Diverse spatial mode bases can be exploited in mode-division multiplexing(MDM)to sustain the capacity growth in fiber-optic communications,such as linearly polarized(LP)modes,vector modes,LP orbital angular momentum(L...Diverse spatial mode bases can be exploited in mode-division multiplexing(MDM)to sustain the capacity growth in fiber-optic communications,such as linearly polarized(LP)modes,vector modes,LP orbital angular momentum(LP-OAM)modes,and circularly polarized OAM(CP-OAM)modes.Nevertheless,which kind of mode bases is more appropriate to be utilized in fiber still remains unclear.Here,we aim to find the superior mode basis in MDM fiber-optic communications via a system-level comparison in air-core fiber(ACF).We first investigate the walk-off effect of four spatial mode bases over 1-km ACF,where LP and LP-OAM modes show intrinsic mode walk-off,while it is negligible for vector and CP-OAM modes.We then study the mode coupling effect of degenerate vector and CP-OAM modes over 1-km ACF under fiber perturbations,where degenerate even and odd vector modes suffer severe mode cross talk,while negligible for highorder degenerate CP-OAM modes based on the laws of angular momentum conservation.Moreover,we comprehensively evaluate the system-level performance for data-carrying single-channel and two-channel MDM transmission with different spatial mode bases under various kinds of fiber perturbations(bending,twisting,pressing,winding,and out-of-plane moving).The obtained results indicate that the CP-OAM mode basis shows superiority compared to other mode bases in MDM fiber-optic communications without using multiple-input multiple-output digital signal processing.Our findings may pave the way for robust shortreach MDM optical interconnects for data centers and high-performance computing.展开更多
The study of the critical zones(CZs) of the Earth link the composition and function of aboveground vegetation with the characteristics of the rock layers, providing a new way to study how the unique rock and soil cond...The study of the critical zones(CZs) of the Earth link the composition and function of aboveground vegetation with the characteristics of the rock layers, providing a new way to study how the unique rock and soil conditions in karst regions affect the aboveground vegetation. Based on survey results of the rocks, soils and vegetation in the dolomite and limestone distribution areas in the karst area of central Guizhou, it was found that woody plant cover increases linearly with the number of cracks with a width of more than 1 mm, while the cover of herbaceous plants shows the opposite trend(p<0.01). The dolomite distribution area is characterized by undeveloped crevices, and the thickness of the soil layer is generally less than 20 cm, which is suitable for the distribution of herbaceous plants with shallow roots. Due to the development of crevices in the limestone distribution area, the soil is deeply distributed through the crevices for the deep roots of trees, which leads to a diversified species composition and a complicated structure in the aboveground vegetation. Based on moderate resolution imaging spectroradiometer(MODIS) remote sensing data from 2001 to 2010, the normalized differentiated vegetation index(NDVI) and annual net primary productivity(NPP) results for each phase of a 16-day interval further indicate that the NDVI of the limestone distribution area is significantly higher than that in the dolomite distribution area, but the average annual NPP is the opposite. The results of this paper indicate that in karst CZs, the lithology determines the structure and distribution of the soil, which further determines the cover of woody and herbaceous plants in the aboveground vegetation. Although the amount of soil in the limestone area may be less than that in the dolomite area, the developed crevice structure is more suitable for the growth of trees with deep roots, and the vegetation activity is strong. At present, the treatment of rocky desertification in karst regions needs to fully consider the rock-soilvegetation-air interactions in karst CZs and propose vegetation restoration measures suitable for different lithologies.展开更多
Lots of research efforts have been devoted to increase the transmission capacity in optical communications using orbital angular momentum(OAM)multiplexing.To enable long-haul OAM mode transmission,an in-line OAM fiber...Lots of research efforts have been devoted to increase the transmission capacity in optical communications using orbital angular momentum(OAM)multiplexing.To enable long-haul OAM mode transmission,an in-line OAM fiber amplifier is desired.A ring-core fiber(RCF)is considered to be a preferable design for stable OAM mode propagation in the fiber.Here,we demonstrate an OAM fiber amplifier based on a fabricated ring-core erbium-doped fiber(RC-EDF).We characterize the performance of the RC-EDF-assisted OAM fiber amplifier and demonstrate its use in OAM multiplexing communications with OAM modes carrying quadrature phase-shift keying(QPSK)and quadrature amplitude modulation(QAM)signals.The amplification of two OAM modes over four wavelengths is demonstrated in a data-carrying OAM-division multiplexing and wavelength-division multiplexing system.The obtained results show favorable performance of the RC-EDF-assisted OAM fiber amplifier.These demonstrations may open up new perspectives for long-haul transmission in capacity scaling fiber-optic communications employing OAM modes.展开更多
Although alpine ecosystems have been commonly recognized as sensitive to recent climate change,few studies have examined its impact on the long-term productivity of vegetation and soil erosion.Using paleoecological re...Although alpine ecosystems have been commonly recognized as sensitive to recent climate change,few studies have examined its impact on the long-term productivity of vegetation and soil erosion.Using paleoecological records,these two aspects were examined in the alpine zone of the Taibai Mountains(elevation,3767 m)in monsoon-dominated East Asia since the middle Holocene.Proxies for the productivity of vegetation and severity of soil erosion from high-resolution alpine lacustrine records show that the productivity and soil erosion were closely related to mean annual temperature and summer precipitation from the East Asian Summer Monsoon(EASM),respectively.Specifically,when the mean annual temperature was low and precipitation was abundant,during 5800–4000 calendar years before the present(cal.yr BP),the alpine ecosystem was characterized by low vegetation productivity and severe soil erosion.However,the productivity increased and soil erosion decreased from 4000 cal.yr BP onwards.These results highlight the role of paleoecological evidence in studying ecosystem services on longer time scales,which is significant in making policies for sustainable development under climate change in regions for which such long-term monitoring data are not available.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.62125503 and 62261160388)the National Key R&D Program of China(Grant No.2019YFB2203604)+2 种基金the Key R&D Program of Hubei Province of China(Grant Nos.2020BAB001 and 2021BAA024)the Shenzhen Science and Technology Program(Grant No.JCYJ20200109114018750)the Innovation Project of Optics Valley Laboratory(Grant No.OVL2021BG004)。
文摘Diverse spatial mode bases can be exploited in mode-division multiplexing(MDM)to sustain the capacity growth in fiber-optic communications,such as linearly polarized(LP)modes,vector modes,LP orbital angular momentum(LP-OAM)modes,and circularly polarized OAM(CP-OAM)modes.Nevertheless,which kind of mode bases is more appropriate to be utilized in fiber still remains unclear.Here,we aim to find the superior mode basis in MDM fiber-optic communications via a system-level comparison in air-core fiber(ACF).We first investigate the walk-off effect of four spatial mode bases over 1-km ACF,where LP and LP-OAM modes show intrinsic mode walk-off,while it is negligible for vector and CP-OAM modes.We then study the mode coupling effect of degenerate vector and CP-OAM modes over 1-km ACF under fiber perturbations,where degenerate even and odd vector modes suffer severe mode cross talk,while negligible for highorder degenerate CP-OAM modes based on the laws of angular momentum conservation.Moreover,we comprehensively evaluate the system-level performance for data-carrying single-channel and two-channel MDM transmission with different spatial mode bases under various kinds of fiber perturbations(bending,twisting,pressing,winding,and out-of-plane moving).The obtained results indicate that the CP-OAM mode basis shows superiority compared to other mode bases in MDM fiber-optic communications without using multiple-input multiple-output digital signal processing.Our findings may pave the way for robust shortreach MDM optical interconnects for data centers and high-performance computing.
基金supported by National Natural Science Foundation of China (Grant Nos. 41571130044 & 41325002)111 Plan (B14001)Peking University Undergraduate Talents Training Program
文摘The study of the critical zones(CZs) of the Earth link the composition and function of aboveground vegetation with the characteristics of the rock layers, providing a new way to study how the unique rock and soil conditions in karst regions affect the aboveground vegetation. Based on survey results of the rocks, soils and vegetation in the dolomite and limestone distribution areas in the karst area of central Guizhou, it was found that woody plant cover increases linearly with the number of cracks with a width of more than 1 mm, while the cover of herbaceous plants shows the opposite trend(p<0.01). The dolomite distribution area is characterized by undeveloped crevices, and the thickness of the soil layer is generally less than 20 cm, which is suitable for the distribution of herbaceous plants with shallow roots. Due to the development of crevices in the limestone distribution area, the soil is deeply distributed through the crevices for the deep roots of trees, which leads to a diversified species composition and a complicated structure in the aboveground vegetation. Based on moderate resolution imaging spectroradiometer(MODIS) remote sensing data from 2001 to 2010, the normalized differentiated vegetation index(NDVI) and annual net primary productivity(NPP) results for each phase of a 16-day interval further indicate that the NDVI of the limestone distribution area is significantly higher than that in the dolomite distribution area, but the average annual NPP is the opposite. The results of this paper indicate that in karst CZs, the lithology determines the structure and distribution of the soil, which further determines the cover of woody and herbaceous plants in the aboveground vegetation. Although the amount of soil in the limestone area may be less than that in the dolomite area, the developed crevice structure is more suitable for the growth of trees with deep roots, and the vegetation activity is strong. At present, the treatment of rocky desertification in karst regions needs to fully consider the rock-soilvegetation-air interactions in karst CZs and propose vegetation restoration measures suitable for different lithologies.
基金This work was supported by the National Key R&D Program of China(2018YFB1801803)the National Natural Science Foundation of China(NSFC)(61761130082,11774116)+5 种基金the Royal Society-Newton Advanced Fellowship,the National Program for Support of Top-Notch Young Professionals,the Yangtze River Excellent Young Scholars Program,the Natural Science Foundation of Hubei Province of China(2018CFA048)the Key R&D Program of Guangdong Province(2018B030325002)the Open Fund of IPOC(BUPT)(IPOC2018A002)the Open Program from the State Key Laboratory of Advanced Optical Communication Systems and Networks(2020GZKF009)the Program for HUST Academic Frontier Youth Team(2016QYTD05)the Fundamental Research Funds for the Central Universities(2019kfyRCPY037).
文摘Lots of research efforts have been devoted to increase the transmission capacity in optical communications using orbital angular momentum(OAM)multiplexing.To enable long-haul OAM mode transmission,an in-line OAM fiber amplifier is desired.A ring-core fiber(RCF)is considered to be a preferable design for stable OAM mode propagation in the fiber.Here,we demonstrate an OAM fiber amplifier based on a fabricated ring-core erbium-doped fiber(RC-EDF).We characterize the performance of the RC-EDF-assisted OAM fiber amplifier and demonstrate its use in OAM multiplexing communications with OAM modes carrying quadrature phase-shift keying(QPSK)and quadrature amplitude modulation(QAM)signals.The amplification of two OAM modes over four wavelengths is demonstrated in a data-carrying OAM-division multiplexing and wavelength-division multiplexing system.The obtained results show favorable performance of the RC-EDF-assisted OAM fiber amplifier.These demonstrations may open up new perspectives for long-haul transmission in capacity scaling fiber-optic communications employing OAM modes.
基金supported by the National Natural Science Foundation of China(Grant Nos.41901092,41171160)the Fundamental Research Funds for the Central Universities of China(Grant No.GK202003069).
文摘Although alpine ecosystems have been commonly recognized as sensitive to recent climate change,few studies have examined its impact on the long-term productivity of vegetation and soil erosion.Using paleoecological records,these two aspects were examined in the alpine zone of the Taibai Mountains(elevation,3767 m)in monsoon-dominated East Asia since the middle Holocene.Proxies for the productivity of vegetation and severity of soil erosion from high-resolution alpine lacustrine records show that the productivity and soil erosion were closely related to mean annual temperature and summer precipitation from the East Asian Summer Monsoon(EASM),respectively.Specifically,when the mean annual temperature was low and precipitation was abundant,during 5800–4000 calendar years before the present(cal.yr BP),the alpine ecosystem was characterized by low vegetation productivity and severe soil erosion.However,the productivity increased and soil erosion decreased from 4000 cal.yr BP onwards.These results highlight the role of paleoecological evidence in studying ecosystem services on longer time scales,which is significant in making policies for sustainable development under climate change in regions for which such long-term monitoring data are not available.
