A reflective hollow-core optical fiber atomic cell and a method of manufacturing the same

Abstract

This invention discloses a reflective hollow-core fiber atomic gas cell, comprising: a single-mode fiber, a hollow-core fiber, a lens fiber, a fiber grating, and a quartz capillary; wherein the single-mode fiber is connected to the hollow-core fiber; the lens fiber is connected to the fiber grating; the hollow-core fiber, the lens fiber, and the fiber grating are all located within the quartz capillary; the quartz capillary is filled with alkali metal atoms and a buffer gas. This invention overcomes the difficulties in assembling reflective hollow-core fiber gas cells and filling them with alkali metal atoms, meeting the application requirements of miniaturized, array-integrated atomic gas cell probes in the field of high spatial resolution weak magnetic field measurement.

Description

Technical Field

[0001] This invention belongs to the technical fields of fiber optics and quantum sensing, and particularly relates to a reflective hollow fiber atomic gas cell and its preparation method. Background Technology

[0002] Hollow-core optical fibers possess advantages such as low transmission loss and controllable dispersion, and their unique hollow core structure allows them to be filled with atomic and gaseous media. Using the hollow core of a hollow-core optical fiber atomic gas cell as a filling chamber for a gaseous medium can effectively enhance the interaction between light and the medium, showing broad application prospects in gas chromatography, fiber optic gas sensing, and precision optical sensing. However, in transmission-type hollow-core optical fiber atomic gas cells, it is inconvenient to connect a pipe for filling the working gas along the optical transmission link, which increases the sample volume. Furthermore, the working area is located in the middle of the sample, hindering the fabrication and application of miniaturized, array-integrated atomic gas cell probes. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a reflective hollow fiber atomic gas cell and its preparation method, thereby reducing the sample assembly volume, overcoming the difficulties in assembling reflective hollow fiber gas cells and filling with alkali metal atoms, and meeting the application requirements of miniaturized, array-integrated atomic gas cell probes in the field of high spatial resolution weak magnetic field measurement.

[0004] The objective of this invention is achieved through the following technical solution: a reflective hollow-core optical fiber atomic gas chamber, comprising: a single-mode optical fiber, a hollow-core optical fiber, a lens optical fiber, a fiber grating, and a quartz capillary; wherein, the single-mode optical fiber is connected to the hollow-core optical fiber; the lens optical fiber is connected to the fiber grating; the hollow-core optical fiber, the lens optical fiber, and the fiber grating are all located within the quartz capillary; the quartz capillary is filled with alkali metal atoms and a buffer gas.

[0005] In the aforementioned reflective hollow-core fiber atomic gas cell, the core of the single-mode fiber is 8–10 μm, and the single-mode fiber propagates only one mode; the inner layer of the hollow-core fiber is hollow, and the air core diameter of the hollow-core fiber is 5–100 μm, and the hollow-core fiber is used to accommodate alkali metal atoms; the incident end of the lens fiber is a conical or spherical lens, which has the function of focusing the beam; the reflectivity of the fiber grating is greater than 70%.

[0006] In the aforementioned reflective hollow fiber atomic gas chamber, the inner diameter of the quartz capillary is 5–10 μm.

[0007] In the aforementioned reflective hollow fiber atomic gas cell, alkali metal atoms serve as the working medium in the hollow fiber, while buffer gas is used to improve the atomic spin relaxation time of the hollow fiber.

[0008] In the aforementioned reflective hollow fiber atomic gas chamber, the single-mode fiber, the hollow fiber, the lens fiber, and the fiber grating are all made of silicon dioxide.

[0009] In the aforementioned reflective hollow fiber atomic gas cell, the signal light is introduced into the hollow fiber through a single-mode fiber and diverges in the form of a Gaussian beam at the end face of the hollow fiber. After spatial transmission, it is focused and converged at the incident end face of the lens fiber and enters the interior of the lens fiber. Finally, the light path is reflected at the fiber grating and re-enters the space and the hollow fiber.

[0010] A method for fabricating a reflective hollow fiber atomic gas chamber includes: fusion-switching a single-mode fiber and a hollow fiber to form a single-mode fiber-hollow fiber assembly; fusion-switching a lens fiber and a fiber grating to form a lens fiber-fiber grating assembly; placing the hollow fiber in the single-mode fiber-hollow fiber assembly into one end of a quartz capillary; fixing and sealing the hollow fiber and one end of the quartz capillary; placing the lens fiber-fiber grating assembly into the other end of the quartz capillary; adjusting the lens fiber-fiber grating assembly and spot-welding it to the quartz capillary; wherein the lens fiber is opposite to the hollow fiber, and the lens fiber-fiber grating assembly is coaxial with the single-mode fiber-hollow fiber assembly; connecting the quartz capillary to a vacuum filling system, and performing leak detection, vacuuming, and filling with alkali metal atoms and buffer gas through the vacuum filling system; and fusion-sealing the other end of the quartz capillary to obtain the reflective hollow fiber atomic gas chamber.

[0011] In the above preparation method, the fusion splicing of single-mode fiber and hollow fiber includes: tapering the hollow fiber or tapering the single-mode fiber in the reverse direction to match the mode field size of the two, and then performing laser fusion splicing after the end face is neatly cut.

[0012] In the above preparation method, fixing and sealing one end of the hollow fiber and the quartz capillary includes: inserting the fused single-mode fiber-hollow fiber assembly into the quartz capillary, placing one end of the hollow fiber inside the quartz capillary, and using a fiber optic fusion splicer to laser bonding and fusion to fix and seal the quartz capillary and the hollow fiber.

[0013] In the above preparation method, placing the lens fiber-fiber grating assembly into the other end of the quartz capillary tube, adjusting the assembly, and spot welding it to the quartz capillary tube includes: placing the lens fiber connected to the fiber grating on a six-dimensional adjustment frame; inserting one end of the single-mode fiber into one end of the bare fiber adapter; connecting the other end of the bare fiber adapter to the two ports of the fiber circulator; connecting one port of the fiber circulator to a laser; and connecting the three ports of the fiber circulator to an optical power meter; emitting a beam of light from the laser; rotating the knob of the six-dimensional adjustment frame to adjust the position of the lens fiber-fiber grating assembly; and simultaneously monitoring the reading of the optical power meter; when the optical power meter reading reaches its maximum value, fixing the lens fiber-fiber grating assembly inside the quartz capillary tube by spot welding.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] (1) The present invention uses fiber optic grating to reflect the signal light from the incident end, and the signal light enters the hollow fiber segment twice. Compared with the transmissive hollow fiber air cell, which requires two hollow fiber segments, the reflective hollow fiber air cell assembly scheme reduces the sample preparation cost and improves the assembly efficiency.

[0016] (2) The working gas filling direction of the present invention is parallel to the direction of the hollow optical fiber, which is more conducive to the filling of the working gas and its diffusion in the sample.

[0017] (3) The present invention directly fills the sample by using a quartz capillary tube containing a single-mode fiber-hollow fiber assembly and a lens fiber-fiber grating assembly, without generating other branches. The volume is determined by the outer diameter and length of the quartz capillary tube, which is beneficial to the miniaturization of the sample.

[0018] (4) The working area of ​​the reflective hollow fiber gas cell of the present invention is located at the end of the sample, which is more conducive to its use as a probe in measurement fields such as fiber gas sensing and precision optical sensing. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0020] Figure 1 This is a schematic diagram of the reflective hollow fiber optic air cell assembly scheme of the present invention;

[0021] Figure 2 This is a flowchart of the assembly method of the present invention;

[0022] Figure 3This is a schematic diagram of the high-precision adjustment process of the lens-fiber-fiber grating position;

[0023] Figure 4 This is a schematic diagram of the assembled reflective hollow fiber optic air cell prototype. Detailed Implementation

[0024] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a schematic diagram of the reflective hollow fiber optic air cell assembly scheme of the present invention; Figure 4 This is a schematic diagram of the assembled reflective hollow fiber optic air cell prototype. (See diagram below.) Figure 1 and Figure 4 As shown, the reflective hollow fiber atomic gas chamber includes: a single-mode fiber 1, a hollow fiber 2, a lens fiber 3, a fiber grating 4, and a quartz capillary tube 5; wherein, the single-mode fiber 1 is connected to the hollow fiber 2; the lens fiber 3 is connected to the fiber grating 4; the hollow fiber 2, the lens fiber 3, and the fiber grating 4 are all located inside the quartz capillary tube 5; the quartz capillary tube 5 is filled with alkali metal atoms 6 and a buffer gas.

[0026] Single-mode fiber 1: The core of the single-mode fiber is 8-10 μm, and it propagates only one mode, used for input and output signal light; Hollow-core fiber 2: The inner layer of the hollow-core fiber is hollow, and the air core diameter is 5-100 μm, used to accommodate alkali metal atoms. The unique structure of the hollow-core fiber enables the propagation of signal light in the hollow core region of the fiber, and the signal light in the hollow-core fiber maintains single-mode transmission; Lens fiber 3: A conical or spherical lens is ground on the end face of the single-mode fiber, which has the function of focusing the beam and is used to gather the spatial light emitted from the end face of the hollow-core fiber; Fiber grating 4: A grating structure with different refractive indices is periodically etched on the single-mode fiber, used to reflect signal light, with a reflectivity greater than 70%.

[0027] The inner diameter of the quartz capillary is comparable to the outer diameter of the hollow optical fiber after the coating is removed; the inner diameter of the quartz capillary is 5–10 μm.

[0028] Alkali metal atoms serve as the working medium in hollow optical fibers, while buffer gas is used to improve the atomic spin relaxation time of hollow optical fibers.

[0029] Single-mode fiber, hollow fiber, lens fiber, and fiber grating are all made of silicon dioxide and consist of a core and a cladding.

[0030] The signal light is introduced into the hollow fiber 2 through the single-mode fiber 1 and diverges in the form of a Gaussian beam at the end face of the hollow fiber 2. After spatial transmission, it is focused and converged at the incident end face of the lens fiber 3 and enters the interior of the lens fiber 3. Finally, the light path is reflected at the fiber grating 4 and re-enters the space and the hollow fiber 2.

[0031] like Figure 2 As shown in the figure, this embodiment also provides a method for preparing a reflective hollow fiber atomic gas cell, the method comprising:

[0032] Single-mode fiber 1 and hollow fiber 2 are fused together to form a single-mode fiber-hollow fiber assembly.

[0033] The lens fiber 3 and the fiber grating 4 are fused together to form a lens fiber-fiber grating assembly;

[0034] Hollow fiber 2 from the single-mode fiber-hollow fiber assembly is placed into one end of the quartz capillary 5; the hollow fiber 2 is then fixed and sealed to one end of the quartz capillary 5. Specifically, the single-mode fiber-hollow fiber assembly is placed into one end of the quartz capillary 5, with one end of the hollow fiber 2 inside. The hollow fiber segment is laser-bonded to the quartz capillary to complete the fixation and sealing.

[0035] The lens fiber-fiber grating assembly is placed into the other end of the quartz capillary tube 5. After adjustment, the lens fiber-fiber grating assembly is spot-welded to the quartz capillary tube 5. The lens fiber 3 is placed inside the quartz capillary tube 5. The lens fiber-fiber grating assembly is coaxial and close to the single-mode fiber-hollow fiber assembly. It is adjusted and spot-welded with high precision.

[0036] The quartz capillary tube 5 is connected to the vacuum filling system, which is used for leak detection, vacuuming, filling with alkali metal atoms and buffer gas.

[0037] The other end of the quartz capillary 5 is fused and sealed to obtain a reflective hollow fiber atomic gas chamber; wherein, the outer side of the fiber grating spot weld inside the quartz capillary 5 is fused and sealed and the entire assembly is removed; thus, a sample of the reflective hollow fiber atomic gas chamber is obtained.

[0038] The fusion splicing of single-mode fiber 1 and hollow fiber 2 includes: tapering the hollow fiber 2 or tapering the single-mode fiber 1 in the opposite direction to match the mode field size of the two, and then performing laser fusion splicing after the end face is neatly cut.

[0039] Fixing and sealing one end of the hollow fiber 2 and the quartz capillary tube 5 includes: neatly cutting the end face of the hollow fiber 2 and the end face of the quartz capillary tube 5; inserting the fused single-mode fiber-hollow fiber assembly into the quartz capillary tube; placing one end of the hollow fiber inside the quartz capillary tube; and using a fiber optic fusion splicer with laser bonding to fix and seal the quartz capillary tube 5 and the hollow fiber 2.

[0040] like Figure 3 As shown, placing the lens-fiber-fiber grating assembly into the other end of the quartz capillary 5, adjusting the assembly, and then spot-welding it to the quartz capillary 5 includes:

[0041] Place the lens fiber 3 connected to the fiber grating 4 on the six-dimensional adjustment frame 10;

[0042] Insert one end of the single-mode fiber 1 into one end of the bare fiber adapter;

[0043] Connect the other end of the bare fiber adapter to port 8 of the fiber optic circulator, connect port 7 of the fiber optic circulator to the laser, and connect port 9 of the fiber optic circulator to the optical power meter.

[0044] The laser emits a beam of light. Rotate the 10 knobs on the six-dimensional adjustment frame to adjust the position of the lens-fiber-fiber grating assembly, and simultaneously monitor the reading of the optical power meter.

[0045] When the optical power meter reading reaches its maximum value, the lens-fiber-fiber grating assembly is fixed inside the quartz capillary by spot welding.

[0046] The specific steps for assembling the air cell of a hollow optical fiber are as follows.

[0047] A special fiber fusion splicer is used to taper and fusion-single single-mode fiber and hollow fiber. The hollow fiber 2 is tapered or the single-mode fiber 1 is tapered in the opposite direction to match the mode field size of the two. After the end face is neatly cut, laser fusion splicing is performed to realize the fusion docking of single-mode fiber 1 and hollow fiber 2 to form a single-mode fiber-hollow fiber combination.

[0048] The lens fiber 3 and the fiber grating 4 are fused together to form a lens fiber-fiber grating assembly.

[0049] The end face of the hollow fiber 2 and the end face of the quartz capillary tube 5 are neatly cut. The fused single-mode fiber-hollow fiber assembly is inserted into the quartz capillary tube 5. One end of the hollow fiber 2 is placed inside the quartz capillary tube 5. The quartz capillary tube 5 and the hollow fiber 2 are fixed and sealed by laser bonding fusion splicing using a fiber optic fusion splicer.

[0050] The lens fiber-fiber grating assembly is placed at the other end of the quartz capillary tube 5, with the lens fiber 3 inside. The lens fiber-fiber grating assembly is coaxial and close to the single-mode fiber-hollow fiber assembly. The single-mode fiber connected to the fiber grating 4 is placed on the six-dimensional adjustment frame 10. One end of the single-mode fiber 1 in the single-mode fiber-hollow fiber assembly is inserted into a bare fiber adapter. Port 7 of the fiber circulator is connected to the laser, port 8 is connected to the bare fiber adapter with the single-mode fiber inserted, and port 9 is connected to the optical power meter. The laser emits a beam of light. The knob of the six-dimensional adjustment frame 10 is rotated to adjust the position of the lens fiber-fiber grating assembly, and the optical power meter reading is monitored simultaneously. When the optical power meter reading reaches its maximum value, the lens fiber-fiber grating assembly is fixed inside the quartz capillary tube 5 by spot welding.

[0051] Quartz capillary tube 5 is connected to the vacuum filling system for leak detection, vacuuming, filling with alkali metal atoms 6 and buffer gas;

[0052] The outer side of the spot weld of the fiber grating 4 inside the quartz capillary tube 5 is sealed by fusion and the entire assembly is removed.

[0053] A sample of a reflective hollow fiber atomic gas chamber was obtained.

[0054] This embodiment uses a fiber optic grating to reflect the signal light from the incident end, allowing the signal light to enter the hollow fiber segment twice. Compared to the transmissive hollow fiber gas cell, which requires two hollow fiber segments, the reflective hollow fiber gas cell assembly scheme reduces sample preparation costs and improves assembly efficiency. In this embodiment, the working gas filling direction is parallel to the hollow fiber direction, which is more conducive to the filling and diffusion of the working gas within the sample. This embodiment directly fills the sample through a quartz capillary containing a single-mode fiber-hollow fiber assembly and a lens fiber-fiber grating assembly, without generating other branches. The volume is determined by the outer diameter and length of the quartz capillary, which is beneficial for sample miniaturization. The working area of ​​the reflective hollow fiber gas cell in this embodiment is located at the end of the sample, making it more suitable for use as a probe in measurement fields such as fiber optic gas sensing and precision optical sensing.

[0055] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A reflective hollow fiber atomic gas cell, characterized in that... include: Single-mode fiber (1), hollow-core fiber (2), lens fiber (3), fiber grating (4), and quartz capillary (5); among which, The single-mode optical fiber (1) is connected to the hollow-core optical fiber (2); The lens fiber (3) and the fiber grating (4) are connected; The hollow fiber (2), the lens fiber (3), and the fiber grating (4) are all located inside the quartz capillary (5); The quartz capillary (5) is filled with alkali metal atoms (6) and buffer gas; The signal light is introduced into the hollow fiber (2) by the single-mode fiber (1) and diverges in the form of a Gaussian beam at the end face of the hollow fiber (2). After spatial transmission, it is focused and converged at the incident end face of the lens fiber (3) and enters the interior of the lens fiber (3). Finally, the light path is reflected at the fiber grating (4) and re-enters the space and the hollow fiber (2).

2. The reflective hollow fiber atomic gas cell according to claim 1, characterized in that: The core of the single-mode fiber (1) is 8-10 μm, and the single-mode fiber (1) propagates only one mode. The inner layer of the hollow fiber (2) is hollow, the air core diameter of the hollow fiber (2) is 5 to 100 μm, and the hollow fiber (2) is used to accommodate alkali metal atoms. The incident end of the lens fiber (3) is a conical or spherical lens, which has the function of focusing the light beam; The reflectivity of the fiber grating (4) is greater than 70%.

3. The reflective hollow fiber atomic gas cell according to claim 1, characterized in that: The inner diameter of the quartz capillary (5) is 5 to 10 μm.

4. The reflective hollow fiber atomic gas cell according to claim 1, characterized in that: Alkali metal atoms serve as the working medium in hollow optical fibers, while buffer gas is used to improve the atomic spin relaxation time of hollow optical fibers.

5. The reflective hollow fiber atomic gas cell according to claim 1, characterized in that: The single-mode fiber (1), the hollow fiber (2), the lens fiber (3), and the fiber grating (4) are all made of silicon dioxide.

6. A method for preparing a reflective hollow fiber atomic gas cell according to any one of claims 1 to 5, characterized in that... include: The single-mode fiber (1) and the hollow fiber (2) are fused together to form a single-mode fiber-hollow fiber assembly; The lens fiber (3) and the fiber grating (4) are fused together to form a lens fiber-fiber grating assembly; Place the hollow fiber (2) in the single-mode fiber-hollow fiber assembly into one end of the quartz capillary (5); fix and seal the hollow fiber (2) and one end of the quartz capillary (5); The lens fiber-fiber grating assembly is placed into the other end of the quartz capillary (5), and after adjustment, it is spot welded to the quartz capillary (5); wherein, the lens fiber (3) is opposite to the hollow fiber (2), and the lens fiber-fiber grating assembly is coaxial with the single-mode fiber-hollow fiber assembly. The quartz capillary tube (5) is connected to the vacuum filling system, and the system is used for leak detection, vacuuming, filling with alkali metal atoms and buffer gas. The other end of the quartz capillary (5) is fused together to obtain a reflective hollow fiber atomic gas chamber.

7. The preparation method according to claim 6, characterized in that: The fusion splicing of single-mode fiber (1) and hollow fiber (2) includes: Taper the hollow fiber (2) or reverse taper the single-mode fiber (1) to match the mode field size of the two, and then perform laser fusion splicing after the end face is neatly cut.

8. The preparation method according to claim 6, characterized in that: Fixing and sealing one end of the hollow optical fiber (2) to the quartz capillary tube (5) includes: The fused single-mode fiber-hollow fiber assembly is inserted into a quartz capillary tube. One end of the hollow fiber is placed inside the quartz capillary tube. The quartz capillary tube (5) and the hollow fiber (2) are fixed and sealed by laser bonding fusion splicing using a fiber optic fusion splicer.

9. The preparation method according to claim 6, characterized in that: The process of placing the lens-fiber-fiber grating assembly into the other end of the quartz capillary (5), adjusting the lens-fiber-fiber grating assembly, and spot welding it to the quartz capillary (5) includes: Place the lens fiber (3) connected to the fiber optic grating (4) on the six-dimensional adjustment frame (10); Insert one end of the single-mode fiber (1) into one end of the bare fiber adapter; Connect the other end of the bare fiber adapter to port 2 (8) of the fiber optic circulator, connect port 1 (7) of the fiber optic circulator to the laser, and connect port 3 (9) of the fiber optic circulator to the optical power meter. The laser emits a beam of light. Rotate the knob of the six-dimensional adjustment frame (10) to adjust the position of the lens fiber-fiber grating assembly and monitor the reading of the optical power meter simultaneously. When the optical power meter reading reaches its maximum value, the lens-fiber-fiber grating assembly is fixed inside the quartz capillary by spot welding.

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