Showing papers on "Interferometry published in 2008"

Realization of spin-wave logic gates

Abstract: We demonstrate the functionality of spin-wave logic exclusive-not-OR and not-AND gates based on a Mach-Zehnder-type interferometer which has arms implemented as sections of ferrite film spin-wave waveguides. Logical input signals are applied to the gates by varying either the phase or the amplitude of the spin waves in the interferometer arms. This phase or amplitude variation is produced by Oersted fields of dc current pulses through conductors placed on the surface of the magnetic films.

Measuring nanomechanical motion with a microwave cavity interferometer

Abstract: Measurements of the position of a nanoscale beam using a microwave cavity detector represents a promising step towards being able to measure displacements at the quantum limit.

Temperature-insensitive miniaturized fiber inline Fabry-Perot interferometer for highly sensitive refractive index measurement

Abstract: We report a miniaturized fiber inline Fabry-Perot interferometer (FPI), with an open micro-notch cavity fabricated by one-step fs laser micromachining, for highly sensitive refractive index measurement. The device was tested for measurement of the refractive indices of various liquids including isopropanol, acetone and methanol at room temperature, as well as the temperature-dependent refractive index of deionized water from 3 to 90 degrees C. The sensitivity for measurement of refractive index change of water was 1163 nm/RIU at the wavelength of 1550 nm. The temperature cross-sensitivity of the device was about 1.1x10(-6) RIU/degrees C. The small size, all-fiber structure, small temperature dependence, linear response and high sensitivity, make the device attractive for chemical and biological sensing.

Non-scanning motionless fluorescence three-dimensional holographic microscopy

Abstract: Holography is an attractive imaging technique as it offers the ability to view a complete three-dimensional volume from one image. However, holography is not widely applied to the field of three-dimensional fluorescence microscopic imaging, because fluorescence is incoherent and creating holograms requires a coherent interferometer system. Although scanning one beam of an interferometer pattern across the rear aperture of an objective to excite fluorescence in a specimen overcomes the coherence limitation, the mechanical scanning is complicated, which makes the image capturing slow, and the process is limited to low-numerical-aperture objectives. Here we present the first demonstration of a motionless microscopy system (FINCHSCOPE) based on Fresnel incoherent correlation holography, and its use in recording high-resolution three-dimensional fluorescent images of biological specimens. By using high-numerical-aperture objectives, a spatial light modulator, a CCD camera and some simple filters, FINCHSCOPE enables the acquisition of three-dimensional microscopic images without the need for scanning. Demonstration of an imaging system that can capture high-resolution 3D fluorescent images of biological speciments without the need for any moving parts.

Miniature fiber-optic high temperature sensor based on a hybrid structured Fabry-Perot interferometer

Abstract: A miniature Fabry-Perot (FP) interferometric fiber-optic sensor suitable for high-temperature sensing is proposed and demonstrated. The sensor head consists of two FP cavities formed by fusion splicing a short hollow-core fiber and a piece of single-mode fiber at a photonic crystal fiber in series. The reflection spectra of an implemented sensor are measured at several temperatures and analyzed in the spatial frequency domain. The experiment shows that the thermal-optic effect of the cavity material is much more appreciable than its thermal expansion. The temperature measurements up to 1000 degrees C with a step of 50 degrees C confirm that it could be applicable as a high-temperature sensor.

Refractive Index Sensing With Mach–Zehnder Interferometer Based on Concatenating Two Single-Mode Fiber Tapers

Abstract: A novel refractive index (RI) sensor based on a fiber Mach-Zehnder interferometer was realized by concatenating two single-mode fiber tapers separated by a middle section. The proposed device had a minimum insertion loss of 3 dB and maximum interferometric extinction ratio over 20 dB. The resolution (0.171 nm) of the two-taper sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of similar structures made from an identical long-period gratings pair, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.

Magneto-optical isolator with silicon waveguides fabricated by direct bonding

Abstract: A magneto-optical isolator is demonstrated for use with a Si waveguide. The isolator is based on a Mach–Zehnder interferometer employing a nonreciprocal phase shift and is fabricated by bonding a magneto-optic garnet CeY2Fe5O12 (Ce:YIG) directly onto the Si waveguide. The surface-activated bonding is based on oxygen-plasma exposure in a high-vacuum chamber. The nonreciprocal phase shift is observed by applying an external magnetic field. An isolation ratio of 21dB is obtained at a wavelength of 1559nm.

A quantum-enhanced prototype gravitational-wave detector

Abstract: The quantum nature of the electromagnetic field imposes a fundamental limit on the sensitivity of optical precision measurements such as spectroscopy, microscopy and interferometry. The so-called quantum limit is set by the zero-point fluctuations of the electromagnetic field, which constrain the precision with which optical signals can be measured. In the world of precision measurement, laser-interferometric gravitational-wave detectors, are the most sensitive position meters ever operated, capable of measuring distance changes of the order of 10- 18 m r.m.s. over kilometre separations caused by gravitational waves from astronomical sources. The sensitivity of currently operational and future gravitational-wave detectors is limited by quantum optical noise. Here, we demonstrate a 44% improvement in displacement sensitivity of a prototype gravitational-wave detector with suspended quasi-free mirrors at frequencies where the sensitivity is shot-noise-limited, by injecting a squeezed state of light. This demonstration is a critical step towards implementation of squeezing-enhancement in large-scale gravitational-wave detectors.

Refractive index sensor based on an abrupt taper Michelson interferometer in a single-mode fiber

Abstract: A simple refractive index sensor based on a Michelson interferometer in a single-mode fiber is constructed and demonstrated. The sensor consists of a single symmetrically abrupt taper region in a short piece of single-mode fiber that is terminated by ~500 nm thick gold coating. The sensitivity of the new sensor is similar to that of a long-period-grating-type sensor, and its ease of fabrication offers a low-cost alternative to current sensing applications.

Pressure sensor realized with polarization-maintaining photonic crystal fiber-based Sagnac interferometer.

Abstract: A novel intrinsic fiber optic pressure sensor realized with a polarization-maintaining photonic crystal fiber (PM-PCF) based Sagnac interferometer is proposed and demonstrated experimentally. A large wavelength-pressure coefficient of 3.42 nm/MPa was measured using a 58.4 cm long PM-PCF as the sensing element. Owing to the inherently low bending loss and thermal dependence of the PM-PCF, the proposed pressure sensor is very compact and exhibits low temperature sensitivity.

Conceptual design of spin wave logic gates based on a Mach–Zehnder-type spin wave interferometer for universal logic functions

Abstract: We present conceptual designs of an emerging class of logic gates, including NOT, NOR, and NAND, that use traveling spin waves (SWs) in the gigahertz range and that are based on a Mach–Zehnder-type SW (MZSW) interferometer. In this MZSW interferometer, logical input and output signals are achievable by the application of currents in order to control the phases that are accumulated by propagating SWs and by either destructive or constructive SW interference, respectively. In this article, the operation mechanism underlying a NOT gate function using a single MZSW interferometer is described and demonstrated numerically. The MZSW interferometer can itself become a NOT gate and be combined in its parallel and serial configurations to form NAND and NOR gates, respectively, which represent emerging classes of universal logic functions for microwave information signal processing.

On the Exploitation of Target Statistics for SAR Interferometry Applications

Abstract: This paper focuses on multiimage synthetic aperture radar interferometry (InSAR) in the presence of distributed scatterers, paying particular attention to the role of target decorrelation in the estimation process. This phenomenon is accounted for by splitting the analysis into two steps. In the first step, we estimate the interferometric phases from the data, whereas in the second step, we use these phases to retrieve the physical parameters of interest, such as line-of-sight (LOS) displacement and residual topography. In both steps, we make the hypothesis that target statistics are at least approximately known. This approach is suited both to derive the performances of InSAR with different decorrelation models and for providing an actual estimate of LOS motion and topography. Results achieved from Monte Carlo simulations and a set of repeated pass ENVISAT images are shown.

Limits to the sensitivity of a low noise compact atomic gravimeter

Abstract: A detailed analysis of the most relevant sources of phase noise in an atomic interferometer is carried out, both theoretically and experimentally. Even a short interrogation time of 100 ms allows our cold atom gravimeter to reach an excellent short term sensitivity to acceleration of 1.4×10-8g at 1 s. This result relies on the combination of a low phase noise laser system, efficient detection scheme and good shielding from vibrations. In particular, we describe a simple and robust technique of vibration compensation, which is based on correcting the interferometer signal by using the ac acceleration signal measured by a low noise seismometer.

Miniaturized fiber inline Fabry-Perot interferometer fabricated with a femtosecond laser.

Abstract: We report a miniaturized inline Fabry-Perot interferometer directly fabricated on a single-mode optical fiber with a femtosecond laser. The device had a loss of 16 dB and an interference visibility exceeding 14 dB. The device was tested and survived in high temperatures up to 1100°C. With an accessible cavity and all-glass structure, the new device is attractive for sensing applications in high-temperature harsh environments.

Single-Mode Fiber Refractive Index Sensor Based on Core-Offset Attenuators

Abstract: Mach-Zehnder and Michelson interferometers using core-offset attenuators were demonstrated. As the relative offset direction of the two attenuators in the Mach-Zehnder interferometer can significantly affect the extinction ratio of the interference pattern, single core-offset attenuator-based sensors appear more robust and repeatable. A novel fiber Michelson interferometer refractive index (RI) sensor was subsequently realized by a single core-offset attenuator and a layer of ~ 500-nm gold coating. The device had a minimum insertion loss of 0.01 dB and maximum extinction ratio over 9 dB. The sensitivity (0.333 nm) of the new sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of an identical long period gratings pair Mach-Zehnder interferometric sensor, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.

Parallel two-step phase-shifting digital holography

Abstract: We propose a parallel two-step phase-shifting digital holography technique capable of instantaneous measurement of three-dimensional objects, with a view toward measurement of dynamically moving objects. The technique is based on phase-shifting interferometry. The proposed technique carries out the two-step phase-shifting method at one time and can be optically implemented by using a phase-shifting array device located in the reference beam. The array device has a periodic two-step phase distribution, and its configuration is simplified compared with that required for three-step and four-step parallel phase-shifting digital holographies. Therefore the optical system of the proposed technique is more suitable for the realization of a parallel phase-shifting digital holography system. We conduct both a numerical simulation and a preliminary experiment in the proposed technique. The results of the simulation and the experiment agree well with those of sequential phase-shifting digital holography, and results are superior to those obtained by conventional digital holography using the Fresnel transform alone. Thus the effectiveness of the proposed technique is verified.

Limits to the sensitivity of a low noise compact atomic gravimeter

Abstract: A detailed analysis of the most relevant sources of phase noise in an atomic interferometer is carried out, both theoretically and experimentally. Even a short interrogation time of 100 ms allows our cold atom gravimeter to reach an excellent short term sensitivity to acceleration of $1.4\times 10^{-8}$g at 1s. This result relies on the combination of a low phase noise laser system, efficient detection scheme and good shielding from vibrations. In particular, we describe a simple and robust technique of vibration compensation, which is based on correcting the interferometer signal by using the AC acceleration signal measured by a low noise seismometer.

Interferometry by deconvolution: Part 1 — Theory for acoustic waves and numerical examples

Abstract: Interferometry allows for synthesis of data recorded at any two receivers into waves that propagate between these receivers as if one of them behaves as a source. This is accomplished typically by crosscorrelations. Based on perturbation theory and representation theorems, we show that interferometry also can be done by deconvolutions for arbitrary media and multidimensional experiments. This is important for interferometry applications in which (1) excitation is a complicated source-time function and/or (2) when wavefield separation methods are used along with interferometry to retrieve specific arrivals. Unlike using crosscorrelations, this method yields only causal scattered waves that propagate between the receivers. We offer a physical interpretation of deconvolution interferometry based on scattering theory. Here we show that deconvolution interferometry in acoustic media imposes an extra boundary condition, which we refer to as the free-point or clamped-point boundary condition, depending on the measured field quantity. This boundary condition generates so-called free-point scattering interactions, which are described in detail. The extra boundary condition and its associated artifacts can be circumvented by separating the reference waves from scattered wavefields prior to interferometry. Three wavefield-separation methods that can be used in interferometry are direct-wave interferometry, dual-field interferometry, and shot-domain separation. Each has different objectives and requirements.

Measurement of the Sensitivity Function in a Time-Domain Atomic Interferometer

Abstract: We present here an analysis of the sensitivity of a time-domain atomic interferometer to the phase noise of the lasers used to manipulate the atomic wave packets. The sensitivity function is calculated in the case of a three-pulse Mach-Zehnder interferometer, which is the configuration of the two inertial sensors we are building at the Laboratoire National de Metrologie et d'Essais-Systeme de References Temps-Espace. We successfully compare this calculation to experimental measurements. The sensitivity of the interferometer is limited by the phase noise of the lasers as well as by residual vibrations. We evaluate the performance that could be obtained with state-of-the-art quartz oscillators, as well as the impact of the residual phase noise of the phase-locked loop. Requirements on the level of vibrations are derived from the same formalism.

Direct measurement of the coherence length of edge states in the integer quantum Hall regime.

Abstract: We have determined the finite temperature coherence length of edge states in the integer quantum Hall effect regime. This was realized by measuring the visibility of electronic Mach-Zehnder interferometers of different sizes, at filling factor 2. The visibility shows an exponential decay with the temperature. The characteristic temperature scale is found inversely proportional to the length of the interferometer arm, allowing one to define a coherence length l_(phi). The variations of l_(phi) with magnetic field are the same for all samples, with a maximum located at the upper end of the quantum Hall plateau. Our results provide the first accurate determination of l_(phi) in the quantum Hall regime.

Spiral-path high-sensitivity silicon photonic wire molecular sensor with temperature-independent response

Abstract: We demonstrate a new silicon photonic wire waveguide evanescent field (PWEF) sensor that exploits the strong evanescent field of the transverse magnetic mode of this high-index-contrast, submicrometer-dimension waveguide. High sensitivity is achieved by using a 2 mm long double-spiral waveguide structure that fits within a compact circular area of 150 μm diameter, facilitating compatibility with commercial spotting apparatus and the fabrication of densely spaced sensor arrays. By incorporating the PWEF sensor element into a balanced waveguide Mach-Zehnder interferometer circuit, a minimum detectable mass of ~10 fg of streptavidin protein is demonstrated with near temperature-independent response.

Phase retrieval using multiple illumination wavelengths.

Abstract: An iterative phase retrieval method is proposed, which uses a sequence of diffraction intensity patterns recorded at different wavelengths. This method has a rapid convergence, and a high immunity to noise and environmental disturbance. The wrap-free phase measurement range is also extended based on the principle of two-wavelength interferometry. Simulation and experimental results are presented to demonstrate the approach.

Seismic and electromagnetic controlled-source interferometry in dissipative media

Abstract: Seismic interferometry deals with the generation of new seismic responses by crosscorrelating existing ones. One of the main assumptions underlying most interferometry methods is that the medium is lossless. We develop an ‘interferometry‐by‐deconvolution’ approach which circumvents this assumption. The proposed method applies not only to seismic waves, but to any type of diffusion and/or wave field in a dissipative medium. This opens the way to applying interferometry to controlled‐source electromagnetic (CSEM) data. Interferometry‐by‐deconvolution replaces the overburden by a homogeneous half space, thereby solving the shallow sea problem for CSEM applications. We demonstrate this at the hand of numerically modeled CSEM data.

Atom interferometry with a weakly interacting Bose-Einstein condensate.

Abstract: We demonstrate the operation of an atom interferometer based on a weakly interacting Bose-Einstein condensate. We strongly reduce the interaction induced decoherence that usually limits interferometers based on trapped condensates by tuning the $s$-wave scattering length almost to zero via a magnetic Feshbach resonance. We employ a $^{39}\mathrm{K}$ condensate trapped in an optical lattice, where Bloch oscillations are forced by gravity. The fine-tuning of the scattering length down to $0.1\text{ }\text{ }{a}_{0}$ and the micrometric sizes of the atomic sample make our system a very promising candidate for measuring forces with high spatial resolution. Our technique can be in principle extended to other measurement schemes opening new possibilities in the field of trapped atom interferometry.

High-accuracy absolute distance measurement using frequency comb referenced multiwavelength source.

Abstract: We propose a new approach to multiple-wavelength interferometry, targeted to high bandwidth absolute distance measurement, with nanometer accuracy over long distances. Two cw lasers are stabilized over a wide range of frequency intervals defined by an optical frequency comb, thus offering an unprecedented large choice of synthetic wavelengths. By applying a superheterodyne detection technique, we demonstrated experimentally an accuracy of 8 nm over 800 mm for target velocities up to 50 mm/s.

Near-field imaging of optical antenna modes in the mid-infrared.

Abstract: Optical antennas can enhance the coupling between free-space propagating light and the localized excitation of nanoscopic light emitters or receivers, thus forming the basis of many nanophotonic applications. Their functionality relies on an understanding of the relationship between the geometric parameters and the resulting near-field antenna modes. Using scattering-type scanning near-field optical microscopy (s-SNOM) with interferometric homodyne detection, we investigate the resonances of linear Au wire antennas designed for the mid-IR by probing specific vector near-field components. A simple effective wavelength scaling is observed for single wires with λeff=λ/(2.0± 0.2), specific to the geometric and material parameters used. The disruption of the coherent current oscillation by introducing a gap gives rise to an effective multipolar mode for the two near-field coupled segments. Using antenna theory and numerical electrodynamics simulations two distinct coupling regimes are considered that scale with gap width or reactive near-field decay length, respectively. The results emphasize the distinct antenna behavior at optical frequencies compared to impedance matched radio frequency (RF) antennas and provide experimental confirmation of theoretically predicted scaling laws at optical frequencies.

Interference without an interferometer: a different approach to measuring, compressing, and shaping ultrashort laser pulses

Abstract: The inherent brevity of ultrashort laser pulses prevents a direct measurement of their electric field as a function of time; therefore different approaches based on autocorrelation have been used to characterize them. We present a discussion, guided by experimental studies, regarding accurate measurement, compression, and shaping of ultrashort laser pulses without autocorrelation or interferometry. Our approach based on phase shaping, multiphoton intrapulse interference phase scan, provides a direct measurement of the spectral phase. Illustrations of this method include new results demonstrating wavelength independence, compatibility with sub-5fs pulses, and a perfect match for experimental coherent control and biomedical imaging applications.

Characterization of Fabry-Perot interferometers and multi-etalon transmission profiles - The IBIS instrumental profile

Abstract: Aims. Properly characterizing Fabry-Perot interferometers (FPI) is essential for determining their effective properties and evaluating the performance of the astronomical instruments in which they are employed. Furthermore, in two-dimensional spectrographs where multiple FPI are used in series, the actual distribution of plate separation errors will be crucial for determining the resulting transmission profiles. We describe techniques that address these issues utilizing the FPI of IBIS, a solar bidimensional spectrometer installed at the Dunn Solar Telescope. Methods. A frequency-stabilized He-Ne laser was used in three different optical layouts to measure the spatially-resolved transmission of the FPI. Analyzing the shape and wavelength shift of the observed profiles allows the characteristics of the cavity errors and the interferometer coating to be determined. Results. We have measured the spatial distribution of the large-scale plate defects, which shows a steep radial trend, as well as the magnitude of the small-scale microroughness. We also extracted the effective reflectivity and absorption of the coating at the laser line wavelength for both interferometers. Conclusions. These techniques, which are generally applicable to any Fabry-Perot interferometer, provide the necessary information for calculating the overall instrumental profile for any illuminated area of the interferometer plates. Accurate knowledge of the spectral transmission profile is important, in particular when using inversion techniques or in comparing observations with simulated data.

Fourier Transform White-Light Interferometry for the Measurement of Fiber-Optic Extrinsic Fabry–PÉrot Interferometric Sensors

Abstract: A Fourier transform white-light interferometry for the absolute measurement of fiber-optic extrinsic Fabry-Perot interferometric sensors is presented The continuous test shows the variation is plusmn03 mum when measuring a cavity length of 2300 mum By combining with an average calculation, the variation of the measured results is only plusmn10 nm