We present a new multi-scale geometrical analysis method for ophthalmic image contrast enhancement based on the contourlet transform. The contourlet transform has better performance in representing edges than wavelets...We present a new multi-scale geometrical analysis method for ophthalmic image contrast enhancement based on the contourlet transform. The contourlet transform has better performance in representing edges than wavelets due to its anisotropy and directionality,and is therefore well-suited for multiscale edge enhancement. We modify the contourlet coefficients in corresponding subband and take the noise into account for mere precise reconstruction and better visualization. We compare this approach with enhancement based on the ourvelet transform,and the traditional Histogram Stretching （HS）. Our findings are that contourlet based enhancement out-performs other enhancement methods on low contrast and dynamic range images,and can clearly identify the vessels and nerves in an ophthalmic image.展开更多
A novel hybrid surface micromachined segmented mirror array is described. This device is capable of scaling to large apertures for correcting time-varying aberrations in laser applications. Each mirror is composed of ...A novel hybrid surface micromachined segmented mirror array is described. This device is capable of scaling to large apertures for correcting time-varying aberrations in laser applications. Each mirror is composed of bottom electrode, support part, and mirror plate, in which a T-shaped beam structure is used to support the mirror plate. It can provide mirror with vertical movement and rotation around two horizontal axes. The test results show that the maximum deflection along the vertical direction of the mirror plate is 2 μm, while the rotation angles around x and y axes are±2.3° and ±1.45°, respectively.展开更多
A high-repetition-rate eye-safe optical parametric oscillator （OPO）, using a non-critically phase-matched KTP crystal intracavity pumped by a passively Q-switched Nd：GdVO4/Cr^4＋ ：YAG laser, is experimentally demo...A high-repetition-rate eye-safe optical parametric oscillator （OPO）, using a non-critically phase-matched KTP crystal intracavity pumped by a passively Q-switched Nd：GdVO4/Cr^4＋ ：YAG laser, is experimentally demonstrated. The conversion efficiency for the average power is 7% from pump diode input to OPO signal output and the slope efficiency is up to 10.3%. With an incident pump power of 7,3 W, the compact intracavity OPO （IOPO） cavity, operating at 15 kHz, produces an average power of 0.57 W at 1570 nm with a pulse width as short as 6 ns. The peak power at 1570 nm is higher than 6.3 kW.展开更多
The twisted Laguerre-Gaussian beam was generated by transforming of Hermite-Gaussian beams through an optical system consisting of three rotated cylindrical lenses. The intensity distribution and phase structure of th...The twisted Laguerre-Gaussian beam was generated by transforming of Hermite-Gaussian beams through an optical system consisting of three rotated cylindrical lenses. The intensity distribution and phase structure of the twisted hollow beam were theoretically analyzed by using Collins diffraction integral. By utilizing the method of mode decomposition, the theory of transformation was analyzed. In the experiment, micro particles were trapped and rotated by this twisted beam.展开更多
Influence of thermal-mechanical properties on the features of the panda polarization-maintaining optical fiber (PMF-) in fabrication process is studied in detail by finite element method (FEM). The stress birefringenc...Influence of thermal-mechanical properties on the features of the panda polarization-maintaining optical fiber (PMF-) in fabrication process is studied in detail by finite element method (FEM). The stress birefringence is 2.13443×10-4 obtained by the static analysis and 2.1269×10-4 by dynamic analysis. The difference in simulation by two methods is around 0.4%. The non-uniformity of stress birefringence in the fiber core is about 1.6%. Predicted results demonstrate that effect of the thermal conductive parameter on fiber thermal stress dominates. The high and uniform stress birefringence in the fiber core is obtained by appropriately selecting suitable stress region area and position.展开更多
40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing （FWM）-based wavelength conversion in a 26.5-km dispersion shifted fiber （DSF） is investigated. The experimental results demonst...40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing （FWM）-based wavelength conversion in a 26.5-km dispersion shifted fiber （DSF） is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave （CW） light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.展开更多
文摘We present a new multi-scale geometrical analysis method for ophthalmic image contrast enhancement based on the contourlet transform. The contourlet transform has better performance in representing edges than wavelets due to its anisotropy and directionality,and is therefore well-suited for multiscale edge enhancement. We modify the contourlet coefficients in corresponding subband and take the noise into account for mere precise reconstruction and better visualization. We compare this approach with enhancement based on the ourvelet transform,and the traditional Histogram Stretching （HS）. Our findings are that contourlet based enhancement out-performs other enhancement methods on low contrast and dynamic range images,and can clearly identify the vessels and nerves in an ophthalmic image.
基金This work was supported by the National Natural Science Foundation of China under Grant No. 10476010.
文摘A novel hybrid surface micromachined segmented mirror array is described. This device is capable of scaling to large apertures for correcting time-varying aberrations in laser applications. Each mirror is composed of bottom electrode, support part, and mirror plate, in which a T-shaped beam structure is used to support the mirror plate. It can provide mirror with vertical movement and rotation around two horizontal axes. The test results show that the maximum deflection along the vertical direction of the mirror plate is 2 μm, while the rotation angles around x and y axes are±2.3° and ±1.45°, respectively.
文摘A high-repetition-rate eye-safe optical parametric oscillator （OPO）, using a non-critically phase-matched KTP crystal intracavity pumped by a passively Q-switched Nd：GdVO4/Cr^4＋ ：YAG laser, is experimentally demonstrated. The conversion efficiency for the average power is 7% from pump diode input to OPO signal output and the slope efficiency is up to 10.3%. With an incident pump power of 7,3 W, the compact intracavity OPO （IOPO） cavity, operating at 15 kHz, produces an average power of 0.57 W at 1570 nm with a pulse width as short as 6 ns. The peak power at 1570 nm is higher than 6.3 kW.
基金This work was partly supported by the National Natural Science Foundation of China (No. 69908001)the Characterization of Optical Company and Laser BeamsⅡof Germany and the internatioual cooperation agreed by DFG and NSFC.
文摘The twisted Laguerre-Gaussian beam was generated by transforming of Hermite-Gaussian beams through an optical system consisting of three rotated cylindrical lenses. The intensity distribution and phase structure of the twisted hollow beam were theoretically analyzed by using Collins diffraction integral. By utilizing the method of mode decomposition, the theory of transformation was analyzed. In the experiment, micro particles were trapped and rotated by this twisted beam.
文摘Influence of thermal-mechanical properties on the features of the panda polarization-maintaining optical fiber (PMF-) in fabrication process is studied in detail by finite element method (FEM). The stress birefringence is 2.13443×10-4 obtained by the static analysis and 2.1269×10-4 by dynamic analysis. The difference in simulation by two methods is around 0.4%. The non-uniformity of stress birefringence in the fiber core is about 1.6%. Predicted results demonstrate that effect of the thermal conductive parameter on fiber thermal stress dominates. The high and uniform stress birefringence in the fiber core is obtained by appropriately selecting suitable stress region area and position.
文摘40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing （FWM）-based wavelength conversion in a 26.5-km dispersion shifted fiber （DSF） is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave （CW） light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.
