Combination Of Interferometer Research Articles

Linear response, multi-order grating interferometry using a reversal shearing imaging system.

Linear response, multi-order grating interferometry is proposed to measure grating displacement. The system, a combination of a reversal shearing interferometer and an imaging system, enables calculating multi-order, integrated intensity signals with a linear waveform response. A theoretical multi-order model for the linear response signal analysis is presented with a Fourier series expansion. The results of the experiment, which prove the validity of the theoretical model, indicate a linear response to displacement with a linearity of 98.7% and a resolution of 10nm. We conclude that the proposed method enables the development of a new class of potent linear response grating interferometry for displacement metrology.

Time-delay interferometry with optical frequency comb

Heterodyne laser phase measurements in a space-based gravitational wave interferometer are degraded by the phase fluctuations of the onboard clocks, resulting in unacceptable sensitivity performance levels of the interferometric data. In order to calibrate out the clock phase noises it has been previously suggested that additional inter-spacecraft phase measurements must be performed by modulating the laser beams. This technique, however, considerably increases system complexity and probability of subsystem failure. With the advent of self-referenced optical frequency combs, it is possible to generate the heterodyne microwave signal that is coherently referenced to the onboard laser. We show in this case that the microwave noise can be cancelled directly by applying modified second-generation Time-Delay Interferometric combinations to the heterodyne phase measurements. This approach avoids use of modulated laser beams as well as the need of additional ultra-stable oscillator clocks.

Analysis of ripple noise in resonant spectrum of SOI micro-ring resonator

Micro-ring resonator has been attracting attentions in studies of filters, modulators, lasers, sensors and other fields owing to the characteristics of highly integrated, low power consumption and high sensitivity. The transmission characteristics of micro-ring resonator directly determine the performance of micro-optical device for its key component of various integrated optical devices. The causes of and influences on resonant spectrum of ripple noise were analyzed by the combination of micro-ring resonator theory and Fabry-Perot Interferometer (FPI). Coupling experiments were designed to obtain and analyze the free spectrum range (FSR) and amplitude of ripple noise. The experimental results show that coupling gratings are the cause of ripple noise, which is well consistent with theoretical analysis. The relationship between etching depth of coupling gratings and ripple amplitude was found and analyzed. The study provides a reference for further optimization of micro-ring resonator and error analysis of micro-ring resonator system.

Group and phase delay sensing for cophasing large optical arrays

The next generation of optical interferometers will provide high-resolution imaging of celestial objects by using either the aperture synthesis technique or the direct imaging principle. To determine the technical requirements, we have developed an interferometric test bench, called SIRIUS. To preserve the quality of the image, fast corrections of the optical path differences within a fraction of a wavelength have to be applied: this is the cophasing of the array, whereas making it coherent aims at stabilizing the optical path differences within a fraction of the coherence length. In the SIRIUS test bench, coherence and cophasing are achieved by fibred delay lines. Air delay lines are also used for the raw delay equalization. We present an original implementation of a piston sensor, called chromatic phase diversity, which is adaptable to any interferometer, whatever the configuration of the entrance pupil and the number of sub-pupils and whatever the interferometric combiner. Our method is based on the dispersed fringes principle and uses a derived version of the dispersed speckles method. The numerical simulation shows the performance of the method in terms of cophasing, accuracy and limiting magnitude. Experimental tests have been carried out both with optical turbulence and without. They show good results in both cases, despite some instrument-related limitations that can be eliminated. We show that our method is able to handle an amplitude of correction of ±11(λ/2) with an accuracy of ∼λ/30 over many minutes.

Carrier-suppressed return-to-zero to non-return-to-zero format conversion based on a single fiber Bragg grating with knife-shaped spectra.

We propose a novel carrier-suppressed return-to-zero (CSRZ) to non-return-to-zero (NRZ) conversion scheme based on a single custom-designed fiber Bragg grating (FBG) with a knife-shaped spectrum. The structure of the FBG is designed and synthesized using a discrete layer-peeling inverse scattering technique. It is shown that such an FBG can replace the combination of interferometer and the cascaded filter that is invariably employed in the reported schemes for CSRZ to NRZ format conversion. Simulation results show that conversion of 40Gbit/s CSRZ into NRZ signals results in a Q factor that is 4.5dB greater than the previously reported schemes.

Pulsed Sagnac polarization-entangled photon source with a PPKTP crystal at telecom wavelength.

We demonstrate pulsed polarization-entangled photons generated from a periodically poled KTiOPO(4) (PPKTP) crystal in a Sagnac interferometer configuration at telecom wavelength. Since the group-velocity-matching (GVM) condition is satisfied, the intrinsic spectral purity of the photons is much higher than in the previous scheme at around 800 nm wavelength. The combination of a Sagnac interferometer and the GVM-PPKTP crystal makes our entangled source compact, stable, highly entangled, spectrally pure and ultra-bright. The photons were detected by two superconducting nanowire single photon detectors (SNSPDs) with detection efficiencies of 70% and 68% at dark counts of less than 1 kcps. We achieved fidelities of 0.981 ± 0.0002 for |ψ(-)〉 and 0.980 ± 0.001 for |ψ(+)〉 respectively. This GVM-PPKTP-Sagnac scheme is directly applicable to quantum communication experiments at telecom wavelength, especially in free space.

RZ-OOK to NRZ-OOK format conversion based on a single fiber Bragg grating

We propose a return-to-zero on-off keying (RZ-OOK) to non-return-to-zero (NRZ) OOK conversion scheme based on a single custom-designed fiber Bragg grating (FBG). The custom-made FBG is designed and syn­thesized using discrete layer-peeling algorithm. It is shown that such a FBG can replace the combination of interferometer and the cascaded filter that are invariably employed together in the reported schemes for ­RZ-OOK to NRZ-OOK format conversion. Simulation results show that the input 20-Gb/s RZ-OOK signals with different duty cycles can be converted into NRZ-OOK signals with high Q-factor.

JOUVENCE OF FLUOR: UPGRADES OF A FIBER BEAM COMBINER AT THE CHARA ARRAY

The FLUOR (Fiber Linked Unit for Optical Recombination) interferometric beam combiner located at the CHARA Array on Mt. Wilson, California has recently undergone a program of major upgrades known as Jouvence of FLUOR (JouFLU). These upgrades seek to improve the precision, use, and observing efficiency of FLUOR as well as introduce new modes of operation. A Fourier Transform Spectrograph (FTS) mode and a spectral dispersion mode have been added to improve calibration and data collection. New mechanized stages and new cameras have been added to FLUOR for alignment and pupil plane imaging. Entirely new control/command software has been written for FLUOR which brings it into compliance with CHARA software standards. This allows for continued software upgrades and full remote operation capability. The new JouFLU instrument is now operating on sky and is expected to achieve accurate interferometric visibility amplitude measurements with 0.1 to 0.3% precision.

THE PLATEAU DE BURE + 30 m ARCSECOND WHIRLPOOL SURVEY REVEALS A THICK DISK OF DIFFUSE MOLECULAR GAS IN THE M51 GALAXY

We present the data of the Plateau de Bure Arcsecond Whirlpool Survey (PAWS), a high spatial and spectral resolution 12CO(1-0) line survey of the inner 10 x 6 kpc of the M51 system, and the first wide-field imaging of molecular gas in a star-forming spiral galaxy with resolution matched to the typical size of Giant Molecular Clouds (40 pc). We describe the observation, reduction, and combination of the Plateau de Bure Interferometer (PdBI) and IRAM-30m "short spacing" data. The final data cube attains 1.1"-resolution over the 270" x 170" field of view, with sensitivity to all spatial scales from the combination of PdBI and IRAM-30m data, and brightness sensitivity of 0.4 K (1 sigma) in each 5 km/s-wide channel map. We find a CO-luminosity of 9.10^8 K km/s pc^2, corresponding to a molecular gas mass of 4.10^9 Msol for a standard CO-to-H2 conversion factor. Unexpectedly, we find that a large fraction, (50 +/- 10)%, of this emission arises mostly from spatial scales larger than 36" or about 1.3 kpc. Through a series of tests, we demonstrate that this extended emission does not result from a processing artifact. We discuss its origin in light of the stellar component, the 12CO/13CO ratio, and the difference between the kinematics and structure of the PdBI-only and hybrid synthesis (PdBI + IRAM-30m) images. The extended emission is consistent with a thick, diffuse disk of molecular gas with a typical scale height of about 200 pc, substructured in unresolved filaments which fills about 0.1% of the volume.

ADAPTIVE SPATIAL FILTERING OF INTERFEROMETRIC DATA STACK ORIENTED TO DISTRIBUTED SCATTERERS

Abstract. Standard interferometry poses a challenge in non-urban areas due to temporal and spatial decorrelation of the radar signal, where there is high signal noise. Techniques such as Small Baseline Subset Algorithm (SBAS) have been proposed to make use of multiple interferometric combinations to alleviate the problem. However, the interferograms used in SBAS are multilooked with a boxcar (rectangle) filter to reduce phase noise, resulting in a loss of resolution and signal superstition from different objects. In this paper, we proposed a modified adaptive spatial filtering algorithm for accurate estimation of interferogram and coherence without resolution loss even in rural areas, to better support the deformation monitoring with time series interferometric synthetic aperture radar (InSAR) technique. The implemented method identifies the statistically homogenous pixels in a neighbourhood based on the goodness-of-fit test, and then applies an adaptive spatial filtering of interferograms. Three statistical tests for the identification of distributed targets will be presented, applied to real data. PALSAR data of the yellow river delta in China is used for demonstrating the effectiveness of this algorithm in rural areas.

Estimating horizontal and vertical movements due to underground mining using ALOS PALSAR

In this paper, the capability of determining the three dimensional (3D) ground displacements due to underground mining using the multiple ALOS PALSAR interferometric pairs acquired with different viewing geometries has been investigated and validated in the area of West Cliff colliery, New South Wales (NSW), Australia. Four ALOS PALSAR interferometric pairs acquired with two different incidence angles from both ascending and descending orbits were used in this study. Three different approaches were used to derive the 3D displacement maps. The first two approaches utilised SAR data only, while the third approach required a one dimensional measurement by using other surveying techniques as inputs. The results were compared with the GPS field survey data obtained between April and May 2008. The obtained results and the GPS data agreed well with each other in the vertical and the east–west directions. However, the precision of displacement measured in the north–south direction was much poorer for the first two approaches compared to the third approach. This was due to two reasons: (1) the lack of viewing geometries, and (2) the poor temporal overlap in the interferometric combination datasets. The results suggested that it is possible to use other one dimensional surveying techniques to assist the InSAR measurements in order to enhance the accuracy of the 3D deformation derived. The horizontal movements in transverse and longitudinal directions were calculated from the 3D deformation results, in order to derive the subsidence parameters that have been caused by mining activities. The subsidence parameters derived matched well with the GPS-derived parameters. The results suggested that an accurate 3D displacement vectors can be derived by combining InSAR-measurement with measurement from other equipment such as extensometer and optical fibre which may carry out measurement in one direction only (ideally north–south direction).

Reliable estimation of orbit errors in spaceborne SAR interferometry

An approach to improve orbital state vectors by orbit error estimates derived from residual phase patterns in synthetic aperture radar interferograms is presented. For individual interferograms, an error representation by two parameters is motivated: the baseline error in cross-range and the rate of change of the baseline error in range. For their estimation, two alternatives are proposed: a least squares approach that requires prior unwrapping and a less reliable gridsearch method handling the wrapped phase. In both cases, reliability is enhanced by mutual control of error estimates in an overdetermined network of linearly dependent interferometric combinations of images. Thus, systematic biases, e.g., due to unwrapping errors, can be detected and iteratively eliminated. Regularising the solution by a minimum-norm condition results in quasi-absolute orbit errors that refer to particular images. For the 31 images of a sample ENVISAT dataset, orbit corrections with a mutual consistency on the millimetre level have been inferred from 163 interferograms. The method itself qualifies by reliability and rigorous geometric modelling of the orbital error signal but does not consider interfering large scale deformation effects. However, a separation may be feasible in a combined processing with persistent scatterer approaches or by temporal filtering of the estimates.

Enhancement of the phase-measurement sensitivity beyond the standard quantum limit by a nonlinear interferometer

A nonlinear interferometer uses nonlinear elements as beam splitters to split and to recombine optical waves for interference. As a result, the interference fringe size has a nonlinear dependence on the intensity of the field for phase sensing and leads to an enhanced phase signal. In this paper, a practical scheme of nonlinear interferometry for precision phase measurement is analyzed with parametric amplifiers as the nonlinear beam splitters. It is found that the signal due to phase shift is enhanced by a factor of the amplification gain as compared to a linear interferometer with the same phase-sensing light intensity while the quantum noise is kept at the vacuum level, thus, effectively increasing the signal-to-noise ratio (SNR) beyond the standard quantum limit. Furthermore, the scheme is not as sensitive to the detection loss as the linear scheme with a squeezed state for noise reduction. However, losses inside the interferometer limit the enhancement factor in SNR. We apply the concept to a Michelson interferometer but with parametric amplifiers involved for gravitational-wave detection. We find that effective power is increased by the gain of the amplifiers without actually increasing the cycling power inside the interferometer. Furthermore, the full benefits with squeezed input and variational output or the combination of a quantum nondemolition interferometer for sensitivity beyond the standard quantum limit apply here with even better results. Such a nonlinear interferometer will find wide applications in precision measurements.

Mass measurement of the astronauts on the International Space Station (ISS) for nutritional control

The most basic parameter of human nutrition is body weight. For a low-earth orbit space flight environment, body mass has to be measured in some way in weightlessness. Medical requirements for the ISS astronauts include monthly body mass measurements. The Russian-built Body Mass Measurement Device (BMMD) is onboard the International Space Station (ISS) for the purpose. NASA has a research device on the ISS. Both are of older designs, and their value of uncertainty is not documented. Both depend on spring constant, but its nature of decay is unknown. The current technology offers other physical principles for precision mass measurements in space. A combination of a laser interferometer, force or accelerometer sensor would make a precision portable mass measurement device, as ground-tested by Fujii, et al. The large cabin size of the ISS is advantageous in improving measurement uncertainty.

Precise Stellar Radial Velocities of an M Dwarf with a Michelson Interferometer and a Medium-Resolution Near-Infrared Spectrograph

ABSTRACTPrecise near-infrared radial velocimetry enables efficient detection and transit verification of low-mass extrasolar planets orbiting M-dwarf hosts, which are faint for visible-wavelength radial velocity surveys. The TripleSpec Exoplanet Discovery Instrument (TEDI) is the combination of a variable-delay Michelson interferometer and a medium-resolution (R = 2700) near-infrared spectrograph on the Palomar 200 inch (5 m) Hale Telescope. We used TEDI to monitor GJ 699, a nearby mid-M dwarf, over 11 nights spread across 3 months. Analysis of 106 independent observations reveals a root-mean-squared precision of less than 37 m s-1 for 5 minutes of integration time. This performance is within a factor of 2 of our expected photon-limited precision. We further decompose the residuals into a 33 m s-1 white noise component and a 15 m s-1 systematic noise component, which we identify as being likely due to contamination by telluric absorption lines. With further development this technique holds promise for broad implementation on medium-resolution near-infrared spectrographs to search for low-mass exoplanets orbiting M dwarfs and to verify low-mass transit candidates.

Clouds at Arctic Atmospheric Observatories. Part I: Occurrence and Macrophysical Properties

Abstract Cloud observations over the past decade from six Arctic atmospheric observatories are investigated to derive estimates of cloud occurrence fraction, vertical distribution, persistence in time, diurnal cycle, and boundary statistics. Each observatory has some combination of cloud lidar, radar, ceilometer, and/or interferometer for identifying and characterizing clouds. By optimally combining measurements from these instruments, it is found that annual cloud occurrence fractions are 58%–83% at the Arctic observatories. There is a clear annual cycle wherein clouds are least frequent in the winter and most frequent in the late summer and autumn. Only in Eureka, Nunavut, Canada, is the annual cycle shifted such that the annual minimum is in the spring with the maximum in the winter. Intersite monthly variability is typically within 10%–15% of the all-site average. Interannual variability at specific sites is less than 13% for any given month and, typically, is less than 3% for annual total cloud fractions. Low-level clouds are most persistent at the observatories. The median cloud persistence for all observatories is 3–5 h; however, 5% of cloud systems at far western Arctic sites are observed to occur for longer than 100 consecutive hours. Weak diurnal variability in cloudiness is observed at some sites, with a daily minimum in cloud occurrence near solar noon for those seasons for which the sun is above the horizon for at least part of the day.

CO( J = 1-0) IMAGING OF M51 WITH CARMA AND THE NOBEYAMA 45 m TELESCOPE

We report the CO(J=1-0) observations of M51 using both the Combined Array for Research in Millimeter Astronomy (CARMA) and the Nobeyama 45m telescope (NRO45). We describe a procedure for the combination of interferometer and single-dish data. In particular, we discuss (1) the joint imaging and deconvolution of heterogeneous data, (2) the weighting scheme based on the root-mean-square (RMS) noise in the maps, (3) the sensitivity and uv-coverage requirements, and (4) the flux recovery of a combined map. We generate visibilities from the single-dish map and calculate the noise of each visibility based on the RMS noise. Our weighting scheme, though it is applied to discrete visibilities in this paper, is applicable to grids in uv-space, and this scheme may advance in future software development. For a realistic amount of observing time, the sensitivities of the NRO45 and CARMA visibility data sets are best matched by using the single dish baselines only up to 4-6 kilo-lambda (about 1/4-1/3 of the dish diameter). The synthesized beam size is determined to conserve the flux between synthesized beam and convolution beam. The superior uv-coverage provided by the combination of CARMA long baseline data with 15 antennas and NRO45 short spacing data results in the high image fidelity, which is evidenced by the excellent overlap between even the faint CO emission and dust lanes in an optical HST image and PAH emission in an Spitzer 8 micron image.

Micro-Brillouin Scattering of Normal and Relaxor Ferroelectrics

The micro-Brillouin scattering spectroscopy (MBSS) has been achieved by the combination of a tandem multipass Fabry-Perot interferometer and an optical microscope to probe the gigahertz to terahertz dynamics focusing on a selected microscopic area or a very small crystal. It gives new insights into the fundamental physics on the variety of vibration, relaxation processes and elementary excitations related to the instability of structural phase transitions, especially ferroic phase transitions. In the mechanism of ferroelectric phase transitions, important problems are still unsolved such as the coexistence/crossover of displacive and order-disorder dynamics, the precursor phenomena of polar regions at nanometer scale, etc. This review highlights the recent progress on the observation and understanding of high frequency dynamics for typical normal and relaxor ferroelectrics.

Laser ranging and communications for LISA

The Laser Interferometer Space Antenna (LISA) will use Time Delay Interferometry (TDI) to suppress the otherwise dominant laser frequency noise. The technique uses sub-sample interpolation of the recorded optical phase measurements to form a family of interferometric combinations immune to frequency noise. This paper reports on the development of a Pseudo-Random Noise laser ranging system used to measure the sub-sample interpolation time shifts required for TDI operation. The system also includes an optical communication capability that meets the 20 kbps LISA requirement. An experimental demonstration of an integrated LISA phase measurement and ranging system achieved a ≈ 0.19 m rms absolute range error with a 0.5Hz signal bandwidth, surpassing the 1 m rms LISA specification. The range measurement is limited by mutual interference between the ranging signals exchanged between spacecraft and the interaction of the ranging code with the phase measurement.

Design and implementation of a non-mechanical scanning F-P type laser warning method

In the laser warning system, a non-mechanical scanning Fabry-Perot (F-P) type laser warning method and its crucial component-laser incident sensor design method are brought out, and the F-P etalon with the interferometric filter combination is adopted. For the incident laser pulse with a certain wavelength, the transmittance difference of the interferometric filters is independent with polarization of incident light, and descends almost linearly as the incident angle gets wider. A laser incident angle sensor experimental platform is built up, and the experiment is carried out with a given laser range finder. As the results indicate, when the incident angle is less than 5°, the transmittance difference measured by the laser angle sensor is significantly lower, and the deviation is more than 10%. While the incident angle is greater than 10°, the deviation is reduced significantly.