Experimental Investigation Of Chaotic Fiber-optic Secure Communications

Chaotic optical secure communications is a hardware-based encryption technique at the physical layer. Compared to the RSA public key encryption system, chaotic optical secure communications has the advantages of security, high-speed and real-time. In recent years, the great progress has been made on the chaotic optical secure communications both in the theoretical and experimental aspects. However, it is still someway from realizing practicality. It is necessary for chaotic optical secure communications to be compatible with the existing optical network. What’s more, in to save fiber link and equipment costs, how to achieve bi-direction transmission over the same optical fiber channel is another problem need further study. In this thesis, the chaotic optical communication system based on optical fiber channel has been experimentally studied. The main works done in this thesis are as follows.(1) The chaotic receiver and the chaos modulation based chaotic optical secure communications are investigated by modeling and simulation. Then, the generation of chaotic optical carrier and synchronization between the transmitter and receiver lasers is achieved experimentally. Using DFB LD as light source, the chaotic optical carrier is generated by optical feedback and proper parameters adjustment. The synchronization between transmitter and receiver lasers can be realized by employing the open-loop scheme. When parameters of the receiver with strong optical injection are well matched with the transmitter, the correlation coefficient of the chaotic optical carriers generated by the transmitter and receiver can be up to0.96.(2) The chaotic optical secure communications with data rate of1.25Gb/s and2.5Gb/s are experimentally realized and the transmission distance is up to90km and25km, respectively. In the experiment, the message is hidden within the chaotic optical carrier by a Mach-Zehnder Modulator. At the receiver, the message can be decrypted through chaotic synchronization between the transmitter and receiver lasers. The Q-factor of the recovered messages can be up to2.1and2.2for the encrypted messages of1.25Gb/s and2.5Gb/s, which means good decryption performance. What’s more, an injected chaotic transmitter is adopted to enhance the bandwidth of the chaotic optical carrier and further increase the security of the2.5Gb/s-message.(3) The wavelength division multiplexing (WDM) between chaotic optical secure channel and conventional fiber-optic channel, and the WDM between two chaotic optical secure channels are experimentally investigated without the dispersion compensation during transmission. When the channel spacing is3nm, the two types of WDM in which each channel carries a1.25-Gb/s message, can be realized by optimizing the injection strength, transmission distance, optical launched power and the amplitude of the message. For the WDM between chaotic optical secure channel and conventional fiber-optic channel, the multiplexing distance can be up to100km, and for the WDM between two chaotic optical secure channels, the multiplexing distance can be up to25km.(4) The bi-direction chaotic optical secure communications with data rate of1.25Gb/s is experimentally achieved based on both single wavelength and dual-wavelength. For the dual-wavelength case, the bi-direction chaotic optical secure communications is realized by using wavelength division multiplexer, and the transmission distance is25km. For the single wavelength case, the bi-direction chaotic optical secure communications is realized by using optical circulator, and the transmission is11km. The bit error rates of the recovered messages at both ends of the communication are10-4.