The precursor sol of alumina was prepared by sol-gel method with aluminum nitrate and malic acid as raw materials.The effects of content of malic acid and polyvinylpyrrolidone (PVP) on sol spinnability were explored...The precursor sol of alumina was prepared by sol-gel method with aluminum nitrate and malic acid as raw materials.The effects of content of malic acid and polyvinylpyrrolidone (PVP) on sol spinnability were explored.The gel fibers with above 80 cm in length were obtained by mixing aluminum nitrate,malic acid and PVP on mass ratio of 10 3 1.5.Thermogravimetry-differential scanning calorimetry (TG-DSC),Fourier transform infrared (FTIR) spectrum,X-ray diffractometry (XRD),and scanning electron microscopy (SEM) were used to characterize the properties of the gel and ceramic fibers.The alumina fibers with a smooth surface and about 20μm in diameter were obtained by sintering at 1 200℃,and their main phase was indentified to be α-Al2O3.展开更多
This article summarizes the comparison between the preparation, structure and mechanical properties of long fiber reinforced thermoplastics (LFT) and short fiber reinforced thermoplastics (SFT). Both of the experi...This article summarizes the comparison between the preparation, structure and mechanical properties of long fiber reinforced thermoplastics (LFT) and short fiber reinforced thermoplastics (SFT). Both of the experiment and theory results showed that the mechanical properties of long glass fiber reinforced thermoplastics pellets (LGFRT) have been enhanced better than that of short glass fiber reinforced thermoplastics pellets (SGFRT) manufactured by molding procession. After regulation of the relative humidity by 50 % , the mechanical properties of 30 % ( weight percent) short glass fiber content in SFT ( SFT-PA6-SGF30 ) are similar to that of 40 % long glass fiber content in LFT. Howev- er, the density of the latter is about 17 % lower than that of the former. Thus, the corresponding weight of products is reduced by 13 % ;output rate is increased by 21% , and the cost is therefore significantly lowered. And it has the fol- lowing advantages: impact strength is increased by 87 % ; the proportion is reduced by 20 % ; molding cycle is short- ened by 10 % ;materials cost is saved by 20 % -30 % and the final total cost is saved by 30 % -40 %. So LFT (LFT-PP-LGF40) can replace SFT (SFT-PA6-SGF30) with the similar basic mechanical properties under normal tem- perature or 160 ℃ lower.展开更多
A high sensitive long period fiber grating(LPFG) sensor for the detection of nitrite is proposed, which is realized by coating multiple poly(sodium 4-styrensulfonate)(PSS) and poly(diallyldimethylammonium) chl...A high sensitive long period fiber grating(LPFG) sensor for the detection of nitrite is proposed, which is realized by coating multiple poly(sodium 4-styrensulfonate)(PSS) and poly(diallyldimethylammonium) chloride (PDDA) layers on the fiber grating surface. The sensitivity of this LPFG sensor is maximum when the number of assembled layers is 70. Under this condition, a nitrite concentration of 3×10^-3 mol/L, which is lower than the National Food Additive Standard, 4.2×10^-3 mol/L, can be distinguished. The sensitivity is further increased by 30% when nitrite was determined in the sucrose solution with a concentration of 65%, which provides a new solution for the best refraction index approaching matched index of the fiber cladding. Compared with chemical methods, this nitrite detection technology offers some advantages, such as high accuracy, non toxicity, high speed, low cost, without chemical reagent, and is suitable for foodstuff security detection.展开更多
The coupled-mode equations for fiber Bragg grating (FBG) and long period fiber grating (LPFG) undergoing linear and quadratic temperature change were given. The effects of temperature gradient and quadratic temper...The coupled-mode equations for fiber Bragg grating (FBG) and long period fiber grating (LPFG) undergoing linear and quadratic temperature change were given. The effects of temperature gradient and quadratic temperature change on the reflectivity spectrum of fiber Braggs grating and the transmission spectrum of long period fiber grating were investigated using the numerical simulation, and the dependence relationships of the central wavelength shift, the full-width-athalf-maximum, and the peak intensity upon temperature gradient were also obtained. These relationships may be used to design a novel fiber optical sensor which can simultaneously measure the temperature and temperature gradient.展开更多
Both acrylate based polymer and silicone resin are proposed as recoating materials surrounding LPFGs for purposes of different applications. For the LPFG recoated with a thin layer of acrylate based polymer, the range...Both acrylate based polymer and silicone resin are proposed as recoating materials surrounding LPFGs for purposes of different applications. For the LPFG recoated with a thin layer of acrylate based polymer, the range of wavelength shift as much as 60nm is expected when temperature changes from 0~100℃. As for that with surrounding material of silicone resin, the temperature stability is greatly improved depicted as the maximum wavelength shift of about 0.6nm with the same temperature variation. The former is potentially a broadband tunable band rejection filter or temperature sensor with enhanced sensitivity. And the latter could be applied as temperature insensitive filter, demultiplexer or strain sensor.展开更多
Photonic crystal fibers are usually divided into two different types of fibers: solid-core photonic crystal fibers (PCFs) and air-core photonic bandgaps fibers (PBFs). We presented the fabrication methods and app...Photonic crystal fibers are usually divided into two different types of fibers: solid-core photonic crystal fibers (PCFs) and air-core photonic bandgaps fibers (PBFs). We presented the fabrication methods and applications of long period fiber gratings (LPFGs) written in these two types of photonic crystal fibers by use of a CO2 laser. A stain sensor with a high sensitivity was demonstrated by use of an LPFG written in solid-core PCFs. An in-fiber polarizer based on an LPFG was fabricated by use of a focused CO2 laser beam to notch periodically on a PCF. A novel LPFG was written in an air-core PBF by use of a CO2 laser to collapse periodically air holes in the fiber cladding.展开更多
<div style="text-align:justify;"> In this paper, a hybrid optical fiber structure for solution concentration measurement with the temperature compensation is proposed. The structure consists of long pe...<div style="text-align:justify;"> In this paper, a hybrid optical fiber structure for solution concentration measurement with the temperature compensation is proposed. The structure consists of long period fiber grating (LPFG) and single mode-multimode-single mode (SMS) fiber structures. The sensing mechanism of the device is studied and verified by experiments. LPFG is sensitive to solution concentration and is affected by temperature crosstalk. SMS structure is not affected by solution concentration, but sensitive to ambient temperature. It can be used as a temperature compensation system. The sensitivity coefficients of LPFG and SMS on temperature and concentration were measured experimentally, and a dual-wavelength matrix was established to realize simultaneous measurement of solution temperature and concentration. </div>展开更多
We propose and demonstrate a sensitive vector twist sensor based on a small period long period fiber grating(SP-LPFG)fabricated with a femtosecond(fs)laser.The fabricated SP-LPFG is compact in size(2.8 mm)and shows st...We propose and demonstrate a sensitive vector twist sensor based on a small period long period fiber grating(SP-LPFG)fabricated with a femtosecond(fs)laser.The fabricated SP-LPFG is compact in size(2.8 mm)and shows strong polarization dependent peaks in its transmission spectrum due to the vectorial behavior of high-order cladding modes.Twist sensing is realized by monitoring the polarization dependent peaks,since the polarization of input light changes with fiber twist.The proposed sensor can be interrogated by the peak intensity and wavelength,with high twist sensitivity that reaches 0.257 dB/deg and 0.115 nm/deg,respectively.展开更多
A long period fiber grating (LPFG) fabricated upon the all-solid photonic bandgap fiber by CO2 laser irradiation was investigated, and its resonance wavelength was at 1335.76nm with a modulation depth of 15dB and a ...A long period fiber grating (LPFG) fabricated upon the all-solid photonic bandgap fiber by CO2 laser irradiation was investigated, and its resonance wavelength was at 1335.76nm with a modulation depth of 15dB and a 3-dB bandwidth of 2.6nm. We studied its strain, temperature, and index sensor characteristics, the strain sensitivity of 0.992 pm/m was obtained by using linear fit, and the relationship between the refractive index and wavelength obeyed the distribution of quadratic function. Also, we demonstrated its temperature response was relatively insensitive (21.51 pm/~C).展开更多
The long period fiber grating (LPFG) is widely used as a sensor due to its high sensitivity and resolution. However, the broad bandwidth of the attenuation bands formed by the mode coupling between the fundamental c...The long period fiber grating (LPFG) is widely used as a sensor due to its high sensitivity and resolution. However, the broad bandwidth of the attenuation bands formed by the mode coupling between the fundamental core mode and the cladding modes constitutes a difficulty when the device is used as a conventional sensor. To overcome this limitation, a Michelson interferometer-type sensor configuration has been developed, using an LPFG grating pair formed by coating a mirror at the distal end of the LPFG. This sensor configuration is more convenient to use and is able to overcome the limitations of the single LPFG based sensor as the shifts in the attenuation bands being more easily detectable due to the formation of the sharp spectral fringe pattern in the LPFG based Michelson interferometer. In this work, I studied the LPFG based Michelson interferometer as the refractive index sensor and discussed the sensitivity enhancement of the LPFG based Michelson interferometer as a refractive index sensor by employing higher order cladding modes and by reducing the cladding radius. The results demonstrated the HE17 mode with a cladding radius of 62.5 μm, in the range of surrounding refractive index (SRI) of 1 - 1.45, and its resonant peak showed a wavelength shift of 26.99nm/RIU. When the cladding region was further reduced to 24μm, the resonant peak showed a wavelength shift of 569.88 nm/RIU, resulting in a sensitivity enhancement of nearly 21 times. However, as the cladding region was etched further, then the HE17 order cladding mode and higher mode would be cut off. Therefore, the implementation of high sensitivity for SRI sensing with the reduced cladding in the LPFG based Michelson interferometer is dependent on the proper combination of the cladding radius and cladding mode order.展开更多
A few-mode erbium-doped fiber(FM-EDF) is fabricated using modified chemical vapor deposition in combination with liquid solution. The core and cladding diameters of the fiber are approximately 19.44 and 124.12 μm,r...A few-mode erbium-doped fiber(FM-EDF) is fabricated using modified chemical vapor deposition in combination with liquid solution. The core and cladding diameters of the fiber are approximately 19.44 and 124.12 μm,respectively. The refractive index difference is 0.98%, numerical aperture(NA) is 0.17, and normalized cut-off frequency at 1550 nm is 6.81. Therefore, it is a five-mode fiber, and can be used as a higher-order mode gain medium. Furthermore, a long period fiber grating(LPFG) is fabricated, which can convert LP〈01 mode to LP11 mode, and its conversion efficiency is up to 99%. The first-order orbital angular momentum(OAM) is also generated by combining the LPFG and polarization controller(PC). Then, an all-fiber amplification system based on the FM-EDF and LPFG, for LP11 mode and first-order OAM beams, is built up. Its on-off gain of the LP11 mode beam is 37.2 d B at 1521.2 nm. The variation, whose transverse mode field intensity of first-order OAM is increased with the increase of pumping power, is obvious. These show that both the LP11 mode and first-order OAM beams are amplified in the all-fiber amplification system. This is a novel all-fiber amplification scheme,which can be used in the optical communication fields.展开更多
A novel method of linear demodulation based on edge filter is presented. An experimental system is built up in which LPG is used as the edge filter. We achieve linear demodulation with a bandwidth of 5nm.
The author studied and demonstrated the various modeling aspects of long period fiber grating (LPFG) such as the core effective index, cladding effective index, coupling coefficient, coupled mode theory, and transmi...The author studied and demonstrated the various modeling aspects of long period fiber grating (LPFG) such as the core effective index, cladding effective index, coupling coefficient, coupled mode theory, and transmission spectrum of the LPFG using three-layer fiber geometry. Actually, there are two different techniques used for theoretical modeling of the long period fiber grating. The first technique was used by Vengsarkar et al who described the phenomenon of long-period fiber gratings, and the second technique was reported by Erdogan who revealed the inaccuracies and shortcomings of the original method, thereby providing an accurate and updated alternative. The main difference between these two different approaches lies in their fiber geometry. Venserkar et al used two-layer fiber geometry which is simple but employs weakly guided approximation, whereas Erdogan used three-layer fiber geometry which is complex but also the most accurate technique for theoretical study of the LPFG. The author further discussed about the behavior of the transmission spectrum by altering different grating parameters such as the grating length, ultraviolet (UV) induced-index change, and grating period to achieve the desired flexibility. The author simulated the various results with the help of MATLAB.展开更多
We propose a high temperature-sensitive long period fiber grating(LPFG) sensor fabricated by using the femtosecond laser transversal-scanning method. The femtosecond pulses scan over the whole fiber core and some pa...We propose a high temperature-sensitive long period fiber grating(LPFG) sensor fabricated by using the femtosecond laser transversal-scanning method. The femtosecond pulses scan over the whole fiber core and some part of the cladding region; the modified regions are more extended. It is found that the LPFG-I fabricated by the transversal-scanning method shows higher temperature sensitivity and better temperature uniformity than that of LPFG-II written by the femtosecond laser point-by-point method. The LPFG-I with a temperature sensitivity of 75.96 pm/°C in the range of 25°C–400°C is measured. Moreover, in the range from 400°C to 800°C, a higher temperature sensitivity of 148.64 pm/°C and good linearity of 0.99 are achieved, while the temperature sensitivity of LPFG-II is only 95.55 pm/°C. LPFG-I exhibits better temperature characteristics, which, to the best of our knowledge, has the highest sensitivity in silica fiber temperature sensors.展开更多
A novel high-speed electro-optic (EO) polymer modulator based on long period gratings (LPG) is designed. Using the theory of multi-cladding optical waveguide, we achieved relationship between modulate voltage and LPG&...A novel high-speed electro-optic (EO) polymer modulator based on long period gratings (LPG) is designed. Using the theory of multi-cladding optical waveguide, we achieved relationship between modulate voltage and LPG's resonant wavelength.展开更多
Two promising post-treatment techniques, i.e. applying tensile strain and rising temperature, are demonstrated to enhance the mode-coupling efficiency of the CO2-1aser-induced long period fiber gratings (LPFGs) with...Two promising post-treatment techniques, i.e. applying tensile strain and rising temperature, are demonstrated to enhance the mode-coupling efficiency of the CO2-1aser-induced long period fiber gratings (LPFGs) with periodic grooves. Such two post-treatment techniques can be used to enhance the resonant attenuation of the grating to achieve a LPFG-based filter with an extremely large attenuation and to tailor the transmission spectrum of the CO2-1aser-induced LPFG after grating fabrication.展开更多
In this paper,a novel liquid level sensor with ultra-high sensitivity is proposed.The proposed sensor is configured by a sliceshaped composite long period fiber grating(SSC-LPFG).The SSC-LPFG is prepared by polishing ...In this paper,a novel liquid level sensor with ultra-high sensitivity is proposed.The proposed sensor is configured by a sliceshaped composite long period fiber grating(SSC-LPFG).The SSC-LPFG is prepared by polishing two opposite sides of a composite multimode-single-mode-multimode fiber structure using a CO;laser.The method improves the sensitivity of the sensor to external environment.Based on the simulation calculation,a liquid level sensor with a length of 3 mm is designed.The experimental transmission spectrum agrees well with the simulation result.The experimental results show that the sensitivity reaches 7080 pm/mm in the liquid level range of 0-1400 μm in water.The temperature sensitivity is24.52 pm/℃ in the range of 20℃-90℃.Due to the ultra-high sensitivity,good linearity,and compact structure,the SSC-LPFG has potential application in the field of high-Drecision liquid level measurement.展开更多
Based on the full vector complex coupled mode theory, a detailed analysis is made on the transmission spectrum characteristics of tilted long period fiber gratings. New transmission peaks are observed, which are locat...Based on the full vector complex coupled mode theory, a detailed analysis is made on the transmission spectrum characteristics of tilted long period fiber gratings. New transmission peaks are observed, which are located beside the long wavelength side of each transmission peak in the transmission spectrum of normal long period fiber gratings. The emerging transmission peaks are quite sensitive to both the grating tilted angle and the surrounding refractive index, and the corresponding relationship is discussed. Furthermore, a novel sensing characteristic is investigated about the tilted long period fiber gratings, which is related to the transmission resonant wavelength and peak amplitude.展开更多
The field of electromagnetic wave absorption(EWA)requires the adaptability,tenability,and multifunction of high-performance materials in the future.The design and preparation of EWA materials aiming at performance req...The field of electromagnetic wave absorption(EWA)requires the adaptability,tenability,and multifunction of high-performance materials in the future.The design and preparation of EWA materials aiming at performance requirements is the latest research hotspot.Here,a performancedriven strategy for simultaneously coordinating different target performances was proposed to optimize the structure of the periodical long continuous carbon/glass fiber fabric(PCGF)materials through algorithm and simulation.The optimized structure of the PCGF not only improves the impedance matching,but also introduces the induced orientation effect for a high cooperative loss of conductivity,resonance,and periodic structure.The flexible PCGF shows a broad effective absorption bandwidth(EAB)of 32.7 GHz covering a part of the C-band and the whole X-,Ku-,K-,and Ka-bands with a thickness(d)of only 0.92 mm and a density of 5.6×10^(−4) kg·cm^(−3).This highly designable fabric is promising for the EWA practical application owing to integrating the characteristics of good flexibility,acid and alkali resistance,bending resistance,excellent mechanical properties,and easy large-scale preparation.展开更多
Carbon fibers reinforced lithium aluminosilicate matrix composites(Cf/LAS)were prepared by slurry infiltration combined with a hot press procedure.The friction,wear behavior,and wear mechanisms of Cf/LAS composites un...Carbon fibers reinforced lithium aluminosilicate matrix composites(Cf/LAS)were prepared by slurry infiltration combined with a hot press procedure.The friction,wear behavior,and wear mechanisms of Cf/LAS composites under dry sliding conditions were investigated.The results show that the coefficient of friction(COF)initially increased with the increase in carbon fiber content,and reached the maximum value of 0.20 for the 33%Cf/LAS composite.The COF increased sharply with increasing sample temperature from RT to 300℃.The COF remained stable in the temperature range of 300–500℃.The two wear mechanisms of LAS glass-ceramics are fatigue wear and abrasive wear.The Cf/LAS composites demonstrate slight spalling and shallow scratches.These results show that carbon fibers improve the mechanical properties and wear resistance of Cf/LAS composites.展开更多
基金Project(2010K10-21) supported by the Natural Science Foundation of Shaanxi Province,China
文摘The precursor sol of alumina was prepared by sol-gel method with aluminum nitrate and malic acid as raw materials.The effects of content of malic acid and polyvinylpyrrolidone (PVP) on sol spinnability were explored.The gel fibers with above 80 cm in length were obtained by mixing aluminum nitrate,malic acid and PVP on mass ratio of 10 3 1.5.Thermogravimetry-differential scanning calorimetry (TG-DSC),Fourier transform infrared (FTIR) spectrum,X-ray diffractometry (XRD),and scanning electron microscopy (SEM) were used to characterize the properties of the gel and ceramic fibers.The alumina fibers with a smooth surface and about 20μm in diameter were obtained by sintering at 1 200℃,and their main phase was indentified to be α-Al2O3.
文摘This article summarizes the comparison between the preparation, structure and mechanical properties of long fiber reinforced thermoplastics (LFT) and short fiber reinforced thermoplastics (SFT). Both of the experiment and theory results showed that the mechanical properties of long glass fiber reinforced thermoplastics pellets (LGFRT) have been enhanced better than that of short glass fiber reinforced thermoplastics pellets (SGFRT) manufactured by molding procession. After regulation of the relative humidity by 50 % , the mechanical properties of 30 % ( weight percent) short glass fiber content in SFT ( SFT-PA6-SGF30 ) are similar to that of 40 % long glass fiber content in LFT. Howev- er, the density of the latter is about 17 % lower than that of the former. Thus, the corresponding weight of products is reduced by 13 % ;output rate is increased by 21% , and the cost is therefore significantly lowered. And it has the fol- lowing advantages: impact strength is increased by 87 % ; the proportion is reduced by 20 % ; molding cycle is short- ened by 10 % ;materials cost is saved by 20 % -30 % and the final total cost is saved by 30 % -40 %. So LFT (LFT-PP-LGF40) can replace SFT (SFT-PA6-SGF30) with the similar basic mechanical properties under normal tem- perature or 160 ℃ lower.
基金Supported by the National Natural Science Foundation of China(Nos.60707016 and 60807030)
文摘A high sensitive long period fiber grating(LPFG) sensor for the detection of nitrite is proposed, which is realized by coating multiple poly(sodium 4-styrensulfonate)(PSS) and poly(diallyldimethylammonium) chloride (PDDA) layers on the fiber grating surface. The sensitivity of this LPFG sensor is maximum when the number of assembled layers is 70. Under this condition, a nitrite concentration of 3×10^-3 mol/L, which is lower than the National Food Additive Standard, 4.2×10^-3 mol/L, can be distinguished. The sensitivity is further increased by 30% when nitrite was determined in the sucrose solution with a concentration of 65%, which provides a new solution for the best refraction index approaching matched index of the fiber cladding. Compared with chemical methods, this nitrite detection technology offers some advantages, such as high accuracy, non toxicity, high speed, low cost, without chemical reagent, and is suitable for foodstuff security detection.
基金Funded by the Natural Science Foundation of Wuhan University of Technology (471-38650024)the National Natural Science Foundation of China (No. 50802069)
文摘The coupled-mode equations for fiber Bragg grating (FBG) and long period fiber grating (LPFG) undergoing linear and quadratic temperature change were given. The effects of temperature gradient and quadratic temperature change on the reflectivity spectrum of fiber Braggs grating and the transmission spectrum of long period fiber grating were investigated using the numerical simulation, and the dependence relationships of the central wavelength shift, the full-width-athalf-maximum, and the peak intensity upon temperature gradient were also obtained. These relationships may be used to design a novel fiber optical sensor which can simultaneously measure the temperature and temperature gradient.
文摘Both acrylate based polymer and silicone resin are proposed as recoating materials surrounding LPFGs for purposes of different applications. For the LPFG recoated with a thin layer of acrylate based polymer, the range of wavelength shift as much as 60nm is expected when temperature changes from 0~100℃. As for that with surrounding material of silicone resin, the temperature stability is greatly improved depicted as the maximum wavelength shift of about 0.6nm with the same temperature variation. The former is potentially a broadband tunable band rejection filter or temperature sensor with enhanced sensitivity. And the latter could be applied as temperature insensitive filter, demultiplexer or strain sensor.
基金This work was supported by the Distinguished Professors Funding from Shenzhen University, the National Science Foundation of China (Grant 11174064), and the Science & Technology Innovation Commission of Shenzhen (Grant KQCX20120815161444632).
文摘Photonic crystal fibers are usually divided into two different types of fibers: solid-core photonic crystal fibers (PCFs) and air-core photonic bandgaps fibers (PBFs). We presented the fabrication methods and applications of long period fiber gratings (LPFGs) written in these two types of photonic crystal fibers by use of a CO2 laser. A stain sensor with a high sensitivity was demonstrated by use of an LPFG written in solid-core PCFs. An in-fiber polarizer based on an LPFG was fabricated by use of a focused CO2 laser beam to notch periodically on a PCF. A novel LPFG was written in an air-core PBF by use of a CO2 laser to collapse periodically air holes in the fiber cladding.
文摘<div style="text-align:justify;"> In this paper, a hybrid optical fiber structure for solution concentration measurement with the temperature compensation is proposed. The structure consists of long period fiber grating (LPFG) and single mode-multimode-single mode (SMS) fiber structures. The sensing mechanism of the device is studied and verified by experiments. LPFG is sensitive to solution concentration and is affected by temperature crosstalk. SMS structure is not affected by solution concentration, but sensitive to ambient temperature. It can be used as a temperature compensation system. The sensitivity coefficients of LPFG and SMS on temperature and concentration were measured experimentally, and a dual-wavelength matrix was established to realize simultaneous measurement of solution temperature and concentration. </div>
基金supported by the National Natural Science Foundation of China (Nos. 11574070, 11874126, and 51803037)the Leading Talents of Guangdong Province Program (No. 2016LJ06D506)the Natural Science FoundationofGuangdongProvince,China(No. 2019A1515011229)
文摘We propose and demonstrate a sensitive vector twist sensor based on a small period long period fiber grating(SP-LPFG)fabricated with a femtosecond(fs)laser.The fabricated SP-LPFG is compact in size(2.8 mm)and shows strong polarization dependent peaks in its transmission spectrum due to the vectorial behavior of high-order cladding modes.Twist sensing is realized by monitoring the polarization dependent peaks,since the polarization of input light changes with fiber twist.The proposed sensor can be interrogated by the peak intensity and wavelength,with high twist sensitivity that reaches 0.257 dB/deg and 0.115 nm/deg,respectively.
文摘A long period fiber grating (LPFG) fabricated upon the all-solid photonic bandgap fiber by CO2 laser irradiation was investigated, and its resonance wavelength was at 1335.76nm with a modulation depth of 15dB and a 3-dB bandwidth of 2.6nm. We studied its strain, temperature, and index sensor characteristics, the strain sensitivity of 0.992 pm/m was obtained by using linear fit, and the relationship between the refractive index and wavelength obeyed the distribution of quadratic function. Also, we demonstrated its temperature response was relatively insensitive (21.51 pm/~C).
文摘The long period fiber grating (LPFG) is widely used as a sensor due to its high sensitivity and resolution. However, the broad bandwidth of the attenuation bands formed by the mode coupling between the fundamental core mode and the cladding modes constitutes a difficulty when the device is used as a conventional sensor. To overcome this limitation, a Michelson interferometer-type sensor configuration has been developed, using an LPFG grating pair formed by coating a mirror at the distal end of the LPFG. This sensor configuration is more convenient to use and is able to overcome the limitations of the single LPFG based sensor as the shifts in the attenuation bands being more easily detectable due to the formation of the sharp spectral fringe pattern in the LPFG based Michelson interferometer. In this work, I studied the LPFG based Michelson interferometer as the refractive index sensor and discussed the sensitivity enhancement of the LPFG based Michelson interferometer as a refractive index sensor by employing higher order cladding modes and by reducing the cladding radius. The results demonstrated the HE17 mode with a cladding radius of 62.5 μm, in the range of surrounding refractive index (SRI) of 1 - 1.45, and its resonant peak showed a wavelength shift of 26.99nm/RIU. When the cladding region was further reduced to 24μm, the resonant peak showed a wavelength shift of 569.88 nm/RIU, resulting in a sensitivity enhancement of nearly 21 times. However, as the cladding region was etched further, then the HE17 order cladding mode and higher mode would be cut off. Therefore, the implementation of high sensitivity for SRI sensing with the reduced cladding in the LPFG based Michelson interferometer is dependent on the proper combination of the cladding radius and cladding mode order.
基金supported by the National Natural Science Foundation of China(Nos.61635006,61520106014,61475096,61422507,and 61635006)the Science and Technology Commission of Shanghai Municipality(No.15220721500)
文摘A few-mode erbium-doped fiber(FM-EDF) is fabricated using modified chemical vapor deposition in combination with liquid solution. The core and cladding diameters of the fiber are approximately 19.44 and 124.12 μm,respectively. The refractive index difference is 0.98%, numerical aperture(NA) is 0.17, and normalized cut-off frequency at 1550 nm is 6.81. Therefore, it is a five-mode fiber, and can be used as a higher-order mode gain medium. Furthermore, a long period fiber grating(LPFG) is fabricated, which can convert LP〈01 mode to LP11 mode, and its conversion efficiency is up to 99%. The first-order orbital angular momentum(OAM) is also generated by combining the LPFG and polarization controller(PC). Then, an all-fiber amplification system based on the FM-EDF and LPFG, for LP11 mode and first-order OAM beams, is built up. Its on-off gain of the LP11 mode beam is 37.2 d B at 1521.2 nm. The variation, whose transverse mode field intensity of first-order OAM is increased with the increase of pumping power, is obvious. These show that both the LP11 mode and first-order OAM beams are amplified in the all-fiber amplification system. This is a novel all-fiber amplification scheme,which can be used in the optical communication fields.
基金Supported by the National '863' high technology project (2002 AA313110)
文摘A novel method of linear demodulation based on edge filter is presented. An experimental system is built up in which LPG is used as the edge filter. We achieve linear demodulation with a bandwidth of 5nm.
文摘The author studied and demonstrated the various modeling aspects of long period fiber grating (LPFG) such as the core effective index, cladding effective index, coupling coefficient, coupled mode theory, and transmission spectrum of the LPFG using three-layer fiber geometry. Actually, there are two different techniques used for theoretical modeling of the long period fiber grating. The first technique was used by Vengsarkar et al who described the phenomenon of long-period fiber gratings, and the second technique was reported by Erdogan who revealed the inaccuracies and shortcomings of the original method, thereby providing an accurate and updated alternative. The main difference between these two different approaches lies in their fiber geometry. Venserkar et al used two-layer fiber geometry which is simple but employs weakly guided approximation, whereas Erdogan used three-layer fiber geometry which is complex but also the most accurate technique for theoretical study of the LPFG. The author further discussed about the behavior of the transmission spectrum by altering different grating parameters such as the grating length, ultraviolet (UV) induced-index change, and grating period to achieve the desired flexibility. The author simulated the various results with the help of MATLAB.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.91323301,51505505,51475482,and 51475481)the Natural Science Foundation of Hunan Province(No.2016JJ3147)+2 种基金the China Postdoctoral Science Foundation(Nos.2015M572264 and 2016T90757)the Self-selected Topic Fund of State Key Laboratory of High Performance and Complex Manufacturing(No.ZZYJKT2015-08)the Fundamental Research Funds for the Central Universities of Central South University
文摘We propose a high temperature-sensitive long period fiber grating(LPFG) sensor fabricated by using the femtosecond laser transversal-scanning method. The femtosecond pulses scan over the whole fiber core and some part of the cladding region; the modified regions are more extended. It is found that the LPFG-I fabricated by the transversal-scanning method shows higher temperature sensitivity and better temperature uniformity than that of LPFG-II written by the femtosecond laser point-by-point method. The LPFG-I with a temperature sensitivity of 75.96 pm/°C in the range of 25°C–400°C is measured. Moreover, in the range from 400°C to 800°C, a higher temperature sensitivity of 148.64 pm/°C and good linearity of 0.99 are achieved, while the temperature sensitivity of LPFG-II is only 95.55 pm/°C. LPFG-I exhibits better temperature characteristics, which, to the best of our knowledge, has the highest sensitivity in silica fiber temperature sensors.
文摘A novel high-speed electro-optic (EO) polymer modulator based on long period gratings (LPG) is designed. Using the theory of multi-cladding optical waveguide, we achieved relationship between modulate voltage and LPG's resonant wavelength.
基金the National Natural Science Foundation of China (grant nos. 61425007, 11174064, 61377090, 61575128, and 61308027), Guangdong Provincial Department of Science and Technology (grant nos. 2014A030308007, 2014A030312008, 2014B050504010, and 2015B010105007), Science and Technology Innovation Commission of Shenzhen/Nanshan (grant nos. ZDSYS20140430164957664, KC2014ZDZJ0008A, and GJHZ20150313093755757), and Pearl River Scholar Fellowships.
文摘Two promising post-treatment techniques, i.e. applying tensile strain and rising temperature, are demonstrated to enhance the mode-coupling efficiency of the CO2-1aser-induced long period fiber gratings (LPFGs) with periodic grooves. Such two post-treatment techniques can be used to enhance the resonant attenuation of the grating to achieve a LPFG-based filter with an extremely large attenuation and to tailor the transmission spectrum of the CO2-1aser-induced LPFG after grating fabrication.
基金supported by the Joint Research Fund in Astronomy under cooperative agreement between the National Natural Science Foundation of China (NSFC) and Chinese Academy of Sciences (CAS) (Nos. U1831115, U2031132, U1931206, and U2031130)Natural Science Foundation of Heilongjiang Province (No. ZD2019H003)Fundamental Research Funds for the Central Universities to the Harbin Engineering University
文摘In this paper,a novel liquid level sensor with ultra-high sensitivity is proposed.The proposed sensor is configured by a sliceshaped composite long period fiber grating(SSC-LPFG).The SSC-LPFG is prepared by polishing two opposite sides of a composite multimode-single-mode-multimode fiber structure using a CO;laser.The method improves the sensitivity of the sensor to external environment.Based on the simulation calculation,a liquid level sensor with a length of 3 mm is designed.The experimental transmission spectrum agrees well with the simulation result.The experimental results show that the sensitivity reaches 7080 pm/mm in the liquid level range of 0-1400 μm in water.The temperature sensitivity is24.52 pm/℃ in the range of 20℃-90℃.Due to the ultra-high sensitivity,good linearity,and compact structure,the SSC-LPFG has potential application in the field of high-Drecision liquid level measurement.
文摘Based on the full vector complex coupled mode theory, a detailed analysis is made on the transmission spectrum characteristics of tilted long period fiber gratings. New transmission peaks are observed, which are located beside the long wavelength side of each transmission peak in the transmission spectrum of normal long period fiber gratings. The emerging transmission peaks are quite sensitive to both the grating tilted angle and the surrounding refractive index, and the corresponding relationship is discussed. Furthermore, a novel sensing characteristic is investigated about the tilted long period fiber gratings, which is related to the transmission resonant wavelength and peak amplitude.
基金supported by the National Natural Science Foundation of China (51772060,51672059,and 51621091)financially sponsored by Heilongjiang Touyan Team Program and the Fundamental Research Funds for the Central Universities (HIT.OCEF.2021003).
文摘The field of electromagnetic wave absorption(EWA)requires the adaptability,tenability,and multifunction of high-performance materials in the future.The design and preparation of EWA materials aiming at performance requirements is the latest research hotspot.Here,a performancedriven strategy for simultaneously coordinating different target performances was proposed to optimize the structure of the periodical long continuous carbon/glass fiber fabric(PCGF)materials through algorithm and simulation.The optimized structure of the PCGF not only improves the impedance matching,but also introduces the induced orientation effect for a high cooperative loss of conductivity,resonance,and periodic structure.The flexible PCGF shows a broad effective absorption bandwidth(EAB)of 32.7 GHz covering a part of the C-band and the whole X-,Ku-,K-,and Ka-bands with a thickness(d)of only 0.92 mm and a density of 5.6×10^(−4) kg·cm^(−3).This highly designable fabric is promising for the EWA practical application owing to integrating the characteristics of good flexibility,acid and alkali resistance,bending resistance,excellent mechanical properties,and easy large-scale preparation.
基金the National Natural Science Foundation of China(Grant Nos.51621091,51872058,51772060,and 51972078)and Key Laboratory of Advanced Structural-Functional Integration Materials&Green Manufacturing Technology,Harbin Institute of Technology,China!。
文摘Carbon fibers reinforced lithium aluminosilicate matrix composites(Cf/LAS)were prepared by slurry infiltration combined with a hot press procedure.The friction,wear behavior,and wear mechanisms of Cf/LAS composites under dry sliding conditions were investigated.The results show that the coefficient of friction(COF)initially increased with the increase in carbon fiber content,and reached the maximum value of 0.20 for the 33%Cf/LAS composite.The COF increased sharply with increasing sample temperature from RT to 300℃.The COF remained stable in the temperature range of 300–500℃.The two wear mechanisms of LAS glass-ceramics are fatigue wear and abrasive wear.The Cf/LAS composites demonstrate slight spalling and shallow scratches.These results show that carbon fibers improve the mechanical properties and wear resistance of Cf/LAS composites.