Chaotic Optical Communication Research Articles

Encrypted Audio Transmission Using Synchronized Nd: YAG Lasers

Encoded information based on synchronization of coupled chaotic Nd:YAG lasers in master-slave configuration is numerically studied. Encoding, transmission, and decoding of information in optical chaotic communication with a single channel is presented. We analyze the robustness of the encrypted audio transmission in a channel noise. In order to illustrate this synchronization robustness, we present two cases of study: synchronization and transmission with a single channel without and with noise in the channel. Keywords—Encryption, Secure coomunication, Chaos, Synchronization, Complex networks, Nd:YAG laser.

Message filtering characteristics of semiconductor laser as receiver in optical chaos communication

The message filtering characteristics of the receiver in closed-loop chaotic optical communication system are numerically studied based on laser rate equations. A pair of external cavity semiconductor lasers was employed as the chaotic carrier transmitter and the synchronized chaos receiver. We examined the filtering properties of the semiconductor laser receiver for message encoded with chaos masking. Our results demonstrate that, the lower the message frequency, the more easily the receiver filters out the message from chaotic carrier. We also analyzed the effects of each parameter mismatches between the transmitter and the receiver on the quality of the recovered message. Comparing the synchronization quality with the signal-to-noise ratio affected by parameter mismatches, we find that the quality of the recovered message depends not only on the synchronization quality but also on the filtering characteristics of the receiver. The filtering characteristics of receiver will be playing an important role on the quality of the recovered message in the case of large mismatches.

Mismatch Robustness and Security of Chaotic Optical Communications Based on Injection-Locking Chaos Synchronization

Mismatch robustness and its effects on security of chaotic optical communication system based on injection-locking chaos synchronization are studied numerically by establishing the corresponding SIMULINK model. Unlike previous studies, we focus on the communication relating issues when parameter mismatches are considered. The mismatch robustness of generalized synchronization is discussed firstly in terms of cross-correlation coefficient and synchronization error. Decoding performances as well as the effects of message strength are examined for both with and without mismatch cases. Effects of injection strength on system decoding performances are also investigated by examining the chaos-pass filtering effect. Finally, a modified decoding scheme is brought forward to improve the system decoding capability. Results show that the system under consideration exhibits unconspicuous difference in both synchronization and decoding characteristics when large parameter mismatches are considered. The system based on injection-locking chaos synchronization is inappropriate for the applications where high transmission security is necessary

Effects of unwanted feedback on synchronized chaotic optical communications

The effects of unwanted external optical feedback on synchronized chaotic optical communication systems are studied numerically. We consider an open-loop configuration consisting of a transmitter laser with double external optical feedbacks and a receiver laser with optical injection from the transmitter laser. First, including the effects of unwanted optical feedback, the synchronization performances of both the complete synchronization and the generalized synchronization are examined. Then the encoding and decoding performances of the generalized synchronization and the effects of the introduced feedback are investigated, respectively. Finally, we study the control of the unwanted feedback on the dynamics of the transmitter laser and briefly discuss the system security when the transmitter laser is driven to operate in a steady state or periodic oscillation state by the additional feedback.

Demonstration of a chaotic optical message relay using DFB laser diodes

The demonstration of chaotic message relay using three chaotic distributed feedback diode lasers is reported. A 1-GHz message has been encoded in a chaotic carrier and relayed to a terminal receiver laser via a mediator laser. The message has been successfully extracted at both the mediator and receiver lasers. The message relay capability thereby demonstrated provides a key functionality for chaotic optical communication networks.

Effects of spontaneous emission noise in semiconductor lasers on chaotic optical communication systems

A chaotic optical communication system based on external optical feedback is constructed. By introducing the Langevin noise sources, the master-slave rate equations including spontaneous emission noise characteristics are deduced. Utilizing the obtained mathematical model, two kinds of possible chaos synchronization in the system, i.e. complete chaos synchronization and generalized mode-locking chaos synchronization, are studied. The effects of the spontaneous emission noises of the two lasers on the two types of synchronization as well as the chaotic outputs of the transmitter and receiver are discucsed. Finally, for a sequence of pseudorandom digital bits at 2.5Gb/s bit rate, the encoding/decoding process basing on chaotic masking method is presented, and the effects of noise on decoding performance are examined.

Spectral synchronization in chaotic optical communication systems

The ability of chaotic carriers to synchronize in optical chaotic communication systems is studied experimentally under a spectral domain analysis. Synchronization of high-frequency components up to tens of gigahertz of the chaotic carriers can thus be evaluated. On the contrary, the traditional method of measuring the synchronization through chaotic carrier time-traces is constrained by the limited bandwidth of the real-time oscilloscopes used for such measurements, excluding the contribution of the high-frequency components of the chaotic carriers to the synchronization characterization of the system.

Chaos Synchronization in Semiconductor Laser Systems and its Application to Optical Fiber Secure Communications

Chaotic laser synchronization applied to optical fiber secure communications is proposed. A synchronous error equation is achieved to the first order approximation. A model of optical fiber chaotic communication is presented by coupling the chaotic laser synchronous system with optical fiber propagation system. The chaotic synchronous system has been successfully stimulated in a long-haul optical fiber communications. The synchronization is limited by the self-phase modulation in the fiber, and the propagation phase-limited formula and the propagation distance-limited formula are demonstrated. Synchronous errors with optical fiber lengths are calculated. The influences of intensity and phase noises on the synchronous error are also numerically analyzed in detail. Analog and digital optical fiber chaotic secure communications in the system at wavelength of 1.31 μm are studied by numerically simulations. The systems show a good ability of robust security and anti-uncover in time-domain and frequency-domain.

Dynamical characterisation of laser diode subject to double optical feedback for chaotic optical communications

A chaotic semiconductor laser subject to double optical feedback is characterised in terms of the statistical analysis, power spectrum analysis and forecast error analysis of the chaotic dynamics. Varying the relative lengths of the two external cavities, the dynamics are observed and compared to that of a single cavity. We show that in the case of integer multiple external-cavity lengths the round-trip time delays can be deduced from the forecast error analysis. In the case of fractional multiple cavity lengths, only the mean value of the cavity resonance frequencies can be deduced from the power spectra and hence the cavity time delays cannot be found. Cavity time delays that differ more than 0.4 ns can be obtained from the forecast error analysis. In the case of similar cavity lengths, the cavity time delays cannot be extracted. The results show that double optical feedback may offer particular advantages for enhancing security in chaos encryption.

Theoretical model and characteristics investigations of dual-channel optical chaotic communication system

A theoretical model characterizing a recent experiment of dual-channel optical chaotic communication has been presented, and is proved to be reasonable by comparing the numerical simulation with the experimental results. After deducing the transmission function of semiconductor laser by small-signal analysis, how toreasonably select the system parameters in order to realize the effective transmission of signal has been specified. Moreover, the cross talk between two channels has been analyzed quantitatively. For a 250MHz modulation message, the nume rical simulation shows that it can be hidden efficiently during the transmission in the system and decoded easily.

Theory and simulation of dual-channel optical chaotic communication system

A theoretical model based on a novel experiment scheme of dual-channel optical chaotic communication has been presented, and is proved to be reasonable by comparing the numerical simulations with the experimental results. After deducing the transmission function of semiconductor laser by small-signal analysis, how to reasonably select the system parameters has been given in order to realize the effective transmission of signal. Moreover, the cross talk between two channels has been analyzed quantitatively. For a 250MHz modulation message, the numerical simulation shows that it can be hidden efficiently during the transmission and decoded easily in the receiver.

Experimental Demonstration of VCSEL-Based Chaotic Optical Communications

Message encoding and decoding using chaotic vertical-cavity surface-emitting lasers (VCSELs) has been experimentally demonstrated. A 200-MHz message has been successfully encoded in an external-cavity VCSEL transmitter and decoded in a stand-alone VCSEL receiver. Message recovery has been achieved with 9-dB signal-to-noise ratio.

Experimental Evaluation of an Open-Loop All-Optical Chaotic Communication System

An experimental investigation of the performance of an open-loop optical chaotic communication system has been carried out under different optical injection conditions. The most popular message encoding techniques have been considered, tested and compared at gigabit rates and for different levels of optical injection to the receiver, by bit-error-rate (BER) measurements. Different low-pass electrical filters have been implemented for the various message bit-rates tested, in order to employ the most appropriate one for message decoding. The best performance of all the examined encryption methods for messages of 1.5 Gb/s bit-rate emerged for the chaos modulation encryption method and was characterized by Q-factor values up to 5.1, after synchronizing in the strong injection regime, while the corresponding BER of the decoded message was as low as 7/spl middot/10/sup -5/. In order to confirm the secure encryption of the message, BER measurements are also performed for the chaotic carrier into which the message is encrypted.

Optical Chaotic Communication Using Laser Diode Transmitter/Receiver Array

We propose a new scheme of digital chaotic communication using the array of transmitter/receiver that consists of two self-pulsating laser diodes (LDs), i.e., a receiver LD and a transmitter LD. Part of the output of a transmitter LD is injected into the corresponding receiver LD that receives a chaotically encoded signal. A neutral density (ND) filter is placed after each transmitter LD to control the amount of light transmitted to and then injected into the corresponding receiver LD. According to the amount of the transmitter output which is injected into the receiver LD, two kinds of chaotic states with different Lyapunov exponents are induced in the receiver LD, and they are utilized to represent a binary digit. In addition, the distribution of the coupling factor between transmitter and receiver is used as a “key”. Only the proper receiver who has been previously given the “key” is able to choose an appropriate threshold of the Lyapunov exponent calculated from the detected chaotic signal that is necessary to decipher each binary bit and to decode finally the entire message. By numerically analyzing the bit error rate, particularly its dependence on the error of the optical confinement coefficient as well as on that of the injection current, we confirmed that the present scheme can provide superior security compared to the conventional chaotic masking scheme.

Performance of Open-Loop All-Optical Chaotic Communication Systems Under Strong Injection Condition

A numerical investigation of the performance of an open-loop optical chaotic communication system for the isochronous synchronization solution has been carried out, under strong optical injection conditions achieved using antireflective coating at the input facet of the receiver laser in combination with an optical erbium-doped fiber amplifier (EDFA). Different message encoding techniques have been considered and tested at multigigabit rates and for different levels of optical injection to the receiver. The effects induced by the amplified spontaneous emission (ASE) noise of the EDFA to the performance of the chaotic communication system have also been studied. The performance of all the examined encryption methods for the 1 Gb/s bit-rate messages was quite satisfactory and was characterized by Q-factor values that exceeded 10, after synchronizing in the strong injection regime. For higher message bit rates, the Q-factor values for all methods decrease considerably due to the residual frequency components of the chaotic carrier that are now more significant in the message spectral region. The effect of the amplifier's ASE noise to the system's performance was deteriorated as long as the EDFA chaotic input was kept in relatively high power levels.

Dual-channel chaotic optical communications using external-cavity semiconductor lasers

We experimentally demonstrate that two chaotic optical communication channels can be configured over a single transmission path by using two external-cavity laser diodes as transmitter lasers and a single stand-alone receiver laser. The two chaotic communication channels are shown to operate independently. Two messages, at different modulation frequencies, generated via direct-current modulation of the transmitter lasers, can be masked by the chaos and recovered at the receiver laser by the use of a decoder laser. The decoder laser is used to select the channel to be utilized. We show that there is good message recovery with little cross talk between the two channels. The channels operate at different laser wavelengths and thus constitute a wavelength-division-multiplexing scheme.

Comparison of closed-loop and open-loop feedback schemes of message decoding using chaotic laser diodes.

An experimental study of a chaotic optical communication scheme using an external cavity laser diode to encode a message is reported. The message is decoded in closed- and open-loop receiver schemes. Both schemes show effective decoding of a 1-GHz message. The synchronization and effectiveness of encoding are compared in both schemes.

Effects of message encoding and decoding on synchronized chaotic optical communications

Chaotic optical communication at 2.5 Gb/s is experimentally investigated using three major encoding and decoding schemes, namely chaos shift keying (CSK), chaos masking (CMS), and additive chaos modulation (ACM). The effects of message encoding and decoding on the chaotic dynamics, the chaos synchronization, and the chaotic communication performance are compared among the three schemes. In the schemes of CSK and ACM, it is found that a small amount of message injected into the chaotic dynamics can increase the complexity of the chaotic state dramatically. In the CMS scheme, the chaotic dynamics are found not to be influenced by the encoded message. The synchronization quality deteriorates dramatically with an increase in the message strength in CSK and CMS. The ACM scheme is found to have the best synchronization quality among the three schemes when there is an encoded message. Message recovery is demonstrated for each of the three schemes. The ACM scheme is found to have the best communication performance.

Synchronisation regimes in chaotic optical communication systems

A careful comparison is made between experimental results and two models describing optical synchronisation of chaotic external cavity semiconductor lasers. It is demonstrated that optical synchronisation regimes for chaotic semiconductor lasers in a master-slave configuration are dependent both on the frequency detuning between the master and slave lasers and also on the slave laser output power.

Optically modulated chaotic communication scheme with external-cavity length as a key to security

A chaotic optical communication scheme is established using three diode lasers as message, transmitter, and receiver lasers. The message laser is amplitude modulated by a simple message and its output is used to optically modulate the transmitter laser. The transmitter laser is rendered chaotic by application of appropriate optical feedback. The receiver laser is used to decode the message. Effective signal masking is enhanced by the selection of an appropriate external-cavity length, which is proposed as a possible key for security of chaotic optical communication.