Hollow-core fiber-based photothermal spectroscopy for hydrogen detection.

We present an optical hydrogen sensor based on photothermal spectroscopy with a hollow-core fiber, specifically targeting the 2121.8-nm quadrupole absorption line of hydrogen. Our experiments demonstrate the sensor's capability for detecting hydrogen gas at concentrations as low as 77 ppm, with a lock-in time constant of 1 second.

Wideband chaos generation using VCSELs with intensity-modulated chaotic optical injection.

We propose what we believe to be a novel approach for generating wideband chaos via intensity-modulated chaotic optical injection, utilizing chaotic signals produced by a free-running vertical-cavity surface-emitting laser. Two injection configurations are considered: parallel injection and orthogonal injection. Specifically, we examine the effect of injection parameters, including injection strength and frequency detuning, on the chaos radio frequency spectrum bandwidth.

Routes to broadband laser chaos with dynamics switching in a 1550-nm VCSEL laser subjected to optical feedback.

Vertical-cavity surface-emitting laser (VCSEL) has received much attention due to its high modulation response bandwidth, two linear polarization modes, and easy integration. The fundamental characteristics of lasers can be observed by simple optical feedback. Here, we experimentally investigate the dynamical characteristics in a 1550-nm VCSEL subjected to mirror optical feedback.

Adjusting frequency response characteristics of fiber optic accelerometers using electromagnetic feedback technology.

A control method of electromagnetic feedback is proposed for adjusting frequency response characteristics of fiber optic accelerometers, which could expand the flat working bandwidth and enhance performance consistency. The proof sensor employs an open-loop disc-type vibration pickup structure, cascaded with an electromagnetic feedback control unit. A proportional-differential control algorithm is utilized to generate the feedback signal, which ultimately acts on the input side of the sensor.

Chirp-pulse pair φOTDR.

We proposed a novel, to the best of our knowledge, chirp-pulse pair phase-sensitive optical time-domain reflectometry (CPP-φOTDR) technique, enhanced by an adaptive filtering algorithm. This technique utilizes a pair of chirp pulses: one with a low chirp rate and another with a high chirp rate, with their Rayleigh backscattering (RBS) processed through a low-pass (LP) electrical filter. The adaptive filtering algorithm effectively preserves the extensive measurement range afforded by the high chirp rate pulse while enhancing the sensitivity provided by the low chirp rate pulse.

Wideband chaos generation based on an integrated mutual coupling laser.

To further enhance the bandwidth of an integrated chaotic semiconductor laser, a structure of an integrated mutual coupling laser is proposed. The laser integrates two distributed feedback lasers and two semiconductor optical amplifiers in the middle of the lasers. The dynamic state of the integrated laser undergoes complex changes with the variation of the bias currents of the distributed feedback (DFB) lasers and semiconductor optical amplifiers (SOAs).

Full-scale OFDR-based distributed strain sensing with enhanced measurement accuracy.

In this Letter, we propose a method to improve strain sensing accuracy across the full-scale distance at the 100 m level in optical frequency domain reflectometry (OFDR) by minimizing residual phase noise (RPN), which significantly degrades strain accuracy. We derive a quantitative relationship between RPN variance and interferometer delay and design a coded delay fiber module (OPEM) that dynamically provides delay fibers of optimal length. By quantitatively analyzing RPN and guiding the output configuration of the OPEM to suppress RPN at the hardware level, we achieved strain sensing with a spatial resolution of 2 mm and a strain accuracy better than 1.

Secure space division multiplexing system based on multi-channel chaos random encryption with synchronized Fabry-Perot lasers.

Chaotic optical communication has recently garnered considerable research interest for providing physical layer security. In this work, we propose and demonstrate a secure space-division-multiplexing (SDM) system based on multi-channel chaos random en/decryption with remotely synchronized Fabry-Perot (FP) lasers. By a random combination of multi-longitudinal modes from the FP lasers, multi-channel low-correlated chaotic signals can be produced and then utilized for encrypting the confidential data, which effectively provides multiple possibilities of optical encryption from a single chaotic laser source.

High-sensitivity hot-wire anemometer using cobalt-doped fiber-based long-period gratings.

A high-sensitivity hot-wire anemometer is proposed for use with a cobalt-doped fiber (CDF) based long-period grating (LPG) heated optically by a 1480 nm laser. The CDF-LPG absorbs laser power and generates heat inherently, thereby eliminating the need for both metal coating and mode coupling devices that are usually required in optical fiber grating anemometers. The dip wavelength of the CDF-LPG shifts with airflow velocity due to the cooling effect of the airflow.

Experimental demonstration of 8190-km long-haul semiconductor-laser chaos synchronization induced by digital optical communication signal.

Common-signal-induced synchronization of semiconductor lasers have promising applications in physical-layer secure transmission with high speed and compatibility with the current fiber communication. Here, we propose an ultra-long-distance laser synchronization scheme by utilizing random digital optical communication signal as the common drive signal. By utilizing the long-haul optical coherent communication techniques, high-fidelity fiber transmission of the digital drive can be achieved and thus ultra-long-distance synchronization is expected.

Parallel generation of multi-channel broadband chaos by a long-cavity FP laser with optical feedback.

Parallel generation of multi-channel chaos is critical to applications, and the key challenge is the simultaneous generation of broadband chaos with multiple channels and low correlation. Here, we experimentally demonstrate a parallel broadband chaos generation scheme using a single long-active-cavity Fabry-Perot (LC-FP) semiconductor laser under optical feedback. The active-cavity length is designed to be 1500 μm, so the power spectrum of chaos is expanded and flattened by the mode-beating effect.

Physical layer security--enhanced optical communication based on chaos masking and chaotic hardware encryption.

The security and confidentiality of information are crucial in contemporary communication systems. In this work, we propose a physical layer security-enhanced optical communication scheme based on dual-level protection with chaos masking (CMS) and chaotic hardware encryption. The integration of CMS and chaotic hardware encryption contributes to enhancing the security of the system.

The JNK signaling pathway in intervertebral disc degeneration.

Intervertebral disc degeneration (IDD) serves as the underlying pathology for various spinal degenerative conditions and is a primary contributor to low back pain (LBP). Recent studies have revealed a strong correlation between IDD and biological processes such as Programmed Cell Death (PCD), cellular senescence, inflammation, cell proliferation, extracellular matrix (ECM) degradation, and oxidative stress (OS). Of particular interest is the emerging evidence highlighting the significant involvement of the JNK signaling pathway in these fundamental biological processes of IDD.

Improving decryption quality of optical chaos communication using neural networks.

Optical chaos communication is a promising secure transmission technique because of the advantages of high speed and compatibility with existing fiber-optic systems. The deterioration of chaotic synchronization quality caused by fiber optic transmission impairments affects the quality of recovery of information, especially high-order modulated signals. Here, we demonstrate that the use of a convolutional neural network (CNN) with a bidirectional long short-term memory (LSTM) layer can reduce the decryption BER in an optical chaos communication system based on common-signal-induced semiconductor laser synchronization.

Phase noise suppression of optic flexural disk accelerometer by studying the thermal stability of optical fiber ring.

As the core sensing elements of ultra-long fiber interferometer, the distributed thermal strain difference of the fiber rings can cause extra noise of the flexural disk, resulting in a penalty of the deterioration accuracy. In this paper, the thermal strain distribution characteristics of the fiber ring are firstly analyzed by the finite element method (FEM), and the distribution result is consistent with that demonstrated by the Rayleigh optical frequency-domain reflectometry (R-OFDR) strain measurement. The interferometer phase noise caused by the distributed strain difference is further studied by constructing a fully symmetric polarization-maintaining fiber-ring Mach-Zehnder interferometer (MZI) with an arm length of over 100 meters.

Statistical properties for an optically injected chaotic semiconductor laser with a high-pass filter.

Chaotic waveforms with Gaussian distributions are significant for laser-chaos-based applications such as random number generation. By exploring the injection parameter space of the optical injection semiconductor lasers, we numerically investigate the associated probability density functions of the generated chaotic waveforms when different high-pass filters with different cutoff frequencies are used. Our results demonstrate that the chaotic waveforms with Gaussian probability density functions can be obtained once the cutoff frequency of the high-pass filter is larger than the laser relaxation resonance frequency.

Wireless-Channel Key Distribution Based on Laser Synchronization.

We propose and experimentally demonstrate a wireless-channel key distribution scheme based on laser synchronization induced by a common wireless random signal. Two semiconductor lasers are synchronized under injection of the drive signal after electrical-optical conversion and emit irregular outputs that are used to generate shared keys. Our proof-of-concept experiment using a complex drive signal achieved a secure key generation rate of up to 150 Mbit/s with a bit error rate below 3.

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.

Physical-layer key distribution based on commonly-driven laser synchronization with random modulation of drive light.

We propose and experimentally demonstrate a physical-layer key distribution scheme using commonly-driven laser synchronization with random modulation of drive light. Two parameter-matched semiconductor lasers injected by a common complex drive light are used as entropy sources for legitimate users. Legitimate users generate their own random signal by randomly time-division multiplexing of two random sequences with a certain duration according to individual control codes, and then independently modulate the drive light.

High-speed secure key distribution based on interference spectrum-shift keying with signal mutual modulation in commonly driven chaos synchronization.

The secure key generation and distribution (SKGD) are unprecedentedly important for a modern secure communication system. This paper proposes what we believe to be a novel scheme of high-speed key distribution based on interference spectrum-shift keying with signal mutual modulation in commonly driven chaos synchronization. In this scheme, delay line interferometers (DLI) are utilized to generate two low-correlation interference spectra from commonly driven synchronous chaos, and then a 2 × 2 optical switch can effectively change the relationship between the two interference spectra in post-processing by shifting the states of the switch.

Security optimization of synchronization in DFB lasers under constant-amplitude random-phase drive light by reducing drive-response correlation.

Common-signal-induced laser synchronization promoted a promising paradigm of high-speed physical key distribution. Constant-amplitude and random-phase (CARP) light was proposed as the common drive signal to enhance security by reducing the correlation between the drive and the laser response in intensity. However, the correlation in light phase is not examined.

Chaos synchronization of VCSELs with common injection of polarization-random light.

We propose and numerically demonstrate chaos synchronization of two vertical-cavity surface-emitting lasers (VCSELs) induced by common injection of constant-amplitude random-polarization light for physical key distribution. Results show that synchronization is sensitive to polarization rotation of injection light, and synchronization coefficients larger than 0.9 can be achieved as the rotation-degree mismatch is smaller than ±10°.

Millimeter-wave noise generation based on a monolithically integrated dual-mode chaotic laser.

A millimeter-wave noise generation scheme is proposed in this paper. The scheme is based on a monolithically integrated dual-mode chaotic laser, which consists of a distributed Bragg feedback (DFB) section, a phase section, and an optical amplification section. The output spectrum state of the dual-mode laser can be controlled by adjusting the injection current in the three regions.

Principles and Applications of Seismic Monitoring Based on Submarine Optical Cable.

Submarine optical cables, utilized as fiber-optic sensors for seismic monitoring, are gaining increasing interest because of their advantages of extending the detection coverage, improving the detection quality, and enhancing long-term stability. The fiber-optic seismic monitoring sensors are mainly composed of the optical interferometer, fiber Bragg grating, optical polarimeter, and distributed acoustic sensing, respectively. This paper reviews the principles of the four optical seismic sensors, as well as their applications of submarine seismology over submarine optical cables.