Polarization measurements are sensitive to the microstructure of tissues and can be used to detect pathological changes. Many tissues contain anisotropic fibrous structures. We obtain the local orientation of aligned fibrous scatterers using different groups of the backscattering Mueller matrix elements. Experiments on concentrically well-aligned silk fibers and unstained human papillary thyroid carcinoma tissues show that the m22, m33, m23, and m32 elements have better contrast but higher degeneracy for the extraction of orientation angles. The m12 and m13 elements show lower contrast, but allow us to determine the orientation angle for the fibrous scatterers along all directions. Moreover, Monte Carlo simulations based on the sphere-cylinder scattering model indicate that the oblique incidence of the illumination beam introduces some errors in the orientation angles obtained by both methods. Mapping the local orientation of anisotropic tissues may not only provide information on pathological changes, but can also give new leads to reduce the orientation dependence of polarization measurements.
Linear CCDs three-dimensional measurement system is constituted with three one dimensional imaging units (ODIUs) composed of charge-couple device (CCD) linear image sensor paired with equivalent cylindrical lens cells. The cylindrical lens is needed for optical transformation from object point to its realistic image line in the ODIU, and the imaging quality of equivalent cylindrical lens (width and distortion aberration of the image line) directly affected the reconstruction precision of three dimension coordinates. At present, the methods of how to design an equivalent cylindrical lens with both high precision and wide field of view were not reported in literatures. An improved Double Gauss structured lenses by replacing the first spherical lens in the traditional Double Gauss lenses with a cylindrical lens is introduced to realize the point to line optical transformation and aberration adjustment. The coma aberration and distortion can be automatically adjusted due to the structure symmetry of composite lenses, and the spherical aberration, astigmatism and curvature of field can also be largely adjusted by appropriately selecting material, luminous flux, curvature, thickness, and distance of lenses. Under the computer simulating by Zemax (an optical systems design software), the composite cylindrical lens was designed and fabricated. Finally, the three-dimensional positioning system made up of above-mentioned composite cylindrical lens and corresponding circuits is constructed, and the direct linear transformation (DLT) is adopted to three dimension coordinated reconstruction. The result of reconstruction error of X, Y, Z axis with in the view field of 700x760x500 mm less than 1mm are obtained.
A precision positioning system with a high displacement resolution has been widely required for modern industrialized applications, such as microelectronics, super-precision manufacturing etc. This paper discusses the design and the features of a new piezo driven precision micro positioning stage utilizing flexure hinges. Theoretical analysis for the stiffness of the flexure hinge is also given briefly. A piezoelectric ceramic is applied to drive the precision state, whose displacement can reach 5 micrometers when employed with 1000 voltage power. In order to testify the robust and measurement stability of the precision sta, three kinds of PZT produced in Germany, Japan and China respectively are utilized. A dual-frequency interferometer with nanometer resolution and accuracy is adopted to evaluate the mechanical characteristics of the positioning stage. The experimental result shows that the open loop control of the stage provides 0.2nm positioning resolution along the moving direction.
The positioning system based on surface plasmon resonance (SPR) can achieve nanometer resolution and repeatility. A special retroreflector is designed that incidence angle of its first reflection surface is equal to resonance angle of SPR to implement the integrate SPR positioning system into the interferometer. At the beginning of a measurement, a zero position is determined by SPR positioning system. If there is drift during measurement, reset interferometer data to diminish drift as soon as the special retroreflector reaches the zero position. The integration interferometer is set up. Experiments show that long time uncertainty of interferometer is reduced from 60nm to 10nm. The measurement precision and stability of interferometer is increased.
A new method for nanometer positioning based on surface plasma wave is reported. A fiber probe approaching a coated prism can be equivalent to a four-layer prism-metal-air- fiber system. Analysis of the near-field beam intensity entering the fiber probe is presented. Theoretical analysis shows that the intensity coupling into the fiber probe changes according to the thickness of air gap. Non-contact nanometer indicating system can be set up according to this characteristic. Experiments show that standard deviation of 2nm and resolution of 0.1nm/nV of positioning repeatability can be achieved under air conditions of +/- 1 degree(s)C/h.
We demonstrate an optical time division demultiplexing from 8x2.5Gb/s pseudorandom data stream using a nonlinear optical loop mirror, or nonlinear fiber Sagnac interferometer switch. To ensure good extinction ratio of the demultiplexed signal, some experimental results show it is necessary to adjust carefully the dc bias, modulation current, compression fiber length and switching width and synchronous between the data and control pulses.
The spectral characteristics of gain-clamped EDFAs including pump- and laser-controlled was investigated theoretically and experimentally. It is found that if the average population inversion can still be managed, the gain profiles should be also clamped.
In this paper, we report the successful demonstration of 10 GHz actively mode-locked fiber ring laser for the first time in China. Pulses train as short as 9 ps has been obtained from this laser. The laser can operate at a wide wavelength range, from 1529 nm to 1564 nm. The mean output power is about 2.1 mW at the wavelength of 1545 nm. Nonlinear polarization rotation was utilized to achieve intra-cavity compression.
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