Investigation Of High Speed Fiber-Optic Transmission System Using A LiNbO₃ External Modulator

Fiber-optic communication has various advantages, it has achieved rapid development since been put into business applications. It has been over two decades since the first experiment of fiber communication was operated in 1978. Fiber-optic communication technologies have been put into commerce step by step. The speed of fiber-optic communication has been growing from 45Mbit/s to 40Gbit/s and more. Fiber-optic communication brings all of world into the information century with very high speed. It has become a new high technique growth pole and the support of economy. Main-bone net of optical telecommunication now covers all cities in the world, and link with metropolitan nets, local nets and access nets. It is objected to be FTTH (Fiber Telecommunication to Home). Multimedia data volume is going to exceed voice data volume and becoming dominant service. Increase of user's requirement enforce developing the data transmission rate and capacity in great speed. A point-to-point single link is one of the key techniques in the field of fiber-optic communication technologies.Under this background, the author develops a 10 Gbit/s fiber-optic transmission system using a LiNbO3 external modulator by Processor Guo Yubin during the postgraduate study which shows advantage of having smaller chirp effect than EA modulator. This system employs NRZ format, GaInAsP multiple-quantum-well DFB lasers and LiNbO3 electro-optic modulator. Transmission distance without regeneration is about 80km. WDM technology is used to multiplex signal. This paper studied and had carried on the experiment in the expectation of offering the theory and experiment reference for the investigation of high speed fiber-optic communication system.Firstly, the thesis introduced the basic principle of fiber-optic communication, organizational structure and its development trend. The transmission characteristics were analyzed. The source of dispersion and optical nonlinear effect limiting transmission rate and characteristics of system were analyzed in details.Secondly, the design principles and methods of fiber-optic transmission system were introduced in details. We studied the thesis on the basic configuration design of 10Gbit/s fiber-optic transmission system, choice of components in the view of low cost and practicality. Through power budget and time budget, we evaluated all system structure on possibility and reasonability. We conducted a computer simulation to optimize the structure.Finally, on the basis of theoretical design, the apparatus and components for the experiment were actively prepared and set up. The structure of 10 Gbit/s fiber-optic transmission system was established, achieving 10G optical signal transmission without regeneration, no bit error. The transmission experiment was carried through, and every parameter of the system was got, the factors that affect the transmission quality were also analyzed, some key questions were studied. Power loss, crosstalk, bit error and other aspects of the transmission characteristics of the system were tested. The eye-diagrams and the eyelid were ideal. The coding jam and signal aberrance were not detected. When back to back the sensitivity of receiver was about -26.76 dBm and the power load was about -1.5 dBm. After 80 km, the lowest power of receiving was about -26.76 dBm. The power penalty was about 0.49dB. There was no BER floor in the system. The system showed a good performance.The relationship between extinction ratio and optical receiver sensitivity was investigated. For long-distance high-speed optical transmission, a limited extinction ratio can partly compensate fiber linear and nonlinear effects. In a certain range, high extinction ratio can improve receiver sensitivity and increase transmission distance. Through experiments, when the optical signal sent to 11.61 dB extinction ratio, the system can be error free transmission. It achieves more satisfactory. BER is the most basic performance indicators. Input optical power has great impact on BER. The relationship between BER and input optical power was also investigated. Input optical power at a certain value, if the optical power to further increase value, the error rate will be increased with the increase of opticalpower. It is due to the nonlinear effect. We had to select the appropriate value of input optical power to carry out such experiments. The impact of Laser for characteristics of system was analyzed in details.In sum, this thesis analyzes the principle, design process, debugging process, output characteristic mensuration of high speed fiber-optic transmission system. I hope that these researches could provide worthy theories and the technique support for further research and development.