阅读说明：本技术 一种新型的毛细管光纤光栅及其制备方法 (Novel capillary fiber grating and preparation method thereof ) 是由 田凤军 刘光宇 姚晨宇 卢艺鹏 韩忠瑞 李立 张建中 于 2021-07-05 设计创作，主要内容包括：本发明提供一种新型毛细管光纤光栅及其制备方法,该包括光纤环形包层、光敏树脂包层、光纤纤芯,光纤纤芯位于光纤环形包层中,或悬挂于环形包层内壁上；光敏树脂包层填充于光纤中央空气孔处,折射率沿光纤长度方向呈周期性分布,且与光纤纤芯距离小于3微米或直接接触以形成弱耦合。将光敏树脂材料注入至毛细管光纤中央空气孔处形成光敏树脂包层,采用紫外激光束正向入射穿过掩模板,通过衍射形成干涉图形,并转移至光敏树脂包层中,该光敏树脂包层受到紫外曝光后折射率沿光纤长度方向呈现周期性分布,形成毛细管光纤光栅。本发明中毛细管光纤光栅对光纤纤芯无物理损伤,具有低插入损耗、免封装、高稳定性等优点,促进了光纤光栅技术进一步发展。(The invention provides a novel capillary fiber grating and a preparation method thereof, wherein the novel capillary fiber grating comprises a fiber annular cladding, a photosensitive resin cladding and a fiber core, wherein the fiber core is positioned in the fiber annular cladding or is suspended on the inner wall of the annular cladding; the photosensitive resin cladding is filled in the central air hole of the optical fiber, the refractive index is periodically distributed along the length direction of the optical fiber, and the distance between the photosensitive resin cladding and the fiber core of the optical fiber is less than 3 microns or the photosensitive resin cladding is in direct contact with the fiber core of the optical fiber to form weak coupling. Injecting a photosensitive resin material into the central air hole of the capillary fiber to form a photosensitive resin cladding, adopting ultraviolet laser beams to enter in the positive direction to penetrate through the mask plate, forming an interference pattern through diffraction, and transferring the interference pattern into the photosensitive resin cladding, wherein the refractive index of the photosensitive resin cladding is periodically distributed along the length direction of the fiber after the photosensitive resin cladding is subjected to ultraviolet exposure to form the capillary fiber grating. The capillary fiber grating has no physical damage to the fiber core, has the advantages of low insertion loss, no packaging, high stability and the like, and promotes the further development of the fiber grating technology.)

1. A novel capillary fiber grating is characterized in that: the optical fiber coupling device comprises an optical fiber annular cladding (1), a photosensitive resin cladding (2) and an optical fiber core (3), wherein the photosensitive resin cladding (2) is positioned at a central air hole (4), a grating is inscribed on the photosensitive resin cladding, the refractive index is periodically distributed along the length direction of the optical fiber, and the distance between the grating and the optical fiber core is less than 3 microns or the grating and the optical fiber core are in direct contact to form weak coupling.

2. A novel capillary fiber grating as in claim 1, wherein: in the capillary optical fiber, the fiber core is positioned in the annular cladding or suspended on the inner wall of the annular cladding through fusion.

3. A novel capillary fiber grating as in claim 1, wherein: the capillary optical fiber air hole is a single hole, a double hole or a plurality of holes.

4. A novel capillary fiber grating as in claim 1 wherein said grating is written in a photosensitive resin cladding.

5. A novel capillary fiber grating as in claim 1, wherein: the refractive index of the fiber core of the capillary optical fiber is larger than that of the annular cladding and that of the photosensitive resin cladding.

6. The method for preparing a novel capillary fiber grating according to claim 1, wherein the method comprises the following steps: the method comprises the following steps:

the method comprises the following steps: heating and breaking the capillary tube to form a conical tip with the diameter of about 2 microns, aligning the capillary tube filled with the photosensitive resin material with an air hole cladding of the capillary optical fiber by using a precise electric displacement platform, and pressurizing an injector to fill the photosensitive resin material in a central air hole (4) of the capillary optical fiber to form the photosensitive resin cladding;

step two: cutting two ends of the capillary optical fiber flatly by a cutting machine respectively, fixing the two ends on a glass slide, connecting one end of the capillary optical fiber as an input with an amplified self-radiation light source through an optical fiber coupler, and connecting the other end of the capillary optical fiber as an output with a spectrometer; fixing two ends of the capillary optical fiber on an electric displacement table respectively;

step three: an ultraviolet laser beam (7) is adopted to be incident in the positive direction to penetrate through a phase mask plate (5), interference fringes are formed through diffraction, and the interference fringes are transferred into a photosensitive resin cladding; the refractive index of the photosensitive resin cladding is periodically distributed along the length direction of the optical fiber after exposure;

step four: and maintaining ultraviolet exposure for a period of time to form a grating array of the capillary optical fiber photosensitive resin cladding, observing the spectrometer in real time in the writing process, and stopping writing until the required reflectivity and reflection peak of the spectrometer are observed to finish grating preparation.

7. The capillary fiber grating as claimed in claim 6, wherein: the period of the capillary fiber grating is half of that of the phase mask plate, and the capillary fiber grating is a long-period grating or a short-period Bragg grating.

8. The capillary fiber grating as claimed in claim 6, wherein: the distance between the phase mask plate and the writing area of the capillary optical fiber is 50-100 mu m.

9. The capillary fiber grating as claimed in claim 6, wherein: the fiber grating adopts an ultraviolet exposure-phase mask method to write the grating in the photosensitive resin cladding of the capillary fiber.

Technical Field

The invention belongs to the technical field of fiber bragg gratings, and particularly relates to a novel capillary fiber bragg grating and an ultraviolet exposure preparation method thereof.

Background

Fiber gratings are formed by periodic changes in the refractive index of the fiber core caused by exposure to an Ultraviolet (UV) laser beam. The fiber grating has the advantages of small volume, small welding loss, corrosion resistance, no influence of light intensity fluctuation, capability of realizing multipoint distributed measurement, light integration and other excellent characteristics, and the resonance wavelength of the fiber grating is sensitive to external environment variables such as temperature, stress, humidity and the like, so the fiber grating has a wide application prospect in the fields of fiber sensing and optical communication.

Currently, methods for manufacturing fiber gratings include lateral side interference exposure manufacturing methods, phase mask methods, and dot-dot writing methods. The first method is that two coherent ultraviolet beams are made to enter optical fiber doped with photosensitizer germanium in certain angle and the optical fiber is made to ultraviolet expose in interference field, and the fiber core is irradiated with ultraviolet interference fringe and has periodically changed refractive index to form grating. Wherein, the ultraviolet light source is a tunable pump dye laser, and the working wavelength range is 486-. The period of the fiber grating manufactured by the transverse side surface interference exposure manufacturing method is determined by the incident wave wavelength and the included angle of two coherent ultraviolet beams. The method has high requirements on the coherence of the light source and the stability of the environment.

The essence of the phase mask method is that a phase mask plate is close to an optical fiber, and the refractive index of the optical fiber is periodically changed by utilizing interference stripes generated by the ultraviolet light passing through the phase mask plate, so as to form the optical fiber grating. The phase mask method has the advantages that the period of the fiber grating is determined by the period of the phase mask plate and the direction of the incident beam, and is irrelevant to the wavelength of writing light.

The point-point writing method is to irradiate the optical fiber with point light source axially and expose the optical fiber at equal interval to form periodical distribution of refractive index of the optical fiber core to produce fiber grating.

With the gradual maturity of the fiber grating preparation technology, more and more researchers are invested in the research on the fiber gratings. For example, CN103412360A patent, "high frequency carbon dioxide laser assisted wet etching method for manufacturing asymmetric corrugated long period optical fiber grating", features that grating is prepared on the outer surface of optical fiber, high frequency carbon dioxide laser is used to ablate the coating layer of optical fiber point by point, then chemical etching is performed to make the surface of optical fiber form asymmetric corrugated structure along axial direction, and finally the surface of optical fiber is cleaned.

However, the fiber grating manufacturing method damages the outer surface of the fiber cladding, which greatly damages the strength of the fiber and results in the service life of the fiber. And the problems of difficult point-by-point punching operation, reduced mechanical strength, difficult packaging and poor anti-interference capability exist.

Disclosure of Invention

The invention aims to provide a novel capillary fiber grating which is in a closed space and has the advantages of stable structure, no physical damage to an inner fiber core of an optical fiber, low insertion loss, no packaging, strong anti-interference capability and the like. The invention is realized by the following technical scheme: the optical fiber comprises an optical fiber annular cladding, a photosensitive resin cladding and an optical fiber core. The photosensitive resin cladding is positioned at the central air hole, the grating is inscribed on the photosensitive resin cladding, the refractive index is periodically distributed along the length direction of the optical fiber, and the distance between the grating and the optical fiber core is less than 3 microns or the grating is directly contacted to form weak coupling.

The present invention may further comprise:

in the capillary optical fiber, the fiber core is positioned in the annular cladding or suspended on the inner wall of the annular cladding.

The air hole of the capillary optical fiber can be a single hole, a double hole or a plurality of holes.

The grating is inscribed on the photosensitive resin cladding.

The photosensitive resin cladding of the capillary optical fiber can be made of other photosensitive materials.

The refractive index of the fiber core of the capillary optical fiber is larger than that of the annular cladding and that of the photosensitive resin cladding.

The invention also aims to provide a preparation method for manufacturing the capillary fiber grating, which has the advantages of no physical damage to the inner fiber core of the optical fiber, low insertion loss, no packaging, strong interference resistance and the like.

The method comprises the following steps: the capillary was heated and snapped off to form a tapered tip, approximately 2 microns in diameter. Aligning a capillary filled with a photosensitive resin material to an air hole cladding of the capillary optical fiber by using a precise potential displacement platform, and pressurizing an injector to enable the photosensitive resin material to fill a central air hole of the capillary optical fiber to form a photosensitive resin cladding;

step two: cutting two ends of the capillary optical fiber flatly by a cutting machine respectively, fixing the two ends on a glass slide, connecting one end of the capillary optical fiber as an input with an amplified self-radiation light source through an optical fiber coupler, and connecting the other end of the capillary optical fiber as an output with a spectrometer; fixing two ends of the capillary optical fiber on an electric displacement table respectively;

step three: adopting ultraviolet laser beam to enter in the positive direction to penetrate through a mask plate, forming interference fringes through diffraction, and transferring the interference fringes into a photosensitive resin cladding; the refractive index of the photosensitive resin cladding is periodically distributed along the length direction of the optical fiber after exposure;

step four: and maintaining the ultraviolet exposure for a period of time to form a grating array of the capillary optical fiber photosensitive resin cladding. And (4) observing the spectrograph in real time in the writing process until the spectrograph has the required reflectivity and reflection peak, stopping writing, and finishing grating preparation.

In the above scheme, the period of the capillary fiber grating is half of the period of the phase mask plate, and the capillary fiber grating can be a long-period grating or a short-period Bragg grating.

In the scheme, the distance between the phase mask plate and the writing area of the capillary optical fiber is 50-100 mu m.

In the scheme, the fiber grating adopts an ultraviolet exposure-phase mask method to write the grating in the photosensitive resin cladding of the capillary fiber.

Compared with the prior art, the invention has the beneficial effects that:

in the existing fiber grating technology, a grating array is usually written in a fiber core of an optical fiber, the fiber core of the optical fiber is physically damaged and has large insertion loss, and the manufacturing method is complicated and is not easy to package. The capillary fiber grating designed by the invention provides a new way for preparing the fiber grating, and the grating is engraved in the built-in photosensitive resin cladding of the capillary fiber by an ultraviolet exposure method and sealed at the central air hole of the capillary fiber. The ultraviolet exposure method is suitable for laser sources in industrial environments, the manufacturing process is mature, and the spectral characteristics are stable. The writing mode has no physical damage to the optical fiber core, and the optical fiber is sealed in the cladding after writing, so that the optical fiber has the advantages of low insertion loss, no packaging, high stability and the like, and the development of the optical fiber grating technology to industrialized large-scale manufacturing is promoted.

Drawings

FIG. 1 is a schematic diagram of a device for manufacturing a capillary fiber grating by UV exposure.

FIG. 2(a) is a schematic cross-sectional view of a capillary fiber grating prepared by UV exposure method according to the present invention.

FIG. 2(b) is a schematic cross-sectional view of a double-hole capillary fiber grating prepared by UV exposure method according to the present invention.

FIG. 2(c) is a schematic cross-sectional view of a single-hole suspended core capillary fiber grating prepared by the UV exposure method according to the present invention.

FIG. 3 is a simulated reflection spectrum of a single-core capillary fiber grating with a grating period of 500nm and a reflection wavelength of 1550 nm.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

The invention uses ultraviolet exposure method to write the grating in the capillary fiber photosensitive resin cladding, the grating is written in the built-in photosensitive resin cladding of the capillary fiber, the fiber core and the grating are coupled, thereby realizing the modulation of the grating to the light path. The formation of the cladding grating is to inject photosensitive resin materials into the air holes, place a phase mask plate at a position 50-100 mu m away from the writing area of the capillary fiber, the direction of the mask fringe is vertical to the axial direction of the grating, ultraviolet laser beams enter the mask plate in the positive direction to form an interference pattern through diffraction and are transferred to the photosensitive resin cladding, the refractive index of the photosensitive resin materials is periodically distributed after exposure, the grating is formed in the cladding along the axial direction of the fiber, and the period of the grating is controlled by the phase mask plate. The invention has the advantages of simple preparation method, no physical damage to the fiber core of the optical fiber, low insertion loss, no encapsulation and the like, thereby improving the modulation effect on the optical path in the fiber core and being applicable to a plurality of fields of optical fiber sensing, communication and the like.

The number of air holes of the capillary optical fiber can be single hole, double holes or multiple holes.

In the interference, the grating period can be changed by adjusting the period of the phase mask plate, the etching depth of the grating is changed by selecting proper exposure time, and finally, the grating is inscribed in the photosensitive resin cladding of the capillary optical fiber by using an ultraviolet exposure method.

Example 1:

as shown in fig. 1, the process for preparing a capillary fiber grating by uv exposure comprises four layers: the optical fiber comprises an optical fiber annular cladding, a photosensitive resin cladding, an inner wall grating and an optical fiber core. The photosensitive resin cladding is positioned at the central air hole, the fiber core is positioned in the annular cladding, and the grating is inscribed on the photosensitive resin cladding. The preparation of the capillary fiber grating by the ultraviolet exposure method comprises the following steps:

step 1.1: the capillary was heated and snapped off to form a tapered tip, approximately 2 microns in diameter. Aligning the capillary filled with the photosensitive resin material to the air hole cladding of the capillary optical fiber by using a precise electric displacement platform, and pressurizing an injector to enable the photosensitive resin material to fill the central air hole of the capillary optical fiber in the step (a) of FIG. 2 to form the photosensitive resin cladding;

step 1.2: cutting two ends of the capillary optical fiber flatly by a cutting machine respectively, fixing the two ends on a glass slide, connecting one end of the capillary optical fiber as an input with an amplified self-radiation light source through an optical fiber coupler, and connecting the other end of the capillary optical fiber as an output with a spectrometer; fixing two ends of the capillary optical fiber on an electric displacement table respectively;

step 1.3: and placing a grating mask plate at a position 50-100 mu m away from the optical fiber, wherein the direction of the mask stripes is vertical to the axial direction of the grating. Adopting ultraviolet laser beam to enter in the positive direction to penetrate through a mask plate, forming an interference pattern through diffraction, and transferring the interference pattern into a photosensitive resin cladding;

step 1.4: the refractive index of the photosensitive resin cladding is periodically distributed after exposure, and a grating with the period related to the period of the phase mask plate is formed in the cladding along the axial direction of the optical fiber;

step 1.5: and maintaining the ultraviolet exposure for a period of time to form a grating array of the capillary optical fiber photosensitive resin cladding. And (4) observing the spectrograph in real time in the writing process until the spectrograph has the required reflectivity and reflection peak, stopping writing, and finishing grating preparation. The grating period is determined by the phase mask period.

The scheme can be expanded to the preparation of the capillary fiber bragg grating with a plurality of air holes.

Example 2:

the experimental apparatus is shown in fig. 1 and fig. 2(b), and the scheme of the double-hole capillary fiber grating prepared by the ultraviolet exposure method is that a fiber core is positioned at the center, two air holes are arranged at two sides of the fiber core and are symmetrically distributed, and each air hole is responsible for one grating array. The specific preparation method comprises the following steps:

step 2.1: the capillary was heated and snapped off to form a tapered tip, approximately 2 microns in diameter. Aligning the capillary filled with the photosensitive resin material to the air hole cladding of the capillary optical fiber by using a precise electric displacement platform, and pressurizing an injector to enable the photosensitive resin material to fill the central air hole of the capillary optical fiber in the step (b) of FIG. 2 to form the photosensitive resin cladding;

step 2.2: cutting two ends of the double-hole capillary optical fiber flatly by using a cutting machine respectively, fixing the two ends on a glass slide, connecting one end of the double-hole capillary optical fiber as an input with an amplified self-radiation light source through an optical fiber coupler, and connecting the other end of the double-hole capillary optical fiber as an output with a spectrometer; fixing two ends of the capillary optical fiber on an electric displacement table respectively;

step 2.3: and placing a grating mask plate at a position 50-100 mu m away from the optical fiber, wherein the direction of the mask stripes is vertical to the axial direction of the grating. An ultraviolet laser beam is adopted to be incident in the positive direction and penetrate through a mask plate, an interference pattern is formed through diffraction, and the interference pattern is transferred to two photosensitive resin claddings of the double-hole capillary optical fiber;

step 2.4: the refractive index of the photosensitive resin cladding is periodically distributed after exposure, and gratings with one period related to the period of the phase mask plate are respectively formed in the two photosensitive resin claddings along the axial direction of the optical fiber;

step 2.5: and after ultraviolet exposure is kept for a period of time, the double-period grating array of the capillary optical fiber photosensitive resin cladding is realized. And (4) observing the spectrograph in real time in the carving process until the spectrograph has the required reflectivity and reflection peak, stopping carving, and finishing grating preparation.

Example 3:

fig. 2(c) is a schematic diagram of a capillary fiber grating prepared by uv exposure in a suspended core capillary fiber, in which the fiber core is located in the fiber cladding, the grating is located in the photosensitive resin cladding, bound by the photosensitive resin material, and the air hole is located at the center. The preparation method comprises the following steps:

step 3.1: the capillary was heated and snapped off to form a tapered tip, approximately 2 microns in diameter. Aligning the capillary filled with the photosensitive resin material to the air hole cladding of the capillary optical fiber by using a precise electric displacement platform, and pressurizing the injector to enable the photosensitive resin material to fill the central air hole of the capillary optical fiber in the step (c) in FIG. 2 to form the photosensitive resin cladding;

step 3.2: cutting and flattening two ends of the capillary optical fiber with the suspended core by a cutting machine respectively, fixing the two ends on a glass slide, connecting one end of the capillary optical fiber with an amplified self-radiation light source through an optical fiber coupler as an input, and connecting the other end of the capillary optical fiber with a spectrometer as an output; fixing two ends of the capillary optical fiber on an electric displacement table respectively;

step 3.3: and placing a grating mask plate at a position 50-100 mu m away from the optical fiber, wherein the direction of the mask stripes is vertical to the axial direction of the grating. Adopting ultraviolet laser beam to enter in the positive direction to penetrate through a mask plate, forming an interference pattern through diffraction, and transferring the interference pattern into a photosensitive resin cladding;

step 3.4: the refractive index of the photosensitive resin cladding is periodically distributed after exposure, and a grating with the period related to the period of the phase mask plate is formed in the cladding along the axial direction of the optical fiber;

step 3.5: and after ultraviolet exposure is kept for a period of time, curing is carried out, and the grating array of the photosensitive resin cladding of the capillary optical fiber with the suspended core is realized. And (4) observing the spectrograph in real time in the carving process until the spectrograph has the required reflectivity and reflection peak, stopping carving, and finishing grating preparation.

The invention discloses a novel capillary fiber grating and a preparation method thereof, belonging to the technical field of fiber gratings. The capillary fiber grating comprises an optical fiber annular cladding, a photosensitive resin cladding and an optical fiber core. The fiber core is positioned in the fiber annular cladding or suspended on the inner wall of the annular cladding; the photosensitive resin cladding is filled in the central air hole of the optical fiber, the refractive index is periodically distributed along the length direction of the optical fiber, and the distance between the photosensitive resin cladding and the fiber core of the optical fiber is less than 3 microns or the photosensitive resin cladding is in direct contact with the fiber core of the optical fiber to form weak coupling. The preparation method of the fiber grating comprises the following steps: injecting a photosensitive resin material into the central air hole of the capillary fiber to form a photosensitive resin cladding, adopting ultraviolet laser beams to enter in the positive direction to penetrate through the mask plate, forming an interference pattern through diffraction, and transferring the interference pattern into the photosensitive resin cladding, wherein the refractive index of the photosensitive resin cladding is periodically distributed along the length direction of the fiber after the photosensitive resin cladding is subjected to ultraviolet exposure, and thus the capillary fiber grating is formed. The capillary fiber grating designed in the invention uses the ultraviolet exposure method to write the grating in the photosensitive resin cladding and seal the grating at the central air hole of the capillary fiber, has no physical damage to the fiber core, has the advantages of low insertion loss, no packaging, high stability and the like, and promotes the further development of the fiber grating technology.