Fiber-optic temperature sensor using low-coherence interferometry

Low-coherence interferometric sensors are an important group of optical fibre sensors. Combining high measurement resolution with broad measurement range, these sensors can measure accurately several physical quantities e.g. temperature. In this article we present the fiber-optic temperature sensor using low-coherent interferometry, which has been designed and elaborated.     

Multi-channel pressure sensor using speckle interferometry

The performance of two-dimensional pressure sensor arrays, consisting of 13 × 13 deformable steel diaphragms, is investigated. The pressureinduced out-of-plane component of the displacement field of all 169 sensors is measured in parallel using phase-stepping speckle interferometry. Subsequent least-squares fitting of the theoretical field provides a quantitative measure of the average pressure acting on each sensor. With monotonically-increasing load and suitable calibration, each pressure value can be measured to an accuracy of better than 1% of the full scale deflection. The current pressure range of 0–2.74 kPa can be extended by increasing the number of interferograms recorded.     

High-performance fiber-optic temperature sensor using low-coherence interferometry

A temperature-sensor system based on low-coherence interferometry with a fiber Mach-Zehnder interferometer as a phase modulator was implemented. A measurement range of 20 to 800 degrees C with a resolution of 0.025 degrees C (corresponding to 0.0004 fringe) was achieved with a 1-mm-long fiber Fabry-Perot interferometer as the sensing element.     

Multiplexed fiber Fabry-Perot temperature sensor system using white-light interferometry

A novel monitoring system for a fiber Fabry-Perot interferometer (FFPI) temperature sensor has yielded a resolution of 0.013 degrees C (0.0025 fringe). Light from a broadband source passes through a scanned Michelson interferometer and is reflected from a FFPI to produce a fringe pattern, the temporal position of which is proportional to a change in the optical length of the fiber interferometer. A second Michelson interferometer with a distributed-feedback laser source is used to correct for variations in the translation rate of the motor-driven scanning mirror. Coherence multiplexing of three such sensors has also been demonstrated.     

New inertial and gravitational effects made measurable by atomic beam interferometry

The aim of this letter is to draw attention to the fact that using atomic beam interferometry two new types of gravi-inertial effects are now within the range of measurability. Beyond the term linear in the earth's acceleration g, an effect quadratic in the acceleration seems to be observable. Furthermore, with regard to rotation, in addition to the Sagnac effect, a spin-rotation effect may be measurable. The respective experiments are of fundamental theoretical importance with regard to quantum mechanics in non-inertial reference frames and to the influence of gravity on quantum systems.     

Capacitive position measurement for high-precision space inertial sensor

Low noise position measurement is fundamental for space inertial sensors, and at present the capacitive position sensor is widely employed for space inertial sensors. The design for the possible suppression of the front-end electric noises for a capacitive sensor is presented. A prototype capacitive sensor with 2×10⁻⁶pF/Hz1/2 at frequency above 0.04 Hz is achieved and further improvements are discussed.      

Quadrature demodulation technique for self-mixing interferometry displacement sensor

A new, to the best of our knowledge, signal processing method based on quadrature demodulation technique is presented for laser diode self-mixing interferometry(LDSMI) displacement sensor. Phase modulation of the laser beam is obtained by an electro-optic modulator (EOM) in the external cavity. Detection of the target's displacement can be easily achieved by sampling the interference signal at those times which satisfied certain conditions. The major advantage of the technique is that it does not involve any complicated calculation and insensitive to the sampling error. Experimental results show that the proposed method can effectively improve the displacement measurement resolution of the laser diode self-mixing displacement sensor to a few nanometers.     

A high accuracy image sensor for sinusoidal phase-modulating interferometry

We proposed a high accuracy image sensor technique for sinusoidal phase-modulating interferometer in the field of the surface profile measurements. It solved the problem of the CCD's pixel offset of the same column under two adjacent rows, eliminated the spectral leakage, and reduced the influence of external interference to the measurement accuracy. We measured the surface profile of a glass plate, and its repeatability precision was less than 8 nm and its relative error was 1.15%. The results show that it can be used to measure surface profile with high accuracy and strong anti-interference ability.     

Developing nanoscale inertial sensor based on graphite-flake with self-retracting motion

We presented simple schematics of a nanoscale inertial measurement unit based on the self-retraction motion of the graphene flakes. When an external force is applied to the nanoscale graphite flake, the inertial force exerted on the movable layer can telescope it, then the self-restoring force also arises as the van der Waals force between the interlayers of the flake, which each suspended flake can automatically and fully retract back onto the top of the graphite platform immediately after the externally applied force is released. Since the van der Waals force linearly increases with the increasing size of the flake, the sensing limitation can be controlled. When the external force does not exceed the retracting force, this addressed nanoscale inertial measurement unit can be semi-permanently used. Therefore, the size and the thickness of the graphene flake should be carefully selected with a tradeoff. These graphite flakes can be utilized as a basic structure in various nanoelectromechanical devices, such as switch and memory, linear and angular accelerometers, and pressure sensors.     

Topological phase shift in a cold-atom interferometer

Matter-wave interferences in a four-pulse version of a Ramsey-Bordé atom interferometer have been utilized to study phase shifts. A topological phase shift analogous to the scalar Aharonov-Bohm effect proposed for charged-particle interferences in the presence of a pulsed electrostatic potential has been investigated. The time-dependent potential has been generated by the interaction of a laser field with an induced atomic dipole without spatial variation along the interferometer arms. The atom interferometer has been run with laser-cooled magnesium atoms stored in a magneto-optical trap.Dedicated to H. Walther on the occasion of his 60th birthday     

Detuning effects in the vertical cold-atom micromaser

The quantum theory of the cold atom micromaser including the effects of gravity is established in the general case where the cavity mode and the atomic transition frequencies are detuned. We show that atoms which classically would not reach the interaction region are able to emit a photon inside the cavity. The system turns out to be extremely sensitive to the detuning and in particular to its sign. A method to solve the equations of motion for non resonant atom-field interaction and arbitrary cavity modes is presented.     

Multi-color XUV interferometry using high-order harmonics

We present a novel interferometric setup operating in the XUV spectral range. The interferometer consists of a combination of a double pinhole (similar to Young’s double slit) and a transmission grating. In the case of a light source consisting of discrete spectral lines, it allows recording interferograms for multi-colors simultaneously. We present two experiments in which high-order harmonics generated by a titanium sapphire laser were used as the light source for the interferometer. First, the temporal coherence lengths of the single harmonics were determined, and second, the index of refraction and the absorption of a thin beryllium foil were measured simultaneously in the range of 17–25 nm.     

Intracavity phase interferometry: frequency combs sensor inside a laser cavity

In traditional interferometric measurements, a physical quantity that changes the phase of a resonator is monitored through a change of its transmission. Interferometry inside a laser exploits the ultimate Q‐factor of that resonator, and converts the phase to be measured into a frequency. A mode‐locked laser with two intracavity pulses emits two frequency combs of the same repetition rate. The quantity to be measured (a sub‐nano displacement, a nonlinear index, an acceleration or rotation, a magnetic or electric field) produces a minute phase change ( rad) in one of the two intracavity pulses, which is converted into a frequency, measured by beating the two pulse trains emitted by the laser. This paper presents methods of operating mode‐locked lasers in which two independent pulses circulate, producing two frequency combs of the same repetition rate. Various examples of physical quantities that can be measured through this technique are presented.     

Needle-based refractive index measurement using low-coherence interferometry

We present a novel needle-based device for the measurement of refractive index and scattering using low-coherence interferometry. Coupled to the sample arm of an optical coherence tomography system, the device detects the scattering response of, and optical path length through, a sample residing in a fixed-width channel. We report use of the device to make near-infrared measurements of tissues and materials with known optical properties. The device could be used to exploit the refractive index variations of tissue for medical and biological diagnostics accessible by needle insertion.     

New relativistic gravitational effects using charged-particle interferometry

A new class of gravitational effects, in the quantum interference of charged particles, are studied in electron interferometry and superconducting Josephson interferometry. These include phase shifts due to the gravitationally induced Schiff-Barnhill field, rotationally induced London moment, and the modification of the Aharonov-Bohm type of phase shifts, due to the general relativistic coupling of the electromagnetic field to the gravitational field. These effects are interesting, even from a purely theoretical point of view, because they involve an elegant interplay between gravitation, electromagnetism, and quantum mechanics. But new predictions are also made which, if confirmed, would provide the first observation of relativistic gravitational effects, involving the electric charge, at the quantum mechanical level. The possibility of using these effects to detect gravitational waves is also discussed.This essay received the first award from the Gravity Research Foundation for the year 1983-Ed.     

Fiber-modes and fiber-anisotropy characterization using low-coherence interferometry

An optical low-coherence interferometry technique has been used to simultaneously resolve the mode profile and to measure the intermodal dispersion of guided modes of a few-mode fiber. Measurements are performed using short samples of fiber (about 50 cm). There is no need for a complex mode-conversion technique to reach a high interference visibility. Four LP mode groups of the few-mode fiber are resolved. Experimental results and numerical simulations show that the ellipticity of the fiber core leads to a distinct splitting of the degenerate high-order modes in group index. For the first time, to the best of our knowledge, it has been demonstrated that degenerate LP11 modes are much more sensitive to core shape variations than the fundamental modes and that intermodal dispersion of high-order degenerate modes can be used for characterizing the anisotropy of an optical waveguide.     

Label-free biomolecular imaging using scanning spectral interferometry

This letter presents a label-free biomolecular imaging technique based on white-light interferometry and spectral detection. The method measures thickness changes caused by specific binding between biomolecules to detect the presence of certain analyte. A spectrum-shifting algorithm is developed to resolve the thickness information from the spectrum. The axial resolution of the experimental instrument can reach ~1 nm, thereby enabling detection of trace amounts （-1 ng/mm2） of proteins or DNA. This letter also presents two experiments to prove the feasibility of the method for detecting proteins and DNA without fluorescent labeling.     

Electronic speckle pattern interferometry using optical fibers

Initial experiments using electronic speckle pattern interferometry with fiberoptic imaging and illumination are described.     

一种利用合成波长法实现的纳米测量方法

本文提出了一种利用合成波长法实现的纳米测量方案。在文中分析了多波长干涉术用于小尺寸测量的基本原理 ,提出了共光路的设计结构。其特点是能够将测量镜的纳米量级被测位移放大到参考镜的亚毫米量级位移 ,从而能够利用相对低精度的测量手段完成测量 ,共光路的设计使系统对外界的扰动有较好的抑制能力。文章还给出了简单的验证实验     

Angle of arrival estimation using spectral interferometry

We have developed a correlative signal processing concept based on a Mach-Zehnder interferometer and spatial-spectral (S2) materials that enables direct mapping of RF spectral phase as well as power spectral recording. This configuration can be used for precise frequency resolved time delay estimation between signals received by a phased antenna array system that in turn could be utilized to estimate the angle of arrival. We present an analytical theoretical model and a proof-of-principle demonstration of the concept of time difference of arrival estimation with a cryogenically cooled Tm:YAG crystal that operates on microwave signals modulated onto a stabilized optical carrier at 793 nm.