2016, 5(5):1-10. DOI: 10.12146/j.issn.2095-3135.201605001
Abstract:The state of polarization (SOP) of optical lightwave in fiber is very sensitive to the external events. Based on this phenomenon, the polarization time domain reflectometer (POTDR) can be used as a distributed sensing means for the detection of fiber pressing, bending, and vibration, etc. However, SOP of optical lightwave at a specific position is dependent to its previous status. That means the first disturbance nearest to the input end is usually fused with subsequent disturbances, which makes the POTDR method difficult to detect multi-disturbances. In this paper, research progress of multi-disturbances detection by POTDR was reviewed. Existing POTDR techniques like analyzing spectrum method, resolving local birefringence method and special sensing fiber method were introduced and analyzed.
2016, 5(5):11-29. DOI: 10.12146/j.issn.2095-3135.201605002
Abstract:Segmentation of cerebral edema from computed tomography (CT) scans for patients with intracranial hemorrhage (ICH) is challenging as edema does not show clear boundary on CT. By exploiting the clear boundary on T2-weighted magnetic resonance images, a method was proposed to segment edema on CT images through the model learned from 14 patients with both CT and T2-weighted images using ground truth edema from T2-weighted images to train and classify the features extracted on CT images. By constructing negative samples around the positive samples, employing the feature selection based on common subspace measures, and using support vector machine, the classification model was attained corresponding to the optimum segmentation accuracy. The method has been validated against 36 clinical head CT scans presenting ICH to yield a mean Dice coefficient of 0.859±0.037, which is significantly higher than that of region growing method (0.789±0.036, P＜0.000 1), semi-automated level set method (0.712±0.118, P＜0.000 1), and threshold based method (0.649±0.147, P＜0.000 1). Comparative experiments have been carried out to find that the classifier purely from CT will yield a significantly lower Dice coefficient (0.686±0.136, P＜0.000 1). The higher segmentation accuracy may suggest that clear boundaries of edema from T2-weighted images provide implicit constraints on CT images that could differentiate edema from its neighboring brain tissues more accurately. The proposed method could provide a potential tool to quantify edema, evaluate the severity of pathological changes, and guide therapy of patients with ICH.
2016, 5(5):30-37. DOI: 10.12146/j.issn.2095-3135.201605003
Abstract:Surface electromyography (sEMG) is a safe and non-invasive electrophysiological signal that has been widely used to provide intuitive control for myoelectric prostheses. Intuitively controlling a prosthetic device is a major challenge for transhumeral amputees (TAs) since they have insufficient residual muscles that could rarely produce enough sEMG signals. To resolve this challenge, targeted muscle reinnervation (TMR) technique which reinnervates the missing muscular has been developed in some previous studies. However, there is no relevant research on the reconstruction of nerve function for TAs in China. In this study, a new surgical method that integrates the TMR technique with targeted nerve function replacement (TNFR) for nerve function regeneration is presented, which is a pioneer study on the reconstruction of nerve function for TA in China. During the surgery, a nerve function model was established while the missing limb muscles were reconstructed for a male TA. To verify the reliability of the reconstructed limb muscles, the high density sEMG technique was used to acquire myoelectric signals corresponding to hand/wrist/elbow movements before and after the surgery. The classification accuracy across all the classes of limb motions were computed and analysed. The results show that the reconstructed muslces play a significant role in providing useful myoelectric control signals for efficiently decoding the different limb motions of the TA. The proposed hybrid (TMR-TNFR) method may be helpful in the reconstruction of the muscle function in residual limb of TAs, and could provide potential information for intuitive control of the myoelectric prostheses.
2016, 5(5):38-48. DOI: 10.12146/j.issn.2095-3135.201605004
Abstract:In this paper, a new calibration method for a specially designed photometric stereo system was presented. Different from conventional photometric stereo systems which adopt parallel or distant point light sources, the quasi-point light sources are used in the proposed system, which permits the system with compact size and short working distance. Subject to the non-isotropic radiance property of the quasi-point light source, the lighting field should be precisely calibrated so as to determine the intensity and direction for each incident light ray. The proposed calibration method was performed in two steps. The first step was to calculate light source position, where a multi-sphere-based method was introduced. By extracting the highlight image points formed from the light source on the specular sphere, and utilizing the sphere contour and radius, it shows that the light source coordinate under camera reference frame can be precisely estimated. In second step, a reference plane-based method was proposed to calculate the principle optical axis of light source. It proves that, the principle optical axis should cross the brightness point in the image of reference plane, and the brightness point can be estimated by fitting the iso-luminance curve in the image. With the calibration parameters, and considering the radiance model of light source, lighting condition for each scene point can be determined. The experiments were conducted with various target surfaces and compared with conventional light models to demonstrate feasibility and accuracy improvement by the proposed calibration method.
2016, 5(5):49-58. DOI: 10.12146/j.issn.2095-3135.201605005
Abstract:Terahertz time domain spectroscopy has been widely used in both spectral analysis and imaging applications. Existing terahertz time domain spectroscopy imaging systems usually suffered the low scanning speed and huge data storage. To solve this problem, an efficient terahertz imaging method based on the compressed sensing theory was presented in this paper. By controlling the scanning motor to perform a nonequal interval sampling of the target, a group of under-sampled terahertz signal can be obtained. Based on the under-sampled signal, the compressed sensing algorithm is applied to reconstruct the complete terahertz image. The results show that, when the compression ratio is 0.5, the correlation coefficient between the reconstructed terahertz signal and the fully sampled THz signal can reach 99.95%. By analyzing the reconstructed terahertz image, the image areas with smooth intensity changing or low frequency component in frequency domain can be well recovered. The proposed method provides a practical means for efficient terahertz imaging applications.
2016, 5(5):59-66. DOI: 10.12146/j.issn.2095-3135.201605006
Abstract:A hundred nano-joules femtosecond (fs) laser amplification system based on the polarizationmaintaining Yb3+ fibers was proposed in this paper. In the proposed system, a Yb-doped mode-locked laser oscillator was used as the light source. Using the chirped pulse amplification method, a two-stage polarizationmaintaining Yb-doped fiber amplifier was adopted. Experimental results show that, with compression of the output light, the output pulse energy can reach 113 nJ and the pulse duration is measured as 221 fs.
2016, 5(5):67-73. DOI: 10.12146/j.issn.2095-3135.201605007
Abstract:A high power narrow linewidth tunable 1 064 nm laser is obtained using three mirror ring cavity with an etalon. Theoretical analysis of unidirectional operation of the ring resonator, narrowing linewidth and tuning wavelength with an etalon and large volume mode operation of the laser was carried out. The mirror curvature and output coupling ratio were optimized in the experiment. Under the 808 nm laser diode pump power of 151 W, 33.7 W of unidirectional 1 064 nm laser output was obtained with beam quality factor of 1.28 and linewidth of 0.1 GHz, and the corresponding optical conversion efficiency was 22.3%. Precise tuning of laser wavelength was realized by controlling precisely temperature of the etalon. Tunable range of 72.6 GHz was achieved by varying the temperature of the etalon, and the tuning accuracy was 220 MHz. The output power of the 1 064 nm laser was changed by about 10% in wavelength tuning process. The whole system is stable and reliable, relatively simple and easy to realize. It provides a practical and effective technical mean for obtaining tunable narrow linewidth 1 064 nm laser.
2016, 5(5):74-82. DOI: 10.12146/j.issn.2095-3135.201605008
Abstract:Upconversional fluorescence materials receive more and more attentions, but their applications suffer from the low conversional efficiency of fluorescence. In other words, it makes precise quantification difficult. In this study, a cube-corner retroreflector was introduced to collect more fluorescence from upconversional materials. A prototyping upconversional fluorescence detection system was developed with a dual optic path containing a cube-corner retroreflector and a coaxial multicore fiber for accepting fluorescence from both sides of the cube-corner retroreflector. A series of experiments were carried out to calibrate this prototyping system. It is found that the dual optic path can collect more fluorescence, and thus it improves the detection efficiency of weak fluorescence. The results confirm the feasibility of the upconversional fluorescence detection system with cube-corner retroreflector.
2016, 5(5):83-89. DOI: 10.12146/j.issn.2095-3135.201605009
Abstract:The micro-manipulation technology has extended its function from particle trapping and transportation to particle sorting and guiding. The silicon-based optical tweezer is one of the most important means in this domain, because it can break through diffraction limit and realize the operation of particles with submicron dimension. Conventional silicon-based optical tweezer systems usually consist of microring, directional coupler and multimode interferometer, and realize the guiding operation by tuning the optical wavelengths. In this paper, a polarization-based particle guiding method and system was investigated. The system parameters were optimized by the finite-different time-domain method. And the feasibility of particle guiding operation was verified. The proposed micro-manipulation system has the advantages of compact size, simple structure and easy to operate.