Mid-infrared hyperchaos of interband cascade lasers

Chaos in nonlinear dynamical systems is featured with irregular appearance and with high sensitivity to initial conditions.Near-infrared light chaos based on semiconductor lasers has been extensively studied and has enabled various applications.Here,we report a fully-developed hyperchaos in the mid-infrared regime,which is produced from interband cascade lasers subject to the external optical feedback.Lyapunov spectrum analysis demonstrates that the chaos exhibits three positive Lyapunov exponents.Particularly,the chaotic signal covers a broad frequency range up to the GHz level,which is two to three orders of magnitude broader than existed mid-infrared chaos solutions.The interband cascade lasers produce either periodic oscillations or low-frequency fluctuations before bifurcating to hyperchaos.This hyperchaos source is valuable for developing long-reach secure optical communication links and remote chaotic Lidar systems,taking advantage of the high-transmission windows of the atmosphere in the mid-infrared regime.

Beyond fundamental resonance mode:high-order multi-band ALN PMUT for in vivo photoacoustic imaging

This paper reports on an aluminum nitride(AlN)piezoelectric micromachined ultrasound transducer(PMUT)array for photoacoustic(PA)imaging,where the high-order resonance modes of the PMUT are utilized to improve imaging resolution.A flexural vibration mode(FVM)PMUT is fabricated and applied in a photoacoustic imaging(PAI)system.Specifically,the microelectromechanical system(MEMS)-based PMUT is suitable for PA endoscopic imaging of blood vessels and bronchi due to its miniature size and high sensitivity.More importantly,AlN is a nontoxic material,which makes it harmless for biomedical applications.In the PAI system,the AlN PMUT array is used to detect PA signals,and the acousto–mechanical response is designed and optimized at the PMUT’s fundamental resonance.In this work,we focus on the high-order resonance performance of the PMUT PAI beyond the fundamental resonance.The acoustic and electrical responses of the PMUT’s high-order resonance modes are characterized and analyzed.The fundamental and three high-order resonance bandwidths are 2.2,8.8,18.5,and 48.2 kHz.Compared with the resolution at the fundamental resonance mode,the resolutions at third-and fourth-order resonance modes increase by 38.7%and 76.9%in a phantom experiment.The high-order resonance modes of the AlN PMUT sensor array provide higher central frequency and wider bandwidth for PA signal detection,which increase the resolution of PAI compared to the PMUT working at the fundamental resonance mode.