TWI696806B - Fiber interferometer and method for manufacturing the same - Google Patents

Abstract

A fiber interferometer includes a sensing unit having a case, a resonating chamber and a first fiber core, and two light guide units respectively connected to two ends of the sensing unit. The case delimits a resonating chamber. The first fiber core is located at a central axis of the resonating chamber. Each light guide unit includes an outer case and a second fiber core. The second fiber core is located at a central axis of the outer case of the light guide unit. The first and second fiber cores are connected in series along the same axis. One of the two light guide units includes an opening portion located on the interconnected part of the sensing unit and the light guide unit. The resonating chamber intercommunicates with the outside through the opening portion. A method for manufacturing the fiber interferometer is also provided.

Description

Optical fiber interferometer and its manufacturing method

The invention relates to a measuring instrument, in particular to an optical fiber interferometer and its manufacturing method used for precise research on measuring small displacement, refractive index, environmental temperature and pressure change.

The optical fiber interferometer system can be used to measure environmental parameters such as temperature, tension, pressure, concentration, refractive index, etc., and combined with optical fiber communication technology, it can realize remote real-time monitoring and increase detection density, which meets the needs of modern industries with large amounts of information and rapid circulation In addition, the optical fiber interferometer has obtained measurement data by interpreting the changes of the optical signal in the environment, so it has the advantages of resisting electromagnetic interference, fast response, high temperature and high pressure resistance, and can be widely used in various systems and fields.

The principle of the conventional optical fiber interferometer is to use two lights to pass through different optical paths. One of the lights is affected by the environment as a sensing signal, and the other light is not affected as a reference signal. The difference (Phase Difference) and the interference spectrum (Interference Spectrum) at the output end, by analyzing the spectrum shift can be estimated changes in environmental parameters.

The conventional optical fiber interferometer system uses acid corrosion, high temperature stretching, femtosecond laser etching, etc. to reduce the diameter of the optical fiber in the sensing section, so that the light entering the optical fiber can be split in the sensing section and then coupled to form interference, and In order to make the size of the optical fiber interferometer as small as the micron level, so as to be more flexibly used in the sensing device, it causes the technical difficulty of manufacturing the optical fiber interferometer to increase, such as: high temperature stretching The increased sensitivity of the etching process is limited, and the mechanical strength of the component is reduced to affect the actual sensing application; femtosecond laser processing has high cost and large loss, and the processing surface is rough and easy to leave environmental media, resulting in accurate sensing Degree is reduced.

In view of this, the conventional optical fiber interferometer and its manufacturing method still need to be improved.

In order to solve the above problems, the object of the present invention is to provide an optical fiber interferometer with an open resonant cavity with a simple structure, which can increase the sensing application range.

The next object of the present invention is to provide an optical fiber interferometer with low material cost and simple structure, which can reduce production costs.

Another object of the present invention is to provide a method for manufacturing an optical fiber interferometer with adjustable process parameters, which can improve sensing accuracy and product yield.

Still another object of the present invention is to provide a method for manufacturing an optical fiber interferometer, which can improve the mechanical strength of components and reduce component losses.

The use of the quantifier "a" or "one" in the elements and components described throughout the present invention is for convenience and provides the usual meaning of the scope of the present invention; in the present invention, it should be interpreted as including one or at least one, and single The concept of also includes the plural case unless it clearly means something else.

The optical fiber interferometer of the present invention includes: a sensing unit having an outer shell layer, a resonant cavity surrounded by the outer shell layer, and a first fiber core located on the central axis of the resonant cavity; and two light guides Unit, each of the light guide units has a fiber shell, and a second fiber core located on the central axis of the fiber shell, the two light guide units are axially coupled to the two ends of the sensing unit, respectively A fiber core and the two second fiber cores are connected in series on the same axis, one of the light guide units has an opening, the The opening is located at the junction of the light guide unit and the sensing unit, and the resonant cavity communicates with the external environment through the opening.

The method for manufacturing an optical fiber interferometer of the present invention includes: joining a first connection surface of a crystal fiber to a butt surface of a single-mode fiber, and cutting the crystal fiber to form a second connection surface; One end of the second connection surface is immersed in an etching solution, and after standing for an etching time, the crystal fiber is cleaned and air-dried to form a resonant cavity and an etched core in the axial direction of the crystal fiber; Grinding at a tilt angle with a polishing sheet, the end surface after grinding forms a fusion surface and a grinding surface; and the second connection surface of the crystal fiber is joined to the fusion surface of the oblique angle fiber, the first Between the two connecting surfaces and the polishing surface is the opening of the resonance cavity.

Accordingly, the optical fiber interferometer and its manufacturing method of the present invention, by etching, grinding, welding and other process methods, combine cores of different thicknesses with the resonant cavity, the produced optical fiber interferometer has high refractive index sensitivity and simplification The process is difficult and the processing cost is reduced. In addition, by controlling the process parameters such as grinding angle and etching time, the size and structure of the fiber interferometer can be controlled, and the specifications of the resonant cavity and core can be adjusted to meet the sensing needs, with a sense of improvement Effectiveness of measuring accuracy and increasing sensing application range.

The sensing unit is an etched photonic crystal fiber. The photonic crystal fiber has a core region and a fiber jacket region. The first core and the resonant cavity are the eroded core region and the resonant cavity, respectively. Slim coat area. In this way, the structure of the resonant cavity and the fiber core can be adjusted by etching, which has the effects of simplifying the difficulty of the manufacturing process and reducing the processing cost.

Wherein, the diameter of the fiber shell of each light guide unit is equal to the diameter of the outer shell layer of the sensing unit. In this way, the fiber shell and the outer shell layer can be smoothly butted, and have the effects of protecting the internal optical channel and enhancing the mechanical strength of the component.

Wherein, the diameter of the second core of each light guide unit is larger than the diameter of the first core of the sensing unit. In this way, light passing through the system can produce split light, which has the function of sensing environmental media effect.

Wherein, the angle between the first connection surface and the second connection surface and the cross-section of the crystal fiber is less than 1 degree, the angle between the butt connection surface and the cross-section of the single-mode fiber is less than 1 degree, the fusion splice and the bevel angle The angle of the cross section of the optical fiber is less than 1 degree. In this way, the crystal fiber, the single-mode fiber and the oblique angle fiber can be connected smoothly, which has the effect of avoiding structural damage during welding.

Wherein, the depth of the crystal fiber immersed in the etching solution is the length of the resonant cavity. In this way, resonant cavities of different lengths can be manufactured, which has the effect of adjusting the specifications to meet the sensing needs.

Wherein, the diameter of the etched core is inversely related to the etching time. In this way, it is possible to adjust the intensity ratio of the spectroscope by etching, which has the effect of adjusting the contrast of the depth of interference fringes.

Wherein, the end surface of the oblique optical fiber is divided into the welding surface and the polishing surface by a secant line, and the angle between the welding surface and the polishing surface is the supplementary angle of the inclination angle, and the inclination angle is 45 degrees. In this way, the opening of the resonant cavity can be formed and structural damage can be reduced as much as possible, which has the effect of maintaining the mechanical strength of the device and improving the yield of the process.

Wherein, the maximum vertical distance between the cutting line and the periphery of the welding surface is the height of one end surface, and the height of the end surface is 66.6 microns to 86 microns. In this way, it can provide space for the medium to pass through and minimize structural damage, which has the effect of maintaining the mechanical strength of the device and improving the yield of the process.

Where, when splicing the crystal fiber and the beveled fiber, the single-mode fiber is connected to the other end of the crystal fiber, and the beveled fiber is located at the other end of the end face, respectively connected to a light source and an optical power meter, when the When the etched core of the crystal fiber is completely aligned with the core of the beveled fiber, the optical power meter can detect the maximum reading. In this way, it can assist the fusion of the core, which has the effect of improving the clarity of the interference spectrum and reducing component losses.

1‧‧‧sensing unit

11‧‧‧Shell

12‧‧‧Resonant cavity

13‧‧‧First core

2‧‧‧Light guide unit

21‧‧‧ Fiber Shell

22‧‧‧second core

23‧‧‧ opening

3‧‧‧Crystal fiber

4‧‧‧Single-mode fiber

5‧‧‧Bevel fiber

C‧‧‧Core area

D‧‧‧fiber clothing area

L1‧‧‧ input light

M‧‧‧ measuring light

R‧‧‧Reference light

L2‧‧‧ output light

S1‧‧‧First connection surface

A‧‧‧ Docking

S2‧‧‧Second connection surface

Q‧‧‧Etching solution

E‧‧‧End

P‧‧‧Polishing tablets

θ‧‧‧Tilt angle

F‧‧‧welding surface

G‧‧‧Grinded surface

T‧‧‧cutting line

H‧‧‧Height

X‧‧‧Light source

W‧‧‧ Optical Power Meter

[Figure 1] An exploded perspective view of a preferred embodiment of the present invention.

[Figure 2] Front view of the sensor unit of the present invention before and after processing.

[Figure 3] A diagram of the light passing state of a preferred embodiment of the invention.

[Figure 4a] A diagram of the operation of the cutting process according to a preferred embodiment of the present invention.

[Figure 4b] A diagram of the operation of the etching process according to a preferred embodiment of the present invention.

[Figure 4c] A diagram of the operation of the polishing process according to a preferred embodiment of the present invention.

[Figure 4d] A diagram of the operation of the welding process according to a preferred embodiment of the present invention.

In order to make the above and other objects, features and advantages of the present invention more obvious and understandable, the preferred embodiments of the present invention are described below in conjunction with the attached drawings, which are described in detail as follows: Please refer to FIG. 1, It is a preferred embodiment of the optical fiber interferometer of the present invention, which includes a sensing unit 1 and two light guide units 2, the two light guide units 2 are axially coupled to the two ends of the sensing unit 1 to form Coaxial structure.

Please refer to FIGS. 1 and 2, the sensing unit 1 has an outer shell layer 11, a resonant cavity 12 surrounded by the outer shell layer 11, and a first core 13, the first core 13 is located in The central axis of the resonant cavity 12. The sensing unit 1 may be a photonic crystal fiber (Photonic Crystal Fiber, PCF) produced through cutting, etching and other processes. As shown in FIG. 2, the photonic crystal fiber is composed of silicon dioxide (Silica, SiO ₂ ). Contains a central solid core region C and a cladding region D surrounding the core. The clad region D is formed by a plurality of unconnected air holes parallel to the core region C. In the etching process, the etching solution enters the plurality of air holes, which can erode the fiber-coating area D to form the resonant cavity 12, and reduce the diameter of the core area C. The diameter can be controlled by the length of the etching time.的第一纤芯13.

Please refer to FIG. 1, the two light guide units 2 have a fiber shell 21, and A second core 22 located in the core 21, the second core 22 passing axially through the center of the core 21, the diameter of the core 21 is preferably equal to the outer shell layer 11 of the sensing unit 1 The diameter of the second core 22 is preferably larger than the diameter of the first core 13 of the sensing unit 1. The two light guide unit 2 series may be cut into two by the same single mode fiber (SMF).

The two light guide units 2 can be respectively connected to the two ends of the sensing unit 1 through a welding process, so that the first core 13 and the two second cores 22 are connected in series to form a coaxial structure optical path, and the housing The layer 11 and the fiber shell 21 are preferably flatly and axially butted to protect the inner core structure. Moreover, at one of the junctions of the light guide unit 2 and the sensing unit 1, part of the fiber shell 21 is removed to form an opening 23, and the resonance cavity 12 communicates with the external environment through the opening 23. Allowing fluid in the environment to enter the resonance cavity 12 through the opening 23 can be used to measure various environmental parameters.

Referring to FIG. 3, according to the foregoing structure, an input light L1 enters the second core 22 from any of the light guide units 2 toward the sensing unit 1 when the input light L1 reaches the first At the junction of the fiber core 13 and the second fiber core 22, the optical path is reduced due to the reduced diameter of the optical path, which generates a measurement light M traveling through the fluid medium in the resonant cavity 12, and a reference light R along the first axis coaxial The core 13 advances, and when the measurement light M and the reference light R reach the junction of the sensing unit 1 and the other light guide unit 2, the measurement light M and the reference light R are coupled into an output light L2, Since the phase difference between the measurement light M and the reference light R is caused by traveling through different optical paths, the output light L2 can be output through the second core 22 of the other light guide unit 2 to form an interference spectrum.

Please refer to FIGS. 4a to 4d, which are the process steps of the preferred embodiment of the method for manufacturing an optical fiber interferometer of the present invention, which includes joining a first connection surface S1 of a crystal fiber 3 to one of a single-mode fiber 4 Butt surface A, and cut the crystal fiber 3 to form a second connection surface S2; immerse the crystal fiber 3 from an end of the second connection surface S2 into an etching solution Q, and after standing for an etching time, clean and air-dry the The crystal fiber 3 makes the crystal fiber 3 form a resonant cavity and an etched core in the axial direction; maintain an inclined angle θ between an end face E of a beveled fiber 5 and a polishing sheet P to grind, After polishing, the end surface E is formed into a fusion surface F and a polishing surface G; the second connection surface S2 of the crystal fiber 3 is joined to the fusion surface F of the oblique optical fiber 5, the second connection surface S2 and the polishing Between the faces G is the opening of the resonant cavity.

Referring to FIG. 4a, the first connection surface S1, the second connection surface S2 of the crystal fiber 3 and the butt surface A of the single-mode fiber 4 preferably have a flat surface and no debris remains; The angle between the first connection surface S1 and the second connection surface S2 and the cross-sectional surface of the crystal fiber 3 is preferably less than 1 degree, and the angle between the butt surface A and the single-mode optical fiber 4 is preferably less than 1 degree. It is possible to avoid structural damage when the crystal fiber 3 and the single-mode fiber 4 are fused, which affects the smoothness of the optical path.

Referring to FIG. 4b, the crystal fiber 3 is preferably immersed in the etching solution Q in an inclined manner, so that the etching solution Q can easily enter the air hole of the crystal fiber 3 to improve the etching efficiency. In addition, the depth of the crystal fiber 3 immersed under the liquid surface is the length of the resonant cavity; in addition, the diameter of the etched core is inversely related to the etching time, that is, the longer the etching time will result in the diameter of the etched core The shorter, therefore, by controlling the etching length and the etching time and other process parameters, the structure of the fiber interferometer can be adjusted to change the characteristics of the interference spectrum (for example: the length of the resonant cavity is positively correlated with the fringe density of the interference spectrum; The core diameter of the crystal fiber 3 affects the contrast of the interference fringes), which can improve the accuracy of analyzing the interference spectrum.

Please refer to FIG. 4c, the end surface E of the oblique optical fiber 5 is divided by a cutting line T into the welding surface F and the grinding surface G after grinding, and the angle between the welding surface F and the grinding surface G is the Complementary angle of the inclination angle θ, the inclination angle θ is preferably 45 degrees, and the angle between the fusion surface F and the cross-section of the oblique optical fiber 5 is preferably less than 1 degree; in addition, the cut line T and the periphery of the fusion surface F The maximum vertical distance is the height H of the end face. The height H of the end face can be 66.6 microns to 86 microns. It can ensure that the opening of the resonant cavity can be used for medium circulation, and at the same time reduce the structural damage to the oblique fiber 5 and maintain fiber interference. The mechanical strength of the instrument and improve the process yield.

Referring to FIG. 4d, when the crystal fiber 3 and the oblique angle fiber 5 are spliced, the other end of the crystal fiber 3 can be connected to the single-mode fiber 4 and the oblique angle fiber 5 is located at the other end of the end face E One end is connected to a light source X and an optical power meter W, respectively, so that the optical power meter W passes through the crystal fiber 3, the single mode fiber 4 and the oblique fiber 5 to measure the light intensity of the light source X, when the crystal fiber 3 When the etched core and the core of the oblique optical fiber 5 are completely aligned, the optical path formed by connecting the cores is clear, the optical power meter W can detect the maximum reading, which can assist the crystal fiber 3. During the fusion splicing process with the oblique optical fiber 5, a slight misalignment of the core joint can be avoided, which can improve the clarity of the interference spectrum and reduce component losses.

In summary, the optical fiber interferometer and its manufacturing method of the present invention, by etching, grinding, welding and other manufacturing methods, combine cores of different thicknesses with the resonant cavity, and the produced optical fiber interferometer has high refractive index sensitivity 、Simplify the process difficulty and reduce the processing cost. In addition, by controlling the process parameters such as grinding angle and etching time, the size and structure of the optical fiber interferometer can be controlled, and the specifications of the resonant cavity and the core can be adjusted according to the sensing needs. Improve the accuracy of sensing and increase the scope of sensing applications.

Although the present invention has been disclosed using the above-mentioned preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art without departing from the spirit and scope of the present invention, making various changes and modifications relative to the above-mentioned embodiments still belongs to this The technical scope of the invention is protected, so the scope of protection of the present invention shall be subject to the scope defined in the appended patent application.

1‧‧‧sensing unit

11‧‧‧Shell

12‧‧‧Resonant cavity

13‧‧‧First core

2‧‧‧Light guide unit

21‧‧‧ Fiber Shell

22‧‧‧second core

23‧‧‧ opening

Claims (11)

An optical fiber interferometer includes: a sensing unit having a shell layer, a resonance cavity surrounded by the shell layer, and a first fiber core located on a central axis of the resonance cavity; and two light guide units, Each of the light guide units has a fiber shell and a second fiber core located on the central axis of the fiber shell, the two light guide units are axially coupled to the two ends of the sensing unit, the first fiber The core and the two second fiber cores are connected in series on the same axis, one of the light guide units has an opening, the opening is located at the junction of the light guide unit and the sensing unit, and the resonant cavity passes through the opening Connect the external environment. The optical fiber interferometer as described in item 1 of the patent application scope, wherein the sensing unit is an etched photonic crystal fiber, the photonic crystal fiber has a core area and a fiber coat area, and the first core and The resonant cavity is the eroded core region and the fiber jacket region, respectively. An optical fiber interferometer as described in item 1 of the patent application range, wherein the diameter of the fiber shell of each light guide unit is equal to the diameter of the outer shell layer of the sensing unit. The optical fiber interferometer according to item 1 of the patent application scope, wherein the diameter of the second core of each light guide unit is larger than the diameter of the first core of the sensing unit. A method for manufacturing an optical fiber interferometer, comprising: joining a first connection surface of a crystal fiber to a butt surface of a single-mode fiber, and cutting the crystal fiber to form a second connection surface; switching the crystal fiber from the second One end of the connection surface is immersed in an etching solution, and after standing for an etching time, the crystal fiber is cleaned and air-dried to form a resonant cavity and an etched core in the axial direction of the crystal fiber; Polishing discs are maintained at an inclined angle for grinding, and the end surface after grinding forms a fusion surface and a grinding surface; and the second connection surface of the crystal fiber is joined to the fusion surface of the oblique angle fiber, the second connection surface Between the grinding surface and the opening of the resonant cavity. The method for manufacturing an optical fiber interferometer as described in item 5 of the patent application range, wherein the angle between the first connection surface and the second connection surface and the cross section of the crystal fiber is less than 1 degree, and the butting surface and the single-mode fiber The angle between the cross-sectional plane is less than 1 degree, and the angle between the fusion plane and the cross-sectional plane of the oblique optical fiber is less than 1 degree. The method for manufacturing an optical fiber interferometer as described in item 5 of the patent application range, wherein the depth of the crystal fiber immersed in the etching solution is the length of the resonant cavity. The method for manufacturing an optical fiber interferometer as described in item 5 of the patent application scope, wherein the diameter of the etched core is inversely related to the etching time. The method for manufacturing an optical fiber interferometer as described in item 5 of the patent application range, wherein the end surface of the beveled optical fiber is divided by a secant into the welding surface and the polishing surface, and the angle between the welding surface and the polishing surface is the The supplementary angle of the tilt angle is 45 degrees. The method for manufacturing an optical fiber interferometer as described in item 9 of the patent application range, wherein the maximum vertical distance between the cutting line and the periphery of the welding surface is the height of one end surface, and the height of the end surface is 66.6 microns to 86 microns. The method for manufacturing an optical fiber interferometer as described in item 5 of the patent application scope, wherein when splicing the crystal fiber and the beveled fiber, the other end of the crystal fiber is connected to the single-mode fiber, and the beveled fiber is located at the end face At the other end, a light source and an optical power meter are respectively connected. When the etched core of the crystal fiber is completely aligned with the core of the beveled fiber, the optical power meter can detect the maximum reading.

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