RED-Shifted Chirp Characteritics Of Semiconductor Optical Amplifiers

The optical-electrical-optical signal exchange system deployed in current optical fiber communication network has seriously limited the further expansion of the bandwidth. Instead, all-optical network has gradually become the development trend of the future network. In all-optical network, to achieve all-optical transparency at the notes, one key factor is todevelop the nonlinear devices used in all-optical signal processing. As one of the nonlinear devices, semiconductor optical amplifiers(SOAs)have widely used in all-optical signal processing because they have the advantages of large nonlinear coefficient, low power consumption, small volume and large scale of integration. However, the long gain recovery time of SOAs limits the operating speed. The frequency chirp is an important physical parameter of SOAs. Sincethe ultrafast frequency chirp can acceletate the gain recovery speed, it has become one of the hot research topics and is widely applied to the ultrafast signal processing,In this paper, we introduce the developmentofSOAs, their application in all-optical signal processing and fundamental theory. Besides, the red-shifted chirp characteristics of SOAs are also introduced. Themain contributions of this dissertation are summarized as following:1. Taking into account the effect of both the ultrafast nonlinear effects ofSOAsand the optical band pass filter, we deduce the basic transport equation and carrier rate equation and set up the corresponding numerical filtering simulation model.With the help of the model, we simulate the frequency chirp characteristics ofSOAs, and its corresponding relation with the gain.2. Analysis the relation between the frequency chirp and the working conditions such as pump pulse energy, detecting signalpower, DC bias current and pulse rate. When the pattern effect caused by the higher pulse rate becomes more serious, the change of the frequency chirp along with the gain is shown. A10 Gbit/s output signal is obtained with a red-detuned optical bandpass filter utilized red-shifted chirp, which also explains theeffect of the red-shiftedchirp characteristics on the output waveform.3. When a signal red-detuned filter is used, with the increase of pulse rate, the influence of pattern effectbecomes more serious. As a consequence, the output waveform becomes poorer. To solve this problem, a new solution, the scheme of the combination of two filters is proposed in this paper. The structure and the principle of the schemeand the roles of two filtersare introduced in detail.A 20 Gbit/s signal are achievedin simulation and experimentsbyusing the new scheme, which further demonstrats the shaping effect of the combination of two filters on the output waveform and verifies the feasibility of the scheme.