Nullified time-of-flight lead-lag in synchronization of chaotic external-cavity laser diodes

Synchronization of three chaotic diode lasers is effected in a transmitter-mediator-receiver configuration. The transmitter laser's output is bidirectionally coupled to the mediator laser to achieve anticipating synchronization in their output intensities. The mediator laser's output is unidirectionally coupled to the receiver laser to achieve lag synchronization in their output intensities. This combination of lead and lag synchronization nullifies the time-of-flight lead-lag in synchronization between the transmitter and receiver lasers. This approach provides a means of eliminating time-of-flight delays in the synchronization of remote transmitters and receivers.     

Encrypted Chaos in Quantum Dot Light Emitting Diode

A communication scheme based on the synchronization of two chaotic quantum dot light emitting diodes (QD-LEDs) is theoretically examined. The Chaos in the QD-LED is generated by means of an optical feedback. Synchronization of the chaos is achieved by varying coupling strength between the transmitter and the receiver as unidirectional coupling. The proposed communication schemes is test a by successfully transmitting messages.     

1.5-GHz message transmission based on synchronization of chaos in semiconductor lasers

Sinusoidal message transmission up to 1.5 GHz is performed based on synchronization of chaos in experimental nonlinear systems of semiconductor lasers with optical feedback. In the chaotic systems the message is almost entirely suppressed in the receiver output, even if the message has nonnegligible power in the transmitter.     

波长可调谐混沌产生和同步的实验研究

分析了掺铒光纤环形激光器中非线性高频混沌产生和同步的基本原理. 提出了高频波长可调谐光混沌产生的实验方案，实验实现了不同波长高频混沌的产生. 实验获得了高频混沌在传输1 km后与接收机激光器产生混沌的同步，为构建高速动态保密光混沌通信网络扫清障碍. 关键词： 保密通信 掺铒光纤环形激光器 混沌 同步     

基于光反馈的单向耦合注入垂直腔表面发射激光器的矢量混沌同步特性研究

基于自旋反向模型(SFM)，数值研究了基于光反馈的单向耦合注入垂直腔表面发射激光器的矢量混沌同步特性，研究结果表明：当外部光反馈时间等于光从发射系统到接收系统传输时间时， x偏振模和y偏振模都能接收最好的完全混沌同步质量.若外部光反馈时间不等于传输时间且注入电流接近阈值电流时，占主导的y偏振模能暂时实现较好的完全混沌同步质量.相比较而言，占主导地位的x偏振模至始至终获得很差的同步质量，另外，当系统输出为混合偏振模时，混合偏振模中的每一个线性偏振模获得很差完全同步质量.然而，当注入电流远大于阈值电流时，系统输出仅为y偏振模，这时y偏振模能稳定地实现最好的完全混沌同步质量.最后，当接收激光器受到线性偏振模的强注入时，每一个注入线性偏振模能与接收激光器输出的对应的线性偏振模实现很好的注入锁定同步.然而，每一个占主导的线性偏振模比另一被抑制的线性偏振模获得更差注入锁定同步质量、如果有相等的能量的两个线性偏振模同时存在，这两个线性偏振模获得差不多一致的注入锁定混同步质量， 换句话说，能量较少的线性偏振能获得较高的注入锁定同步质量. 关键词： 线性偏振态 垂直腔表面发射激光器 完全矢量混沌同步 强注入锁定矢量混沌同步     

Secure communication based on a four-wing chaotic system subject to disturbance inputs

In this paper, a two-input two-output secure communication scheme based on a four-wing four-dimensional chaotic system with disturbance inputs is discussed. Based on parameter modulation theory and Lyapunov stability theory, synchronization and secure communication between transmitter and receiver are achieved and two message signals are recovered via a convenient robust high-order sliding mode adaptative controller. In addition, the gains of the receiver system can be adjusted continually, the unknown parameters can be identified precisely and the disturbance inputs can be suppressed simultaneously by the proposed adaptative controller. Synchronization under the effect of noise is also considered. Computer simulations are done to verify the proposed methods and the numerical results show that the obtained theoretic results are feasible and efficient.     

Synchronization of chaotic VCSELs by external chaotic signal parameter modulation

Synchronization of chaotic vertical-cavity surface-emitting lasers （VCSELs） is achieved by external chaotic signal modulation successfully. Simulation indicates that we can get chaos synchronization if the intensity of external chaotic signal is large enough. First of all, we use direct current modulation to achieve the chaos of VCSELs, and determine the laser＇s chaotic state by analyzing time series of the output and the corresponding power spectrum. And then we achieve synchronization of the two chaotic systems by external chaotic signal parameter modulation. We also find that the larger the modulation intensity is, the easier it is to achieve synchronization for chaotic VCSELs. This approach can also be applied to systems with a number of modulated lasers.     

Chaotic on off keying for secure communications

We experimentally demonstrate a chaotic on-off keying method for secure communications by using chaos synchronization in two microchip lasers. The output of the microchip laser in the transmitter is externally modulated with an acousto-optic modulator at ~4 MHz . One encodes a digital message in the chaotic carrier by turning the modulation on and off at 100 kHz. Because the accuracy of synchronization for the slave laser in the receiver tends to be degraded in the presence of external modulation in the injection laser signal, one can distinguish two binary states. The digital message can be recovered as an envelope of the chaotic oscillation when the difference between the two laser outputs of the transmitter and the receiver is calculated.     

A novel method of polarization state control for olarization division multiplexing system

We describe a new algorithm in a cost effective polarization division multiplexing (PDM) system. Without modifying the existing transmitter, receiver electronics, or softwares, we use a special optical scheme to demultiplex the signal multiplexed and improve it with a conjugated gradient algorithm. We experimentally resume the polarization state with a deviation under 5% and the power loss less than 20 dB which proves the feasibility of the polarization control algorithm in the new polarization multiplexing system.     

基于双光反馈半导体激光器的单向开环混沌同步通信

利用双光反馈半导体激光器作为混沌发射源, 构建了一个单向开环混沌通信系统, 并对系统的通信性能进行了相关仿真研究. 研究表明: 通过合理选取系统参量, 双光反馈半导体激光器所产生的混沌载波能很好地抑制外腔延时特征; 发射激光器和接收激光器在强注入锁定下能实现很好的混沌同步, 并且同步性能对频率失谐具有很好的容忍性; 采用附加混沌调制加密方式, 500 Mbits/s的信号能够很好地隐藏于混沌载波中, 并可在接收端成功解调. 关键词： 半导体激光器 单向耦合 混沌通信     

Free-space optical interconnection: A technology comparison of vertical-cavity surface-emitting lasers and multiple-quantum-well modulators

We evaluate current vertical-cavity surface-emitting laser (VCSEL) and multiple-quantum-well (MQW) modulator technologies for low-fanout system applications. Si-CMOS transimpedance receiver circuits are used in the comparison. The aggregate bandwidth per unit area is calculated from the bandwidth and the total on-chip power dissipation. The results indicate that the electrical power dissipation in the receiver circuits dominates at low operating frequencies. At high operating frequencies the receiver gain drops significantly, thus more electrical power is dissipated in the transmitter to provide more optical power to the receiver to satisfy the voltage requirement at the receiver output. In VCSEL based systems, the optical power is generated entirely on-chip. Thus, only VCSELs with low threshold current and low series resistance would be able to provide the same aggregate bandwidth as the MQW modulator based systems.     

Transition between anticipating and lag synchronization in chaotic external-cavity laser diodes

Chaotic synchronization is investigated by use of two diode lasers as transmitter and receiver. The transmitter laser is rendered chaotic by application of optical feedback in an external-cavity configuration. Changes in the spectrum of the synchronized system are shown to be associated with the transition between anticipating and lag synchronization.     

Design of full-duplex and multifunction bidirectional CMOS transceiver for optical interconnect applications

This work presents a full-duplex and multifunction bidirectional transceiver for optical interconnect application. The transceiver utilizes a common limiting amplifier/gain stage, thus reducing total chip area and total power consumption. While providing a full-duplex bidirectional transmission with the aid of a hybrid circuit between the electrical input/output (I/O) and the optoelectronic signals from the transmitter and receiver circuits, it also allows for a half-duplex operation with the aid of a switch between the transimpedance amplifier signals and the transmitter electrical input from the I/O port. The multifunction bidirectional CMOS transceiver is designed in a 0.13 µm Si-CMOS technology, with power dissipation of 79 and 54.4 mW for the transmitter and receiver, respectively. It shows a 3-dB bandwidth of 5.58 and 5.69 GHz for the transmitter and the receiver respectively and with a 3-dB gain of 66.14 and 69.6 dB, in full-duplex mode. The transceiver operates up to 7 Gb/s in full-duplex mode.     

Theoretical investigations of cascaded chaotic synchronization and communication based on optoelectronic negative feedback semiconductor lasers

In this paper, a novel chaotic relay system, based on cascaded synchronization in optoelectronic negative feedback chaotic semiconductor lasers, is presented. Synchronization characteristics and the influence of parameter mismatches on synchronization performances are investigated. The results show that the complete synchronization can be achieved under suitable system parameters; internal parameter mismatches of the lasers have influence on synchronization quality, but the system possesses more robustness to parameter mismatches compared with cascaded synchronization based on coherent optical feedback. Moreover, communication related issues are also investigated. Under the additive chaos modulation (ACM) encryption scheme, encoded messages can be successfully extracted at both mediator laser (ML) and receiver laser (RL) parts; parameter mismatches of the lasers will affect messages decoding, but the influence is not strong.     

Simulation research of medium-short distance free-space optical communication with optical amplification based on polarization shift keying modulation

Circular polarization shift keying (CPolSK) modulation technique has many advantages such as excellent BER performance and freedom from the alignment of polarization coordinates of the transmitter and the receiver, etc., and it turns out to be a good choice to FSO system. In this paper, a FSO system using CPolSK modulation is studied by simulation; it is found that the communication performance of the system is excellent in most weather condition. Additionally, three ways of optical signal amplification are proposed, and contrastive analysis on performance of corresponding optical amplification systems is carried out by examining SNR、BER and transmission distance with different specific attenuation. The results show that the system with optical amplifier at the transmitter have the optimum performance, and then the system with optical amplifier at the both ends with the same total gain, it is worst for the system with optical amplifier at the receiver. In addition, the safety factor for high emission power induced by optical amplification is also considered in this paper for practical application. The study above may be utilized in the system design for enhancing performance.     

Separate Polarization Modes Synchronization and Synchronization Switches between Vertical-Cavity Surface-Emitting Lasers

For vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated feedback, there exist several synchronization types such as synchronizations between total powers and synchronizations between separate polarization modes. Based on the two-mode rate equations, we study and compare numerically the performances of different synchronization types. Our results show that three synchronization types exhibit good performances when their synchronization conditions are satisfied. They are the complete synchronization between total powers, complete synchronization between x-polarized modes, and generalized synchronization between x-polarized and y-polarized modes. The former two types are sensitive to the injection rate and spontaneous emission, while the third type is contrary. Synchronization type with the best performance may switch from one to another, with changing of injection rate and spontaneous emission factor.     

A discrete-time chaos synchronization system for electronic locking devices

This paper presents a novel electronic locking key based on discrete-time chaos synchronization. Two Chen chaos generators are synchronized using the Model-Matching Approach, from non-linear control theory, in order to perform the encryption/decryption of the signal to be transmitted. A model/transmitter system is designed, generating a key of chaotic pulses in discrete-time. A plant/receiver system uses the above mentioned key to unlock the mechanism. Two alternative schemes to transmit the private chaotic key are proposed. The first one utilizes two transmission channels. One channel is used to encrypt the chaotic key and the other is used to achieve output synchronization. The second alternative uses only one transmission channel for obtaining synchronization and encryption of the chaotic key. In both cases, the private chaotic key is encrypted again with chaos to solve secure communication-related problems. The results obtained via simulations contribute to enhance the electronic locking devices.     

Jones precoder for polarization mode dispersion compensation

A new electrical-domain precoder is proposed to mitigate polarization mode dispersion (PMD) in optical communications by modeling a PMD-dominant fiber optical channel using a single input multiple output (SIMO) channel. Employing a bank of finite impulse response filters and a polarization modulator, and using parameters derived from the Jones matrix representation of PMD, the proposed precoder efficiently adapts to the time-varying nature of PMD and simultaneously pre-equalizes both polarization modes at the transmitter. The transmitter-only structure avoids losing phase and polarization information due to the nonlinearity of the commonly used square law direct-detection receiver. Analysis is performed to evaluate the impact of channel mismatch due to feedback delay, channel estimation errors, and the impact of the finite length of the precoder filters. The analytical results are used to guide selection of the appropriate feedback rate for the adaptive system. Extensive simulation results confirm the efficiency of the proposed Jones precoder, and present it as an effective, low-cost replacement to the complicated, expensive optical-domain counter-parts.     

光纤混沌双芯双向保密通信系统研究

把量子阱激光混沌耦合反馈同步系统应用于光纤保密通信中,提出光纤混沌双芯双向保密通信设想.通过耦合外部光注入多量子阱激光混沌全光耦合反馈同步系统和光纤传输信道,建立了光纤混沌双芯双向通信系统物理模型.理论和数值证明了激光混沌同步,理论分析指出光纤中的自相位调制是限制激光混沌在光纤传输中同步的主要原因,并推导出混沌信号双芯双向传输中的非线性相移以及混沌激光功率限制和传输距离公式.数值实现了该系统在长距离二根光纤传输中的同步,详细地分析了系统同步时间随光纤传输长度的关系.模拟了调制频率06 GHz的混沌模拟通 关键词： 混沌 同步 光纤 保密通信     

Analysis of an integrated optical coherent receiver with optical state of polarization control

An integrated optical coherent receiver with continuous state of polarization control is proposed and analyzed. The receiver consists of an integrated optical polarization rotator, a state of polarization detector and a balanced mixer receiver. Continuous state of polarization control can be achieved by using two polarization rotators in series and feeding the polarization rotator outputs into the state of polarization detector whose subsequent output is used to control the voltage settings on the polarization rotator. For the general case, the polarization rotator is comprised of two phase shifters and a TE - TM mode converter. The state of polarization detector stage consists of a δβ directional coupler mode splitter. A novel fabrication technique for achieving efficient polarization splitting is discussed. A balanced mixer receiver is implemented using a passive directional coupler with 50/50 power splitting. The need for a passive device is demonstrated and a method for achieving accurate power splitting ratios using the proton exchange fabrication technique is discussed and experimentally demonstrated. An analysis of the performance of such a system including the balanced mixer receiver is carried out to identify the critical areas of fabrication. Discussion is also given to the function and characteristics of the electronic control loop.