3D chaos lidar system with a pulsed master oscillator power amplifier scheme

Predicting the largest Lyapunov exponent of chaotic optically injected lasers by machine learning

We demonstrate for the first time to our knowledge successful prediction of the largest Lyapunov exponent (LLE) for chaotic semiconductor lasers using a convolutional neural network. Chaotic emission intensity waveforms are first generated using an optically injected laser. For training the machine learning model, LLEs of different chaotic intensity waveforms are first calculated based on a traditional phase-space reconstruction method. After carefully optimizing the neural network operating parameters, the prediction of the LLE is found successful with an error of less than 5% in both simulations and experiments. Moreover, by using the proposed method for LLE estimation, the computation efficiency is effectively improved. As compared to traditional methods, the computation time is reduced from about 100 s to less than 1 s, while the required input data length is also reduced by 80%. The effects of laser inherent noise and measurement noise on the prediction performance are also investigated. The proposed method provides a new perspective on studying the laser dynamics.

TDM/WDM hybrid real-time multi-channel pulsed chaos lidar system

We present a real-time multi-channel pulsed chaos lidar system that integrates time-division multiplexing (TDM) and wavelength-division multiplexing (WDM) to achieve enhanced performance and efficiency. The system employs WDM with a multi-mode laser to generate multiple spectral channels, each producing uncorrelated chaos-modulated pulses. To minimize the number of required detectors and analog-to-digital converters while mitigating signal interference between channels, TDM is utilized to temporally stagger the channels, preventing overlap. Using four adjacent International Telecommunication Union channels as a demonstration, the proposed architecture achieves millimeter-level precision with robust anti-interference capabilities. To evaluate the effectiveness of TDM in a WDM-based multi-channel lidar system, we performed a comparative analysis of 3D imaging with and without TDM. By implementing normalized cross-correlation and Spline interpolation algorithms on a field-programmable gate array, the developed system achieves a remarkable pixel processing rate of 330k pixels/s per channel, with an overall throughput of 1.32M pixels/s. These results underscore the potential of the proposed system for high-speed, interference-resistant lidar applications.

Active Region Mode Control for High-Power, Low-Linewidth Broadened Semiconductor Optical Amplifiers for Light Detection and Ranging

This paper introduces a semiconductor optical amplifier (SOA) with high power and narrow linewidth broadening achieved through active region mode control. By integrating mode control with broad-spectrum epitaxial material design, the device achieves high gain, high power, and wide band output. At a wavelength of 1550 nm and an ambient temperature of 20 °C, the output power reaches 757 mW when the input power is 25 mW, and the gain is 21.92 dB when the input power is 4 mW. The 3 dB gain bandwidth is 88 nm, and the linewidth expansion of the input laser after amplification through the SOA is only 1.031 times. The device strikes a balance between high gain and high power, offering a new amplifier option for long-range light detection and ranging (LiDAR).

Broadband chaos generation in a distributed-feedback laser by selecting residual side modes

Chaotic dynamics with spectral broadening is experimentally obtained by selective excitation of residual side modes in a distributed-feedback (DFB) laser. For the single-mode laser that emits only at the main mode when free-running, feedback to a residual side mode is introduced via a fiber Bragg grating (FBG). The FBG feedback suppresses the main mode, selectively excites the residual side mode, and generates broadband chaotic dynamics. Such a chaos of the residual side mode has a broad electrical bandwidth reaching at least 26 GHz, which corresponds to a significant broadening by over 50% when compared with the main mode. The dynamics are attributed entirely to the one selected mode without invoking multimode interactions. The wavelength is tunable beyond 10 nm by using different FBGs. Through avoiding multimode interactions, this approach of broadband chaos generation is potentially simple to model and thus promising for applications.

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.

A Review of High-Power Semiconductor Optical Amplifiers in the 1550 nm Band

The 1550 nm band semiconductor optical amplifier (SOA) has great potential for applications such as optical communication. Its wide-gain bandwidth is helpful in expanding the bandwidth resources of optical communication, thereby increasing total capacity transmitted over the fiber. Its relatively low cost and ease of integration also make it a high-performance amplifier of choice for LiDAR applications. In recent years, with the rapid development of quantum-well (QW) material systems, SOAs have gradually overcome the shortcomings of polarization sensitivity and high noise. The research on quantum-dot (QD) materials has further improved the noise characteristics and transmission loss of SOAs. The design of special waveguide structures-such as plate-coupled optical waveguide amplifiers and tapered amplifiers-has also increased the saturation output power of SOAs. The maximum gain of the SOA has been reported to be more than 21 dB. The maximum saturation output power has been reported to be more than 34.7 dBm. The maximum 3 dB gain bandwidth has been reported to be more than 120 nm, the lowest noise figure has been reported to be less than 4 dB, and the lowest polarization-dependent gain has been reported to be 0.1 dB. This study focuses on the improvement and enhancement of the main performance parameters of high-power SOAs in the 1550 nm band and introduces the performance parameters, the research progress of high-power SOAs in the 1550 nm band, and the development and application status of SOAs. Finally, the development trends and prospects of high-power SOAs in the 1550 nm band are summarized.

Parallel random LiDAR with spatial multiplexing of a many-mode laser

We propose and experimentally demonstrate parallel light detection and ranging (LiDAR) using random intensity fluctuations from a highly multimode laser. We optimize a degenerate cavity to have many spatial modes lasing simultaneously with different frequencies. Their spatio-temporal beating creates ultrafast random intensity fluctuations, which are spatially demultiplexed to generate hundreds of uncorrelated time traces for parallel ranging. The bandwidth of each channel exceeds 10 GHz, leading to a ranging resolution better than 1 cm. Our parallel random LiDAR is robust to cross-channel interference, and will facilitate high-speed 3D sensing and imaging.

Random-modulated pulse lidar using a gain-switched semiconductor laser with a delayed self-homodyne interferometer

We propose the generation of random-modulated pulses using a gain-switched semiconductor laser with a delayed self-homodyne interferometer (DSHI) for lidar applications. By emitting non-repetitive random-modulated pulses, ambiguity in ranging and interference in detection can be mitigated. When gain-switched, the wavelength of the laser fluctuates abruptly at the beginning of the pulse and then drops until it stabilizes toward its continuous-wave (CW) state. By beating the two pulses with instantaneous frequency detuning from the DSHI, pulses consisting of random and down-chirped modulations can be generated without any complex code generation and modulation. In this study, we investigate the waveforms and spectra of the random-modulated pulses generated under various homodyne delay lengths, switching currents, and pulsewidths. We characterize their signal-to-noise ratio (SNR), precision, and cross-correlation between consecutive pulses to evaluate their performance in lidar applications. For a good SNR of over 12 dB, the generated pulses have an optimal precision of approximately 1 mm in ranging, which is substantially better than the chaos-modulated pulses generated based on laser feedback dynamics. By establishing a random-modulated pulse lidar based on the proposed gain-switched homodyne scheme, we successfully demonstrate 3D imaging and profiling with good precision.

High-resolution and a wide field-of-view eye-safe LiDAR based on a static unitary detector for low-SWaP applications

High three-dimensional (3D) resolution for a wide field-of-view (FoV) is difficult in LiDARs because of the restrictions concerning size, weight, and power consumption (SWaP). Using a static unitary detector (STUD) approach, we developed a photodetector and a laser module for a LiDAR. Utilizing the fabricated photodetector and laser module, a LaserEye2 LiDAR prototype for low-SWaP applications was built using the STUD approach, which efficiently enables short-pulse detection with the increased FoV or large photosensitive area. The obtained 3D images demonstrated a diagonal FoV of > 31°, a frame rate of up to 15 Hz, and a spatial resolution of 320 × 240 pixels within a detection range of > 55 m. This prototype can be applied to drones to rapidly detect small or thin hazardous objects such as power lines.

Pulsed-chaos MIMO radar based on a single flat-spectrum and Delta-like autocorrelation optical chaos source

We propose and demonstrate a pulsed-chaos multiple-input-multiple-output (MIMO) radar system in this paper. In the proposed MIMO radar system, multi-channel pulsed chaotic signals are extracted from an optical seed chaos source with Delta-like autocorrelation and flat spectrum. The seed chaos source is generated by passing the chaotic output of an external-cavity semiconductor laser through a dispersive self-feedback phase-modulation loop and used for MIMO radar signal generation. The cross-correlation characteristics of MIMO radar signals, the maximum channel number of separable mixed echoes, as well as the performances of multi-target ranging and anti-interference in the proposed pulsed-chaos MIMO radar system are systematically investigated. The results indicate that multi-channel pulsed-chaos signals with Delta-like autocorrelation can be simultaneously generated from the seed chaos source, and excellent quasi-orthogonality of transmission radar signals can be guaranteed. Moreover, it is demonstrated that the proposed pulsed-chaos MIMO radar supports multi-target ranging with a centimeter-level resolution and can maintain satisfactory performance under low SNR scenarios with various interferences.

Competition between Entrainment Phenomenon and Chaos in a Quantum-Cascade Laser under Strong Optical Reinjection

The topic of external optical feedback in quantum-cascade lasers is relevant for stability and beam-properties considerations. Albeit less sensitive to external optical feedback than other lasers, quantum-cascade lasers can exhibit several behaviors under such feedback, and those are relevant for a large panel of applications, from communication to ranging and sensing. This work focused on a packaged Fabry–Perot quantum-cascade laser under strong external optical feedback and shows the influence of the beam-splitter characteristics on the optical power properties of this commercially available laser. The packaged quantum-cascade laser showed extended conditions of operation when subject to strong optical feedback, and the maximum power that can be extracted from the external cavity was also increased. When adding a periodic electrical perturbation, various non-linear dynamics were observed, and this complements previous efforts about the entrainment phenomenon in monomode quantum-cascade lasers, with the view of optimizing private communication based on mid-infrared quantum-cascade lasers. Overall, this work is a step forward in understanding the behavior of the complex quantum-cascade-laser structure when it is subjected to external optical feedback.