True random numbers occupy a core role in the field of encryption and security by virtue of their properties such as unpredictability and independence. In this paper, we propose a high-speed physical random number generator based on a dual-emission random fiber laser. The system improves the spectral bandwidth characteristics of the output signals by adjusting the pump power and the feedback length of the single mode fiber. This study effectively suppresses the autocorrelation feature by performing exclusive-OR operations on the forward and backward random laser signals, and obtain the random number sequence with a generation rate of 20 Gbps by post-processing with high-order finite difference and least significant bit extraction. In order to verify the practical application performance, we apply the random sequence as encryption key to digital image encryption, and the experimental results show that the generator has both theoretical security and practical application value.

As foldable smartphones typically operate in two primary states-unfolded state and folded state, the structural changes between the two states, which can significantly impact antenna performance, such as frequency shifts and efficiency reduction, are critical for practical applications. This paper proposes to use a quarter-wavelength parasitic branch to mitigate the effect of the structural changes between the two states. With the quarter-wavelength parasitic branch, a high-efficiency deca-band mobile antenna with similar performance in both the unfolded and folded states is achieved. Prototype testing shows negligible frequency shifts (approximately 0 MHz) in the low band (LB) of 0.704–0.960 GHz, middle high band (MHB) of 1.71–2.69 GHz, and new radio (NR) bands of 3.3–3.8 GHz and 4.7–5.0 GHz between the unfolded and folded states. The efficiency reductions are 0.45 dB (from −4.98 dB to −5.43 dB) in the LB band, 0.28 dB (from −2.70 dB to −2.98 dB) in the MHB band, and 0.81 dB (from −2.34 dB to −3.15 dB) in the NR band. The proposed antenna, which demonstrates minimal frequency shifts and slight efficiency degradation in the unfolded and folded states, makes it highly promising for practical applications.

Responsive photonic crystals (PCs) are attractive because of their unique photonic bandgap (PBG) effect, but existing systems tend to have challenges such as narrow PBG tuning range, slow response to external stimuli, poor reversibility, and difficulty in device integration. To address these issues, magneto-responsive colloidal PCs have been developed with the advantages of fast response, high sensitivity, good reversibility, and contactless manipulation. In addition, magneto-optical responsive flexible lasers are developed to bring new solutions for information encryption and anti-counterfeiting. Combining magnetic nanoparticles and spiropyran molecules to create a composite film that can be both magnetically and optically color-changing, achieving non-contact, multi-stimulus-responsive color-changing, and expanding the application fields for color display and anti-counterfeiting technologies. Further, a flexible laser is designed that achieves efficient and reversible laser wavelength tuning from 580 to 700 nm through dual control of the f & ouml;rster resonance energy transfer effect and magnetic field and UV irradiation. This laser's wavelength tuning combines the structural regulation of magnetic particles with the photo-responsive properties of spiropyran. It not only advances the field of optical communication but also enhances the security of information encoding and anti-counterfeiting through the synergy of magneto- and photochromism, bringing revolutionary improvements to anti-counterfeiting technology.

Hydrogen (H-2) is a renewable energy gas and an important industrial raw material playing important roles in many fields. However, H-2 is colorless, odorless and highly flammable within a wide concentration range. So H-2 detection is very important for leakage monitoring especially at low concentration. Here we propose an ultrahigh sensitivity H-2 sensor with a perforated palladium (Pd) film on the tip of an optical fiber. The suspended Pd nanohole film forms a Fabry-P e'rot (FP) interferometer with a silica capillary fused onto the fiber. Upon H2 adsorption, the Pd nanohole film bends inwards leading to spectral shift of the FP cavity. With the film perforated, its Young's modulus becomes effectively smaller giving rise to larger spectral shift and higher H-2 sensitivity. We experimentally studied the effect of the structural parameters of the holey film on the H-2 sensing performance and achieved a H-2 detection sensitivity of 7.1 pm/ppm and a detection limit of 1.7 ppm. The sensor also shows good repeatability and gas selectivity and is expected to find applications as optical H-2 sensors working at low concentrations.

Modulation of scattering in random lasers (RLs) by magnetic fields has attracted much attention due to its rich physical insights. We fabricate magnetic gain polymer optical fiber to generate RLs. From macroscopic experimental phenomena, with the increase of the magnetic field strength, the magnetic transverse photocurrent exists in disordered multiple scattering of RLs and the emission intensity of RLs decreases, which is the experimental observation of photonic Hall effect (PHE) and photonic magnetoresistance (PMR) in RLs. At the microscopic level, based on the field dependence theory of magnetic disorder in scattered nanoparticles and the replica symmetry breaking theory, the magnetic-induced transverse diffusion of photons reduces the scattering disorder, and then decreases the intensity fluctuation disorder of RLs. Our work establishes a connection between the above two effects and RLs, visualizes the influence of magnetic field on RL scattering at the microscopic level, which is crucial for the design of RLs.

The rise in oil extraction and transportation in marine environments has led to frequent oil spill incidents, posing a severe threat to marine ecosystems and becoming an urgent environmental issue. This paper presents a laser-induced fluorescence light detection and ranging (LiDAR) system specifically designed for monitoring marine oil spills. The system comprises a laser emission module, a receiving module, a data processing module, and a wireless transmission module. Through outdoor experiments, the system has demonstrated its effectiveness and reliability in detecting and identifying various oil types, including crude oil, diesel, heavy oil, gasoline, and lubricating oil. Additionally, a BP neural network model was employed to process the fluorescence spectral data collected by the LiDAR system. This model successfully predicted oil types with an accuracy of 96.58

This study presents the design and development of a high-resolution convex grating dispersion hyperspectral imaging system tailored for unmanned aerial vehicle (UAV) remote sensing applications. The system operates within a spectral range of 400 to 1000 nm, encompassing over 150 channels, and achieves an average spectral resolution of less than 4 nm. It features a field of view of 30°, a focal length of 20 mm, a compact volume of only 200 mm × 167 mm × 78 mm, and a total weight of less than 1.5 kg. Based on the design specifications, the system was meticulously adjusted, calibrated, and tested. Additionally, custom software for the hyperspectral system was independently developed to facilitate functions such as control parameter adjustments, real-time display, and data preprocessing of the hyperspectral camera. Subsequently, the prototype was integrated onto a drone for remote sensing observations of Spartina alterniflora at Yangkou Beach in Shouguang City, Shandong Province. Various algorithms were employed for data classification and comparison, with support vector machine (SVM) and neural network algorithms demonstrating superior classification accuracy. The experimental results indicate that the UAV-based hyperspectral imaging system exhibits high imaging quality, minimal distortion, excellent resolution, an expansive camera field of view, a broad detection range, high experimental efficiency, and remarkable capabilities for remote sensing detection.

In this study, the two-dimensional (2D) triangular lattice metallic photonic crystals (PCs) in visible and infrared bands have been utilized to achieve light confinement at the Dirac frequency. Distinct from the traditional bandgap or total internal reflection cavity modes, the unique photonic localization mechanism leads to an unusual algebraic decay of state and a unique frequency located beyond any bandgaps. This investigation delves into the band structure analysis of 2D metallic PCs, specifically focusing on their distinctive features, such as photonic bandgaps and Dirac cones. The plane wave expansion (PWE) method, enhanced with a linearization technique, is employed for band structure calculations, considering both the frequency-dependent dielectric properties and the intrinsic lossy nature of metallic materials described by the Drude model. The study provides a comprehensive derivation of the PWE equations for metallic PCs and investigates their band characteristics under both TM and TE polarizations. Focusing on TM modes in triangular lattice metallic PCs, it reveals zero density of states (DOS) at K points of the Brillouin corner and the existence of Dirac cones with linearly dispersion and linearly vanishing DOS. The study extends to exploring localized modes at Dirac frequencies, employing a relativistic quantum mechanics approach analogous to graphene's charge carriers. Theoretical predictions are corroborated by numerical simulations, and the potential for tunable Dirac localized modes is highlighted. This research not only deepens the understanding of Dirac properties in graphene-like systems but also lays the groundwork for further exploration of the practical quasi-2D devices, which will provide assistance in the integration of micro- and nano- devices, especially in applications requiring long-range coupling, given the critical importance of optical cavities in contemporary optical technologies.

Carbon-based hole-conductor-free perovskite solar cells (PSCs) exhibit promising potential on the road to commercialization for their low-cost production, scalable fabrication, and superior stability. However, the insufficient back interface contact between the carbon counter electrode (CE) and the perovskite is an urgent issue that hinders device performance. Herein, we report the preparation and application of defect-rich boron-doped graphite (BG) as the main CE medium for efficient printable mesoscopic PSCs (p-MPSCs). Boron doping induces the formation of abundant defective sites, including dangling bonds and oxygen-containing groups, onto the surface of graphite. These sites activate the inert surface and improve the surface affinity of CE with the perovskite. p-MPSCs based on BG achieve a firm interfacial contact, which improves the power conversion efficiency from 17.94% to 19.43% by enhancing charge collection.

Random lasers are a type of lasers that lack typical resonator structures,offering benefits such as easy integration,low cost,and low spatial coherence.These features make them popular for speckle-free imaging and random number gen-eration.However,due to their high threshold and phase instability,the production of picosecond random lasers has still been a challenge.In this work,we have developed three dyes incorporating polymer optical fibers doped with various scat-tering nanoparticles to produce short-pulsed random fiber lasers.Notably,stable picosecond random laser emission lasting 600 ps is observed at a low pump energy of 50 μJ,indicating the gain-switching mechanism.Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level. When the intensity of the continuously pumped light reaches a specific value,the number of inversion populations in the"scattering cavity"surpasses the threshold rapidly.Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon.This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.

To realize multiparameter simultaneous sensing measurement and eliminate cross-sensitivity, we cascade three micro-tapered long period fiber grating (TLPG) sensors and analyze the transmission characteristics and sensing capabilities of cascaded micro-tapered long period fiber gratings (CTLPG) in detail. Based on the modulation of the resonant wavelength of the sensor by the change of the surrounding environment, the synchronous real-time detection of refractive index (RI), temperature, and liquid level is realized. The CTLPG sensor, not only inherits the advantages of TLPG sensors, and reduces the influence of cross-sensitivity when measuring multiparameters, but also improves the sensitivity and accuracy of the sensor. Experimental results show that the maximum RI sensitivity is 693 nm/RIU, the maximum temperature sensitivity is -93 pm/°C, and the maximum liquid level sensitivity is 12 nm/mm. The sensor has a simple structure, low manufacturing cost, high sensitivity, and potential applications in monitoring ocean temperature, salinity, and depth.

Hydrogen (H2) sensors are critical to various applications such as the situation where H2 is used as the clean energy for industry or the indicator for human disease diagnosis. Palladium (Pd) is widely used as the hydrogen sensing material in different types of sensors. Optical fiber H2 sensors are particularly promising due to their compactness and spark-free operation. Here, we report a Fabry–Pérot (FP)-cavity-based H2 sensor that is formed with a freestanding Pd membrane and integrated on a conventional single-mode optical fiber end. The freestanding Pd membrane acts both as the active hydrogen sensing material and as one of the reflective mirrors of the cavity. When the Pd film absorbs H2 to form PdHx, it will be stretched, resulting in a change of the cavity length and thus a shift of the interference spectrum. The H2 concentration can be derived from the amplitude of the wavelength shift. Experimental results showed that H2 sensors based on suspended Pd membranes can achieve a detection sensitivity of about 3.6 pm/ppm and a detection limit of about 3.3 ppm. This highly sensitive detection scheme is expected to find applications for sensing low-concentration H2.

Hydrogel materials have great applications in biomedical and flexible optical sensors due to their good flexibility and biocompatibility. In this paper, two hydrogel structures of dye-doped poly(acrylamide-co-poly(ethylene glycol) diacrylate) (p(AM-co-PEGDA)) films and optical fibers were prepared to obtain low threshold and flexible random lasers. The random laser is attributed to the light scattering from the porous structure of the hydrogel, and the random lasing wavelength can be tuned of -7 nm and -11.8 nm for the hydrogel film and fiber in the temperature range of 25 to 85 degrees C, respectively. In addition, the hydrogel film can be bent repeatedly, and the bending strain has a positive effect on the random laser, and the random laser threshold is reduced by 10 mu J/mm2 when the bending strain reaches 47 % for hydrogel film. When the hydrogel optical fiber is stretched to 15 % of its original length, the random laser threshold can be reduced by 12 mu J/mm2.The p(AM-co-PEGDA) hydrogel optical fiber structure has better temperature sensing performance and excellent flexibility than the thin film structure. This work paves a way to extend random laser applications to photothermal therapy, ion detection, and biosensing.

In this study, a practical and straightforward method is presented for measuring the optical feedback coefficient C and the linewidth enhancement factor ?? by means of the mode-hopping phenomena in the self-mixing interferometric system. A theoretical analytical model, in combination with the laser energy transition area of the phase jumping points and the C-parameter, is described deeply. In the experiment, a laser self-mixing vibration sensing system is fabricated to further verify this proposed theoretical model and simultaneously obtain the geometric area S (R,F) under different C values. From the actual measurements, the C-parameter is exactly measured by tracking the change of the geometric area S (R,F), over the range of 1.0-4.5. Then, the alpha-factor of this self-mixing sensor is obtained as 2.41 +/- 0.15 with an accuracy of 6%. In addition, the absolute and relative error of the experimental results are less than 0.14 and 7.43%, respectively. In a word, the measured results agree well with the simulated values, of which validates the good applicability and practicability of this measurement method.

Reliable gas sensors are very important for hydrogen (H2) gas detection and storage. Detection methods based on palladium (Pd) metal are cost-effective and widely studied. When Pd is exposed to H2, it turns into palladium hydride with modified optical properties, which thus can be monitored for H2 sensing. Here, we fabricated large-area Pd nanostructures, including Pd nanotriangles and nanohole arrays, using colloidal lithography and systematically studied their H2-sensing performance. After hydrogen absorption, both the Pd nanoholes and nanotriangles showed clear transmittance changes in the visible–near infrared range, consistent with numerical simulation results. The influences of the structural parameters (period of the array P and diameter of the nanohole D) of the two structures are further studied, as different structural parameters can affect the hydrogen detection effect of the two structures. The nanohole arrays exhibited bigger transmittance changes than the nanotriangle arrays.

An ultrasensitive refractive index sensor based on a lossy all-dielectric nanosphere.

In order to control the divergence angle of the optical fiber and reduce the focal spot size of the beam, we have proposed and experimentally proved a simple and low-cost method for fabricating microlens on the end facet of the fiber, which involves only two steps: dripping and curing. We successfully fabricated hemispherical microlenses with different sizes on the fiber end facets and proved that the shape of microlens can be adjusted through multiple titration and curing processes. The measured characteristics of the beam output from a lensed fiber are in agreement with numerical simulation results.

A compact fiber-optic acceleration sensor based on Fabry-Perot interferometer is proposed and fabricated. The experimental results show that the minimum detectable acceleration of the accelerometer is 0.928 mg and the available bandwidth is 10-90 Hz.

A long distance voice transmission system based on a visible light communication technology (VLCT) is proposed in the paper. Our proposed system includes transmitter, receiver and the voice signal processing of single chip microcomputer. In the compact-sized LED transmitter, we use on-off-keying and not-return-to-zero (OOK-NRZ) to easily realize high speed modulation, and then systematic complexity is reduced. A voice transmission system, which possesses the properties of the low-noise and wide modulation band, is achieved by the design of high efficiency receiving optical path and using filters to reduce noise from the surrounding light. To improve the speed of the signal processing, we use single chip microcomputer to code and decode voice signal. Furthermore, serial peripheral interface (SPI) is adopted to accurately transmit voice signal data. The test results of our proposed system show that the transmission distance of this system is more than100 meters with the maximum data rate of 1.5 Mbit/s and a SNR of 30dB. This system has many advantages, such as simple construction, low cost and strong practicality. Therefore, it has extensive application prospect in the fields of the emergency communication and indoor wireless communication, etc.