Sensing the content of macronutrients in the agricultural soil is an essential task in precision agriculture.It helps the farmers in the optimal use of fertilizers.It reduces the cost of food production and also the n...Sensing the content of macronutrients in the agricultural soil is an essential task in precision agriculture.It helps the farmers in the optimal use of fertilizers.It reduces the cost of food production and also the negative environmentalimpacts on atmosphere and water bodies due to indiscriminate dosageof fertilizers.The traditional chemical-based laboratory soil analysis methodsdo not serve the purpose as they are hardly suitable for site specific soil management.Moreover,the spectral range used in the chemical-based laboratory soil analysismay be of 350-2500 nm,which leads to redundancy and confusion.Developing sensors based on the discovery of spectral wavebands that respondto soil macronutrient concentrations,on the other hand,is an innovative and successfultechnology since the results are dependable and timely.The goal of thisarticle is to use a supervised neuro-fuzzy based dimensionality reduction approachin the sensor development process to determine sensitive wavebands of soilmacronutrients.Accordingly,the spectral signatures of the soil are collected inan outdoor environment and mapped with its macronutrient concentrations.In thisspectral analysis,the spectral reflectance of 424 wavelengths has been obtainedand these wavelengths are evaluated through combined and individual modesas well.Appropriate wavelengths are selected in each case by minimizing the fuzzy reflectance assessment index.The effectiveness of these selected wavelengthsin each mode is validated by modeling the relation between the reduced reflectancespace and each macronutrient concentration using Partial Least Squares Multi Variable Regression(PLS-MVR)method.Set of optimal wavebands areidentified and the results are compared with the existing systems.展开更多
The objectives of the study were to select suitable wavebands for rice leaf area index （LAI） estimation using the data acquired over a whole growing season, and to test the efficiency of the selected wavebands by co...The objectives of the study were to select suitable wavebands for rice leaf area index （LAI） estimation using the data acquired over a whole growing season, and to test the efficiency of the selected wavebands by comparing them with feature positions of rice canopy spectra. In this study, the field experiment in 2002 growing season was conducted at the experimental farm of Zhejiang University, Hangzhou, China. Measurements of hyperspectral reflectance （350-2500 nm） and corresponding LAI were made for a paddy rice canopy throughout the growing season. And three methods were employed to identify the optimal wavebands for paddy rice LAI estimation： correlation coefficient-based method, vegetation index-based method, and stepwise regression method. This research selected 15 wavebands in the region of 350-2500 nm, which appeared to be the optimal wavebands for the paddy rice LAI estimation. Of the selected wavebands, the most frequently occurring wavebands were centered around 554, 675, 723, and 1633 rim. They were followed by 444, 524, 576, 594, 804, 849, 974, 1074, 1219, 1510, and 2194 rim. Most of them made physical sense and had their counterparts in spectral known feature positions, which indicates the promising potential of the 15 selected wavebands for the retrieval of paddy rice LAI.展开更多
Rail irregularities, in particular for urban rail- way infrastructures, are one of the main causes for the generation of noise and vibrations. In addition, repetitive loading may also lead to decay of the structural e...Rail irregularities, in particular for urban rail- way infrastructures, are one of the main causes for the generation of noise and vibrations. In addition, repetitive loading may also lead to decay of the structural elements of the rolling stock. This further causes an increase in main- tenance costs and reduction of service life. Monitoring these defects on a periodic basis enables the network rail managers to apply proactive measures to limit further damage. This paper discusses the measurement methods for rail corrugation with particular regard to the analysis tools for evaluating the thresholds of acceptability in re- lation to the tramway Italian transport system. Further- more, a method of analysis has been proposed： an application of the methodology used for treating road profiles has been also utilized for the data processing of rail profilometric data.展开更多
Soil salinization is a serious ecological and environmental problem because it adversely affects sustainable development worldwide, especially in arid and semi-arid regions. It is crucial and urgent that advanced tech...Soil salinization is a serious ecological and environmental problem because it adversely affects sustainable development worldwide, especially in arid and semi-arid regions. It is crucial and urgent that advanced technologies are used to efficiently and accurately assess the status of salinization processes. Case studies to determine the relations between particular types of salinization and their spectral reflectances are essential because of the distinctive characteristics of the reflectance spectra of particular salts. During April 2015 we collected surface soil samples(0–10 cm depth) at 64 field sites in the downstream area of Minqin Oasis in Northwest China, an area that is undergoing serious salinization. We developed a linear model for determination of salt content in soil from hyperspectral data as follows. First, we undertook chemical analysis of the soil samples to determine their soluble salt contents. We then measured the reflectance spectra of the soil samples, which we post-processed using a continuum-removed reflectance algorithm to enhance the absorption features and better discriminate subtle differences in spectral features. We applied a normalized difference salinity index to the continuum-removed hyperspectral data to obtain all possible waveband pairs. Correlation of the indices obtained for all of the waveband pairs with the wavebands corresponding to measured soil salinities showed that two wavebands centred at wavelengths of 1358 and 2382 nm had the highest sensitivity to salinity. We then applied the linear regression modelling to the data from half of the soil samples to develop a soil salinity index for the relationships between wavebands and laboratory measured soluble salt content. We used the hyperspectral data from the remaining samples to validate the model. The salt content in soil from Minqin Oasis were well produced by the model. Our results indicate that wavelengths at 1358 and 2382 nm are the optimal wavebands for monitoring the concentrations of chlorine and sulphate compounds, the predominant salts at Minqin Oasis. Our modelling provides a reference for future case studies on the use of hyperspectral data for predictive quantitative estimation of salt content in soils in arid regions. Further research is warranted on the application of this method to remotely sensed hyperspectral data to investigate its potential use for large-scale mapping of the extent and severity of soil salinity.展开更多
Partial least squares discriminant analysis (PLS-DA) with integrated moving-window (MW) waveband screening was applied to the discriminant analysis of liquor brands with near-infrared (NIR) spectroscopy. Luzhou Laojia...Partial least squares discriminant analysis (PLS-DA) with integrated moving-window (MW) waveband screening was applied to the discriminant analysis of liquor brands with near-infrared (NIR) spectroscopy. Luzhou Laojiao, a popular liquor with strong fragrant flavor, was used as the identified liquor brand (160 samples, negative, 52 vol alcoholicity). Liquors of 10 other brands with strong fragrant flavor were used as the interferential brands (200 samples, positive, 52 vol alcoholicity). The Kennard-Stone algorithm was used for the division of modeling samples to achieve uniformity and representativeness. Based on the MW-PLS-DA, a simplified optimal model set with 157 wavebands was further proposed. This set contained five types of wavebands corresponding to the NIR absorption bands of water, ethanol, and other micronutrients (i.e., acids, aldehydes, phenols, and aromatic compounds) in liquor for practical choice. Using five selected simple models with 4775 - 4239, 7804 - 6569, 6264 - 5844, 9435 - 7896, and 12066 - 10373 cm-1, the validation recognition rates were obtained as 99.3% or higher. Results show good prediction performance and low model complexity, and also provided a valuable reference for designing small dedicated instruments. The proposed method is a promising tool for large-scale inspection of liquor food safety.展开更多
High-end wine brand is made through the use of high-quality grape variety and yeast strain, and through a unique process. Not only is it rich in nutrients, but also it has a unique taste and a fragrant scent. Brand id...High-end wine brand is made through the use of high-quality grape variety and yeast strain, and through a unique process. Not only is it rich in nutrients, but also it has a unique taste and a fragrant scent. Brand identification of wine is difficult and complex because of high similarity. In this paper, visible and near-infrared (NIR) spectroscopy combined with partial least squares discriminant analysis (PLS-DA) was used to explore the feasibility of wine brand identification. Chilean Aoyo wine (2016 vintage) was selected as the identification brand (negative, 100 samples), and various other brands of wine were used as interference brands (positive, 373 samples). Samples of each type were randomly divided into the calibration, prediction and validation sets. For comparison, the PLS-DA models were established in three independent and two complex wavebands of visible (400 - 780 nm), short-NIR (780 - 1100 nm), long-NIR (1100 - 2498 nm), whole NIR (780 - 2498 nm) and whole scanning (400 - 2498 nm). In independent validation, the five models all achieved good discriminant effects. Among them, the visible region model achieved the best effect. The recognition-accuracy rates in validation of negative, positive and total samples achieved 100%, 95.6% and 97.5%, respectively. The results indicated the feasibility of wine brand identification with Vis-NIR spectroscopy.展开更多
The level of chemical oxygen demand(COD)is an important index to evaluate whether sewage meets the discharge requirements,so corresponding tests should be carried out before discharge.Fourier transform infrared spectr...The level of chemical oxygen demand(COD)is an important index to evaluate whether sewage meets the discharge requirements,so corresponding tests should be carried out before discharge.Fourier transform infrared spectroscopy(FTIR)and attenuated total reflectance(ATR)can detect COD in sewage effectively,which has advantages over conventional chemical analysis methods.And the selection of characteristic bands was one of the key links in the application of FTIR/ATR spectroscopy.In this work,based on the moving window partial least-squares(MWPLS)regression to select a characteristic wavelength,a method of equivalent wavelength selection was proposed combining with paired t-test equivalent concept.The results showed that the prediction effect of the selected wavelength was very close to that of the MWPLS method,while the number of wavelength points was much smaller.SEPAve,RP,Ave,SEPStd,and RP,Std which characterized the modeling effect were 26.3 mg L^-1,0.969,3.49 mg L^-1,and 0.006,respectively.The validation effect V-SEP and V-RP were 28.64 mg L^-1 and 0.960,respectively.The selected waveband was between 1809 cm^-1 and 1568 cm^-1.The method was of more reference value for the design of FTIR/ATR spectral instrument for COD detection.展开更多
Influence of duty ratio of metallic gratings applied in quantum well infrared photodetector (QWIP) with detection ranging from 3 μm to 5 μm was studied in this paper. The influence on longer enhanced w...Influence of duty ratio of metallic gratings applied in quantum well infrared photodetector (QWIP) with detection ranging from 3 μm to 5 μm was studied in this paper. The influence on longer enhanced wavelength working at infrared waveband was investigated. A relationship between the duty ratio and the enhanced peak intensity is given. Some results can be applied to optimize the enhanced efficiency of the metallic gratings.展开更多
Development of a high power fiber laser at special waveband,which is difficult to achieve by conventional rare-earth-doped fibers,is a significant challenge.One of the most common methods for achieving lasing at speci...Development of a high power fiber laser at special waveband,which is difficult to achieve by conventional rare-earth-doped fibers,is a significant challenge.One of the most common methods for achieving lasing at special wavelength is Raman conversion.Phosphorus-doped fiber(PDF),due to the phosphorus-related large frequency shift Raman peak at 40 THz,is a great choice for large frequency shift Raman conversion.Here,by adopting 150 m large mode area triple-clad PDF as Raman gain medium,and a novel wavelength-selective feedback mechanism to suppress the silica-related Raman emission,we build a high power cladding-pumped Raman fiber laser at 1.2μm waveband.A Raman signal with power up to 735.8 W at 1252.7 nm is obtained.To the best of our knowledge,this is the highest output power ever reported for fiber lasers at 1.2μm waveband.Moreover,by tuning the wavelength of the pump source,a tunable Raman output of more than 450 W over a wavelength range of 1240.6–1252.7 nm is demonstrated.This work proves PDF’s advantage in high power large frequency shift Raman conversion with a cladding pump scheme,thus providing a good solution for a high power laser source at special waveband.展开更多
Based on a silicon platform, we design and fabricate a four-mode division(de)multiplexer for chip-scale optical data transmission in the 2 μm waveband for the first time, to the best of our knowledge. The(de)multiple...Based on a silicon platform, we design and fabricate a four-mode division(de)multiplexer for chip-scale optical data transmission in the 2 μm waveband for the first time, to the best of our knowledge. The(de)multiplexer is composed of three tapered directional couplers for both mode multiplexing and demultiplexing processes. In the experiment, the average crosstalk for four channels is measured to be less than-18 dB over a wide wavelength range(70 nm) from 1950 to 2020 nm, and the insertion losses are also assessed. Moreover, we further demonstrate stable 5 Gbit/s direct modulation data transmission through the fabricated silicon photonic devices with nonreturn-to-zero on–off keying signals. The experimental results show clear eye diagrams, and the penalties at a bit error rate of 3.8 × 10-3 are all less than 2.5 dB after on-chip data transmission. The obtained results indicate that the presented silicon four-mode division multiplexer in the mid-infrared wavelength band might be a promising candidate facilitating chip-scale high-speed optical interconnects.展开更多
Indoor airborne bioaerosols of outdoor origin play an important role in determining the exposure of humans to bioaerosols because people spend most of their time indoors. However, there are few studies focusing on ind...Indoor airborne bioaerosols of outdoor origin play an important role in determining the exposure of humans to bioaerosols because people spend most of their time indoors. However, there are few studies focusing on indoor bioaerosols originating from outdoors. In this study, indoor versus outdoor size-resolved concentrations and particle asymmetry factors of airborne fluorescent bioaerosols in an office room were measured continuously for 6 days （144 h） using a fluorescent bioaerosol detector. The windows and door of this room were closed to ensure that there was only air infiltration; moreover, any human activities were ceased during sampling to inhibit effects of indoor sources. We focused on fine particles, since few coarse particles enter indoor environments, when windows and doors are closed. Both indoor and outdoor fluorescent bioaerosol size distributions were fit with two-mode lognormal distributions （indoor R2 = 0.935, outdoor R2 = 0.938）. Asymmetry factor distributions were also fit with lognormal distributions （indoor R2 = 0.992, outdoor R2 = 0.992）. Correlations between indoor and outdoor fluorescent bioaerosol concentrations show significant concentration-attenuation and a time lag during the study period. A two-parameter, semi-empirical model was used to predict concentrations of indoor fluorescent bioaerosols of outdoor origin. The measured and predicted concentrations had a linear relationship for the studied size fractions, with an R2 for all size fractions of larger than 0.83.展开更多
We propose a cascade system of filters for realizing a non-uniform waveband separation for optical networks. The use of such separation is required at the DEMUX stage in a optical OXC switching wavebands. The design o...We propose a cascade system of filters for realizing a non-uniform waveband separation for optical networks. The use of such separation is required at the DEMUX stage in a optical OXC switching wavebands. The design of the system is based on optimized balanced tree, which minimizes the overall optical loss.展开更多
A new routing and wavelength assignment method applied in hierarchical wavelength division multiplexing(WDM)networks is proposed.The algorithm is called offline band priority algorithm(offline BPA).The offline BPA tar...A new routing and wavelength assignment method applied in hierarchical wavelength division multiplexing(WDM)networks is proposed.The algorithm is called offline band priority algorithm(offline BPA).The offline BPA targets to maximize the number of waveband paths under the condition of minimum number of wavelengths,and solve the routing and wavelength assignment(RWA)problem with waveband grooming to reduce cost.Based on the circle construction algorithm,waveband priority function is introduced to calculate the RWA problem.Simulation results demonstrate that the proposed algorithm achieves significant cost reduction in WDM network construction.展开更多
文摘Sensing the content of macronutrients in the agricultural soil is an essential task in precision agriculture.It helps the farmers in the optimal use of fertilizers.It reduces the cost of food production and also the negative environmentalimpacts on atmosphere and water bodies due to indiscriminate dosageof fertilizers.The traditional chemical-based laboratory soil analysis methodsdo not serve the purpose as they are hardly suitable for site specific soil management.Moreover,the spectral range used in the chemical-based laboratory soil analysismay be of 350-2500 nm,which leads to redundancy and confusion.Developing sensors based on the discovery of spectral wavebands that respondto soil macronutrient concentrations,on the other hand,is an innovative and successfultechnology since the results are dependable and timely.The goal of thisarticle is to use a supervised neuro-fuzzy based dimensionality reduction approachin the sensor development process to determine sensitive wavebands of soilmacronutrients.Accordingly,the spectral signatures of the soil are collected inan outdoor environment and mapped with its macronutrient concentrations.In thisspectral analysis,the spectral reflectance of 424 wavelengths has been obtainedand these wavelengths are evaluated through combined and individual modesas well.Appropriate wavelengths are selected in each case by minimizing the fuzzy reflectance assessment index.The effectiveness of these selected wavelengthsin each mode is validated by modeling the relation between the reduced reflectancespace and each macronutrient concentration using Partial Least Squares Multi Variable Regression(PLS-MVR)method.Set of optimal wavebands areidentified and the results are compared with the existing systems.
基金supported by the National Natural Science Foundation of China (No. 40571115)the Hi-Tech Research and Development Program (863) of China (No. 2006AA120101)the National Basic Research Program (973) of China (No. 2006BAD10A09)
文摘The objectives of the study were to select suitable wavebands for rice leaf area index （LAI） estimation using the data acquired over a whole growing season, and to test the efficiency of the selected wavebands by comparing them with feature positions of rice canopy spectra. In this study, the field experiment in 2002 growing season was conducted at the experimental farm of Zhejiang University, Hangzhou, China. Measurements of hyperspectral reflectance （350-2500 nm） and corresponding LAI were made for a paddy rice canopy throughout the growing season. And three methods were employed to identify the optimal wavebands for paddy rice LAI estimation： correlation coefficient-based method, vegetation index-based method, and stepwise regression method. This research selected 15 wavebands in the region of 350-2500 nm, which appeared to be the optimal wavebands for the paddy rice LAI estimation. Of the selected wavebands, the most frequently occurring wavebands were centered around 554, 675, 723, and 1633 rim. They were followed by 444, 524, 576, 594, 804, 849, 974, 1074, 1219, 1510, and 2194 rim. Most of them made physical sense and had their counterparts in spectral known feature positions, which indicates the promising potential of the 15 selected wavebands for the retrieval of paddy rice LAI.
文摘Rail irregularities, in particular for urban rail- way infrastructures, are one of the main causes for the generation of noise and vibrations. In addition, repetitive loading may also lead to decay of the structural elements of the rolling stock. This further causes an increase in main- tenance costs and reduction of service life. Monitoring these defects on a periodic basis enables the network rail managers to apply proactive measures to limit further damage. This paper discusses the measurement methods for rail corrugation with particular regard to the analysis tools for evaluating the thresholds of acceptability in re- lation to the tramway Italian transport system. Further- more, a method of analysis has been proposed： an application of the methodology used for treating road profiles has been also utilized for the data processing of rail profilometric data.
基金supported by the International Platform for Dryland Research and Education, Tottori University and the National Key R&D Program of China (2016YFC0500909)
文摘Soil salinization is a serious ecological and environmental problem because it adversely affects sustainable development worldwide, especially in arid and semi-arid regions. It is crucial and urgent that advanced technologies are used to efficiently and accurately assess the status of salinization processes. Case studies to determine the relations between particular types of salinization and their spectral reflectances are essential because of the distinctive characteristics of the reflectance spectra of particular salts. During April 2015 we collected surface soil samples(0–10 cm depth) at 64 field sites in the downstream area of Minqin Oasis in Northwest China, an area that is undergoing serious salinization. We developed a linear model for determination of salt content in soil from hyperspectral data as follows. First, we undertook chemical analysis of the soil samples to determine their soluble salt contents. We then measured the reflectance spectra of the soil samples, which we post-processed using a continuum-removed reflectance algorithm to enhance the absorption features and better discriminate subtle differences in spectral features. We applied a normalized difference salinity index to the continuum-removed hyperspectral data to obtain all possible waveband pairs. Correlation of the indices obtained for all of the waveband pairs with the wavebands corresponding to measured soil salinities showed that two wavebands centred at wavelengths of 1358 and 2382 nm had the highest sensitivity to salinity. We then applied the linear regression modelling to the data from half of the soil samples to develop a soil salinity index for the relationships between wavebands and laboratory measured soluble salt content. We used the hyperspectral data from the remaining samples to validate the model. The salt content in soil from Minqin Oasis were well produced by the model. Our results indicate that wavelengths at 1358 and 2382 nm are the optimal wavebands for monitoring the concentrations of chlorine and sulphate compounds, the predominant salts at Minqin Oasis. Our modelling provides a reference for future case studies on the use of hyperspectral data for predictive quantitative estimation of salt content in soils in arid regions. Further research is warranted on the application of this method to remotely sensed hyperspectral data to investigate its potential use for large-scale mapping of the extent and severity of soil salinity.
文摘Partial least squares discriminant analysis (PLS-DA) with integrated moving-window (MW) waveband screening was applied to the discriminant analysis of liquor brands with near-infrared (NIR) spectroscopy. Luzhou Laojiao, a popular liquor with strong fragrant flavor, was used as the identified liquor brand (160 samples, negative, 52 vol alcoholicity). Liquors of 10 other brands with strong fragrant flavor were used as the interferential brands (200 samples, positive, 52 vol alcoholicity). The Kennard-Stone algorithm was used for the division of modeling samples to achieve uniformity and representativeness. Based on the MW-PLS-DA, a simplified optimal model set with 157 wavebands was further proposed. This set contained five types of wavebands corresponding to the NIR absorption bands of water, ethanol, and other micronutrients (i.e., acids, aldehydes, phenols, and aromatic compounds) in liquor for practical choice. Using five selected simple models with 4775 - 4239, 7804 - 6569, 6264 - 5844, 9435 - 7896, and 12066 - 10373 cm-1, the validation recognition rates were obtained as 99.3% or higher. Results show good prediction performance and low model complexity, and also provided a valuable reference for designing small dedicated instruments. The proposed method is a promising tool for large-scale inspection of liquor food safety.
文摘High-end wine brand is made through the use of high-quality grape variety and yeast strain, and through a unique process. Not only is it rich in nutrients, but also it has a unique taste and a fragrant scent. Brand identification of wine is difficult and complex because of high similarity. In this paper, visible and near-infrared (NIR) spectroscopy combined with partial least squares discriminant analysis (PLS-DA) was used to explore the feasibility of wine brand identification. Chilean Aoyo wine (2016 vintage) was selected as the identification brand (negative, 100 samples), and various other brands of wine were used as interference brands (positive, 373 samples). Samples of each type were randomly divided into the calibration, prediction and validation sets. For comparison, the PLS-DA models were established in three independent and two complex wavebands of visible (400 - 780 nm), short-NIR (780 - 1100 nm), long-NIR (1100 - 2498 nm), whole NIR (780 - 2498 nm) and whole scanning (400 - 2498 nm). In independent validation, the five models all achieved good discriminant effects. Among them, the visible region model achieved the best effect. The recognition-accuracy rates in validation of negative, positive and total samples achieved 100%, 95.6% and 97.5%, respectively. The results indicated the feasibility of wine brand identification with Vis-NIR spectroscopy.
基金This work was financially supported by the Natural Science Foundation of Hainan Province(417087)the Key Research and Development Program of Hainan Province(ZDYF2018007)Research Fund for Advanced Talents of Hainan University(No.kyqd1577).
文摘The level of chemical oxygen demand(COD)is an important index to evaluate whether sewage meets the discharge requirements,so corresponding tests should be carried out before discharge.Fourier transform infrared spectroscopy(FTIR)and attenuated total reflectance(ATR)can detect COD in sewage effectively,which has advantages over conventional chemical analysis methods.And the selection of characteristic bands was one of the key links in the application of FTIR/ATR spectroscopy.In this work,based on the moving window partial least-squares(MWPLS)regression to select a characteristic wavelength,a method of equivalent wavelength selection was proposed combining with paired t-test equivalent concept.The results showed that the prediction effect of the selected wavelength was very close to that of the MWPLS method,while the number of wavelength points was much smaller.SEPAve,RP,Ave,SEPStd,and RP,Std which characterized the modeling effect were 26.3 mg L^-1,0.969,3.49 mg L^-1,and 0.006,respectively.The validation effect V-SEP and V-RP were 28.64 mg L^-1 and 0.960,respectively.The selected waveband was between 1809 cm^-1 and 1568 cm^-1.The method was of more reference value for the design of FTIR/ATR spectral instrument for COD detection.
文摘Influence of duty ratio of metallic gratings applied in quantum well infrared photodetector (QWIP) with detection ranging from 3 μm to 5 μm was studied in this paper. The influence on longer enhanced wavelength working at infrared waveband was investigated. A relationship between the duty ratio and the enhanced peak intensity is given. Some results can be applied to optimize the enhanced efficiency of the metallic gratings.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.61635005,61905284,and 62305391)the National Postdoctoral Program for Innovative Talents(No.BX20190063).
文摘Development of a high power fiber laser at special waveband,which is difficult to achieve by conventional rare-earth-doped fibers,is a significant challenge.One of the most common methods for achieving lasing at special wavelength is Raman conversion.Phosphorus-doped fiber(PDF),due to the phosphorus-related large frequency shift Raman peak at 40 THz,is a great choice for large frequency shift Raman conversion.Here,by adopting 150 m large mode area triple-clad PDF as Raman gain medium,and a novel wavelength-selective feedback mechanism to suppress the silica-related Raman emission,we build a high power cladding-pumped Raman fiber laser at 1.2μm waveband.A Raman signal with power up to 735.8 W at 1252.7 nm is obtained.To the best of our knowledge,this is the highest output power ever reported for fiber lasers at 1.2μm waveband.Moreover,by tuning the wavelength of the pump source,a tunable Raman output of more than 450 W over a wavelength range of 1240.6–1252.7 nm is demonstrated.This work proves PDF’s advantage in high power large frequency shift Raman conversion with a cladding pump scheme,thus providing a good solution for a high power laser source at special waveband.
基金National Natural Science Foundation of China(NSFC)(61761130082,11574001,11774116,61705072)Royal Society-Newton Advanced Fellowship+4 种基金National Program for Support of Top-notch Young ProfessionalsNatural Science Foundation of Hubei Province(2018CFA048,ZRMS2017000413)Beijing University of Posts and Telecommunications(BUPT))(IPOC2018A002)Program for HUST Academic Frontier Youth Team(2016QYTD05)Fundamental Research Funds for the Central Universities(2019kfyRCPY037)
文摘Based on a silicon platform, we design and fabricate a four-mode division(de)multiplexer for chip-scale optical data transmission in the 2 μm waveband for the first time, to the best of our knowledge. The(de)multiplexer is composed of three tapered directional couplers for both mode multiplexing and demultiplexing processes. In the experiment, the average crosstalk for four channels is measured to be less than-18 dB over a wide wavelength range(70 nm) from 1950 to 2020 nm, and the insertion losses are also assessed. Moreover, we further demonstrate stable 5 Gbit/s direct modulation data transmission through the fabricated silicon photonic devices with nonreturn-to-zero on–off keying signals. The experimental results show clear eye diagrams, and the penalties at a bit error rate of 3.8 × 10-3 are all less than 2.5 dB after on-chip data transmission. The obtained results indicate that the presented silicon four-mode division multiplexer in the mid-infrared wavelength band might be a promising candidate facilitating chip-scale high-speed optical interconnects.
基金This work was supported by the National Key Research and Development Plan from the Ministry of Science and Technology of China through Grant No. 2016YFC0700500, as well as funding from Innovative Research Groups of the National Natural Science Foundation of China （No. 51521005）, and the National Natural Science Foundation of China （No. 51678328 ＆ 21221004 ＆ 41227805 ＆ 21190054）.
文摘Indoor airborne bioaerosols of outdoor origin play an important role in determining the exposure of humans to bioaerosols because people spend most of their time indoors. However, there are few studies focusing on indoor bioaerosols originating from outdoors. In this study, indoor versus outdoor size-resolved concentrations and particle asymmetry factors of airborne fluorescent bioaerosols in an office room were measured continuously for 6 days （144 h） using a fluorescent bioaerosol detector. The windows and door of this room were closed to ensure that there was only air infiltration; moreover, any human activities were ceased during sampling to inhibit effects of indoor sources. We focused on fine particles, since few coarse particles enter indoor environments, when windows and doors are closed. Both indoor and outdoor fluorescent bioaerosol size distributions were fit with two-mode lognormal distributions （indoor R2 = 0.935, outdoor R2 = 0.938）. Asymmetry factor distributions were also fit with lognormal distributions （indoor R2 = 0.992, outdoor R2 = 0.992）. Correlations between indoor and outdoor fluorescent bioaerosol concentrations show significant concentration-attenuation and a time lag during the study period. A two-parameter, semi-empirical model was used to predict concentrations of indoor fluorescent bioaerosols of outdoor origin. The measured and predicted concentrations had a linear relationship for the studied size fractions, with an R2 for all size fractions of larger than 0.83.
文摘We propose a cascade system of filters for realizing a non-uniform waveband separation for optical networks. The use of such separation is required at the DEMUX stage in a optical OXC switching wavebands. The design of the system is based on optimized balanced tree, which minimizes the overall optical loss.
文摘A new routing and wavelength assignment method applied in hierarchical wavelength division multiplexing(WDM)networks is proposed.The algorithm is called offline band priority algorithm(offline BPA).The offline BPA targets to maximize the number of waveband paths under the condition of minimum number of wavelengths,and solve the routing and wavelength assignment(RWA)problem with waveband grooming to reduce cost.Based on the circle construction algorithm,waveband priority function is introduced to calculate the RWA problem.Simulation results demonstrate that the proposed algorithm achieves significant cost reduction in WDM network construction.
