Polarization-preserved Optical Injection Research Articles

Optical chaotic flip-flop operations with multiple triggering under clock synchronization in the VCSEL with polarization-preserved optical injection.

We investigate the evolution of nonlinear dynamic behaviors of two polarization components (x-PC and y-PC), as well as the interplay of polarization bistability and injection strength in the vertical-cavity surface-emitting laser (VCSEL) with polarization-preserved optical injection. We explore a new threshold mechanism to judge two logic outputs encoded in different dynamic behaviors of the x-PC and y-PC emitted by the VCSEL with polarization-preserved optical injection. We demonstrate implementations of two parallel optical chaotic reset-set flip-flop operations and two parallel chaotic toggle flip-flop operations that are synchronized by a clock signal and response for as short as 1 ns bit time. We further observe the reconfiguration of these two kinds of flip-flop operations with clock synchronization in different time periods by controlling the duration-time of the reset (toggle) signal with high-level. The probability of the correct trigger responses for these two kinds of flip-flop operations is controlled by the interplay of the duration-time of the reset (toggle) signal and the noise strength of the spontaneous emission. The probability that is equal to 1 for the reset-set flip-flop operations occurs in the long duration-time of the reset (toggle) signal ranging from 480 ps to 592 ps. The probability with 1 for the toggle flip-flop operations takes place in the short duration-time between 116 ps and 170 ps. Moreover, these two kinds of flip-flop operations have strong robust to the spontaneous emission noise. The optical chaotic flip-flop operation device with clock synchronization and reconfigurable trigger function proposed in our scheme offers interesting perspectives for applications where noise is unavoidable and synchronized multiple triggering is required.

Dual-channel physical random bits generation by a master-slave vertical-cavity surface-emitting lasers chaotic system

Taking the chaotic output from a master-slave framework chaotic system as chaotic entropy resource, we propose a scheme for acquiring dual-channel high-speed physical random bits (PRBs). For such a scheme, a vertical-cavity surface-emitting laser (VCSEL) under polarization-preserved optical feedback from a fiber Bragg grating is utilized as the master VCSEL (M-VCSEL). Under suitable operating parameters, both X and Y polarization components (X-PC and Y-PC) of the M-VCSEL can output chaotic signals with comparable power and weak time-delay signatures. The chaotic outputs from the X-PC and Y-PC of the M-VCSEL are divided into two parts, and then injected into the corresponding polarized component of another VCSEL (named as slave VCSEL, S-VCSEL) after undergoing different flight-time, and such an injection method is named as dual-path polarization-preserved optical injection (DP-PPOI). The X-PC and Y-PC in the S-VCSEL under DP-PPOI can simultaneously output chaotic signals with enhanced bandwidth, which are quantified by 8-bit analog-to-digital converters and taken as the entropy sources for generating dual-channel bit sequence after adopting m least significant bits (m-LSBs) extraction and logical exclusive-OR post-processing. Finally, the randomness of the bit sequences generated under optimized parameters is tested by NIST SP 800-22 statistical test suite. The results demonstrate that dual-channel random bits at rate of 500 Gbit s−1 can be obtained, and the rate of random bits can be further increased to 1 Tbit s−1 through adopting cross-merging method.

Anticipation in the Polarization Chaos Synchronization of Uni-Directionally Coupled Vertical-Cavity Surface-Emitting Lasers With Polarization-Preserved Optical Injection

We investigate numerically the anticipated synchronization in the two uni-directionally coupled vertical-cavity surface-emitting lasers (VCSELs) as master and slave configuration. The master VCSEL is rendered chaotic state by an isotropic optical feedback and master’s chaotic output uni-directionally injected to a slave VCSEL under polarization-preserved optical injection. The synchronization quality and lag time between lasers are obtained by performing cross-correlation analysis. When the laser’s parameters are identical, a regime of anticipatory synchronization is found in both of the linearly polarized mode dynamics of the master and slave lasers, if the feedback delay time is greater than the coupling time. Anticipation is robust to a small variation in injection rate, frequency detuning, and laser’s internal parameter mismatches, but the synchronization is not complete. Injection-locking synchronization regime occurs between master and slave lasers for higher injection, positive detuning, and larger mismatch in the internal parameters. We show the mapping of synchronization quality, sustenance of anticipatory synchronization and switching of regimes in the injection rate and parameter mismatch plane. The anticipation maintained even for higher injection rates if mismatch is introduced in certain internal parameters.

Photonic Approach for Generating Randomness-Enhanced Physical Chaos Via Dual-Path Optically Injected VCSELs

The randomness enhancement of physical chaos generated by slave vertical-cavity surface-emitting lasers (S-VCSEL) subject to dual-path polarization-preserved optical injection (DP-PPOI) from single master VCSEL (M-VCSEL) with variable-polarization optical feedback (VPOF) is investigated numerically. The randomness of chaotic signals is evaluated quantitatively by an information-theory-based quantifier, the permutation entropy. The randomness properties for S-VCSEL with DP-PPOI and S-VCSEL with single-path PPOI are compared, as well as the effects of injection strength, frequency detuning, and VPOF are considered. It is shown that, the PE values for S-VCSELs with two different injection schemes are both much higher than those for M-VCSEL, and increase initially and then decrease until they saturate at a constant level. The region of injection parameter space contributing to randomness-enhanced chaos in S-VCSEL can be greatly broadened by adopting DP-PPOI. The generation of randomness-enhanced chaos via photonic approach is highly desirable for high-speed random number generators based on chaotic VCSELs.

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.

Enhanced chaotic communication in VCSELs with variable-polarization optical feedback and polarization-preserved optical injection

The communication performance and security enhancement in vertical-cavity surface-emitting lasers (VCSELs) subject to variable-polarization optical feedback (VPOF) are investigated numerically. Unidirectional polarization-preserved optical injection (PPOI) scheme is adopted, chaos modulation is utilized for message encryption, and two decoding methods are discussed and compared. The influences of VPOF on the performances of two decoding methods are focused on, and the effects of injection strength and frequency detuning are also considered. The security enhancement is further discussed by analyzing the robustness to mismatched feedback configuration and polarizer angle, as well as the intrinsic parameters. It is shown that, successful message encoding and decoding with Q-factors greater than 6 can be achieved by using unpredictability-enhanced chaotic carrier. In particular, the Q-factors are quite sensitive to the feedback configuration and laser parameters. When an attacker with open-loop is considered, Q-factors are smaller than 3 (6) for division (subtraction) decoding method. Specifically, even when an attacker with close-loop is considered, the Q-factors are lower than 6 when mismatched polarizer angles or intrinsic parameters exceed ±20% for subtraction method, and are more sensitive to parameter mismatch for division method, which enhances significantly the security, and thus is extremely useful for the security-enhanced chaotic communication system.

Message Encoding/Decoding Using Unpredictability-Enhanced Chaotic VCSELs

Successful message encoding/decoding in an unpredictability-enhanced chaotic vertical-cavity surface-emitting lasers (VCSELs) system is achieved numerically via the chaos-shift-keying technique. Both VCSELs are subject to variable-polarization optical feedback (VPOF), and polarization-preserved optical injection is adopted. Better decoding performance is achieved by choosing proper polarizer angle, and the security is, to some extent, enhanced owing to the VPOF.

Synchronization of Unpredictability-Enhanced Chaos in VCSELs With Variable-Polarization Optical Feedback

The generation and synchronization of unpredictability-enhanced chaos in vertical-cavity surface-emitting lasers (VCSELs) are investigated numerically. The master VCSEL is subject to variable-polarization optical feedback. Two injection schemes, the polarization-preserved optical injection (PPOI) and variable-polarization optical injection (VPOI) are considered for the slave VCSELs. The influences of unpredictability degree on the synchronization quality and the synchronization properties of unpredictability-enhanced chaos are focused on. For the PPOI scheme, the synchronization quality is hardly affected by the unpredictability degree; high-quality synchronization can be achieved between unpredictability-enhanced chaos due to injection locking. However, for the VPOI scheme, the unpredictability degree affects the synchronization quality significantly. High degree of unpredictability leads to low synchronization quality. Only the low-unpredictability chaos can be well synchronized, while the unpredictability-enhanced chaos cannot be synchronized even with large injection strength. The achievement of unpredictability-enhanced chaos synchronization by the PPOI scheme is extremely useful for the security-enhanced VCSELs-based chaos communication systems.

Impact of unpredictability on chaos synchronization of vertical-cavity surface-emitting lasers with variable-polarization optical feedback

The effects of unpredictability degree on the chaos synchronization properties of vertical-cavity surface-emitting lasers with variable-polarization optical feedback are investigated numerically. For variable-polarization optical injection, only low-unpredictability chaos can be well synchronized, while high-unpredictability chaos cannot be synchronized even with large injection strength. On the other hand, for the polarization-preserved optical injection, the synchronization quality is hardly affected by the unpredictability degree, and high-quality synchronization can be achieved for both low- and high-unpredictability chaos due to injection locking.

Chaos synchronization and communication of the polarization modes for two unidirectionally coupled vertical-cavity surface-emitting lasers

We theoretically investigate the synchronization performance of the polarization modes of two unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs), where the master VCSEL subjects to polarization-preserved optical feedback and the slave VCSEL subjects to polarization-preserved optical injection. We demonstrate that high synchronization can be achieved between corresponding polarization components of the master laser and the slave laser. We also analyze the influence of the internal mismatched parameters on the synchronization performance. Furthermore, this system is used to dual-channel communication and the different transmitted digital information is respectively recovered at each polarization branch of the slaver laser successfully with the encryption scheme of chaos masking (CM). The results open an opportunity for multichannel chaotic communication by utilizing different polarization components in single-mode or multi-transverse-mode VCSELs.

GHz Bandwidth Message Transmission Using Chaotic Vertical-Cavity Surface-Emitting Lasers

Chaotic message encoding and decoding in unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs) with polarization-preserved and polarization-selected optical injection has been studied experimentally. A GHz message has been successfully encoded in the chaotic transmitter and decoded from the receiver with polarization-preserved optical injection. In contrast decoding using polarization-selected optical injection was achieved at only 330 MHz. It has also been demonstrated that GHz message extraction can be achieved using both normal and inverse chaos synchronization thus providing an opportunity for exploiting polarization properties of VCSELs for duplexed chaotic message transmission.

Dual-channel chaos synchronization and communication based on unidirectionally coupled VCSELs with polarization-rotated optical feedback and polarization-rotated optical injection

A novel dual-channel chaotic synchronization configuration is proposed. This system is constructed on the basis of two unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs), where a VCSEL subjected to polarization-rotated optical feedback is used as a transmitter and the other VCSEL subjected to polarization-rotated optical injection is used as a receiver. The synchronization and communication performances of such a system are numerically investigated. The results show that, similar to polarization-preserved coupled system with polarization-preserved optical feedback at the T-VCSEL port and polarization-preserved optical injection at the R-VCSEL port, such polarization-rotated coupled system can also realize complete synchronization between each pair of linear polarization (LP) modes and the total output of T-VCSEL and R-VCSEL. Compared with the polarization-preserved coupled system, this proposed system has higher tolerance to mismatched parameters. Furthermore, the average intensities of two orthogonal LP modes are almost the same so that this framework may be used to realize dual-channel chaos communication. Under the additive chaos modulation (ACM) encryption scheme, the encoded messages can be successfully extracted for both of orthogonal LP modes.

Enhanced chaos synchronization in unidirectionally coupled vertical-cavity surface-emitting semiconductor lasers with polarization-preserved injection

We experimentally study chaos synchronization in unidirectionally coupled vertical-cavity surface-emitting semiconductor lasers (VCSELs) with polarization-preserved and polarization-selected optical injection. The measurements show, in agreement with theoretical predictions, that the maximum cross coefficient of 0.884 obtained with polarization-preserved optical injection is significantly higher than the maximum cross coefficient of 0.724 obtained with polarization-selected optical injection.