Hollow-core optical fiber coupling system

Abstract

The hollow-core optical fiber coupling system comprises a laser light source, a coupling device and a hollow-core optical fiber, the coupling device comprises a coupling mirror and an optical fiber coupling cavity, and the coupling mirror comprises a reflecting mirror group, a lens group and a focusing lens; the optical fiber coupling cavity is made of a copper material with good thermal conductivity and is fixed on the three-dimensional displacement table, a laser beam emitted by the laser light source is guided by the reflector group and then enters the lens group, and the lens group is used for adjusting the diameter of the laser beam, so that the laser beam is matched with a hollow-core optical fiber mode field, and high coupling efficiency is achieved. After passing through the focusing lens, the laser beam is coupled into the hollow-core optical fiber, so that the laser beam can be perfectly matched with the mode field of the hollow-core optical fiber, the maximum beam transmission can be finally realized by adjusting the three-dimensional displacement table, and the loss in the beam transmission process is reduced. According to the utility model, the structure design is simple, and the adjustability, the detachability and the coupling efficiency are effectively improved; and secondly, the heat dissipation performance is good, and damage to the incident end face of the optical fiber can be avoided.

Description

TECHNICAL FIELD

[0001] The utility model discloses a hollow core fiber coupling system with high coupling efficiency, and belongs to the technical field of optical fiber energy transmission. BACKGROUND

[0002] Hollow core fiber has important application prospects in high-power laser beam transmission and other fields due to its low nonlinear effect, low group velocity dispersion and other advantages. However, low-loss coupling between laser output and optical fiber is a key problem for better application of optical fiber devices in engineering.

[0003] In hollow core fiber coupling, heat management is an important problem. In the article published on February 6, 2024, 10.3788 / LOP232478, when the average power of the fiber coupling system is increased, the output beam will oscillate rapidly between different modes without effective heat load management, the spot will constantly jitter, resulting in unstable output beam, and thus greatly affecting the coupling efficiency and transmission results.

[0004] The hollow core fiber system has high requirements for operational stability during long-time transmission of high-power laser. In the article published in October 2021, 10.3788 / IRLA20210236, although the fiber coupling module achieved a coupling efficiency of more than 83%, there were problems of strong beam quality degradation and insufficient system stability during long-time use and with the increase of laser power.

[0005] In actual engineering application, the influence of alignment error will directly lead to low single-mode fiber coupling efficiency, so accurate correction of error is crucial. In the article published on July 13, 2023, 10.3788 / LOP221102, when the alignment error is 0, the fiber coupling efficiency reaches a maximum of 81.43%, but when there is a small amount of deviation, the coupling efficiency will decrease to 10%, the coupling loss is serious, and the efficiency will decrease sharply with the increase of alignment error. UTILITY MODEL CONTENTS

[0006] The utility model provides a hollow core fiber coupling system which overcomes the above problems or at least partially solves the above problems, and solves the problem of poor heat management and low coupling efficiency in hollow core fiber transmission in the prior art.

[0007] The technical solution of the utility model is as follows:

[0008] A hollow core fiber coupling system, characterized in that it comprises:

[0009] A laser light source for emitting a laser beam;

[0010] A coupling device is arranged behind the laser light source and used to couple the laser light beam into the hollow core fiber;

[0011] A hollow core fiber is used to transmit the coupled-in laser light beam;

[0012] A three-dimensional displacement table is used to fix and adjust the position of the hollow core fiber to achieve optimal coupling;

[0013] The coupling device includes a coupling mirror and a fiber coupling cavity, the coupling mirror includes a mirror group, a lens group and a focusing lens; the laser light beam emitted by the laser light source is guided into the lens group after passing through the mirror group, the lens group is used to adjust the diameter of the laser light beam to match the mode field of the hollow core fiber to achieve high coupling efficiency, the laser light beam is coupled into the hollow core fiber after passing through the focusing lens, which can perfectly match the mode field of the laser light beam and the hollow core fiber, and by adjusting the three-dimensional displacement table, the maximum beam transmission can be achieved to reduce the loss in the beam transmission process.

[0014] As a preferred, the mirror group includes a first mirror and a second mirror; the second mirror is arranged on the reflection light path of the first mirror, the axis of the second mirror intersects the axis of the first lens, the position and angle of the first mirror and the second mirror are adjustable, and the first lens and the second lens constitute a beam collimation device.

[0015] As a preferred, the lens group includes a first lens and a second lens with selectable focal length, the first lens and the second lens are located on the same light path, the first lens and the second lens constitute a telescope system and are used as a beam transformation device, and the position and spacing of the first lens and the second lens are adjustable.

[0016] As a preferred, the first mirror, the second mirror, the first lens and the second lens are coaxially installed. The meaning of coaxial is that the centers of the devices are on the same straight line, and the devices are placed perpendicular to the axis.

[0017] As a preferred, the focusing lens is arranged on the transmission light path of the second lens. The focal point of the focusing lens is located on the end face of the hollow core fiber, and the input end of the hollow core fiber faces the focused light spot. The focal length of the focusing lens is determined by the core size of the hollow core fiber.

[0018] As a preferred, the fiber coupling cavity is provided with a groove for arranging the incident end of the hollow core fiber.

[0019] As a preferred, the fiber coupling cavity is provided with water cooling interfaces on both sides for connecting a water cooling cavity to inject and drain water into the water cooling machine.

[0020] As preferred, the three-dimensional displacement table has a high-precision regulator, which can be coarsely adjusted and finely adjusted, to reduce the alignment error.

[0021] As preferred, the coupling mirror further comprises a lens holder, and the mirror surface and the lens holder are on a common track, allowing flexible adjustment.

[0022] The application provides a hollow-core fiber coupling system with high coupling efficiency, which has simple optical path design and portable structure and is easy to install and adjust. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 FIG. 1 is a structural schematic diagram of an embodiment of the hollow-core fiber coupling system of the application;

[0024] Figure 2 FIG. 2 is a structural schematic diagram of a fiber coupling cavity 8 according to the embodiment of the application.

[0025] Reference signs:

[0026] Laser light source 1; mirror group 2; first mirror 21;

[0027] Second mirror 22; lens group 3; first lens 31;

[0028] Second lens 32; focusing lens 4; first three-dimensional displacement table 5;

[0029] Fiber coupling cavity 6; flange 61; groove 62;

[0030] Sealing sheet 63; second three-dimensional displacement table 7; hollow-core fiber 8;

[0031] Water-cooled machine 9 DETAILED DESCRIPTION

[0032] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be clearly and completely described below, obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0033] The embodiment provides a hollow core fiber coupling system, which is composed of a laser light source, a coupling device and a hollow core fiber.

[0034] Please refer to Figure 1 , Figure 1 The structure diagram of the hollow core fiber coupling system embodiment of the present application is shown in the figure, which comprises:

[0035] The laser light source 1 is a spatial output ultrafast laser with high repetition frequency and high peak power, which provides high-quality laser light beams.

[0036] The coupling device comprises a coupling mirror and a fiber coupling cavity, wherein the coupling mirror comprises

[0037] The mirror group 2 is used for guiding the laser light beams, and by adjusting the position and angle, the light beams are coaxial with the focusing lens 4 and the incident end face of the hollow core fiber.

[0038] The lens group 3 is used as a telescope system as a beam transformation device, and by adjusting the diameter of the laser light beams, the laser light beams are matched with the mode field of the hollow core fiber, so that high coupling efficiency is achieved.

[0039] The focusing lens 4 focuses and couples the adjusted laser light beams into the hollow core fiber.

[0040] The fiber coupling cavity 6 is made of copper material with good heat conductivity and is fixed on the three-dimensional displacement table 7.

[0041] The laser beam emitted by the laser source 1 is guided by the mirror group 2 into the lens group 3, which is used to adjust the diameter of the laser beam to match the mode field of the hollow core fiber 8, achieve high coupling efficiency, and focus through the focusing lens 4 to couple the laser beam into the hollow core fiber 8. By adjusting the three-dimensional displacement table, the maximum beam transmission can be realized, and the loss in the beam transmission process can be reduced. When coupling the laser into the hollow core fiber for transmission, the coupling efficiency can be very high, and the light propagates in the air without the influence of material itself, the transmission bandwidth can be very wide, the transmission loss can be very low, and the light can be transmitted over a long distance without the influence of material nonlinearity.

[0042] The laser source 1 is a high-repetition-frequency, high-peak-power spatial output ultrafast laser of various types. In this embodiment, the laser source 1 is a 1064nm solid-state laser with a pulse width of less than 15ps and an output power of up to 50W.

[0043] In this embodiment, the mirror group 2 includes a first mirror 21 and a second mirror 22. The second mirror 22 is arranged on the reflected light path of the first mirror 21. The positions and angles of the first mirror 21 and the second mirror 22 are adjustable. By adjusting the angles and positions of the first mirror 21 and the second mirror 22, the light beam can be coaxial with the focusing lens 4 and the entrance end face of the hollow core fiber 8. The first mirror 21 and the second mirror 22 constitute a beam collimation device.

[0044] In this embodiment, the lens group 3 includes a first lens 31 and a second lens 32 with selectable focal lengths. The lens group 3 is located on the same light path as the mirror group 2. The axis of the first lens 31 intersects the axis of the second mirror 22. The first lens 31 and the second lens 32 are coaxially installed.

[0045] The first lens 31 and the second lens 32 constitute a telescope system, which is used as a beam transformation device. The positions and spacings of the first lens 31 and the second lens 32 are adjustable. The transformation principle of the telescope system is as follows: when a light beam with a diameter of d1 passes through the first lens 31 with a focal length of F1 and is focused at a focal point position with a distance of F1 from the first lens 31, the light beam after the focal point diverges. A second lens 32 with a focal length of F2 is placed at a position with a distance of F2 from the focal point. The divergent light beam is transformed into a collimated light beam with a diameter of d2. At this time, the diameter of the light beam is d2 = d1*(F2 / F1). By designing reasonable F1 and F2, the light beam emitted by the light source can be transformed into other diameters.

[0046] In the embodiment, the focal point of the second lens-32 is near the focal point of the first lens-31, the second lens-32 can move, by adjusting the position of the second lens-32, the diameter of the laser beam is expanded or reduced, so that the laser beam and the hollow core fiber-8 are matched in mode field, and high coupling efficiency is achieved.

[0047] The focusing lens-4 is arranged on the reflection path of the second mirror-22, and is coaxially arranged with the lens group-3, in the embodiment, in order to perfectly match the mode field of the beam and the hollow core fiber-8, the focusing lens-4 with different focal lengths can be replaced, so that the diameter of the focal spot 1 / e 2 of the hollow core fiber-8 is 0.64 times the diameter of the input end core.

[0048] In the embodiment, the hollow core fiber-8 is fixedly arranged in the fiber coupling cavity-6, the fiber coupling cavity-6 is mounted on the second three-dimensional displacement table-7, by adjusting the knob of the second three-dimensional displacement table-7, the front and back, left and right, up and down of the incident end of the hollow core fiber-8 are controlled, and the focused spot is coupled into the core.

[0049] Considering that in actual use, the position of the hollow core fiber-8 may deviate due to external environment, a first three-dimensional displacement table-5 with high precision adjustment is arranged on the focusing lens-4, so that higher coupling efficiency can be obtained. Specifically, in the embodiment, the transmission efficiency can reach more than 85%, and the coupling efficiency can reach more than 90%.

[0050] Figure 2 The structure diagram of the fiber coupling cavity-6.

[0051] As Figure 2 shown, the length of the fiber coupling cavity-6 is about 8cm, a groove-62 is arranged in the inside, the hollow core fiber-6 is fixedly arranged in the groove of the fiber coupling cavity-6, in the embodiment, the hollow core fiber-6 is also fixed by vacuum adhesive, so as to ensure the stability and safety of the hollow core fiber-6.

[0052] The front end of the fiber coupling cavity-6 shell is provided with a flange-61, which includes a flange plate and a window piece. The window piece is connected to the flange plate on the side close to the laser incidence, and the window piece is connected to the fiber coupling cavity-6 on the side away from the laser incidence. An annular limiting groove is arranged at the front end of the flange plate and the fiber coupling cavity-6 shell, and a gasket is arranged in the flange plate. In this embodiment, the gasket is made of rubber, which can buffer and reduce pressure by using the elasticity of rubber, thereby reducing the damage of the window piece under stress; by arranging the sealing o-ring in the annular limiting groove at the front end of the fiber coupling cavity-6 shell, and abutting against the window piece, the effect of buffering and reducing pressure can be achieved, thereby improving the precision of the coupling system. The surface of the window piece is provided with a coating layer, which is coated on the surface of the window piece, and can realize selective transmission of specific wavelength laser, which is conducive to reducing the background noise of the emitted laser.

[0053] The rear end of the fiber coupling cavity-6 shell is provided with a sealing piece-63, and the center hole of the sealing piece-63 is used to connect the hollow core optical fiber-8.

[0054] The fiber coupling cavity-6 is provided with a water cooling interface on both sides, which is used to connect a water cooling cavity, and the purpose of water cooling is achieved by injecting and draining water into the water cooling machine-9. This scheme in this embodiment has great advantages for the transmission of high-power ultrashort pulses, and has good application prospects in the fields of industry, medical treatment, business, optical communication and military application.

[0055] In the examples shown and described herein, any specific values should be interpreted as merely exemplary and not as a limitation, and thus other examples of the example embodiments can have different values.

[0056] It should be noted that similar reference numbers and letters represent similar items in the following drawings, and thus, once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.

[0057] The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A hollow-core optical fiber coupling system, characterized in that, include: A laser source used to emit a laser beam; A coupling device, disposed after the laser source, is used to couple the laser beam into the hollow optical fiber; Hollow-core optical fiber is used to transmit the coupled-in laser beam; A three-dimensional displacement stage is used to fix and adjust the position of the hollow optical fiber to achieve optimal coupling. The coupling device includes a coupling mirror and an optical fiber coupling cavity. The coupling mirror includes a mirror group, a lens group, and a focusing lens. The laser beam emitted by the laser source is guided by the mirror group and then enters the lens group. The lens group is used to adjust the diameter of the laser beam to match the mode field of the hollow fiber, achieving high coupling efficiency. After passing through the focusing lens, the laser beam is coupled into the hollow fiber, which can perfectly match the mode field of the laser beam and the hollow fiber. By adjusting the three-dimensional displacement stage, the maximum beam transmission can be achieved and the loss during beam transmission can be reduced.

2. The hollow-core optical fiber coupling system according to claim 1, characterized in that, The mirror assembly includes at least two mirrors for guiding the laser beam; the lens assembly, disposed behind the mirror assembly, includes a first lens and a second lens with selectable focal length, forming a telescope system for changing the diameter of the laser beam to match the mode field of the hollow fiber; the focusing lens, disposed behind the lens assembly, is used to focus and couple the adjusted laser beam into the hollow fiber.

3. The hollow-core optical fiber coupling system according to claim 1, characterized in that, The optical fiber coupling cavity (6) is made of copper with good thermal conductivity, and a groove (62) is provided inside for fixing the hollow optical fiber (8). The hollow optical fiber (8) is fixed in the groove (62) by vacuum adhesive.

4. The hollow-core optical fiber coupling system according to claim 1, characterized in that, The laser source is a space-output ultrafast laser with high repetition rate and high peak power.

5. The hollow-core optical fiber coupling system according to claim 1, characterized in that, The reflector group (2) includes a first reflector (21) and a second reflector (22). The second reflector (22) is disposed on the reflected light path of the first reflector (21). The position and angle of the first reflector (21) and the second reflector (22) are adjustable to guide the laser beam to be perfectly coaxial with the incident end face of the focusing lens (4) and the hollow fiber (8).

6. The hollow-core optical fiber coupling system according to claim 2, characterized in that, The position and spacing of the first lens (31) and the second lens (32) are adjustable to form a telescope system, and the diameter of the laser beam is adjusted by changing the focal length and position of the first lens (31) and the second lens (32).

7. The hollow-core optical fiber coupling system according to claim 1, characterized in that, The focal length of the focusing lens (4) is selectable so that the focal spot 1 / e 2 The diameter at the point is 0.64 times the core diameter at the input end of the hollow fiber, achieving a perfect match with the mode field of the hollow fiber (8).

8. The hollow-core optical fiber coupling system according to claim 1, characterized in that, The fiber coupling cavity (6) is provided with a flange (61) at the front end, including a flange and a window. The side of the window that is close to the laser incident point is connected to the flange, and the side that is away from the laser incident point is connected to the fiber coupling cavity (6). The surface of the window is provided with a coating layer to achieve selective transmission of laser of a specific wavelength.

9. The hollow-core optical fiber coupling system according to claim 8, characterized in that, The fiber coupling cavity (6) is provided with a sealing plate (63) at the rear end. The central hole of the sealing plate (63) is used to connect the hollow fiber (8). Both sides of the fiber coupling cavity (6) are provided with water cooling interfaces for connecting to the water cooling cavity and cooling by a water chiller (9).

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