Li Qiliang

A digital audio watermark embedding algorithm with WT and CCT

This paper propose an audio digital watermarking algorithm based on the wavelet transform (WT) and the complex cepstrum transform (CCT). The algorithm realized to embed a binary image watermark into the audio signal and improved the imperceptibility of watermarks. Experimental results show that this algorithm has a better robustness against common signal processing such as noise, filtering, resampling and lossy compression.

Watermarking for the digital images based on model of human perception

As an effective method to provide copyright protection for digital media, digital watermarking has drawn extensive attention recently. The paper proposes a scheme of digital watermarking based on the modulation transfer function (MTF) of the human visual system(HVS). The experimental results demonstrate its better unification between the watermarking robustness and watermarking invisibility, the watermarking with the proposed scheme is robust against noise interference and commonly used image technique.

Exact periodic solution in coupled nonlinear Schrodinger equations

The coupled nonlinear Schrodinger equations (CNLSEs) of two symmetrical optical fibres are nonintegrable, however the transformed CNLSEs have integrability. Integrability of the transformed CNLSEs is proved by the Hamilton dynamics theory and Galilei transform. Making use of a transform for CNLSEs and using the ansatz with Jacobi elliptic function form, this paper obtains the exact optical pulse solutions.

Numerical study of short pulse propagation and switching in active two-core nonlinear fiber couplers

The propagation and switching of short pulses in an active two-core fiber nonlinear directional coupler have been investigated theoretically by using the numerical simulation method. The analysis highlight the effects of the second order coupling coefficient dispersion, the linear gain coefficient and the finite gain bandwidth on the propagation and switching of short pulses. We demonstrate that with the influences of the second order coupling coefficient dispersion, the linear gain can sharpen the switching characteristic, lower considerably the switching threshold power, as well as increase significantly the switching efficiency. On the contrary, both the second order coupling coefficient dispersion and the finite gain bandwidth, degrade the switching characteristics. The interplay between the second order coupling coefficient dispersion and the linear gain coefficient on pulse propagation can cause pulse periodic fluctuation associated with pulse compression and amplification. Additionally, pulse compression and amplification induced by linear gain can be significantly suppressed by the interplay between the second order coupling coefficient dispersion and the finite gain bandwidth on pulse propagation, consequently, as in the case of the passive fiber coupler, optical pulses tend to restore periodical coupling propagation in active two-core fiber coupler.

Theoretical analysis of the wavelength-dependent gain for fiber optical parametric amplifier driven by one pump wave

By use of the coupled equations of pump, signal and idler field, this paper have derived the gain expression of fiber optical parametric amplifier with high-order dispersion and high nonlinear optics. It is indicated that the optical parametric amplifierpsilas gain is dependent of pump wavelength near zero dispersion wavelength. Gain and bandwidth are better when pump wavelength is close to zero dispersion wavelength. But when the difference of pump wavelength and zero dispersion wavelength exceeds some value, gain and bandwidth are smaller. If pump power is not exhausted, gain is linear with transmission distance.

Effects induced by the third-order dispersion in TPC system

This paper shows the compensation progress of the second-order dispersion and the self-phase modulation (SPM) in temporal phase conjugation (TPC) system. And it gives a description of oscillations induced by the third-order dispersion. The theoretical analysis and numerical simulations reveal that TPC can only compensate for second-order dispersion and SPM but enhance effects caused by the third-order dispersion.