We propose a weak feedback effect based fiber laser sensor demodulated by a phase generated carrier (PGC) scheme.
The weak feedback, realized by an optical fiber pigtail with a fiber end-face, couples a small part of light back to the
fiber laser cavity to realize the light intensity modulation of the fiber laser. The sensor system based on the PGC
demodulation scheme avoided the signal fading, caused by out of quadrature, and realizes the reliable vibration
We proposed a novel intensity modulation based composite cavity optical fiber laser (CCFL) sensor, which is
suitable for the vibration measurement. The intensity modulation of the CCFL is caused by the modulation of the
weak feedback of the CCFL. The weak feedback of the CCFL is based on the end face reflection and the Rayleigh
scattering of optical fiber. An acoustic measurement of the CCFL sensor in anechoic water pool is demonstrated to
prove that the simple sensing scheme is feasible.
We proposed a novel optical fiber hydrophone based on the feedback effect of a composite cavity optical fiber laser
(CCFL) and a corresponding intensity demodulation scheme. The feedback of the CCFL is introduced by the end face
reflection of the single mode optical fiber. The intensity modulation of the CCFL is caused by the modulation of the
DFB Fiber laser based sensors, including strain sensing, temperature sensing and acoustic sensing, have attached a lot
interests because of high performance and small size.We demonstrate a simple DFB fiber laser hydrophone and its
demodulation is realized by a simple intensity based scheme. The reasons of the intensity modulation of DFB fiber laser,
including gain demodulation, feedback effect, and polarization demodulation, are discussed in detail based on rate
equations. The frequency response of the DFB fiber laser based hydrophone is measured in an anechoic water pool and
compared with a referenced B&K8104 hydrophone.
We investigate an ultra-weak feedback effect of DBR fiber lasers based on the steady-state rate equations. The
ultra-weak-feedback effects of DBR fiber lasers are introduced by the fiber Rayleigh scattering and the scattering of the
fiber splicing point. The output powers of the DBR fiber lasers are modulated when their feedbacks are modulated. A
simple vibration sensing scheme based on this effect is proposed and demonstrated. The optimized design of the sensing
scheme is discussed at last.
Resolution of continuous-wave (CW) terahertz scanning image is limited by many factors among which the aperture effect of finite focus diameter is very important. We have investigated the factors that affect terahertz (THz) image resolution in details through theory analysis and simulation. On the other hand, in order to enhance THz image resolution, Richardson-Lucy algorithm has been introduced as a promising approach to improve image details. By analyzing the imaging theory, it is proposed that intensity distribution function of actual THz laser focal spot can be approximatively used as point spread function (PSF) in the restoration algorithm. The focal spot image could be obtained by applying the pyroelectric camera, and mean filtering result of the focal spot image is used as the PSF. Simulation and experiment show that the algorithm implemented is comparatively effective.
Parametric edge detector has been reported to be successfully applied in actual coherent ladar intensity images corrupted
by speckle. But there are isolated erroneous test points in the image processed by parametric test detector. By
morphological filter, most isolated missing pixels in edge image background can be removed. Thus, the error of the edge
detection can decrease exceedingly which is useful for subsequent image processing. Edge detection plays an important
role in ladar image processing. Its capability has direct influence on precision and performance of ladar imaging system.
Therefore it is necessary to evaluate the performance of a detector. In order to demonstrate the advantages of
morphological filter based on parametric edge detection, the probability that an image pixel may be marked as an edge
by this detector is calculated. This detector is applied to detect a large number of images degraded by speckle with
different patterns and different carrier-noise-ratio. From the simulation results, the performance of morphological filter
based on parametric edge detection is described.
In Terahertz continuous-wave laser scanning imaging system, the laser output power's fluctuation and the aperture
effects of a finite focus diameter have significant influence on the image quality, which reduces the image resolution and
causes the imaging noise. The most common problem of image denoising is that some interesting structures in the image
will be removed from the concerned image during noise suppression. Because Markov random field (MRF) can be used
to describe the spatial continuity, the structures of images can be modeled if a proper neighborhood system is selected.
Therefore, MRF and simulated annealing are used to suppress the image noise and increase the image resolution.
Simulation and experiment show that the method can preserve the object structures of THz images.
In the paper, the two-dimensional THz imaging methods are described. The SIFIR-50 FPL Far-Infrared Laser is used as
the THz source. The output frequency is 2.5THz in the experiment, because the THz laser operates steadily at this
frequency. The P4-42 detector works at room temperature and offers relatively high sensitivity. The software of THz
imaging system is self-designed, and it plays a crucial role in this imaging system because it controls nearly all the
operations of this system, including the two-dimensional scanning, image data collection, image data storage, image
display and image processing. Utilizing this setup, THz transmission images of concealed objects are obtained. In the
experiment, a bottle cap and a plastic board covered by reflective materials are chosen as the imaging objects; paper and
Teflon are placed before the object to test the transmission imaging effect. The experimental results show that this
imaging system can generate clear images.
Terahertz radiation has high penetration capability and will not cause harmful ionization to human beings; therefore THz
reflection imaging has wide application prospect in security inspection and counter-terrorism. However the reflection
signal in THz active imaging is weak and the sensitivity of existing detectors in this wave band is low. In this paper the
2.52-THz laser reflection imaging system based on scanning imaging is constructed. The FIR laser of SIFIR-50FPL
made by Coherent Inc in America is chosen as the THz radiation source and its power is about 30mW. The detector of
P4-42 made by the Molectron Corporation is adopted, which works at the room temperature with the spectral range from
1nm to over 1mm. The imaging experiments on knives and some other objects are made utilizing this system. The
images of concealed objects are obtained and the images are clearer after image preprocessing. The experimental results
show that this imaging system has wide application potential in security inspection.
Laser radar could obtain the intensity image and range image synchronously, and the target is easily distinguished because of different range values, so the "Ladar" has abroad applications. However, in the range image proceeding, the target is always disturbed to illegible by speckle and random noise, how to retrain the noise as well as keep the image information becomes the crucial problem. This paper is based on the three filter methods: histogram, median, multiple level median, the methods are all based on the theory that the probability of range anomaly is far less than that of no anomaly, using the theory of stat sequence filter, could restrain the speckle and random noise very efficiency. The three methods have the different effect on the noise restraining and keeping edge from each other. To choose the methods, the contrast of each other method is made and the contrast and the characteristic have been got, the simulated result is obtained. This paper draws the conclusion that the histogram method has the best synthetically effect of the three methods, especially in the keeping edge. In the last, the filter methods are combined together to filter the raw image in different order and is found that the different order will make the effect different on the image; the reason is that the different order makes the initialization diverse for the filter methods. The result was showed in the end of the paper, while discussing the reason of the effect of the order.
Laser radar can simultaneously produce the intensity and range images, and the space resolution is high, so the
recognition performance is well, and it can choose the aim point of target. Laser radar is applied to many fields, such as
guidance, navigation, and becomes the research hot point in recent years. In the vertical detection of laser radar, the
algorithm is required not only solving in-plane rotation-invariant problem, also the distortion-invariant problem, and it
must satisfied the real-time. Correlation algorithm is a parallel processing procedure, detecting many targets at one time,
and its design can be implemented on the high speed digital signal processor. In the paper, a new filter named
CHF-MACH filter is presented, which combine multiple circular harmonic expansions into one filter through MACH
criteria. Because of the filter having the characters of the two filters, it can solve the problems of in-plane
rotation-invariance and distortion-invariance simultaneously, and meet the real-time requirement. The simulated range
image of laser radar is regarded as research target, and computing the PSR (peak to sidelobe ratio) values of correlation
output of the different objects, and plotting the PSR curves of the different angles. Simulating the scene of laser radar
which includes multiple objects, CHF-MACH filter performance is validated through testing with the different angles for
the objects, and the non-training images can obtain the well correlation output.
The target recognition of laser radar is a hot research because laser radar can produce the intensity and range imagery. Laser radar has high space resolution, and can obtain rich target information. Correlation recognition has been used to many fields, such as infrared as well as synthetic aperture radar (SAR). In this paper, the two filters are used in experiment of laser radar. MACH filter is used to detect the target, and DCCFs are used to recognize the unknown target. The samples are generated by OpenGL technology, and the filters are designed using the simulated ladar images. The test samples are added noise according to the imaging principle of laser radar. Two sample sets, one adding noise, another filtering the noise, are used in order to contrast the different performance. At last, the experiment results are given.
This paper describes a display platform of imaging laser radar system. A display platform is developed for imaging laser radar system, as well as the design, compose and software flow of display platform is introduced. We use Visual C++ 6.0 to build it in Windows system, and display the intensity and distance image of the target. Farther, display platform realizes the grayscale transformation of the image, and gets the different pictures with the different grayscale transformation of the same image. Display platform also can select the specific distance value of the target before detecting and save the image data. The soft met the need of laser radar imaging through experiment.
Intensity, range and Doppler images can be obtained by using laser radar. Laser radar can detect much more object information than other detecting sensor, such as passive infrared imaging and synthetic aperture radar (SAR), so it is well suited as the sensor of object recognition. Traditional method of laser radar object recognition is extracting target features, which can be influenced by noise. In this paper, a laser radar recognition method-Support Vector Machine is introduced. Support Vector Machine (SVM) is a new hotspot of recognition research after neural network. It has well performance on digital written and face recognition. Two series experiments about SVM designed for preprocessing and non-preprocessing samples are performed by real laser radar images, and the experiments results are compared.
There has been much interest in the field of laser radar (ladar) owing to its high-resolution three-dimensional imagery. However, the coherent ladar images are affected badly by speckle, which is a multiplicative noise and has the statistical features of the negative exponential density. In the paper, the morphological filter based on the parametric edge detection is introduced in detail. Then, this detector and the ratio edge detector are compared with the conventional LOG (Laplacian of Gaussian) operator and Canny operator. At last, the edge detection results for coherent laser radar image are obtained. The experimental results show that the morphological filter based on parametric edge detection and the ratio edge detector are better than other algorithms for coherent ladar image, and the morphological filter based on the parametric edge detection is the best algorithm in this paper.