Harnessing microcomb-based parallel chaos for random number generation and optical decision making

Time-delay signature elimination of chaotic laser via a self-feedback antisymmetric resonator

A scheme for generating a chaotic output from a semiconductor laser while eliminating the time-delay signature (TDS) is proposed, leveraging the multi-path feedback provided by a self-feedback antisymmetric coupling fiber ring resonator (SACFRR). A theoretical model is developed to elucidate the feedback perturbation process in the proposed structure. The multi-path feedback can be modeled by incorporating the unit impulse response of the SACFRR into the modified Lang-Kobayashi-based model. We successfully eliminated the TDS using the SACFRR structure in our experimental demonstration. Further investigation into the impact of the coupling coefficient on the TDS revealed that the optimal value is 0.3, which results in the largest mapping area with the TDS below 0.03. The proposed structure is highly effective and simple to implement and integrate. As a result, the chaotic laser generated by this structure can serve as an efficient optical source for encrypted communications, chaotic Lidar, and random bit generation.

Chaos in Optomechanical Systems Coupled to a Non-Markovian Environment

We study the chaotic motion of a semi-classical optomechanical system coupled to a non-Markovian environment with a finite correlation time. By studying the emergence of chaos using the Lyapunov exponent with the changing non-Markovian parameter, we show that the non-Markovian environment can significantly enhance chaos. It is observed that a non-Markovian environment characterized by the Ornstein-Uhlenbeck type noise can modify the generation of chaos with different environmental memory times. As a comparison, the crossover properties from Markov to non-Markovian regimes are also discussed. Our findings indicate that the quantum memory effects on the onset of chaos may become a useful property to be investigated in quantum manipulations and control.

Broadband chaos of an interband cascade laser with a 6-GHz bandwidth

Near-infrared semiconductor lasers subject to optical feedback usually produce chaos with a broad bandwidth of a few GHz. However, the reported mid-infrared interband cascade lasers (ICLs) only show chaos with a limited bandwidth below 1 GHz. Here we show that an ICL with optical feedback is able to generate broadband chaos as well. The mid-infrared chaos exhibits a remarkable bandwidth of about 6 GHz, which is comparable to that of the near-infrared counterpart. In addition, the spectral coverage in the electrical domain reaches as high as 17.7 GHz. It is found that the chaos bandwidth generally broadens with increasing feedback ratio and/or increasing pump current of the laser, while it is insensitive to the feedback length.

Quantum randomness introduced through squeezing operations and random number generation

Quantum random numbers play a crucial role in diverse applications, including cryptography, simulation, and artificial intelligence. In contrast to predictable algorithm-based pseudo-random numbers, quantum physics provides new avenues for generating theoretically true random numbers by exploiting the inherent uncertainty contained in quantum phenomena. Here, we propose and demonstrate a quantum random number generator (QRNG) using a prepared broadband squeezed state of light, where the randomness of the generated numbers entirely originates from the quantum noise introduced by squeezing operation rather than vacuum noise. The relationship between entropy rate and squeezing level is analyzed. Furthermore, we employ a source-independent quantum random number protocol to enhance the security of the random number generator.

Nonlinear dynamics of an interband cascade laser with optical injection

This work reports the nonlinear dynamics of a mid-infrared interband cascade laser (ICL) subject to optical injection. It is shown that the stable locking regime is asymmetric and broadens with increasing injection strength. Outside the locking regime, the ICL mostly produces period-one oscillations. However, three categories of periodic pulse oscillations are observed in the vicinity of the Hopf bifurcation and the saddle-node bifurcation. In particular, it is found that the ICL generates broadband chaos at a near-threshold pump current, and the chaos bandwidth is over 300 MHz.

Hybrid integrated optical chaos circuits with optoelectronic feedback

A chip-scale chaotic laser system with optoelectronic delayed feedback is proposed and analyzed by numerical simulation. This chip eliminates the need for bulky delay components such as long optical fibers, free propagation and external cavities, relying solely on internal devices and waveguides to achieve feedback delay. This approach simplifies integration, maintaining a compact chip size. According to the results, the chip-scale system exhibits rich dynamics, including periodicity, quasi-periodicity, and chaotic states. Chaos resembling Gaussian white noise is achieved with picosecond-level delay time, highlighting the complexity of chip-scale signals. Furthermore, time delay signature (TDS) concealment is enhanced with a short delay comparable to the inverse bandwidth τ, albeit at a cost of sacrificing chaotic signal complexity. Applying the photonic integrated circuits to practical applications, 1 Gbps back-to-back communication transmission is feasible. Results demonstrate low bit error rates (BERs) for authorizers (<10-6) and high BERs for eavesdroppers (>10-2), ensuring communication confidentiality and chaotic synchronization. Lastly, preliminary experiments validate the feasibility. Our theoretical work has demonstrated the feasibility of hybrid integrated optical chaos circuits with optoelectronic feedback based on photonic wire bonding, which can provide a stable and flexible integrated chaos source.

3D parallel pulsed chaos LiDAR system

We propose and experimentally demonstrate a parallel pulsed chaos light detection and ranging (LiDAR) system with a high peak power, parallelism, and anti-interference. The system generates chaotic microcombs based on a chip-scale Si3N4 microresonator. After passing through an acousto-optic modulator, the continuous-wave chaotic microcomb can be transformed into a pulsed chaotic microcomb, in which each comb line provides pulsed chaos. Thus, a parallel pulsed chaos signal is generated. Using the parallel pulsed chaos as the transmission signal of LiDAR, we successfully realize a 4-m three-dimensional imaging experiment using a microelectromechanical mirror for laser scanning. The experimental results indicate that the parallel pulsed chaos LiDAR can detect twice as many pixels as direct detection continuous wave parallel chaos LiDAR under a transmission power of -6 dBm, a duty cycle of 25%, and a pulse repetition frequency of 100 kHz. By further increasing the transmission power to 10 dBm, we acquire an 11 cm × 10 cm image of a target scene with a resolution of 30 × 50 pixels. Finally, the anti-jamming ability of the system is evaluated, and the results show that the system can withstand interferences of at least 15 dB.

Scalable parallel ultrafast optical random bit generation based on a single chaotic microcomb

Random bit generators are critical for information security, cryptography, stochastic modeling, and simulations. Speed and scalability are key challenges faced by current physical random bit generation. Herein, we propose a massively parallel scheme for ultrafast random bit generation towards rates of order 100 terabit per second based on a single micro-ring resonator. A modulation-instability-driven chaotic comb in a micro-ring resonator enables the simultaneous generation of hundreds of independent and unbiased random bit streams. A proof-of-concept experiment demonstrates that using our method, random bit streams beyond 2 terabit per second can be successfully generated with only 7 comb lines. This bit rate can be easily enhanced by further increasing the number of comb lines used. Our approach provides a chip-scale solution to random bit generation for secure communication and high-performance computation, and offers superhigh speed and large scalability.

Investigation on the monolithically integrated chaotic optical transmitting chip based on parallel EAMs

Chaotic optical communication ensures information security at the physical layer. However, the monolithic integration of lasers and lithium niobate Mach-Zehnder modulators remains a challenge, limiting the progress of integrated chaotic optical communication systems based on an electro-optic feedback. Here, we propose the monolithically integrated chaotic optical transmitting chip based on the parallel EAMs and validate its performance from the perspectives of phase portraits, fast Fourier transform (FFT), probability density function (PDF), largest Lyapunov exponents, and bifurcation. The results demonstrate the feasibility of the chip, which is beneficial for the miniaturization and integration of the system.

Synchronization of two chaotic microresonator frequency combs

We explore the synchronization of chaotic microresonator frequency combs, emphasizing the modulation instability state, which is known for its inherent chaotic behaviors. Our study confirms that the synchronization of two such combs is feasible by injecting the output from the lead microresonator into the next microresonator's input. We also identify the optimal parameters for this synchronization. Remarkably, even partial injection from the leader is sufficient for synchronization, paving the way for versatile future system configurations. Such systems could simultaneously utilize distinct spectral components for synchronization and transmission. This work advances our understanding of chaotic microresonator combs, showing them to be pivotal elements in next-generation optical communication systems.

On prediction of chaotic dynamics in semiconductor lasers by reservoir computing

Studying the chaotic dynamics of semiconductor lasers is of great importance for their applications in random bit generation and secure communication. While considerable effort has been expended towards investigating these chaotic behaviors through numerical simulations and experiments, the accurate prediction of chaotic dynamics from limited observational data remains a challenge. Recent advancements in machine learning, particularly in reservoir computing, have shown promise in capturing and predicting the complex dynamics of semiconductor lasers. However, existing works on laser chaos predictions often suffer from the need for manual parameter optimization. Moreover, the generalizability of the approach remains to be investigated, i.e., concerning the influences of practical laser inherent noise and measurement noise. To address these challenges, we employ an automated optimization approach, i.e., a genetic algorithm, to select optimal reservoir parameters. This allows efficient training of the reservoir network, enabling the prediction of continuous intensity time series and reconstruction of laser dynamics. Furthermore, the impact of inherent laser noise and measurement noise on the prediction of chaotic dynamics is systematically examined through numerical analysis. Simulation results demonstrate the effectiveness and generalizability of the proposed approach in achieving accurate predictions of chaotic dynamics in semiconductor lasers.