High-quality Chaos Synchronization Research Articles

Experimental demonstration of an 8-Gbit/s free-space secure optical communication link using all-optical chaos modulation.

For the first time, to the best of our knowledge, we experimentally demonstrate a high-speed free-space secure optical communication system based on all-optical chaos modulation. The effect of atmospheric turbulence on optical chaos synchronization is experimentally investigated via a hot air convection atmospheric turbulence simulator. It is shown that, even under moderately strong turbulent conditions, high-quality chaos synchronization could be obtained by increasing the transmission power. Moreover, a secure encryption transmission experiment using a high bias current induced chaotic carrier for 8-Gbit/s on-off-keying data over a ∼10-m free-space optical link is successfully demonstrated, with a bit-error rate below the FEC threshold of 3.8 × 10-3. This work favorably shows the feasibility of optical chaotic encryption for the free-space optical transmission system.

Dual-Channel Secure Communication Based on Wideband Optical Chaos in Semiconductor Lasers Subject to Intensity Modulation Optical Injection

Chaotic optical communication was initially proposed to provide advanced physical layer security for optical communication. Here, we propose and numerically demonstrate an optical chaos communication scheme based on semiconductor lasers subject to intensity modulation optical injection for secure transmission of quadrature amplitude modulation (QAM) messages. In this scheme, two chaotic sources were generated with different modulation parameters and acted as chaotic carriers at the transmitter side, which were subsequently used to drive two receivers in two separate channels. Numerical results demonstrate that this scheme allows for broadband chaos generation and high-quality chaos synchronization can be achieved to simultaneously encrypt two messages for secure communication; a 20 GBaud 16-QAM message was recovered correctly with a transmission distance in standard single mode fiber (SMF) over 120-km, while the other 20 GBaud 64-QAM message was limited to a 20-km fiber transmission distance. The system performance was systematically evaluated by analyzing the bit error ratio (BER) of the recovered message versus the masking coefficient and the transmission distance. Furthermore, our simulations justify the robustness against the mismatch of parameters. Therefore, we hope that this scheme can be experimentally implemented for high-speed chaos communication and secure key distribution.

Security-enhanced watermark embedding and transmission based on synchronized chaotic semiconductor lasers

In this paper, we propose and numerically demonstrate a chaotic watermarking encryption and secure transmission scheme based on two synchronized response lasers (RLs) subject to identical injection from a driving laser (DL). In this proposed system, the chaotic signal from DL can be optimized after passing through a phase modulator and a dispersion component, then the chaotic signal with large bandwidth and low time delay signature is obtained. Simultaneously injecting this chaotic signal into two identical RLs, high-quality chaos synchronization between two RLs can be realized. Both synchronized chaotic signals are, respectively, divided into two parts. One is used to generate shared keys required by the watermarking encryption, and the other is used as chaotic carrier to realize the secure message transmission. After introducing the synchronized optical chaos into the watermarking encryption algorithm, the normalized correlation of the extracted watermark without long-distance transmission is 0.9554 and can still maintain above 0.9 over 200 km transmission fiber. The message transmission and watermark extraction have good robustness to the fiber parameter mismatches, and excellent performances can be maintained even within 20% mismatches range. In our method, synchronized high-quality optical chaotic signals from two RLs are used to watermark embedding and transmission, and double encryption can be realized, which can open a new path for future high-speed and security-enhanced watermark embedding and transmission.

High-speed secure key distribution based on chaos synchronization in optically pumped QD spin-polarized VCSELs.

We propose and numerically demonstrate a high-speed secure key distribution (SKD) based on polarization-keying chaos synchronization in two quantum dot (QD) spin-polarized vertical-cavity surface-emitting lasers (VCSELs) without any external feedback. In this scheme, high-quality chaos synchronization can be obtained when the response lasers have the same polarization ellipticity. The proposed SKD scheme is benefited from the feasible tunability of the pump polarization ellipticity, and no other complex components are necessary. Moreover, the open-loop configuration is constructed in the commonly driven lasers and results in a short synchronization recovery time of hundreds of picoseconds, which is much shorter than that in most previous reports. Combined with these merits, a 1.34 Gb/s SKD with a bit error ratio lower than 3.8 × 10-3 can be achieved. The current study provides a new way to realize high-speed physical key distribution.

Chaos synchronization based on cluster fusion in asymmetric coupling semiconductor lasers networks.

A novel cluster fusion method is proposed, based on which chaos synchronization in asymmetric coupling semiconductor lasers (ACSLs) networks is systematically demonstrated. Take the cluster fusion of a mutually-coupled network composed of 7 semiconductor lasers (SLs) for instance, the characteristics of chaos synchronization as well as the influences of coupling strength, bias current, and mismatches of intrinsic parameters and injection strength on the quality of chaos synchronization in hybrid clusters composed of ACSLs are thoroughly investigated. The results show that by using cluster fusion, the ACSLs which originally belong to different clusters can form three types of new hybrid clusters, namely, trivial-hybrid cluster, trivial-nontrivial-hybrid cluster, and nontrivial-hybrid cluster. Compared with the low-correlation inter-cluster ACSLs of original SLs network, high-quality chaos synchronization is achieved in three types of newly generated hybrid clusters over a wide parameter range. Moreover, the cluster fusion and synchronization of side-SLs clusters of star-type SLs networks are also verified, which indicate the universality of the proposed method. This work provides a new way to realize the chaos synchronization among ACSLs of different clusters.

Bidirectional digital image secure transmission and recognition based on a long-distance chaos synchronization system with machine learning capability

Based on chaos synchronization of two response lasers (RLs) injected by the common chaos signals from a driving laser (DL) with double optical feedback (DOF) and an additional neural network (NN), a bidirectional chaotic secure communication system with machine learning capability is proposed and the long-distance digital image transmission and recognition performances are numerically investigated. The simulated results show that the time delay signature (TDS) of the driving chaotic signals from DL with DOF is greatly weakened under suitable operation conditions. Two RLs can generate chaos signals with low TDS and broad bandwidth, and the high-quality chaos synchronization between two RLs can be achieved while the synchronization quality between DL and any one of RLs is extremely bad, which is helpful to realize the secure communication. Using the synchronized chaos output signals from two RLs as chaos carriers and chaos masking (CM) encoding method, the bidirectional 10 Gb/s secure communication over 140 km fiber channel can be realized and the effects of the fiber parameters on the communication performances are discussed. After adopting an additional NN, a long-distance digital image transmission and recognition based on this proposed secure communication system can be realized and the communication distance can be extended to 220 km.

Secure Optical Communication Based on Cluster Chaos Synchronization in Semiconductor Lasers Network

We propose and numerically demonstrate a secure optical communication scheme in a small-world semiconductor lasers network based on cluster chaos synchronization and false-message scrambling. According to the symmetries of network, the semiconductor lasers are divided into sets of heterogeneous coupled clusters. The properties of cluster chaos synchronization, the performance and security of optical chaotic communication, as well as the influence of false message on the synchronization of clusters are systematically investigated. It is demonstrated that, by properly setting the parameters of the lasers network, high-quality chaos synchronization can be achieved between the intra-cluster lasers, whereas incoherent states are observed between inter-cluster lasers. Moreover, by inserting false messages into the inter-cluster couplings, the privacy of chaotic carriers transmitted over the inter-cluster public links can be significantly enhanced, as such secure bidirectional communication among intra-cluster lasers is achievable with a message bit rate of several Gbit/s. Compared with the conventional point-to-point communication systems, the proposed scheme supports multipoint-to-multipoint secure communications.

Experiment on 10-Gb/s message transmission using an all-optical chaotic secure communication system

We experimentally demonstrate 10-Gb/s message transmission using an all-optical chaotic secure communication system. In this system, a semiconductor laser subject to mirror optical feedback, operating under a high bias current, is employed as the transmitter. Owing to the high bias current, the transmitter’s relaxation oscillation frequency is greatly increased, and consequently, the carrier bandwidth of the transmitted message is also enhanced. By injecting the bandwidth-enhanced signal into an open-loop receiver, we establish a chaos synchronization with a correlation coefficient of 0.94 between the transmitter and the receiver. Based on the high-quality chaos synchronization, a 10 Gb/s message is experimentally encrypted and decrypted with a bit error ratio (BER) below 3.8 ×10−3, i.e., the hard decision forward error correction (HD-FEC) threshold. Bit error analysis indicates that the transceiver, using chaotic decryption, has a BER below the HD-FEC threshold over a wide parameter region. In this parameter region, it is difficult for an eavesdropper using direct decryption to obtain a message with a BER below the HD-FEC threshold.

Chaos synchronization and communication in closed-loop semiconductor lasers subject to common chaotic phase-modulated feedback.

We propose and demonstrate a closed-loop chaos system composed of external-cavity semiconductor lasers subject to common chaotic phase-modulated optical feedback (CCPMOF). The efficient-bandwidth and time-delay signature (TDS) characteristics of the chaotic carrier, the properties of chaos synchronization, as well as the performance and security of chaos communication are systematically investigated. The numerical results demonstrate that wideband chaotic carrier with effective TDS suppression can be easily obtained, high-quality chaos synchronization with considerable mismatch robustness, frequency detuning tolerance, and phase fluctuation tolerance can be achieved in a wide operation range, and high-speed chaos communication is available. With respect to the conventional closed-loop systems, the bandwidth and complexity of chaotic carrier is greatly enhanced, and the performances of chaos synchronization and communication are obviously improved.

Secure communication systems based on chaos in optically pumped spin-VCSELs.

We report on a master and slave configuration consisting of two optically pumped spin-vertical-cavity surface-emitting lasers for chaos synchronization and secure communication. Under appropriate conditions, high-quality chaos synchronization is achieved. We propose two encryption schemes, where either the pump magnitude or polarization is modulated. The results show that these allow for Gb/s transmission of secure data, but exhibit different features: one indicates that the message can be recovered by the total intensity, but not the polarization components, whereas the other shows that the message can be better or exclusively retrieved from the polarization components at high bit rates.

Exploiting Optics Chaos for Image Encryption-Then-Transmission

A novel symmetric image encryption-then-transmission system based on optical chaos using semiconductor lasers is proposed. In this paper, with identical chaotic injection from a master laser, two slave lasers (SL1 and SL2) can output similar chaotic signals served as chaotic carrier to transmit image. Meanwhile, the chaotic signal of SL1 can be used to generate the key of the encryption scheme. After employing the three-dimensional (3D) cat map and logistic chaotic map, the positions of image pixels are shuffled, and the relationship between the cipher-image and the plain-image is confused simultaneously. Therefore, the system can resist the common attacks such as statistical attack, differential attack, and brute force attack. Through numerical simulations, the high quality chaos synchronization between SL1 and SL2 is obtained. When the chaos masking technique is adopted, the image encrypted by the proposed encryption scheme can be successfully transmitted and decrypted in a 10 km single mode fiber channel from SL1 to SL2, which is accompanied by a bit error rate of less than ${\rm{6.18\,\times \,10}}^{- 19}$ . Exhaustive tests about security analysis are carried out, demonstrating the valuable feasibility and high security of the image encryption-then-transmission system.

Physically enhanced secure wavelength division multiplexing chaos communication using multimode semiconductor lasers

A physically enhanced secure wavelength division multiplexing chaos communication scheme in virtue of the chaos synchronization of two multimode semiconductor lasers (MSLs) is introduced. In this scheme, two communicating MSLs are subjected to identical optical injections from a chaotic external-cavity MSL, and each mode of the communicating MSLs is used as a chaotic carrier. The messages are divided into a set of blocks, and these blocks are transmitted by different modes in different time slots, according to a pre-negotiated pattern. The numerical results indicate that high-quality chaos synchronization with a wide operation region and relatively strong frequency detuning tolerance can be achieved between the communicating MSL modes, which can afford multiple simultaneous bidirectional message transmissions. Moreover, because of the carrier-consumption competition in the MSL cavity, the peak average power ratios of the chaotic carriers are much larger and more widely distributed with respect to selected single-mode injection or feedback cases, which can obviously enhance the link security against the attack of linear filtering. Also, the carrier-consumption competition induces a cross talk between the transmission messages, which can greatly improve the link security when eavesdroppers adopt the synchronization utilization method to attack the public link. Furthermore, with the non-fixed wavelength transmission technology, the system security can also be further improved greatly. The proposed scheme provides a new way to implement high-speed multichannel chaos communication with high physically enhanced security.

Long-distance multi-channel bidirectional chaos communication based on synchronized VCSELs subject to chaotic signal injection

A novel long-distance multi-channel bidirectional chaos communication system over multiple paths based on two synchronized 1550nm vertical-cavity surface-emitting lasers (VCSELs) is proposed and studied theoretically. These two responding VCSELs (R-VCSELs) can output similar chaotic signals served as chaotic carrier in two linear polarization (LP) modes with identical signal injection from a driving VCSEL (D-VCSEL), which is subject to optical feedback and optical injection, simultaneously. Through the numerical simulations, high quality chaos synchronization between the two R-VCSELs can be obtained. Besides, the effects of varied qualities of chaos synchronization on communication performances in 20km single mode fiber (SMF) channels are investigated by regulating different internal parameters mismatch after adopting chaos masking (CMS) technique. With the decrease of the maximum cross correlation coefficient (Max-C) between the two R-VCSELs, the bit error rate (BER) of decoded message increase. Meanwhile, the BER can still be less than 10−9 when the Max-C degrades to 0.982. Based on high quality synchronization, when the dispersion compensating fiber (DCF) links are introduced, 4n messages of 10Gbit/s can transmit in 180km SMF channels over n coupling paths, bidirectionally and simultaneously. Thorough tests are carried out with detailed analysis, demonstrating long-distance, multi-channel, bidirectional chaos communication based on VCSELs with chaotic signal injection.

Secure WDM-PON based on chaos synchronization and subcarrier modulation multiplexing

A novel secure passive optical network (PON) configuration jointly based on the chaos synchronization of wavelength division multiplexed (WDM) chaotic signals and the subcarrier modulation multiplexing is introduced. The upstream and downstream carriers consist of a set of wavelength division multiplexed chaotic signals, and each wavelength takes on several bidirectional optical line terminal (OLT)-optical network unit (ONU) transmissions in virtue of the subcarrier modulation multiplexing technology. The numerical results demonstrate that with proper selection of the wavelength spacing, high-quality chaos synchronization can be achieved on each wavelength, and each wavelength can afford several OLT-ONU transmissions by properly allocating the frequency spacing of subcarriers. The proposed scheme can improve the bandwidth utilization efficiency and obviously enhance the information security at the physical layer of the WDM-PON.

Performance of chaos synchronization and security in dual-chaotic optical multiplexing system

Based on a novel multiplexing system of two distinct chaotic signals, the corresponding modified Lang-Kobayashi rate equations are established. The numerical investigations into the performance of chaos synchronization are carried out. In more detail, the influences of single-parameter mismatch, multi-parameter mismatch, feedback-strength discrepancy, and frequency detuning between the two master semiconductor lasers (MLs) on synchronization performance are investigated, respectively. Moreover, the security and spectrum characteristics are addressed briefly in this work. The numerical simulations show that by adopting parameter mismatch, i.e., choosing appropriate system parameters of the two MLs, the correlation between the two MLs becomes extremely low, while the matched master-slave laser pairs can achieve high-quality chaos synchronization, indicating that the condition of optical chaos multiplexing is satisfied; the parameter mismatch between the MLs has a significant influence on their synchronization quality, but no obvious influence on their synchronization quality of the matched master-slave laser pairs, which further demonstrates the validity and feasibility of the chaos multiplexing scheme. More importantly, in this paper, the multiplexed chaotic signals in the time and frequency domains in terms of autocorrelation function and power spectrum are analyzed, demonstrating that the present system could provide higher security than the single external-cavity semiconductor laser.

Modeling and Simulation of Chaos-Based Security-Enhanced WDM-PON

A physical security-enhanced wavelength division multiplexed passive optical network (WDM-PON) based on chaos synchronization between twin laser pairs is introduced. Differing from the conventional WDM-PON systems, the downstream and upstream data are physically encrypted by chaotic carriers, and the decryption processes are performed based on WDM chaos synchronization. We numerically demonstrate that with sufficient wavelength spacing, a high quality chaos synchronization between the chaotic carriers with identical wavelength can be maintained, which enables the proposed WDM-PON to afford multichannel chaotic communications at high bit rates in both the downstream and upstream directions; in addition, the security of the physical layer can be greatly enhanced. The proposed scheme shows a potential way for implementing physically-secure PONs.

Route to broadband optical chaos generation and synchronization using dual-path optically injected semiconductor lasers

The generation and synchronization of broadband optical chaos in dual-path optically injected (DPOI) semiconductor lasers (SLs) are numerically demonstrated. The effective bandwidth enhancement is achieved up to about 35.84GHz, under appropriate injection strength and frequency detuning. We systematically study and compare the bandwidth enhancement in single-path optically injected SLs (SPOI-SLs) and DPOI-SLs, and find that better performance can be obtained for the latter over a larger parameter span. Furthermore, two schemes for synchronization of bandwidth-enhanced chaos generated in two similar or identical (twin) DPOI-SLs are proposed, where the twins are driven by a common DPOI signal injected from another chaotic SL. High-quality chaos synchronization, an isochronous type, is observed between the twin DPOI-SLs. Also, the effect of parameter mismatch and frequency detuning is numerically examined. The simple technique of bandwidth enhancement using dual-path injection may pave way for various applications such as high-speed random number generators (RNGs) and chaos-based communications.

Simulation of Bidirectional Long-Distance Chaos Communication Performance in a Novel Fiber-Optic Chaos Synchronization System

A novel fiber-optic chaos synchronization system allowing bidirectional long-distance chaos communication is proposed. For this system, chaos synchronization between two response lasers (RLs) is achieved via an identical driven chaotic signal injection from a remote driving laser (DL) over a long-distance fiber. The simulated results show that under suitable operation conditions, high-quality chaos synchronization between the two RLs can be obtained while the synchronization quality between any one of RLs and the DL is bad, which is useful for improving the system security. Using the two synchronized chaos output signals from RLs as two chaotic carriers and adopting a novel message encryption and decryption method, the communication performances, the impact of long-distance fiber channel and the security of this system, have been analyzed. After adopting an optimized system configuration, two 10 Gb/s messages propagating along opposite direction can be effectively decrypted over 100 km fiber channel.

Investigation of bidirectional dual-channel long-distance chaos secure communication based on 1550nm vertical-cavity surface-emitting lasers

Based on the chaos synchronization between two pairs of corresponding linear polarization modes in two 1550 nm vertical-cavity surface-emitting lasers (1550 nm-VCSELs) subject to optical injection of common chaotic signals, a novel bidirectional and dual-channel long-distance chaos secure communication system is proposed. The chaotic synchronization characteristics, bidirectional dual-channel communication performance, and the influences of the fiber channel on the message transmission are numerically investigated. Results show that, driven by a common chaotic signal generated from a driver VCSEL (D-VCSEL), two pairs of responding linear polarization modes in two response 1550nm-VCSELs (R-VCSELs) can be synchronized completely and isochronally. Meanwhile, the synchronization coefficients between the two pairs of responding linear polarization modes in D-VCSEL and R-VCSELs are low. Based on the high quality chaos synchronization between two pairs of responding linear modes in two R-VCSELs, bidirectional and dual-channel chaos secure communication can be achieved. After adopting a single mode polarization-maintaining fiber (or dispersion-shifted polarization-maintaining fiber), for 2.5 Gbit/s messages, the Q factor of the decryption signals after transmitting 60 km (or 200 km) can be more than 6.

Dual-channel chaos synchronization and communication based on a vertical-cavity surface emitting laser with double optical feedback

Using two orthogonal polarization mode outputs from a vertical-cavity surface emitting lasers (VCSEL) with double optical feedback as two chaotic carriers, a dual-channel chaos secure communication system is established, and the synchronization and communication performances of such a system are numerically investigated. The results show that under suitable operated condition, the time-delay signatures of two chaotic carriers originating from two linear polarization modes in the T-VCSLE with double optical feedback can be suppressed efficiently. Under the strong injection locking case, high-quality chaos synchronization between two corresponding modes of T-VCSEL and R-VCSEL can be realized by polarization-preserved optical injection from T-VCSEL to R-VCSEL. Moreover, the tolerance of the synchronization quality on the frequency detuning between T-VCSEL and R-VCSEL is enhanced with the increase of the injection strength. Adopting additive chaos modulation encryption scheme, two pieces of 500 Mbit/s encoded message can be hidden efficiently in the two chaotic carriers in the propagation process and can be successfully extracted at the receiver. Although Q factor decreases with the increase of message transmission rate, the values of Q factor for two channels are still larger than 6 for 6 Gbit/s message.