Orthogonal DPSK/CSK modulation and public-key cryptography-based secure optical communication

In this letter, the information security of an optical code-based communication system employing orthogonal differential phase-shift keying (DPSK)/code-shift keying (CSK) modulation is first investigated using two eaves dropping methods, one-bit delay interference detection and differential detection. The investigation results show that the security vulnerability exists only in the CSK channel while the DPSK channel can thwart these attacks. Therefore, the concept of public-key cryptography is introduced into the system to efficiently use these two orthogonal channels for both public key distribution and encrypted data transmission. The privacy of the transmitted data can be double guaranteed by public-key cryptography scheme logically and optical code-processing techniques physically.