EDGE LOCALIZATION BY MULTIPLE OF GAUSSIANs THEORY

Zero-crossing of a derivative of Gaussian filter is a well-known edge location criterion. Examples are the Laplacian, the second derivative in the gradient direction (SDGD) and the sum of the Laplacian and SDGD (PLUS). Derivative operators can easily be implemented by convoluting the primitive image with a derivative of a Gaussian. Gaussian filter displaces the equipotential of half height inwards for convex edge and outwards for concave edges. A Difference-of-Gaussian (DoG) filter is similar to the Laplacian-of-Gaussian but with opposite sign and causes a convex edge shift inwards. This paper introduces the Multiple-of-Gaussian niters to reduce curvature-based location error. Using a linear combination of N Gaussians(N】2) with proper weights, the edge shifts can be reduced to 1/(2N-3) of the ones produced by a similar Laplacian-of-Gaussian filter.

Lasing characteristics of strongly pumped Yb-doped photonic crystal fiber laser

A strongly pumped Yb-doped large-mode-area photonic crystal fiber （LMA-PCF） laser is analyzed. The lasing characteristics of an improved Fabry-Perot （F-P） cavity fiber laser using LMA-PCF are studied theoretically based on a rate equation model and the exact numerical solution of the rate equations is in excellent agreement with the experimental result.

Novel trichromatic phosphor Co-doped with Eu, Tb in SiO_2 gel matrix

The Eu, Tb co-doped SiO2 matrix tricolor fluorescence system was prepared by sol-gel technique. Red emission at 618 nm, green emission at 543 nm and blue emission at 350―500 nm were observed in the PL spectra of the sample, indicating that Eu3+, Eu2+ and Tb3+ ions coexisted in the matrix. In the co-doped sample, the blue emission of Eu2+ was much stronger than that of the sample single doped with Eu, which implied that the electron transfer between Eu3+ and Tb3+ maybe happened in the SiO2 matrix. The influences of the annealing temperature and Tb concentration on the PL spectra of the samples were investigated. The optimal doped concentration of Tb was determined to be 0.2% and the optimal annealing temperature 850℃. Annealed at 600℃, Tb3+ had a sensitizing effect on Eu3+ in the SiO2 matrix, and the emission intensity of Eu3+ in the Eu, Tb co-doped sample was more than four times that of the single doped sample, which could be attributed to the energy transfer from Tb3+ to Eu3+.

High power single-mode large-mode-area photonic crystal fiber laser with improved Fabry-Perot cavity

An Yb^3＋ -doped double-clad large-mode-area photonic crystal fiber （LMA PCF） laser with 103-W singlemode continuous-wave output power isdemonstrated using an improved Fabry-Perot （F-P） configuration.The slope efficiency of 83.2% and good beam quality （M^2 = 1.2 ± 0.1） are achieved without any thermooptical problems, dichroic mirror surface damage, and drop of the slope efficiency in this system.

Tricolor white emitting phosphor co-doped with Eu,Dy in SiO_2 matrix

A Eu, Dy co-doped SiO2 matrix, white emitting phosphor was prepared by the sol-gel technique. Strong red, green and blue emissions located at 618 nm, 573 nm and 400-550 nm were observed under UV laser excitation at room temperature. Such techniques as FT-IR and TGA-DSC were used to measure the microstructure of the luminescent material. The influence of the preparation techniques on the luminescence property of the Eu, Dy co-doped SiO2 matrix, such as anneal temperature, anneal time, dried atmosphere and the components of the matrix, was systematically studied, and the luminescence mechanism was interpreted. The red emission is the strongest when annealed at 750 ℃ . However, blue emission appears when annealed at 700 ℃ and is the intensest at 900℃ . For the samples dried in vacuum, Eu3+ is more easily deoxidized to Eu2+ at lower temperatures, because the samples dried in the air compared with that dried in vacuum need higher temperature to form network structures. Only the SA and SAB matrix annealed at 850 ℃ had blue emission in the four matrices (SA, SAB, SB, S) xerogel and the emission in the SAB matrix was stronger than that in the SA matrix. This may be due to the eutectic phase formed by the oxide boron, alkaline oxide and alumina in the SAB matrix, which constructs network structures and stabilizes the emission center and enhances the blue emission.

20-GHz optical pulse source based on cascaded electroabsorption modulators

A high-quality low-timing-jitter 20-GHz optical pulse train is generated by using two cascaded sinusoidally driven electroabsorption modulators （EAMs） at very low bias voltage of -0.8 V in conjunction with atunable distributed feedback （DFB） semiconductor laser. An approximate transform-limited optical pulse, with the pulse width less than 7 ps, the spectral width of 0.3 nm, and the side-mode suppression ratio （SMSR） above 20 dB, is obtained by tuning the optical delay line.