Photonic layer security in fiber-optic networks and optical OFDM transmission

Abstract

Currently the Internet is experiencing an explosive growth in the world. Such growth leads to an increased data transmission rate demand in fiber-optical networks. Optical orthogonal frequency multiplexing (OFDM) is considered as a promising solution to achieve data rate beyond 100Gb/s per wavelength channel. In the meanwhile, because of extensive data transmission and sharing, data security has become an important problem and receives considerable attention in current research literature. This thesis focuses on data security issues at the physical layer of optical networks involving code-division multiple access (CDMA) systems and steganography methods. The thesis also covers several implementation issues in optical OFDM transmission.

Optical CDMA is regarded as a good candidate to provide photonic layer security in multi-access channels. In this thesis we provide a systematic analysis of the security performance of incoherent optical CDMA codes. Based on the analysis, we proposed and experimentally demonstrated several methods to improve the security performance of the optical CDMA systems, such as applying all-optical encryption, and code hopping using nonlinear wavelength conversion. Moreover, we demonstrate that the use of wireless CDMA codes in optical systems can enhance the security in one single-user end-to-end optical channel.

Optical steganography is another method to provide photonic data security and involves hiding the existence of data transmissions. In the thesis, we demonstrate that an optical steganography channel can exist in phase modulated public channels as well as traditional on-off-keying (OOK) modulated channels, without data synchronization. We also demonstrate an optical steganography system with enhanced security by utilizing temporal phase modulation techniques. Additionally, as one type of an overlay channel, the optical steganography technology can carry the sensor data collected by wireless sensor network on top of public optical networks, without disturbing normal public transmission.

Regarding optical OFDM, we investigated the effects of limited analog-to-digital converter (ADC) bandwidth on the reception of wide-spectrum optical OFDM signals. The results provide some insights in optical OFDM system design and implementation. Another innovation on optical OFDM in this thesis is that arrayed waveguide gratings (AWG), which are traditionally used as wavelength multiplexing/demultiplexing devices, are proposed to perform FFT/IFFT operation in pure optical domain, and therefore can be applied to implement an all-optical OFDM transmission system, in a real-time fashion. Therefore OFDM demultiplexing process can be achieved by a passive optical device without much power consumption.