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Optics Letters

Rapid programmable/code-length-variable, time-domain bit-by-bit code shifting for high-speed secure optical communication

Zhensen Gao, Bo Dai, Xu Wang, Nobuyuki Kataoka, Naoya Wada

Published Apr 26, 2011• 29 citations
Publisher

Abstract

We propose and experimentally demonstrate a time-domain bit-by-bit code-shifting scheme that can rapidly program ultralong, code-length variable optical code by using only a dispersive element and a high-speed phase modulator for improving information security. The proposed scheme operates in the bit overlap regime and could eliminate the vulnerability of extracting the code by analyzing the fine structure of the time-domain spectral phase encoded signal. It is also intrinsically immune to eavesdropping via conventional power detection and differential-phase-shift-keying (DPSK) demodulation attacks. With this scheme, 10 Gbits/s of return-to-zero-DPSK data secured by bit-by-bit code shifting using up to 1024 chip optical code patterns have been transmitted over 49 km error free. The proposed scheme exhibits the potential for high-data-rate secure optical communication and to realize even one time pad.

DOI
10.1364/ol.36.001623

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We propose and experimentally demonstrate a time-domain bit-by-bit code-shifting scheme that can rapidly program ultralong, code-length variable optical code by using only a dispersive element and a high-speed phase modulator for improving information security. The proposed scheme operates in the bit overlap regime and could eliminate the vulnerability of extracting the code by analyzing the fine structure of the time-domain spectral phase encoded signal. It is also intrinsically immune to eavesdropping via conventional power detection and differential-phase-shift-keying (DPSK) demodulation attacks. With this scheme, 10 Gbits/s of return-to-zero-DPSK data secured by bit-by-bit code shifting using up to 1024 chip optical code patterns have been transmitted over 49 km error free. The proposed scheme exhibits the potential for high-data-rate secure optical communication and to realize even one time pad.
We propose and demonstrate a novel bit-by-bit code scrambling technique based on time domain spectral phase encoding/decoding (SPE/SPD) scheme using only a single phase modulator to simultaneously generate and decode the code hopping sequence and DPSK data for secure optical communication application. In the experiment, 2.5-Gb/s DPSK data has been generated, decoded and securely transmitted over 34 km by scrambling five 8-chip, 20-Gchip/s Gold codes with prime-hop patterns. The proposed scheme can rapidly reconfigure the optical code hopping sequence bit-by-bit with the DPSK data, and thus it is very robust to conventional data rate energy detection and DPSK demodulation attack, exhibiting the potential to provide unconditional transmission security and realize even one-time pad.
Achieving high speed physical layer security is a constant pursuit but critical challenge for the information society. In this paper, a novel symbol-by-symbol optical phase encryption technique relying on ultra-long, reconfigurable optical phase patterns and commercial off-the-shelf dispersive components is proposed for high speed physical layer security. A record 40Gb/s secure optical communication system with symbol overlapped, optical phase encrypted differential-phase-shift-keying modulated signal is experimentally demonstrated based on the proposed technique. Security robustness against various eavesdropper's attacks has been validated for three optical codes with a chip rate of 40Gchip/s and variable code-length of 128-chip, 512-chip and 1024-chip, respectively. The demonstrated technique exhibits the advantages of supporting high bit rate operation and advanced optical modulation formats, improving code flexibility and cardinality, which makes it very promising for future ultra-fast secure optical communication.
We propose and experimentally demonstrate a 40 Gb/s secure optical communication system with on-off-keying (OOK) modulation format by using a time domain spectral phase en/decoding scheme, which employs a highly dispersive element and high-speed phase modulator for introducing significant symbol overlapping for both the encoded and incorrectly decoded noiselike signals to enhance the information security against eavesdropping using a power detector. The influence of dispersion and chip modulation rate on the symbol overlapping of the incorrectly decoded signal has been analytically investigated and experimentally verified. Security enhancement for 40 Gb/s OOK data using fast reconfigurable 40 Gchip/s optical codes with code lengths of up to 1024 has been demonstrated and compared with a 10 Gb/s system.
In this paper, we review the recent advances and demonstrations of time domain pseudorandom optical phase encoding technology for high speed 40Gb/s OOK and DPSK secure optical communication systems. Bit-by-bit code shifting technique for enhancing the information security is proposed and demonstrated in different optical transmission systems with various bit rates and modulation formats. The potential application of the proposed techniques for high speed secure optical transmission systems is envisioned.
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.
We propose and experimentally demonstrate a transparent optical-code-division multiplexing (OCDM) overlay public dense wavelength-division multiplexing (DWDM) network architecture enabled by a passive spectral notch filter for extracting and detecting a secure OCDM signal, which employs a time domain spectral phase encoding/decoding scheme that can simultaneously generate differential-phase-shift-keying (DPSK) data and optical code patterns using only a single phase modulator. The time domain encoded OCDM signal has been scrambled bit-by-bit by a prime hopping pattern and concealed in the public DWDM channels to significantly improve the OCDM channel security. The effect of optical code patterns, the channel number, and bandwidth of the spectral notch filters on the system performance has been theoretically simulated and experimentally validated. In the experiment, error-free transmission of a 2.5-Gb/s time domain spectral phase encoded DPSK–OCDM signal with three 8-chip, 20-Gchip/s optical codes and a scrambled code pattern in the transparent OCDM overlay two-channel 10-Gb/s DWDM network has been successfully demonstrated.