Characteristic Study On The Actively Mode-locked Fiber Laser Based On SOA

Ultra-short optical pulse sources with high repetition rate and the tunable central wavelength play an important role in the wavelength division multiplexing/optical time division multiplexing (WDM/OTDM) high-speed optical fiber communication system, all-optical transaction and all-optical network. Semiconductor optical amplifier (SOA) has some advantages such as the broad gain spectrum, high nonlinear coefficient, low power penalty and easily integrated, therefore it takes important effect in the mode-locked fiber laser. Recently, actively mode-locked ring lasers taking SOA as the gain medium have attracted much attention for generating high repetition rate, ultra-short and transform-limited optical pulses. However, we have noticed that, in the relative theoretical model describing the SOA based actively mode-locked ring lasers, the facet residual reflectivity and the nonlinear polarization rotation of the SOA are usually neglected for simplicity. Although the facet residual reflectivity and the nonlinear polarization rotation can be decreased by adopting all sorts of methods, they always exist. Therefore it is necessary to investigate the influences of the facet residual reflectivity and the nonlinear polarization rotation on the characteristics of mode-locked ring lasers based on SOA.In this paper, after considering the facet reflectivity of the SOA, using the rate equation including gain compression and the gain asymmetric distribution to describe the influence of SOA on the optical pulse and adopting the Schrodinger equation to describe the pulse amplitude evolution in the fiber, a theoretical model of the harmonic mode-locked fiber ring laser based on SOA has been established. Based on this model and self-reproduction theory, the mode-locked pulse shape can be obtained through numerical simulation. Therefore the influence of the facet residual reflectivity on the shape, peak power, and pulse width of the pulse output from the harmonic mode-locked fiber ring laser can be investigated. The results show that the facet residual reflectivity will affect greatly the mode-locked pulse, with the increase of the facet residual reflectivity, the peak power will increase and the mode-locked pulse will be wider.After considering the nonlinear polarization rotation in SOA, a theoretical model of the harmonic mode-locked fiber ring laser has been established in this paper. Based on this model, it has been investigated that the influence of the nonlinear polarization rotation in SOA on the shape,...