Mengfan Cheng

Security-Enhanced OFDM-PON Using Hybrid Chaotic System

A dual-field encryption scheme of an orthogonal frequency division multiplexing passive optical network (OFDM-PON) is proposed based on analog-digital hybrid chaotic system. In our scheme, the downstream data are encrypted in optical field, and the upstream data are encrypted in electrical field. The hybrid chaotic system circumvents the security vulnerabilities of both analog and digital chaos, e.g., the periodicity of digital chaos is masked by the analog one, and the time delay signature of the analog system is concealed by injecting digital chaos. Meanwhile, the key space dimension of the system is enlarged. Simulation results show both the feasibility and security of the proposed OFDM-PON system.

Secure OFDM-PON System Based on Chaos and Fractional Fourier Transform Techniques

We propose a novel method to simultaneously improve the physical layer security and the transmission performance of the orthogonal frequency division multiplexing (OFDM) passive optical network system by using chaos and fractional Fourier transform (FrFT) techniques. The designed 3-D chaotic sequences are used to form the training sequence for time synchronization, to perform the OFDM subcarriers masking, and to control the fractional order of the FrFT operation. The analyses show that the whole key space size of the proposed scheme could be beyond 1050, and the peak-to-average-power-ratio of the transmitted OFDM signal can be decreased by about 0.5 dB. Furthermore, we successfully demonstrate an 8.18 Gbps 16-quadrature-amplitude- modulation (QAM)-OFDM data transmission experiment with chaotic and FrFT operations over 25 km single mode fiber. The results show that the proposed scheme could effectively enhance the system security and the transmission performance without additional bandwidth requirement.

Enhanced secure strategy for electro-optic chaotic systems with delayed dynamics by using fractional Fourier transformation

We propose a scheme whereby a time domain fractional Fourier transform (FRFT) is used to post process the optical chaotic carrier generated by an electro-optic oscillator. The time delay signature of the delay dynamics is successfully masked by the FRFT when some conditions are satisfied. Meanwhile the dimension space of the physical parameters is increased. Pseudo random binary sequence (PRBS) with low bit rate (hundreds of Mbps) is introduced to control the parameters of the FRFT. The chaotic optical carrier, FRFT parameters and the PRBS are covered by each other so that the eavesdropper has to search the whole key space to crack the system. The scheme allows enhancing the security of communication systems based on delay dynamics without modifying the chaotic source. In this way, the design of chaos based communication systems can be implemented in a modular manner.

Time-Delay Concealment in a Three-Dimensional Electro-Optic Chaos System

A three-dimensional (3D) chaotic system with/without time delay based on electro-optic nonlinear devices is proposed. The dynamical properties of the system are demonstrated using the bifurcation diagram, and the dynamical complexity is quantified by the permutation entropy. Moreover, when a time delay module is added to the system model, the security performance is analyzed via the autocorrelation function, delayed mutual information, and permutation information analysis. Numerical simulations show that the time-delay signature can be concealed by the system itself without any additional operations. The proposed 3D chaotic oscillator has potential applications in secure communication, random number generation, and chaos computing.

Electro-optic chaotic system based on the reverse-time chaos theory and a nonlinear hybrid feedback loop

A novel electro-optic chaos source is proposed on the basis of the reverse-time chaos theory and an analog-digital hybrid feedback loop. The analog output of the system can be determined by the numeric states of shift registers, which makes the system robust and easy to control. The dynamical properties as well as the complexity dependence on the feedback parameters are investigated in detail. The correlation characteristics of the system are also studied. Two improving strategies which were established in digital field and analog field are proposed to conceal the time-delay signature. The proposed scheme has the potential to be used in radar and optical secure communication systems.

Enhanced Secure Strategy for OFDM-PON System by Using Hyperchaotic System and Fractional Fourier Transformation

We propose and experimentally demonstrate a scheme whereby hyperchaos and fractional Fourier transform (FrFT) techniques are integrated in an orthogonal frequency-division multiplexing (OFDM) passive optical network system. In our experiment, both security issues and transmission performance are investigated under an overall frame, and 7.64-Gb/s 16-quadrature-amplitude-modulation OFDM data with a four-level encryption scheme are successfully transmitted over a 25-km standard single-mode fiber. The results show that the system security and the transmission performance can be improved simultaneously. Moreover, the proposed scheme allows a flexible adjustment between the safety and the transmission performance according to the actual requirements.

An Optically Coupled Electro-Optic Chaos System With Suppressed Time-Delay Signature

We present an optically coupled chaotic system involving three-phase modulated electro-optic nonlinear loops and an optical coupler. The dynamical properties and the time delay signature (TDS) suppressing performance of the system is analyzed in detail. Numerical results show that the TDS can be suppressed not only under statistical analysis of a single output, but also under mutual statistical analysis of the multiple outputs. Compared with the intensity modulated electrically coupled scheme, the presented system has less interior noise due to the simpler construction.

A new switching parameter varying optoelectronic delayed feedback model with computer simulation

In this paper, a new switching parameter varying optoelectronic delayed feedback model is proposed and analyzed by computer simulation. This model is switching between two parameter varying optoelectronic delayed feedback models based on chaotic pseudorandom sequences. Complexity performance results show that this model has a high complexity compared to the original model. Furthermore, this model can conceal the time delay effectively against the auto-correlation function, delayed mutual information and permutation information analysis methods, and can extent the key space, which greatly improve its security.

High-frequency reverse-time chaos generation using an optical matched filter

The optical reverse-time chaos is realized by modulating a binary pseudo-random bit sequence onto an optical carrier, and then driving an optical matched filter. The filter is demonstrated experimentally by using two fiber Bragg gratings and a Fourier-domain programmable optical processor. The complexity relationship between the binary input sequence and the output chaos signal is studied. This approach could be a novel way to generate a high speed repeatable and controllable optical chaos signal, which has the potential to be used in optical secure communication systems.

Inverse-designed single-step-etched colorless 3 dB couplers based on RIE-lag-insensitive PhC-like subwavelength structures

Inverse-designed free-form nanophotonic structures have shown great potential in designing ultra-compact integrated photonic devices, but strict fabrication requirements may hinder further applications. We propose here a photonic-crystal-like (PhC-like) subwavelength structure, which is insensitive to the lag effect that is the most common fabrication error. A colorless 3 dB coupler employing such a structure is designed, fabricated, and characterized. With only one-step etching, the coupling region of our final device occupies a compact footprint of 2.72×2.72  μm. The simulated insertion loss of each output port is about 3.2 dB over 100 nm bandwidth around 1550 nm, and the measured insertion losses of both ports are 3.35 dB, on average, over the observable 60 nm bandwidth with a near zero loss imbalance.