or step excitation for dynamic characterization, have been used for mirror driving.     

Dispersion control over 150 THz with chirped dielectric mirrors

Ultrabroad-band chirped multilayer dielectric mirrors providing nearly constant negative group delay dispersion over the wavelength range of 640-950 nm and high reflectance between 590 and 970 nm are demonstrated. A key to this performance has been an improved design method, which also substantially reduces the computing time needed for ultimate optimization. The presented devices constitute an enabling technology for producing high-quality terawatt pulses in the sub-10-fs regime. The generation of 5-fs 0.1-TW pulses by using exclusively these mirrors as negative delay line demonstrates this potential     

Electrostatic actuation of three-dimensional MEMS mirrors using sidewall electrodes

We propose and demonstrate electrostatic sidewall-electrodes actuation of three-dimensional (3-D) microelectromechanical systems (MEMS) gimbal mirrors. The linearity of the mirror angle dependence on actuation voltage is improved with the sidewall-electrodes actuation. In addition, the undesired spring-softening effect commonly found in electrostatic actuation, where the mirror resonance frequency decreases with increased tilt angle, is significantly reduced. Sidewall actuation enables superior performance of 3-D MEMS mirrors including large pull-in angles, reduced actuation voltages, improved device reliability, and fast switching times.     

Electromagnetic torsion mirrors for self-aligned fiber-opticcrossconnectors by silicon micromachining

We report a micromechanical fiber-optic switch (1 cm×1 cm×1 mm) based on an electromagnetically operated torsion mirror which is suitable for self-latching operation. The switch is fabricated by silicon micromachining technology, and self-alignment technique is employed to align optical fibers to the mirror. A small mirror of gold finished FeNiCo/polysilicon (150 μm×500 μm) is supported by two beams, and rotated around the axis in the magnetic field induced by an electromagnet. An incident light is redirected by the mirror in a free-space smaller than 1 mm³. Multimode fibers are used for optical coupling of small loss (-2.5 dB for reflection and -0.83 dB for transmission) at a wavelength 1.55 μm. Typical switching time is 10-25 ms, and switching contrast is larger than 45 dB. Magnetic torque and optical coupling are theoretically investigated     

基于嵌入式平台控制的变形镜面形展平研究

变形镜是自适应光学系统中最主要的波前矫正器,它可以通过高频地改变镜面的面形来实时补偿波前像差。由压电陶瓷驱动的变形镜在自由状态下并非理想的平坦表面。由这种初始面形误差所产生的光学畸变将严重削弱变形镜闭环控制的性能。在使用变形镜进行光学像差矫正之前,需要首先对变形镜进行镜面展平。本文拟设计一种基于嵌入式平台的变形镜控制系统来实现面形展平和镜面变形。嵌入式平台选用英伟达公司的Jetson Nano开发平台。面形展平的关键环节是需要精确地获得变形镜对每个促动器行程（电压）的光学响应（影响函数）,进而计算出响应矩阵。我们设计了基于Arm多核处理器的多线程算法显著提高了响应矩阵的计算速率。受压电材料的迟滞效应影响,变形镜的展平过程需要进行迭代收敛。经过数次迭代后,变形镜的面形误差RMS值由初始时的0.92λ降低到0.03λ,变形镜获得了比较好的展平效果。该系统的设计不但有利于变形镜系统的商用化,且较大程度地提高了变形镜闭环控制的能力,消除了自适应光学系统中变形镜自身的初始像差。     

基于可变形镜的稳像方法研究

提出了一种基于可变形镜的稳像方法,利用可变形镜连续改变面型的特点实现光学稳像。首先,建立了基于平面反射面的稳像数学模型,得到了稳像补偿角的数学表达;其次,通过研究可变形镜的关键参数,分析了可变形镜的面型误差;最后,通过实验验证了可变形镜的稳像能力,分析了稳像误差。实验数据表明,利用所选可变形镜可实现光轴偏转的功能,稳像的最大相对误差绝对值为1.87%,对应的稳定精度为2.11。     

适可而止的基于节点搜索的可变形块运动补偿

基于节点搜索的可变形块搜索是一种新型的运动估计方法,它比传统的基于平移的运动搜索有更高的精度,但该方法运算量比较大.本文在基于节点搜索可变形块运动补偿算法中采用适可而止的措施,对搜索精度足够的非平移块终止当前搜索,直接跳到半像素精度搜索.实验结果表明,只要门限选择得当,就能以预测质量降低很小的代价换来运算速度的大幅提高.     

Design of freely configurable safety light curtain using hemispherical mirrors

Safety light curtains provide reliable and cost‐effective protection against access into hazardous points or areas. However, in practice, peopl still need to adjust the light detection element accurately in order to receive the safe amount of irradiating laser light. In our proposed system, we utilized light emitting diodes (LEDs) as the light source, and designed two hemispherical mirrors to receive the LED light, and used PSoC microcomputer to determine the threshold voltage value. Compared with recent market products, the proposed system is freely configurable, and with no dead zone detection. In addition, compared to the laser light, the LED light has the advantages of no radiation, small electropult, low‐cost, and high efficiency. After conducting sufficient experiments, the proposed system has been found to successfully detect the intruder with 100% recognition rate, which can meet the needs of industrialization. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Large deflection micromechanical scanning mirrors for linear scansand pattern generation

An electrostatically driven silicon micro scanning mirror (MSM) for one-dimensional (1-D) and two-dimensional (2-D) deflection of light is presented. A special configuration of the driving electrodes allows the use of small electrode gaps without restricting the deflection of the plate geometrically. In this paper, the starting of the oscillation and the operation of the scanner is discussed. Experimental results show that scan angles of up to 60° can be achieved at a driving voltage of only 20 V. The 2-D deflection of a laser beam is obtained by a gimbal mounting of the mirror plate. For the fabrication of the devices, SOI-wafers are used as the base material. The mechanical structures are defined by a deep silicon etch. For the electrical isolation of areas on the movable frame, polysilicon-filled trenches are used. The mechanical stability of the scanners is tested. The devices resist shocks of more than 1000 g and show no change of the resonance frequency even after long run tests of 7×10⁹ periods     

Nano-precision metrology of X-ray mirrors with laser speckle angular measurement

X-ray mirrors are widely used for synchrotron radiation, free-electron lasers, and astronomical telescopes. The short wavelength and grazing incidence impose st...     

基于可变形卷积改进SSD算法的目标检测方法

为了提高传统SSD算法对小目标检测的准确率,提出一种改进的SSD目标检测算法:采用基于可变形卷积的ResNet50作为SSD算法的特征提取网络,提高对目标的处理能力;设计特征金字塔(FPN)来融合不同层的特征图,丰富浅层特征图的语义信息;在特征融合时引入通道注意机制,提取相应的通道权重,增加重要信息的比例,提高检测效果。最后采用PASCAL-VOC2007开源数据集进行仿真实验,并与传统SSD目标检测算法进行对比,准确率得到显著提高,验证了该算法对小目标检测的有效性。