High-resolution electrostatic analog tunable grating with a single-mask fabrication process

We present the design, modeling, fabrication, and characterization of the microelectromechanical systems (MEMS) analog tunable diffraction grating with the concept of transverse actuation. In contrast to the vertically actuated "digital" tunable grating, our prototype design trades angular tunable range for tuning resolution. The prototype shows an angular tunable range of 250 /spl mu/rad with 1-/spl mu/rad resolution at 10 V. Grating pitch changes corresponding to the full range and resolution are 57 nm and 2.28 /spl Aring/, respectively confirmed by experimental measurement and theoretical calculation. Simulation shows that subradian tunable range is feasible with better lithographic design rules or higher actuation voltage. The single-mask fabrication process offers several advantages: 1) Excellent optical flatness; 2) ease of fabrication; and 3) great flexibility of device integration with existing on-chip circuitry. Tunable gratings such as the one presented here can be used for controlling dispersion in optical telecommunications, sensing, etc., applications.     

Enhanced oxygen detection using porous polymeric gratings with integrated recognition elements

The development of ordered porous nanostructured materials, such as polymeric Bragg gratings, offers an attractive platform for the encapsulation of chemical and biological recognition elements. To date, various types of polymer gratings have been developed with several demonstrated applications in switching, lasing, and display devices. Here, we focus on a new class of holographically ordered porous polymer (HOPP) gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. We present biochemical sensing using HOPP gratings that include a volatile solvent as the phase separation fluid. The resulting HOPP gratings are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of recognition elements. As a prototype, we developed an oxygen (O₂) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. The resulting O₂ sensors performed across the full-scale range (0–100%) of oxygen in nitrogen, with a response time of less than 1 s. The O₂ sensor system uses a LED excitation source and a silicon photodiode detector. The ability of these HOPP reflection gratings to transmit or reflect a particular wavelength range, based on the grating spacing, enables us to selectively enhance the detection efficiency for the wavelengths of interest.     

Analog piezoelectric-driven tunable gratings with nanometer resolution

This work presents the design, fabrication, and characterization of a piezoelectrically actuated MEMS diffractive optical grating, whose spatial periodicity can be tuned in analog fashion to within a fraction of a nanometer. The fine control of the diffracted beams permits applications in dense wavelength-division multiplexing (DWDM) optical telecommunications and high-resolution miniaturized spectrometers. The design concept consists of a diffractive grating defined on a deformable membrane, strained in the direction perpendicular to the gratings grooves via thin-film piezoelectric actuators. The tunable angular range for the first diffracted order is up to 400 /spl mu/rad with 0.2% strain (/spl sim/8 nm change in grating periodicity) at 10 V actuation, as predicted by device modeling. The actuators demonstrate a piezoelectric d/sub 31/ coefficient of -100 pC/N and dielectric constant /spl epsiv//sub r/ of 1200. Uniformity across the tunable grating and the out-of-plane deflections are also characterized and discussed.     

MOEMS tuning element for a Littrow external cavity laser

A miniature grating-tunable external cavity laser diode constructed using microoptoelectromechanical systems (MOEMS) technology is described. The tuning element is a vertically etched blazed grating mounted on a compound flexure, which consists of a cantilever in series with a portal frame. The flexure is deflected using comb electrostatic drives to rotate and translate the grating. The tuning element is prototyped using deep reactive ion etching of bonded silicon-on-insulator (SOI) material. Interferometric measurements of electromechanical performance are presented, and departures from the ideal behavior are identified. Electrostatic tuning of a Littrow external cavity laser over a range of 20 nm using a 50-V drive is demonstrated.     

A High-Q Widely Tunable Gigahertz Electromagnetic Cavity Resonator

This paper describes the design, fabrication and testing of a quasi-static electromagnetic cavity resonator fabricated using potassium-hydroxide (KOH) etching, shallow reactive-ion etching (RIE), metalization and wafer bonding. The resonator is distinguished by its simultaneous high-Q near 200, and wide high-frequency tuning range, 2.5-4.0 GHz for the experimental resonator presented here. When combined with an integrated actuator, it should be suitable for use in electronically tunable radio-frequency (RF) bandpass filters and oscillators. The experimental resonator, however, is tuned with an external piezoelectric actuator for simplicity     

Wet etching of silicon gratings with triangular profiles

Triangular silicon gratings of different size (periods from 0.8 to 25.0 m) are manufactured by wet chemical etching. Two main principles of preparation are used and improved. The received gratings are investigated and characterized by SEM concerning the uniformity and the sharpness of the convex edges and the concave notches. Their very small radii determined by TEM are reported for the first time. The gratings can be applied to optical purposes or as standards for surface metrology.     

Fabrication of high precision X-ray mask for X-ray grating of X-ray Talbot interferometer

X-ray imaging is used in many applications such as medical diagnosis and non-destructive inspection, and has become an essential technologies in these areas. In one image technique, X-ray phase information is obtained using X-ray Talbot interferometer, for which X-ray diffraction gratings are required; however, the manufacture of fine, highly accurate, and high aspect ratio gratings is very difficult. X-ray lithography could be used to fabricate structures with high precision since it uses highly directive syncrotron radiation. Therefore, we decided to fabricate X-ray gratings using X-ray lithography technique. The accuracy of the fabricated structure depends largely on the accuracy of the X-ray mask used. In our research, we combined deep silicon dry etching technology with ultraviolet lithography in order to fabricate untapered and high precision X-ray masks containing rectangular patterns. We succeeded in fabricating an X-ray mask with a pitch of 5.3 μm. The thickness of the Au absorber was about 5 μm, and the effective area was 60  × 60 mm², which is a sufficient size for phase tomography imaging. We demonstrated the utility of the Si dry etching process for making high precision X-ray masks.     

A 1-D Photonic Band Gap Tunable Optical Filter in (110) Silicon

In this paper, we describe an electrostatically tunable optical bandpass filter that is fabricated in (110) silicon. Deep reactive-ion etching is the main process that is used to fabricate the overall device structure. To create the highly parallel surfaces that are needed for the photonic band gap elements, electrochemical (KOH) etching of the vertical (111) planes is then used. Back etching is used to release the moving parts. Fiber pigtails are attached in etched alignment grooves, and fiber-fiber insertion loss below 11 dB was obtained. The measured passband width was 3 nm with a tuning range of 8 nm.     

A Real Pivot Structure for MEMS Tunable Lasers

This paper presents the design of a real pivot formed by a double-clamped beam for the rotational tuning structures in microelectromechanical systems (MEMS) tunable lasers. Micromechanical properties such as beam deformation, pivot position and pivot shift are investigated and compared with the virtual pivot formed by a cantilever beam. It is shown that the real pivot has negligible shift when subjected to load and fabrication error owing to its feature of structural symmetry, while the virtual pivot suffers from significant pivot shift, which would severely limit the wavelength tuning range. The two pivot designs are implemented into MEMS tuning structures that are fabricated by deep etching and released using a dry release approach. The real pivot measures a depth variation of 16% over the double-clamped beam but maintains the symmetry to the midpoint, and is still able to produce a rotation angle of 4.7deg. In contrast, the virtual pivot has a depth reduction of 4% over the cantilever beam, but achieves only a 2.4deg rotation due to the pull-in problem originated from the severe pivot shift. The real pivot design is more suitable for the MEMS tunable lasers as it is simple, symmetric, robust, and suitable for single-chip integration     

基于匹配滤波解调的光纤光栅振动传感器研究

采用双悬臂梁结构,研制了基于匹配滤波解调的光纤光栅振动传感器,可通过悬臂梁对匹配光栅静态工作点进行精确调整.该传感器集振动传感和动态波长解调于一体,并具有温度补偿功能.对传感器的工作原理进行了理论分析,通过与压电式加速度传感器进行的比较实验,得到了一致的实验测量结果.     

碳化硅薄膜的ICP浅刻蚀工艺研究

选用SF6/O2 混合气体对等离子体增强化学气相淀积( PECVD)法制备的碳化硅( SiC)薄膜进行了浅槽刻蚀,并通过正交试验设计方法,研究了感应耦合等离子体( ICP)刻蚀技术中反应室压强、偏压射频( BRF)功率、O2 比例三个工艺参数对碳化硅薄膜刻蚀速率的影响及其显著性.实验结果表明:BRF功率对于刻蚀速率的影响具有高度显著性,各因素对刻蚀速率的影响程度依次为BRF功率>反应室压强>O2 比例,并讨论了所选因素对碳化硅薄膜刻蚀速率的影响机理.     

USB接口在数据采集系统中的应用

本文介绍一种快速漏电流分选仪，对其电路原理进行了概述。它适用于钽电解电容器整条排测分选，具有整机造价低，测试速度快的特点。     

Fabrication of a thin plasmonic color sheet embedded with Al subwavelength gratings in parylene

In this study, we developed a thin plasmonic color sheet (TPCS) embedded with Al subwavelength gratings for use in flexible optical transmission filters, and experimentally demonstrated its transmission characteristics. Al subwavelength gratings were formed in a freestanding thin poly-para-xylylene (parylene-N) film less than 1-μm thick by using electron beam (EB) direct writing and sacrificial etching. The fabricated TPCS contained Al subwavelength gratings with periods ranging from 400 nm to 600 nm, and succeeded in shifting the transmission peak wavelength from 510 nm to 650 nm in the visible range. The freestanding thin parylene-N film deposited by room-temperature chemical vapor deposition provided enough flatness to the TPCS with a height difference of 900 nm in a whole filter area, resulting in uniform transmission spectra. The experimentally obtained peak shift dependent on the grating period agreed well with theoretical calculation results.     

Nonlinear ceramics for tunable microwave devices

The research on materials and systems for tunable microwave devices has gained attraction within the last years. The radio frequency characterization and the component design of tunable microwave components based on dielectric ceramics especially barium-strontium-titanate (BST) are presented in this second part, whereas the basic material properties are discussed in detail in the first part. After a short introduction to the processing technology used for the fabrication of tunable components based on a BST thick film, the relations between microwave properties and material properties as well as the microstructure are presented in detail. The design process for tunable microwave components based on BST thick films is described. Especially the considerations related to micro- and macrostructure and their connection are highlighted. The paper closes with two different application examples: a reconfigurable array antenna for satellite communication and varactors for high power applications.     

Interrogation technique using a novel spectra bandwidth measurement method with a blazed FBG and a fiber-optic array for an FBG displacement sensor

A double-arched-beam-based fiber Bragg grating (FBG) displacement sensor is presented. Unlike most interrogation methods by measuring the resonance wavelength shifts, this kind of FBG sensor is proposed to measure the displacement by measuring the FBG's reflective spectra bandwidth using a blazed fiber Bragg grating (blazed FBG) and a fiber optic array. According to the strain distribution on the novel double-arched beam surface, the positive and negative strain will act on only one FBG, which is stuck on the beam surface. Thus, the positive and negative strain will make the spectra broaden as the displacement increases. What is more, the problem of cross-sensitivity in the FBG sensor is solved because temperature only affects the wavelength shift, but not the spectra bandwidth. The reflective signal of FBG sensor will be lead into a blazed FBG and the radiation light from blazed FBG with a certain radiation angle will be received by a fiber optic array, and then recorded by the infrared linear detector (IRLD). Based on the Gauss distribution theory, the radiation light spot size related to the FBG's reflective spectra bandwidth can be determined. Simulation and preliminary experimental results indicate the feasibility of the proposed idea.     

Piezoelectrically actuated tunable capacitor

This paper describes the design, fabrication, and characterization of the first MEMS piezoelectric tunable capacitors employing zinc oxide (ZnO) actuation. Relatively simple design rules for the device-structure optimization for largest deflection are shown from simulation results based on theoretical equations. The ZnO-actuated tunable capacitors are accordingly designed and fabricated with both surface and bulk micromachining techniques. Through the surface micromachining process, sacrificial silicon is removed with XeF/sub 2/, and parylene is successfully used as a supporting layer for a piezoelectric unimorph cantilever. For comparison, other two different structures using plasma-enhanced chemical-vapor deposition (PECVD) SiN and SU-8 as supporting layers are also fabricated. Deflection analyses are performed for three specific structures, among which the parylene-supported one is demonstrated to have the largest displacement and most suitable for tunable capacitor application. For bulk-micromachined tunable capacitor, we have implemented a novel design of a large structure driven by a ZnO unimorph, and obtained a tuning ratio of more than 21:1 (0.46 pF-10.02 pF). This is the highest tuning ratio reported to date for parallel-plate tunable capacitors while requiring an applied voltage of only 35 V.     

Hole-type two-dimensional photonic crystal fabricated in silicon on insulator wafers

We report the realization of two-dimensional (2D) photonic crystal (PhC) holes array using synthesized processing techniques of deep UV lithography, time-multiplexed reactive ion etching (TMRIE) and focus ion beam (FIB) etching. In this study, mixed density of holes and waveguide patterns of 2D PhC structures was first formed in silicon on insulator wafers through use of a scanner. Ultra wide grooves were then defined, aligned to the deep submicron size devices. Following deep etching of more than 50 μm by TMRIE, PhC structures were then revealed for device etching. Such design of fabrication process allows realization of disparate pattern dimensions and also etching depths. Through avoidance of etch lag effect, notching of devices at interface of device silicon and buried oxide layer was avoided. At the same time, through a singular FIB etch in the final step of the process following buried oxide release for PhC structures on critical dimension structures, severe loading effects of such structures were avoided to enable a wide process window of lithography and etch.     

An eclectic approach to design tunable amplifiers

Broadband amplifiers that can accommodate commercial communication standards such as GSM, UMTS, Wi‐Fi, and Wi‐Max are extremely important for radio equipment manufacturers. To achieve this coverage, the amplifier should provide high gain and efficiency over a band from 800 to 5200 MHz. Although there are transistor devices that have cut‐off frequencies well over these frequencies, amplifiers covering such a broad‐bandwidth are difficult to design due to the requirement of broadband matching networks. In this work, design of broadband tunable matching networks is investigated using Real Frequency Direct Computational Technique (RF‐DCT). In order to be able to work on sample structures, impedance transforming filters are chosen and a broadband tunable matching network has been designed. Implementation of tunable inductors is investigated and the performance of a tunable matching network using tunable inductors and capacitors is demonstrated. Eventually a broadband frequency tunable amplifier has been designed using the tunable inductor concept. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

A micromachined tunable resonator fabricated by the CMOS post-process of etching silicon dioxide

This work investigates the fabrication of a micromechanical tunable resonator using the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and the post-process of only one maskless wet etching. The post-process has advantages of easy execution and low cost. The post-process employs an etchant (silox vapox III) to etch the silicon dioxide layer to release the suspended structures of the resonator. The tunable resonator comprises a driving unit, a tuning unit and a sensing unit. The resonant frequency of the resonator can be tuned using a dc-biased electrostatic comb of linearly varied finger-length. Experimental results show that the resonant frequency of the resonator is about 4.8 kHz, and it has a frequency-tuning range of 6.8% at the tuning voltage of 0–25 V.     

Modeling of grating/moiré based micro motion sensor

 The design of a micro optical motion sensor is proposed. Fourier series analysis is used to determine the optical transmission function (OTF) of gratings. The optical flux generated by a grating (pair) and received by photodetector is then calculated through an integration of the OTF over the receiving window. A general relationship between photo-detector output current and grating translation displacement is finally established. The analysis is carried out for linear binary grating sensors, with single and double grating sensors. The influence of grating (pair) structure and receiving window on sensor sensitivity and linearity of output response is investigated. A numerical work is completed to simulate the various cases of optical structure design. Several types of photoresist gratings are fabricated and are used to experimentally characterize the grating sensor. The tested result is found to be in general agreement with the analysis result.