Time-delay Signature Suppression Research Articles

Generation of Wideband Chaos With Time-Delay Signature Suppression in Semiconductor Lasers by Asymmetrical Mutual Injection

Generation of Wideband Chaos With Time-Delay Signature Suppression in Semiconductor Lasers by Asymmetrical Mutual Injection

Time-Delay Signature Suppression and Communications of Nanolaser Based on Phase Conjugate Feedback

The nonlinear dynamics of nanolasers (NLs), an important component of optical sources, has received much attention. However, there is a lack of in-depth research into the high-quality chaotic output of NLs and their applications in chaotic secure communications. In this paper, we make the NLs generate broadband chaotic signals whose time-delay signatures (TDS) are completely hidden by a phase conjugate feedback structure. And in the two-channel communication scheme, we make the NLs achieve a combination of a low-latency high degree of synchronization and two-channel transmission technique, which enhances the security of message encryption and decryption. We also investigate the effects of system parameters, Purcell factor F, spontaneous emission coupling factor β, and bias current I on the TDS, as well as the effects of parameter mismatch and injection parameters on chaos synchronization and message recovery. The results show that the phase conjugate feedback-based NLs can achieve the suppression of the TDS within a certain parameter range, and it can achieve high-quality synchronization and enhance the security of chaotic communication under appropriate injection conditions.

Time-delay signature suppression in delayed-feedback semiconductor lasers as a paradigm for feedback control in complex physiological networks.

Physiological networks, as observed in the human organism, involve multi-component systems with feedback loops that contribute to self-regulation. Physiological phenomena accompanied by time-delay effects may lead to oscillatory and even chaotic dynamics in their behaviors. Analogous dynamics are found in semiconductor lasers subjected to delayed optical feedback, where the dynamics typically include a time-delay signature. In many applications of semiconductor lasers, the suppression of the time-delay signature is essential, and hence several approaches have been adopted for that purpose. In this paper, experimental results are presented wherein photonic filters utilized in order to suppress time-delay signatures in semiconductor lasers subjected to delayed optical feedback effects. Two types of semiconductor lasers are used: discrete-mode semiconductor lasers and vertical-cavity surface-emitting lasers (VCSELs). It is shown that with the use of photonic filters, a complete suppression of the time-delay signature may be affected in discrete-mode semiconductor lasers, but a remnant of the signature persists in VCSELs. These results contribute to the broader understanding of time-delay effects in complex systems. The exploration of photonic filters as a means to suppress time-delay signatures opens avenues for potential applications in diverse fields, extending the interdisciplinary nature of this study.

Time-delay signature suppression of the chaotic signal in a semiconductor laser based on optoelectronic hybrid feedback.

An approach to generating chaotic signals with low time-delay signatures (TDSs) from a semiconductor laser (SCL) is proposed and demonstrated based on optoelectronic hybrid feedback. Through using a chirped fiber Bragg grating (CFBG) to provide distributed feedback, a chaotic signal with a low TDS is generated from the SCL. With the assistance of the nonlinear optoelectronic feedback provided by a microwave photonic link, the relaxation oscillation effect in the SCL is effectively suppressed, and the periodicity of the oscillation is greatly weakened. Hence, the TDS of the generated chaotic signal from the SCL is further suppressed, and the effective bandwidth is enlarged. Both simulation and experiment are carried out to verify the feasibility of the proposed scheme to suppress the TDS. In the experiment, a chaotic signal with a large effective bandwidth of 12.93 GHz, an extremely high permutation entropy (PE) of 0.9983, and a low TDS of 0.04, is generated by using a CFBG with a dispersion coefficient of 22.33 ps/nm. This TDS value is at the same level as that obtained by using the SCL-based scheme relying solely on distributed feedback in a CFBG with a dispersion coefficient of 2000 ps/nm.

Complete and partial time-delay signature suppression in a laser array.

We model dynamics of a quantum dot based micropillar laser array subject to the time-delayed optical feedback. The global coupling provided by the feedback generates a rich set of various instabilities including chaotic regimes with strong time-delay signature in the autocorrelation function. We demonstrate that the dispersion of the array coupling phases leads to effective suppression of the time-delay signature due to the dispersion of the system's internal timescales. We find that the transition to the complete suppression of the time-delay signature appears via a chimera state where highly correlated and non-correlated laser outputs coexist. The degree of correlation in the chimera state depends on the coupling phase dispersion.

Evolution of the time delay signature of chaos generated in three types of optical injection systems.

The time delay signature (TDS) of chaos generated in three schemes of optical injection has been investigated, and the mechanism of TDS suppression (TDSS) is revealed. The first scheme is a continuous-wave (CW) laser unidirectionally injecting into a chaotic laser, and the TDS of the chaotic laser is suppressed below 0.08 in this structure. The second scheme is a chaotic laser unidirectionally injecting into a CW laser, where the parameter range of TDSS lower than 0.06 of this structure is the largest among the three schemes. The third scheme is two CW lasers coupling to each other, and two chaotic lasers with TDS (T D S<0.1) suppression can be obtained simultaneously. For the further analysis of the mechanism of TDSS, the quasi-linear relationship between the synchronization coefficient and TDS is revealed. This study will provide insight into the generation of chaotic lasers by optical injection and promote the application of chaotic lasers.

Numerical and experimental investigation of a dispersive optoelectronic oscillator for chaotic time-delay signature suppression.

Chaos generation from a novel single-loop dispersive optoelectronic oscillator (OEO) with a broadband chirped fiber Bragg grating (CFBG) is numerically and experimentally investigated. The CFBG has much broader bandwidth than the chaotic dynamics such that its dispersion effect rather than filtering effect dominates the reflection. The proposed dispersive OEO exhibits chaotic dynamics when sufficient feedback strength is guaranteed. Suppression of chaotic time-delay signature (TDS) is observed as the feedback strength increases. The TDS can be further suppressed as the amount of grating dispersion increases. Without compromising bandwidth performance, our proposed system extends the parameter space of chaos, enhances the robustness to modulator bias variation, and improves TDS suppression by at least five times comparing to the classical OEO. Experimental results qualitatively agree well with numerical simulations. In addition, the advantage of dispersive OEO is further verified by experimentally demonstrating random bit generation with tunable rate up to 160 Gbps.

Strategy for Attacking the Key Parameters of Electro-Optic Self-Feedback Phase Encryption System

In this paper, we propose a method for cracking the key parameters of an electro-optic self-feedback temporal optical phase encryption system and experimentally demonstrate the feasibility of the scheme. By scanning a tunable dispersion compensation (TDC) module at the receiver, the time delay signature (TDS) of an encrypted signal can be exposed, making it possible to extract other key parameters of the system and reconstruct a decryption setup. The TDS characteristics for three typical modulation formats are investigated, revealing that while such an encryption system is secure against power detection attack, there is a risk of TDS leakage. The findings can guide the design of advanced optical encryption schemes with TDS suppression for security enhancement.

Time-delay signature suppression in single loop optoelectronic oscillators based on sine hyperbolic nonlinear amplifier

Time-delay signature suppression in single loop optoelectronic oscillators based on sine hyperbolic nonlinear amplifier

Strong cluster synchronization in complex semiconductor laser networks with time delay signature suppression.

Cluster synchronization is a state where clusters of nodes inside the network exhibit isochronous synchronization. Here, we present a mechanism to realize the strong cluster synchronization in semiconductor laser (SL) networks with complex topology, where stable cluster synchronization is achieved with decreased correlation between dynamics of different clusters and time delay signature concealment. We elucidate that, with the removal of intra-coupling within clusters, the stability of cluster synchronization could be enhanced effectively, while the statistical correlation among dynamics of each cluster decreases. Moreover, it is demonstrated that the correlation between clusters can be further reduced with the introduction of dual-path injection and frequency detuning. The robustness of strong cluster synchronization on operation parameters is discussed systematically. Time delay signature in chaotic outputs of SL network is concealed simultaneously with heterogeneous inter-coupling among different clusters. Our results suggest a new approach to control the cluster synchronization in complex SL networks and may potentially lead to new network solutions for communication schemes and encryption key distribution.

Tunable Chaotic External-Cavity Semiconductor Laser With Time-Delay Signature Suppression Including a Broadband Chirped FBG

A wavelength tunable chaotic external cavity semiconductor laser (ECSL) composed by a distributed-feedback laser diode (DFB-LD) and a broadband chirped fiber Bragg grating (CFBG), is proposed and experimentally demonstrated for generating tunable chaos signals with time delay signature (TDS) suppression. The experimental results show that by using a CFBG with a 3-dB reflection bandwidth of approximately 30 nm and a low dispersion of approximately 1.25 ps/nm, the chaotic ECSL can be tuned over a wide wavelength range, and the generated chaos possesses a low TDS of about 0.04. With the increase of the bias current of the DFB-LD, the chaotic ECSL is tuned towards long-wavelength direction, the effective bandwidth of the chaotic signal is extended, and the TDS of the chaotic signal remains effectively suppressed. To highlight the advantages of the proposed scheme, relevant experiments for the DFB-LD under fiber mirror feedback and fiber Bragg grating feedback are also performed and compared.

Security-Enhanced Chaotic Optical Communication Based on External Temporal Self-Feedback Hardware Encryption and Decryption

Chaotic optical communication based on conventional external cavity semiconductor laser is a very promising solution for physical layer secure communication. However, the intrinsic time delay signature (TDS) associated with the external cavity length and the potential direct linear filtering (DLF) or synchronization utilization attack greatly threaten the system security. In this work, we propose and numerically demonstrate a novel scheme for TDS suppression and security enhancement of chaotic optical communication based on external temporal self-feedback hardware encryption and decryption. In this scheme, the confidential chaotic modulated signal is temporally scrambled in the time domain by two optical dispersion components and an electro-optic self-feedback phase modulation loop between them, which simultaneously conceal the TDS and enhance the security against malicious attacks. Proof-of-principle demonstration for a security enhanced chaotic optical communication system with error free transmission is successfully achieved. The proposed scheme may provide a promising way for pure-hardware based physical secure chaotic optical communication systems.

Optimizations of optical chaos in semiconductor lasers based on multiobjective genetic algorithms.

We investigated the frequency bandwidth, autocorrelation function, and complexity of chaotic temporal waveforms in unidirectionally coupled semiconductor lasers with time-delayed optical feedback. The effective bandwidth, peak value of autocorrelation function, and maximum Lyapunov exponent were simultaneously optimized by searching several control parameters of the laser systems based on multiobjective genetic algorithms. We found a conflicting relation between the effective bandwidth enhancement and the time-delay signature suppression, and a detailed relationship between the maximum Lyapunov exponent and the peak value of autocorrelation function.

Band-Rejection Feedback for Chaotic Time-Delay Signature Suppression in a Semiconductor Laser

Chaos generation from a semiconductor laser under band-rejection optical feedback is proposed and investigated numerically and experimentally. The band-rejection feedback performs better than the conventional broadband mirror feedback in concealing the feedback delay time information measured by the time-delay signature (TDS) of optical field and intensity. In this work, the optical band-rejection filter (BRF) is built up based on the transmission of a Bragg grating. The best concealment of delay time information is achieved in the form of simultaneous TDS suppression in optical field and intensity when the BRF is negatively detuned from the free-running laser frequency. Such concealment is due to the suppression of feedback cavity modes by the band-rejection effect. The concealment prefers negative detuning frequency because the laser cavity resonance is red-shifted by optical feedback due to the antiguidance effect. The negatively detuned BRF suppresses the TDS of optical field and intensity by more than an order of magnitude than mirror feedback. The simulation results are qualitatively confirmed by the experimental measurements.

Research on methods of enhancing physical layer security of optical fiber communication system in the smart grid

We investigate numerically the security enhanced optical communication which can be used in smart grid, while the time-delay signature suppression, intelligent control and high quality communication are reached at the same time. In this paper, the communication system includes the driven part, national dispatching control centre (NDCC) and the controlled substations (CSs). To enhance the security of communication system, the driven part which includes two semiconductor lasers, is employed to suppress the time-delay signature. Also, the chaos synchronization between NDCC and different CSs can be selectively realized by controlling the injection parameters. Finally, the high quality communication between NDCC and CS1 is discussed. This research paves the way to the application of chaotic communication in smart grid.

Chaotic dimension enhancement by optical injection into a semiconductor laser under feedback.

Optical injection into a chaotic laser under feedback is investigated for dimension enhancement. Although injecting a solitary laser is known to be low-dimensional, injecting the laser under feedback is found to enhance the correlation dimension D2 in experiments. Using an exceptionally large data size with a very large reconstruction embedding dimension, efficient computation is enabled by averaging over many short segments to carefully estimate D2. The dimension enhancement can be achieved together with time-delay signature suppression. The enhancement of D2 as a fundamental geometric quantifier of attractors is useful in applications of chaos.

Generation of Chaotic Signals With Concealed Time-Delay Signature Based on a Semiconductor Laser Under Multi-Path Optical Feedback

A simple schemefor generating chaotic signals with concealed time-delay signature (TDS) is proposed and experimentally demonstrated. The architecture of the system is based on a semiconductor laser (SL) under multi-path optical feedback (MPOF) provided by a 2 × 2 fiber coupler (FC) and a fiber mirror (FM). The results show that SLs with MPOF are more beneficial for achieving TDS suppressed chaotic output than those with single optical feedback (SOF) systems. In addition, the TDS of the chaotic signal generated by the SL under MPOF is insensitive to the length deviation of the feedback cavities, and therefore such a scheme is convenient for practical application. Furthermore, the influence of FC coupling ratio in the MPOF module, feedback strength, and bias current of the SL on the TDS is comprehensively studied. By selecting suitable parameters, the TDS of the chaotic signal generated by the SL under MPOF can be completely concealed. Finally, permutation entropy (PE) is adopted to evaluate the complexity of the generated chaotic signal, and the result demonstrates that the suppression of TDS does not lead to the degradation of complexity for the proposed scheme.

Dynamic behaviors and bandwidth-enhanced time-delay signature suppression of mutually coupled spin-polarized vertical-cavity surface-emitting lasers

A novel symmetric model based on the mutually coupled spin-polarized vertical-cavity surface-emitting lasers (MCSP-VCSELs) subject to optically pumped is implemented and analyzed in this paper. Numerous nonlinear dynamic behaviors containing the state of steady, period, period-doubling, and chaos have been observed in the bifurcation diagram, revealing the period-doubling route to chaos. The characteristics of these dynamic behaviors are analyzed in detail along with clarifying the physical mechanism of their occurrence. The influences of laser parameters on the dynamic behaviors are investigated through mapping diagrams, and the results show that both the pump intensity and pump ellipticity are crucial to the complicated dynamic behaviors including chaos. Additionally, the increase of the coupling strength, coupling time delay, and frequency detuning have beneficial impacts to chaos while the spin relaxation rate has a harmful effect on the contrary. The comparison results on different parameter planes illustrate that the time-delay signature (TDS) suppression and bandwidth enhancement can be achieved simultaneously when coupling strength, frequency detuning and pump strength are relatively large. Therefore, the MCSP-VCSELs have an application prospect in chaos-based fields.

Chaotic time-delay signature suppression using quantum noise.

The time-delay signature (TDS) suppression of semiconductor lasers with external optical feedback is necessary to ensure the security of chaos-based secure communications. Here we numerically and experimentally demonstrate a technique to effectively suppress the TDS of chaotic lasers using quantum noise. The TDS and dynamical complexity are quantified using the autocorrelation function and normalized permutation entropy at the feedback delay time, respectively. Quantum noise from quadrature fluctuations of the vacuum state is prepared through balanced homodyne measurement. The effects of strength and bandwidth of quantum noise on chaotic TDS suppression and complexity enhancement are investigated numerically and experimentally. Compared to the original dynamics, the TDS of this quantum noise improved chaos is suppressed up to 94%, and the bandwidth suppression ratio of quantum noise to chaotic laser is 1:25. The experiment agrees well with the theory. The improved chaotic laser is potentially beneficial to chaos-based random number generation and secure communication.

Chaotic Time-Delay Signature Suppression and Entropy Growth Enhancement Using Frequency-Band Extractor.

By frequency-band extracting, we experimentally and theoretically investigate time-delay signature (TDS) suppression and entropy growth enhancement of a chaotic optical-feedback semiconductor laser under different injection currents and feedback strengths. The TDS and entropy growth are quantified by the peak value of autocorrelation function and the difference of permutation entropy at the feedback delay time. At the optimal extracting bandwidth, the measured TDS is suppressed up to 96% compared to the original chaos, and the entropy growth is higher than the noise-dominated threshold, indicating that the dynamical process is noisy. The effects of extracting bandwidth and radio frequencies on the TDS and entropy growth are also clarified experimentally and theoretically. The experimental results are in good agreements with the theoretical results. The skewness of the laser intensity distribution is effectively improved to 0.001 with the optimal extracting bandwidth. This technique provides a promising tool to extract randomness and prepare desired entropy sources for chaotic secure communication and random number generation.