Subpicometer length measurement using heterodyne laser interferometry and all-digital rf phase meters

We present an all-digital phase meter for precision length measurements using heterodyne laser interferometry. Our phase meter has a phase sensitivity of 3 μrad/√Hz at signal frequencies of 1 Hz and above. We test the performance of our phase meter in an optical heterodyne interferometric configuration, using an active Sagnac interferometer test bed that is flexible and low noise. We demonstrate more than 70 dB of laser frequency noise suppression to achieve an optical phase sensitivity of 5 μrad/√Hz and a corresponding displacement sensitivity of 0.5 pm/√Hz at signal frequencies above 10 Hz. In addition, we demonstrate the ability of our phase meter to follow full fringe signals accurately at 100 Hz and to track large signal excursions in excess of 10(5) fringes without cycle slipping. Finally, we demonstrate a cyclic error of ≤1 pm/√Hz, above 10 Hz.     

Precision angle sensor using an optical lever inside a Sagnac interferometer

We built an ultra-low-noise angle sensor by combining a folded optical lever and a Sagnac interferometer. The instrument has a measured noise floor of 1.3 prad/√Hz at 2.4 kHz. We achieve this record angle sensitivity using a proof-of-concept apparatus with a conservative N=11 bounces in the optical lever. This technique could be extended to reach subpicoradian/√Hz sensitivities with an optimized design.     

Laser frequency noise immunity in multiplexed displacement sensing

Digitally enhanced interferometry (DI) can be used to distinguish between interferometric signals and simultaneously monitor in-line object displacements with subnanometer sensitivity. In contrast to conventional interferometry-where these signals interfere with each other and degrade performance-we experimentally show that by using DI, each of these signals can be isolated and measured at the same time. We present what we believe to be the first demonstration of DI's signal multiplexing capabilities, showing simultaneous length sensing of three sections of an optical fiber. The cross talk between length measurements was less than 2.6×10(-3) with a displacement noise floor of 200 pm/√Hz, which corresponds to a strain sensitivity of less than 80 picostrain(p?) in each sensor. We also enhance our system's displacement sensitivity at low frequencies by combining information from multiple lengths to suppress errors due to laser frequency noise.     

Towards a fiber-coupled picowatt cryogenic radiometer

A picowatt cryogenic radiometer (PCR) has been fabricated at the microscale level for electrical substitution optical fiber power measurements. The absorber, electrical heater, and thermometer are all on a micromachined membrane less than 1 mm on a side. Initial measurements with input powers from 50 fW to 20 nW show a response inequivalence between electrical and optical power of 8%. A comparison of the response to electrical and optical input powers between 15 pW to 70 pW yields a repeatability better than ±0.3% (k=2). From our first optical tests, the system has a noise equivalent power of ≈5×10(-15) W/√Hz at 2 Hz, but simple changes to the measurement scheme should yield an NEP 2 orders of magnitude lower.     

全光型石英增强光声光谱

设计并演示了一种全光型石英增强光声光谱技术, 该技术在传统的石英增强光声光谱系统中增加了另一束探测光束, 把与气体浓度成正比的石英晶振振臂的振动幅值转化为探测光束的强度变化, 实现了探测气体处无电子元件的全光学系统. 如此的设计使该系统具有较强的抗电磁干扰能力和非常小的传感头体积, 能够用于探测空间受限或探测环境恶劣的情况下, 并实现远距离探测. 在这种配置下, 探测大气压下的水汽, 获得的噪声等效吸收系数为1.13×10^-6 cm^-1W/√Hz. 进一步讨论了优化系统和提升其探测灵敏度的途径. 关键词： 石英增强光声光谱 音叉式石英晶振 气体传感     

High frequency GaAs nano-optomechanical disk resonator

Optomechanical coupling between a mechanical oscillator and light trapped in a cavity increases when the coupling takes place in a reduced volume. Here we demonstrate a GaAs semiconductor optomechanical disk system where both optical and mechanical energy can be confined in a subwavelength scale interaction volume. We observe a giant optomechanical coupling rate up to 100 GHz/nm involving picogram mass mechanical modes with a frequency between 100 MHz and 1 GHz. The mechanical modes are singled-out measuring their dispersion as a function of disk geometry. Their Brownian motion is optically resolved with a sensitivity of 10(-17) m/√Hz] at room temperature and pressure, approaching the quantum limit imprecision.     

光泵抽运3He极化程度监控系统的设计与实现

极化³He的一项重要应用是中子的极化.中国绵阳研究堆（CMRR）已建立国内首个自旋交换光学泵浦（SEOP）极化³He中子极化系统.为了监测³He的极化率随时间的相对变化情况,本文首先设计了基于核磁共振（NMR）技术的³He相对极化率测量系统,通过Matlab控制程序实现了对³He相对极化率的定时检测.然后对拾波线圈的构形和信噪比（SNR）进行了优化.结果表明当绕线长度一样时,Brooks构形的线圈有利于提高SNR;当线圈的平均半径为（a₀+d）/√2（a₀为³He气室的半径,d为拾波线圈与气室之间的距离）时,其SNR最高.最后对该系统的本底噪声进行了测量,发现其主要来源于环境噪声（0.27 μV/√Hz）和数据采集（DAQ）卡的噪声（0.40 μV/√Hz）,系统的总噪声功率谱密度约为√0.16+0.073G² μV/√Hz（G为放大器的增益倍数）.     

Low-noise fiber optics receiver with super-beta bipolar transistors

Abstract

A low-noise wideband optical fiber receiver has been successfully designed using super-beta bipolar transistors (BJTs) at the front end. Even with commercially available super-beta devices, which are not optimized for our application, the obtainable input sensitivity for medium- and high-bandwidth optical receivers is comparable or superior to the best FET design. To demonstrate this concept, a 10-MHz analog receiver was built with a super-beta BJT at the input stage. This receiver achieved an expected average input noise current density of less than 0.4 PA/√Hz over the full bandwidth for a transresistance of 500 kΩ. Detailed design procedures are given in this paper. The noise characteristics of a 50-MHz receiver using super-beta BJTs are also obtained.     

Ultrahigh sensitivity electric field detection with a liquid electro-optical film

In this Letter, an electro-optical probe configuration with polar molecule liquids as the sensing film is proposed to improve the voltage sensitivity. This method exhibited increases in intrinsic sensitivities better than 0.1 mV/√Hz, 2 orders of magnitude larger than the normal method using a GaAs probe in the same measurement system. Based on the mechanism of orientation polarization, the electro-optic coefficient was measured to be 250 pm/V by the Teng-Man method at a modulation field of 100 Hz. This technology will be promising in applications of low-frequency field detection.     

Range discrimination in ultrasonic vibrometry: theory and experiment

A technique has been developed to demodulate periodic broadband ultrasonic interrogation signals that are returned from multiple scattering sites to simultaneously determine the low-frequency displacement time histories of each individual site. The technique employs a broadband periodic transmit signal. The motions of scattering sites are separately determined from the echoed receive signal by an algorithm involving comb filtering and pulse synthesis. This algorithm permits spatial resolution comparable to pulse-echo techniques and displacement sensitivities comparable to pure-tone techniques. A system based on this technique was used to image transient audio-frequency displacements on the order of 1-10 μm peak (≥?50 nm/√Hz) that were produced by propagating shear waves in a tissue phantom. The system used concentric transmitting and receiving transducers and a carrier signal centered at 2.5 MHz with an 800 kHz bandwidth. The system was self-noise-limited and capable of detecting motions of strongly reflecting regions on the order of 1 nm/√Hz. System performance is limited by several factors including signal selection, component hardware, and ultrasonic propagation within the media of interest.     

Low frequency behaviour of the Pisa seismic noise super-attenuator for gravitational wave detection

The absolute displacements, for frequencies below 20 Hz, of the 400 kg test mass seismically isolated by the Pisa super-attenuator, to be used in long base interferometer for gravitational wave research, are presented. In the region below 6 Hz, the maximum displacement is about 14 μm. The displacements, at 10 and 20 Hz, are ≤ 1.5 × 10^-13 and ≤ 4 × 10^-14 m/√Hz respectively and represent presumably the lowest ever reached by a suspended mass on earth. The super-attenuator transfer function, which has been measured using the seism as an exciter for 0<υ<6 Hz, shows a remarkable agreement with the theoretical one and demonstrates the necessity of having an attenuating system working in three dimensions.     

A low noise 2 × 16 Ge:Sb focal-plane array: Paving the way for large format FPAs for far IR astronomy

Future astronomical instruments call for large format and high sensitivity far infrared focal-plane arrays to meet their science objectives. Arrays as large as 128 × 128 with sensitivities equal to or better than 10⁻¹⁸ W/√Hz are set as targets for the far IR instruments to be developed within the next 10 years. These seemingly modest goals present a not-so-modest quantum leap for far IR detector technology whose progress is hampered by a number of complexities; chief among them the development of low noise readouts operating at deep cryogenic temperatures and a viable hybridization scheme suitable for far IR detectors. In an effort to incrementally develop large-format photoconductor arrays, we have fabricated a 2 × 16 Ge:Sb array using the SBRC190 readout – a cryogenic 1 × 32 CTIA readout multiplexer initially developed for SOFIA’s AIRES instrument. In this paper we report the results of the extensive parametric tests performed on this array showing an impressive noise performance of 2.2 × 10⁻¹⁸ W/√Hz and a DQE of 0.41 despite some design limitations. With such an encouraging performance, this prototype array will serve as a platform for our future developmental effort.     

An Inverter-Based,CMOS, Low-Power Optical Receiver Front-End

In this paper, a low-power optical receiver front-end which consists of a transimpedance amplifier (TIA) and three stages of limiting amplifier (LA) for 2.5 Gb/s applications is proposed in 0.18 µm CMOS technology. The proposed TIA benefits from a modified inverter structure, in which the input resistance is properly reduced due to the use of diode-connected transistors in comparison with conventional inverter circuit. Also, an active inductor is used in parallel with a diode-connected transistor at the output node, which provides a low output resistance, while it resonates with the load capacitance to extend the ?3 dB frequency bandwidth. Moreover, three stages of LAs are used to obtain extra gain, in which each LA cell uses active inductor load. However, HSPICE simulations for the proposed TIA circuit show a 42.24 dBΩ transimpedance gain, 1.96 GHz frequency bandwidth, 11.7 pA/√Hz input referred noise, and only 972 µW of power consumption at 1.5 V supply. Also, simulation results for the whole receiver system show a 75.6 dB gain, 1.7 GHz frequency bandwidth, and 6.54 mW of power consumption at 1.5 V supply. Finally, simulation results indicate that the proposed receiver system has good performances to be used as a low-power optical receiver front-end.     

A CMOS Low-Power Optical Front-End for 5 Gbps Applications

In this paper, a new low-power optical receiver front-end is proposed in 90 nm CMOS technology for 5 Gb/s AApplications. However, to improve the gain-bandwidth trade-off, the proposed Trans-Impedance Amplifier (TIA) uses an active modified inverter-based topology followed by a common-source amplifier, which uses active inductive peaking technique to enhance the frequency bandwidth in an increased gain level for a reasonable power consumption value. The proposed TIA is analyzed and simulated in HSPICE using 90 nm CMOS technology parameters. Simulation results show a 53.5dBΩ trans-impedance gain, 3.5 GHz frequency bandwidth, 16.8pA/√Hz input referred noise, and 1.28 mW of power consumption at 1V supply voltage. The Optical receiver is completed using three stages of differential limiting amplifiers (LAs), which provide 27 dB voltage gain while consume 3.1 mW of power. Finally, the whole optical receiver front-end consumes only 5.6 mW of power at 1 V supply and amplifies the input signal by 80 dB, while providing 3.7 GHz of frequency bandwidth. Finally, the simulation results indicate that the proposed optical receiver is a proper candidate to be used in a low-power 5 Gbps optical communication system.     

Two-dimensional scanning probe driven by a solenoid-based single actuator for optical coherence tomography

We propose the two-dimensional scanning probe operating with a single actuator, which is thought useful as a sample probe for optical coherence tomography (OCT). The probe was designed to use a single-body lensed fiber cantilever loaded with an iron-bead and driven by a single-solenoid actuator. Elliptic spiral trace patterns were achieved using off-axis magnetic fields of the solenoid. A three-dimensional OCT image was obtained for a scanning area of 3.8 mm × 3.4 mm at an acquisition speed of 16.7 s/V. Up to 27 Hz B-scan rate, the proposed probe worked well, and 1000 A-scans were made per each B-scan.     

Infrared detector arrays with multiplexing cryogenic read-out electronics for isophot

Cryogenic Read out Electronic circuits (CRE) are developed in a CMOS technology for the multiplexing operation at temperatures around 4 K and below of extrinsic photoconducting detectors and detector arrays of Ge and Si in the Infrared Space Observatory (ISO) instrument ISOPHOT covering a wavelength region between 10–200 μm. Measurements on the 66 elements spectroscopic array ISOPHOTS2 show performance data of an NEP around 4 × 10⁻¹⁷W/√Hz and a voltage responsivity of 10¹⁴V/Ws at low background operation.     

Multiresolution pattern spectrum and its optical implementation using visual area coding technique

We described recently the multiresolution pattern spectrum (MPS), a method to extract the size distribution of image objects based on visual impression. In this paper, an optical implementation method of MPS is proposed using the visual area coding technique, an encoding method to operate gray scale images optically while preserving visual impressions of these.     

Reduction of thermal fluctuations in a cryogenic laser interferometric gravitational wave detector

The thermal fluctuation of mirror surfaces is the fundamental limitation for interferometric gravitational wave (GW) detectors. Here, we experimentally demonstrate for the first time a reduction in a mirror's thermal fluctuation in a GW detector with sapphire mirrors from the Cryogenic Laser Interferometer Observatory at 17 and 18 K. The detector sensitivity, which was limited by the mirror's thermal fluctuation at room temperature, was improved in the frequency range of 90 to 240 Hz by cooling the mirrors. The improved sensitivity reached a maximum of 2.2×10(-19) m/√Hz at 165 Hz.     

压电矢量传感器的低噪声设计

针对压电矢量传感器的低噪声设计问题,建立了基于压电敏感器件、悬挂结构、前置放大电路及电缆的同振式矢量传感器等效自噪声分析模型;结合敏感器件的低噪声设计、悬挂结构对自噪声的影响以及前置放大电路低噪声匹配等内容提出了一种低噪声设计方法。设计了低噪声矢量传感器样机,研制了自噪声测量平台并对样机进行了测试。结果表明:样机的等效噪声声压谱级达到了55.5 dB/√Hz2@200 Hz,低于同频率Knudsen零级海况下海洋环境噪声;测试结果与设计结果相符,验证了低噪声设计方法的有效性,也为压电矢量传感器的低噪声设计提供了理论依据。      

Subkilohertz enhanced-power diode-laser spectrometer in the visible

We report on a high-performance diode-laser spectrometer operating near 657 nm with narrow linewidth (<0.6kHz) , enhanced power (as much as 40 mW), and low drift (<10Hz/s) . The spectrometer comprised an extended-cavity diode-laser frequency stabilized to a high-finesse optical resonator and a broad-area antireflection coated laser diode as an amplifier with a single-lobe emission pattern of good spatial purity. The spectrometer was used to record time-domain optical Ramsey spectra of laser-cooled Ca atoms with a resolution of 0.6 kHz.