Photonic crystal fiber of coupling lens

Abstract

The invention relates to a photonic crystal fiber of a coupling lens, and belongs to the technical field of microstructure optical fibers. The photonic crystal fiber and the lens are welded, so that the light beam collimation emergent condition can be met, the light beam collimation emergent position and the property of an output light beam can be flexibly adjusted according to needs, and the adjustability of optical fiber output is improved; the design and manufacturing difficulty of the photonic crystal fiber is reduced, meanwhile, the problem that the photonic crystal fiber is prone to being blocked, damaged and polluted is solved, and light beam auto-collimation emergence is achieved so as to improve the coupling efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of microstructure optical fibers, and in particular to a photonic crystal optical fiber coupled with a lens. Background Art

[0002] With the advancement and development of science and technology, people have higher and higher requirements for Internet speed. To meet this demand, optical fiber communication systems are developing towards higher transmission rates, larger capacity, and longer transmission distances. Especially for high-power lasers, it is necessary to increase the single-mode transmission power. Traditional optical fibers are limited by their structure, materials, and manufacturing processes. It is very difficult to reduce losses and achieve high-power transmission while ensuring single-mode transmission.

[0003] At present, although photonic crystal fiber is suitable for high-power laser transmission, its special microporous structure is prone to contamination, damage, and blockage. In the construction of optical fiber networks, optical connectors are indispensable. At present, PC optical fiber connectors are commonly used. The end faces of the butt joint are in physical contact. The principle is to grind and polish the end face of the optical fiber ceramic ferrule into a convex arch structure. By applying a certain pressure, the ball end face of the ceramic ferrule is slightly deformed and pressed against each other to ensure close contact between the two optical fiber end faces. For photonic crystal fiber, due to the fragility of the microporous structure, if the conventional grinding and polishing process is performed on it when using the optical fiber connector, the glass fiber around the microporous pores will be broken into the pores, which will inevitably lead to the blockage of the microporous pores. The change in its structure will lead to a decrease in transmission efficiency and performance; the butt joint process also requires very fine control, otherwise it is easy to cause damage to the optical fiber. The microporous pores on the end face of the photonic crystal fiber are easily contaminated when exposed to the air for a long time, and the entry of dust and water vapor will also affect the transmission performance of the optical fiber.

[0004] In addition, the light beam will be emitted from the output end face of the optical fiber at a certain angle. This divergence angle is related to the numerical aperture NA of the optical fiber. When the optical fiber is coupled to the subsequent device, due to the large divergence angle and fiber mode field mismatch, a large coupling loss will be generated, thus affecting the light transmission performance. Summary of the invention

[0005] In view of the above problems, the present invention provides a photonic crystal fiber coupled with a lens. The present invention fuses the photonic crystal fiber with a convex lens, and adjusts the thickness and curvature radius of the convex lens to meet the conditions for collimated light beam emission. The waist position and Rayleigh distance of the collimated light beam output by the lens are further adjusted to achieve the adjustment of the collimated position of the light beam. By adjusting the curvature radius of the lens, light beams at different positions can also be focused. The adjustability of the optical fiber output is increased, and the difficulty of designing and manufacturing the photonic crystal fiber is reduced. At the same time, the problem that the photonic crystal fiber is easily blocked, damaged, and contaminated is solved, and the self-collimated light beam is achieved to improve the coupling efficiency.

[0006] The present invention provides a photonic crystal fiber coupled with a lens, comprising: a photonic crystal fiber 1 and a lens 2;

[0007] The output end face of the photonic crystal fiber 1 is fused with the end face 21 of the lens 2; preferably, the photonic crystal fiber 1 comprises: a core layer and a cladding layer; the core layer and the cladding layer are concentric;

[0008] Optionally, the output end face of the photonic crystal fiber 1 is welded to the end face 21 of the lens 2 using a CO2 laser welding machine, and the light passing position is close to one side of the lens 2 to avoid the collapse of the pores on the output end face of the photonic crystal fiber 1, thereby causing a large loss;

[0009] For example, an LZM-100 welding machine is used, and the light transmission position is set to 60 μm toward lens 2, the light transmission power is -100 bits, and the light transmission time is 1000 ms.

[0010] Furthermore, the core layer is made of quartz material; the cladding layer is a two-dimensional photonic crystal structure;

[0011] Exemplarily, the two-dimensional photonic crystal structure is composed of a periodic arrangement of silicon dioxide SiO2 and air holes.

[0012] Preferably, the lens 2 comprises an end surface 1 21, an end surface 22 and an outer peripheral surface 2; the outer peripheral surface 2 is respectively connected to the end surface 1 21 and the end surface 2 22;

[0013] Further, the second end face 22 of the lens is an arc surface; the second end face 22 is the output surface of the photonic crystal fiber coupled to the lens;

[0014] Exemplarily, the arcuate surface is a convex spherical surface;

[0015] Furthermore, the photonic crystal fiber 1 is a refractive index guided photonic crystal fiber; the material of the lens 2 is a solid capillary quartz rod;

[0016] Preferably, the ratio of the refractive index n1 of the core layer to the refractive index n3 of the lens 2 is 1:1;

[0017] Preferably, the focal length EFL of the lens 2 is the distance between the focus F of the light transmitted from the end face 1 21 and the front principal point H of the light on the lens 2 or the distance between the focus F' of the light transmitted from the end face 22 and the rear principal point H' of the light on the lens 2;

[0018] Preferably, the focal length EFL of the lens 2 is expressed as:

[0019]

[0020] Among them, R is the radius of curvature of the second end surface of the lens, and n3 is the refractive index of the lens.

[0021] The expression for the front focal length of the lens is:

[0022]

[0023] Where, t is the lens thickness, FFL is the front focal length of the lens;

[0024] The focal plane of the lens 2 is located at the output end face of the optical fiber, which is a plane perpendicular to the main optical axis of the focus F of the light transmitted from the end face 21, and is used to realize the collimated emission of the light beam 3;

[0025] The focal plane of the lens 2 is located at the output end face of the optical fiber, and the expression is:

[0026]

[0027] The expression of the curvature radius of the second end face of the lens 2 is:

[0028]

[0029] Among them, R is the radius of curvature of the second end surface of the lens, n3 is the refractive index of the lens, and t is the thickness of the lens.

[0030] The present invention does not need to design and manufacture a complex gradient refractive index optical fiber lens. It only needs to design the output end face of the quartz rod as a convex spherical surface according to the length of the fused solid-core quartz capillary rod, adjust the thickness and curvature radius of the convex lens to design the geometric structure of the lens output end face, and the light beam collimation emission condition can be met. By adjusting the thickness of the coupling lens, the curvature radius of the lens is matched with it, and the waist position and Rayleigh distance of the collimated light beam output by the lens are further adjusted to change accordingly, thereby realizing the adjustment of the light beam collimation position. By adjusting the curvature radius of the lens, light beam focusing at different positions can also be realized. The adjustability of the optical fiber output is increased, and the difficulty of designing and manufacturing the photonic crystal optical fiber is reduced. At the same time, the problem that the photonic crystal optical fiber is easily blocked, damaged, and contaminated is solved, and the self-collimation emission of the light beam is realized to improve the coupling efficiency.

[0031] The refractive index-guided photonic crystal fiber of the present invention effectively adjusts the equivalent refractive index of the cladding to be smaller than the refractive index of the core by introducing a periodically arranged micro air hole array in the cladding. The refractive index difference allows light to undergo total internal reflection in the core, thereby limiting the propagation of light waves in the core of the fiber in the air hole-free region of the fiber.

[0032] The photonic crystal fiber used in the present invention has a large mode area (LMA) and can realize high-power laser transmission. On the one hand, since the size of the mode area of ​​the photonic crystal fiber directly affects the strength of the nonlinear effect, by increasing the mode area, while ensuring the quality of laser transmission, the laser power density in the fiber can be significantly reduced, the damage threshold of the fiber material can be effectively increased, and the nonlinear effect in the transmission process can be reduced, which is conducive to the stable transmission of pulses therein. On the other hand, the photonic crystal fiber can achieve a larger numerical aperture, thereby improving the coupling efficiency of the optical fiber transmission light to achieve high-power output.

[0033] Photonic crystal fiber achieves a large effective mode field area by adjusting the geometric characteristics of the cross section, changing the diameter of the air hole in the cladding area, the center distance between two adjacent air holes, and the diameter of the central equivalent solid core. When the duty cycle (the ratio of the air hole diameter to the center distance between two adjacent air holes) is less than 0.4, large mode field transmission can be achieved while maintaining single mode.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] (1) The present invention solves the problem that photonic crystal optical fibers are easily contaminated when stored and easily blocked and damaged when used in optical fiber networks;

[0036] (2) The present invention can realize self-collimation of the light beam, reduce the coupling loss with subsequent devices, and improve the coupling efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings are only for the purpose of illustrating particular embodiments and are not to be construed as limiting the invention.

[0038] Figure 1 Schematic diagram of the cross-sectional structure of a photonic crystal fiber coupled with a lens in an embodiment of the present invention;

[0039] Figure 2 A geometric structure diagram of a lens of a photonic crystal fiber coupled with a lens in an embodiment of the present invention;

[0040] Figure 3 Graph showing the output ray trajectory of the photonic crystal fiber coupled with the lens in an embodiment of the present invention.

[0041] Reference numerals:

[0042] Photonic crystal fiber 1, lens 2, end face 1 21, end face 2 22, beam 3, core refractive index n1, cladding refractive index n1, lens 2 refractive index n3, end face 1 21 focus F, end face 2 22 focus F', distance of rear principal point H', front focal length FFL of lens 2, focal length EFL of lens 2, front principal point H, rear principal point H' DETAILED DESCRIPTION

[0043] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. In addition, the present invention can also be implemented in other ways different from those described herein, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0044] A specific embodiment of the present invention, as Figure 1-3 , discloses a photonic crystal fiber coupled with a lens. In order to illustrate the effectiveness of the method proposed by the present invention, the above technical solution of the present invention is described in detail through a specific embodiment below. The specific implementation steps are as follows:

[0045] The present invention provides a photonic crystal fiber coupled with a lens, comprising: a photonic crystal fiber 1 and a lens 2;

[0046] The output end face of the photonic crystal fiber 1 is fused with the end face 21 of the lens 2;

[0047] Optionally, the output end face of the photonic crystal fiber 1 is welded to the end face 21 of the lens 2 using a CO2 laser welding machine, and the light passing position is close to one side of the lens 2 to avoid the collapse of the pores on the output end face of the photonic crystal fiber 1, thereby causing a large loss;

[0048] For example, using an LZM-100 welding machine, the light transmission position is set to 260 μm toward the lens, the light transmission power is -100 bits, and the light transmission time is 1000 ms.

[0049] Preferably, the photonic crystal optical fiber 1 comprises: a core layer and a cladding layer; the core layer and the cladding layer are concentric;

[0050] Furthermore, the core layer is made of quartz material; the cladding layer is a two-dimensional photonic crystal structure;

[0051] Exemplarily, the two-dimensional photonic crystal structure is composed of a periodic arrangement of silicon dioxide SiO2 and air holes.

[0052] Preferably, the lens 2 comprises an end surface 1 21, an end surface 22 and an outer peripheral surface 2; the outer peripheral surface 2 is respectively connected to the end surface 1 21 and the end surface 2 22;

[0053] Further, the second end face 22 of the lens is an arc surface; the second end face 22 is the output surface of the photonic crystal fiber coupled to the lens;

[0054] Exemplarily, the arcuate surface is a convex spherical surface;

[0055] Furthermore, the photonic crystal fiber 1 is a refractive index guided photonic crystal fiber; the material of the lens 2 is a solid capillary quartz rod;

[0056] Preferably, the ratio of the refractive index n1 of the core layer to the refractive index n3 of the lens 2 is 1:1;

[0057] Preferably, the focal length EFL of the lens 2 is the distance between the focus F of the light transmitted from the end face 1 21 and the front principal point H of the light on the lens 2 or the distance between the focus F' of the light transmitted from the end face 22 and the rear principal point H' of the light on the lens 2;

[0058] The expression for the front focal length of the lens is:

[0059]

[0060] Where, t is the lens thickness, FFL is the front focal length of the lens;

[0061] The focal plane of the lens 2 is located at the output end face of the optical fiber, which is a plane perpendicular to the main optical axis of the focus F of the light transmitted from the end face 21, and is used to realize the collimated emission of the light beam 3;

[0062] The focal plane of the lens 2 is located at the output end face of the optical fiber, and the expression is:

[0063]

[0064] The expression of the curvature radius of the second end face of the lens 2 is:

[0065]

[0066] Among them, R is the radius of curvature of the second end surface of the lens, n3 is the refractive index of the lens, and t is the thickness of the lens.

[0067] The present invention does not need to design and manufacture a complex gradient refractive index optical fiber lens. It only needs to design the output end face of the quartz rod as a convex spherical surface according to the length of the fused solid core quartz capillary rod, adjust the thickness and curvature radius of the convex lens to design the geometric structure of the lens output end face, and the light beam collimation emission condition can be met. By adjusting the thickness of the coupling lens, the curvature radius of the lens is matched with it, and the waist position and Rayleigh distance of the collimated light beam output by the lens are further adjusted to change accordingly, thereby realizing the adjustment of the light beam collimation position. By adjusting the curvature radius of the lens, light beam focusing at different positions can also be realized. The adjustability of the optical fiber output is increased, and the difficulty of designing and manufacturing the photonic crystal optical fiber is reduced. At the same time, the problem that the photonic crystal optical fiber is easily blocked, damaged, and contaminated is solved, and the self-collimation emission of the light beam is realized to improve the coupling efficiency.

[0068] The refractive index-guided photonic crystal fiber of the present invention effectively adjusts the equivalent refractive index of the cladding to be smaller than the refractive index of the core by introducing a periodically arranged micro air hole array in the cladding. The refractive index difference allows light to undergo total internal reflection in the core, thereby limiting the propagation of light waves in the core of the fiber in the air hole-free region of the fiber.

[0069] The photonic crystal fiber used in the present invention has a large mode area (LMA) and can realize high-power laser transmission. On the one hand, since the size of the mode area of ​​the photonic crystal fiber directly affects the strength of the nonlinear effect, by increasing the mode area, while ensuring the quality of laser transmission, the laser power density in the fiber can be significantly reduced, the damage threshold of the fiber material can be effectively increased, and the nonlinear effect in the transmission process can be reduced, which is conducive to the stable transmission of pulses therein. On the other hand, the photonic crystal fiber can achieve a larger numerical aperture, thereby improving the coupling efficiency of the optical fiber transmission light to achieve high-power output.

[0070] Photonic crystal fiber achieves a large effective mode field area by adjusting the geometric characteristics of the cross section, changing the diameter of the air hole in the cladding area, the center distance between two adjacent air holes, and the diameter of the central equivalent solid core. When the duty cycle (the ratio of the air hole diameter to the center distance between two adjacent air holes) is less than 0.4, large mode field transmission can be achieved while maintaining single mode.

[0071] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A photonic crystal fiber coupled with a lens, characterized in that: include: A photonic crystal optical fiber (1) and a lens (2); the lens (2) comprises an end face 1 (21) and an end face 2 (22); The output end face of the photonic crystal fiber (1) is fused with the end face one (21) of the lens (2); the end face two (22) is the output face of the photonic crystal fiber coupled with the lens; the end face two (22) of the lens is an arc-shaped surface.

2. The photonic crystal fiber of the coupling lens according to claim 1, characterized in that: The photonic crystal optical fiber (1) comprises: a core layer and a cladding layer; the core layer and the cladding layer are concentric; The core layer is made of quartz material; the cladding layer is a two-dimensional photonic crystal structure.

3. The photonic crystal fiber of the coupling lens according to claim 1, characterized in that: The lens (2) comprises a second outer peripheral surface; the second outer peripheral surface is respectively connected to the first end surface (21) and the second end surface (22).

4. The photonic crystal fiber of the coupling lens according to claim 1, characterized in that: The arc surface is a convex spherical surface.

5. The photonic crystal fiber of the coupling lens according to claim 1, characterized in that: The photonic crystal fiber (1) is a refractive index guided photonic crystal fiber; The lens (2) is made of a solid capillary quartz rod.

6. The photonic crystal fiber of the coupling lens according to claim 1, characterized in that: The focal length of the lens (2) is the distance between the focus of the light transmitted from the first end face (21) and the front principal point of the light on the lens (2), or the distance between the focus of the light transmitted from the second end face (22) and the rear principal point of the light on the lens.

7. The photonic crystal fiber of the coupling lens according to claim 6, characterized in that: The lens (2) comprises a focal plane; the focal plane is located at the output end face of the optical fiber and is used to achieve collimated emission of the light beam (3).

8. The photonic crystal fiber of the coupling lens according to claim 7, characterized in that: The focal length EFL of the lens (2) is expressed as: Among them, EFL is the focal length of the lens, R is the radius of curvature of the second end surface of the lens, and n3 is the refractive index of the lens.

9. The photonic crystal fiber of the coupling lens according to claim 8, characterized in that: The expression for the front focal length of the lens is: Where, FFL is the front focal length of the lens, and t is the thickness of the lens; 10. The photonic crystal fiber of the coupling lens according to claim 9, characterized in that: The expression for the curvature radius of the second end face of the lens (2) is: Among them, R is the radius of curvature of the second end surface of the lens, n3 is the refractive index of the lens, and t is the thickness of the lens.

Images