High extinction ratio polarization maintaining coupling device

Abstract

The utility model relates to a kind of high extinction ratio polarization maintaining coupling devices, including first polarization maintaining optical fiber, birefringent crystal lens and second polarization maintaining optical fiber in order;The first polarization maintaining optical fiber is used to input and transmit linearly polarized light;The optical axis of the birefringent crystal lens and the optical axis of input light form 45 ° angle, for coupling o light in input light to the fiber core of the second polarization maintaining optical fiber, and refract e light in input light to the fiber core outside second polarization maintaining optical fiber, realize o light and e light in input light in the end face space separation of second polarization maintaining optical fiber;The second polarization maintaining optical fiber is used to transmit and output linearly polarized light.The utility model not only avoids depolarization, but also improves the polarization extinction ratio of output light.

Description

Technical Field

[0001] This utility model relates to the field of optical technology, specifically to a high extinction ratio polarization-maintaining coupling device. Background Technology

[0002] Polarization-maintaining fibers, through special structural designs such as panda-type and elliptical-clad types, introduce fixed stress regions within the fiber, resulting in a high birefringence effect. This allows two mutually perpendicular polarization modes (polarized light along the fast and slow axes) to propagate at different speeds within the fiber, thus maintaining the polarization state of the light. Coupling between polarization-maintaining fibers typically uses ordinary lenses as collimators for mutual coupling. Ordinary lenses are usually made of isotropic optical materials, such as common glass, and do not exhibit the stress birefringence found in polarization-maintaining fibers. When light exits a polarization-maintaining fiber, passes through an ordinary lens, and is coupled into another polarization-maintaining fiber, the lens does not maintain the same polarization state as the fiber. This unconstrained propagation causes the polarization state of the light to gradually change, with some light deviating from the direction maintained by the polarization-maintaining fiber. When this light, after propagating through the lens, is then coupled into another polarization-maintaining fiber, it cannot perfectly match the fast and slow axis polarization states of the new fiber, resulting in depolarization. Summary of the Invention

[0003] To address the above-mentioned problems, this invention proposes a high extinction ratio polarization-maintaining coupling device to solve the depolarization problem.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A high extinction ratio polarization-maintaining coupling device, comprising, in sequence, a first polarization-maintaining fiber, a birefringent crystal lens, and a second polarization-maintaining fiber; The first polarization-maintaining fiber is used to input and transmit line-polarized light; The optical axis of the birefringent crystal lens forms a 45° angle with the optical axis of the input light, which is used to couple the o-light in the input light into the core of the second polarization-maintaining fiber and refract the e-light in the input light to the outside of the core of the second polarization-maintaining fiber, thereby realizing the spatial separation of the o-light and e-light in the input light at the end face of the second polarization-maintaining fiber. The second polarization-maintaining fiber is used to transmit and output linearly polarized light.

[0005] Furthermore, the first and second polarization-maintaining fibers are panda-type, bowtie-type, elliptical, or photonic crystal-type polarization-maintaining fibers.

[0006] Furthermore, the angle between the end face of the first polarization-maintaining fiber and the optical axis of the second polarization-maintaining fiber is 0° to 10°.

[0007] Furthermore, the birefringent crystal lens is a cemented lens, which is made of two or more birefringent crystal lenses cemented together, or made of a non-birefringent crystal lens and a birefringent crystal plate cemented together; or made of a birefringent crystal lens and a non-birefringent crystal plate cemented together.

[0008] Furthermore, the front and rear surfaces of the birefringent crystal lens are spherical, aspherical, or planar.

[0009] Furthermore, the front and rear surfaces of the birefringent crystal lens are respectively coated with antireflective films of corresponding wavelengths.

[0010] Furthermore, when the front and rear surfaces of the birefringent crystal lens are planes, the angle between the plane and the optical axis of the birefringent crystal lens is 0°~10°.

[0011] Furthermore, the material of the birefringent crystal lens is barium α-borate crystal, lithium niobate crystal, yttrium vanadate crystal, quartz crystal, calcite, or Iceland spar.

[0012] This invention also includes a second birefringent crystal lens; The birefringent crystal lens, as the first birefringent crystal lens, has its optical axis at a 45° angle to the optical axis of the input light. The optical axis of the second birefringent crystal lens forms a 45° angle with the optical axis of the output light; The optical axes of the first birefringent crystal lens and the second birefringent crystal lens are perpendicular to each other; The first polarization-maintaining fiber and the first birefringent crystal lens are combined to form a fiber collimator structure; The second birefringent crystal lens and the second polarization-maintaining fiber are combined to form an optical fiber collimator structure.

[0013] By adopting the above technical solution, the beneficial effects of this utility model are as follows: This invention utilizes a birefringent crystal as the coupling lens material, with its optical axis at a 45° angle to the input light's optical axis. This allows the o-ray in the input light to propagate normally and couple into the core of the target polarization-maintaining fiber, while preventing the e-ray in the input light from coupling into the core of the target polarization-maintaining fiber. This not only avoids depolarization but also improves the polarization extinction ratio of the output light. Attached Figure Description

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a side view of the structure of Embodiment 1 of the present utility model; Figure 2 This is a top view of the structure of Embodiment 1 of this utility model; Figure 3This is a side view of the structure of Embodiment 2 of this utility model; Figure 4 This is a top view of the structure of Embodiment 2 of this utility model; Figure 5 This is a side view of the structure of Embodiment 3 of this utility model; Figure 6 This is a top view of the structure of Embodiment 3 of this utility model; Figure 7 This is a side view of the structure of Embodiment 4 of this utility model; Figure 8 This is a top view of the structure of Embodiment 4 of this utility model; In the diagram, the solid line represents the transmission path of the o-light, the dashed line represents the transmission path of the e-light, and c represents the direction of the optical axis. Detailed Implementation Example 1

[0015] like Figure 1 and Figure 2 As shown, the high extinction ratio polarization-maintaining coupling device sequentially includes a first polarization-maintaining fiber 101, a birefringent crystal lens 102, and a second polarization-maintaining fiber 103. The angle between the end faces of the first polarization-maintaining fiber 101 and the second polarization-maintaining fiber 103 and the optical axis is 0° to 10°. The first polarization-maintaining fiber 101 is a panda-type polarization-maintaining fiber (it can also be a bow-tie type, elliptical type, or photonic crystal type polarization-maintaining fiber). The material of the birefringent crystal lens 102 is yttrium vanadate crystal (it can also be lithium niobate crystal, yttrium vanadate crystal, quartz crystal, calcite, or Iceland spar). Its optical axis forms a 45° angle with the optical axis of the input light. Both the front and rear surfaces of the birefringent crystal lens 102 are coated with antireflection films of the corresponding wavelength. The front and rear surfaces of the birefringent crystal lens 102 are also coated with antireflection films of the corresponding wavelength. It is an integral structure. Its front surface is a plane (the angle between this plane and the optical axis of the birefringent crystal lens 102 is 0°~10°), and its rear surface is a spherical surface. The second polarization-maintaining fiber 103 is a panda-type polarization-maintaining fiber (it can also be a bow-tie type, elliptical type, or photonic crystal type polarization-maintaining fiber).

[0016] After the input light passes through the first polarization-maintaining fiber 101, it is incident on the birefringent crystal lens 102. The o-ray component of the input light propagates within the birefringent crystal lens 102 according to the normal optical path and is coupled into the core of the second polarization-maintaining fiber 103. Meanwhile, the e-ray component of the input light is deflected by the birefringent crystal lens 102 and remains outside the core of the second polarization-maintaining fiber 103. The second polarization-maintaining fiber 103 ultimately only receives the linearly polarized light of the o-ray component and outputs it, thus improving the extinction ratio of the output linearly polarized light. Example 2

[0017] like Figure 3 and Figure 4As shown, the high extinction ratio polarization-maintaining coupling device includes a first polarization-maintaining fiber 201, a first birefringent crystal lens 202, a second birefringent crystal lens 203, and a second polarization-maintaining fiber 204. The end faces of the first polarization-maintaining fiber 201 and the second polarization-maintaining fiber 204 form an angle of 0° to 10° with the optical axis. The first polarization-maintaining fiber 201 is a panda-type polarization-maintaining fiber (it can also be a bowtie-type, elliptical, or photonic crystal type polarization-maintaining fiber); the first birefringent crystal lens 202 is made of yttrium vanadate crystal (it can also be lithium niobate crystal, yttrium vanadate crystal, quartz crystal, calcite, or Iceland spar), and it is an integral structure. Its front surface is planar (the angle between this planar surface and the optical axis of the first birefringent crystal lens 202 is 0° to 10°), and its rear surface is spherical; the second birefringent crystal lens 203 is made of yttrium vanadate crystal (it can also be lithium niobate crystal, yttrium vanadate crystal, quartz crystal, calcite, or Iceland spar). The optical fiber 103, made of calcite or Iceland spar, is a single-piece structure. Its rear surface is flat (the angle between this flat surface and the optical axis of the second birefringent crystal lens 203 is 0°~10°), and its front surface is spherical. The optical axis of the first birefringent crystal lens 202 forms a 45° angle with the input light axis; the optical axis of the second birefringent crystal lens 203 forms a 45° angle with the output light axis; the optical axes of the first and second birefringent crystal lenses 202 are perpendicular to each other; the second polarization-maintaining fiber 103 is a panda-type polarization-maintaining fiber (it can also be a bowtie-type, elliptical, or photonic crystal-type polarization-maintaining fiber). The first polarization-maintaining fiber 201 and the first birefringent crystal lens 202 combine to form an optical fiber collimator structure; the second polarization-maintaining fiber 204 and the second birefringent crystal lens 203 combine to form an optical fiber collimator structure.

[0018] After the input light passes through the first polarization-maintaining fiber 201, it is incident on the first birefringent crystal lens 202. The o-ray component of the input light is transmitted through the first birefringent crystal lens 202 and the second birefringent crystal lens 203 according to the normal optical path and is coupled into the core of the second polarization-maintaining fiber 204. However, the e-ray component of the input light is deflected outside the core of the second polarization-maintaining fiber 204 by the second birefringent crystal lens 203 due to the presence of the first birefringent crystal lens 202 and the second birefringent crystal lens 203. The second polarization-maintaining fiber 204 ultimately only receives the linearly polarized light of the o-ray component and outputs it, thus improving the extinction ratio of the output linearly polarized light. Example 3

[0019] like Figure 5 and Figure 6As shown, the high extinction ratio polarization-maintaining coupling device sequentially includes a first polarization-maintaining fiber 301, a birefringent crystal lens, and a second polarization-maintaining fiber 304. The structural difference between this third embodiment and the first embodiment lies in the following: the birefringent crystal lens is a cemented lens, formed by cementing together a conventional glass plano-convex lens 302 and a birefringent crystal plate 303 arranged sequentially. The first polarization-maintaining fiber 301 is a panda-type polarization-maintaining fiber, and the birefringent crystal plate 303 is made of yttrium vanadate crystal, with its optical axis forming a 45° angle with the input light optical axis; the second polarization-maintaining fiber 304 is also a panda-type polarization-maintaining fiber. After the input light passes through the first polarization-maintaining fiber 301, it is incident on the ordinary glass plano-convex lens 302. The light is then focused by the ordinary glass plano-convex lens 302 and incident on the birefringent crystal plate 303. The o-ray component of the input light propagates normally within the birefringent crystal plate 303 and is coupled into the core of the second polarization-maintaining fiber 304. Meanwhile, the e-ray component of the input light is deflected by the birefringent crystal plate 303 and remains outside the core of the second polarization-maintaining fiber 304. The second polarization-maintaining fiber 304 ultimately only receives the linearly polarized o-ray component and outputs it, thus improving the extinction ratio of the output linearly polarized light. Example 4

[0020] like Figure 7 and Figure 8 As shown, the high extinction ratio polarization-maintaining coupling device includes, in sequence, a first polarization-maintaining fiber 401, a first birefringent crystal lens, a second birefringent crystal lens, and a second polarization-maintaining fiber 406.

[0021] The structural difference between Embodiment 4 and Embodiment 2 is that both the first birefringent crystal lens and the second birefringent crystal lens are cemented lenses. The first birefringent crystal lens is formed by cementing a first birefringent crystal plate 402 and a first ordinary glass plano-convex lens 403 together, arranged sequentially. The second birefringent lens is formed by cementing a second ordinary glass plano-convex lens 404 and a second birefringent crystal plate 405 together, arranged sequentially.

[0022] The first polarization-maintaining fiber 401 is a panda-type polarization-maintaining fiber; the first birefringent crystal plate 402 and the second birefringent crystal plate 405 are made of yttrium vanadate crystal; the optical axis of the first birefringent crystal plate 402 forms a 45° angle with the input optical axis; the optical axis of the second birefringent crystal plate 405 forms a 45° angle with the output optical axis; the optical axes of the first birefringent crystal plate 402 and the second birefringent crystal plate 405 are perpendicular to each other; the second polarization-maintaining fiber 103 is a panda-type polarization-maintaining fiber. The first polarization-maintaining fiber 401, the first birefringent crystal plate 402, and the first ordinary glass plano-convex lens 403 are combined to form an optical fiber collimator structure; the second ordinary glass plano-convex lens 404, the second birefringent crystal plate 405, and the second polarization-maintaining fiber 406 are combined to form an optical fiber collimator structure. After the input light passes through the first polarization-maintaining fiber 401, it is incident on the first birefringent crystal plate 402. The o-ray component of the input light passes through the first birefringent crystal plate 402 according to the normal optical path, is then collimated by the first ordinary glass plano-convex lens 403, and then incident on the second ordinary glass plano-convex lens 404 before being focused onto the second birefringent crystal plate 405. After passing through the second birefringent crystal plate 405 according to the normal optical path, it is coupled into the core of the second polarization-maintaining fiber 406. The e-ray component of the input light deviates from the normal optical path, passing through the first birefringent crystal plate 402, being collimated by the first ordinary glass plano-convex lens 403, and then incident on the second ordinary glass plano-convex lens 404 before being focused onto the second birefringent crystal plate 405. After deviating from the normal optical path, it is focused outside the core of the second polarization-maintaining fiber 406. Ultimately, the second polarization-maintaining fiber 406 only receives the linearly polarized o-ray component and outputs it, thus improving the extinction ratio of the output linearly polarized light.

[0023] The specific embodiments of this utility model have been described above. However, those skilled in the art should understand that this is only an example. Those skilled in the art can make various changes or modifications to this embodiment without departing from the principle and essence of this utility model, but all such changes and modifications fall within the protection scope of this utility model.

Claims

1. A high extinction ratio polarization-maintaining coupling device, characterized in that: The components are, in sequence, a first polarization-maintaining fiber, a birefringent crystal lens, and a second polarization-maintaining fiber; The first polarization-maintaining fiber is used to input and transmit line-polarized light; The optical axis of the birefringent crystal lens forms a 45° angle with the optical axis of the input light, which is used to couple the o-light in the input light into the core of the second polarization-maintaining fiber and refract the e-light in the input light to the outside of the core of the second polarization-maintaining fiber, thereby realizing the spatial separation of the o-light and e-light in the input light at the end face of the second polarization-maintaining fiber. The second polarization-maintaining fiber is used to transmit and output linearly polarized light.

2. The high extinction ratio polarization-maintaining coupling device according to claim 1, characterized in that: The first and second polarization-maintaining fibers are panda-type, bowtie-type, elliptical, or photonic crystal-type polarization-maintaining fibers.

3. The high extinction ratio polarization-maintaining coupling device according to claim 1, characterized in that: The angle between the end face of the first polarization-maintaining fiber and the optical axis of the second polarization-maintaining fiber is 0° to 10°.

4. The high extinction ratio polarization-maintaining coupling device according to claim 1, characterized in that: The birefringent crystal lens is a cemented lens, which is made of two or more birefringent crystal lenses cemented together, or made of a non-birefringent crystal lens and a birefringent crystal plate cemented together; or made of a birefringent crystal lens and a non-birefringent crystal plate cemented together.

5. The high extinction ratio polarization-maintaining coupling device according to claim 1, characterized in that: The front and rear surfaces of the birefringent crystal lens are spherical, aspherical, or planar.

6. The high extinction ratio polarization-maintaining coupling device according to claim 1, characterized in that: The front and rear surfaces of the birefringent crystal lens are coated with antireflective films of corresponding wavelengths.

7. The high extinction ratio polarization-maintaining coupling device according to claim 1, characterized in that: When the front and rear surfaces of the birefringent crystal lens are planes, the angle between the plane and the optical axis of the birefringent crystal lens is 0° to 10°.

8. The high extinction ratio polarization-maintaining coupling device according to claim 1, characterized in that: The material of the birefringent crystal lens is barium α-borate crystal, lithium niobate crystal, yttrium vanadate crystal, quartz crystal, calcite, or Iceland spar.

9. A high extinction ratio polarization-maintaining coupling device according to claim 1, characterized in that: It also includes a second birefringent crystal lens; The birefringent crystal lens, as the first birefringent crystal lens, has its optical axis at a 45° angle to the optical axis of the input light. The optical axis of the second birefringent crystal lens forms a 45° angle with the optical axis of the output light; The optical axes of the first birefringent crystal lens and the second birefringent crystal lens are perpendicular to each other; The first polarization-maintaining fiber and the first birefringent crystal lens are combined to form a fiber collimator structure; The second birefringent crystal lens and the second polarization-maintaining fiber are combined to form an optical fiber collimator structure.

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