Mid-infrared hyperchaos of interband cascade lasers

Experimental Study on Damage Effect of Mid-Infrared Pulsed Laser on Charge Coupled Device (CCD) and HgCgTe Detectors

As the weak link in electro-optical imaging systems, photodetectors have always faced the threat of laser damage. In this paper, we experimentally investigated the damage mechanism of the photodetector induced by the out-of-band laser. The damage thresholds of the mid-infrared pulsed laser for Charge Coupled Device (CCD) and HgCdTe detectors were determined through damage experiments. The analysis of the damage phenomena and data for both CCD and HgCdTe detectors clearly demonstrated that out-of-band mid-infrared pulsed lasers could entirely incapacitate CCD and HgCdTe detectors. Our analysis of the damage process and data revealed that the primary mechanism of damage to CCD and HgCdTe detectors by mid-infrared pulsed lasers was primarily thermal. This study serves as a reference for further research on the mid-infrared pulsed laser damage mechanisms of CCD and HgCdTe detectors, as well as for laser protection and performance optimization in imaging systems.

Crystal clear: unveiling giant birefringence in organic-inorganic cocrystals

Coplanar groups with large anisotropic polarizability are suitable as birefringence-active groups for investigating compounds with significant birefringence. In this study, the organic coplanar raw reagent, o-C5H5NO (4HP), was selected as an individual complement. Utilizing the cocrystal engineering strategy, we successfully designed two cocrystals: [LiNO3·H2O·4HP]·4HP (Li-4HP2) and [Mg(NO3)2·6H2O]·(4HP)2 (Mg-4HP), and one by-product: LiNO3·H2O·4HP (Li-4HP), which were grown using a mild aqua-solution method. The synergy of the coplanar groups of NO3 - and 4HP in the structures resulted in unexpectedly large birefringence values of 0.376-0.522@546 nm. Furthermore, the compounds exhibit large bandgaps (4.08-4.51 eV), short UV cutoff edges (275-278 nm), and favorable growth habits, suggesting their potential as short-wave UV birefringent materials.

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.

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.

Wavelength extension beyond 3 µm in a Ho3+/Pr3+ co-doped AlF3-based fiber laser

In this Letter, we report continuous-wave (CW) lasers with wavelengths beyond 3 µm in homemade Ho3+/Pr3+ co-doped AlF3-based glass fibers. The laser cavity was established through the integration of a dichroic mirror (DM, HR@3-3.1 µm) positioned at the pump end and a partial reflectivity (PR) fiber Bragg grating (FBG) situated at the laser emission end. The FBGs in AlF3-based glass fibers were fabricated by a fs laser direct-writing method, and the resonant wavelengths were 3.009, 3.036, and 3.064 µm, respectively. Under the pump of 1.15 µm laser, a maximum unsaturated output power of 1.014 W was obtained at 3.009 µm with an overall laser efficiency of 11.8% and FWHM bandwidth of 0.88 nm. Furthermore, in order to enhance the optical-thermal stability, the FBG was heat-treated at 200°C for 30 min, and a higher output power of 1081 mW (348 mW without heat treatment) at 3.036 µm was achieved. To the best of our knowledge, this is the first demonstration of 3-3.1 µm lasers by using FBGs in Ho3+/Pr3+ co-doped AlF3-based fibers.

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.

Feedback insensitivity in a self-chaotic microcavity laser

Insensitivity to external optical feedback is experimentally demonstrated in a self-chaotic deformed square microcavity laser for the first time, to the best of our knowledge. Both the optical and radio frequency (RF) spectra of the microlaser remain unaffected for external optical feedback with feedback strength as high as 9.9 dB. In addition, the autocorrelation function curve exhibits no time-delayed peaks. The insensitivity makes the self-chaotic microcavity laser promising for applications in feedback-insensitive optical sources.

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.

Low-frequency regular pulse and intermittent oscillation in a mid-infrared interband cascade laser with optoelectronic feedback

In this work, we experimentally investigate the nonlinear dynamics of a mid-infrared interband cascade laser (ICL) subject to optoelectronic feedback (OEF) through inspecting the time series and power spectrum of the laser output. The results show that, within the range of feedback strength limited by the experiment condition, the ICL sequentially presents stable state, continuously periodical oscillation (CPO), low-frequency regular pulse (LF-RP) and intermittent oscillation state with the increase of feedback strength. For the LF-RP state, the peak-to-peak value and the oscillation period increase with the increase of feedback strength. For the intermittent oscillation state, the time series is composed of the laminar region and burst region appeared alternately, and the average value and standard deviation for the duration of burst region gradually decrease with the increase of feedback strength.

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

Optical chaos is vital for various applications such as private communication, encryption, anti-interference sensing, and reinforcement learning. Chaotic microcombs have emerged as promising sources for generating massive optical chaos. However, their inter-channel correlation behavior remains elusive, limiting their potential for on-chip parallel chaotic systems with high throughput. In this study, we present massively parallel chaos based on chaotic microcombs and high-nonlinearity AlGaAsOI platforms. We demonstrate the feasibility of generating parallel chaotic signals with inter-channel correlation <0.04 and a high random number generation rate of 3.84 Tbps. We further show the application of our approach by demonstrating a 15-channel integrated random bit generator with a 20 Gbps channel rate using silicon photonic chips. Additionally, we achieved a scalable decision-making accelerator for up to 256-armed bandit problems. Our work opens new possibilities for chaos-based information processing systems using integrated photonics, and potentially can revolutionize the current architecture of communication, sensing and computations.

QCL Active Area Modeling with a View to Being Applied to Chemical Substance Detection Systems

Numerical research into the QCL tunability aspects in respect to being applied in chemical substance detection systems is covered in this paper. The QCL tuning opportunities by varying power supply conditions and geometric dimensions of the active area have been considered. Two models for superlattice finite (FSML) and infinite (RSM) size were assumed for simulations. The results obtained have been correlated with the absorption map for selected chemical substances in order to identify the potential detection possibilities.

Nonlinear Dynamics of Mid-Infrared Interband Cascade Lasers Subject to Variable-Aperture Optical Feedback

In this work, we experimentally investigate the nonlinear dynamics of an interband cascade laser (ICL) under variable-aperture optical feedback implemented by a gold mirror combining with a ring-actuated iris diaphragm (RAID). By continuously varying the diameter of RAID (DR), the evolution of the dynamical state of ICL with the aperture of the optical feedback can be inspected. The characteristics of each dynamical state are characterized by time series, power spectra, phase portraits, and Lyapunov exponents. The results show that, with the decrease of DR, the dynamical state of the ICL under variable-aperture optical feedback presents an evolution from complex, simple to stable. Diverse dynamical states including period one state (P1), period two state (P2), multi-period state (MP), quasi-period state (QP), low-frequency fluctuation (LFF), chaotic state (C), and hyperchaos have been observed. Through mapping the evolution of dynamical states with DR for the ICL biased at different currents, different evolved routes of the dynamical states are revealed.

Predicting the dynamical behaviors for chaotic semiconductor lasers by reservoir computing

We demonstrate the successful prediction of the continuous intensity time series and reproduction of the underlying dynamical behaviors for a chaotic semiconductor laser by reservoir computing. The laser subject to continuous-wave optical injection is considered using the rate-equation model. A reservoir network is constructed and trained using over 2 × 10⁴ data points sampled every 1.19 ps from the simulated chaotic intensity time series. Upon careful optimization of the reservoir parameters, the future evolution of the continuous intensity time series can be accurately predicted for a time duration of longer than 0.6 ns, which is six times the reciprocal of the relaxation resonance frequency of the laser. Moreover, we demonstrate for the first time, to the best of our knowledge, that the predicted intensity time series allows for accurate reproduction of the chaotic dynamical behaviors, including the microwave power spectrum, probability density function, and the chaotic attractor. In general, the demonstrated approach offers a relatively high flexibility in the choice of reservoir parameters according to the simulation results, and it provides new insights into the learning and prediction of semiconductor laser dynamics based on measured intensity time series.