Interferometric Applications Research Articles

Postprocessing Phase Stabilizer for Wide Frequency Range Photonic-Microwave Signal Distribution

In the field of leading-edge techniques, such as broadband communications and large-scale radio interferometer applications, the need for a highly stable/wide-frequency-range photonic-microwave signal (continuous sine wave) is increasing. The main purpose of this research is to provide a highly stable photonic-microwave signal over a large broadband from microwave to terahertz frequencies using the same optical signal generation/transmission system. While transmitting signals through an optical cable, the transmission delay fluctuates and it suffers from chromatic dispersion that affects the distribution signal coherence. We have developed a postprocessing scheme transmission phase stabilizer. In the scheme, the measured phase of the round-tripped signal is acquired at time intervals at the optical transmitting port (an optical input port), and then the measured phase data are sent to the destination port (an optical output port) for the transmission phase compensation. The postprocessing method has advantages for a frequency dynamic range and compensation range issue. Theoretically, there is no upper frequency limit on the proposed phase stabilizer. We also discuss a high-frequency signal generator based on an optical comb signal generator up to terahertz frequencies.

A phase-locked laser system based on double direct modulation technique for atom interferometry

We demonstrate a laser system based on phase modulation technology and phase feedback control. The two laser beams with frequency difference of 6.835 GHz are modulated using electro-optic and acousto-optic modulators, respectively. Parasitic frequency components produced by the electro-optic modulator are filtered using a Fabry–Perot Etalon. A straightforward phase feedback system restrains the phase noise induced by environmental perturbations. The phase noise of the laser system stays below −125 rad2/Hz at frequency offset higher than 500 kHz. Overall phase noise of the laser system is evaluated by calculating the contribution of the phase noise to the sensitivity limit of a gravimeter. The results reveal that the sensitivity limited by the phase noise of our laser system is lower than that of a state-of-the-art optical phase-lock loop scheme when a gravimeter operates at short pulse duration, which makes the laser system a promising option for our future application of atom interferometer.

Bandwidth Considerations for Interferometric Applications Based on TanDEM-X

For present and next-generation spaceborne synthetic aperture radar (SAR) missions the use of always larger bandwidths, higher pulse repetition frequencies (PRFs), and multiple acquisition channels is being required. Among the numerous parameters characterizing a SAR system, the specific range and azimuth bandwidth, selected for the SAR image formation, are of primary importance, since they directly affect the quality, the resolution, and the accuracy of the derived products. The purpose of this paper is to investigate their influence with particular focus on interferometric SAR (InSAR) applications. Exploiting the well-known relationships available from SAR theory, the impact of the range and the azimuth bandwidths on the coherence and on the interferometric phase errors is evaluated by means of simulations based on typical TanDEM-X acquisition scenarios. Some examples from real TanDEM-X data are provided as well. The results discussed in this paper can be used as recommendation for those who want to apply for a TanDEM-X science acquisitions proposal, exploiting the high commanding flexibility of the TanDEM-X system, and represent a valuable input for all users dealing with interferometric SAR data and for the design of future InSAR systems in general.

A Review on Monitoring the Everglades Wetlands in the Southern Florida Using Space-based Synthetic Aperture Radar (SAR) Observations

Space-based Synthetic Aperture Radar (SAR) observations have been widely and successfully applied to acquire invaluable temporal and spatial information on wetlands, which are unique environments and regarded as important ecosystems. One of the best studied wetland area is Everglades, which is located in southern Florida, USA. As a World Heritage Site, the Everglades is the largest natural and subtropical wilderness in the United States. The Everglades wetlands have been threatened by anthropogenic activities such as urban expansion and agricultural development, as well as by natural processes, as sea level changes due to climate change. In order to conserve this unique wetland environment, various restoration plans have been implemented. In this review paper, we summarize the main studies using space-based SAR observations for monitoring the Everglades. The paper is composed of the following two sections: (1) review of backscattered amplitude analysis and observations, and (2) review of interferometric SAR (InSAR) analysis and applications. This study also provides an overview of a wetland InSAR technique and space-based SAR sensors. The goal of this review paper is to provide a comprehensive summary of space-based SAR monitoring of wetlands, using the Everglades wetlands as a case study.

On the Phase Calibration by Multisquint Analysis in TOPSAR and Stripmap Interferometry

The availability of accurate trajectory information is paramount for the processing and exploitation of synthetic aperture radar (SAR) data. Considering the particular case of spaceborne SARs designed for repeat-pass interferometric applications, errors in the trajectory translate into phase artifacts that affect the interferometric performance. In this paper, we propose a model-based procedure to calibrate the trajectories of spaceborne SAR systems by the multisquint (MS) phase. The technique allows to estimate the along and the derivative of across track geometric errors. The geometric model of the InSAR phase is derived as a function of positioning errors and the MS phase model as derivative of the InSAR phase geometric model, with respect to the squint angle. We perform a sensitivity analysis of the model in order to define which geometric errors can be estimated by the MS phase, justifying the assumption that the MS phase is very poorly affected by the atmospheric phase screen. We particularly concentrate on the TOPSAR acquisition mode, where the phase is very sensitive to geometric errors. We start from the classical two-image case and then consider the extension to the multibaseline case. Experimental results obtained by processing of interferometric pairs acquired by the Sentinel-1A sensor are reported.

Sentinel-1 SAR Data Revealing Fluvial Morphodynamics in Damghan (Iran): Amplitude and Coherence Change Detection

The Sentinel-1 Satellite (S-1) of ESA's Copernicus Mission delivers freely available C-Band Synthetic Aperture Radar (SAR) data that are suited for interferometric applications (InSAR). The high geometric resolution of less than fifteen meter and the large coverage offered by the Interferometric Wide Swath mode (IW) point to new perspectives on the comprehension and understanding of surface changes, the quantification and monitoring of dynamic processes, especially in arid regions.

Highly birefringent large mode area photonic crystal fiber-based sensor for interferometry applications

In this work, highly birefringent large mode area (LMA) photonic crystal fiber (PCF) structure for interferometric sensor applications is proposed. The effective mode area, birefringence and the sensitivity coefficient of the proposed PCF structure by employing the full vectorial finite element method (FV-FEM) have been thoroughly investigated. The numerical results have shown that proposed structure simultaneously offers high birefringence of order 10[Formula: see text], adequately LMA and high sensitivity for various liquid analytes by employing the elliptical liquid core holes.

Modified Statistically Homogeneous Pixels’ Selection With Multitemporal SAR Images

Statistically homogeneous pixels (SHPs) are considerably significant in many interferometric applications, such as interferometric filtering, distributed scatterer selection, small baseline subset, and SqueeSAR processing. It is very important to achieve SHPs efficiently and accurately. Previous studies on SHPs’ selection are based on spatial restrictions and likelihood ratio test, such as Lee filtering, Kolmogorov–Smirnov test, and Anderson–Darling test. However, these algorithms do not stand up to test for the spatial similarity hypothesis for complex terrains with a few images. To solve the problems, this letter proposes a modified SHPs’ selection algorithm. It utilizes geometric distance and target features for reaching a priori information to help the similarity hypothesis tests. The proposed algorithm has been tested on simulated and real data to prove the improvements in terms of accuracy and computational efficiency.

Viscosity of fused silica and thermal noise from the standard linear solid model

The fluctuation-dissipation theorem states that each source of dissipation yields corresponding fluctuations. The most obvious source of dissipation in liquids is viscosity---internal friction between layers of matter. However, this property also exists in solid materials in a glass state, i.e., an amorphous substance that cannot become a crystal due to high viscosity. Fused silica is a low-loss glass material used in many interferometric applications demanding high stability, such as Fabry-Perot etalons and gravitational-wave detector mirrors and suspensions. Very high viscosity (from $1{0}^{17}$ to $1{0}^{40}\text{ }\mathrm{Pa}\text{ }\mathrm{s}$ in the literature) can be the source of additional noise and can influence the performance of such devices. We show that fused silica may be described with the standard linear solid model of viscoelastisity and present a method to estimate this type of noise.

Stationary and traveling solitons via local dissipation in Bose-Einstein condensates in ring optical lattices

A model of a Bose-Einstein condensate in a ring optical lattice with atomic dissipations applied at a stationary or at a moving location on the ring is presented. The localized dissipation is shown to generate and stabilize both stationary and traveling lattice solitons. Among many localized solutions, we have generated spatially stationary quasiperiodic lattice soltions and a family of traveling lattice solitons with two intensity peaks per potential well with no counterpart in the discrete case. Collisions between traveling and stationary lattice solitons as well as between two traveling lattice solitons display a critical dependence from the lattice depth. Stable counterpropagating solitons in ring lattices can find applications in gyroscope interferometers with ultra-cold gases.

Compressive sensing for interferometric inverse synthetic aperture radar applications

The applicability of interferometric inverse synthetic aperture radar (InISAR) techniques to images reconstructed via compressive sensing (CS)-based algorithms is investigated. Specifically, the three-dimensional (3D) reconstruction algorithm is applied after exploiting CS for data compression and image reconstruction. The InISAR signal model is derived and formalised in a CS framework. A comparison between conventional CS reconstruction and global sparsity constrained reconstruction techniques is performed for different compression rates and different signal-to-noise ratio conditions. Performances on the 2D and 3D reconstructions are evaluated. Results obtained on real data acquired during the NATO-SET 196 trial are shown.

Model for a pulsed terahertz quantum cascade laser under optical feedback.

Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation.

Generation and application of bessel beams in electron microscopy

We report a systematic treatment of the holographic generation of electron Bessel beams, with a view to applications in electron microscopy. We describe in detail the theory underlying hologram patterning, as well as the actual electron-optical configuration used experimentally. We show that by optimizing our nanofabrication recipe, electron Bessel beams can be generated with relative efficiencies reaching 37±3%. We also demonstrate by tuning various hologram parameters that electron Bessel beams can be produced with many visible rings, making them ideal for interferometric applications, or in more highly localized forms with fewer rings, more suitable for imaging. We describe the settings required to tune beam localization in this way, and explore beam and hologram configurations that allow the convergences and topological charges of electron Bessel beams to be controlled. We also characterize the phase structure of the Bessel beams generated with our technique, using a simulation procedure that accounts for imperfections in the hologram manufacturing process.

Measurement of thermal influence on a two-dimensional motion trajectory using a tracking interferometer

Conventional thermal deformation tests in ISO 230-3:2007 only measure the tool displacement when it is positioned at a single point. This paper proposes the application of a tracking interferometer to the evaluation of the thermal influence on two-dimensional motion trajectory. The full multilateration algorithm requires at least four tests repeated at different tracking interferometer positions, when only one tracking interferometer is available. This paper proposes the identification of 2D geometric errors of linear axes by single-setup tests. Since the measurement time is significantly reduced, it can be applied within a thermal test. The uncertainty analysis is also presented.

Temperature dependence of beat-length and confinement loss in an air-core photonic band-gap fiber

The temperature dependence of polarization-maintaining (PM) property and loss in a highly-birefringent air-core photonic band-gap fiber (PBF) is investigated. The effects of temperature variation on the effective index, beat-length and confinement loss are studied numerically by using the full-vector finite element method (FEM). It is found that, the PM property of this PBF is insensitive to the temperature, and the temperature-dependent beat-length coefficient can be as low as 2.86×10−8m/°C, which is typically 200 times less than those of conventional panda fibers, the PBF has a stable confinement loss of 0.01dB/m over the temperature range of −30 to 20°C for the slow axis at the wavelength of 1.55μm. The PBF with ultra-low temperature-dependent PM property and low loss can reduce the thermally induced polarization instability apparently in interferometric applications such as resonant fiber optic gyroscope (RFOG), optical fiber sensors, and so on.

Experimental implementation of phase locking in a nonlinear interferometer

Based upon two cascade four-wave mixing processes in two identical hot rubidium vapor cells, a nonlinear interferometer has been experimentally realized [Jing et al., Appl. Phys. Lett. 99, 011110 (2011); Hudelist et al., Nat. Commun. 5, 3049 (2014)]. It has a higher degree of phase sensitivity than a traditional linear interferometer and has many potential applications in quantum metrology. Phase locking of the nonlinear interferometer is needed before it can find its way into applications. In this letter, we investigate the experimental implementation of phase locking of the relative phase between the three beams at different frequencies involved in such a nonlinear interferometer. We have utilized two different methods, namely, beat note locking and coherent modulation locking. We find that coherent modulation locking can achieve much better phase stability than beat note locking in our system. Our results pave the way for real applications of a nonlinear interferometer in precision measurement and quantum manipulation, for example, phase control in phase-sensitive N-wave mixing process, N-port nonlinear interferometer and quantum-enhanced real-time phase tracking.

Impact study of anisotropic optical fibers winding with different tension value on the H-parameter invariance degree

Subject of Research. We have investigated the effect of anisotropic optical fibers winding with an elliptical sheath subjecting to stress on the H-parameter invariance degree. This type of optical fiber is used in the manufacture of fiber loop in fiber-optic gyroscopes. Method of Research. The method of research is based on the application of Michelson polarization scanning interferometer as a measuring device. Superluminescent diode with a central wavelength of 1575 nm and a half-width of the spectrum equal to 45 nm is used as a radiation source. The studies were carried out with anisotropic optical fiber with 50 m long elliptical sheath subjecting to stress. The fiber was wound with one layer turn to turn on the coil with a diameter of 18 cm, which is used in the design of fiber-optic gyroscope. The tension force of the optical fiber was controlled during winding on a special machine. Main Results. It was found that at the increase of tension force from 0.05 N to 0.8 H the value of H -parameter increases from 7×10-6 1/m up to 178×10-6 1/m, respectively; i.e. the coupling coefficient of orthogonal modes in the test fiber is being increased. Thus, it is necessary to consider the longitudinal tension force of fiber in the design and manufacture of the fiber-optic sensors of high accuracy class: the less the fiber winding power, the higher invariance degree of distributed H -parameter. The longitudinal tension force of anisotropic optical fiber with elliptical sheath subjecting to stress equal to 0.2 N is recommended in the process of designing fiber-optic gyroscopes. Practical Relevance. The proposed method of Michelson scanning interferometer is usable in the production process for quality determination of the optical fiber winding: no local defects, value controlling of fiber H -parameter.

Integrated heterodyne interferometer with on-chip modulators and detectors.

We demonstrate, to our knowledge, the first on-chip heterodyne interferometer fabricated on a 300-mm CMOS compatible process that exhibits root-mean-square (RMS) position noise on the order of 2nm. Measuring 1mm by 6mm, the interferometer is also, to our knowledge, the smallest heterodyne interferometer demonstrated to date and will surely impact numerous interferometric and metrology applications, including displacement measurement, laser Doppler velocimetry and vibrometry, Fourier transform spectroscopy, imaging, and light detection and ranging (LIDAR). Here we present preliminary results that demonstrate the displacement mode.

Scanning balanced-path homodyne I/Q-interferometer scheme and its applications.

The balanced-path scheme of a heterodyne interferometer proposed by Yoon et al. has been applied to the scanning homodyne I/Q-interferometer. This provides an 11-dB improvement on common vibration rejection over the heterodyne scheme and, thereby, allows high sensitivity and high stability phase and amplitude measurements for high-speed scanning interferometer applications. It is shown that our new scanning interferometer scheme is very useful for diagnosing a sample that requires complex analysis. As an example, our new scanning interferometer scheme has been applied for obtaining phase and amplitude images of the protein biochip samples prepared by using the sandwich ELISA. The amplitude images are used for diagnosing homogeneity of the sample, while the phase images are used for measuring the phase difference between samples treated with different concentrations of IL-5.

Ellipse fitting for interferometry. Part 3: dynamic method.

We describe a dynamically based method for fitting an ellipse to noisy data, which has for interferometric applications a number of advantages over conventional static methods (originally developed for image processing). Our method relies on the observation that each data point belongs to an ordered time series and thus has a well-defined phase parameter. We demonstrate that for real experimental data it can achieve much greater accuracy than static methods. The precision of the fit is limited only by the statistical reliability of the data, even in extreme cases such as ellipses with a minor axis smaller than the measurement noise.