Single-photon detectors(SPDs)exhibit high sensitivity and strong anti-interference capability,and are often integrated with the traditional pulse position modulation(PPM)technique for long-distance laser communication.However,this integration suffers from low communication rates.To address the rate per-formance limitations of PPM modulation,a broadband reconfigurable pulse sampling data transmission scheme based on single-photon detectors is proposed.In addition,an adaptive pulse-width algorithm tailored to this modulation method is designed to achieve optimal pulse-width selection for the data acquired by single-photon detectors.At the transmitter,the FPGA GTX high-speed transceiver and real-time serial port transceiving are adopted to optimize the transmitted code pattern;at the receiver,a bit error rate(BER)mon-itoring and adaptive algorithm module is developed.Link simulations and adaptive simulations are conduc-ted to evaluate the impacts of actual channel scenarios,and a 1 550 nm single-photon detection experimental system is built for validation.Experimental results show that this modulation scheme enables single-photon laser communication with a rate range from kbps to Mbps.Meanwhile,preliminary tests based on avalanche photodiodes(APDs)demonstrate the feasibility of Gbps-level high-speed communication using this scheme.At the kbps and Mbps rate levels,compared with the default pulse width,the adaptive pulse-width modula-tion algorithm reduces the communication BER by one and two orders of magnitude,respectively.In com-parison with traditional single-photon laser communication systems,this modulation scheme supports wide-rate-range adjustment from kbps to Gbps and optimal pulse-width selection at kbps-Mbps rates,thus provid-ing a novel solution for single-photon detection devices based on different technical routes.
This research reported a novel integrated strategy based on microfluidic technology for the syn-thesis and surface ligand modification of CdSe quantum dots(QDs).The strategy aims to achieve precise and efficient regulation of the luminescence properties of QDs to meet the specific requirements for their optical characteristics in fields such as display,imaging,and optical sensing.Firstly,a microfluidic platform suitable for QDs synthesis was developed,enabling high-throughput and precise control of multiple reaction condi-tions for efficient synthesis.We systematically investigated the influence of reaction temperature,time,and precursor ligand ratios on the growth process and luminescence properties of CdSe QDs.Benefiting from the efficient mass and heat transfer of the microfluidic platform,the reaction time was significantly reduced from the 1 hours required by traditional ligand modification methods to just 5 minutes in our design.To address the issue of spectral shifts in luminescence properties(such as emission color and full width at half maxim-um,FWHM)during functional ligand modification,this research introduced oleic acid(OA)as a surface modification ligand in the microfluidic system.Through efficient and stable anchoring of OA ligands,the lu-minescence efficiency of the quantum dots was enhanced by threefold,while successfully suppressing re-growth and agglomeration behaviors,thereby maintaining the stability of the emission wavelength and FWHM.The innovative use of microfluidic technology in this research not only provides a reproducible and scalable platform technology for precise regulation of QD size and luminescence color but also achieves syn-ergistic optimization of QD luminescence efficiency and stability.Our strategy paves a technical avenue for the practical application of QDs materials in fields such as luminescent displays and quantum light sources.
This study investigates the performance degradation and underlying damage mechanisms of silicon PIN photodiodes under xenon lamp irradiation. To this end, detectivity is defined and operationalized. A 50 kW xenon lamp irradiation test platform was established, where the S5106-type silicon PIN photodiodes were selected as the representative test device. Real-time monitoring of output photocurrent and surface temperature enabled systematic analysis of the factors governing detectivity degradation, as well as characterization of the damage threshold. A damage threshold model for silicon PIN photodiodes was developed based on the one-dimensional heat diffusion equation. Model accuracy was verified by comparing with the experimentally measured threshold data. Silicon PIN photodiode damage was categorized into two regimes-soft damage and hard damage-based on the recoverability of detectivity. Under soft damage conditions, the de tectivity of the device exhibited a nonlinear negative correlation with both irradiation time and surface temperature. The hard damage irradiance thresholds followed an inverse-square-root dependence on irradiation time, a trend fully consistent with the damage threshold model. Hard damage was observed at a minimum irradiance of approximately 6.6 W/cm2, corresponding to an irradiation time of about 382 s. Under this threshold condition, the surface temperature ranged within (385.77 +/- 4.16)degrees C. Theoretical analysis indicated that soft damage primarily arose from thermally induced degradation of carrier mobility and increased leakage current. Conversely, hard damage resulted from melting and cracking of the silicone rubber optical window, as well as thermally induced functional failure of the PN junction. The findings provide a quantitative basis for performance evaluation and protection design of silicon PIN photodiodes employed in broad-spectrum high-intensity optical detection scenarios.
To accurately monitor methane emissions from point sources,this paper explores the use of a Fabry-Perot(F-P)interferometer as the spectroscopic element of a spatial imaging spectrometer,aiming to achieve both high spatial and high spectral resolution.The study focuses on constructing both theoretical and physical models of the F-P cavity to meet the technical requirements of methane point-source monitoring.First,an initial theoretical model of F-P cavity interference under ideal conditions is developed based on multi-beam interference theory.Building upon this,a corresponding geometric model is established by con-sidering the effect of finite throughput aperture,from which a theoretical model under finite aperture condi-tions is derived.In addition,a more comprehensive theoretical framework is constructed by incorporating surface defect distribution functions to account for microscopic random inhomogeneities and curvature de-fects.In the physical model development,the F-P cavity is initially designed based on the ideal theoretical model to match the spectral characteristics of methane absorption.Using the finite-aperture theoretical model,the transmission intensity curve and its slope are analyzed,and the aperture size is precisely determined based on the physical meaning of the slope.Subsequently,the physical model is further optimized by adjusting the wedge angle at the rear surface of the mirror.To meet specific spectral and technical targets,the allowable variation in the gap spacing between the two parallel mirrors is thoroughly analyzed,thereby defining the tol-erance range for the cavity gap.Surface roughness,figure accuracy,and parallelism of the reflective surfaces are then specified according to surface defect considerations.Ultimately,the optimized F-P cavity achieves a spectral resolution of 0.29 nm,meeting the technical requirements for methane point-source monitoring.By constructing a comprehensive theoretical model and optimizing the physical design,this study enables the realization of both high spectral and spatial resolution,provides a theoretical foundation for applying F-P in-terferometers in spatial imaging spectrometry,and supports the advancement of high-precision spectral detec-tion technologies.
