Optical fiber beam combining device and use method thereof

Abstract

The invention belongs to the technical field of space beam combining application, and particularly relates to an optical fiber beam combining device and a using method thereof. The optical fiber beam combining device comprises a first off-axis parabolic mirror group and a second off-axis parabolic mirror group; the first off-axis parabolic mirror group comprises a plurality of off-axis parabolic mirrors, focuses of the off-axis parabolic mirrors coincide with wire cores of the corresponding incident optical fibers respectively, and emergent light rays of the incident optical fibers are collimated into parallel light rays; the focus of the second off-axis parabolic mirror group coincides with the emergent optical fiber core; the light output directions of the off-axis parabolic mirrors coincide with the light input direction of the second off-axis parabolic mirror set. According to the invention, beam combination of high coupling efficiency and wide coupling wave band can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of space beam combining applications, and in particular relates to an optical fiber beam combining device and a use method thereof. Background Art

[0002] With the rapid development of optical fiber communication technology, people have higher and higher requirements for the transmission capacity and transmission distance of optical signals. In optical fiber communication systems, multiple optical signals need to be efficiently coupled into one optical fiber for transmission to increase communication capacity. For example, in a wavelength division multiplexing (WDM) system, optical signals of different wavelengths represent different channels. Through optical fiber beam combining, these optical signals carrying different information can be combined into one optical fiber, thereby realizing the simultaneous transmission of multiple signals. This is like on a highway, merging multiple lanes of traffic into fewer lanes in a reasonable way to make full use of road resources.

[0003] Long-distance fiber transmission also requires fiber beam combining technology. When optical signals are transmitted over a long distance in an optical fiber, losses will occur. In order to compensate for these losses, a fiber amplifier can be used. Fiber beam combining technology can effectively combine pump light and signal light, so that the pump light can provide energy amplification for the signal light, thereby extending the transmission distance of the optical signal.

[0004] Therefore, there is an urgent need for an optical fiber beam combining device to improve coupling efficiency and cope with a wide coupling band. Summary of the invention

[0005] In view of the above problems, the present invention discloses an optical fiber beam combining device, which comprises a first off-axis parabolic mirror group and a second off-axis parabolic mirror group;

[0006] The first off-axis parabolic mirror group includes a plurality of off-axis parabolic mirrors, the focal points of the plurality of off-axis parabolic mirrors respectively coincide with the cores of the corresponding incident optical fibers, and collimate the outgoing light rays of the plurality of incident optical fibers into parallel light rays;

[0007] The focus of the second off-axis parabolic mirror group coincides with the core of the output optical fiber;

[0008] The light output direction of the plurality of off-axis parabolic mirrors coincides with the light input direction of the second off-axis parabolic mirror group.

[0009] Furthermore, the aperture of the second off-axis parabolic mirror group is larger than the diameter of the circumscribed circle of the first off-axis parabolic mirror group.

[0010] Furthermore, the core diameter of the output optical fiber should not be less than the core diameter of the input optical fiber 3 .

[0011] Furthermore, the diameter D of the circumscribed circle of the first off-axis parabolic mirror group is 外接 The relationship with the core diameter D0 of the output optical fiber is as follows:

[0012] D0=D 外接 +Hd1 / 2f1

[0013] Wherein, H is the distance between the first off-axis parabolic mirror group and the second off-axis parabolic mirror group, d1 is the core diameter of the incident optical fiber, and f1 is the focal length of the first off-axis parabolic mirror group.

[0014] Furthermore, the focal length f1 and aperture D1 of the first off-axis parabolic mirror assembly 1 and the NA value of the incident optical fiber satisfy the following relationship:

[0015] f1≤(D1-d1) / 2 / tan(arcsin(NA))

[0016] Where d1 is the core diameter of the incident optical fiber.

[0017] Furthermore, the relationship between the core diameter D2 of the output optical fiber and the core diameter D1 of the input optical fiber satisfies:

[0018]

[0019] Wherein, f1 is the focal length of the first off-axis parabolic mirror group, and f2 is the focal length of the second off-axis parabolic mirror group.

[0020] Furthermore, the incident optical fibers are arranged in a staggered manner;

[0021] Or the incident optical fibers are arranged in a tower structure.

[0022] Furthermore, the multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group and the second off-axis parabolic mirror group are all 90° off-axis parabolic mirrors.

[0023] Furthermore, the present invention also discloses a method for using the optical fiber combining device described in any of the above embodiments, and the method specifically comprises the following steps:

[0024] A first flange is installed at one end of each incident optical fiber, and the relative position between the first flange and the first off-axis parabolic mirror group is adjusted and fixed so that the focal points of the multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group coincide with the cores of the corresponding incident optical fibers;

[0025] Install a second flange at one end of the output optical fiber, adjust the relative position of the first flange and the second off-axis parabolic mirror group and fix them so that the focus of the second off-axis parabolic mirror group coincides with the core of the output optical fiber;

[0026] The relative positions of the first off-axis parabolic mirror and the second off-axis parabolic mirror group are adjusted and fixed so that the light output direction of the multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group coincides with the light input direction of the second off-axis parabolic mirror group.

[0027] Furthermore, multiple incident optical fibers are arranged in a staggered manner or in a tower structure.

[0028] The present invention can realize beam combining with high coupling efficiency and wide coupling band.

[0029] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A schematic diagram of the propagation of a meridian fiber in an optical fiber according to the prior art is shown;

[0032] Figure 2 A schematic diagram showing the propagation of oblique light in an optical fiber according to the prior art is shown;

[0033] Figure 3 A schematic diagram of an optical path of an optical fiber beam combining device according to an embodiment of the present invention is shown;

[0034] Figure 4 A transverse cross-sectional view of a first off-axis parabolic mirror group and a second off-axis parabolic mirror group in a fiber beam combining device according to an embodiment of the present invention is shown.

[0035] In the figure: 1. first off-axis parabolic mirror group; 2. second off-axis parabolic mirror group; 3. incident optical fiber; 4. output optical fiber. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] When light propagates in optical fiber, it can be divided into two cases according to its propagation path, namely meridional rays and oblique rays.

[0038] 1. Meridian fiber propagation in optical fiber

[0039] like Figure 1 As shown, the meridional ray refers to the ray passing through the central axis of the optical fiber. Figure 1 Schematic diagram of the propagation of meridional light in step-index fiber, where n0 is the refractive index of the medium surrounding the fiber, n1 and n2 are the refractive indices of the fiber core and cladding, respectively. According to the law of total reflection, the output light should be limited to the incident angle at the interface between the core and cladding in the fiber waveguide. Must be greater than or equal to the critical angle Then we have:

[0040]

[0041] It can also be expressed as

[0042]

[0043] in,

[0044]

[0045] Using the law of refraction

[0046]

[0047] Available,

[0048]

[0049] When n0 is air, the maximum incident angle corresponding to the meridian ray is:

[0050]

[0051] It is called the maximum aperture angle of the optical fiber, which reflects the energy of the fiber laser and determines the numerical aperture NA of the optical fiber in the meridian plane.

[0052] 2. Propagation of oblique light in optical fiber

[0053] Any light ray in an optical fiber that is not transmitted in the meridian plane can be called an oblique ray. The oblique ray is neither intersecting nor parallel to the optical axis of the optical fiber. The optical path is a left-handed or right-handed broken line in space, and the distance from the oblique ray to the central axis of the optical fiber is equal.

[0054] According to the principles of geometric optics, the total reflection conditions of oblique light can be obtained, such as Figure 2 As shown, KQ is the oblique light incident into the step-index optical fiber, and point H on the optical fiber cross section is the projection of the incident point K. Then the total reflection condition of the oblique light is:

[0055]

[0056] According to the law of refraction of light,

[0057]

[0058] The above formula will become:

[0059]

[0060] The numerical aperture of the oblique light is expressed as follows:

[0061]

[0062] Since cosγ≤1, the NA of oblique rays is larger than that of meridional rays.

[0063] Therefore, in spatial beam combining, there are two necessary conditions to efficiently couple light into optical fibers:

[0064] 1. The incident angle of the light meets the requirements of the numerical aperture (NA) of the optical fiber

[0065] 2. At the optical fiber end plane, the light incident point is inside the optical fiber core. Light incident outside the optical fiber core cannot enter the optical fiber even if it meets the NA of the optical fiber.

[0066] like Figure 3 and Figure 4 As shown, this embodiment discloses a fiber beam combining device, which includes a first off-axis parabolic mirror group 1 and a second off-axis parabolic mirror group 2;

[0067] The first off-axis parabolic mirror group 1 includes a plurality of off-axis parabolic mirrors, the focal points of which coincide with the cores of the corresponding incident optical fibers 3, respectively, to collimate the outgoing light rays of the plurality of incident optical fibers 3 into parallel light rays;

[0068] The focus of the second off-axis parabolic mirror group 2 coincides with the core of the output optical fiber 4;

[0069] The light output direction of the multiple off-axis parabolic mirrors coincides with the light input direction of the second off-axis parabolic mirror group 2 .

[0070] Specifically, multiple incident optical fibers 3 correspond to an off-axis parabolic mirror in the first off-axis parabolic mirror group 1 respectively. The incident optical fiber 3 refers to a small optical fiber that needs to be coupled. The core center of the incident optical fiber 3 coincides with the focus of the corresponding off-axis parabolic mirror. The outgoing light in the incident optical fiber 3 is reflected by the off-axis parabolic mirror, and the outgoing light is collimated from the original scattered light into a parallel light beam. The light output direction of the first off-axis parabolic mirror group 1 coincides with the light input direction of the second off-axis parabolic mirror group 2, so multiple groups of parallel light beams coupled by the first off-axis parabolic mirror group 1 are transmitted to the second off-axis parabolic mirror group 2. After entering the second off-axis parabolic mirror group 2, the parallel light beams converge at its focus. The focus of the second off-axis parabolic mirror group 2 coincides with the core of the outgoing optical fiber 4, completing the beam combination. The outgoing optical fiber 4 refers to the output optical fiber after coupling. Preferably, the multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group 1 and the second off-axis parabolic mirror group 2 are all 90° off-axis parabolic mirrors.

[0071] Furthermore, in order to make all the outgoing light of the incident optical fiber 3 enter the outgoing optical fiber 4, the aperture of the second off-axis parabolic mirror group 2 is larger than the diameter of the circumscribed circle of the first off-axis parabolic mirror group 1.

[0072] Specifically, multiple off-axis parabolic mirrors in the first off-axis parabolic mirror are evenly arranged, wherein the output directions of all the off-axis parabolic mirrors are located within the input range of the second off-axis parabolic mirror group 2, thereby preventing the output light of the incident optical fiber 3 from being converted into a parallel light beam and then entering the second off-axis parabolic mirror group 2, thereby preventing the output light of the incident optical fiber 3 from overflowing.

[0073] Furthermore, the diameter D of the circumscribed circle of the first off-axis parabolic mirror group 1 is 外接 The relationship with the core diameter D0 of the output optical fiber 4 is as follows:

[0074] D0=D 外接 +Hd1 / 2f1

[0075] Wherein, H is the distance between the first off-axis parabolic mirror group 1 and the second off-axis parabolic mirror group 2 , d1 is the core diameter of the incident optical fiber 3 , and f1 is the focal length of the first off-axis parabolic mirror group 1 .

[0076] Specifically, each off-axis parabolic mirror in the first off-axis parabolic mirror group 1 has the same shape and size. The focal length f1 and the aperture D1 of the first off-axis parabolic mirror group 1 refer to the focal length and the aperture of each off-axis parabolic mirror in the first off-axis parabolic mirror group 1, and the circumscribed circle diameter D 外接 It refers to the diameter of the circumscribed circle obtained by compactly oscillating multiple off-axis parabolic mirrors. From the previous light propagation method in the optical fiber, it can be known that only the circumscribed circle diameter D of the first off-axis parabolic mirror group 1外接 The relationship between the core diameter D0 of the output optical fiber 4 meets the above requirements, so that the coupled light can completely enter the output optical fiber 4.

[0077] It can be seen from the above relationship that the larger the diameter of the circumscribed circle, the larger the diameter of the output optical fiber 4. In actual production, in order to control costs, it is necessary to minimize the diameter of the output optical fiber 4. In order to reduce the diameter of the circumscribed circle, the incident optical fibers 3 are arranged in a staggered manner; or the incident optical fibers 3 are arranged in a tower structure.

[0078] Furthermore, the focal length f1 and aperture D1 of the first off-axis parabolic mirror assembly 1 and the NA value of the incident optical fiber 3 satisfy the following relationship:

[0079] f1≤(D1-d1) / 2 / tan(arcsin(NA))

[0080] Wherein, d1 is the core diameter of the incident optical fiber 3.

[0081] Specifically, it can be known from the previous light propagation mode in the optical fiber that only when the focal length and aperture of the first off-axis parabolic mirror satisfy the above relationship, the incident angle of the optical fiber can meet the requirement of the numerical aperture NA of the optical fiber.

[0082] Furthermore, the core diameter of the output optical fiber 4 should not be smaller than the core diameter of the input optical fiber 3 .

[0083] Specifically, the larger the core diameter of the optical fiber, the higher its luminous flux. The core diameter of the output optical fiber 4 is larger than the core diameter of the input optical fiber 3 so that the coupled output optical fiber 4 can transmit more optical fibers.

[0084] Furthermore, the relationship between the core diameter D2 of the output optical fiber 4 and the core diameter D1 of the input optical fiber 3 satisfies:

[0085]

[0086] Wherein, f1 is the focal length of the first off-axis parabolic mirror group 1, and f2 is the focal length of the second off-axis parabolic mirror group 2.

[0087] In another embodiment of the present invention, a method for using the optical fiber bundle combining device in any of the above embodiments is also disclosed, and the method for using the optical fiber bundle combining device specifically comprises the following steps:

[0088] A first flange is installed at one end of each incident optical fiber, and the relative position between the first flange and the first off-axis parabolic mirror group is adjusted and fixed so that the focal points of the multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group coincide with the cores of the corresponding incident optical fibers;

[0089] Install a second flange at one end of the output optical fiber, adjust the relative position of the first flange and the second off-axis parabolic mirror group and fix them so that the focus of the second off-axis parabolic mirror group coincides with the core of the output optical fiber;

[0090] The relative positions of the first off-axis parabolic mirror and the second off-axis parabolic mirror group are adjusted and fixed so that the light output direction of the multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group coincides with the light input direction of the second off-axis parabolic mirror group.

[0091] Furthermore, multiple incident optical fibers are arranged in a staggered manner or in a tower structure.

[0092] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions 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 invention.

Claims

1. An optical fiber beam combining device, characterized in that: The optical fiber beam combining device comprises a first off-axis parabolic mirror group (1) and a second off-axis parabolic mirror group (2); The first off-axis parabolic mirror group (1) comprises a plurality of off-axis parabolic mirrors, the focal points of the plurality of off-axis parabolic mirrors respectively coincide with the cores of the corresponding incident optical fibers (3), and collimate the outgoing light rays of the plurality of incident optical fibers (3) into parallel light rays; The focus of the second off-axis parabolic mirror group (2) coincides with the core of the output optical fiber (4); The light output direction of the plurality of off-axis parabolic mirrors coincides with the light input direction of the second off-axis parabolic mirror group (2).

2. The optical fiber combining device according to claim 1, characterized in that: The aperture of the second off-axis parabolic mirror group (2) is larger than the diameter of the circumscribed circle of the first off-axis parabolic mirror group (1).

3. The optical fiber combining device according to claim 1, characterized in that: The core diameter of the output optical fiber (4) should not be less than the core diameter of the input optical fiber (3).

4. The optical fiber combining device according to claim 3, characterized in that: The diameter D of the circumscribed circle of the first off-axis parabolic mirror group (1) is 外接 The relationship with the core diameter D0 of the output optical fiber (4) is as follows: D0=D 外接 +Hd1 / 2f1 Wherein, H is the distance between the first off-axis parabolic mirror group (1) and the second off-axis parabolic mirror group (2), d1 is the core diameter of the incident optical fiber (3), and f1 is the focal length of the first off-axis parabolic mirror group (1).

5. The optical fiber combining device according to claim 1, characterized in that: The focal length f1 and the aperture D1 of the first off-axis parabolic mirror assembly (1) and the NA value of the incident optical fiber (3) satisfy the following relationship: f1≤(D1-d1) / 2 / tan(arcsin(NA)) Wherein, d1 is the core diameter of the incident optical fiber (3).

6. The optical fiber combining device according to claim 1, characterized in that: The relationship between the core diameter D2 of the output optical fiber (4) and the core diameter D1 of the input optical fiber (3) satisfies: Wherein, f1 is the focal length of the first off-axis parabolic mirror group (1), and f2 is the focal length of the second off-axis parabolic mirror group (2).

7. The optical fiber combining device according to claim 1, characterized in that: The incident optical fibers (3) are arranged in a staggered manner; Or the incident optical fibers (3) are arranged in a tower structure.

8. The optical fiber bundle combining device according to claim 1, characterized in that: The multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group (1) and the second off-axis parabolic mirror group (2) are all 90° off-axis parabolic mirrors.

9. The method for using the optical fiber bundle combining device according to any one of claims 1 to 8, characterized in that: The method of use specifically comprises the following steps: A first flange is installed at one end of each incident optical fiber, and the relative position between the first flange and the first off-axis parabolic mirror group is adjusted and fixed so that the focal points of the multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group coincide with the cores of the corresponding incident optical fibers; Install a second flange at one end of the output optical fiber, adjust the relative position of the first flange and the second off-axis parabolic mirror group and fix them so that the focus of the second off-axis parabolic mirror group coincides with the core of the output optical fiber; The relative positions of the first off-axis parabolic mirror and the second off-axis parabolic mirror group are adjusted and fixed so that the light output direction of the multiple off-axis parabolic mirrors in the first off-axis parabolic mirror group coincides with the light input direction of the second off-axis parabolic mirror group.

10. The method of use according to claim 9, characterized in that: Arrange multiple input optical fibers in a staggered arrangement or in a tower structure.

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