Three-dimensional measurement based on structured light has been widely used in many fields. Since center locations are used for calculating 3D coordinates, it is important for measurement accuracy. However, affected by the occlusion, shape or color of the measurement object, the angle between object and measurement system and so on, the gray distribution of stripe is degenerated from symmetric to asymmetric. Stripe center locating accuracy is decreased by asymmetric, and some measurement data with big error which decreasing the measurement accuracy seriously appears. In order to recognize those large error data, a new method is proposed by evaluating the quality of stripe gray distribution. The asymmetrical degree of stripe gray distribution is evaluated by the skewness coefficient of stripe gray distribution. The skewness coefficient is defined by the third-order central moment. Then the relationship between the skewness coefficient of stripe gray distribution and the stripe center locating error is analyzed and established by statistical methods. Based on the relationship, the threshold of skewness coefficient is set according to the requirement of measurement accuracy. The asymmetry of gray distribution is estimated by calculating the coefficients. According to the skewness of stripe gray distribution and threshold large error data with low reliability are identified. Higher measuring accuracy is achieved by rejecting the identified data. The validity and reliability of the method have been proved by experiments.
This paper presents the results revealing the influence of the nonlinear gain on the stability limit of a semiconductor laser (SL) with external optical feedback (EOF). A new system determinant is derived from the original Lang and Kobayashi (L-K) equations. By making analysis on the locus of the roots of the system determinant, the stability limit of the system is obtained, from which a number of important and interesting phenomenon revealed by the nonlinear gain is uncovered. The correctness of results is verified by numerical simulations.
Optical feedback Self-mixing Interferometry (OFSMI) can achieve a high-resolution displacement sensing and
measurement by using advanced digital signal processing. However, most existing signal processing algorithms used for
OFSMI signals are implemented on a PC by Matlab or other programming languages. In this case, the whole structure of
OFSMI sensing system is incompact and the measurement is in low speed. The design trends in sensing systems are
towarding to small size, high integration and fast real time processing. These trends require us to improve the existing
OFSMI design. It is a good solution to apply Field-programmable gate arrays (FPGAs) technique onto OFSMI sensing
systems. In this work, we designed a FPGA based signal processing unit for an OFSMI displacement sensing system.
The OFSMI sensing signals observed from an OFSMI system is connected to a FPGA development board (Spartan-3E)
for high speed signal processing. The FPGA processing unit retrieves the displacement information carried in the OFSMI
signals. The FPGA design includes noise reduction, signal peak detection and impulse magnitude tracking. As the
magnitude of the sensing signal is time-varying, for adapting the variation, a dynamic updating algorithm is introduced
in the magnitude tracking unit. Both simulation and hardware co-simulation show that the OFSMI system with a FPGA
based signal processing unit can achieve fast and reliable displacement sensing.
Displacement information of a moving target can be detected using an optical feedback self-mixing interferometry
(OFSMI) system. A sensing signal observed from the OFSMI system is called self-mixing signal (SMS). The paper
studies the waveform features of the SMSs and proposes an algorithm for reconstructing the displacement of a moving
target. The reconstruction accuracy of the algorithm mainly depends on the locating accuracy for those characteristic
points on a SMS. A set of rules for identifying those characteristic points are described in the paper. The proposed
algorithm is verified by simulation signals firstly, and then applied on extensive SMSs which are obtained from the
experimental set-up. The results show that the displacement of the external moving target can be reconstructed under
different feedback levels.
The paper reviewed the new emerging technique: optical feedback self-mixing interferometry (OFSMI) and its applications. Three different methods on measuring the linewidth enhancement factor (LEF) based on OFSMI are presented here and compared. The experimental results show that LEF can be measured by OFSMI with a simple set-up and good accuracy.
The impacts of PMD on optical fiber transmission system are investigated briefly. A new compensation scheme is proposed using a single compensator in multichannel systems to compensate several channels at the same time. The DOP of the received signal requires no high-speed circuit and is independent of bit rate. In the proposed scheme the DOP of the optical signal is used as the control signal, and the maximized DOP is fed in polarization controller.
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