It has been recently demonstrated that negative-index dispersion and mode degeneracy can be achieved by manipulating a spoof-insulator-spoof（SIS） waveguide. In this paper, we propose a new SIS waveguide, which is co...It has been recently demonstrated that negative-index dispersion and mode degeneracy can be achieved by manipulating a spoof-insulator-spoof（SIS） waveguide. In this paper, we propose a new SIS waveguide, which is composed of two spoof surface plasmon polaritons（SSPPs） waveguides drilled with periodic rhomboidal grooves. Both the symmetric and asymmetric cases are investigated. Our simulation results show that the asymmetric SIS waveguides are more significant.By tailoring the tilt of the rhomboidal grooves, the negative-index dispersion can be achieved and the microwave band gap（MBG） can be effectively modulated. At a critical tilt, there appears an accidental mode degeneracy at the edge of the first Brillouin zone. The excitation and propagation of the two coupled modes sustained by the asymmetric SIS waveguides are also demonstrated.展开更多
A refractive index insensitive temperature sensor based on waist-enlarged few mode fiber(FMF) bitapers is presented. The first section of FMF is spliced between two single-mode fibers. In fusion process,the waist-enla...A refractive index insensitive temperature sensor based on waist-enlarged few mode fiber(FMF) bitapers is presented. The first section of FMF is spliced between two single-mode fibers. In fusion process,the waist-enlarged FMF bitapers can be obtained by large current discharging repeatedly. The refractive index and temperature sensing mechanisms are analyzed. For the sensors with different sizes,the refractive index and temperature experiments have been performed. The results show that in the refractive index ranges of 1.335 0—1.346 6 and 1.348 2—1.419 3,the refractive index insensitivity is verified. In a temperature range of 31.9—90 °C,the sensor sensitivity can be up to 85.57 pm/°C. In addition,it has a compact structure. Therefore,the sensor can avoid the cross sensitivity for measuring the refractive index and temperature simultaneously.展开更多
Based on an empirical orthogonal function （EOF） analysis of the monthly NCEP Optimum Interpolation Sea Surface Temperature （OISST） data in the South China Sea （SCS） after removing the climatological mean and tre...Based on an empirical orthogonal function （EOF） analysis of the monthly NCEP Optimum Interpolation Sea Surface Temperature （OISST） data in the South China Sea （SCS） after removing the climatological mean and trends of SST, over the period of January 1982 to October 2003, the corresponding TCF correlates best with the Dipole Mode Index （DMI）, Nino1＋2, Nino3.4, Nino3, and Niflo4 indices with time lags of 10, 3, 6, 5, and 6 months, respectively. Thus, a statistical hindcasts in the prediction model are based on a canonical correlation analysis （CCA） model using the above indices as predictors spanning from 1993/1994 to 2003/2004 with a 1-12 month lead time after the canonical variants are calculated, using data from the training periods from January 1982 to December1992. The forecast model is successful and steady when the lead times are 1-12 months. The SCS warm event in 1998 was successfully predicted with lead times from 1-12 months irrespective of the strength or time extent. The prediction ability for SSTA is lower during weak ENSO years, in which other local factors should be also considered as local effects play a relatively important role in these years. We designed the two forecast models： one using both DMI and Nino indices and the other using only Nino indices without DMI, and compared the forecast accuracies of the two cases. The spatial distributions of forecast accuracies show different confidence areas. By turning off the DMI, the forecast accuracy is lower in the coastal areas off the Philippines in the SCS, suggesting some teleconnection may occur with the Indian Ocean in this area. The highest forecast accuracies occur when the forecast interval is five months long without using the DMI, while using both of Nino indices and DMI, the highest accuracies occur when the forecast interval time is eight months, suggesting that the Nino indices dominate the interannual variability of SST anomalies in the SCS. Meanwhile the forecast accuracy is evaluated over an independent test period of more than 11 years （1993/94 to October 2004） by comparing the model performance with a simple prediction strategy involving the persistence of sea surface temperature anomalies over a 1-12 month lead time （the persisted prediction）. Predictions based on the CCA model show a significant improvement over the persisted prediction, especially with an increased lead time （longer than 3 months）. The forecast model performs steadily and the forecast accuracy, i.e., the correlation coefficients between the observed and predicted SSTA in the SCS are about 0.5 in most middle and southern SCS areas, when the thresholds are greater than the 95% confidence level. For all 1 to 12 month lead time forecasts, the root mean square errors have a standard deviation of about 0.2. The seasonal differences in the prediction performance for the 1-12 month lead time are also examined.展开更多
A general numerical tool, based on thermal diffusion equation and full-vectorial eigen-mode equation, has been presented for the systematic analysis of graded index channel waveguide fabricated by ion exchange on Er^3...A general numerical tool, based on thermal diffusion equation and full-vectorial eigen-mode equation, has been presented for the systematic analysis of graded index channel waveguide fabricated by ion exchange on Er^3＋ doped glass. Finite difference method with full-vectorial formulation （FV-FDM） is applied to solving the full-vectorial modes of graded index channel waveguide for the first time. The coupled difference equations based on magnetic fields in FV-FDM are derived from the Taylor series expansion and accurate formulation of boundary conditions. Hybrid nature of vectorial guided modes for both pump （980 nm） and signal light （1550 nm） are demonstrated by the simulation. Results show that the fabrication parameters of ion exchange, such as channel opening width and time ratio of second step to first step in ion exchange, have large influence on the properties of waveguide. By optimizing the fabrication parameters, maintenance of monomode for signal light and improvement of the gain dynamics can be achieved in Er^3＋ doped waveguide amplifier （EDWA） fabricated by ion exchange technique. This theoretical model is significant for the design and fabrication of EDWA with ion exchange technique. Furthermore, a single polarization EDWA, which operates at wavelength from 1528 nm to 1541 nm for HE polarization, is numerically designed.展开更多
The 850-nm oxide-confined vertical-cavity surface-emitting lasers with petal-shape holey structures are presented. An area-weighted average refractive index model is given to analyse their effective index profiles, an...The 850-nm oxide-confined vertical-cavity surface-emitting lasers with petal-shape holey structures are presented. An area-weighted average refractive index model is given to analyse their effective index profiles, and the graded index distribution in the holey region is demonstrated. The index step between the optical aperture and the holey region is obtained which is related merely to the etching depth. Four types of holey vertical-cavity surface-emitting lasers with different parameters are fabricated as well as the conventional oxide-confined vertical-cavity surface-emitting laser. Compared with the conventional oxide-confined vertical-cavity surface-emitting laser without etched holes, the holey vertical-cavity surface-emitting laser possesses an improved beam quality due to its graded index distribution, but has a lower output power, higher threshold current and lower slope efficiency. With the hole number increased, the holey vertical-cavity surface-emitting laser can realize the single-mode operation throughout the entire current range, and reduces the beam divergence further. The loss mechanism is used to explain the single-mode characteristic, and the reduced beam divergence is attributed to the shallow etching. High coupling efficiency of 86% to a multi-mode fibre is achieved for the single-mode device in the experiment.展开更多
An electrically driven, single-longitudinal-mode GaAs based photonic crystal （PC） ridge waveguide （RWG） laser emitting at around 850 nm is demonstrated. The single-longitudinal-mode lasing characteristic is achiev...An electrically driven, single-longitudinal-mode GaAs based photonic crystal （PC） ridge waveguide （RWG） laser emitting at around 850 nm is demonstrated. The single-longitudinal-mode lasing characteristic is achieved by introducing the PC to the RWG laser. The triangle PC is etched on both sides of the ridge by photolithography and inductive coupled plasma （ICP） etching. The lasing spectra of the RWG lasers with and without the PC are studied, and the result shows that the PC purifies the longitudinal mode. The power per facet versus current and current-voltage characteristics have also been studied and compared.展开更多
For the traditional photonic crystal fibers with circular air holes, rectangular air holes are added to the fiber cladding. The periodic arrangement of the inner rectangular air holes allows the fiber structure to bet...For the traditional photonic crystal fibers with circular air holes, rectangular air holes are added to the fiber cladding. The periodic arrangement of the inner rectangular air holes allows the fiber structure to better match the annular mode field distribution of the vortex beam. The fiber structure was analyzed and calculated by COMSOL Multiphysics 5.4 finite element software, and the characteristics of fiber were analyzed, such as the dispersion, confinement loss, effective mode area and nonlinear coefficient. The results reveal that the photonic crystal fiber structure capable of carrying 50 orbital angular momentum (OAM) modes at the wavelength of 1.15 to 2.0 μm (850 nm). The effective refractive index difference Δneff between vector modes can reach 1 × 10-3, and larger difference can effectively separate the vector modes and improve the transmission performance of OAM modes. Moreover, the fiber has good performance, such as flat dispersion distribution of the low-order modes, low confinement loss below 10-9 dB·m-1, large effective mode field area and small nonlinear coefficient in the 850 nm wavelength range. Therefore, this fiber structure can be applied to the high-capacity communication system of fiber multiplexing OAM. In addition, the good characteristics of this fiber structure are of great significance for the transmission of vortex beam in fiber.展开更多
This paper focuses on the investigation of modal characteristics and sensing properties of long period grating photonic crystal fibers (LPG-PCFs). An improved effective index method is employed with an objective to st...This paper focuses on the investigation of modal characteristics and sensing properties of long period grating photonic crystal fibers (LPG-PCFs). An improved effective index method is employed with an objective to study its limitations for various designs of LPG-PCFs. Results so obtained with the above method are compared with the corresponding values of multiple multipole (MMP) method results which points the range of validity and applicability of the improved effective index method to LPG-PCFs. It is shown that this method is excellent when the surrounding media is assumed to be air. However, it becomes less accurate when the fiber is immersed into a liquid with a refractive index close to that of the cladding.展开更多
A study of mode coupling phenomenon of coaxial resonators has been conducted with theories. Through establishing the source-free transmission line equation, boundary conditions of the coaxial resonators with a corruga...A study of mode coupling phenomenon of coaxial resonators has been conducted with theories. Through establishing the source-free transmission line equation, boundary conditions of the coaxial resonators with a corrugated inner conductor are analyzed. In the end, calculations are performed in a wide range of corrugation parameters for the resonator of the Karlsruhe Institute of Technology （KIT） relevant coaxial gyrotron.展开更多
In this study, a reliability index vector formula is proposed for series system with two failure modes in term of the concept of reliability index vector and equivalent failure modes. Firstly, the reliability index ve...In this study, a reliability index vector formula is proposed for series system with two failure modes in term of the concept of reliability index vector and equivalent failure modes. Firstly, the reliability index vector is introduced to determine the correlation coefficient between two failure modes, and then, the reliability index vector of a series system can be obtained. Several numerical cases and an analysis on offshore platform are performed, and the results show that this scheme provided here has better computational accuracy, and its calculation process is simpler for the series systems reliability calculations compared with the other methods. Also this scheme is more convenient for the engineering applications.展开更多
基金Project supported by the National Basic Research Program of China(Grant No.2013CBA01702)the National Natural Science Foundation of China(Grant Nos.61377016,61575055,10974039,61307072,61308017,and 61405056)
文摘It has been recently demonstrated that negative-index dispersion and mode degeneracy can be achieved by manipulating a spoof-insulator-spoof（SIS） waveguide. In this paper, we propose a new SIS waveguide, which is composed of two spoof surface plasmon polaritons（SSPPs） waveguides drilled with periodic rhomboidal grooves. Both the symmetric and asymmetric cases are investigated. Our simulation results show that the asymmetric SIS waveguides are more significant.By tailoring the tilt of the rhomboidal grooves, the negative-index dispersion can be achieved and the microwave band gap（MBG） can be effectively modulated. At a critical tilt, there appears an accidental mode degeneracy at the edge of the first Brillouin zone. The excitation and propagation of the two coupled modes sustained by the asymmetric SIS waveguides are also demonstrated.
基金supported by the National Natural Science Foundation of China(Nos.61475133 and 61575170)the Key Basic Research Program of Hebei Province(Nos.16961701D and QN2016078)+1 种基金the Natural Science Foundation of Hebei Province(Nos.F2015203270 and F2016203392)the“Xin Rui Gong Cheng”Talent Project of Yanshan University
文摘A refractive index insensitive temperature sensor based on waist-enlarged few mode fiber(FMF) bitapers is presented. The first section of FMF is spliced between two single-mode fibers. In fusion process,the waist-enlarged FMF bitapers can be obtained by large current discharging repeatedly. The refractive index and temperature sensing mechanisms are analyzed. For the sensors with different sizes,the refractive index and temperature experiments have been performed. The results show that in the refractive index ranges of 1.335 0—1.346 6 and 1.348 2—1.419 3,the refractive index insensitivity is verified. In a temperature range of 31.9—90 °C,the sensor sensitivity can be up to 85.57 pm/°C. In addition,it has a compact structure. Therefore,the sensor can avoid the cross sensitivity for measuring the refractive index and temperature simultaneously.
基金Supported by National Natural Science Foundation of China (No. 40706011)the Key Program of Knowledge Innovation Project of Chinese Academy of Sciences (No. KZCX1-YW-12)+2 种基金the National Science Foundation of China (Nos. 405201 and 40074)the International Cooperative Program of the Ministry of Science and Technology (No. 2006DFB21630)by the Open Foundation of Key Laboratory of Marine Science and Numerical Modeling (MASNUM)
文摘Based on an empirical orthogonal function （EOF） analysis of the monthly NCEP Optimum Interpolation Sea Surface Temperature （OISST） data in the South China Sea （SCS） after removing the climatological mean and trends of SST, over the period of January 1982 to October 2003, the corresponding TCF correlates best with the Dipole Mode Index （DMI）, Nino1＋2, Nino3.4, Nino3, and Niflo4 indices with time lags of 10, 3, 6, 5, and 6 months, respectively. Thus, a statistical hindcasts in the prediction model are based on a canonical correlation analysis （CCA） model using the above indices as predictors spanning from 1993/1994 to 2003/2004 with a 1-12 month lead time after the canonical variants are calculated, using data from the training periods from January 1982 to December1992. The forecast model is successful and steady when the lead times are 1-12 months. The SCS warm event in 1998 was successfully predicted with lead times from 1-12 months irrespective of the strength or time extent. The prediction ability for SSTA is lower during weak ENSO years, in which other local factors should be also considered as local effects play a relatively important role in these years. We designed the two forecast models： one using both DMI and Nino indices and the other using only Nino indices without DMI, and compared the forecast accuracies of the two cases. The spatial distributions of forecast accuracies show different confidence areas. By turning off the DMI, the forecast accuracy is lower in the coastal areas off the Philippines in the SCS, suggesting some teleconnection may occur with the Indian Ocean in this area. The highest forecast accuracies occur when the forecast interval is five months long without using the DMI, while using both of Nino indices and DMI, the highest accuracies occur when the forecast interval time is eight months, suggesting that the Nino indices dominate the interannual variability of SST anomalies in the SCS. Meanwhile the forecast accuracy is evaluated over an independent test period of more than 11 years （1993/94 to October 2004） by comparing the model performance with a simple prediction strategy involving the persistence of sea surface temperature anomalies over a 1-12 month lead time （the persisted prediction）. Predictions based on the CCA model show a significant improvement over the persisted prediction, especially with an increased lead time （longer than 3 months）. The forecast model performs steadily and the forecast accuracy, i.e., the correlation coefficients between the observed and predicted SSTA in the SCS are about 0.5 in most middle and southern SCS areas, when the thresholds are greater than the 95% confidence level. For all 1 to 12 month lead time forecasts, the root mean square errors have a standard deviation of about 0.2. The seasonal differences in the prediction performance for the 1-12 month lead time are also examined.
基金supported by the Foundation for Development of Science and Technology of Shanghai (Grant No 022261002)
文摘A general numerical tool, based on thermal diffusion equation and full-vectorial eigen-mode equation, has been presented for the systematic analysis of graded index channel waveguide fabricated by ion exchange on Er^3＋ doped glass. Finite difference method with full-vectorial formulation （FV-FDM） is applied to solving the full-vectorial modes of graded index channel waveguide for the first time. The coupled difference equations based on magnetic fields in FV-FDM are derived from the Taylor series expansion and accurate formulation of boundary conditions. Hybrid nature of vectorial guided modes for both pump （980 nm） and signal light （1550 nm） are demonstrated by the simulation. Results show that the fabrication parameters of ion exchange, such as channel opening width and time ratio of second step to first step in ion exchange, have large influence on the properties of waveguide. By optimizing the fabrication parameters, maintenance of monomode for signal light and improvement of the gain dynamics can be achieved in Er^3＋ doped waveguide amplifier （EDWA） fabricated by ion exchange technique. This theoretical model is significant for the design and fabrication of EDWA with ion exchange technique. Furthermore, a single polarization EDWA, which operates at wavelength from 1528 nm to 1541 nm for HE polarization, is numerically designed.
基金supported by the National Key Basic Research Special Foundation of China (Grant No. 2011CB922000)the National Natural Science Foundation of China (Grant Nos. 61025025 and 60838003)the National High Technology Research and Development Program of China (Grant Nos. 2007AA03Z410 and 2007AA03Z408)
文摘The 850-nm oxide-confined vertical-cavity surface-emitting lasers with petal-shape holey structures are presented. An area-weighted average refractive index model is given to analyse their effective index profiles, and the graded index distribution in the holey region is demonstrated. The index step between the optical aperture and the holey region is obtained which is related merely to the etching depth. Four types of holey vertical-cavity surface-emitting lasers with different parameters are fabricated as well as the conventional oxide-confined vertical-cavity surface-emitting laser. Compared with the conventional oxide-confined vertical-cavity surface-emitting laser without etched holes, the holey vertical-cavity surface-emitting laser possesses an improved beam quality due to its graded index distribution, but has a lower output power, higher threshold current and lower slope efficiency. With the hole number increased, the holey vertical-cavity surface-emitting laser can realize the single-mode operation throughout the entire current range, and reduces the beam divergence further. The loss mechanism is used to explain the single-mode characteristic, and the reduced beam divergence is attributed to the shallow etching. High coupling efficiency of 86% to a multi-mode fibre is achieved for the single-mode device in the experiment.
基金Project supported by the National Natural Science Foundation of China (Grant No. 91121019)the National Basic Research Program of China (Grant No. 2013CB632105)
文摘An electrically driven, single-longitudinal-mode GaAs based photonic crystal （PC） ridge waveguide （RWG） laser emitting at around 850 nm is demonstrated. The single-longitudinal-mode lasing characteristic is achieved by introducing the PC to the RWG laser. The triangle PC is etched on both sides of the ridge by photolithography and inductive coupled plasma （ICP） etching. The lasing spectra of the RWG lasers with and without the PC are studied, and the result shows that the PC purifies the longitudinal mode. The power per facet versus current and current-voltage characteristics have also been studied and compared.
文摘For the traditional photonic crystal fibers with circular air holes, rectangular air holes are added to the fiber cladding. The periodic arrangement of the inner rectangular air holes allows the fiber structure to better match the annular mode field distribution of the vortex beam. The fiber structure was analyzed and calculated by COMSOL Multiphysics 5.4 finite element software, and the characteristics of fiber were analyzed, such as the dispersion, confinement loss, effective mode area and nonlinear coefficient. The results reveal that the photonic crystal fiber structure capable of carrying 50 orbital angular momentum (OAM) modes at the wavelength of 1.15 to 2.0 μm (850 nm). The effective refractive index difference Δneff between vector modes can reach 1 × 10-3, and larger difference can effectively separate the vector modes and improve the transmission performance of OAM modes. Moreover, the fiber has good performance, such as flat dispersion distribution of the low-order modes, low confinement loss below 10-9 dB·m-1, large effective mode field area and small nonlinear coefficient in the 850 nm wavelength range. Therefore, this fiber structure can be applied to the high-capacity communication system of fiber multiplexing OAM. In addition, the good characteristics of this fiber structure are of great significance for the transmission of vortex beam in fiber.
文摘This paper focuses on the investigation of modal characteristics and sensing properties of long period grating photonic crystal fibers (LPG-PCFs). An improved effective index method is employed with an objective to study its limitations for various designs of LPG-PCFs. Results so obtained with the above method are compared with the corresponding values of multiple multipole (MMP) method results which points the range of validity and applicability of the improved effective index method to LPG-PCFs. It is shown that this method is excellent when the surrounding media is assumed to be air. However, it becomes less accurate when the fiber is immersed into a liquid with a refractive index close to that of the cladding.
基金supported by the National High Technology Research and Development Program under Grant No.803-410-7
文摘A study of mode coupling phenomenon of coaxial resonators has been conducted with theories. Through establishing the source-free transmission line equation, boundary conditions of the coaxial resonators with a corrugated inner conductor are analyzed. In the end, calculations are performed in a wide range of corrugation parameters for the resonator of the Karlsruhe Institute of Technology （KIT） relevant coaxial gyrotron.
文摘In this study, a reliability index vector formula is proposed for series system with two failure modes in term of the concept of reliability index vector and equivalent failure modes. Firstly, the reliability index vector is introduced to determine the correlation coefficient between two failure modes, and then, the reliability index vector of a series system can be obtained. Several numerical cases and an analysis on offshore platform are performed, and the results show that this scheme provided here has better computational accuracy, and its calculation process is simpler for the series systems reliability calculations compared with the other methods. Also this scheme is more convenient for the engineering applications.
