This paper has established a thermal model of Vertical-external-cavity surface-emitting semiconductor laser (VECSELs)
with water-cooled heatsink, calculated the distribution of temperature field with finite element method, and studied the
effects of pumping light, heat transfer coefficient, and heatsink characteristics on the maximum temperature of the
quantum well. Calculations show that there is an optimal heat transfer coefficient value interval, thermal conductivity of
the VECSELs heatsink will have a significant impact on the maximum temperature of the quantum well, and increasing
area of cooler heatsink would help to improve heat dissipation performance. It also shows that the maximum temperature
of the quantum well has a linear relationship with pump power, and a nearly inverse relationship with the spot size. Due
to thermal diffusion of water-cooled heatsink for VECSELs point heat source, the maximum temperature of quantum
well is not sensitive to thickness and area of the heatsink, heat dissipation performance which uses a diamond heatsink is
about 1.7 times the oxygen-free copper heatsink.
In this study, we investigated a promising method for measuring three-axis force based on an optical tactile sensing
system. Such system consists of a waveguide, an array of tactile cell, a light source and an image sensor (a CCD
camera). When the tactile cells are subjected to external forces, the condition for total internal reflection of the attached
waveguide is spoiled. The original symmetrical planar waveguide then changes to an asymmetrical one, leading to light
leakage in the transverse direction, which is used as the sensing mechanism for the applied forces. A numerical study
involving three-dimensional finite element analysis was carried out to study the deformation of tactile cells due to
contact forces. A linear relationship between the applied three-axis force and the spot sizes of the image of the leaked
light was obtained and validated by experiments.
OPS with feedback shared FDL buffer produce large voids due to FDL buffers only supplying discrete step delay and causing FDL queue virtually occupation. By analyzing the TCP traffic and ACK packets feature, the ACK packet void filling first scheduling is presented to decrease packet loss rate and to reduce the FDL voids. When the FDL buffer void size is fit for the ACK packet, the ACK packet is scheduled to FDL immediately. An ACK and non-ACK packets difference and process flow is designed according the TCP packet frame structure. Compared with the conventional FIFO scheduling and smallest FDL void first scheduling, the algorithm reduces greatly the number of ACK occupying the FDL buffer and eliminates large numbers of ACK's bad influence on efficiency of IP data transmission under different FDL buffer depth and traffic load. The results of simulation show that the proposed scheduling makes use of ACK packets first void filling scheduling mechanism to reduce FDL excess load, increases output utilization and reduce packet loss ratio for asynchronous optical network. This approach is shown to minimize the FDL numbers with the feature of high stabilization and photonic integration and to improve real time TCP traffic performance for Internet network.
In this paper, multivariable linear regression analysis was employed to obtain the relationship among facial geometric
features, and a discriminant function was used to evaluate the significance of different features. Finally, classification
rates were compared with different combinations of geometric features. The results showed that the geometric feature
with more significance probably improved the classification performance in the cases studied.
In order to measure three-axis force, two four-part tactile sensing systems based on piezoelectricity and optics were
designed and fabricated. The feasibility and reliability of the two systems were evaluated both numerically and
experimentally. A general formula between the applied three-axis force and the four-part tactile sensing signals was
developed. It is expected that this formula should benefit the design and fabrication of new tactile sensing systems.
In the research and development of multi-parameter precision detecting system, various parameters need to be measured (such as length, diameter, surface roughness and so on). We not only measure some parameters statically but also measure others dynamically and calculate others (such as volume, density) using some detected parameters. At the same time, this system need higher precision and higher measuring speed. We propose a new detecting idea for this system--detecting devices in dynamic, module and time-sharing. And we design and optimize multi-parameter high precision measurement system employing the method. This idea includes three parts: the first part is dynamical part. We can make system more stability and more continuity in high detecting speed. The second part is module part. We can settle on a solution to measure similar parameters and make system structure more reasonable and reduce error factors. The third is time-sharing part. We solve the problem how to allot time to every parameter and make every measurement part and its software tie in. The detecting idea has been employed to design and optimize several multi-parameter precision detecting systems. Now these systems are running successfully in workshop.
The average queue delay of optical packet increases when the packets block in the virtual output queue header in the
asynchronous optical packet switching. We analyze the character of variable length Internet packet and propose the
preemptive short packets priority (PSPP) algorithm for reducing the total packet waiting time in the queue. In the PSPP
algorithm, the short packet can preempt the transmission time of the long packet and can be served first. The analysis and
the simulation shows the PSPP algorithm can make the average waiting time of the short packet decrease to zero almost
and can decrease the total packet average waiting time largely when the traffic load is middle and low. The PSPP can
guarantee the low average waiting delay for the real time TCP traffic implementation.
An optical header extraction and recognition structure was presented in the paper. The optical header is extracted by the
improved iTOAD structure with DPSK modulation, while the header recognition is realized by discrete time stretch
technology with super-continuum pulse to slow down the optical header speed for the high-speed asynchronous optical
packet switch. Analysis and Experimental results shows that the iTOAD with time stretch technique can enlarge the
output header 20dB and improve the switching ratio to 15dB when the input pulse is only 0.1pJ. By adjusting the tunable
FDL length, the two pulses after the coupler switching have the π phase shift in the iTOAD SOA. The structure can slow
down the high-speed optical header speed. Furthermore, the low speed header has the low latency time decreases
(latency time less than 100μs) and overcomes the drawbacks of time bandwidth limitation associated with dispersion in
long lengths of fiber. The system is highly scalable, lower power consumption and photonic integration.
The paper studies the performance of an all-optical packet switch (OPS) for different packet length. The packet loss ratio, considered the OPS without FDL and with FDL buffer, with different length distribution are analyzed under the Poisson arrival process and a burst super exponential arrival process respectively. The experiment and analysis show that the performance of different length packet is influence by the packet arrival process and the buffer size. When the OPS without buffer, the PLR under bursty traffic yields the higher packet loss ratio (PLR). PLR with Poisson arrival packet is not influenced by the packet length distribution, while with the super exponential traffic, the packet length distribution influences the PLR, and the fixed length packet yields higher PLR compared to the variable length exponential packet and the experiential Internet traffic. When the OPS with buffer, PLR with Poisson arrival packet yields lower than with super exponential packet under the same load, and the experiential length super exponential packet leads to highest PLR, while the fixed length Poisson process packet brings on lowest PLR.
Singular values (SVs) feature vectors of face image have been used for face recognition as the feature recently. Although SVs have some important properties of algebraic and geometric invariance and insensitiveness to noise, they are the representation of face image in its own eigen-space spanned by the two orthogonal matrices of singular value decomposition (SVD) and clearly contain little useful information for face recognition. This study concentrates on extracting more informational feature from a frontal and upright view image based on SVD and proposing an improving method for face recognition. After standardized by intensity normalization, all training and testing face images are projected onto a uniform eigen-space that is obtained from SVD of standard face image. To achieve more computational efficiency, the dimension of the uniform eigen-space is reduced by discarding the eigenvectors that the corresponding eigenvalue is close to zero. Euclidean distance classifier is adopted in recognition. Two standard databases from Yale University and Olivetti research laboratory are selected to evaluate the recognition accuracy of the proposed method. These databases include face images with different expressions, small occlusion, different illumination condition and different poses. Experimental results on the two face databases show the effectiveness of the method and its insensitivity to the face expression, illumination and posture.
After presenting an improved theoretical model that describes the dynamic process of optical pulse amplification by the semiconductor light amplifiers (SLAs), both the rising and falling time of amplified picosecond optical pulses by the SLAs have been investigated numerically. The results show that with the increase of the bias current of SLAs, the rising time will decrease and the falling time increase; the input pulse with a large peak power will accelerate the rising time shortening and the falling time lengthening; the gain compression has an obvious influence on the rising and falling time for several picosecond width input pulses; the gain asymmetry and shift violently affects the rising and falling time.
As the development of intelligent robots, more and more sensors of higher-technique are required, and tactile sensing technology gets extensively attention. It is the three-axis force that is working when the robot is grasping or walking, but it is quite difficult to measure the three-axis force directly in the numerous tactile sensors. To get the contact-alike nonlinear solution in FEA(Finite Element Analysis), an advanced analysis method of ANSYS - APDL(Advanced Program Description Language) is employed, with which the miscellaneous and time-consuming process is automatically completed in an intelligent way. This paper introduces a series of simulation experiments about an innovative optical wave-guided three-axis tactile sensing system and brings forward the corresponding mathematical model to calculate the three-axis force. A special sensing system is designed for the experiments, and the results
considerably conform to the theoretical analysis. Thus, a new method comes into being for tactile sensing of intelligent robots.
In this paper, a novel method of Regional Facial Geometric Feature Recognition (RFGFR) is presented. With the development of biometrics technology, the recognition of human-face becomes the most acceptant way of identification. Based on the consideration that China is such a country with expansive regions, numerous peoples and different facial geometric structures and features, the six geographic regions based on facial geometric features have been classified according to China Administrative District. The 300 front face images of the Han nationality in the classified six regions have been sampled and registered into a face image gallery through a 3-D digital camera system. Subsequently, some geometric features (distance between two pupils, ratio of distance between two inner canthi to distance between two pupils and etc.) have been extracted and used as the facial feature recognition parameters. Furthermore, through lots of recognition experiments, we found that the Han people in different regions have different facial features to some extent. As a result, the feasibility and reliability of the RFGFR method are finally verified.
Based on image theory under incoherent illumination, the requirements of focus and distance between two gratings are discussed
for the Lau effect under incoherent illumination by means of a divergent beam. The relationship between the pitch of the Lau fringes and the geometric parameters of the optical system is also discussed. Our conclusion expands former achievements. The experimental results agree with those of the theory.
For the distributed fiber optical force sensor based on the principle of modecoupling
of polarization-maintaining fiber and that of optical path compensation in
the interference of quasi-monochromatic light, it is very important to process the
weak optical signal from the sensing fiber. The paper analyzes the characteristics of
the optical signal and suggests a Mach- Zehnder interferometer which includes an
acouto-optical modulator and a polarized beam splitter to realize the polarization
heterodyne interference. The method elimilates the iiifluences of light source
fluctuation and back ground and cuts down the loss of the signal processing, so that
it improves S/N ratio.
The experiments coinicde well with the analysis.
A method for measuring a distributed external pressure field along an optic fiber is discussed, which is based on the principle of mode-coupling of polarization-maintaining fiber and optical path compensation in the interference of two beams from a broadband light source. A modified Mach-Zehnder interferometer is used to process the optical signal representing the distributed pressure information, and a polarization light heterodyne detecting technique is used to improve the signal-to-noise ratio and to eliminate the influences of light source fluctuation and background light. For the automatic measurement of the distributed pressure information, an A/D and interface circuit is designed. Under the control of the microcomputer, the arm of the interferometer with an optical path scanning setup scans a distance corresponding to the length of the fiber, then the information of the pressure field is obtained. The experimental results have shown that the measuring system has a high measurement accuracy and a rather large pressure measuring range (10 g/mm - 500 g/mm).