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- Brno University of Technology
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- Institut National Polytechnique Felix Houphou?t-Boigny Yamoussoukro
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Performance improvement of optical negative feedback laser by reducing feedback loop length
摘要： The Optical path length of an input/output optical waveguide in a Si ring ?lter is reduced to shorten the feedback loop length of an optical negative feedback laser. Thanks to the increase in phase margin in the optical negative feedback system, the spectral linewidth of a single-mode semiconductor laser can be reduced to 99.8 kHz.
关键词： Si ?lter,semiconductor laser,spectral linewidth,integration,negative feedback
更新于2025-09-23 15:19:57
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5G/NGPON Evolution and Convergence: Developing on Spatial Multiplexing of Optical Fiber Links for 5G Infrastructures
摘要： The offering of demanding telecommunication services as promised by the 5G specifications raise the necessity for high capacity, flexible, adaptive, and power conserving fronthaul. Toward this goal, the role of the passive optical network which is responsible for interconnecting the central office (CO) with the cell-sites is crucial. Among the latest related technologies that need to be integrated in the context of the next generation passive optical networks (NGPONs), the most promising for increasing the provided bandwidth, is the optical spatial multiplexing. In this paper, we present the key 5G technologies, focusing on spatial division multiplexing, which constitutes the main innovation of the blueSPACE 5G Infrastructure Public Private Partnership (5G PPP) project. Exploiting the recent developments on multicore fibers (MCFs), optical beamforming networks (OBFNs), analog radio over fiber (ARoF), and spatial-spectral resources granularity in the context of Spectrally Spatially Flexible Optical Networks (SS-FONs), we describe a complete approach for the 5G fronthaul, emphasizing on the efficient allocation of optical resources while aiming at minimizing energy consumption. The modeled optimization problem is thoroughly presented, and the introduced scheme is evaluated through a real-world based simulation scenario, exhibiting quite promising results.
关键词： power saving optimization,5G fronthaul,ODN granularity,optical SDM,spatial and spectral dimensions,NGPON
更新于2025-09-23 15:19:57
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Self-Powered Filterless Narrow-Band pa??n Heterojunction Photodetector for Low Background Limited Near-Infrared Image Sensor Application
摘要： Photonic detection with narrow spectrum selectivity is very important to eliminate the signal from obtrusive light, which can improve the anti-interference ability of the infrared imaging system. While self-driving effect inherent to p-n junction is very attractive in optic-electronic integration, the application of p-n junction in narrow-band photodetector is limited by the usual broad absorption range. In this work, a self-powered filterless narrowband near-infrared photodetector based on CuGaTe2/silicon p-n junction was reported. The as-fabricated photodetector exhibited typical narrow-band response which shall be ascribed to the slightly smaller bandgap of Si than CuGaTe2 and the restricted photocurrent generation region in the p-n heterojunction by optimizing CuGaTe2 thickness. It is observed that when the thickness of CuGaTe2 film is 143 nm, the device exhibits a response peak centered around 1050 nm with a full-width at half-maximum of ~118 nm. Further device analysis reveals a specific detectivity of ~1012 Jones and a responsivity of 114 mA/W under 1064 nm illumination at zero bias. It was also found that image system based on the narrowband CuGaTe2/Si photodetector showed high noise immunity for its spectral selective characteristics.
关键词： p-n heterojunction,near infrared light,image sensing,spectral selectivity,narrow band photodetector
更新于2025-09-23 15:19:57
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Qualitative and Quantitative Distinction of <i>ortho</i> -, <i>meta</i> -, and <i>para</i> -Fluorotoluene by Means of Chirped Femtosecond Laser Ionization
摘要： Femtosecond-laser ionization mass spectrometry (fs-LIMS) is demonstrated to be a powerful analytical method providing access to the qualitative distinction of structural isomers of ortho-, meta-, and para-fluorotoluene. The key point of the approach presented is a systematic variation of the spectral phase of the fs-laser pulses, which characteristically affects the fragmentation pattern observed in the mass spectra. Variation of the linear chirp parameter is also helpful for rationalizing the fragmentation mechanism. Ultimately two ternary mixtures of the three title isomers are quantitatively analyzed in situ with an accuracy of 5% for the molar fractions.
关键词： structural isomers,Femtosecond-laser ionization mass spectrometry,fragmentation pattern,spectral phase,quantitative analysis,fluorotoluene
更新于2025-09-23 15:19:57
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High-power, cascaded random Raman fiber laser with near complete conversion over wide wavelength and power tuning
摘要： Cascaded Raman fiber lasers based on random distributed feedback (RDFB) are proven to be wavelength agile, enabling high powers outside rare-earth doped emission windows. In these systems, by simply adjusting the input pump power and wavelength, high-power lasers can be achieved at any wavelength within the transmission window of optical fibers. However, there are two primary limitations associated with these systems, which in turn limits further power scaling and applicability. Firstly, the degree of wavelength conversion or spectral purity (percentage of output power in the desired wavelength band) that can be achieved is limited. This is attributed to intensity noise transfer of input pump source to Raman Stokes orders, which causes incomplete power transfer reducing the spectral purity. Secondly, the output power range over which the high degree of wavelength conversion is maintained is limited. This is due to unwanted Raman conversion to the next Stokes order with increasing power. Here, we demonstrate a high-power, cascaded Raman fiber laser with near complete wavelength conversion over a wide wavelength and power range. We achieve this by culmination of two recent developments in this field. We utilize our recently proposed filtered feedback mechanism to terminate Raman conversion at arbitrary wavelengths, and we use the recently demonstrated technique (by J Dong and associates) of low-intensity noise pump sources (Fiber ASE sources) to achieve high-purity Raman conversion. Pump-limited output powers >34W and wavelength conversions >97% (highest till date) were achieved over a broad – 1.1μm to 1.5μm tuning range. In addition, high spectral purity (>90%) was maintained over a broad output power range (>15%), indicating the robustness of this laser against input power variations.
关键词： wavelength conversion,spectral purity,random distributed feedback,Raman fiber laser,high-power
更新于2025-09-23 15:19:57
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Self-driven all-inorganic perovskite microplatelet vertical Schottky junction photodetectors with a tunable spectral response
摘要： Wavelength-selective perovskite photodetectors (PDs) have many applications in optoelectronic field, such as machine vision, imaging and full-color display. However, the instability of organo-inorganic hybrid perovskite material severely limits the commercialization of perovskite-based PDs. In this work, a more stable all-inorganic perovskite, CsPbBr(3-x)Clx (x = 0, 1, 2, 3) microplatelets (MPs), were employed to fabricate Schottky PDs with a simple vertical structure of ITO/MP/Au. The optimized CsPbBr3 MP Schottky PDs exhibit rapid response speed (75 μs) and very low dark current (2 pA) at zero bias. Meanwhile, the device shows a high on/off ratio (>106), a large specific detectivity (>1012 Jones) and linear dynamic range (LDR = 137 dB) with excellent thermal and long-term stability. Furthermore, a tunable spectral response covering from the ultraviolet to visible range is also demonstrated. These results provide a simple avenue to realize self-driven and spectral tunable all-inorganic perovskite Schottky PDs with good stability.
关键词： all-inorganic perovskite,high temperature tolerance,tunable spectral response,vertical structure Schottky photodetector,weak-light sensitivity
更新于2025-09-23 15:19:57
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Novel Combined Spectral Indices Derived from Hyperspectral and Laser-Induced Fluorescence LiDAR Spectra for Leaf Nitrogen Contents Estimation of Rice
摘要： Spectra of re?ectance (Sr) and ?uorescence (Sf) are signi?cant for crop monitoring and ecological environment research, and can be used to indicate the leaf nitrogen content (LNC) of crops indirectly. The aim of this work is to use the Sr-Sf features obtained with hyperspectral and laser-induced ?uorescence LiDAR (HSL, LIFL) systems to construct novel combined spectral indices (NCIH-F) for multi-year rice LNC estimation. The NCIH-F is in a form of FWs*Φ + GSIs*Φ, where Φ is the Sr-Sf features, and FWs and GSIs are the feature weights and global sensitive indices for each characteristic band. In this study, the characteristic bands were chosen in di?erent ways. Firstly, the Sr-Sf characteristics which can be the intensity or derivative variables of spectra in 685 and 740 nm, have been assigned as the Φ value in NCIH-F formula. Simultaneously, the photochemical re?ectance index (PRI) formed with 531 and 570 nm was modi?ed based on a variant spectral index, called PRIfraction, with the Sf intensity in 740 nm, and then compared its potential with NCIH-F on LNC estimation. During the above analysis, both NCIH-F and PRIfraction values were utilized to model rice LNC based on the arti?cial neural networks (ANNs) method. Subsequently, four prior bands were selected, respectively, with high FW and GSI values as the ANNs inputs for rice LNC estimation. Results show that FW- and GSI-based NCIH-F are closely related to rice LNC, and the performance of previous spectral indices used for LNC estimation can be greatly improved by multiplying their FWs and GSIs. Thus, it can be included that the FW- and GSI-based NCIH-F constitutes an e?cient and reliable constructed form combining HSL (Sr) and LIFL (Sf) data together for rice LNC estimation.
关键词： hyperspectral LiDAR,combined spectral index,leaf nitrogen content,laser-induced ?uorescence LiDAR
更新于2025-09-23 15:19:57
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Excitation-Emission Synchronization Mediated Directional Fluorescence: Insight into Plasmon Coupled Emission at the Vibrational Resolution
摘要： Light-matter interaction is always the fundamentally significant topic to attract much attentions. It is important to reveal fluorophore-plasmon interaction at the nanoscale. Although as a powerful investigative tool, fluorescence spectroscopy still suffers from the limited spectral resolution and its susceptibility to interfering substances. In this work, the excitation-emission synchronization mediated surface plasmon coupled emission (EES-SPCE) is proposed to break the bottleneck. By actively screening the energy transitions for observation, the improved spectral resolution has been achieved, which is advantageous to the investigation of the fluorophore-plasmon interactions under different coupling modes. The spectral information related to the plasmonic interactions through tuning vibrational energy levels are clearly distinguished at directional emission angles. EES-SPCE is demonstrated to selectively and efficiently extract the coupled emission with the vibrational resolution, which would open up the opportunities to improve the capability of spectral feature identification and signal collection for practical applications of plasmonic fluorescence spectroscopy.
关键词： synchronous fluorescence spectroscopy,energy difference,directional emission,surface plasmon coupled emission,spectral resolution
更新于2025-09-23 15:19:57
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Noise and spectral stability of deep-UV gas-filled fiber-based supercontinuum sources driven by ultrafast mid-IR pulses
摘要： Deep-UV (DUV) supercontinuum (SC) sources based on gas-filled hollow-core fibers constitute perhaps the most viable solution towards ultrafast, compact, and tunable lasers in the UV spectral region, which can even also extend into the mid-infrared (iR). noise and spectral stability of such broadband sources are key parameters that define their true potential and suitability towards real-world applications. In order to investigate the spectral stability and noise levels in these fiber-based DUV sources, we generate an SC spectrum that extends from 180 nm (through phase-matched dispersive waves - DWs) to 4 μm by pumping an argon-filled hollow-core anti-resonant fiber at a mid-IR wavelength of 2.45 μm. We characterize the long-term stability of the source over several days and the pulse-to-pulse relative intensity noise (RIN) of the DW at 275 nm. The results indicate no sign of spectral degradation over 110 hours, but the RIN of the DW pulses at 275 nm is found to be as high as 33.3%. Numerical simulations were carried out to investigate the spectral distribution of the RIN and the results confirm the experimental measurements and that the poor noise performance is due to the high Rin of the mid-IR pump laser, which was hitherto not considered in numerical modelling of these sources. The results presented herein provide an important step towards an understanding of the noise mechanism underlying such complex light-gas nonlinear interactions and demonstrate the need for pump laser stabilization.
关键词： Deep-UV,supercontinuum sources,spectral stability,ultrafast mid-IR pulses,gas-filled fiber,noise
更新于2025-09-23 15:19:57
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Influence of the polarization of the laser beam in femtosecond laser-induced breakdown spectroscopy
摘要： Laser-induced breakdown spectroscopy (LIBS) is an important technique which is widely used to analyze element composition. In order to improve the sensitivity of LIBS, researchers have been dedicated to enhance the spectral intensity of LIBS by proposing a number of methods. In addition, we find that laser polarization has great influence on the emission intensity of femtosecond LIBS. By comparing the emission intensity of femtosecond LIBS in the circular and linear polarizations, the spectral intensity in the case of circular polarization is stronger than that in the case of linear polarization. Moreover, this phenomenon is more obvious as laser energy increases. The polarization plays an important role in LIBS signal intensity. Based on the observation, the enhanced mechanism of the laser polarization on the spectral intensity is discussed in this paper, which will be helpful to spectral analysis and component analysis.
关键词： femtosecond laser,LIBS,spectral enhancement,laser polarization
更新于2025-09-23 15:19:57