Optical fiber pressure gradient sensors possess the merits of no suspension and easy installation compared to the co-vibration vector sensors. Recent studies are focused on the discrete structure made by individual pressure sensing units. Because the sensor is extremely sensitive to the difference between the units, improvements should be made in many areas, such as the manufacturing process, calibration method, and error correction. Benefited by the mature manufacturing process, a vector sensor with directivity larger than 40 dB is obtained. Considering that the measurement uncertainty is up to 0.7 dB in standing wave tube, an optimized calibration method is developed, which can eliminate the relative measurement error. Besides, an enhanced demodulation method is carried out to decrease the fluctuation of phase shift to within ±0.5 dB. 2-D and 3-D sensors are fabricated and tested on the lake and on the sea. Results show that the sensors have achieved good acoustic measurements.
A self-calibration method for camera using two views of unknown-structure planar scene is introduced. The planar scene is common in the environment and can be easily identifiable outside the lab. Firstly, two orientation- and scale-covariant features, which can be provided by the SIFT feature detector, is used to estimate the homography of two views. Then the homography is decomposed into the camera parameters. A RANSAC scheme is adapted to cope with the outliers of SIFT correspondences. Finally, the camera parameters are optimized with a non-linear parameter optimization using the inliers of two views. This method calibrates the camera parameters and recovers the planar scenes simultaneously. Real scene data experiment demonstrates that the proposed method is easy to operate and provides the reliable calibration results for non-expert users.
The phase noise induced by the intensity noise fluctuates in some sensing systems, which could affect the assessment of system performance. In this paper, the phase noise induced by the intensity noise in the phase generated carrier (PGC) detection system is modeled. It manifests that the phase noise level has a trigonometric relation with the initial phase of the interference fringes, namely workpoint-related fluctuation. Besides, the shape of the fluctuation to the workpoint is also a function of the modulation depth. As a result, the measurement for phase noise should iterate over many workpoint sets at a special modulation depth. Whereas the workpoint iteration is not always actually viable, a modified PGC detection scheme that combined the 3×3 coupler multi-phase method is proposed. To average out the three demodulated outputs, the phase noise is theoretically independent of the workpoint, which is also smaller than the traditional value. The tested results show good accordance with the theory. The theoretical model and method in this paper can be used as a guidance of the noise assessment in large-scale multiplexed sensing networks.
In this paper a novel optical fiber interferometer structure for ultra-large dynamic range detection is proposed. The structure combines conventional 3×3 interferometer with optical differential 3×3 interferometer. And the sensing fiber of the conventional interferometer is used as the transmission fiber of the differential interferometer while sensing. When the external signal acts on the sensing fiber, the conventional coherent detection and differential coherent detection can be carried out simultaneously. Conventional interferometer is used to detect the normal phase change of interferometric signals. However differential interferometer can detect the difference of the phase change, that is, the undistorted phase compression signal. Then the actual signal waveform can be obtained by integrating the compressed signal, so that the detection of large signal can be realized. The simulation analysis and experimental results show that the dynamic range of 200dB can be obtained within 20Hz-10kHz band. The structure of combined interferometer uses continuous light injection and has the advantages of simple structure and low cost. It can be used to detect wide-band and ultra-large signal and has good application prospects.
Signal detection stability is very important for vector fiber-optic hydrophone and hydrophone array, because the instability of the demodulated signal directly leads to the target azimuth estimation error and the degradation of system performance. In this paper, a method to achieve high-stability signal demodulation for interferometric vector fiber-optic hydrophone is studied. A parameter estimation and demodulation parameter compensation method for phase generated carrier demodulation system is proposed based on elliptic curve parameter fitting algorithm. An elliptic curve is constructed using the second and third frequency of the reference interference signal. The ellipse curve fitting algorithm is introduced to estimate the distortion parameter of the modulation and demodulation system by fitting the value of each elliptic curve parameter. By compensating the PGC demodulation for the tested signal with the estimated parameters, the instability of demodulation system caused by PGC modulation depth variation and additional modulation intensity of the light source can be effectively reduced. The feasibility of the method is verified by simulation experiments and actual system experiments. High stability signal detection is realized using the proposed method, which can effectively improves the detection effect of the vector fiber-optic hydrophone array.
The conventional electronic accelerometer meets electromagnetic compatibility problem in environments with strong electromagnetic filed. We herein design an all-optical accelerometer to solve this problem. A series of miniature plane spring-mass components were micromachined on silicon wafer by means of lithography and reactive ion etching. These components were served as sensitive structures. The fiber-optic extrinsic Fabry-Perot interferometer is adopted as the sensing structure. Two reflectors, one of which is cleaved fiber end while the other is sensitive structure with Au film, are used to constitute the F-P cavity. The proposed structure did not require high-precision alignment. Therefore, it is easily fabricated. The assembled sensor possesses small volume, which is 5 mm in radical and 12 mm in longitudinal. High-precision interferometric optical phase detection technique is used for signal recovery. The sensitivity of the fabricated sensor is about -11.2 dB re. rad/g with the resonance frequency at 2530 Hz. The equivalent noise acceleration is about 31.2 μg/√Hz. All these experimental results indicated a high-performance accelerometer. The fabricated accelerometer has potentials in large engine testing.
Digital orthogonal receiver is one of the key techniques in digital receiver of soft radar, and compressed sensing is
attracting more and more attention in radar signal processing. In this paper, we propose a CS digital orthogonal
receiver for wideband radar which utilizes compressed sampling in the acquisition of radar raw data. In order
to reconstruct complex signal from sub-sampled raw data, a novel sparse dictionary is proposed to represent the
real-valued radar raw signal sparsely. Using our dictionary and CS algorithm, we can reconstruct the complex-valued
radar signal from sub-sampled echoes. Compared with conventional digital orthogonal radar receiver, the
architecture of receiver in this paper is more simplified and the sampling frequency of ADC is reduced sharply.
At the same time, the range profile can be obtained during the reconstruction, so the matched filtering can
be eliminated in the receiver. Some experiments on ISAR imaging based on simulated data prove that the
phase information of radar echoes is well reserved in our orthogonal receiver and the whole design is effective for
Radar imaging is an ill-posed linear inverse problem and compressed sensing (CS) has been proved to have
tremendous potential in this field. This paper surveys the theory of radar imaging and a conclusion is drawn
that the processing of ISAR imaging can be denoted mathematically as a problem of 2D sparse decomposition.
Based on CS, we propose a novel measuring strategy for ISAR imaging radar and utilize random sub-sampling
in both range and azimuth dimensions, which will reduce the amount of sampling data tremendously. In order
to handle 2D reconstructing problem, the ordinary solution is converting the 2D problem into 1D by Kronecker
product, which will increase the size of dictionary and computational cost sharply. In this paper, we introduce the
2D-SL0 algorithm into the reconstruction of imaging. It is proved that 2D-SL0 can achieve equivalent result as
other 1D reconstructing methods, but the computational complexity and memory usage is reduced significantly.
Moreover, we will state the results of simulating experiments and prove the effectiveness and feasibility of our