Wideband chaos synchronization using discrete-mode semiconductor lasers.

Optical chaos communication encounters difficulty in high-speed transmission due to the challenge of realizing wideband chaos synchronization. Here, we experimentally demonstrate a wideband chaos synchronization using discrete-mode semiconductor lasers (DMLs) in a master-slave open-loop configuration. The DML can generate wideband chaos with a 10-dB bandwidth of 30 GHz under simple external mirror feedback. By injecting the wideband chaos into a slave DML, an injection-locking chaos synchronization with synchronization coefficient of 0.888 is realized. A parameter range with frequency detuning of -18.75 GHz to approximately 1.25 GHz under strong injection is identified for yielding the wideband synchronization. In addition, we find it more susceptible to achieve the wideband synchronization using the slave DML with lower bias current and smaller relaxation oscillation frequency.

Performance improvement of coherent optical chaos communication using probabilistic shaping.

We numerically investigate the effects of probabilistic shaping on the performance improvement of coherent optical chaos communication. Results show that the decryption bit-error ratio (BER) of the 16-ary quadrature amplitude modulation (QAM) signal decreases upon increasing the probabilistic shaping factor. It is predicted that the BER of 10-GBd 16QAM can be decreased by one order of magnitude. On the other hand, for the forward error correction threshold of the BER, the requirement for synchronization quality is no longer strict for successful decryption. This means that probabilistic shaping improves the system's tolerance to residual synchronization error. Thus, the transmission rate can be increased by approximately 30∼60%. The side effect of probabilistic shaping is that the valid masking coefficient range is narrowed.

Instability of optical phase synchronization between chaotic semiconductor lasers.

The instability of optical phase chaos synchronization between semiconductor lasers under master-slave open-loop configuration is investigated. The phase difference between the master and slave lasers is obtained and analyzed in experiment by heterodyne detection and Hilbert transform, and in simulation by solving the rate equations. The results show that the phase difference only maintains in a short duration time and then jumps to another value. A statistical analysis shows that both duration time and jumping values are random, proving that the phase chaos synchronization is unstable. A theoretical analysis shows that the instability of phase synchronization is caused by the jumping of the external cavity mode in the master laser.

Scheme of coherent optical chaos communication.

We propose and numerically demonstrate a scheme of coherent optical chaos communication using semiconductor lasers for secure transmission of optical quadrature amplitude modulation (QAM) signals. In this scheme, a laser intensity chaos and its delayed duplicate are used to amplitude-quadrature modulate a continuous-wave light to generate a chaotic carrier. High-quality chaotic carrier synchronization between the transmitter and receiver is guaranteed by laser intensity chaos synchronization, avoiding laser phase fluctuation. Decryption is implemented by a 90 deg optical hybrid using the synchronous chaotic carrier as local light. Secure transmission of an optical 40 Gb/s 16QAM signal is demonstrated by using a laser intensity chaos with a bandwidth of 11.7 GHz. The system performances are evaluated by analyzing a bit error ratio with different masking coefficients, signal rates, synchronization coefficients, parameter mismatches, and dispersion compensation. It is believed that this scheme can pave a way for high-speed optical chaos communication.

Fusion of optical coherence tomography and angiography for numerical simulation of hemodynamics in bioresorbable stented coronary artery based on patient-specific model.

Three-dimensional simulations of coronary artery using finite element analysis are considered as effective means to understand the biomechanical properties after the stent was deployed. Bioresorbable vascular scaffolds are new-generation stents used by people. Intravascular optical coherence tomography is an emerging technique for detecting struts. The common 3 D reconstruction methods are using Intravascular Ultrasound (IVUS) or angiographies. However, it loses the details about geometry model. Fusing of optical coherence tomography and angiography to reconstruct the bioresorbable stented coronary artery based on patient-specific mode is an innovative method to reconstruct the high fidelity geometry. This study aimed to use computer-aided design models and computational fluid dynamics research tools to conduct a systematic investigation of blood flow in an isolated artery with realistically deployed coronary stents. Some important hemodynamic factors such as wall shear stress, wall pressure and streamline were calculated. The doctors could evaluate the local hemodynamic alterations within coronary arteries after stent deployment by reconstructing the high-fidelity geometry about each clinical case.