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This paper studies the constellation optimization approach for multiple-input multiple-output (MIMO) visible light communication (VLC) systems with signal-dependent noise (SDN). We propose a constellation optimization method aiming at minimizing the system pairwise error probability. In order to obtain the transmitter constellation, we design the demapping rules from the perspective of energy efficiency and illumination uniformity. For the scenario where receiver randomly moves, the constellation lookup table is proposed to transform real-time optimization into table lookup operation, which effectively reduces the real-time computational complexity. Simulation results show that the optimized constellation leads to lower symbol error rate (SER) than the method of maximizing minimum Euclidean distance. In addition, the constellation lookup table operation shows negligible SER performance degradation.

To tackle the efficiency droop, we employed an epitaxial structure engineering approach and utilized SimuLED software to thoroughly investigate the influence of the quantum barrier (QB) thickness on the performance of Micro-LEDs, and delve into the corresponding carrier transport behavior. The results demonstrate that the effect of QB thickness on the performance of Micro-LEDs is closely related to injection current density. Within the current density range of 0–30 A/cm2, a thicker QB layer leads to a higher internal quantum efficiency (IQE) for Micro-LEDs. Conversely, when the current density is in the range of 30–100 A/cm2, employing a thinner QB layer in the LED structure can yield higher IQE values. In addition, this work suggests that tunneling effects and Quantum Confined Stark Effect (QCSE) dominate at different current densities, resulting in an opposite dependency of IQE on QB thickness. Furthermore, our findings indicate that adjusting QB thickness can significantly affect both the peak external quantum efficiency (EQE) and peak current density of Micro-LEDs.

Broad-area 976 nm semiconductor lasers have garnered widespread attention for their applications in generating high-power 488 nm blue laser light and as pump sources for solid-state and ytterbium-doped fiber lasers. Nevertheless, these lasers exhibit a wide gain bandwidth, short cavity length, and usually use the natural cleavage surface as the output window, resulting in a broad emitting spectrum in free-running state. We investigated a high-power narrow-linewidth 976 nm edge emitting broad area semiconductor laser (EEL) through external cavity feedback technology by employing a transmission grating as the dispersive element. This configuration achieved a high output power of 11 W and a spectral linewidth of 0.36 nm at 976 nm, corresponding to an intracavity power of 15.7 W. It provided a more flexible cavity structure for direct frequency doubling of the semiconductor laser to generate a high power of 488 nm blue laser.

Abstract The stability of integrated photonic circuits is crucial for applications requiring high frequency precision or robust operation over time, such as optomechanical sensing, frequency conversion, optical communication, and quantum optics. Photonic memory is useful for low-energy optical computing and interconnects. Thin-film lithium niobate (TFLN), an emerging photonic platform, exhibits complex material properties including pyroelectric and photorefractive effects which could cause intra-device drift and excess noise under different conditions and enable photonic memory. However, the long-term stability and memory effect of these properties remain unexplored. Herein, we discovered a long-lived refractive index change in Z-cut TFLN microresonators induced by light excitation and temperature variation, with recovery times exceeding 10 h. This instability strongly depends on thin film’s crystal orientations. Leveraging the long-term photonic memory, we realize optical trimming of cavity resonance frequencies. Our result offers insights towards understanding the fundamental noise properties and dynamic behavior of integrated TFLN material and devices.

Abstract We introduce a novel material for integrated photonics and investigate aluminum gallium nitride (AlGaN) on aluminum nitride (AlN) templates as a platform for developing reconfigurable and on-chip nonlinear optical devices. AlGaN combines compatibility with standard photonic fabrication technologies and high electro-optic modulation capabilities with low loss over a broad spectral range, from UVC to long-wave infrared, making it a viable material for complex photonic applications. In this work, we design and grow AlGaN/AlN heterostructures and integrate several photonic components. In particular, we fabricate edge couplers, low-loss waveguides, directional couplers, and tunable high-quality factor ring resonators. These devices will enable nonlinear light-matter interaction and quantum functionality. The comprehensive platform we present in this work paves the way for photon-pair generation applications, on-chip quantum frequency conversion, and fast electro-optic modulation for switching and routing classical and quantum light fields.

Abstract Non-Hermitian topological photonics plays a key role in bridging topological matter with gain and loss engineering in optics. Here we report the experimental observation of the break of chiral currents in a Hall ladder from the non-Hermiticity by constructing synthetic frequency dimension in two rings, where currents on both legs of the ladder co-propagate in the same direction. The origin of such phenomena is resulted from the interplay between the effective magnetic flux and the on-site gain and loss. Such non-Hermitian co-propagating currents exhibit characteristics of unidirectional frequency conversion in both rings, and moreover, different from the counterpart in Hermitian systems, can provide a method to probe the signatures of the non-Hermitian skin effect from steady-state bulk dynamics. Our model is further extended to models including next-nearest-neighbor couplings, pointing to a way for observing the non-Hermitian signature with higher winding number, and provides a new control knob for light manipulation with the topological dissipation engineering.

Abstract Colloidal quantum dots (CQDs) are attractive gain media due to their wavelength-tunability and low optical gain threshold. Consequently, CQD lasers, especially the surface-emitting ones, are promising candidates for display, sensing and communication. However, it remains challenging to achieve a low-threshold surface-emitting CQD laser array with high stability and integration density. For this purpose, it is necessary to combine the improvement of CQD material and laser cavity. Here, we have developed high-quality CQD material with core/interlayer/graded shell structure to achieve a low gain threshold and high stability. Subsequently, surface-emitting lasers based on CQD-integrated circular Bragg resonator (CBR) have been achieved, wherein the near-unity mode confinement factor (Γ of 89%) and high Purcell factor of 22.7 attributed to the strong field confinement of CBR enable a low lasing threshold of 17 μJ cm− 2, which is 70% lower than that (56 μJ cm− 2) of CQD vertical-cavity surface-emitting laser. Benefiting from the high quality of CQD material and laser cavity, the CQD CBR laser is capable of continuous stable operation for 1000 hours (corresponding to 3.63 × 108 pulses) at room temperature. This performance is the best among solution-processed lasers composed of nanocrystals. Moreover, the miniaturized mode volume in CBR allows the integration of CQD lasers with an unprecedentedly high density above 2100 pixels per inch. Overall, the proposed low-threshold, stable and compactly integrated CQD CBR laser array would advance the development of CQD laser for practical applications.

Abstract 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. Experiments were implemented with distributed feedback lasers injected by a random-digital phase-modulated drive light. Results show that high-quality synchronization can be achieved as the drive signal rate is larger than the laser relaxation frequency and the transmission bit error ratio is below a critical value. Chaos synchronization over 8191-km fiber transmission was experimentally achieved. Compared to traditional common-signal-induced synchronization using analog drive signal such as chaos, the distance is increased by 8 times, and complicated hardware devices for channel impairment compensation are no longer required. In addition, the proposed method does not sacrifice communication capacity like traditional methods which need a channel to transmit analog drive signal. It is therefore believed that this common-digital-signal induced laser synchronization paves a way for secure backbone and submarine transmission.

Abstract Nanostructured dielectric metasurfaces offer unprecedented opportunities to control light-matter momentum exchange, and thereby the forces and torques that light can exert on matter. Here we introduce optical metasurfaces as components of ultracompact untethered microscopic metaspinners capable of efficient light-induced rotation in a liquid environment. Illuminated by weakly focused light, a metaspinner generates torque via photon recoil through the metasurfaces’ ability to bend light towards high angles despite their sub-wavelength thickness, thereby creating orbital angular momentum. We find that a metaspinner is subject to an anomalous transverse lateral optical gradient force that acts in concert with the classical gradient force. Consequently, when two or more metaspinners are trapped together in a laser beam, they collectively orbit the optical axis in the opposite direction to their spinning motion, in stark contrast to rotors coupled through hydrodynamic or mechanical interactions. The metaspinners delineated herein not only serve to illustrate the vast possibilities of utilizing optical metasurfaces for fundamental exploration of optical torques, but they also represent potential building-blocks of artificial active matter systems, light-driven micromachinery, and general-purpose optomechanical devices.

Abstract We propose and demonstrate a data-driven plasmonic metascreen that efficiently absorbs incident light over a wide spectral range in an ultra-thin silicon film. By embedding a double-nanoring silver array within a 20 nm ultrathin amorphous silicon (a-Si) layer, we achieve a significant enhancement of light absorption. This enhancement arises from the interaction between the resonant cavity modes and localized plasmonic modes, requiring precise tuning of plasmon resonances to match the absorption region of the silicon active layer. To facilitate the device design and improve light absorption without increasing the thickness of the active layer, we develop a deep learning framework, which learns to map from the absorption spectra to the design space. This inverse design strategy helps to tune the absorption for selective spectral functionalities. Our optimized design surpasses the bare silicon planar device, exhibiting a remarkable enhancement of over 100%. Experimental validation confirms the broadband enhancement of light absorption in the proposed configuration. The proposed metascreen absorber holds great potential for light harvesting applications and may be leveraged to improve the light conversion efficiency of ultra-thin silicon solar cells, photodetectors, and optical filters.

Abstract Coherent broadband light generation has attracted massive attention due to its numerous applications ranging from metrology, sensing, and imaging to communication. In general, spectral broadening is realized via third-order and higher-order nonlinear optical processes (e.g., self-phase modulation, Raman transition, four-wave mixing, multiwave mixing), which are typically weak and thus require a long interaction length and the phase matching condition to enhance the efficient nonlinear light-matter interaction for broad-spectrum generation. Here, for the first time, we report octave-spanning coherent light generation at the nanometer scale enabled by a phase-matching-free frequency down-conversion process. Up to octave-spanning coherent light generation with a −40dB spectral width covering from ~565 to 1906 nm is demonstrated in discreate manner via difference-frequency generation, a second-order nonlinear process in gallium selenide and niobium oxide diiodide crystals at the 100-nanometer scale. Compared with conventional coherent broadband light sources based on bulk materials, our demonstration is ~5 orders of magnitude thinner and requires ~3 orders of magnitude lower excitation power. Our results open a new way to possibly create compact, versatile and integrated ultra-broadband light sources.

Abstract Perovskite quantum dots (PQDs) show promise in light-emitting diodes (LEDs). However, near-infrared (NIR) LEDs employing PQDs exhibit inferior external quantum efficiency related to the PQD emitting in the visible range. One fundamental issue arises from the PQDs dynamic surface: the ligand loss and ions migration to the interfacial sites serve as quenching centers, resulting in trap-assisted recombination and carrier loss. In this work, we developed a chemical treatment strategy to eliminate the interface quenching sites and achieve high carrier utilization. We employ a bidentate and liquid agent (Formamidine thiocyanate, FASCN) with tight binding to suppress the ligand loss and the formation of interfacial quenching sites: the FASCN-treated films exhibit fourfold higher binding energy than the original oleate ligands. Furthermore, the short ligands (carbon chain

Abstract Exceptional points (EPs) have been extensively explored in mechanical, acoustic, plasmonic, and photonic systems. However, little is known about the role of EPs in tailoring the dynamic tunability of optical devices. A specific type of EPs known as chiral EPs has recently attracted much attention for controlling the flow of light and for building sensors with better responsivity. A recently demonstrated route to chiral EPs via lithographically defined symmetric Mie scatterers on the rim of resonators has not only provided the much-needed mechanical stability for studying chiral EPs, but also helped reduce losses originating from nanofabrication imperfections, facilitating the in-situ study of chiral EPs and their contribution to the dynamics and tunability of resonators. Here, we use asymmetric Mie scatterers to break the rotational symmetry of a microresonator, to demonstrate deterministic thermal tuning across a chiral EP, and to demonstrate EP-mediated chiral optical nonlinear response and efficient electro-optic tuning. Our results indicate asymmetric electro-optic modulation with up to 17 dB contrast at GHz and CMOS-compatible voltage levels. Such wafer-scale nano-manufacturing of chiral electro-optic modulators and the chiral EP-tailored tunning may facilitate new micro-resonator functionalities in quantum information processing, electromagnetic wave control, and optical interconnects.

Abstract Graphene has unique properties paving the way for groundbreaking future applications. Its large optical nonlinearity and ease of integration in devices notably makes it an ideal candidate to become a key component for all-optical switching and frequency conversion applications. In the terahertz (THz) region, various approaches have been independently demonstrated to optimize the nonlinear effects in graphene, addressing a critical limitation arising from the atomically thin interaction length. Here, we demonstrate sample architectures that combine strategies to enhance THz nonlinearities in graphene-based structures. We achieve this by increasing the interaction length through a multilayered design, controlling carrier density with an electrical gate, and modulating the THz field spatial distribution with a metallic metasurface substrate. Our study specifically investigates third harmonic generation (THG) using a table-top high-field THz source. We measure THG enhancement factors exceeding thirty and propose architectures capable of achieving a two-order-of-magnitude increase. These findings underscore the potential of engineered graphene-based structures in advancing THz frequency conversion technologies for signal processing and wireless communication applications.

While micro-LEDs are crucial for ultrahigh resolution micro-displays, the efficiency of currently reported micro-LEDs degrades dramatically with decreasing size. Recently, the bottom-up nanowire approach has shown promise to break the efficiency bottleneck of this size effect. In this article, we investigated the design of nanowire photonic crystal structure for micro-LED applications and revealed its correlation with the Purcell effect. Key performance characteristics including efficiency, emission directionality, and spectral linewidth are thoroughly studied. For an LED structure with low internal quantum efficiency (IQE) of 10% due to high non-radiative recombination, an enhancement of ∼30% is found viable by using a properly designed photonic crystal. High emission directionality and a narrow spectral linewidth (∼ 5 nm) can be obtained with 60% of the light being emitted within a 20° acceptance angle.

Abstract Acetone is a widely used volatile organic compound in various industries, and several gas sensors have been developed for its detection and real-time monitoring. This study reported a novel method for determining the acetone vapor concentration based on correlated laser speckles using polymer-dispersed liquid crystals (PDLCs). Here, PDLC films comprising a mixture of the thermotropic nematic liquid crystal (LC) and ultraviolet-curable polymers were fabricated using different LC mass ratios and ultraviolet curing conditions. The laser beam was transmitted through the PDLC film to generate scattered light and speckles. When the PDLC film was exposed to the acetone vapor, the acetone molecules diffused into the PDLC film and interacted with the LC molecules, modifying the orientation of the LC molecules and the equivalent refractive index of the LC droplets. This in turn decreased the correlation coefficient of the speckle images. The experimental results indicated that the PDLC gas sensor was selectively sensitive to different concentrations of the acetone vapor, ranging from 1 800 ppm to 3 200 ppm. In comparison with traditional LC gas sensors that use a polarizing microscope to detect the change in brightness of the modulated light field, the proposed method is simpler, less expensive, and more robust under external disturbances such as vibrations.

Abstract Optical fiber sensors have gained significant attention in recent years owing to their remarkable advantages of remote operation and rapid response. The integration of optical fiber sensing with the microfluidics technology has paved the way for the establishment of optical fiber optofluidic sensing. Optical fiber optofluidic systems possess the advantages of the low invasiveness, compact structure, excellent biocompatibility, and the ability to handle small analyte volumes, rendering them particularly suitable for serving as chemical sensors and biosensors. In this paper, we present an in-depth overview of optical fiber optofluidic chemical sensors and biosensors. Firstly, we provide a comprehensive summary of the types of optical fibers commonly employed in optofluidic chemical and biosensing, elucidating their distinct attributes and performance characteristics. Subsequently, we introduce and thoroughly analyze several representative sensing mechanisms employed in optical fiber optofluidic systems and main performance parameters. Furthermore, this review delves into the modification and functionalization of optical fibers. Additionally, we showcase typical biosensing and chemical sensing applications to demonstrate the practicality and versatility of optical fiber optofluidic sensing. Finally, the conclusion and outlook are given.

Abstract Holography is an essential technique of generating three-dimensional images. Recently, quantum holography with undetected photons (QHUP) has emerged as a groundbreaking method capable of capturing complex amplitude images. Despite its potential, the practical application of QHUP has been limited by susceptibility to phase disturbances, low interference visibility, and limited spatial resolution. Deep learning, recognized for its ability in processing complex data, holds significant promise in addressing these challenges. In this report, we present an ample advancement in QHUP achieved by harnessing the power of deep learning to extract images from single-shot holograms, resulting in vastly reduced noise and distortion, alongside a notable enhancement in spatial resolution. The proposed and demonstrated deep learning QHUP (DL-QHUP) methodology offers a transformative solution by delivering high-speed imaging, improved spatial resolution, and superior noise resilience, making it suitable for diverse applications across an array of research fields stretching from biomedical imaging to remote sensing. DL-QHUP signifies a crucial leap forward in the realm of holography, demonstrating its immense potential to revolutionize imaging capabilities and pave the way for advancements in various scientific disciplines. The integration of DL-QHUP promises to unlock new possibilities in imaging applications, transcending existing limitations and offering unparalleled performance in challenging environments.

Abstract Soliton molecules (SMs) play a crucial role in nonlinear optical systems, enriching our understanding of nonlinear science through the study of their interaction dynamics. While passively mode-locked fiber lasers offer an efficient platform for generating diverse types of SMs, the complex internal dynamics of the laser often pose challenges in achieving predetermined temporal separations between SMs. Here, we implement a delayed optical feedback technique within a femtosecond optical parametric oscillator, enabling the generation of SMs with precise and controllable temporal separations. A theoretical model, which models the intracavity iterations of the signal with a simplified Ikeda map, is proposed to study the impact of parametric gain, intracavity feedback delay, and cavity length on the internal separations of the SMs. Our experimental results confirm that adjusting the cavity length allows for producing desired temporal separations within SMs. To reveal the evolution dynamics of the SMs, we further develop a rigorous numerical model using the carrier-resolved Forward Maxwell Equation, which is capable of modeling ultra-broadband complex dynamics based on a single equation without relying on the slowly-varying envelope approximation. The numerical model unveils the rich formation dynamics of the SMs at various separations, which confirms the critical role of the gain window provided by the pump. This work opens up new opportunities for the on-demand generation of SMs and provides valuable insights into the complex dynamics in femtosecond optical parametric oscillator systems with optical delayed feedback.

Digital image correlation (DIC) is a non-contact measurement technique used to evaluate surface deformation of objects. Typically, pointwise moving least squares (PMLS) fitting is applied to process the noisy data from DIC to obtain an accurate strain field. In this study, a self-adaptive pointwise moving least squares (SPMLS) method was developed to optimize the process of window size selection, thereby attaining superior accuracy in measurements. The premise of this method is that the noise in the displacement field follows white Gaussian noise. Under this assumption, it analyses the random errors and systematic errors of the PMLS method under different calculation window sizes. The optimal size of the calculation window is determined by minimizing the errors. Subsequently, the strain field is computed based on the optimized calculation window. The results were compared with a typical PMLS method. Whether calculating low-gradient strain fields or high-gradient strain fields, the computational accuracy of SPMLS is close to the optimal accuracy of PMLS. This study effectively addresses the inherent challenge of manually selecting window size in the PMLS method.

This paper outlines the design and fabrication of a portable optomechatronic system based on the theta-2theta configuration, which explores various optical characterization techniques for transparent materials and dielectric thin films. These techniques include Brewster angle and Abelès-Brewster angle measurements, critical angle measurements, and the surface plasmon resonance technique. The system consists of a mechanical assembly of rotating stages, a semiconductor laser, a photodiode connected to a data acquisition card, and a user interface for controlling the stepper motor rotation stages. Utilizing a BK7 substrate, the motorized stage achieved a resolution of 0.010. The Brewster angle measured was 56.550, with a refractive index (n) of 1.5137. The relative error obtained was Δn/n = 3.82 × 10−4, with a sensitivity of 164.27 RIU/degree and an accuracy of 0.37/degree. Furthermore, the discrepancies between theoretical and experimental refractive indices for different prisms at 639 nm ranged from ±7 × 10−4 to ±73 × 10−4. After testing various samples, the system demonstrated its capability to perform fast, precise, and non-invasive measurements. Its portability allows for use in diverse environments and applications.

Additive manufacturing (AM) is a fast-growing technology that supports the rapid fabrication of prototypes. Already, employing AM technologies in early product development stages can help to accelerate the time from conceptualisation phase to the market entry. Furthermore, advances in the field of materials, such as highly transparent resins in the visible wavelength spectrum, also open application potentials for the design and fabrication of optical components. Three highly transparent resins from different suppliers are studied in this work regarding their influence on the geometrical and optical properties of additively manufactured components. The different materials were processed using a masked stereolithography 3D printer. Geometrical and optical properties of the generated test samples were analysed by means of laser scanning microscopy and spectrophotometry, respectively. A clear correlation between optical properties of the resin and the solidified samples was identified. It was further found that while spin coating does not significantly affect the geometrical properties, a strong influence on the resulting optical properties could be observed. The highest transmission properties, in the range of up to 90%, were determined for samples that were spin-coated on both surfaces. Thus, applying a spin coating operation to additively manufactured optical components is recommended for the highest transmission properties.

Airy beams showing curved paths have found extensive applications in fields such as optical trapping, biomedical analysis, and material processing. Despite their utility, dynamic control of Airy beams poses a significant challenge. This work investigates the experimental realization of dynamic steering of Airy beams by utilizing computer-generated holograms with phase-amplitude encoding on a phase-only spatial light modulator (SLM). We successfully generated and controlled Airy beams by imposing dynamic phase masks that manipulated both the phase and amplitude of the field, which sets our approach apart from conventional methods with only phase manipulation. By directly encoding in situ such a hologram and transferring it to an SLM, we are able to control the initial position and rotational orientation of Airy beams without relying on mechanical movement or traditional optical setups involving lenses and apertures. Generating Airy beams in any initial position and rotational direction is anticipated to significantly impact applications such as optical trapping, optical communication, and biomedical imaging by providing a flexible platform for dynamic Airy beam manipulation.

Abstract The authors provide an example roadmap for realising the space division multiplexing (SDM)‐based ecosystem. The authors investigate whether the new standard for multi‐core fibre can be specified by considering a 125 μm standard cladding diameter and backward compatibility with the existing single‐core single‐mode fibre. The authors propose that well‐planned standardisation activities need to be initiated considering mandatory technologies for realising the terrestrial SDM ecosystem in the near future.

Abstract Amplification technologies needed for spatial division multiplexing (SDM) signal transmission have been reported, especially focusing on submarine systems, which have stricter requirements than terrestrial ones. As the first step of a large‐scale commercialisation, 2‐core un‐coupled (UC) fibre production has already been announced. However, optical amplifiers for SDM signals are still under investigation because SDM amplifiers have various architectural possibilities, depending on the requirements to be considered in designing systems. The multicore erbium‐doped fibre amplifier (MC‐EDFA) architecture is classified from the viewpoint of the number of erbium‐doped fibre (EDF) cores and its pumping method. Core pumped MC‐EDFA is more compatible with the conventional single‐core fibre (SCF)‐ based system and more mature than cladding pumped MC‐EDFA. However, cladding pumped MC‐EDFA has a unique feature of collective amplification of all cores in a single multicore fibre (MCF) and the potential of large‐scale integration of amplification cores in a single package. For a feasibility study, a C‐band 19‐core cladding pumped MC‐EDFA prototype is fabricated using a 19‐core isolator. A half volume of the equivalent conventional single‐core (SC‐) EDFA is successfully demonstrated. One unique feature of UC‐MCF is bidirectional (BD‐) transmission using a single UC‐MCF. Signal transmission direction can differ from core to core. This feature is useful for efficiently accommodating traffic of asymmetric communication data and expanding transmission capacity at a constant transmission distance. A C‐band 7‐core cladding pumped BD‐MC‐EDFA prototype is fabricated for the bidirectional MCF transmission line. Experimental results show transmission capacity was expanded by 17% using the prototype when bidirectional signal assignment was adapted. Towards practical use, optical components suitable for MC‐EDFA need to be developed to draw out potential advantages of SDM technologies.

Abstract 2‐core fibre for submarine cable is becoming the first commercial application of multi‐core fibre, which should enable to expand the capacity beyond the current limitation of submarine cable size. For successful commercial applications of 2‐core fibre, it is important to minimise the complexities in manufacturing, splicing, and fibre handling. The 2‐core fibre design for minimum complexity is reviewed.

Abstract The authors examine the state of submarine cable systems and conditions affecting potential widespread deployment of new spatial division multiplexing technologies, such as multicore optical fibre. The authors address areas such as cable capacity requirements, techno‐economic constraints, multicore fibre characteristics, and performance and other necessary technology advances.

Abstract The electronic and optical properties of IIB‐VIA Zn‐based monochalcogenides w‐ZnCh (Ch: O, S and Se) were reported. The band structures using the FP‐LAPW method at zero pressure with the Tran–Blaha‐modified Becke–Johnson potential evidence that w‐ZnO, w‐ZnS and w‐ZnSe reveal direct band gaps (Γ–Γ) of 2.72, 3.87, and 2.88 eV, respectively. The complex dielectric function ε(ω), refractive index n(ω), extinction coefficient k(ω), absorption coefficient α(ω), reflectivity R(ω), energy‐loss function L(ω) and complex conductivity σ(ω), are determined. The microscopic origin of the observed fine‐structure peculiarities in the spectra of the imaginary part of the dielectric function (ε2(ω)) is identified. An intensive X‐Ray PhotoElectron Spectroscopy (XPES) investigation shows the effect of controlled UHV treatment (Ar+ ionic bombardment followed by gradual heating) as a method of cleaning and/or re‐crystallising the upper layers. XPES and XAES (Auger Electron induced by X‐Ray Excitation) transitions substantiate successfully the UHV in situ cleaning. The valence band structure was studied. The PLS technique employing UVvis excitation source of a 325 nm (He‐Cd) gas laser unveils that ZnO, zinc sulfide and ZnSe luminescence mechanism concerns the energy band gap. The results of the experimental studies are found to be in good agreement with the theoretical predictions.

Abstract Nonlinear Raman-Nath diffraction (NRND) is a unique diffraction pattern formed when a high-intensity laser interacts with a nonlinear microstructure bulky medium relying only on the transverse phase matching condition. Here, we report on the first experimental observation of NRND in a submicron-thick periodically poled lithium niobate thin film (PPLNTF) by geometric reflection pumped via a near-infrared femtosecond pulse laser. We further observe the evolution of the diffracted signals after broadening of the pump laser via a fused silica plate. We systematically analyze the spectral properties of multi-order second harmonic generation (SHG) diffracted signals exhibiting asymmetric distributions and explicitly clarify their phase matching conditions, simultaneously considering the impacts of the incident pump wavelength, the sample poling period, and the incident angle on the properties of the angular distribution diffracted beams. The realization of NRND phenomena with appreciable on-chip efficiency at a submicron interaction length is mainly attributed to the significant contribution of domain walls to enhance the nonlinear effects along with the modulation of second-order nonlinear susceptibilities $${\chi }^{(2)}$$ χ ( 2 ) . This NRND scheme provides a high-resolution, non-destructive on-chip microstructure diagnostic method, and even has the potential to develop novel on-chip integrated optoelectronic devices for applications such as precision metrology, biosensing, and spectral analysis.

Abstract Micro/nanorobots have shown great potential to execute different tasks in microenvironments due to their small size, high controllability and environmental adaptability. However, it is still challenging to precisely control the deformation and navigation of soft micro/nanorobots to better adapt to unstructured and complex surroundings. Here, we report a photonic nanojet (PNJ)-regulated soft microalga robot (saBOT) based on Euglena gracilis with controlled deformation and precise navigation capability. The deformability of the saBOT was precisely controlled by the highly focused light energy from a microlens-based PNJ bound to a tapered optical fiber probe (TFP), which can precisely stimulate the channelrhodopsin-2 (ChR2) in the photoreceptor of the microalga. This saBOT can be further precisely navigated toward different positions in complex and unstructured microenvironments by combining the deformability with the phototaxis ability of the microalga via the flexible manipulation of TFP. Notably, due to the ability of controllable deformation and precision navigation, the saBOT can travel across cell clusters for precision drug delivery toward a target cell. This PNJ-regulated saBOT holds great promise in executing different biomedical tasks in complex and unstructured microenvironments that cannot be reached by conventional tools and rigid microrobots.

【Objective】Affected by factors such as atmospheric attenuation and atmospheric turbulence, wireless laser communication will produce a certain degree of bit error, and it is often necessary to add error correction codes to improve the signal transmission quality. Low Density Parity Check codes (LDPC) have performance close to the Shannon's limit, and their error-correcting ability will increase significantly with the increase of codeword length. For codes with a large length of information segment, when each code corresponds to an Ethernet frame, its encoding efficiency will be seriously affected. Designing the transmission method for Ethernet frames in a way that allows both different speeds and lengths of Ethernet frames to fully leverage the encoding and decoding efficiency is crucial for enhancing the transmission rate of Ethernet data sources.【Methods】Based on the LDPC (4 050, 2 700) encoding with a data bit width of 16 bit, this paper designs a gigabit network service transmission method. The functions of each module are clearly divided, and the state machine is used in the design of the module. Therefore, the problems in the design process can be quickly located, and the development efficiency is very high. Setting an appropriate operational cycle at the transmitting end to process Ethernet frames, through operations such as framing, packet assembly, and filling with random sequences, enables Ethernet traffic of different frame lengths and rates to adaptively match the information segment length of the LDPC encoding module, thereby fully utilizing the efficiency of LDPC encoding. Each Ethernet frame can be finally recovered by deframing at the receiving end.【Results】Finally, this article verified the design scheme on the Field Programmable Gate Array (FPGA) board of XILINX, and tested the transmission rate of Ethernet data with different frame lengths by using a gigabit network tester. The results show that the data rate can reach the limit rate of 1 Gbit/s. Afterwards, different services such as video and files are successfully tested.【Conclusion】The article proposes an Ethernet service transmission method specifically designed for scenarios where the information segment length exceeds the Ethernet frame length, enabling it to accommodate Ethernet data transmission with varying lengths, rates, and types of services. The efficiency of the encoding module can be fully utilized to meet the demand for high-speed Gigabit Ethernet service transmission in wireless laser communication.

【Objective】The world has entered the era of 5th Generation Mobile Communication Technology (5G) and satellite Internet, and the demand for communication speed and capacity in various fields has surged, while the application of traditional parabolic and narrowband planar phased array antenna systems is limited by factors such as bandwidth and beamforming. Based on the current trend of related industries and the application requirements of broadband multi-target, this paper studies the Ka-band wideband multi-beam solid-state phased array technology.【Methods】This paper theoretically establishes and derives a general vector mathematical simulation model of phased array antenna pattern, studies the subarray division, aperture effect, and crossing time of phased array antenna, and designs a broadband multibeam phased array system based on the combination of element-level electro-shift phase shift and sub-array stage optical-delay. The front-end single integrated subarray adopts the three-dimensional high-density heterogeneous tile integration scheme of different material substrates, which greatly improves the integration degree of the subarray. The sub-array post-stage adopts the Optical True Time Delay (OTTD) method based on optical switching, high-precision optical fiber delay line and wavelength division multiplexing to realize multi-channel delay and multi-beam synthesis of the sub-array stage.【Results】By integrating and testing the principle prototype of the Ka-band wideband multi-beam receiving phased array system, it is verified that the principle prototype overcomes the bandwidth limitation problems such as aperture crossing time and beam skew. The prototype can realize the wide-angle scanning of eight independent receiving beams in the Ka-band, and the maximum transmission data rate of each receiving beam can reach 1 500 Mbit/s.【Conclusion】The test results show that the system has the advantages of high integration, large bandwidth, and multiple independent beams. The research results will help promote the further development of wideband multi-beam solid-state phased array, and lay a theoretical and practical foundation for the subsequent engineering and productization of Ka-band wideband multi-target phased array.

【Objective】In order to obtain a higher sensitivity fiber optic humidity sensor,this paper proposes a humidity sensor of D-shaped silver (Ag)-coated optical fiber based on Surface Plasmon Resonance (SPR) effect.【Methods】Graphene Oxide (GO) is coated on the surface of D-shaped Ag-coated optical fiber. Since GO has water absorption characteristics and the effective Refractive Index (RI) will change after absorbing water, SPR will be excited when certain conditions are met. Therefore, it can be used as a humidity sensor. In order to obtain the maximum SPR sensitivity of the sensor, the structure of D-type Ag-coated optical fiber is firstly modeled by COMSOL Multiphysics software, and the influence of polishing depth and Ag film thickness on the sensing characteristics is explored by finite element analysis. Then the structure is verified by experiments Validity and rationality of parameters. Finally, a layer of GO film is coated on the surface of the D-shaped Ag-coated optical fiber to explore its performance of humidity detection.【Results】The simulation results show that the optimal sensor structure is the polishing depth of 58.4 μm, the thickness of the Ag film is 50 nm, and the maximum wavelength sensitivity of 5 500 nm/RIU is obtained between the ambient RI of 1.34 and 1.40. On the basis of this parameter, the RI sensing characteristics are verified through experiments. The sensor has a maximum wavelength sensitivity of 3 668 nm/RIU, and the R square value is 0.98, which has good linearity. After coating the GO film on the surface, the humidity sensitivity of 0.545 nm/%RH is obtained when the relative humidity changes from 30% to 90%, and the linear R-squared values under the two conditions of increasing and decreasing relative humidity are 0.961 1 and 0.971 1, respectively.【Conclusion】The simulation results and the actual experiment have the same resonance peak change range, which shows the effectiveness and rationality of the sensor.GO isolates the Ag film from contact with air, preventing oxidation. The optical fiber humidity sensor obtained by combining its water-absorbing properties with the SPR properties of the metal film demonstrates high sensitivity, providing a novel approach for the development of highly sensitive humidity sensors.

Electronic integrated chips based on metal interconnections face increasing challenges, including crosstalk, delay, heat dissipation, and power consumption, making it difficult to meet the growing demand for data processing. Optoelectronic integration is considered to be the next generation interconnect technology. As this technology continuous to evolve, the industry's requirements for the size and performance of optoelectronic devices are becoming increasingly demanding.【Objective】To address the device size and loss of the Bragg phase shift grating, this paper proposes a Bragg phase shift grating based on Silicon-on-Insulator (SOI) nanowires.【Methods】By leveraging photolithography technology, periodic grooves are created on silicon nanowires to construct the grating structure, effectively reducing the transmission loss of optical signals. In order to verify the performance of the Bragg phase-shifted grating, the transmission modes and characteristics of the device are analyzed and studied using the finite element method and the finite-difference time-domain method under conditions with an incident wavelength range of 1 400 to 1 600 nm. Additionally, to obtain the best structural parameters of the Bragg phase-shift grating, the Q factor is introduced as the optimization target parameter.【Results】The results show that the Bragg phase shift grating has excellent wavelength selection performance in the wavelength range of 1 400～1 600 nm, and has a ultra-low transmission loss. Notably, when the maximum Q factor is 159, the Bragg phase shift grating achieves the best performance, with the grating period N of 60.【Conclusion】This grating offers significant advantages over surface plasmon-based Bragg phase shift gratings in terms of manufacturing cost and transmission loss of optical signal. As a result, it has wide applications in dense wavelength division multiplexing, biological sensing, filtering, and other related fields.

【Objective】In the modern field of communications, optical fibers have become an important transmission medium in optical network systems due to their ultra-high transmission bandwidth and excellent optical properties. Multi-core optical fibers integrate multiple cores within a single fiber cladding to significantly enhance the data transmission capacity of a single fiber. However, an increase in the number of cores can also lead to additional channel impairment effects, which in turn affect the transmission performance and communication quality of the fiber link. Therefore, studying the theoretical model of the channel effects in coupled-core optical fibers, especially clarifying the relationship between the optical time-domain reflectometry process and channel response, can provide important references for the practical deployment and application of multi-core fibers.【Methods】To refine the model of optical time-domain reflection effects in coupled-core optical fibers, the article begins with basic principles, outlining the theories of forward transmission and backward Rayleigh scattering in coupled-core optical fibers. It details the derivation of coupled mode equations and the general expression for Rayleigh scattering power, including definitions and calculation methods for various coefficients such as the total capture factor. Based on the theoretical research, the article also proposes a modeling scheme for Rayleigh scattering effects in coupled-core optical fibers, taking into account the impact of fiber end-face reflection on the transmission process and providing a technical route to verify the Rayleigh scattering effects. Finally, the article processes the transmission data simulated by the model and conducts a comparative analysis based on the set parameters.【Results】The article constructs a simulation model for Rayleigh scattering effects, calculating the scattering power curve received after optical time-domain reflection. The simulation results show that the received scattering power is consistent with the set parameters, with an error within 5%.【Conclusion】The high precision of the results indicates that the model proposed in the article effectively reflects the Rayleigh scattering effects in coupled-core optical fibers, laying a theoretical foundation for accurately testing parameters of coupled-core optical fibers using optical time-domain reflectometry technology.

【Objective】In Reconfigurable Optical Add Drop Multiplexer (ROADM) downstream transmission, Tunable Optical Filters (TOF) are used to dynamically select wavelengths within a certain optical bandwidth range. By performing wavelength selection filtering and optical intensity attenuation equalization at the output ports of Wavelength Selective Switches (WSS) or Multicast Switches (MCS), the optical intensity at each output port of the ROADM is made consistent. MCS operates based on the Optical Switch (OSW) principle, enabling fast, accurate, and reliable transmission of multicast data by simultaneously switching multiple input channels to one or more output ports. Currently, most MCSs need to work in conjunction with TOF arrays to avoid accidental channels and ensure that the power entering the receiver after the MCS does not saturate or experience severe crosstalk. Most current TOF arrays are large, making integration with MCS difficult, thus affecting the realization of Colorless, Directionless and Contentionless (CDC)-ROADM. To reduce the implementation complexity of the ROADM downstream transmission system, it is necessary to address the issue of bulky module sizes. Therefore, this article designs an OSW device integrated with TOF functionality to reduce the size of the MCS module and optimize its structure.【Methods】The article integrates TOF functionality into the MCS module and designs a device that can achieve both optical channel selection and optical wavelength selection functions simultaneously. It is noted that Micro Electro Mechanical Systems (MEMS) can respectively realize the functions of OSW and TOF, and MEMS devices are relatively easy to implement with advantages such as fast tuning speed, wide tunable range, and small size. The article designs a new device combining both functions based on existing MEMS OSW and TOF solutions. This device is based on MEMS technology and is equipped with a multi-fiber collimator, enabling the X and Y axes of the device to respectively realize OSW and TOF functions with minimal mutual interference. The article introduces the basic principles and optical structure of this device and conducts optical design and simulation verification.【Results】Simulation results show that the device has good optical performance and can meet the usage requirements of MCS devices.【Conclusion】The MCS module using the TOF-OSW device proposed in the article integrates the TOF function, thereby saving the cost and space of the original TOF, reducing costs, space occupation, and system complexity. Therefore, the TOF-OSW device has broad application prospects and practical demand, better meeting the ROADM system's need for implementing CDC functionality.

【Objective】In order to solve the technical problems of large volume, low integration and small bandwidth of electro-optic modulator, a design method of parallel multi-channel thin film Lithium niobate electro-optic modulator is proposed. The design principle of thin film Lithium niobate electro-optic modulator is presented, and the gain and noise figure of microwave optical transmission link are analyzed.【Methods】A simulation model of microwave optical transmission links is established using Lumerical Interconnect optical simulation software. The effects of modulator half wave voltage on link gain and noise figure are then compared and analyzed. Finally, the key parameters of the 40 GHz four channel integrated thin film Lithium niobate electro-optic modulator are tested.【Results】The test results show that the insertion loss, half wave voltage, 3 dB bandwidth and size of the designed four-channel integrated film Lithium niobate electro-optic modulator are 4.5 dB, 3.5 V, 40 GHz and 30 mm×20 mm×10 mm, respectively. The noise figure of microwave optical transmission link using thin-film Lithium niobate modulator is about 30 dB.【Conclusion】The designed four channel integrated film Lithium niobate electro-optic modulator in this paper is superior to the traditional Lithium niobate electro-optic modulator.

Space division multiplexing technology is one of the effective ways to improve the transmission capacity of optical communication system. The main technologies include Multi Core Fiber (MCF), few mode multiplexing and orbital angular momentum multiplexing, among which MCF technology is a mature one.【Objective】To solve the problem of capacity limitation in optical communication system, this article designed and developed a new four-core Wavelength Division Multiplexing (WDM) original sample.【Methods】Firstly, the technology of WDM, air division multiplexing, MCF and multicore fiber coupling is analyzed. The four core fan-in fan-out device made with capillary, lens and etch fiber is selected as the medium. Then, by combining MCF technology and WDM technology, starting from the selection of four-core fiber, the debugging principle and debugging method of four-core WDM, a new four-core WDM original sample is designed and developed by using four-core fan-in fan-out device. The index of the device is tested by using the difference method of four-core fan-in fan-out device.【Results】According to the test results of the experimental samples, the insertion loss of each reflection end and transmission end of the original four-core WDM 1 can be controlled within 0.8 dB, the isolation degree of each reflection end is >15 dB, and the isolation degree of each transmission end is ≥ 40 dB.【Conclusion】According to the test results, the following conclusions can be drawn: compared with the traditional single-core WDM scheme, the new four-core WDM can realize four-channel communication under the same device volume, and greatly improve the optical communication capacity. At the same time, it fills the gap in the research of air division multiplexing optical devices based on MCF technology and expands the application range of air division multiplexing, demonstrating the potential of multi-core fiber based long-distance transmission. WDM device based on space division multiplexing system has a wide application prospect in optical fiber communication system.

【Objective】Common optical switches are usually polarization sensitive or have complex structures, the article proposes a 2×2 microfluidic optical switch.【Methods】The optical switch proposed in this article employs a waveguide structure. It utilizes microfluidic driving technology based on magnetic fluids, along with trace amounts of liquid and air, to achieve optical path selection and switching functions for the optical switch. The transmission characteristics of optical switch are studied and discussed, and the structure of optical switch is optimized.【Results】The results show that the insertion losses at two output ports of optical switch are 0.42 and 0.20 dB, and the crosstalk are -24.13 and -42.63 dB, respectively.【Conclusion】The proposed 2×2 microfluidic optical switch has simple structure and is not sensitive to polarization. It also has lower insertion loss and crosstalk than common optical switches. It can be used as the switching core for building Optical Cross Connect (OXC) equipment to realize the fault protection function of the optical network.

【Objective】In order to achieve a highly sensitive refractive index sensor in a nanoscale spatial dimension, a square composite resonant cavity containing a stub resonator has been proposed as a resonant element adjacent to Metal-Dielectric-Metal (MDM) Surface Plasmon Polaritons (SPPs) waveguide in this paper.【Methods】The paper employs the finite element method to comparatively analyze the characteristics of the transmission peak spectrum and the mode field distribution at the peak position of the square resonant cavity coupled MDM waveguide structure before and after the introduction of the stub cavity. The analysis results reveal that the degeneracy separation phenomenon of the first and second order quasi resonant modes in the composite cavity can be observed clearly when the stub resonator is added in the square-shaped cavity. Consequently, four transmission peaks with sharp edges have emerged in the transmission spectra, which are generated by the quadruple Fano resonance. By changing the structural parameters such as the side length of the square cavity and stub length, as well as the refractive index of the medium filled in the cavity, the dependence of the transmission spectra on the structural and material parameters of the resonant cavity was calculated in detail.【Results】By analyzing the quantitative impact of structural parameters on the peak wavelength, the resonance conditions responsible for the transmission peaks have been derived and the increments of the effective cavity length contributed by the stub resonator have been analyzed in turn for the four resonant modes. By calculating the transmission spectra associated with the varied medium filled in the composite cavity, the peak wavelength shows an approximate linear relationship with the refractive indexes of the filled medium. The sensing sensitivity of the quadruple transmission peaks has been obtained based on the linear fitting results.【Conclusion】The calculation results in the article indicate that the sensitivity of refractive index sensing is directly proportional to the effective cavity length of the composite cavity, and inversely proportional to the resonance order. When selecting a square composite cavity structure with a side length of 360 nm and a stub length of 210 nm, the sensing sensitivity of the transmission peak produced by the first-order Fano resonance can reach 2 000 nm/RIU. The research conclusion of this paper can provide a valuable reference for the design of nanoscale high sensitivity refractive index sensors.

【Objective】Optical Signal-to-Noise Ratio (OSNR) is an important criterion for evaluating the performance of communication systems. For optical fiber communication systems, stable operation can only be ensured if the OSNR at the receiver end exceeds the receiver's OSNR receiving tolerance. The larger the value, the better the system stability. Therefore, monitoring the OSNR value of the transmission system is very important, and real-time and accurate monitoring of OSNR has always been a challenge in optical fiber communication systems.【Methods】To achieve a simple, efficient, and high-precision OSNR monitoring, based on the mean and variance of the signal amplitude histogram, combined with a Deep Neural Network (DNN), the article proposes a highly accurate OSNR monitoring method. This method utilizes the mean and variance of different regions of the received signal amplitude histogram to extract correlation features of the signal amplitude histogram as it changes with OSNR using the DNN, thereby enabling the monitoring of the system's OSNR.【Results】This monitoring scheme is used to experimentally monitor the receiver OSNR of Quadrature Phase Shift Keying (QPSK) /16 Quadrature Amplitude Modulation (QAM) /32QAM transmission systems with three different modulation formats. The results show that the maximum standard errors of the estimated and actual OSNR values of the three different modulation formats in the back-to-back transmission system are 0.048, 0.140, and 0.180 dB without fiber transmission. After passing through 2 000, 800 and 800 km optical fiber transmission, the maximum standard errors of the estimated and actual OSNR values of the receiving end of the three different modulation formats transmission systems are 0.082, 0.250 and 0.630 dB, respectively. Compared with the non fiber transmission system, the maximum error of the estimated OSNR values of the system after optical fiber transmission does not exceed 0.5 dB. This indicates that the OSNR monitoring scheme can achieve precise monitoring of transmission system performance and is not affected by fiber optic lines.【Conclusion】The DNN OSNR monitoring method based on the mean and variance of the signal amplitude histogram proposed in this paper has been experimentally verified. The maximum error between this scheme and the actual system receiver OSNR does not exceed 1dB, indicating that this scheme can accurately predict the system receiver OSNR value.

【Objective】With the continuous advancement of Integrated Circuit (IC) design and manufacturing process, the design scale of System on Chip (SoC) has become increasingly larger, and the corresponding Software Development Kit (SDK) has also become more complex. Shortening the development time and rapid application of SDK is the key to the success of chip development.【Methods】In this paper, a chip SDK simulation platform is designed, which supports automatic extraction of chip logic design information. The software local image of extracted logic information based on the designed chip data structure is realized. The multi-threading of configuration, alarm and performance is developed to simulate the multi-task polling and network management reporting in the actual single-disk application. By connecting the SDK project to the serial port tool through the virtual serial port, the Shell command set provides interaction among developers and the SDK projects under the SDK simulation platform.【Results】The test results based on optical communication chip show that the SDK simulation platform can realize the functions of chip software level simulation, multi-thread debugging simulation and multi-function interaction under Shell command set.【Conclusion】The SDK simulation platform implemented in this paper can be applied to the early development and late application maintenance of chips. It has the functions of avoiding the development obstruction caused by the shortage of hardware resources, converging the difference of chip conversion, and providing a convenient SDK debugging method, which is of great significance to shorten the development time and accelerate the rapid application of chips.

Distributed optical fiber perimeter security systems have proven to be an effective method for security monitoring of important targets such as power plants, substations, and telecommunications base stations. However, this method can be challenging to distinguish between different types of intrusion behaviors and is prone to false alarms triggered by various environmental interferences. With the increasing actual demand, there are higher requirements for the accuracy of perimeter signal recognition. The perimeter security system in the new era not only needs to perform real-time monitoring, recognition, and response alarms for various types of intrusion behaviors, but also requires features such as remote control and response, high-precision intrusion location, multi-environmental adaptability, resistance to various disturbances, and low energy consumption. Therefore, it is necessary to conduct research on effective extraction and accurate recognition algorithms for intrusion signal characteristics. This article reviews the feature extraction methods combining the time domain, frequency domain, and time-frequency domain of optical fiber perimeter signals, and the classification and recognition methods based on vector machines, neural networks, and deep learning. It specifically discusses the principles and application scenarios of various algorithms, and conducts a comparative analysis of their advantages and disadvantages.

【Objective】Silicon photonic chips can achieve low-loss coupling with optical fibers through the on-chip silicon-based edge couplers (here in after referred to as edge couplers) integrated on the chips. In the packaging process of commercial silicon photonic chips, the demand for large-scale alignment of optical fibers and silicon photonic chips has raised higher requirements for the alignment efficiency of optical fibers and edge couplers. The research purpose of this paper is to optimize the alignment process between optical fibers and edge couplers based on the Fabry-Perot (FP) cavity formed between the optical fiber facet and the edge coupler facet. After measuring the distance between the optical fiber and the edge coupler in the axial direction of the fiber (represented as the x- axis in this article), high-precision alignment of the optical fiber and the edge coupler can be achieved by a single adjustment of the fiber position in this direction.【Methods】This paper studied the FP cavity structure formed between the optical fiber facet and the edge coupler facet. It also established the physical model between the reflection / transmission spectrum of the FP cavity and the distance between the facets. The optical fiber alignment platform is constructed to experimentally measure the distance between the facets through the FP cavity. Based on the distance measurement results, a single position adjustment of the optical fiber is realized along the axial direction of the optical fiber to achieve the alignment with the edge coupler.【Results】The deviation between the FP cavity length obtained in the experiment and the FP cavity length simulated by the ideal FP cavity model is less than 1 μm. The measured displacement of the optical fiber is within the error range (± 1 μm) of the actual displacement. After adjusting the position of the optical fiber based on the distance measurement results, the optical coupling loss is 3.52 dB between the optical fiber and the edge coupler at the output port, and the error with the reference value (3.30 dB) is only 0.22 dB.【Conclusion】The work verifies the feasibility of achieving efficient alignment between optical fibers and edge couplers based on FP cavity. Through the FP cavity, the measurement accuracy of the distance between the optical fiber and the edge coupler is at the sub-micrometer level and the measurement accuracy of the optical fiber displacement is also at the sub-micrometer level. The experiments demonstrate that the high-precision alignment between the optical fiber and the edge coupler could be realized with only a single adjustment of fiber position according the measurement results obtained by the FP cavity.

【Objective】Direct Sequence Spread Spectrum (DSSS) has been widely used in military and civilian communications due to its strong resistance to various common interferences, high security, and ease of implementation. It has been widely used in Code Division Multiple Access (CDMA) system. However, in non-cooperative communication scenarios, detecting DSSS signals, estimating DSSS signal parameters, and even intercepting information are all issues that need to be considered. In DSSS, correctly identifying the spread spectrum sequence used is an important prerequisite for correcting despreading. To address the problem of low success rate of spread code identification for low signal-to-noise ratio DSSS signals, this paper combines the Third-order Correlation Function (TCF) of m-sequences and its peak characteristics to identify the pseudo-code period of DSSS signals as prior information through power spectrum secondary processing on the premise of denoising preprocessing. The problem of spread code identification is transferred into a peak detection classification problem. The peak identification and classification is then studied.【Methods】This paper proposes a method of using Sparrow Search Algorithm (SSA) to optimize Extreme Gradient Boosting (XGBOOST) for third-order correlation peak classification of direct spread signals to improve the accuracy of m-sequence classification and identification.【Results】By comparing conventional peak detection and decision tree classification methods at different signal-to-noise ratios and comparing the classification accuracy of different sequence periods, the simulation results show that the spread code identification and classification method optimized by SSA with XGBOOST after preprocessing has a higher classification and identification success rate than conventional machine learning and peak detection methods. Its performance gradually improves at high sequence periods.【Conclusion】This method can more accurately identify and classify m-sequence spread codes under low signal-to-noise ratio conditions.

【Objective】To avoid the operational risk of high-voltage transmission lines caused by thermal faults of composite insulators, a method for identifying abnormal hot spots on the surface of composite insulators is studied.【Methods】Three types of abnormal surface heating forms of composite insulators, current heating type, voltage heating type, and comprehensive heating type, are analyzed. Based on the analysis results, the fiber Bragg grating centralized temperature measurement technology is used to deploy the fiber Bragg grating sensor near the composite insulator. The fiber optic dispersion centralized temperature measurement unit is used to calculate the corresponding wavelength offset and temperature change value. After being analyzed by the digital signal processing unit, the thermal image of the composite insulator is generated. Using the maximum inter class variance method to segment the thermal image of composite insulators, the average gray level of the thermal image of composite insulators is calculated, and the optimal threshold to partition the pixels in the thermal image of composite insulators is obtained. Based on the thermal image segmentation results of composite insulators, pixel statistical methods are used to calculate the horizontal row pixel points of the composite insulator segmentation image and divide the structural area of the composite insulator. According to the application specification of thermal image diagnosis for live equipment and the principle of fiber grating centralized temperature measurement, the thermal image of composite insulator collected by the fiber grating sensor is displayed in pseudo color to show the surface temperature distribution of composite insulator. The abnormal hot spots on the surface of composite insulators are identified through the temperature relationship among various structural regions of the target image.【Results】The experimental results show that this method can accurately measure the temperature of any point on the surface of composite insulators, and the maximum Root-mean-square deviation is only 1.39%. It is shown that the proposed method can effectively divide the structural regions of composite insulator segmentation images, with clear boundaries between each structure and no overlap phenomenon.【Conclusion】The recognition performance of abnormal hot spots on the surface of composite insulators in different areas of high-voltage transmission lines is relatively ideal, and the division effect of composite insulator structure areas is relatively good.

【Objective】To meet the requirements of timeliness, accuracy, and completeness of delay data in delay-sensitive application scenarios, it is necessary to implement end-to-end service delay estimation in Optical Transport Networks (OTN).【Methods】This paper first analyzes the transmission characteristics of OTN services, and collects service routing information according to the sub-net connections. Next, it discretizes the basic data such as Network Elements (NE), links, and cross-connection in service route. Then the characteristic variables for delay estimation are obtained. Finally, the paper proposes a delay estimation model based on engineering live network, and compares the simulation results of various machine learning algorithms.【Results】The Mean Absolute Percentage Errors (MAPE) of the delay estimation results based on Support Vector Regression (SVR) and decision tree regression were 3.362 8% and 1.284 9%, respectively.【Conclusion】The OTN service delay estimation method based on machine learning and the characteristic of OTN transmission in this paper has high accuracy and wide application scenarios.

With the rapid growth of big data demand, electronic chips and their interconnection technologies cannot meet the requirements of high-speed data transmission and high energy efficiency in computing and storage systems. Compared to traditional electronic chips, Silicon based Photonic (SiP) integrated chips have lower costs, higher integration density, and larger communication capacity. Micro Ring Resonator (MRR), as an important optical device, has the advantages of high sensitivity, small size, and low power consumption, and is widely used in fields such as optical communication, optoelectronics, and sensors. MRR can be used for applications such as high-speed optical communication and optical signal processing. By injecting optical signals into the MRR, functions such as filtering, modulation, and amplification of optical signals can be achieved, thereby improving the transmission rate and reliability of optical communication. This article mainly summarizes the research progress of silicon based MRR at home and abroad from the perspectives of different structures and materials. It also analyzes the application limitations and performance effects of different structures on MRR, and compares the advantages and disadvantages of different materials in preparing MRR. The detailed horizontal and vertical comparison is made for the quality factor, free spectrum width, 3 dB bandwidth and other parameters that affect the device performance. This provides ideas for the further development of MRR photonic devices with higher integration and performance in the future.

【Objective】Visible Light Positioning (VLP) technology has gained increasing attention due to its potential for providing low-cost, high-precision indoor location services. However, traditional VLP systems rely on Line-of-Sight (LOS) paths and cannot function properly when obstructed by obstacles.【Methods】To address this issue, we propose a novel Non-Line-of-Sight (NLOS) VLP system based on deep learning. This system utilizes reflected light for VLP, overcoming the challenge of LOS obstruction and enhancing the robustness of the VLP system. Considering the low signal-to-noise ratio of the reflected light, the accuracy and adaptability of conventional image detection methods for extracting Light Emitting Diode (LED) spots are limited, resulting in reduced positioning accuracy for NLOS VLP. Therefore, the proposed system employs the deep learning model U-shaped Network (U-Net) to detect LED spots, which demonstrates high accuracy and adaptability after being trained on datasets collected from various environments, thereby improving the system performance. In the simulation, the system estimates the Three-Dimensional (3D) position of the receiver using the Perspective-Three-Point (P3P) algorithm.【Results】This paper constructed a 1.84 m×1.84 m ×1.96 m 3D space simulating an indoor environment for indoor positioning experiments. The experimental results show that under NLOS paths, the system's 3D mean error and Root Mean Square Error (RMSE) are 16.09 and 17.18 cm, respectively. The Two-Dimensional (2D) positioning error has a 90% confidence level at less than 21 cm, and the 3D positioning error has a 90% confidence level at less than 24 cm.【Conclusion】The proposed system has high positioning accuracy and robustness, which can meet the positioning requirements of most indoor applications.

Remote sensing is one of the most useful tools when it comes to studying earth phenomena along large terrain extensions. Within this broad field, Differential Interferometric Synthetic Aperture Radar (DInSAR) has been evolving, and at this point is able to provide terrain deformation in millimetre-level precision. This analysis was conducted over the Sabancaya Volcano, in Perú, which is part of the Ampato-Sabancaya Volcanic Complex. This volcano has been active and continuously erupting since 2016, with various fault systems surrounding the volcanic complex. The main objective of this work was to map deformation caused by the volcanic system, processing Sentinel-1 products from 2016 and an interval that started in 2014 to 2017 to be able to study the effects of temporal decorrelation on interferometric products, being Sentinel-1 the first of the Copernicus Program satellite constellations conducted by the European Space Agency. The analysis showed deformation in the interval in which the eruption started and a deformation centre in the northern region of the volcanic complex, although the last one was found when studying a longer temporal baseline. Overall, the experiment shows that DInSAR is an effective tool to study volcanic systems.