This paper introduces a new structure of WDM local area network. Each node uses WDMA (Wavelength Division Multiplexing Access) to access the network. The switching router of WDM LANs proposed before often use PSC (Passive Star Coupler), but now has been replaced by AWG (Arrayed Waveguide Grating), while each user equipped one tunable transmitter and one tunable receiver is reserved. As we all know, in WDM LAN, destination collision is inevitable when two or more then two nodes want to communicate with the same destination node and this degrades the network performance. So, in all related papers, transmission and receiving procedure must be pre- scheduled in order to preventing from destination collision. However, if there is a configuration, which has the possibility of permitting more than one to access the same destination simultaneously, access scheduling can be more efficient and system performance can be improved. Obviously, adding receiver number or transmitter number is impractical, thus, the only solution is to introduce buffer at the router output side. This is a distinctive difference of the network router we proposed from others. We believe this design can improve the network performance and simulation and numerical results have confirmed that.
The dynamic response characters of the wavelength scanning fiber-optic interferometry for distance measurement have been studied. When the measurand moves, the output signals are analyzed in the time-domain and frequency-domain. Then the measurement errors are obtained with the numerical simulation methods. It is important for the deformation process measurement.
A sensing and control system of process quality in CO2 laser deep penetration welding has been developed, including plasma photo sensor (PS) and plasma charge sensor (PCS), signal processing circuit, personal computer, and optimization and control software. By using the information of plasma radiation and plasma charge, the focusing lens is adjusted to the optimum focal point position (at which the maximum penetration can be achieved) and closed-loop control is realized to assure the focal point position and penetration depth constant. In laser welding of the workpiece aslant placed with larger angle, the variation of focal point position is less than 0.2 mm and the fluctuation of penetration depth is less than 0.05 mm. The control system has been preliminarily applied in laser precision welding of 2.5 m long zircaloy fuel channel used in nuclear heat-supply reactor.
Using numerical calculation methods, we have studied the relations among the key system parameters - the center wavelength, spectral width, crystal thickness, and their influence on the measurement accuracy, resolution, dynamic range, linearity. The optical parameters of the source and crystal are obtained, in the compensation configuration which can provide enough accuracy, resolution and stability. The theoretical and experimental methods proposed in this paper have important roles in other polarization-modulated fiber optic senors.
A novel wavelength scanning fiber optic interferometer for absolute distance measurement has been proposed. In this paper, the source properties, which affect the measurement accuracy, resolution and dynamic range etc., are comprehensively studied. A tunable external-cavity semiconductor laser is taken as the wavelength scanning source, which can satisfy the demands on the spectrum bandwidth, scanning range and output power. Using the frequency-spectrum analysis, it is found that the random wavelength drift of the scanning can decrease the signal-to- noise ratio SNR of the output interferometric signal. The reduction of SNR limits the measurement accuracy. We can optimize the system with the analysis results. The preliminary experiment results correspond the theoretical analysis well.
A wavelength scanning fiber-optic interferometer for distance measurement is introduced in this paper. The system includes two fiber-optic Fabry-Perot interferometers, one as a reference interferometer, the other as a sensing interferometer. These two interferometer models are analyzed and the optimal design is done. The theoretical estimation corresponds the experiments well.
A developed wavelength scanning fiber-optic interferometry has been studied in this paper. Using this method for distance/displacement measurement, we adopt a tunable external cavity semiconductor laser to simultaneously illuminate two Fabry-Perot interferometers, one as the sensing interferometer, the other as the reference interferometry. We analyze the characteristics of the scanning source and the interferometric signals, then illustrate the limitation of the measurement accuracy and resolution in terms of theory. The experimental results show that the accuracy of 0.05 micrometers and resolution of 0.01 micrometers are achieved, in the range of 1 mm.
We have developed a reflecting fiber-optic temperature sensor with a small quartz crystal, based on the birefringence effect. The methods of designing and selecting the optical system parameters, such as optical source, crystal, and transmission fibers, are illustrated comprehensively in this paper. These theoretical and experimental methods proposed in this paper have important roles in other polarization-modulated fiber-optic sensors.
We have proposed a novel wavelength scanning fiber-optic interferometer for absolute distance measurement. Based on the digital signal processing techniques, an algorithm to effectively discriminate phase information, eliminate perturbations and overcome the random sway of the scanning, is established. So that the practical demands of precision 0.05 micrometers and resolution 0.01 micrometers can be satisfied.
A novel reflective bridge-shaped compensation configuration has been developed for the polarization-modulated fiber- optic temperature sensors. We comprehensively study the compensation effects with this configuration in terms of theory. Then we design the corresponding experiments to verify the theoretical analysis. It proved that this system can improve the measuremental accuracy and long-term stability.
In this paper, we have proposed a novel wavelength scanning fiber-optic interferometer for absolute distance measurement. A wavelength scanning source is used to simultaneously illuminate two F-P cavities, one as a sensing interferometer, the other as reference interferometer. With this method, we can obtain absolute measurement, and decrease the demands on the light source, such as its stability of wavelength and power, its repeatability of scanning range. The accuracy of 0.2 micrometer and resolution of 0.04 micrometer are achieved, in the range of 0 - 2 mm.
The authors have found a third process--unstable-mode welding (UMW) under a certain condition, besides already known stable deep penetration welding (DPW) and stable heat conduction welding (HCW) during high-power CO2 laser welding. UMW has basic feature that the two welding modes (DPW and HCW) appear intermittently, with the penetration depth and weld width jumping between large and small grades. In this paper, the physical phenomena, especially the signal of plasma during welding and the weld-forming of three kinds of process have been investigated. Effects of welding parameters (focal position, laser power and travel speed) on laser welding mode and weld-forming have been comprehensively studied. Double-U curves of laser welding mode transition have been obtained, which indicate the parameter ranges of the three monitored welding process.
An advanced plasma detecting system of CO2 laser welding has been developed. The system consists of three sensors, signal processing, A/D data converting and photo-electric coupling units connected with a rapid personal computer. The Photocell Sensor (PS) detects the intensity of the blue light irradiated by the plasma. The Plasma Charge Sensor (PCS) detects the electric density of the plasma plume. The Microphone Sensor detects the sound pressure coming from the rapidly expanding vapor in the keyhole. All of the sensors can exactly distinguish three kinds of welding processes--heat conduction welding, deep penetration welding, unstable mode welding. When the welding parameters are given, the PCS signal depend on the distance between the welding nozzle and the workpiece, the PS signals are correlated closely to the focal point position. Three sensors can be used to control the focal point position (penetration depth) under given laser power and welding speed. In addition, the relation between detecting signals and penetration depth is given. The sensors of the system have features of simple structure, low cost and high sensitivity, which are especially suitable for on-line plasma detecting, quality controlling and off-line plasma analyzing of CO2 laser welding.
In this paper, optimal parameter selection method is proposed to determine two working wavelengths, and selection of their bandwidths is also studied in detail. It's of great significance in practical applications.