54 results about "Cladding mode" patented technology

The invention provides a temperature, strain and acoustic emission measurement method and device based on a tilted fiber bragg grating. The method comprises the following steps: carrying out cladding mode and Ghost mode demodulation on a transmission spectrum of a tilted fiber grating to obtain cladding mode wavelength shift and Ghost mode wavelength shift; wherein the tilted fiber bragg grating is mounted on a target structure; the cladding mode wavelength shift and the Ghost mode wavelength shift are substituted into the two-parameter matrix and solved, and the temperature variation and the strain variation of the target structure are obtained; wherein the two-parameter matrix comprises cladding mode-temperature sensitivity, Ghost mode-temperature sensitivity, cladding mode-strain sensitivity and Ghost mode-strain sensitivity of the tilted fiber bragg grating; and the Bragg reflection spectrum of the tilted fiber grating is demodulated and analyzed to obtain an acoustic emission signal of the target structure. According to the invention, simultaneous measurement of temperature, strain and acoustic emission signals can be realized only by using a single fiber bragg grating.

The present invention belongs to the technical field of optical fiber sensing. Provided are a ring-type small-period long-period fiber grating sensor, and a preparation method therefor and the application thereof. A ring-type small-period long-period fiber grating provided in the present invention matches the cross-sectional shape of an optical fiber, and rings can more effectively expand the area of each refractive index modulation region in the cross section of the optical fiber, such that the ring-type grating has large refractive index modulation regions in both the axial direction and longitudinal direction of the optical fiber, and the intensities of a Bragg resonance peak and a cladding mode resonance peak can thus be simultaneously enhanced. Therefore, the Bragg resonance peak and the cladding mode resonance peak can be simultaneously observed in a transmission spectrum of the ring-type grating, such that simultaneous measurement of an ambient refractive index and temperature can be realized, and there is no longer a need to observe a reflection peak, thereby simplifying multi-parameter sensing test steps of the small-period long-period fiber grating.

The invention discloses a laser cladding method for a wind power sliding bearing, and particularly relates to the technical field of laser cladding. The method comprises the following steps that a wind power gear box pin shaft is fixed to a positioner and adjusted to be axially horizontal, and a laser cladding head is positioned to the position above the central axis of the pin shaft through an industrial robot; laser cladding is conducted in a synchronous powder feeding mode, a cladding head is controlled to horizontally move in the axial direction, meanwhile, a positioner drives a pin shaft to rotate, and a spiral coating is formed on the surface of the pin shaft in a cladding mode; and after single-layer full covering is completed every time, the cladding head is moved reversely to conduct next-layer cladding, coating thickness accumulation is achieved through direction alternation and interlayer superposition, and the technology is terminated till the preset value is reached. By the adoption of the technical scheme, the problem that in the prior art, a sliding bearing is insufficient in friction and wear performance is solved, a flat-topped beam is adopted to replace a traditional Gaussian beam for cladding, the particle size of powder is refined, and the prepared coating has the advantages of being few in crack defect and good in friction and wear performance.

The invention provides an anti-resonance hollow-core optical fiber and application thereof. The anti-resonance hollow-core optical fiber comprises a cladding and a fiber core, a protective tube is arranged outside the cladding, a plurality of single-layer resonant tubes and a plurality of double-layer nested tubes which are tangent to the cladding are arranged in the cladding, the single-layer resonant tubes are circumferentially and uniformly distributed by taking the circle center of the fiber core as the center, and one double-layer nested tube is arranged between every two single-layer resonant tubes; the diameter of the single-layer resonant tube is greater than that of the double-layer nested tube; the double-layer nesting pipe comprises an inner pipe and an outer pipe, and the inner pipe and the outer pipe are internally tangent. According to the invention, coupling of a fiber core LP11 mode and a cladding mode is realized through the single-layer resonant tube, so that the mode capability of a high-order mode is leaked to realize single-mode transmission of the optical fiber; and fiber core fundamental mode energy is locked in the fiber core through a double-layer nested tube arranged between the two single-layer resonant tubes, so that fiber fundamental mode low-loss transmission is realized. According to the invention, the fundamental mode limiting loss can be effectively reduced, and optical fiber single-mode transmission is realized through mode coupling.

The invention provides a waveguide integrated superconducting single-photon detector, which can be applied to the technical field of photoelectric detection, and comprises a substrate, a lower cladding, a spot size converter, a waveguide detector and an upper cladding, the lower cladding is located on the upper surface of the substrate; the spot size converter and the waveguide detector are located between the lower cladding and the upper cladding; the spot size converter comprises two conical spot size converters of which the symmetrical narrow ends are arranged in a staggered manner; the waveguide detector comprises a waveguide core layer, a photon absorption layer and an electrode layer; the photon absorption layer is positioned on the upper surface of the waveguide core layer and is connected with the electrode layer; and the wide end of one conical spot size converter is connected with the waveguide core layer. The detector provided by the invention has the advantages of polarization independence and stray light interference resistance. The invention further provides a preparation method and a testing device of the waveguide integrated superconducting single-photon detector.

The invention provides a cladding mode efficient filtering method for microstructure optical fibers, and relates to the technical field of optical fibers, and the method comprises the steps: taking two microstructure optical fibers which are different in structure and have a diameter difference value of a fiber core fundamental mode field within a diameter difference value range, and carrying out the non-oblique-angle cutting of the end faces of the two microstructure optical fibers through a cutting knife; and aligning the axial directions of the two sections of cut micro-structure optical fibers, and splicing at the cutting end surface to obtain a spliced micro-structure optical fiber. The method has the beneficial effects that two sections of microstructure optical fibers with different structures but similar fiber core fundamental mode field diameters are selected, oblique-angle-free cutting is carried out, splicing (welding, butt joint or coupler coupling) is carried out at the cutting end face, and it is ensured that splicing points are axially coaxial but cladding waveguide structures have differences. At a continuous connection point, because the cladding microstructures (such as air hole arrangement, number, shape and the like) of the two sections of optical fibers are discontinuous, the continuity of the cladding waveguide is damaged. Therefore, cladding mode energy is efficiently filtered or scattered, and the strength of the cladding mode energy is greatly weakened.

The application discloses a few-mode fiber double-cascaded mode converter and a high-power few-mode fiber laser. A core base mode and a core high-order mode converter and a core high-order mode and a cladding mode converter are cascaded on the few-mode fiber. The refractive index modulation distribution of the core base mode and the core high-order mode converter is uniformly distributed in the core center, and is used for coupling the core base mode to the core high-order mode. The refractive index modulation distribution of the core high-order mode and the cladding mode converter is distributed at the junction of the core and the cladding, and is used for coupling the core high-order mode to the cladding to form loss. The few-mode fiber double-cascaded mode converter is connected before an output end cap of the high-power few-mode fiber laser, and can inhibit stimulated Raman scattering in the large-mode-field few-mode fiber laser, so as to improve the output performance of the fiber laser.

The invention provides a multimode optical fiber connector device based on a thermal expansion core, and relates to the technical field of optical fibers. The multi-mode optical fiber connector comprises a non-core-expanded multi-mode optical fiber core module, a thermal core-expanded multi-mode optical fiber core module, a cladding module and an outer sleeve module, and by introducing the thermal core-expanded multi-mode optical fiber core module, the mode field matching condition of the multi-mode optical fiber connector under the condition of lateral deviation is remarkably improved, the connection loss is effectively reduced, and the service life of the multi-mode optical fiber connector is prolonged. The thermal core expansion multimode optical fiber core module is the core of the optical fiber module, the module uses a thermal core expansion processing technology and a standard TEC technology to expand the diameter of the multimode optical fiber core at the connecting end, and mode field distribution is optimized; and the outer sleeve module is sleeved outside the cladding module, and a standard optical fiber connector packaging process is adopted, so that the stability is high, the durability is strong, and the economical efficiency is excellent.

The invention, which relates to the technical field of the hollow-core optical fiber, provides a hollow-core optical fiber with an anti-resonance layer having a multi-layer opening structure, comprising an outer cladding sleeve, an anti-resonance area and a hollow-core fiber core area enclosed by the anti-resonance area. The anti-resonance area comprises a plurality of anti-resonance units, each anti-resonance unit comprises at least one anti-resonance layer of an opening structure, and the edges of the two sides of an opening of each anti-resonance layer are connected with the inner wall of the outer cladding sleeve through two parallel thin walls. The optical fiber has the beneficial effects that multiple anti-resonance effects are generated through the opening anti-resonance layer, so that a light field is prevented from leaking to the cladding from the fiber core, and the light field is effectively limited in the hollow fiber core area for transmission; each anti-resonance layer is indirectly connected with the inner wall of the outer sleeve through a parallel thin wall, so that a connection node is far away from the fiber core, node coupling is reduced, and leakage of a light field to the cladding is weakened. The anti-resonance layer and the sleeve form a closed cavity, so that a high-refractive-index area is compared with a low-refractive-index medium in the cavity, a specific wavelength is reflected, a light field is prevented from being coupled with a cladding mode, and the light limiting capability is enhanced.

This invention relates to the field of LC connector testing technology and discloses a B-value testing device for LC fiber optic connectors. This invention solves the problem that existing LC connector B-value testing using mechanized equipment does not consider the influence of the fiber cladding mode on the test data. The invention utilizes an electric push rod, a first push plate, a second push plate, and a compression spring. Activating the electric push rod causes the upper clamping block to move upwards and outwards. This raises one end of the output and input fibers connected to the upper clamping block to a certain height, then pulls one end towards the other. Since the lower clamping block remains stationary, the movement of the upper clamping block causes the output and input fibers to be squeezed into a loop. Due to the special shape of this loop, a signal attenuation effect is generated, thereby eliminating the additional optical signal brought by the cladding mode and avoiding deviations in the test values. Furthermore, the looping is controlled mechanically, making it easier to control the loop diameter compared to manual looping, preventing excessively large loop diameters and excessive losses.

The invention discloses a distributed pumping optical fiber amplifier. The amplifier is characterized in that a multi-mode pumping source is injected into a multi-section double-cladding active optical fiber through a pumping / signal light beam combiner to provide pumping light for the amplifier; the low-power seed source is injected into the multi-section double-cladding active optical fiber through the optical fiber isolator and the pumping / signal light beam combiner for power amplification; the multiple sections of long-period fiber bragg gratings and the multiple sections of double-clad active optical fibers are sequentially connected in a crossed manner; the multiple sections of long-period fiber gratings have harmonic peaks at pumping wavelengths, and due to different periods, cladding mode orders corresponding to the harmonic peaks are different; the multi-section long-period fiber bragg grating couples the cladding pump light into the fiber core to perform distributed fiber core pumping on the double-cladding active fiber, the distributed fiber core pumping is combined with cladding pumping to optimize gain distribution and heat distribution of the fiber amplifier, and high-efficiency and high-power amplification of the seed light is realized. While the heat distribution of the amplifier is optimized, the pumping efficiency is improved, the length of the amplification-stage optical fiber is effectively shortened, the nonlinear effect is inhibited, and high-power optical fiber laser amplification is realized.

The invention discloses a tilted fiber grating demodulation method based on continuous wavelet transform. The method comprises the following steps: reading spectral data and focusing a cladding mode area; performing continuous wavelet transform on the spectrum to generate a scale-wavelength domain coefficient matrix, performing visualization processing on the scale-wavelength domain coefficient matrix, and positioning a cut-off mode through an energy gathering area in a graph; extracting a coefficient curve amplification peak value characteristic under the characteristic scale; detecting a first peak wavelength as a cut-off wavelength by adopting a multi-scale automatic peak searching algorithm; calculating the RMS of the overall matrix to verify the accuracy of the cut-off wavelength under the single scale; calculating sensitivity and goodness of fit based on the linear relationship between the cut-off wavelength and the refractive index; cascade TFBG and FBG are adopted to compensate the spectrum and eliminate external environment interference. According to the method, traditional complex preprocessing such as denoising and envelope fitting is abandoned, accurate and rapid positioning of the cut-off mode is achieved directly through the CWT and the AMPD algorithm, the demodulation efficiency is remarkably improved, and the method is suitable for high-precision real-time refractive index monitoring.

The application discloses a kind of magnetic field sensors based on periodic structure filled by optical fiber resonant cavity, it includes broadband light source, first single-mode optical fiber, periodic structure, second single-mode optical fiber, spectrometer;The light output by broadband light source is coupled into the single-mode core of first single-mode optical fiber, then propagates to periodic structure to carry out interference superposition, and the light after interference superposition is transmitted to spectrometer by second single-mode optical fiber;Periodic structure includes multiple single-mode optical fibers and is filled with magnetic fluid between adjacent single-mode optical fibers;Periodic structure satisfies phase condition: so that the light intensity output to spectrometer is interfered and superposed greatly, wherein Δn is the effective refractive index difference between core mode and cladding mode, L is sensor length, and λ is central wavelength.The application also provides a kind of periodic structure manufacturing method.The application solves the problems of insufficient sensitivity and easy leakage failure of existing optical fiber magnetic field sensor.

The invention belongs to the field of optical fiber sensing, and particularly relates to a material and structure combined sensitization optical fiber SPR (surface plasmon resonance) sensor and a manufacturing and using method thereof, the sensor comprises a cladding mode attenuation area, a fiber core angle regulation and control area, an SPR sensing area and a thick core light receiving area which are connected in sequence; the cladding mode attenuation area is a six-core optical fiber of which the surface is provided with a coating layer; the fiber core angle regulation and control region is a torsion type six-core optical fiber; a gold film, an MOF-808 material and a medicine component are sequentially arranged on the surface of the SPR sensing area. Cladding mode light is attenuated to zero under the absorption of the cladding and the high-refractive-index coating layer, SPR incident angles when light beams in the six fiber cores are incident to a gold film in an SPR sensing area are adjusted, and then the intensity of an electric field is enhanced through MOF-808, so that the sensitivity of the sensor is improved; when the drug component is combined with the target spot, the SPR resonance valley moves to realize drug-target spot affinity detection; the invention solves the problem of low sensitivity of the traditional optical fiber SPR sensor, and has the advantage of high mechanical strength.

The application discloses a multimode coupling eccentric core fiber Bragg grating sensor, which comprises the following modules: an optical source module, which is used for generating an optical source with a fixed wavelength range to provide excitation light for an evanescent field sensing area; an evanescent field sensing module, which is used for sensing the refractive index information in the evanescent field by utilizing the eccentric core structure of the Bragg grating and the multimode fiber to excite the evanescent field, so as to detect the refractive index of a to-be-detected liquid and a molecular combination process related to the refractive index; a signal detection module, which is used for collecting spectral signals carrying detection information transmitted by the multimode fiber and performing real-time spectral recording; and a micro flow cell, which is used for placing the evanescent field sensing area and the to-be-detected liquid. The application excites a Bragg cladding mode by using an eccentric core welding technology, simplifies a manufacturing process, avoids the damage of a traditional mechanical processing to a Bragg fiber grating structure, significantly improves the consistency and mechanical strength of a product, enhances the long-term stability of the Bragg fiber grating sensor, and is suitable for large-scale application.

The application discloses a method for suppressing stimulated Brillouin scattering effect by using a cascaded long-period fiber grating. The transmission spectrum of the cascaded long-period fiber grating has a series of comb-shaped resonance peaks, two adjacent resonance peaks are regarded as a passband and two stopbands, the passband bandwidth and resonance wavelength are changed by adjusting the parameters of the cascaded long-period fiber grating, the passband and stopband formed by the adjacent resonance peaks of the transmission spectrum correspond to signal light and Stokes light generated by the stimulated Brillouin scattering effect respectively, so that the non-working side lobe laser is coupled from the core mode to the cladding mode while the signal light passes through. The performance stability of the cascaded long-period fiber grating is improved by using a water ring flow-based desensitization packaging technology, so that the output power level and beam quality of the fiber laser are improved, and the possibility of laser damage is reduced. The application has the characteristics of low cost, high flexibility and strong applicability.

The invention discloses a laser cleaning and cladding cooperative control method and device based on an unmanned aerial vehicle, electronic equipment, a readable storage medium and a computer program product. The method comprises the following steps: determining an operation target; when the surface corrosion depth of the operation target exceeds a preset depth threshold value, the current operation mode of the unmanned aerial vehicle is adjusted to be a cleaning mode; performing laser cleaning operation on the operation target in the cleaning mode; when it is detected that the target metal ion characteristic peak intensity on the surface of the operation target reaches a preset intensity threshold value, the current operation mode of the unmanned aerial vehicle is switched from a cleaning mode to a cladding mode; and performing cladding operation on the operation target in the cladding mode. According to the method, the problems that in the prior art, due to step-by-step cleaning and cladding operation, the exposure time of the metal surface is too long, secondary oxidation is prone to occurring, and the bonding quality and the operation efficiency of a cladding layer are affected can be solved.

The utility model discloses a double-parameter optical fiber sensor based on a conical few-mode fiber grating, which belongs to the technical field of optical fiber sensors and comprises a broadband light source (1), a sensing structure (2) and a spectrum analyzer (3). The sensing structure (2) comprises a first single-mode fiber (201), a coreless fiber (202), a conical few-mode fiber grating (203) and a second single-mode fiber (204); more cladding modes are generated through mode field mismatch of the single-mode optical fiber and the coreless optical fiber and bending of a conical area, the double-parameter sensitivity of the sensor is improved, and two transmission characteristic peaks appear on the fiber bragg grating inscribed on the few-mode optical fiber by using different mode numbers in the few-mode optical fiber. The reliability and repeatability of the sensor are greatly improved, the corresponding double-parameter sensitivity can be respectively calculated by observing the position change of an interference spectrum and a transmission characteristic peak, and a sensitivity matrix is further established, so that the simultaneous measurement of double parameters is realized. The sensor has the characteristics of high sensitivity, strong reliability, strong anti-interference capability, small size, simplicity in manufacturing and the like.

The present invention discloses a cascaded cladding light stripper and a manufacturing method thereof. The cladding light stripper includes a first optical fiber, a second optical fiber, a quartz tube and a metal shell. The cascaded cladding light stripper proposed by the present invention can gradually strip the cladding light layer by layer through cascading multiple cladding light strippers and the segmented etching method, and guide away the cladding light or the heat generated by the cladding light step by step and stage by stage, so as to achieve high-power cladding light stripping, effectively avoid local high temperature, and can be applied to high-power fiber lasers; moreover, the manufacturing difficulty is low.

The invention provides a fiber core alignment welding device of a soft glass active optical fiber, which comprises a first monitoring light source, a second monitoring light source, a wavelength division multiplexer, an optical fiber to be welded, a cladding mode stripper, the soft glass active optical fiber, an optical fiber welding machine, a dichroscope, a light spot analyzer and a power meter, the wavelength of the output first monitoring laser is located in an absorption band of the soft glass active optical fiber; a tail fiber of the second monitoring light source is a single-mode optical fiber, the wavelength for outputting the second monitoring laser is located outside the absorption band of the soft glass active optical fiber, and a fiber core of the soft glass active optical fiber is a single-mode waveguide for the second monitoring laser; the dichroscope is used for splitting the first monitoring laser and the second monitoring laser output by the soft glass active optical fiber; and the power meter is used for measuring the power of the first monitoring laser. The invention further provides a fiber core alignment welding parameter optimization method of the soft glass active optical fiber.

The invention belongs to the field of optical fiber interference sensors, and particularly relates to an optical fiber Mach-Zehnder interferometer strain sensor based on a bending structure and a manufacturing and using method of the optical fiber Mach-Zehnder interferometer strain sensor. Comprising a light injection area, a bent optical fiber sensing area and a light receiving area which are sequentially arranged on an optical fiber; the bent optical fiber sensing area is divided into an oxyhydrogen flame heating spiral wave structure and a capillary copper pipe wrapped spring structure; a cladding mode field of the bent optical fiber sensing area deflects to the outer side of the bent structure, and under the action of strain, the strain is concentrated on the inner side of the bent optical fiber sensing area; a cladding mode field offset area and a strain concentration area of the bent optical fiber sensing area are separated in space, the reduction amount of effective refractive index of a cladding mode in the strain process is reduced, and high-sensitivity MZI strain sensing is achieved; the problem that an existing MZI strain sensor is low in sensitivity is solved.

The application provides a kind of optical fiber polarizer based on hollow negative curvature optical fiber, which comprises: a base layer with a hollow structure inside; a core layer arranged at the center of the base layer; an asymmetric cladding structure arranged between the base layer and the core layer, comprising: a pair of first capsule nesting units arranged in the y direction of the core layer, and six second capsule nesting units uniformly distributed in non-y direction.According to the application, the two schemes of air area in the asymmetrically distributed different tube thickness and expanded y direction cladding are combined, which effectively enhances y the coupling of polarization state and cladding mode, realizes excellent single-mode single-polarization performance; effectively increases the confinement loss of y polarization base mode, and further realizes high enough polarization extinction ratio in a larger bandwidth range, and has good bending and spiral resistance.

The invention discloses a few-mode fiber double-cascade mode converter and a high-power few-mode fiber laser. A fiber core fundamental mode and fiber core high-order mode converter and a fiber core high-order mode and cladding mode converter are cascaded on a few-mode fiber; the refractive index modulation distribution of the fiber core fundamental mode and fiber core high-order mode converter is uniformly distributed in the center of the fiber core and is used for coupling the fiber core fundamental mode to a fiber core high-order mode; the refractive index modulation of the fiber core high-order mode and cladding mode converter is distributed at the junction of the fiber core and the cladding, and is used for coupling the fiber core high-order mode into the cladding to form loss. The few-mode fiber double-cascade mode converter is connected in front of an output end cap of a high-power few-mode fiber laser, so that stimulated Raman scattering in the large-mode-field few-mode fiber laser can be inhibited, and the output performance of the fiber laser is improved.

The invention relates to a multimode coupling core-shift fiber Bragg grating sensor, which comprises a light source module used for generating a light source with a wavelength in a fixed range and providing exciting light for an evanescent field sensing area; the evanescent field sensing module is used for realizing evanescent field excitation by utilizing a core shift structure of a Bragg grating and a multimode optical fiber so as to sense refractive index information in the evanescent field and is used for detecting the refractive index of liquid to be detected and a molecular binding process related to the refractive index; the signal detection module is used for collecting a spectral signal which is transmitted by the multimode optical fiber and carries detection information, and carrying out real-time spectral recording; and the micro-flow cell is used for placing the evanescent field sensing area and liquid to be detected. The core shift welding technology is adopted to excite the Bragg cladding mode, the manufacturing process is simplified, damage of traditional machining to the Bragg fiber grating structure is avoided, the consistency and mechanical strength of products are remarkably improved, the long-term stability of the Bragg fiber grating sensor is enhanced, and the sensor is suitable for large-scale application.

The invention discloses a linear polarization narrow linewidth fiber laser based on fast and slow axis orthogonal gratings, which comprises two polarization-maintaining cladding mode stripping devices, a polarization-maintaining pumping beam combiner, an output head, a polarization-maintaining gain fiber, a polarization-maintaining high-reflectivity grating and a polarization-maintaining low-reflectivity grating, wherein the etching grating surfaces of the polarization-maintaining high-reflectivity grating and the polarization-maintaining low-reflectivity grating are vertically orthogonal; each of the polarization-maintaining high-reflectivity grating and the polarization-maintaining low-reflectivity grating comprises a polarization-maintaining optical fiber and a grating body, the polarization-maintaining optical fiber comprises two stress rods, a fiber core and a cladding, the fiber core is located between the two stress rods, the cladding is used for wrapping the stress rods and the fiber core, and the grating body is arranged in the fiber core. In the invention, due to the application of the orthogonal grating and optical fiber vertical welding mode, the polarization mode of vertical welding is suppressed due to large loss and loss of advantages in competition, otherwise, the laser signal in the other polarization direction obtains advantages in competition and is continuously subjected to gain amplification, so that the laser signal obtains a relatively high linear polarization degree, and the polarization extinction ratio is improved.

An annular small-period-long-period fiber grating (SP-LPG) sensor, a preparation method and applications thereof are provided. The annular (SP-LPG) sensor matches the cross-section shape of the optical fibers, the annulus can expand the area of the refractive index modulation region more effectively in the section of the optical fibers, so that the annular grating has a large refractive index modulation region in both the axial and longitudinal directions of the optical fibers, which can simultaneously enhance the intensity of the Bragg resonance peak and the resonance peaks of the cladding modes. Therefore, the Bragg resonance peak and the resonance peaks of the cladding modes can be observed simultaneously in the transmission spectra. It can realize the simultaneous measurement of the refractive index and temperature of the surrounding environment without the need to observe the reflection peak, which simplifies the multi-parameter sensing test steps of the (SP-LPG) sensor.

The invention provides an optical fiber polarizer based on a hollow-core negative-curvature optical fiber, and the optical fiber polarizer based on the hollow-core negative-curvature optical fiber comprises a base layer which is of a hollow structure; the fiber core layer is arranged at the center in the base layer; the asymmetric cladding structure is arranged between the base layer and the fiber core layer, and the asymmetric cladding structure comprises a pair of first capsule nesting units arranged in the y direction of the fiber core layer and six second capsule nesting units uniformly distributed in the non-y direction. According to the invention, by combining two schemes of asymmetrically distributing different tube thicknesses and expanding an air area of the cladding in the y direction, coupling of a y polarization state and a cladding mode is effectively enhanced, and excellent single-mode single-polarization performance is realized; the limiting loss of a y polarization fundamental mode is effectively increased, the polarization extinction ratio is high enough in a large bandwidth range, and good bending resistance and spiral resistance are achieved.

An optical fiber device has a fiber core, a cladding layer around the fiber core and a plurality of tilted fiber Bragg gratings, FBGs, in the fiber core at a sequence of positions along the optical axis of the fiber core. The tilted FBGs are configured to reflect and transmit respective non zero fractions of the optical power of light with a predetermined optical reflection wavelength defined by the tilted FBG from the fiber core at the position of the tilted FBG. The tilted FBGs having a tilt angle in an angle range wherein the tilted FBG reflects light from the fiber core perpendicularly to the fiber core or with a deviation from perpendicular reflection at which the reflected light does not give rise to cladding mode generation at the predetermined optical reflection wavelength of the tilted FBG. Photo-acoustic conversion material is provided on the cladding layer at least in areas where light reflected by the tilted FBGs at said positions emerges from the cladding layer, the cladding layer extending continuously at said areas.

The present invention provides a ring-shaped small-period long-period fiber grating sensor and a preparation method and application thereof, which belongs to the field of optical fiber sensing technology. The ring-shaped small-period long-period fiber grating described in the present invention matches the shape of the optical fiber cross section, and the ring can more effectively expand the area of ​​the refractive index modulation region in the optical fiber cross section, so that the ring grating has a large refractive index modulation region in both the axial and longitudinal directions of the optical fiber, thereby simultaneously enhancing the intensity of the Bragg resonance peak and the cladding mode resonance peak. Therefore, the Bragg resonance peak and the cladding mode resonance peak can be observed simultaneously in its transmission spectrum, and the simultaneous measurement of the refractive index and temperature of the surrounding environment can be achieved, and there is no need to observe the reflection peak, which simplifies the multi-parameter sensing test steps of the small-period long-period fiber grating.

The invention relates to a method for testing a fiber core absorption coefficient of a high-doping-concentration double-cladding erbium-doped optical fiber, and belongs to the technical field of optical fiber lasers. And performing end face processing on two ends of the first matching passive optical fiber, the double-cladding erbium-doped optical fiber to be measured and the second matching passive optical fiber. One end of the first matching passive optical fiber is connected with the light source output end, and an input cladding light filtering module is arranged on the first matching passive optical fiber; one end of the second matching passive optical fiber is connected with the input end of the optical signal receiving device, and the second matching passive optical fiber is provided with an output cladding light filtering module; the other end of the first matching passive optical fiber is welded with one end of a to-be-tested double-cladding erbium-doped optical fiber to form a first welding point; the other end of the to-be-tested double-cladding erbium-doped fiber is welded with the other end of the second matching passive fiber to form a second welding point; and respectively carrying out measurement and data processing on the transmission light power of the to-be-measured double-cladding erbium-doped optical fibers with the lengths of L1 and L2. According to the invention, effective separation of fiber core signals and cladding light is realized, interference of a cladding mode on fiber core transmission light is eliminated, and the test accuracy is improved.