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Optics Express

Bit-by-bit optical code scrambling technique for secure optical communication

Xu Wang, Zhensen Gao, Xuhua Wang, Nobuyuki Kataoka, Naoya Wada

Published Feb 8, 2011• 22 citations
Publisher

Abstract

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.

DOI
10.1364/oe.19.003503

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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.
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.
A theoretical model is proposed to analyze the time-domain spectral phase en/decoding and evaluate the unconditional security of the optical code-based secure optical communication systems with DPSK modulation. The confidentiality of the systems with and without bit-by-bit code scrambling technique is investigated. It mathematically proves that the system without code scrambling lacks confidentiality and the system employing code scrambling can realize unconditionally secure transmission. Furthermore, encoding only within the central band of the spectrum is sufficient for perfect secrecy, and the secrecy rate can be potentially improved. It allows the system to operate in the burst mode for code generation and encoding and thus have an idle time for rearm.
In this paper, we propose a novel synchronous time-domain spectral phase encoding/decoding (SPED) scheme for secured optical communication. The pulse generator generates short optical pulses at data-rate, the SPE consists of a pair of dispersive components with opposite dispersion values (+D and -D) to stretch/compress the optical pulse and a phase modulator (PM) or a hybrid intensity/phase modulator (IM/PM) for data and OC modulation. The spectral phase decoding (SPD) is similar to the SPE with a PM synchronously driven by OC (the complementary pattern of OC) at a repetition rate equal to the data-rate. The OCs thus can be rapidly reconfigured even bit-by-bit to enhance the system confidentiality.
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.