Previous work have shown that the combined effects of negative third-order dispersion (TOD) and Raman self-scattering (RSS) can significantly enhance soliton compression in dispersion decreasing fibers (DDFs). In this paper, the effects of the negative TOD coefficient and the effective amplification of DDF′s on the performance of soliton compression are investigated. It is shown that for a given initial soliton width and a given effective amplification, there exists an optimum value of the negative TOD coefficient of the DDF at which the enhancement in soliton compression is maximum. It is also shown that the compression enhancement saturates when the effective amplification exceeds a certain value, which has been explained as a compromise between the higher-order effects induced increase of the ratio of input to output group-velocity dispersion coefficients of the DDF and the TOD induced non-adiabatic compression characteristics. The dependence of the compression enhancement on the initial soliton width have also be studied and the scheme is found works well for solitons with initial widths less than 3 ps.
Split-step Fourier method is used to numerically solve coupled nonlinear Schrdinger equation,and to study the properties of pulse propagation in the fiber with randomly varying birefringence.It is found that when the incidence power of the pulse exceeds a certain value,two polarizing parts will catch each other and propagate with the same velocity.This phenomenon is called strapping effect,which can validly repress polarization mode dispersion.
A scheme which reduced sliton interaction by initially soliton carring frequency shifts was introduced.The interaction of different soliton sequency was studied.The result show that the two solitons most outside were influenced mostly,so the introduction of a frequency shifts on them is suggested.The effect of frequency shift was studied,and the result show that there is an optmal amount of frequency shift to a certain system.
Recent works show that amplification and compression of ultrashort fundamental solitons in a gain-distributed nonlinear fiber loop mirror can not only avoid pulse distortion caused by nonlinear effects such as self-phase modulation etc.,but also overcome the difficulty of adiabatic amplification that the amplifier length must increase exponentially with the input pulse-width.Weak pulse amplification and compression in the gain-distributed nonlinear fiber loop mirror was investigated.Numerical results show that,as in the cases where the input pulses are fundamental solitons,distortion-free amplification and compression can also be realized when the input pulses have peak powers much lower than those of fundamental solitons,and that the amplified pulses are also close to fundamental solitons.The weaker the input pulse is, the larger the optimum gain of the loop mirror should be,and the higher-order effects have larger influences on the amplified pulses.
We suggested that single-mode fibers with slowly decreasing dispersion (FSDD) should be used for the generation of tunable ultrashort RAman pulses. A mathematical model is obtained for the description of ultrafast stimulated Raman scattering in optical fibers with slowly decreasing dispersion. Numerical simulations show that, under identical pump conditions, Raman pulse generated from this kind of fiber is shorter with a higher peak power than that generated from conventional fibers. This means that the Raman threshold of fibers with slowly decreasing dispersion may be lower than that of conventional fibers. Given pump conditions, we found that the highest peak power and narrowest width of the Raman pulse correspond to an optimal decrement velocity of the fiber dispersion.
Vector polarization mode switch mechanism of the vertical-cavity surface-emitting laser with anisotropic optical injection is numerically investigated. The results are as follows:First, when the injection current is near the threshold current, the polarization state of the VCSEL output is determined by the power of each polarization mode of the optical feedback injection,which is controlled by the external parameter of the VCSEL and the polarizer. Second, the polarization state of the VCSEL output induced by anisotropic optical feedback injection under the controll of polarizer changes periodically. Third, the x^-polarization mode competes drastically with the y^_polarization mode when the power of the x^-polarization of the feedback injection is equivalent to that of the y^_polarization, which induces slight external disturbance of the laser to break the balance of two competing polarization modes. So, on this condition, the polarization state is sensitive to the external parameter change. At last，the y^_polarization mode obtains enough big gain when the injection current is much higher above the threshold current. At this time, the output of the VCSEL is in steady y^_polarization mode. In other words, the polarization state of the VCSEL output is now independent of other parameters.
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