CN102866468A - Hollow photonic crystal optical fiber gas absorption cell device and manufacturing method thereof - Google Patents

Abstract

A hollow photonic crystal fiber gas absorption cell device and its manufacturing method. The device is composed of a hollow photonic crystal fiber, a protective sleeve, an airtight chamber, a vacuum gauge, a vacuum valve, a window glass, a coupling mirror and an adjustment component. The invention utilizes the characteristics that the hollow photonic crystal fiber is flexible and bendable, and the fiber core can be filled with gas, and the quantitative injection of gas is realized by using an airtight chamber, a vacuum gauge, and a vacuum threshold, and the light beam is coupled into the hollow photonic crystal fiber through a coupling mirror and a window glass. , sealed with optical fiber metallization and feed-through welding process, the device of the present invention has the characteristics of compact structure, high reliability, controllable air pressure, reusable, high coincidence degree of beam cross-section and gas cross-section. It can be used for gas spectrum analysis experiments and gas absorption cells for frequency-stabilized laser frequency reference.

Description

Hollow photonic crystal fiber gas absorption cell device and manufacturing method thereof

technical field

The invention relates to a hollow photonic crystal fiber gas absorption cell device and a manufacturing method thereof, which can be applied to the fields of gas absorption spectrum analysis, laser frequency stabilization, cold atomic clocks and the like.

Background technique

In the fields of gas absorption spectrum analysis, laser frequency stabilization, and cold atomic clocks, a laser with a specific frequency and high frequency stability is required. Using gas absorption lines as a frequency reference to stabilize frequency is a method to realize this laser.

The gas absorption cell is one of the necessary components to use the gas absorption line as a frequency reference to achieve laser frequency stabilization. For some gases with relatively weak absorption intensity, a longer interaction distance between light and gas is required. In addition, especially for spaceborne, airborne, and vehicle-mounted applications, there are requirements for weight and shock resistance for frequency-stabilized lasers. Therefore, the gas absorption cell must have the characteristics of small size, light weight, and high robustness. Typical representatives of traditional gas absorption cells are White type absorption cells (refer to prior art [1]: J.U.White. "Long optical paths of large aperture", J.O.S.A, Vol.32, May 1942) and Herriott type absorption cells (refer to prior art Technology [2]: D. Herriott, H. Kogelnok, and R. Kompfner, "Off-Axis Paths in SphericalMirror Interferometers", Applied Optics, Vol.3, Iss.4, 1 April 1964), all need to control the beam incident angle , the use of cavity mirrors allows light to achieve multiple reflections in space to increase the interaction distance between light and gas, and it is difficult to ensure optical stability; these two structures are large in size and heavy in weight, and it is difficult to make airtightness ; And easily damaged, the reliability is not high. Therefore, the gas absorption cells of these two structures cannot meet the special requirements for optical stability, airtightness, and reliability of spaceborne, airborne, and vehicle-mounted applications.

P.S.Light et al. proposed a scheme to realize small volume, light weight and high robustness of acetylene gas absorption cell by using hollow-core photonic crystal fiber (refer to prior art [3]: P.S.Light, F.Couny, and F.Benabid. "Low optical insertion-loss and vacuum-pressure all-fiberacetylene cell based on hollow-core photonic crystal fiber", Optics Letters, Vol.31, No.17, 1 September 2006), this scheme is first in the hollow-core photonic crystal fiber Fill the acetylene gas with the specified pressure, and then fill it with helium until the pressure is slightly higher than the ambient pressure, then weld the two ends of the hollow-core photonic crystal fiber to the ordinary single-mode fiber, and finally wait for the helium to penetrate and diffuse through the cladding of the hollow-core photonic crystal fiber To the outside of the optical fiber, the fabrication of the hollow photonic crystal optical fiber gas absorption cell is completed. However, this solution has the following problems: once the gas absorption cell is fabricated, the air pressure or gas type in the gas cell cannot be changed. Therefore, this scheme can only make gas absorption cells that determine the various types of gases and determine the air pressure, and is not suitable for the experimental link of frequency stabilization parameter optimization that needs to adjust the air pressure.

Poberezhskiy IY et al. proposed a solution for a hollow photonic crystal fiber gas absorption cell that can realize gas filling and discharging and air pressure control (refer to the prior art [4]: Ilya Y.Poberezhskiy, PatrickMeras, and et al. "Compact and robust refilling and connectorization of a hollow core photonic crystal fiber gas reference cells", The 20 ^th Annual Meeting of the IEEE Laser and Electro-Optics Society, 2007), this scheme aligns the hollow core photonic crystal fiber with the multimode fiber with a silicon-based V-groove, Optical coupling is realized, and there is a little space between the two fiber ends for filling and discharging gas. The aligned optical fiber and V-groove are placed on an aluminum plate, and the optical fiber joint is protected by a quartz tube and sealed with epoxy resin , the quartz tube can be connected to a valve, a vacuum device or an inflatable device to realize an absorption pool that can be filled and discharged with air pressure control. However, the airtightness and firmness of the epoxy resin sealing method are inferior to those of the metal welding method; in addition, the fiber diameter of the hollow-core photonic crystal fiber is different from that of the ordinary single-mode or multi-mode fiber, and the V-groove for fiber alignment is realized. It is impossible to realize it by machining, and it must be made by photolithography.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art, and provide a hollow photonic crystal fiber gas absorption cell device and a manufacturing method thereof. Robust, gas-filled and gas-controlled hollow-core photonic crystal fiber gas absorption cell.

Technical solution of the present invention is as follows:

A hollow photonic crystal fiber gas absorption cell device is characterized in that the device is composed of a hollow photonic crystal fiber and airtight joints at both ends thereof, and the airtight joints have the same structure:

The airtight joint includes a protective cover, an airtight chamber, a vacuum gauge, a vacuum valve, a window glass, an external adjustment assembly, an internal adjustment assembly, and a coupling mirror. The connection relationship of the above components is as follows: the airtight chamber has an optical fiber interface, The ventilation tube and the window of the airtight chamber, the optical fiber interface is opposite to the window of the airtight chamber, the optical fiber interface is used to connect the hollow photonic crystal fiber, and the connection part between the hollow photonic crystal fiber and the optical fiber interface is protected by a protective sleeve. The vacuum gauge and vacuum valve are installed on the vent pipe, the window glass is coated with a ring-shaped metal film, and connected with the window of the airtight chamber by metal welding process, and the external adjustment assembly is connected from the window of the airtight chamber The direction and the airtight chamber are fixed with screws, the inner adjustment assembly is a hollow cylinder with fine threaded components outside the cylinder, and the coupling mirror is fixed inside the cylinder of the inner adjustment assembly On the end, the outer end of the inner adjustment component is connected with an ordinary optical fiber with a FC connector. The outer fine thread of the inner adjustment component is screwed into the inner thread of the outer adjustment component, and the inner adjustment component is rotated to change the inner thread. The matching depth of the adjustment assembly and the outer adjustment assembly, the position of the inner adjustment assembly is locked by the radial screw of the outer adjustment assembly.

The hollow photonic crystal fiber is connected to the airtight chamber by a feed-through welding process, that is, the hollow photonic crystal fiber is inserted into the optical fiber interface of the airtight chamber after the optical fiber metallization process, and is welded by a feed-through welding process. connect.

The manufacturing method of the hollow photonic crystal fiber gas absorption cell device is characterized in that the method comprises the following steps:

1), the hollow photonic crystal fiber is connected with the airtight connector:

①Firstly, a layer of annular metal film is coated on the area where the window glass contacts the airtight chamber by magnetron sputtering, and then the window glass is welded to the window of the airtight chamber by a metal welding process;

② Install a vacuum gauge and a vacuum valve on the vent pipe of the airtight chamber;

③ Select a suitable length of coating layer removed from one end of the hollow-core photonic crystal fiber, and apply protective glue on the end face to seal the opening of the end face of the hollow-core photonic crystal fiber to prevent chemical reagents from entering the hollow-core photonic crystal fiber during the metallization process of the fiber The interior of the hollow photonic crystal fiber is blocked by using the existing optical fiber metallization process to plate a metal layer on the surface of the hollow photonic crystal fiber that has been removed from the coating layer, and then cut off the head coated with the protective glue, and the hollow photonic crystal fiber that has undergone the above treatment One end of the photonic crystal fiber is inserted into the fiber interface of the airtight chamber and welded with the existing feed-through welding process, and finally the protective sleeve is put on the outside of the connection;

④Fix the coupling mirror on the inner adjustment assembly with optical epoxy glue, assemble the outer adjustment assembly and the inner adjustment assembly in sequence, and the outer end of the inner adjustment assembly is connected with a common optical fiber with FC connector;

2) The other end of the hollow-core photonic crystal fiber is connected to the airtight joint according to step 1) above;

3) Adjust the optical path of the connected hollow photonic crystal fiber gas absorption cell device: connect the ordinary optical fiber of one of the airtight joints to the laser; the external adjustment component of the other airtight joint is temporarily separated from the airtight chamber. Use an optical power meter to detect the optical power emitted from the hollow photonic crystal fiber at the window of the secret room; adjust the position of the outer adjustment component and the inner adjustment component of the previous airtight joint until the optical power detected by the optical power meter is maximum; then put the optical power meter Remove it, connect the outer adjustment component of the latter airtight joint with the airtight chamber, connect an optical power meter behind the ordinary optical fiber, and adjust the positions of the outer adjustment component and the inner adjustment component until the optical power detected by the optical power meter reaches the maximum , the optical path adjustment is completed, and the production is completed.

The airtight chamber is used to maintain the airtightness inside the hollow photonic crystal fiber, and the air pressure inside the hollow photonic crystal fiber can be adjusted and controlled by a vacuum gauge and a vacuum valve. In addition, the ventilation pipe of the airtight chamber can be sealed, and the vacuum gauge can be removed. , vacuum valve, cylinder and vacuum pump, used as a small gas absorption pool.

The outer adjustment component and the inner adjustment component are used to adjust the relative position of the hollow-core photonic crystal fiber and the ordinary fiber, so as to ensure the maximum coupling efficiency between the two.

Compared with the prior art, the present invention has the following advantages and positive effects:

1. Compared with the prior art [1] and [2], the hollow photonic crystal optical fiber gas absorption cell of the present invention is small in volume, light in weight, firm and reliable in structure, and high in air tightness, and is more suitable for spaceborne and airborne Use in harsh environments.

2. Compared with the prior art [3], the hollow photonic crystal fiber gas absorption cell of the present invention can replace the gas and change the air pressure, and can be used in the experiment link of optimizing the frequency stabilization parameters of the air pressure.

3. Compared with the prior art [4], the hollow photonic crystal fiber gas absorption cell of the present invention is sealed with a feed-through welding process and a metal welding process, and the airtightness and firm structure are better than epoxy resin or other adhesives The method is better, in addition, no V-groove is used, no photolithography process is required, and the processing is simpler.

In a word, the device of the present invention has the characteristics of compact structure, high reliability, controllable air pressure, reusability, and high coincidence degree of beam cross-section and gas cross-section. Can be used for gas spectrum analysis experiments, gas absorption cells for frequency-stabilized laser frequency reference,

Description of drawings

Fig. 1 is the structural representation of hollow photonic crystal fiber gas absorption cell device of the present invention

Fig. 2 is a structural schematic diagram of another embodiment of the structure of the hollow photonic crystal fiber gas absorption cell device of the present invention

Detailed ways

The present invention will be further described below in conjunction with examples and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

Please refer to FIG. 1 first. FIG. 1 is a schematic diagram of the structure of the hollow photonic crystal fiber gas absorption cell device of the present invention. It can be seen from the figure that the hollow photonic crystal fiber gas absorption cell device of the present invention is composed of a hollow photonic crystal fiber 1 and airtight joints at both ends thereof, and the airtight joints have the same structure:

The airtight joint includes a protective cover 2, an airtight chamber 3, a vacuum gauge 4, a vacuum valve 5, a window glass 6, an external adjustment assembly 7, an internal adjustment assembly 8, and a coupling mirror 9. The connection relationship of the above components is as follows: Described airtight chamber 3 has optical fiber interface 3a, air pipe 3b and airtight chamber window 3c, and described optical fiber interface 3a is opposite to airtight chamber window 3c, and described optical fiber interface 3a is used for connecting described hollow photonic crystal fiber 1, and this hollow The connection part between the photonic crystal fiber 1 and the optical fiber interface 3a is protected by a protective cover 2, the vacuum gauge 4 and the vacuum valve 5 are installed on the vent pipe 3b, the window glass 6 is coated with a ring-shaped metal film, It is connected with the airtight chamber window 3c by a metal welding process, the outer adjustment assembly 7 is fixed with the airtight chamber 3 from the direction of the airtight chamber window 3c, and the inner adjustment assembly 8 is a hollow cylinder , a member with fine threads outside the cylinder, the coupling mirror 9 is fixed on the inner end of the cylinder of the inner adjustment assembly 8, the outer end of the inner adjustment assembly 8 is connected with a common optical fiber 10 with an FC connector, The external fine thread of the internal adjustment assembly 8 is screwed into the internal thread of the external adjustment assembly 7, and the depth of cooperation between the internal adjustment assembly 8 and the external adjustment assembly 7 can be changed by the rotation of the internal adjustment assembly 8. The position of the assembly 8 is locked by the radial screws of the outer adjustment assembly 7 .

The connection between the hollow photonic crystal fiber 1 and the airtight chamber 3 is connected by a feed-through welding process, that is, one end 1a of the hollow photonic crystal fiber 1 is inserted into the airtight chamber 3 after being processed by optical fiber metallization. The optical fiber interface 3a is connected by a feed-through welding process.

The outer adjustment component 7 and the airtight chamber 3 are fixed with screws, and the displacement in the direction of the contact surface can be slightly adjusted by means of machining tolerances. The inner adjustment component 8 and the outer adjustment component 7 are connected by fine threads, and the inner adjustment component 8 and the outer adjustment can be changed by rotation. The matching depth of the component 7 can be locked by the external adjustment component 7 with screws to lock the position of the internal adjustment component 8, the coupling mirror 9 is fixed on the internal adjustment component 8, and the ordinary optical fiber 10 of the FC connector is connected to the internal adjustment component 8.

During use, one end 1a of the hollow-core photonic crystal fiber 1 is used as a gas inlet, and the vent pipe 3b of the connected airtight chamber 3 is connected with a gas bottle to realize filling of gas; the other end of the hollow-core photonic crystal fiber 1 is a gas outlet. The vent pipe 3b at the end is connected with a vacuum pump to realize gas extraction.

The airtight chamber 3 is used to maintain the airtightness inside the hollow photonic crystal fiber 1 , and the air pressure inside the hollow photonic crystal fiber 1 is adjusted and controlled by a vacuum gauge 4 and a vacuum valve 5 installed on the vent pipe 3 b.

In addition, the ventilation pipe of the airtight chamber can be sealed, the vacuum gauge and the vacuum valve can be removed, and it can be used as a small and exquisite gas absorption cell, as shown in Figure 2.

The outer adjusting component 7 and the inner adjusting component 8 are used to adjust the relative position of the photonic crystal fiber 1 and the common optical fiber 10 to ensure the maximum coupling efficiency between the two.

The specific manufacturing steps of the hollow photonic crystal fiber gas absorption cell device of the present invention are as follows:

1. The hollow photonic crystal fiber 1 is connected to the airtight joint:

1. Firstly, the area where the window glass 6 contacts the airtight chamber 3 is coated with an annular metal film by magnetron sputtering, and then the window glass 6 is welded to the window 3c of the airtight chamber 3 by a metal welding process;

②A vacuum gauge 4 and a vacuum valve 5 are installed on the ventilation pipe 3b of the airtight chamber 3;

③ Select a suitable length of the coating layer removed from one end 1a of the hollow-core photonic crystal fiber 1, and apply protective glue on the end face to seal the opening of the end face of the hollow-core photonic crystal fiber 1 to prevent chemical reagents from entering the hollow core during the metallization process of the optical fiber. The inside of photonic crystal fiber 1 causes blockage; Use existing optical fiber metallization process to have removed coating layer on the surface of hollow photonic crystal fiber 1 one end 1a and plate metal layer, then the head that is coated with protective glue is cut off, Insert one end 1a of the above-mentioned processed hollow photonic crystal fiber 1 into the optical fiber interface 3a of the airtight chamber 3 and weld it with the existing feed-through welding process, and finally put the protective sheath 2 on the outside of the connection;

④ Fix the coupling mirror 9 on the inner adjustment component 8 with optical epoxy glue, assemble the outer adjustment component 7 and the inner adjustment component 8 in sequence, and the outer end of the inner adjustment component 8 is connected with the ordinary optical fiber 10 with FC connector;

2. The other end of the hollow photonic crystal fiber 1 is connected according to the above step 1;

3. Adjust the optical path of the connected hollow photonic crystal fiber gas absorption cell device: connect the ordinary optical fiber 10 of one of the airtight joints to the laser; the external adjustment component 7 of the other airtight joint is temporarily separated from the airtight chamber 3, Use an optical power meter to detect the optical power emitted from the hollow photonic crystal fiber 1 at the window 3c of the airtight chamber; adjust the positions of the outer adjustment assembly 7 and the inner adjustment assembly 8 of the previous airtight joint until the optical power detected by the optical power meter is the largest Then remove the optical power meter, connect the outer adjustment assembly 7 of the last airtight joint with the airtight chamber 3, connect the optical power meter after its ordinary optical fiber 10, and adjust the positions of its outer adjustment assembly 7 and inner adjustment assembly 8 , until the optical power detected by the optical power meter reaches the maximum, the optical path adjustment is completed, and the manufacture of the hollow photonic crystal fiber gas absorption cell device of the present invention is completed.

The operating method of the present invention is as follows:

1. One of the vent tubes 3b of the airtight joint is connected to the gas cylinder as the gas inlet; the vent tube 3b of the other airtight joint is connected to the vacuum pump as the gas outlet;

2. Before filling the experimental gas, use a vacuum pump to evacuate the airtight joints of the hollow photonic crystal fiber 1 and its two ends, and connect the helium gas cylinder to the other vent pipe 3b, and use helium gas to the hollow photonic crystal fiber. 1 Rinse, and finally vacuumize with a vacuum pump;

2. Change the air pipe 3b into the cylinder of the gas required for the experiment, and fill it with the experimental gas. The air pressure reading of the vacuum gauge 2 on the air pipe 3b at the gas inlet can be slightly greater than the required air pressure, and wait for the gas to slowly flow to the gas outlet. Until the pressure reading of the vacuum gauge 2 at the gas inlet is equal to the pressure reading of the vacuum gauge 2 at the gas outlet, then alternately turn on the vacuum pump and the gas cylinder to pump and inflate until the pressure readings at the gas inlet and gas outlet are both the required pressure. When the gas is filled, it can be used as a gas absorption cell for experiments;

3. When it is necessary to make an absorption pool with a compact structure, clamp and flatten the vent tube 3b to prevent air leakage, cut off the vacuum gauge 4 and vacuum valve 5, and then fill the vent tube 3b with solder to seal it, as shown in Figure 2.

The invention adopts optical fiber metallization, feed-through welding and metal welding processes to realize the production of the gas absorption pool, which can well ensure the airtightness of the absorption pool and the firmness of the structure. In addition, its compact structure, light weight and small size can It is well suited to the spaceborne application environment. The design structure of the airtight chamber can meet the adjustment of the air pressure during the experimental stage, and the ventilation tube can also be sealed and used as a small gas absorption pool.

Claims (3)

1. A hollow photonic crystal fiber gas absorption cell device, characterized in that the device is made of a hollow photonic crystal fiber (1) and airtight joints at both ends thereof, and the airtight joints have the same structure: The airtight joint includes a protective cover (2), an airtight chamber (3), a vacuum gauge (4), a vacuum valve (5), a window glass (6), an outer adjustment component (7), an inner adjustment component (8) , coupling mirror (9), the connection relationship of the above components is as follows: the airtight chamber (3) has an optical fiber interface (3a), a vent pipe (3b) and an airtight chamber window (3c), and the optical fiber interface (3a) Opposite to the airtight chamber window (3c), the optical fiber interface (3a) is used to connect the hollow photonic crystal fiber (1), and the connection part between the hollow photonic crystal fiber (1) and the optical fiber interface (3a) is covered with a protective sleeve (2) protection, install the vacuum gauge (4) and vacuum valve (5) on the vent pipe (3b), the window glass (6) is coated with a ring-shaped metal film, and the The airtight chamber window (3c) is connected by metal welding process, the outer adjustment assembly (7) is fixed with the airtight chamber (3) from the direction of the airtight chamber window (3c), and the inner adjustment assembly (8 ) is a hollow cylinder with fine threaded components outside the cylinder, the coupling mirror (9) is fixed on the inner end of the cylinder of the inner adjustment assembly (8), the inner adjustment assembly (8) The external end of the ordinary optical fiber (10) with FC connector, the external fine thread of the internal adjustment component (8) is screwed into the internal thread of the external adjustment component (7), and the internal adjustment component (8) Rotate to change the matching depth between the inner adjustment component (8) and the outer adjustment component (7), and the position of the inner adjustment component (8) is locked by the radial screw of the outer adjustment component (7). 2. The hollow photonic crystal fiber gas absorption cell device according to claim 1, characterized in that the hollow photonic crystal fiber (1) and the airtight chamber (3) are connected by a feed-through welding process, that is, the The hollow photonic crystal optical fiber (1) is inserted into the optical fiber interface (3a) of the airtight chamber (3) after being treated with optical fiber metallization, and connected by a feed-through welding process. 3. the manufacture method of hollow photonic crystal fiber gas absorption cell device described in claim 1 or 2, it is characterized in that the method comprises the steps: 1), the hollow photonic crystal fiber (1) is connected with the airtight joint: ①Firstly, coat the area where the window glass (6) touches the airtight chamber (3) with a ring-shaped metal film by magnetron sputtering, and then weld the window glass (6) to the airtight chamber (3) by metal welding process. on window (3c); ② Install the vacuum gauge (4) and vacuum valve (5) on the air pipe (3b) of the airtight chamber (3); ③ Select a suitable length of the coating layer removed from one end (1a) of the hollow-core photonic crystal fiber (1), and apply protective glue on the end face to seal the opening of the end face of the hollow-core photonic crystal fiber (1) to prevent metallization in the fiber. During the process, chemical reagents enter the interior of the hollow-core photonic crystal fiber (1) to cause blockage; use the existing optical fiber metallization process to plate a metal layer on the surface of the hollow-core photonic crystal fiber (1) where the coating layer has been removed, Then cut off the head coated with protective glue, insert one end (1a) of the above-mentioned processed hollow photonic crystal fiber (1) into the optical fiber interface (3a) of the airtight chamber (3) and use the existing feedthrough welding process Welding, and finally put a protective cover (2) on the outside of the joint; ④Fix the coupling mirror (9) on the inner adjustment assembly (8) with optical epoxy glue, assemble the outer adjustment assembly (7), the inner adjustment assembly (8) in sequence, and the outer terminal of the inner adjustment assembly (8) Common optical fiber (10) with FC connector; 2), the other end of the hollow photonic crystal fiber (1) is connected to the airtight connector according to the above step 1); 3) Adjust the optical path of the connected hollow photonic crystal fiber gas absorption cell device: connect the ordinary optical fiber (10) of one of the airtight joints to the laser; the external adjustment component (7) of the other airtight joint and the airtight chamber (3) Temporarily separate, and use an optical power meter to detect the optical power emitted from the hollow photonic crystal fiber (1) at the window (3c) of the airtight chamber; adjust the outer adjustment component (7) and the inner adjustment component (7) of the previous airtight joint ( 8) until the optical power detected by the optical power meter reaches the maximum; then remove the optical power meter, and connect the outer adjustment component (7) of the latter airtight joint with the airtight chamber (3), and connect the ordinary optical fiber (10 ) and connect the optical power meter, adjust the positions of the outer adjustment component (7) and the inner adjustment component (8) until the optical power detected by the optical power meter reaches the maximum, the optical path adjustment is completed, and the production is completed.

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