Experimental Research Of Alloptical Switch Based On Nonlinear Sagnac Interferometer Contained EDFA

With the rise of the demand for the information transmit capacity and transmit speed, all optical network with the help of Dense Wavelength-Division Multiplexing (DWDM) and all optical exchange technique will be consider firstly as the new-generation high-speed integrated network .The optical switches as key devices in all-optical exchange are increasingly play an important role.They mainly apply to the functions of the optical routing, the wavelength selection,the OXC and the self-reparation and protection. With the rapid increase of communication rate, it has a higher demand on the switching speed of optical switch. The optical switch controlling with light, i.e. all optical switch (AOS), is paid more and more attention by scientists due to their advantages: stable, high speed, large capability, and without O-E-O conversion.As a new type and widely applied fiber device, Sagnac interferometer has many advantages: with compact structure, working stable, easy fabrication, insensitive to the environment etc. It can be flexible to made the all-optical devices with different configurations.In this thesis, based on the working principle of the nonlinear Sagnac interferometer, we firstly introduce several all-optical switches based on the third-order optical nonlinearity (Kerr effect) in the fiber, deduce their switching power threshold, and analyze their advantage and disadvantage. Then we focus on the switching properties under the continuous and pulse input signal in the nonlinear Sagnac interferometer optical switch, in which an optical amplifier is asymmetrically inserted into the fiber loop.On the aspect of experiment, we fabricated a Bi-direction EDFA in the laboratory condition. The performances of fabricated EDFA are measured and analyzed. We asymmetrically inserted it into the fiber loop of Sagnac interferometer, and then measured its switching properties. In the case of continuous input signal, the EDFA increases the optical power in the loop, the SBS was induced, and it seriously influences the measurement results. In order to avoid the influence of SBS, the laser source is changed to be a femtosecond pulsed laser. At the same time, a short erbium-doped fiber is instead of several- thousand-meter common single-mode fiber as the loop fiber, so that the nonlinearity in the loop is enhanced. Taking account of that the gain of EDFA drops quickly when increasing the signal power, we fix the input signal power. By changing the pump power of EDFA, we can observe the switching change of transmitted output power. This is a cross-modulation all-optical switch.