117 results about "Bend loss" patented technology

The embodiment of the utility model provides an optical fiber recognizer and an optical fiber recognition system, and belongs to the technical field of optical communication, the optical fiber recognizer comprises a vibration structure and a bending structure, an optical signal on an optical fiber firstly passes through the vibration structure and then passes through the bending structure, the vibration structure drives the optical fiber to reciprocate so as to repeatedly bend the optical fiber, and an optical signal with periodically changed optical power is generated. The bending structure drives part of the optical fiber to move to bend the optical fiber, and the variation of the optical power can be judged by detecting the light leakage amount caused by bending of the optical fiber. When the detector detects and identifies the periodically changing optical signal, online lossless identification of the optical fiber is realized, and the periodically changing optical signal is taken as a criterion, so that misjudgment can be avoided. According to the variable quantity of the optical power, feedback adjustment of the bending quantity of the optical fiber can be achieved, the bending quantity can be correspondingly adjusted according to optical fibers with different wire diameters and wavelengths, optical signals with certain optical power variable quantity and periodical change are generated, accurate lossless identification is achieved, and the risk of service interruption caused by too large bending loss is avoided.

The invention provides a multi-mode hollow-core anti-resonance optical fiber, and relates to the technical field of optical fibers, and the multi-mode hollow-core anti-resonance optical fiber comprises a hollow outer layer tube and a plurality of cladding capillary tubes arranged on the inner wall of the outer layer tube; each cladding capillary tube comprises a circular tube, an elliptical tube and an anti-resonance plate, and the elliptical tube is nested in the circular tube through the anti-resonance plate and is coaxially arranged with the circular tube. In the technical scheme provided by the invention, the elliptical tube is nested in the circular tube by the anti-resonance plate, and the elliptical tube and the circular tube are coaxially arranged, so that a nested integrated cladding capillary tube is formed, and the multi-mode hollow-core anti-resonance optical fiber with the structure can reduce bending loss and limiting loss of the fiber core in a high-order mode.

The embodiment of the invention provides an anti-bending optical fiber and a production process thereof, and relates to the technical field of optical fibers. The first wrapping layer wraps the core layer; the gradient layer wraps the first wrapping layer; the second wrapping layer wraps the gradient layer; and the refractive indexes of the core layer, the first cladding, the gradient layer and the second cladding are gradually reduced in sequence. According to the bending-resistant optical fiber and the production process thereof provided by the embodiment of the invention, the problem of relatively large bending loss of the optical fiber in the prior art is solved.

The invention discloses a double-layer waveguide 2 * 2 microring optical switch, an optical switch array thereof and an optical signal processing method, and belongs to the technical field of optical communication devices. Aiming at the technical problem that a traditional micro-ring optical switch is difficult to realize a large free spectral range and low-loss transmission at the same time, the invention provides an innovative structure combining a silicon nitride micro-ring resonator and an annular Bragg grating, and the outer side of the silicon nitride micro-ring resonator is nested with the annular Bragg grating; and a light field forbidden band is constructed to suppress a light field radiated outwards by the resonator, so that strong light field constraint is realized to remarkably reduce bending loss. A silicon-silicon nitride double-layer waveguide interlayer coupling technology is adopted, the lower layer is a silicon coupling waveguide, the upper layer is a silicon nitride micro-ring resonator and concentric annular grating structure, and a titanium nitride micro-heater is integrated to adjust the resonant wavelength. The invention effectively solves the technical problem that the silicon nitride micro-ring optical switch is difficult to obtain in the aspects of large free spectral range and low loss at the same time, and is a key technical support for constructing a high-integration wavelength selection optical switching chip.

The present disclosure provides a fiber bending loss test system and method based on spectral analysis, which relates to the field of fiber detection technology. This application uses multi-wavelength scanning to obtain power values ​​and interference signals, and transmits at least two measurement data in parallel within one transmission cycle; writes to the storage array according to the wavelength index and batch identifier, pauses and fills in points when insufficient alignment is detected; after filling in points, transmission is resumed and distributed loss information is calculated. In this way, data integrity, transmission throughput and real-time loss calculation accuracy are taken into account in a large-scale measurement environment, effectively avoiding the extension of measurement cycles and index confusion in conventional linear detection or fixed offset methods, and significantly improving the efficiency and reliability of fiber loss testing.

The invention provides a non-inductive fatigue pressure monitoring cushion system and method based on multi-mode optical fiber sensing. Relates to the technical field of health monitoring and medical instruments, and comprises an optical fiber multi-mode sensing layer which is embedded in a cushion foaming elastomer, forms a two-dimensional sensing grid by staggered Bragg grating array optical fibers and micro-bend loss plastic optical fibers, and is used for collecting heart and lung micro vibration signals and body pressure distribution-micro body movement signals; and the optical signal conditioning and synchronous acquisition unit is coupled with an optical path of the optical fiber multi-mode sensing layer and is used for carrying out amplitude-phase demodulation and temperature drift compensation on optical fiber reflection / transmission light and digitally outputting multichannel original data. The non-inductive fatigue pressure monitoring cushion system and method based on multi-mode optical fiber sensing have the advantages of noninvasive comfort, high-precision recognition, self-adaptive intervention, low power consumption, long endurance and the like, and an accurate and continuous fatigue and pressure management solution is provided for sedentary people.

To provide an optical fiber cable that includes both a photonic bandgap fiber and an antiresonant fiber and has good bending characteristics, and a transmission method using the same. [Solution] An optical fiber cable includes a photonic bandgap fiber placed in a first state and an antiresonant fiber placed in a second state, wherein at least one of the macrobending loss of an optical fiber when placed in the first state is greater than the macrobending loss when placed in the second state, and the microbending loss of the optical fiber when placed in the first state is greater than the microbending loss when placed in the second state.

The invention relates to an optical fiber drawing method integrated with a coloring function and a production system, and relates to the technical field of optical fiber manufacturing, and the method comprises the following steps: melting and drawing an optical fiber preform to form a bare fiber; the bare fiber is cooled; coating the cooled bare fiber twice to form an inner coating and an outer coating; performing primary UV curing on the inner coating and the outer coating to enable the outer coating to reach a semi-cured state; coating coloring ink on the surface of the outer coating in a semi-cured state; performing secondary UV curing on the coloring ink, so that the coloring ink is cured, and the inner coating and the outer coating are finally cured; and the cured optical fiber is detected and taken up. The coloring procedure is integrated into the wire drawing process, integrated continuous production is achieved, and optical fiber microbend loss caused by multiple times of winding and unwinding is avoided; by means of molecular activity in a semi-cured state, coloring ink permeates to form an interpenetrating network structure, and adhesive force is improved.

The present invention keeps bend loss at a low level in an optical waveguide in which a core includes a bend section. This optical waveguide (1) comprises: a core (11) that includes a bend section (11b); and a cladding (12) that surrounds the core (11) and has a lower refractive index than the core (11). The refractive index of the cladding (12) on the opposite side of the bend section (11b) from the curvature center (o) side of the bend section (11b) is lower than the refractive index of the cladding (12) on the curvature center (o) side of the bend section (11b).

The invention discloses a hollow-core and solid-core optical fiber hybrid optical fiber bundle and an optical cable comprising the same, and belongs to the technical field of optical fiber communication, the hollow-core and solid-core optical fiber hybrid optical fiber bundle comprises a hollow-core optical fiber, a solid-core optical fiber (the solid-core optical fiber can be G.652D, G.654E or G.655 and the like), a first layer of resin and a second layer of resin; a hollow-core optical fiber is arranged in the center of an optical fiber bundle to ensure that the bending radius of the hollow-core optical fiber is maximum when the optical fiber bundle is bent, the bending loss of the hollow-core optical fiber is reduced, and meanwhile, the periphery of the hollow-core optical fiber is coated with a layer of low-modulus resin to reduce the bending stress of the hollow-core optical fiber; meanwhile, the periphery of the low-modulus resin is filled with the high-modulus resin, so that the mechanical performance of the optical fiber bundle is guaranteed, the solid-core optical fibers arranged in the optical fiber bundle in a mixed mode are annularly distributed on the outer sides of the hollow-core optical fibers, the hollow-core optical fibers in the middle are protected through the solid-core optical fibers, and the overall mechanical strength of the optical fiber bundle is further improved.

This invention discloses a system and method for achieving single-mode transmission of sapphire optical fiber using a mechanically wound helical structure, belonging to the technical field of optical fiber transmission and high-temperature optical devices. The method involves winding sapphire optical fiber along a specific pitch to form a helical structure on a core, introducing controllable bending loss to suppress higher-order modes. Subsequently, high-temperature annealing and structural fixation ensure uniform stress distribution within the fiber and maintain a stable structure. Finally, optical testing verifies the single-mode transmission effect. This method offers advantages such as simple structure, no need for complex processing equipment, low cost, and high stability, and can be widely applied in high-temperature optical fiber sensing and high-power laser transmission.

The invention provides a thulium-doped optical fiber with high spectral purity and a preparation method thereof, and the thulium-doped optical fiber with high spectral purity adopts a profile design that the refractive index of a main gain layer follows linear gradual change distribution of a linear function and the refractive index of a secondary gain layer is constant, so that the mode distribution of an optical fiber fundamental mode is precisely overlapped with the main gain layer; the secondary gain layer is located at the lowest point of the waveguide refractive index; the design can effectively solve the problem that in the prior art, due to the limitation of the MCVD technology, the doping concentration difference of the main gain layer and the secondary gain layer is caused, and then the optimal emission wavelengths of different gain areas are inconsistent. Besides, depending on the bending loss difference of the main gain layer and the secondary gain layer, on the premise that the gain efficiency of the optical fiber is not sacrificed, effective separation of emission wavelengths of the main gain layer and the secondary gain layer can be achieved through bending regulation, the target wavelength of the main gain layer is reserved, and the non-target wavelength of the secondary gain layer is filtered out. And finally, the spectral purity of the thulium-doped optical fiber is improved.

The application relates to a three-component distributed optical fiber acoustic sensing device, system and detection method based on microstructure air hole sound wave sensitization, which comprises a distributed optical fiber acoustic sensing system and a sensing device, the device comprises at least one sensing unit, the sensing unit comprises an elastomer and a sensing optical fiber with air holes, and the sensing units are connected by connecting blocks; at least one sensing optical fiber is tightly attached to the elastomer to detect the deformation of the elastomer, and the cladding of the sensing optical fiber comprises air holes; the sensing device is connected with the distributed optical fiber acoustic sensing system. By adopting the microstructure air hole optical fiber as the sensing optical fiber, the equivalent Young's modulus and the effective refractive index of the sensing optical fiber are reduced, the bending loss is lower under the condition of ensuring that the optical fiber attenuation is lower, and the sound wave detection sensitization is realized.

This optical fiber comprises a core, an inner cladding, a trench, and an outer cladding. When the relative refractive index difference of the core is ∆1, the relative refractive index difference of the inner cladding is ∆2, the relative refractive index difference of the trench is ∆3, the relative refractive index difference of the outer cladding is ∆4, the outer diameter of the core is 2r1, the outer diameter of the inner cladding is 2r2, the outer diameter of the trench is 2r3, and the outer diameter of the outer cladding is 2r4, the following relationships are established.　2.2 ≤ r2 / r1 ≤ 3.6; 3μm ≤ r3 － r2 ≤ 12μm; 0.25% ≤ ∆1 － ∆2 ≤ 0.50%; − 0.70% ≤ ∆3 ≤ − 0.10%; A zero-dispersion wavelength is 1296-1306 nm. A zero-dispersion slope is 0.088 ps / nm2 / km or less. A 500-meter cable cutoff wavelength is 1260 nm or less. A bending loss for light with a wavelength of 1310 nm when the optical fiber is wound around a mandrel having a diameter of 15 mm is 0.5 dB or less per turn.

The utility model discloses a tension-resistant tightly-wrapped aramid fiber optical fiber for ultra-long-distance flight of a small unmanned aerial vehicle in the related technical field of optical fibers, which comprises an optical fiber main body, two aramid fibers are symmetrically arranged on two sides of the optical fiber main body, tightly-wrapped layers are arranged on the outer sides of the optical fiber main body and the aramid fibers, and the optical fiber main body is a single-mode optical fiber which is not sensitive to bending loss. The optical fiber main body is a 6.657. A2 type optical fiber, and the outer side of the tight wrapping layer is provided with a super-hydrophobic layer. According to the utility model, the aramid fibers are arranged at the two sides of the optical fiber main body, the tight wrapping layer is extruded outside the optical fiber and the aramid fibers, and the three are combined together to form the tension-resistant tight wrapping aramid fiber optical fiber for the unmanned aerial vehicle, so that the mechanical performance of the optical fiber is improved while the good conductivity of the optical fiber is ensured, and meanwhile, the optical fiber in the application state is light in weight and convenient to manufacture. The ultra-long flight distance signal wired transmission of a small unmanned aerial vehicle can be easily realized, a common wireless electromagnetic wave control signal is prevented from being interfered, and the hydrophobic and oleophobic characteristics of the optical fiber are effectively improved due to the arrangement of the super-hydrophobic layer.

A method for measuring a bending loss of an optical fiber includes: determining a reference number of turns by which a wavelength dependency of a bending loss value of the optical fiber in a region of a predetermined transmission wavelength or less when the optical fiber is wrapped around a mandrel has an exponential function shape with respect to a transmission wavelength; measuring a first power of light for the optical fiber wrapped by the reference number of turns; and measuring a second power of light for the optical fiber wrapped by a number of turns larger than the reference number of turns. The method further includes obtaining, based on the first power of light and the second power of light, a bending loss value of the optical fiber at the predetermined transmission wavelength when the optical fiber is bent with the predetermined diameter.

This invention discloses a distributed optical fiber temperature measurement and calibration device, comprising a housing, a cover, an optical fiber body, and a temperature measurement and calibration module. The cover is hinged and rotated at the top of the housing, located at an opening. Inside the housing, a wireframe assembly for supporting and positioning the optical fiber body is fixedly installed. The temperature measurement and calibration module is fixedly mounted on the wireframe assembly. The wireframe assembly includes a wireframe body and an optical fiber slot. This invention effectively solves the problem of low calibration accuracy caused by the small coiling radius and high micro-bending loss of the optical fiber body in existing devices through the rational design of the wireframe assembly. The annular wireframe body increases the coiling radius of the optical fiber body, and the spacers, combined with the spacers, support the optical fiber body to form gaps, reducing bending stress and friction loss. Through holes and slots ensure airflow, further reducing micro-bending loss and improving signal transmission stability. The side heat dissipation assembly achieves forced heat dissipation through a cooling fan and an airflow guide shroud.

A detection system includes: at least one light source that outputs a plurality of test beams input to a proximal end portion side of an optical fiber and having different wavelengths and providing different bending losses of the optical fiber; at least one reflector that reflects each of the test beams propagating through the optical fiber, on a distal end portion side of the optical fiber; a plurality of light receiving units that receive a plurality of reflected beams each being a beam reflected by the at least one reflector, on the proximal end portion side; and a determination unit that, based on information about the reflected beams at the plurality of light receiving units, compares the information about the reflected beams with reference set values.

The invention belongs to the field of optical fiber sensing, and particularly relates to a three-layer step type optical fiber structure which has a wide bending radius sensing range and high bending sensitivity on the premise that bending loss can be resisted. By regulating and controlling the refractive index of the second layer of the fiber core, balance between low bending loss and high bending sensitivity is achieved. And meanwhile, two groups of spatially separated acoustic modes are excited under a specific refractive index condition, so that double Brillouin gain peaks can be formed. Specifically, when the refractive index of the second layer of the fiber core changes, the characteristics of optical and acoustic modes and opto-acoustic interaction are studied, and finally a W-type optical fiber structure with excellent performance is determined. The structure has a wider bending radius sensing range and higher bending sensitivity while keeping a good bending loss resistance characteristic. In a word, the optical fiber structure provided by the invention has important application value in the field of optical fiber double-physical parameter distributed sensing, and a new thought is provided for realizing high-performance Brillouin bending sensing.

The invention discloses a method for adaptively adjusting the coiling diameter of a gain optical fiber and a laser system, and relates to the field of optical fiber lasers, and the method comprises the steps: obtaining the temperature of the gain optical fiber under the current coiling diameter and the current LD current; determining the current transverse refractive index distribution of the gain fiber according to the temperature of the gain fiber based on a thermo-optic effect and a numerical modeling mode; according to the current transverse refractive index distribution, bending loss curves of conduction modes LP01 and LP11 in the gain fiber are calculated; according to a preset optimization principle, the optimal coiling diameter of the gain fiber is determined according to the bending loss curves of the conduction modes LP01 and LP11; the optimal coiling diameter is used as an adjustment basis of the coiling diameter of the gain fiber. The coiling diameter of the gain optical fiber is automatically adjusted according to self-adaptive feedback according to the temperature of the optical fiber, so that the TMI threshold value is increased.

This invention provides a transient displacement sensor based on uniform macro-bending loss of optical fiber and dynamic changes in tension and compression of an elastic substrate, along with its fabrication method and applications, belonging to the field of optical fiber sensor design. It includes an elastic substrate and an optical fiber inserted into the elastic substrate. The optical fiber is inserted into the elastic substrate at equal intervals and fixedly connected to the substrate at the insertion points. After insertion, the optical fiber exhibits a continuous wavy bend with identical shapes. One end of the optical fiber is connected to a light source, and the other end is connected to a photodiode. Deformation of the elastic substrate along the length of the optical fiber causes a change in the fiber's curvature. The width of the elastic substrate is 20-500 times the diameter of the optical fiber. The sensor fabrication method is simple, convenient, reliable, and easy to operate. The sensor measures a wider displacement range, can perform continuous measurements, and has a larger dynamic monitoring range. In application, this invention exhibits a large linear region and high reliability.

The fiber optic cable (1) of the present invention is characterized in that a plurality of F with geometric micro-bending loss characteristics are housed in the internal space (3S) of the sheath (3). μBL_G and optical microbending loss characteristics F μBL_Δβ The fiber (10), when the cable characteristics Dc of the fiber cable (1) are defined using the porosity a of the internal space (3S) and the number of cores b of the fiber (10) housed in the internal space (3S), has the microbending loss characteristic factor F expressed by the following formula. μBL_GΔβ The value is 1.2 × 10 －9 The following F μBL_GΔβ =F μBL_G ×F μBL_Δβ ×Dc.

The invention belongs to the technical field of anti-resonance optical fibers, and particularly relates to a middle-infrared band hollow-core anti-resonance optical fiber which comprises an outer cladding layer, a fiber core area is coaxially arranged in the outer cladding layer, and an inner cladding layer area is arranged between the outer cladding layer and the fiber core area; the inner cladding layer area comprises a plurality of anti-resonance units, the anti-resonance units are arranged along the length direction of the outer cladding layer, and the plurality of anti-resonance units are arranged at equal intervals in the circumferential direction; the anti-resonance unit comprises a first medium pipe, and a second medium pipe is arranged in the first medium pipe in a penetrating mode. According to the middle-infrared band hollow-core anti-resonance optical fiber provided by the invention, the second dielectric tube is additionally arranged in the first dielectric tube, so that the opportunity that light generates resonance and overflows out of the fiber core is reduced, the limiting loss and the bending loss are reduced, the low limiting loss requirement of long-distance transmission and the better single-mode characteristic are considered in a wider wavelength range, and the application range of the middle-infrared band hollow-core anti-resonance optical fiber is widened. And the structure is simple.

The application relates to a non-zero dispersion-shifted single-mode optical fiber with a low cutoff wavelength and a low macro-bending loss and an application, which comprises a core layer and a cladding layer surrounding the core layer, the cladding layer comprises a depression layer, an inner cladding layer and an outer cladding layer arranged in sequence from inside to outside, the inner cladding layer comprises a first inner cladding layer and a second inner cladding layer arranged in sequence from inside to outside, the relative refractive index difference Delta 1 of the core layer is 0.500% to 0.570%, and the refractive index curve of the core layer is a gradually decreasing parabolic shape, and the refractive index decreases with the increase of the core diameter. The shape of the refractive index profile of the optical fiber is adjusted, the conventional multi-core layer step type design is avoided, the gradually decreasing parabolic design is adopted, compared with the triangular depression core structure, the core center high refractive index range and the effective refractive index area of the application are larger, the waveguide of the light can be effectively bound in the core, and compared with the trapezoidal core, the core layer decreases in a parabolic mode with the radius, the radius of the core layer can be effectively reduced, and the purposes of reducing the cutoff wavelength and the bending loss are achieved.

The utility model relates to the field of fiber lasers, and particularly discloses a composite core layer large-mode-field single-mode fiber. The structure of the optical fiber sequentially comprises a composite fiber core layer, a trapezoidal gradient refractive index coupling ring, a sunken groove structure and a wrapping layer from inside to outside. The fiber core layer is formed by compounding three layers of fiber cores with different refractive indexes, and the refractive indexes of the fiber cores are sequentially reduced from inside to outside; the refractive index change condition of the trapezoidal gradient refractive index coupling ring is an isosceles trapezoid, the refractive index of the top of the trapezoidal gradient refractive index coupling ring is consistent with the refractive index of the innermost fiber core, and the refractive index values of the waist parts at the two sides are uniformly and progressively decreased from the top fiber core value to the two sides to the refractive index value of the cladding; the refractive index of the sunken groove structure is lower than that of the cladding, and the sunken groove structure is of an annular structure. The optical fiber can improve the transmission quality of the optical fiber under the bending condition, increase the mode field area of the optical fiber and reduce the bending loss generated by a fundamental mode under the condition of small-size radius bending, has the capability of meeting the single-mode transmission condition under the condition of long-wave-band wavelength, and has good use potential.

Glasses with high Er2O3 concentration that exhibit low concentration quenching and low hydroxyl quenching of the emission of Er3+ near 1550 nm are described. The glasses include Al2O3 and optically non-interfering lanthanide components to disperse Er2O3 to minimize clustering of Er3+ ions as the concentration of Er2O3 in the glass composition increases to mitigate concentration quenching. Hydroxyl quenching is mitigated by calcining the batch components before melting and including a reducing agent in the batch composition. Optical fibers with cores made from the glasses exhibit high gain, low bending loss, and uniform gain across the C-band.

The present invention provides an optical fiber and a method for preparing the same, which relates to the field of optical communication technologies. The optical fiber includes, from inside to outside in sequence, a germanium-doped silica core layer, a separation layer, a fluorine-doped silica optical cladding layer, and an outer cladding layer. The separation layer is used to prevent the diffusion of germanium in the germanium-doped silica core layer and fluorine in the fluorine-doped silica optical cladding layer; wherein the fluorine-doped silica optical cladding layer is divided into three layers, which are, from inside to outside in sequence, a shallow fluorine-doped layer, a main fluorine-doped layer, and an auxiliary fluorine-doped layer, and the refractive indices of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are both greater than the refractive index of the main fluorine-doped layer. Through the layered arrangement of the fluorine-doped silica optical cladding layer, the amount of fluorine doped in SiO2 has a process of gradually changing concentration in the radial direction. This changing process can make the viscosity of the optical fiber cross-section change gradually in the radial direction. This structure can reduce the generation of optical fiber stress while obtaining low macro-bending loss of the optical fiber, and obtain an optical fiber with low loss and low bending loss.

This invention discloses a hollow-core fiber easy-splitting optical cable and its preparation method, belonging to the field of optical cable technology. It includes an outer sheath and two reinforcing members embedded within the outer sheath; the inner edge cross-section of the outer sheath is elliptical; and a hollow-core fiber ribbon disposed within the outer sheath, comprising multiple hollow-core fibers. A bridging resin layer is disposed between adjacent hollow-core fibers, with one end of the bridging resin layer connected to the hollow-core fiber and the other end forming an adhesive mesa. An adhesive layer is disposed between the two adhesive mesas, and the modulus of the adhesive layer is lower than that of the bridging resin layer. By configuring the hollow-core fibers in a ribbon-like form, this invention allows multiple hollow-core fibers to form a single structure. When the hollow-core fiber easy-splitting optical cable is subjected to pressure bending or stripping, the bridging resin layer and adhesive layer on the hollow-core fiber ribbon can distribute the pressure on the hollow-core fibers throughout the entire hollow-core fiber ribbon, resulting in uniform stress distribution. This avoids localized stress accumulation in the hollow-core fibers and alleviates the problem of excessive bending loss in hollow-core fibers.

The present invention provides a hollow-core antiresonant single-mode optical fiber. The hollow-core antiresonant single-mode optical fiber comprises: a cladding region and a core region; the cladding region comprises an outer cladding and an inner cladding region arranged sequentially from the outside to the inside; the inner cladding region comprises a cladding capillary and a teardrop-shaped inner tube disposed within the cladding capillary; the cladding capillary is tangent to the inner surface of the outer cladding and is uniformly distributed circumferentially at a first distance along the circumferential direction of the inner surface of the outer cladding, surrounding the core region; the teardrop-shaped inner tube comprises a teardrop tube structure composed of a semi-ellipse and a semi-circle, one end of the semi-ellipse is tangent to the inner surface of the cladding capillary; the cladding capillary forms a first internal tangent point with the outer cladding, and one end of the semi-ellipse forms a second internal tangent point with the cladding capillary, which coincides with the first internal tangent point. The method provided by the present invention suppresses light leakage through a nested structure, thereby enabling the optical fiber to have lower confinement loss and bending loss over a longer wavelength range while maintaining a larger gap between adjacent tubes.

This invention discloses a fluorine-free, environmentally friendly, bend-insensitive single-mode optical fiber, belonging to the field of optical fiber communication technology. The invention comprises a core layer and an outer cladding arranged sequentially from the inside out. The core layer includes a first recessed core layer and a second protruding core layer, with the second protruding core layer disposed outside the first recessed core layer. The outer cladding is a silica cladding. The refractive index of the core layer is higher than that of the outer cladding, and the refractive index profile of the core layer exhibits a step-like distribution. The relative refractive index difference ΔN1 of the first recessed core layer is smaller than the relative refractive index difference ΔN2 of the second protruding core layer. This invention, through a redesign of the optical fiber's refractive index profile, achieves a bend-insensitive optical fiber that still meets the standards in a fluorine-free state, satisfying the requirements of the G.657.A2 standard. This solves the technical problem of existing technologies using an outer fluorine cladding to reduce bending loss, which fails to meet safety and environmental protection requirements. The invention features a simple structure and excellent performance.