All-optical XOR Logic Gates And Encryption/decryption Based On Semiconductor Optical Amplifier

As the communication techniques advance, information security is an important concern in many aspects. The optical fiber links, once thought to be inherently secure, can be accessed at ease and directly tapped using simple optical equipment, which will threathen the optical network security. There are increasing reliance on the logic circuits of optoeletronic conversion for the optical encryption. However, the electronic devices have an inherent “electronic bottleneck” in dealing with high-speed optical speed. Recently, much attention has been focused on the all-optical signal processing, as it can not only avoid the complicated optical/electrical/optical(O-E-O) conversion but also reduce the latency in processing the high-speed optical signals. As a key part, the all-optical(Exclusive-or) XOR logic gate is the main building block in data encryption and decryption. Semiconductor optical amplifier(SOA) is very suitable for the all-optical XOR logic gate due to its advantages such as high nonlinearity and potential for easy integration.This paper will focus on the realization of high-speed all-optical XOR logic gates based on SOA and the technique for all-optical encryption and decryption further. Our research work is conducted as follows:(1) We established the frequency domain model of turbo-switch and investigate the experiment of multiple cascaded SOAs. The SOA inherent slow carrier recovery time limits its operation speed, but the novel switch structure—turbo-switch can enhance its response speed extensively. The frequency domain model of turbo-switch will be established which has taken the spatial inhomogeneity of the saturated SOA gain into consideration for the first time. The small signal frequency response cures will be simulated to analyze its operation bandwidth. At the same time, we will demonstrate the experiment of multiple cascaded SOAs and analyze impact of the number of SOA on the operation speed.(2) We conducted the 85 Gbit/s all-optical XOR logic based on turbo-switch and dual ultrafast nonlinear interferometer and propose a novel switch configuration based on turbo-switch to realize XOR logic gate. We demonstrated the 85 Gbit/s all-optical XOR logic gate experiment to verify the fast gain response of turbo-switch. In order to realize more stable all-optical XOR logic, a novel structure is put forward which sets the turbo-switch in the arms of Mach-Zehnder Interferomter(MZI).(3) Utilizing the XOR logic gate based on four wave mixing(FWM) in SOA, the all-optical encryption/decryption for non-return-to-zero differential phase-shift keying(NRZ-DPSK) signals at 10 Gbit/s was successfully demonstrated in the experiment. The proposed all-optical encryption/decryption scheme can be operated at much higher data rate as the XOR logic is originated from the ultrafast intraband FWM process. Due to the constant envelope nature of NRZ-DPSK signals, the pattern effect associated with SOA carrier dynamics is also alleviated.