Fiber optic coupler, structure and assembly method based on GRIN lens optical cementing

Abstract

The application discloses a GRIN lens optical cementing-based optical fiber coupler, a structure and an assembling method, and the optical fiber coupler comprises a ring-shaped metal plug sleeve, an input end through pipe and an output end through pipe; the ring-shaped metal plug sleeve is provided with a lens channel, a GRIN lens comprises an input GRIN lens and an output GRIN lens, and the input GRIN lens and the output GRIN lens are optically cemented and connected; the input end through pipe is sleeved on the ring-shaped metal plug sleeve, and the output end through pipe is sleeved on the ring-shaped metal plug sleeve; a side wall of the input end through pipe is provided with an input cavity for flowing fluid, and the side wall of the input end through pipe is provided with an input inlet and an input outlet which are in communication with the input cavity; a side wall of the output end through pipe is provided with an output cavity for flowing fluid, and the side wall of the output end through pipe is provided with an output inlet and an output outlet which are in communication with the output cavity. The application has the advantages of stable structure and small optical transmission loss, and can support high-power laser transmission.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical fiber coupling, and more particularly relates to an optical fiber coupler based on GRIN lens optical cementation, a structure and an assembling method. BACKGROUND

[0002] High-power fiber lasers have high optical-to-optical conversion efficiency, compact structure, long service life and other advantages, and have been widely used in industrial manufacturing and military defense fields.

[0003] High-power fiber laser energy transmission adopts double-clad fiber technology, and the fiber core is small, so the power density of the output end of the laser is very high. Generally, a quartz end cap is fused on the end face of the optical fiber, and the output end face of the quartz end cap is designed with a lens, so that the output light remains collimated, and then the two end caps are spatially coupled to realize optical coupling. However, spatial coupling can reduce the stability of the coupler and increase the loss.

[0004] GRIN (Graded Index) lenses are also widely used in optical fiber collimators. GRIN lenses, i.e. gradient refractive index lenses, are cylindrical optical lenses whose refractive index distribution varies radially. Unlike traditional lenses, which control the surface curvature of the lens to change the direction of light transmission by controlling the surface curvature of the lens, GRIN lenses use the principle that light propagating in different refractive index media will change the direction of transmission. The material of the GRIN lens causes the light propagating along the axis to refract, and the refractive index distribution decreases radially, so that the light is smoothly and continuously converged to a point. Therefore, the output end face of the GRIN lens collimation head is a plane rather than a curved surface. Therefore, how to use the GRIN lens to solve the problems of low stability and high loss caused by spatial coupling is a difficult problem that needs to be solved by those skilled in the art. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides an optical fiber coupler based on GRIN lens optical cementation, a structure and an assembling method.

[0006] The present application discloses an optical fiber coupler based on GRIN lens optical cementation, comprising:

[0007] A ring-shaped metal plug sleeve and a through pipe, the through pipe comprising an input end through pipe and an output end through pipe;

[0008] The ring-shaped metal plug sleeve is provided with a lens channel for accommodating a GRIN lens, the GRIN lens comprising an input GRIN lens for connecting with an input optical fiber and an output GRIN lens for connecting with an output optical fiber, the input GRIN lens and the output GRIN lens being optically cemented and connected;

[0009] The input end through pipe corresponds to the input GRIN lens and is arranged outside the annular metal plug sleeve, and the output end through pipe corresponds to the output GRIN lens and is arranged outside the annular metal plug sleeve; the side wall of the input end through pipe is provided with an input cavity for flowing fluid, and the side wall of the input end through pipe is provided with an input inlet and an input outlet in communication with the input cavity; the side wall of the output end through pipe is provided with an output cavity for flowing fluid, and the side wall of the output end through pipe is provided with an output inlet and an output outlet in communication with the output cavity.

[0010] Optionally, the input cavity is circumferentially arranged outside the input GRIN lens; and / or the output cavity is circumferentially arranged outside the output GRIN lens.

[0011] Optionally, one or more of the input inlet, the input outlet, the output inlet and the output outlet is provided with an interface.

[0012] Optionally, the inner diameter of the annular metal plug sleeve matches the outer diameter of the GRIN lens; and / or the inner diameter of the through pipe matches the outer diameter of the annular metal plug sleeve.

[0013] Optionally, the length of the input GRIN lens and the output GRIN lens matches the optical wavelength of the transmitted light of the input optical fiber and the output optical fiber.

[0014] Optionally, the radius of the GRIN lens is 20 μm to 20 mm.

[0015] Optionally, the radius of the GRIN lens matches the mode field area of the transmitted light in the input optical fiber and the output optical fiber.

[0016] The application also discloses a GRIN lens-based optical fiber coupling structure, comprising an optical fiber and the GRIN lens-based optical fiber coupler.

[0017] Optionally, the core diameter of the optical fiber ranges from 1 to 200 μm, and the inner cladding diameter of the optical fiber ranges from 20 to 2000 μm.

[0018] The application also discloses an assembling method of the GRIN lens-based optical fiber coupling structure.

[0019] S1, fuse the input optical fiber and the input GRIN lens, and fuse the output optical fiber and the output GRIN lens;

[0020] S2, sleeve the annular metal ferrule sleeve into the input end through pipe and the output end through pipe and glue to realize the connection of the annular metal ferrule sleeve with the input end through pipe and the output end through pipe;

[0021] S3, polish the end face of the input GRIN lens close to the side of the output GRIN lens to meet the optical cementing connection requirement, polish the end face of the output GRIN lens close to the side of the input GRIN lens to meet the optical cementing connection requirement, and cement the input GRIN lens and the output GRIN lens.

[0022] Overall, compared with the prior art, the above technical scheme conceived by the present application can achieve the following beneficial effects:

[0023] The present application adopts GRIN lens as a collimator, which can make the output surface of the collimator head a plane, and through optical cementing, the molecules on the end face surfaces of the two GRIN lenses are attracted to each other and even bonded together, thereby greatly reducing the end face reflection inside the coupler, and finally realizing low-loss high-power fiber coupling without air gap and spatial alignment. More preferably, when the optical fiber transmission optical power of the present application is high (such as an average power of not less than 1000W), the present application can be cooled by circulating cooling fluid in the input cavity and the output cavity to realize the cooling of the present application, realize the low-temperature operation of the present application, and the working efficiency is high and stable. More preferably, when the input cavity and the output cavity of the present application respectively flow into fluids with temperature difference, the temperature difference between the input GRIN lens and the output GRIN lens is realized through heat transfer, so that the input GRIN lens and the output GRIN lens will produce different thermal expansion deformation, thereby realizing the automatic separation of the input GRIN lens and the output GRIN lens. More preferably, the present application has compact and firm structure. More preferably, the annular metal ferrule sleeve made of metal has good heat conduction performance, high temperature resistance and high structural strength, which improves the heat exchange efficiency between the fluid in the through pipe and the optical fiber, improves the stability and high efficiency of the operation of the present application, and realizes good operation in high temperature environment. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is an embodiment structure schematic diagram of the present application based on GRIN lens optical cementing fiber coupling structure;

[0025] Figure 2 It is a refractive index distribution diagram of GRIN lens;

[0026] Figure 3 It is a light transmission trajectory diagram of one period (one sine wave occupied by light propagation in GRIN lens) of GRIN lens;

[0027] Figure 4 Figure 1 is a schematic diagram of an embodiment of the method for determining the length dimension of the GRIN lens of the present application.

[0028] In all the figures, the same reference signs refer to the same technical features, in particular: 1 - input optical fiber, 2 - input inlet interface, 3 - input end tube, 4 - output inlet interface, 5 - output end tube, 6 - annular metal ferrule sleeve, 7 - output optical fiber, 8 - output GRIN lens, 9 - output outlet interface, 10 - input outlet interface, 11 - input GRIN lens, 12 - quarter pitch, 13 - input inlet, 14 - input outlet, 15 - output inlet, 16 - output outlet, 17 - input cavity, 18 - output cavity. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0030] In one embodiment of the present application, as shown in Figures 1-4 Figure 1, a GRIN lens-based optical fiber coupler includes an annular metal ferrule sleeve 6 and a tube, which includes an input end tube 3 and an output end tube 5; the annular metal ferrule sleeve 6 is provided with a lens channel for accommodating a GRIN lens, the GRIN lens includes an input GRIN lens 11 for connecting with an input optical fiber 1 and an output GRIN lens 8 for connecting with an output optical fiber 7, the input GRIN lens 11 and the output GRIN lens 8 are optically cemented and connected; the input end tube 3 is sleeved on the outside of the annular metal ferrule sleeve 6 corresponding to the input GRIN lens 11, and the output end tube 5 is sleeved on the outside of the annular metal ferrule sleeve 6 corresponding to the output GRIN lens 8; the side wall of the input end tube 3 is provided with an input cavity 17 for flowing fluid, and the side wall of the input end tube 3 is provided with an input inlet 13 and an input outlet 14 in communication with the input cavity 17; the side wall of the output end tube 5 is provided with an output cavity 18 for flowing fluid, and the side wall of the output end tube 5 is provided with an output inlet 15 and an output outlet 16 in communication with the output cavity 18.

[0031] Optionally, the input cavity 17 is circumferentially surrounded on the outside of the input GRIN lens 11, and the output cavity 18 is circumferentially surrounded on the outside of the output GRIN lens 8. Preferably, the length of the input end tube 3 is equal to and flush with the length of the input GRIN lens 11, and the length of the output end tube 5 is equal to and flush with the length of the output GRIN lens 8.

[0032] Optionally, one or more of the input inlet 13, the input outlet 14, the output inlet 15 and the output outlet 16 is provided with an interface. The input inlet 13 is provided with an input inlet interface 2, the input outlet 14 is provided with an input outlet interface 10, the output inlet 15 is provided with an output inlet interface 4, and the output outlet 16 is provided with an output outlet interface 9. Preferably, the interface is an interface with a valve, so that the interface can be selectively opened or closed as needed.

[0033] In actual application, when the optical fiber transmission power of the present application is high, the input inlet interface 2 is used to connect with a fluid device for inputting low-temperature fluid into the input cavity 17, the input outlet interface 10 is used to connect with a pipeline for leading out the fluid in the input cavity 17 or directly communicate with the external environment to ensure that the fluid in the input cavity 17 is in a flowing state, so as to circulate to cool the present optical fiber coupler, thereby realizing long-term low-temperature work of the present optical fiber coupler and equipment; the output inlet interface 4 is used to connect with a fluid device for inputting low-temperature fluid into the output cavity 18, and the output outlet interface 9 is used to connect with a pipeline for leading out the fluid in the output cavity 18 or directly communicate with the external environment to ensure that the fluid in the output cavity 18 is in a flowing state, so as to circulate to cool the present optical fiber coupler, thereby realizing long-term low-temperature work of the present optical fiber coupler and equipment.

[0034] When the optical fiber coupler of the present application needs to be disassembled, the input inlet interface 2 is used to connect with a fluid device for inputting low-temperature (or high-temperature) fluid into the input cavity 17, the input outlet interface 10 is used to connect with a pipeline for leading out the fluid in the input cavity 17 or directly communicate with the external environment to ensure that the fluid in the input cavity 17 is in a flowing state; the output inlet interface 4 is used to connect with a fluid device for inputting high-temperature (or low-temperature) fluid into the output cavity 18, and the output outlet interface 9 is used to connect with a pipeline for leading out the fluid in the output cavity 18 or directly communicate with the external environment to ensure that the fluid in the output cavity 18 is in a flowing state; so that the temperature difference of the two GRIN lenses (the input GRIN lens 11 and the output GRIN lens 8) connected by optical cementing produces different thermal expansion deformations, realizing automatic separation of the two GRIN lenses, and further realizing automatic disassembly of the present optical fiber coupling structure. Of course, in another embodiment of the present application, the optical fiber coupler can also directly realize the flow of fluid through the input inlet 13, the input outlet 14, the output inlet 15 and the output outlet 16. In actual application, the fluid can be gas or liquid.

[0035] Optionally, the inner diameter of the annular metal ferrule sleeve 6 matches the outer diameter of the GRIN lens to ensure high-precision alignment of the input GRIN lens 11 and the output GRIN lens 8. Preferably, the difference between the inner diameter of the annular metal ferrule sleeve 6 and the outer diameter of the GRIN lens is 2-15 μm. Preferably, one of the input GRIN lens 11 and the output GRIN lens 8 is glued to the annular metal ferrule sleeve 6, thereby avoiding axial movement of the input GRIN lens 11 and the output GRIN lens 8 connected to each other along the axis of the annular metal ferrule sleeve 6. Of course, in other embodiments of the present application, the GRIN lens can also be connected to the annular metal ferrule sleeve 6 through a flexible fixing component, such as a sealing ring, a soft pad, etc., thereby achieving flexible fixing of the GRIN lens, protecting the GRIN lens, prolonging the service life of the GRIN lens, and avoiding stress contact of the GRIN lens. Of course, in another embodiment of the present application, the GRIN lens and the annular metal ferrule sleeve 6 are connected by being tightly attached to each other, and in this case, the GRIN lens and the annular metal ferrule sleeve 6 do not need to be glued or provided with a flexible fixing component.

[0036] Optionally, the inner diameter of the through pipe matches the outer diameter of the annular metal ferrule sleeve 6 to ensure that the annular metal ferrule sleeve 6 can be put into and tightly contact the inner wall of the through pipe. Preferably, the annular metal ferrule sleeve 6 is glued to the through pipe. When the annular metal ferrule sleeve 6 is glued to the through pipe, the through pipe and the annular metal ferrule sleeve 6 are clearance fit.

[0037] Optionally, the lengths of the input GRIN lens 11 and the output GRIN lens 8 match the wavelength of the light transmitted by the input optical fiber 1 and the output optical fiber 7. This ensures that the output light of the input GRIN lens 11 is in a collimated state, and the collimated light enters the output GRIN lens 8 and is transmitted to the position of the output optical fiber 7 with a NA (numerical aperture) less than or equal to the NA of the output optical fiber 7.

[0038] That is, the transmission path of the light in the input GRIN lens 11 and the output GRIN lens 8 is the same as the transmission path of the light in the same GRIN lens, so that the transmission path of the light in the input GRIN lens 11 and the output GRIN lens 8 is seamlessly connected. For example, when the lengths of the input GRIN lens 11 and the output GRIN lens 8 are both equal to one-quarter pitch 12 of the light transmitted by the GRIN lens, it is ensured that there is no light leakage at the position of the one-quarter pitch 12 during the transmission of the light by the input GRIN lens 11 and the output GRIN lens 8.

[0039] Optionally, the radius of the GRIN lens is 20 μm-20 mm. Optionally, the core diameter of the optical fiber ranges from 1 to 200 μm, and the inner cladding diameter of the optical fiber ranges from 20 to 2000 μm.

[0040] Optionally, the radius of the GRIN lens matches the mode field area of the transmitted light in the input optical fiber 1 and the output optical fiber 7. In order to achieve no light leakage of the transmitted light of the input GRIN lens 11 and the output GRIN lens 8 at the position of the quarter pitch 12.

[0041] In another embodiment of the present application, as shown in Figures 1-4 A GRIN lens-based optical fiber coupling structure, comprising: an optical fiber and the GRIN lens-based optical fiber coupler according to any one of the preceding embodiments; the optical fiber comprises an input optical fiber 1 and an output optical fiber 7; the input optical fiber 1 is connected to the end face of the input GRIN lens 11 away from the output GRIN lens 8, the output optical fiber 7 is connected to the end face of the output GRIN lens 8 away from the input GRIN lens 11, and the input optical fiber 1 and the output optical fiber 7 are coaxially arranged.

[0042] Optionally, the core diameter of the optical fiber ranges from 1 to 200 μm, and the inner cladding diameter of the optical fiber ranges from 20 to 2000 μm.

[0043] In another embodiment of the present application, a method for assembling a GRIN lens-based optical fiber coupling structure, comprising the steps of:

[0044] S1, fusing the input optical fiber and the input GRIN lens, and fusing the output optical fiber and the output GRIN lens;

[0045] S2, sleeving the annular metal ferrule sleeve into the input end tube and the output end tube and gluing to realize the connection of the annular metal ferrule sleeve with the input end tube and the output end tube;

[0046] S3, polishing the end face of the input GRIN lens close to the side of the output GRIN lens to meet the optical cementing connection requirement, polishing the end face of the output GRIN lens close to the side of the input GRIN lens to meet the optical cementing connection requirement, and connecting the input GRIN lens and the output GRIN lens by optical cementing.

[0047] In practical application, the fusion of the optical fiber and the GRIN lens is preferably realized by a fusion machine.

[0048] Optionally, before step S1, the method further comprises the step of:

[0049] S01, designing the refractive profile n(r) of the GRIN lens according to different sizes of the input optical fiber and the output optical fiber, and the wavelength characteristics of the transmitted light, and n(r) satisfies formula (1):

[0050]

[0051] wherein n1 is the refractive index on the optical axis, is the gradient constant, and r is the radial position, as shown in Figure 2shown;

[0052] S02, determining the length of the GRIN lens, the pitch and the relationship of the length of the GRIN lens satisfy formula (2):

[0053]

[0054] Wherein, P is the pitch of the GRIN lens, Z is the length of the GRIN lens.

[0055] Preferably, the pitch of the GRIN lens is a part of the entire sinusoidal period of the fiber passing through the GRIN lens (such as Figure 3 shown), the light propagates in the input GRIN lens and the output GRIN lens just occupies one sinusoidal wave, that is, the length of the GRIN lens and the output GRIN lens is one fourth of the sinusoidal wavelength.

[0056] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A fiber optic coupler based on GRIN lens optical bonding, characterized in that, include: An annular metal insert sleeve and a through pipe, wherein the through pipe includes an input through pipe and an output through pipe; The annular metal ferrule is provided with a lens channel for accommodating a GRIN lens. The GRIN lens includes an input GRIN lens for connecting to an input optical fiber and an output GRIN lens for connecting to an output optical fiber. The input GRIN lens and the output GRIN lens are optically bonded together. The input end pipe is fitted onto the outside of the annular metal ferrule sleeve, corresponding to the input GRIN lens; the output end pipe is fitted onto the outside of the annular metal ferrule sleeve, corresponding to the output GRIN lens; the side wall of the input end pipe is provided with an input cavity for fluid flow, and the input cavity is circumferentially surrounding the outside of the input GRIN lens. The side wall of the input end pipe is provided with an input inlet and an input outlet communicating with the input cavity; the side wall of the output end pipe is provided with an output cavity for fluid flow, the output cavity is circumferentially surrounding the outside of the output GRIN lens, and the side wall of the output end pipe is provided with an output inlet and an output outlet communicating with the output cavity; One or more of the input inlet, the input outlet, the output inlet, and the output outlet are provided with interfaces, and these interfaces are equipped with valves; The radius of the GRIN lens is 20μm to 20mm; the radius of the GRIN lens is matched with the mode field area of ​​the transmitted light in the input optical fiber and the output optical fiber; The input inlet interface is connected to a fluid device that inputs low-temperature or high-temperature fluid into the input cavity, and the input outlet interface is connected to a pipe that leads the fluid out of the input cavity or directly to the external environment. The output inlet interface is connected to a fluid device that inputs high-temperature or low-temperature fluid into the output cavity, and the output outlet interface is connected to a pipe that leads the fluid out of the output cavity or directly to the external environment. This allows the input GRIN lens and the output GRIN lens, which are connected by optical bonding, to undergo different thermal expansion deformations due to the temperature difference.

2. The fiber coupler based on GRIN lens optical bonding as described in claim 1, characterized in that: The inner diameter of the annular metal ferrule matches the outer diameter of the GRIN lens; and / or, The inner diameter of the through pipe matches the outer diameter of the annular metal insert sleeve.

3. The fiber coupler based on GRIN lens optical bonding as described in claim 1, characterized in that: The lengths of the input GRIN lens and the output GRIN lens are matched to the wavelengths of the light transmitted by the input optical fiber and the output optical fiber.

4. A fiber coupling structure based on GRIN lens optical bonding, characterized in that, include: Optical fiber and the optical fiber coupler based on GRIN lens optical bonding as described in any one of claims 1-3 above; The optical fiber includes an input optical fiber and an output optical fiber; the input optical fiber is connected to the end face of the input GRIN lens away from the output GRIN lens, and the output optical fiber is connected to the end face of the output GRIN lens away from the input GRIN lens; the input optical fiber and the output optical fiber are coaxially arranged.

5. The fiber coupling structure based on GRIN lens optical bonding as described in claim 4, characterized in that: The fiber core diameter ranges from 1 to 200 μm, and the inner cladding diameter ranges from 20 to 2000 μm.

6. An assembly method for an optical fiber coupling structure based on GRIN lens optical bonding, characterized in that, Including the following steps: S1, fusion splice the input fiber and the input GRIN lens, and fusion splice the output fiber and the output GRIN lens; S2, insert the annular metal ferrule into the input and output tubes and glue them together to achieve the connection between the annular metal ferrule and the input and output tubes; S3, polish the end face of the input GRIN lens near the output GRIN lens to meet the requirements for optical adhesive bonding, polish the end face of the output GRIN lens near the input GRIN lens to meet the requirements for optical adhesive bonding, and connect the input GRIN lens and the output GRIN lens with optical adhesive.

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