Digital watermark is a type of technology to hide some significant information which is mainly used to protect digital data. A high capacity multiple watermarking method is proposed, which adapts the Fourier descriptor to pre-process the watermarks, while a Sudoku puzzle is used as a reference matrix in embedding process and a key in extraction process. It can dramatically reduce the required capacity by applying Fourier descriptor. Meanwhile, the security of watermarks can be guaranteed due to the Sudoku puzzle. Unlike previous algorithms applying Sudoku puzzle in spatial domain, the proposed algorithm works in transformed domain by applying LWT2.In addition, the proposed algorithm can detect the temper location accurately. The experimental results demonstrated that the goals mentioned above have been achieved.
A high-stability erbium-doped superfluorescent photonic crystal fiber source (SPCFS) is presented. Optimization of
the high-stable SPCFS is achieved by combining high-performance EDPCF, optimal fiber length, and source
structure with suitable pump power. The result shows a 56.979 ppm mean wavelength stability of a prototype SPCFS
is demonstrated with the temperature varied in the range of −40 °C—70 °C. Especially, in the room temperature, the
mean wavelength stability of a prototype SPCFS is less than 2.59 ppm, which will be approaching the requirement
for inertial-grade fiber optic gyroscopes.
A 30-mm-length YVO<sub>4</sub>/Nd:YVO<sub>4</sub>/ YVO<sub>4</sub> composite crystal was used as self-Raman gain material. Yellow
radiation at 587 nm was obtained by utilizing a 15-mm-length LBO as frequency-doubling crystal. The maximum
average power at 587 nm is up to 8.05 W at the pulse repetition rate of 50 kHz and the pump power of 65 W, with
the corresponding optical conversion efficiency of 12.38%. The shortest pulse width, the highest peak power and the
maximum pulse energy were measured to be 5.57 ns, 22.1 kW, and 161 μJ, respectively.