CN216348360U - Tapered thin-core optical fiber mode interferometer - Google Patents
Tapered thin-core optical fiber mode interferometer Download PDFInfo
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- CN216348360U CN216348360U CN202123246406.2U CN202123246406U CN216348360U CN 216348360 U CN216348360 U CN 216348360U CN 202123246406 U CN202123246406 U CN 202123246406U CN 216348360 U CN216348360 U CN 216348360U
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Abstract
The utility model discloses a tapered thin-core optical fiber mode interferometer, relates to the technical field of optical fiber interferometers, and solves the problems that in strain-related detection, an intermode interferometer based on a thin-core optical fiber has low response characteristic and cannot meet the requirement of high-precision test, and the method comprises the following steps: the tapered fine-core optical fiber is prepared by a secondary arc discharge tapering method, so that the strain response characteristic of the dislocation structure mode interferometer is improved, the advantages of convenience in manufacture, compact structure, low cost, good stability and the like are achieved, the tapered fine-core optical fiber is suitable for strain and strain related engineering tests, and the preparation of structures with different waist cone diameters can be achieved by changing the welding speed during secondary arc discharge tapering. And furthermore, by selecting the diameter of the waist cone, wavelength demodulation and intensity demodulation switching in a strain test can be realized, the flexibility of the interferometer is enhanced, and the application range of the interferometer in the field of engineering test is expanded.
Description
Technical Field
The utility model relates to the technical field of optical fiber interferometers, in particular to a tapered thin-core optical fiber mode interferometer.
Background
Due to the cylindrical waveguide structure of the fiber and the refractive index profile of the core cladding, single or multiple modes may be excited when incident light is transmitted in the fiber. Due to different propagation constants, optical path differences can be generated between modes after transmission for a certain distance. And thus mode interference occurs when the light beams are coupled. Researchers have developed a variety of fiber optic sensors based on inter-mode interference in order to obtain high sensitivity and high resolution fiber optic sensors.
The typical mode interference type mach-zehnder interferometer mainly comprises two structures of a fiber core mismatch type and a fiber core dislocation type. The traditional fiber core mismatch type Mach-Zehnder interferometer is prepared into a multimode fiber-single mode fiber-multimode fiber structure by welding a section of single mode fiber between two sections of multimode fibers. After the incident light is expanded in the multimode fiber, a part of light enters a cladding of the single-mode fiber for transmission and is excited to emit a high-order mode; another portion of the light continues to propagate along the core of the single mode fiber in the fundamental mode. Because the refractive indexes of the core and the cladding of the optical fiber are different, a fixed optical path difference is generated after the two parts of light transmit the same distance. The two parts of light are optically coupled in the multimode optical fiber and output in the mode of intermode interference. The other type of the fiber core dislocation Mach-Zehnder interferometer is formed by welding a section of single-mode fiber between two sections of single-mode fiber in a core-shifting dislocation mode. When the incident light is transmitted to the first fusion point, a part of the light is transmitted along the core of the single mode fiber in the form of a fundamental mode, and the other part of the light enters the cladding and excites a high-order mode. Similarly, since the core and the cladding have a refractive index difference, the fundamental mode in the core and the higher-order mode in the cladding generate an optical path difference when transmitted over the same distance. When the second fusion point is reached, the two portions of light will undergo mode coupling and form inter-mode interference. Compared with the common interference type optical fiber sensor, the sensor based on the intermode interference has higher sensitivity and is suitable for high-precision physical and biochemical detection.
The fine core fiber is a single mode fiber with a core diameter of about 3 to 4 μm. When the fiber core is welded between two sections of single-mode fibers by an eccentric dislocation method, the fiber core and the cladding can be fully coupled under the condition of proper dislocation. Because of its ultra-high temperature response consistency and ultra-low temperature crosstalk characteristics, the intermodal interferometer based on the thin-core optical fiber and the related sensor and device are receiving much attention. However, in the strain-related detection, the response characteristic of the intermode interferometer based on the thin-core optical fiber is low, generally 1-2 pm/mu epsilon, and the requirement of high-precision test cannot be met.
SUMMERY OF THE UTILITY MODEL
In view of the above-mentioned problems, it is an object of the present invention to provide a tapered fine-core fiber mode interferometer.
In order to achieve the purpose, the utility model adopts the technical scheme that:
a tapered fine-core fiber mode interferometer, comprising: leading-in single mode fiber 1, deriving single mode fiber 2 and toper thin core fiber 3, the one end of toper thin core fiber 3 with leading-in single mode fiber 1 dislocation connection is in order to form first core dislocation splice point 4, the other end of toper thin core fiber 3 with lead-out single mode fiber 2 dislocation connection is in order to form second core dislocation splice point 5, and the section radius at the middle part of toper thin core fiber 3 is less than the section radius of the tip of toper thin core fiber 3, leading-in single mode fiber 1 lead-out single mode fiber 2 with toper thin core fiber 3 all includes: the fiber core and the parcel the cladding of fiber core, the section radius of the middle part of the fiber core of toper thin core fiber 3 is less than the section radius of the tip of the fiber core of toper thin core fiber 3, the fiber core of toper thin core fiber 3 with the fiber core of leading in single mode fiber 1 is connected, the fiber core of toper thin core fiber 3 with the fiber core of deriving single mode fiber 2 is connected.
In the tapered fine core fiber mode interferometer, the single mode introduction fiber 1 and the tapered fine core fiber 3 are fusion-spliced.
In the tapered fine core fiber mode interferometer, the lead-out single mode fiber 2 and the tapered fine core fiber 3 are fusion-spliced.
In the tapered fine core fiber mode interferometer, the central axis of the single mode fiber 1 and the central axis of the tapered fine core fiber 3 are parallel to each other.
In the tapered fine-core fiber mode interferometer, the central axis of the single-mode fiber 2 and the central axis of the tapered fine-core fiber 3 are parallel to each other.
In the tapered fine-core fiber mode interferometer, the central axis of the lead-in single-mode fiber 1 and the central axis of the lead-out single-mode fiber 2 are located on the same straight line.
In the tapered fine-core fiber mode interferometer, the lead-in single-mode fiber 1 is used for collecting input light, and the lead-out single-mode fiber 2 is used for emitting output light.
Due to the adoption of the technology, compared with the prior art, the utility model has the following positive effects:
(1) according to the utility model, the tapered thin-core optical fiber is prepared by the secondary arc discharge tapering method, the strain response characteristic of the dislocation structure mode interferometer is improved, and the device has the advantages of convenience in manufacturing, compact structure, low cost, good stability and the like, and is suitable for strain and strain related engineering tests;
(2) according to the utility model, the preparation of structures with different waist cone diameters can be realized by changing the welding speed during secondary arc discharge tapering. And furthermore, by selecting the diameter of the waist cone, wavelength demodulation and intensity demodulation switching in a strain test can be realized, the flexibility of the interferometer is enhanced, and the application range of the interferometer in the field of engineering test is expanded.
Drawings
FIG. 1 is a schematic diagram of a tapered fine-core fiber mode interferometer of the present invention.
FIG. 2 is a schematic side view of a tapered fine-core fiber mode interferometer of the present invention.
FIG. 3 is a graph of the fusion velocity versus the waist cone diameter for a tapered fine core fiber mode interferometer of the present invention.
FIG. 4 is a plot of normalized energy versus waist cone diameter for a tapered fine-core fiber mode interferometer of the present invention.
FIG. 5 is a plot of extinction ratio versus waist cone diameter for a tapered fine-core fiber mode interferometer of the present invention.
FIG. 6 is a strain test plot of wavelength variation for a tapered fine-core fiber mode interferometer of the present invention.
FIG. 7 is a strain test plot of the intensity variation of a tapered fine-core fiber mode interferometer of the present invention.
In the drawings: 1. leading in a single mode fiber; 2. leading out a single mode fiber; 3. a tapered fine core optical fiber; 4. a first core-shifting dislocation welding point; 5. and a second core-shifting dislocation welding point.
Detailed Description
The utility model is further described with reference to the following drawings and specific examples, which are not intended to be limiting.
Referring to fig. 1 to 7, a tapered fine-core fiber mode interferometer is shown, which includes: leading-in single mode fiber 1, derive single mode fiber 2 and the thin core fiber 3 of toper, the one end of the thin core fiber 3 of toper and leading-in single mode fiber 1 dislocation connection are in order to form first core dislocation splice point 4, the other end of the thin core fiber 3 of toper and leading-out single mode fiber 2 dislocation connection are in order to form second core dislocation splice point 5, the section radius at the middle part of the thin core fiber 3 of toper is less than the section radius of the tip of the thin core fiber 3 of toper, leading-in single mode fiber 1, derive single mode fiber 2 and the thin core fiber 3 of toper and all include: the section radius of the middle part of the fiber core of the tapered fine-core optical fiber 3 is smaller than that of the end part of the fiber core of the tapered fine-core optical fiber 3, the fiber core of the tapered fine-core optical fiber 3 is connected with the fiber core of the leading-in single-mode optical fiber 1, and the fiber core of the tapered fine-core optical fiber 3 is connected with the fiber core of the leading-out single-mode optical fiber 2.
Further, in a preferred embodiment, the lead-in single mode fiber 1 and the tapered fine core fiber 3 are fusion-spliced.
Further, in a preferred embodiment, the single mode fiber 2 and the tapered fine core fiber 3 are fusion spliced.
Further, in a preferred embodiment, the central axis of the lead-in single mode fiber 1 and the central axis of the tapered fine core fiber 3 are parallel to each other.
Further, in a preferred embodiment, the central axis of the lead-out single mode fiber 2 and the central axis of the tapered fine core fiber 3 are parallel to each other.
Further, in a preferred embodiment, the central axis of the lead-in single mode fiber 1 and the central axis of the lead-out single mode fiber 2 are located on the same straight line.
Further, in a preferred embodiment, a single mode fiber 1 is introduced for collecting input light and a single mode fiber 2 is derived for emitting output light.
The above are merely preferred embodiments of the present invention, and the embodiments and the protection scope of the present invention are not limited thereby.
The present invention also has the following embodiments in addition to the above:
in a further embodiment of the present invention, to improve the strain response characteristics of the fiber optic sensor, it is an object of the present invention to provide a mode interferometer based on a tapered fine-core fiber.
In a further embodiment of the present invention, a tapered fine-core fiber mode interferometer, wherein the tapered fine-core fiber structure comprises a lead-in single mode fiber 1, a tapered fine-core fiber 3, and a lead-out single mode fiber 2. One end of the tapered thin-core optical fiber 3 is in core-shifting fusion with the lead-in single-mode optical fiber 1, and the other end of the tapered thin-core optical fiber 3 is in core-shifting fusion with the lead-out single-mode optical fiber 2;
in a further embodiment of the utility model, all structures are heat fused by a fusion machine.
In a further embodiment of the utility model, the single mode fiber 1 is led in for collecting input light and the single mode fiber 2 is led out for emitting output light.
In a further embodiment of the present invention, please refer to fig. 1 to 4, which show a tapered thin-core fiber mode interferometer, wherein the tapered thin-core fiber structure includes a leading-in single-mode fiber 1, a tapered thin-core fiber 3, and a leading-out single-mode fiber 2, one end of the tapered thin-core fiber 3 is welded to the leading-in single-mode fiber 1 in an offset-core and staggered manner, and the other end of the tapered thin-core fiber 3 is welded to the leading-out single-mode fiber 2 in an offset-core and staggered manner;
in a further embodiment of the utility model, all structures are welded by a welding machine.
In a further embodiment of the utility model, the single mode fiber 1 is led in for collecting input light and the single mode fiber 2 is led out for emitting output light.
In a further embodiment of the utility model, the problem that the traditional wavelength demodulation interferometer needs an expensive and heavy high-precision spectrometer is solved, and the interferometer has the advantages of compact structure, simplicity in preparation and good practicability.
In a further embodiment of the utility model, the input light is transmitted into the tapered thin-core optical fiber 3 through the introduced single-mode optical fiber 1, and reaches the first core-shifting dislocation welding point 4 after being transmitted through the introduced single-mode optical fiber 1; the first core-shifting fusion point 4 is divided into two beams, one beam of light is continuously transmitted along the fiber core of the tapered fine-core optical fiber 3, and the other beam of light enters the corresponding cladding for transmission.
In a further embodiment of the present invention, when the two beams of light transmitted through the tapered fine-core optical fiber 3 reach the second core-shifting fusion-splicing point 5, due to the difference between the refractive indexes of the core and the cladding of the tapered fine-core optical fiber 3, an obvious optical path difference and phase difference are generated, and interference is formed.
In a further embodiment of the utility model, two beams of light are coupled into the derived single-mode fiber 2 through the second core-shifting dislocation welding point 5, and obvious interference fringes can be observed by deriving the single-mode fiber 2; evanescent field effect exists in the conical structure, so that the structure is more sensitive to the change of external physical quantity; and the conical structure can cause the leakage of the energy of the optical field, thereby providing possibility for intensity demodulation.
In a further embodiment of the present invention, as shown in fig. 1 and 2, the core-offset staggered welding structure is prepared by a manual mode of a welding machine; and controlling parameters such as discharge amount, stretching length, welding speed and the like to perform secondary discharge tapering on the thin-core optical fiber to obtain the tapered thin-core optical fiber 3.
In a further embodiment of the present invention, as shown in fig. 3, a cone-shaped structure having different diameters can be prepared by changing the welding speed, which is a relationship between the welding speed and the diameter of the lumbar cone. For tapered fine-core fibers 3, the leakage of light energy increases with decreasing waist cone diameter and exhibits a non-linear variation. When the waist cone diameter is less than 50 μm, loss due to light energy leakage increases rapidly. The results are shown in FIG. 4.
In a further embodiment of the present invention, shown in FIG. 5, which is a plot of extinction ratio versus waist cone diameter, a maximum extinction ratio of 23.75dB was obtained for a waist cone diameter of 30 μm.
In a further embodiment of the present invention, because of the formation of the intra-fiber mach-zehnder interference, the fringes formed by the interference are related to the free spectral range and extinction ratio according to the theory of two-beam interference. The free spectral range is affected by the length of the tapered fine core fiber 3, and the longer the length, the smaller the free spectral range, and the larger the number of fringes formed. The intensity of the two beams propagating through the cladding and the fiber core affects the extinction ratio of the fringes, which is the largest when the intensities of the two beams are equal. Due to the photoelastic effect, the applied axial strain will cause the wavelength of the interference fringe valley point to shift, and thus sense the external stress variation. In addition, because of the existence of evanescent field effect in the conical structure, the reduction of the waist cone diameter leads to further attenuation of light field energy based on the evanescent wave field principle. Therefore, in the axial strain test of the tapered fine-core fiber mode interferometer, when the waist cone diameter is smaller than 50 μm, besides the wavelength shift caused by the photoelastic effect, the intensity of the interference fringes can also have obvious change, which provides the possibility for the interferometer to implement strain sensing facing intensity demodulation.
In a further embodiment of the present invention, as shown in FIG. 6, the tapered fine core optical fiber 3 has a waist cone diameter of 60 μm. As the axial strain increases, the spectrum appears mainly as a shift in wavelength due to the photoelastic effect. At this time, the waist cone has a large diameter, so that the light field energy leakage is small and the intensity change is small. As shown in FIG. 7, the tapered fine-core fiber 3 has a 30 μm waist taper diameter, and the spectrum shows mainly the intensity change caused by the attenuation of the optical field energy as the axial strain increases. The above results indicate that the interferometer can be applied to stress/strain-related intensity demodulation detection.
In the further embodiment of the utility model, the interferometer has the advantages of simple manufacture, good stability and capability of realizing intensity demodulation, and the tapered thin-core fiber mode interferometer based on core-shifting dislocation fusion is constructed by adopting a secondary arc discharge tapering mode, so that the requirement on a high-precision spectrometer is reduced. The sensor has the advantages of sensitivity, preparation and detection, has higher potential and practicability in strain and strain-related engineering sensing and detection application, and has important values for ensuring the safety of large facilities and preventing malignant and catastrophic accidents.
While the utility model has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the utility model.
Claims (7)
1. A tapered fine-core fiber mode interferometer, comprising: leading-in single mode fiber (1), deriving single mode fiber (2) and toper thin core fiber (3), the one end of toper thin core fiber (3) with leading-in single mode fiber (1) dislocation connection is in order to form first core dislocation splice point (4), the other end of toper thin core fiber (3) with derive single mode fiber (2) dislocation connection in order to form second core dislocation splice point (5), the section radius at the middle part of toper thin core fiber (3) is less than the section radius of the tip of toper thin core fiber (3), leading-in single mode fiber (1), derive single mode fiber (2) with toper thin core fiber (3) all includes: the fiber core and the parcel the cladding of fiber core, the section radius of the middle part of the fiber core of toper thin core fiber (3) is less than the section radius of the tip of the fiber core of toper thin core fiber (3), the fiber core of toper thin core fiber (3) with the fiber core of leading in single mode fiber (1) is connected, the fiber core of toper thin core fiber (3) with the fiber core of deriving single mode fiber (2) is connected.
2. The tapered fine-core fiber mode interferometer according to claim 1, wherein the lead-in single mode fiber (1) and the tapered fine-core fiber (3) are fusion-spliced.
3. The tapered fine-core fiber mode interferometer according to claim 1, wherein the leading-out single-mode fiber (2) and the tapered fine-core fiber (3) are fusion-spliced.
4. The tapered fine-core fiber mode interferometer according to claim 1, wherein the central axis of the lead-in single mode fiber (1) and the central axis of the tapered fine-core fiber (3) are parallel to each other.
5. The tapered fine-core fiber mode interferometer according to claim 1, wherein the central axis of the derived single-mode fiber (2) and the central axis of the tapered fine-core fiber (3) are parallel to each other.
6. The tapered fine-core fiber mode interferometer according to claim 1, wherein the central axis of the lead-in single mode fiber (1) and the central axis of the lead-out single mode fiber (2) are located on the same line.
7. The tapered fine-core fiber mode interferometer according to claim 1, wherein the lead-in single mode fiber (1) is used for collecting input light and the lead-out single mode fiber (2) is used for emitting output light.
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