CN111562686A - A spatial light adaptive coupling device based on crystal electro-optic effect - Google Patents

Abstract

The invention belongs to the technical field of photoelectric communication, and more particularly, relates to a spatial light adaptive coupling device based on crystal electro-optic effect. It includes a self-focusing lens, a supporting platform and a trapezoidal optical fiber. The optical fiber core diameter of the trapezoidal optical fiber decreases from the front section to the tail section. The trapezoidal optical fiber includes at least three sections of optical fiber, wherein the front section is a multi-mode fiber, and the tail section is a single-mode optical fiber and a multi-mode optical fiber. The front end of the optical fiber is located at the focal point of the self-focusing lens, and the trapezoidal optical fiber is arranged on the supporting platform. The device has the characteristics of automatic response and dynamic adjustment, and the potential distribution can be adjusted according to the coupling efficiency, thereby changing the focusing constant and focal length of the self-focusing lens, optimizing the structure of the device, and ensuring the efficient coupling of space light to single-mode fiber. In addition, because the device is easy to control, has no mechanical structure, and has a high degree of integration, the device has higher application value.

Description

A spatial light adaptive coupling device based on crystal electro-optic effect

technical field

The invention belongs to the technical field of photoelectric communication, and more particularly, relates to a spatial light adaptive coupling device based on crystal electro-optic effect.

Background technique

The electro-optic effect of a crystal refers to an effect in which the optical refractive index of a crystal changes due to an applied electric field. When the refractive index varies linearly with the applied electric field, this effect is called the linear electro-optic effect. For LiNbO ₃ crystal, when the applied electric field direction is along the Z direction of the crystal optical axis, the principal axis direction does not change and the refractive index in each direction is related to the applied electric field strength.

Self-focusing lens refers to that the refractive index of the medium changes according to a certain rule along the radial direction, and the refractive index distribution is used to guide the refraction and propagation of the beam to achieve beam width compression. Therefore, the self-focusing lens is also called a gradient index lens. Ordinary lenses will increase the divergence angle when compressing the beam width. Since the refractive index of the self-focusing lens is distributed in a gradient, spherical aberration and astigmatism can be corrected at the same time. Therefore, the self-focusing lens reduces the divergence caused by the beam waist radius. The degree of angle increase is much smaller than that of ordinary lenses. The end face of the self-focusing lens is flat and can be directly bonded to the end face of the optical fiber. The structure is compact, stable and easy to adjust. ) and the mode power distribution in the fiber.

Spatial optical coupling is one of the key technologies in the field of free-space optical communication. Since most optical communication technologies need to use erbium-doped fiber amplification technology, the coupling technology usually requires single-mode fiber as a carrier for coupling, but the diameter of the single-mode fiber is only 9-10 μm, and the numerical aperture is only about 0.14, so from the space optical signal Coupling efficiency to single mode fiber is limited. Moreover, the structure of such a device is relatively complex, and the adjustment of the system structure is also very difficult.

SUMMARY OF THE INVENTION

In order to solve the problems of low spatial light coupling efficiency, complex structure and difficult adjustment, the present invention provides a high-efficiency automatic coupling device for spatial light without mechanization and electronic control based on the electro-optic effect of crystal.

The invention combines the characteristics of large-area reception of the self-focusing lens and the low coupling energy loss of the trapezoidal optical fiber, and uses the distributed potential points to dynamically adjust the self-focusing lens module and the trapezoidal structure module, and proposes a space optical self-focusing system based on the crystal electro-optic effect. The adaptive coupling device can be applied to technical fields such as fiber laser, space optical communication and astronomical observation. Compared with the traditional coupling system, it solves the problems of difficult structural optimization, difficult processing, and low coupling efficiency.

For achieving the above object, the present invention provides the following technical solutions:

A space light adaptive coupling device based on crystal electro-optic effect, comprising a self-focusing lens, a support platform and a trapezoidal optical fiber, the optical fiber core diameter of the trapezoidal optical fiber decreases from the front section to the tail section, and the trapezoidal optical fiber includes at least three sections of optical fiber, wherein the front section of the optical fiber is reduced. It is a multi-mode fiber, the tail section is a single-mode fiber, the front end of the multi-mode fiber is located at the focal point of the self-focusing lens, and the trapezoidal fiber is arranged on the support platform.

The technical solution is further optimized, and the middle section of the trapezoidal optical fiber is a multi-mode optical fiber and/or a few-mode optical fiber.

The technical solution is further optimized. The front section of the trapezoidal optical fiber is a multi-mode fiber, the middle section is a few-mode fiber, and the tail section is a single-mode fiber. Trapezoidal fiber refers to the coupling structure of multi-mode fiber-few-mode fiber-single-mode fiber. The self-focusing lens compresses the beam waist of the space light, so that the focus of the lens is located on the end face of the multimode fiber, and the optical signal coupled into the multimode fiber passes through the trapezoidal fiber and is output from the single mode fiber.

The technical solution is further optimized. The trapezoidal fiber is set to have a cladding radius of 125 μm, a multimode fiber core diameter of 100 μm, a single-mode fiber core diameter of 10 μm, and a few-mode fiber core diameter of 20 to 80 μm.

The technical solution is further optimized, and the self-focusing lens is made of LiNbO ₃ crystal.

The technical solution is further optimized. A plurality of potential points are densely distributed on the LiNbO ₃ crystal, and different potential values can be applied to each potential point. Since a potential difference can be formed between potential points of different potentials, according to the electro-optic effect of the crystal, the refractive index of the crystal is related to the applied electric field strength, so applying the corresponding potential at the potential points at different positions can realize the refraction of each part of the workbench. Control of the rate distribution.

Different from the prior art, the above-mentioned technical scheme has the following beneficial effects:

The invention utilizes the distributed potential control self-focusing lens and the high coupling efficiency of the trapezoidal optical fiber to realize the efficient coupling of the space light. The self-focusing lens has the characteristics of receiving the mode field in a large area, which can increase the numerical aperture of the receiving end. At the same time, the device has the characteristics of automatic response and dynamic adjustment, and the potential distribution can be adjusted according to the coupling efficiency, thereby changing the focusing constant and focal length of the self-focusing lens, optimizing the structure of the device, and ensuring the efficient coupling of space light to single-mode fiber. In addition, because the device is easy to control, has no mechanical structure, and has a high degree of integration, the device has higher application value.

Description of drawings

FIG. 1 is a schematic structural diagram of a spatial light adaptive coupling device based on crystal electro-optic effect;

2 is a schematic structural diagram of a self-focusing lens;

Figure 3 is a schematic diagram of the optical path of the self-focusing lens.

In the picture: 1. LiNbO ₃ crystal, 2. Potential point, 3. Self-focusing lens, 4. Support platform, 5. Multimode fiber, 6. Few mode fiber, 7. Single mode fiber.

Detailed ways

In order to describe in detail the technical content, structural features, achieved objectives and effects of the technical solution, the following detailed description is given in conjunction with specific embodiments and accompanying drawings.

The invention proposes a space light adaptive coupling device based on crystal electro-optic effect, comprising a self-focusing lens, a support platform and a trapezoidal optical fiber, the ladder-shaped optical fiber includes a multi-mode optical fiber and a single-mode optical fiber, and the front section of the multi-mode optical fiber is located in the self-focusing optical fiber At the focal point of the lens, the trapezoidal fiber is set on the support platform.

A preferred embodiment of the present invention is a spatial light adaptive coupling device based on crystal electro-optic effect. Please refer to FIG. 1 , which is a schematic structural diagram of a spatial light adaptive coupling device based on crystal electro-optic effect. Support platform 4 and trapezoidal fiber. The self-focusing lens 3 is arranged on the front section of the trapezoidal optical fiber, the trapezoidal optical fiber is fixed on the support platform 4, and the end face of the front section is located at the focal point of the lens.

The trapezoidal fiber structure refers to inserting a few-mode fiber between the multi-mode fiber and the single-mode fiber, which reduces the loss of high-order modes in the multi-mode fiber, can effectively improve the coupling efficiency of the multi-mode fiber to the single-mode fiber, and improve the loss resistance of the equipment. sex. The coupling efficiency of the trapezoidal fiber has a great relationship with the fiber structure. The number of structural layers and the fiber length directly determine the coupling efficiency and the sensitivity to the coupling angle of the trapezoidal fiber. Compared with the traditional split lens coupling, the coupling efficiency of the trapezoidal fiber structure is higher, and the coupling efficiency of the multimode fiber to the single mode fiber can be increased from 4% to 52% without transition; Tapered fibers and trapezoidal fibers are less difficult to process and have better damage resistance, making them more suitable for engineering applications.

The coupling efficiency of the ladder fiber has a great relationship with the fiber structure. According to the simulation results, the number of layers and the fiber length of the ladder fiber directly determine the coupling efficiency and the sensitivity to the coupling angle of the ladder fiber. Therefore, in different applications, a trapezoidal fiber with adjustable parameters such as core diameter, fiber length, and layer number of the trapezoidal fiber is required, which is difficult to achieve for traditional SiO2 fibers.

The front section of the trapezoidal optical fiber in this embodiment is a multi-mode fiber 5 , the middle section is a few-mode fiber 6 , and the tail section is a single-mode fiber 7 . The self-focusing lens 3 compresses the beam waist of the spatial light so that the focus of the lens is located on the end face of the multimode fiber 5, and the optical signal coupled into the multimode fiber passes through the trapezoidal fiber and is output from the single mode fiber. Since the core diameter of the multimode fiber 5 is large and the coupling efficiency of the trapezoidal fiber is high, the coupling efficiency of the spatial optical coupling scheme is high. The space light passes through the self-focusing lens 3 and then compresses the beam waist and couples into the multi-mode fiber 5. The end face of the multi-mode fiber 5 is located at the focal point of the self-focusing lens 3, and the converged light is coupled into the trapezoidal fiber, and the optical signal is output from the tail section of the coupling structure. The tail section of the trapezoidal fiber is a single-mode fiber 7 .

In the trapezoidal fiber of this embodiment, the cladding radius is set to be 125 μm, the core diameter of the multi-mode fiber is 100 μm, the core diameter of the single-mode fiber is 10 μm, and the optimal range of the core diameter of the few-mode fiber is 20-80 μm. It should be noted that one of the innovations of the present invention is a trapezoidal fiber, the front section of the ladder fiber is a multimode fiber, the tail section is a single mode fiber, and the middle section is not limited, and is a multimode fiber or/and a few mode fiber. Therefore, those skilled in the art know that the ladder fiber can be composed of multi-mode fiber, multi-mode fiber, few-mode fiber, single-mode fiber, or multi-mode fiber, few-mode fiber, few-mode fiber, and single-mode fiber. From the front section to the tail section of the trapezoidal fiber, the fiber core diameter gradually decreases.

Referring to FIG. 2 , it is a schematic diagram of the structure of the self-focusing lens. The self-focusing lens 3 of this embodiment is composed of a LiNbO ₃ crystal 1 in which a plurality of potential points 2 are densely distributed. In the coupling device, a plurality of potential points 2 are densely distributed on the LiNbO ₃ crystal 1 , and different potential values can be applied to each potential point 2 . Since a potential difference can be formed between potential points of different potentials, according to the electro-optic effect of the crystal, the refractive index of the crystal is related to the applied electric field strength, so applying the corresponding potential at the potential points at different positions can realize the refraction of each part of the workbench. Control of the rate distribution. Based on the control of the refractive index distribution in each region, the self-focusing lens has different focusing constants and focal points under different potential distributions. The potential points 2 are densely distributed on the LiNbO ₃ crystal 1, and the higher the distribution density, the better the optimization effect. The refractive index of the self-focusing lens 3 is set as a gradient distribution, so that the focal point of the lens is located at the multimode fiber 5 .

By changing the potential distribution to change the focusing parameter A of the self-focusing lens, for example, a computer can be used to obtain the output power under different A values, obtain the A value corresponding to the maximum output power, and optimize the lens structure.

Refer to Figure 3, which is the schematic diagram of the optical path of the self-focusing lens. The end face of the self-focusing lens is flat and can be directly bonded to the end face of the optical fiber. The structure is compact, stable and easy to adjust. The coupling loss is taken on each optical surface to reduce reflection measures. It can then be less than 0.5dB and is essentially independent of the lens spacing (<20mm) and the mode power distribution in the fiber.

The refractive index of the self-focusing lens is

Among them, n ₀ is the refractive index of the lens axis, A is the focusing constant of the self-focusing lens, and r is the off-axis distance.

The focal length of the self-focusing lens is

There is a relationship between the incident spot radius R and the outgoing spot radius R'

Among them, NAs is the numerical aperture corresponding to the output angle of the light source, L is the distance from the light source to the self-focusing lens, and l is the distance from the exit end face to the self-focusing lens. The above formula shows that the spot radius of the receiving end face is directly related to the distance between the incident end face and the receiving end face, and when the length of the self-focusing lens is short, the focal point of the self-focusing lens can be inside the lens.

The self-focusing lens module uses the computer to give the corresponding potential value to the edge of the lens, and the potential difference formed between the potential points acts on the LiNbO ₃ crystal, and finally realizes the refractive index gradient distribution in different regions. Using the special distribution of the refractive index, the light can be focused with a low divergence angle. During the potential feedback, the focusing constant can be regulated by controlling the regional distribution of the refractive index.

In the present invention, high-efficiency automatic coupling is realized by utilizing the spatial light adaptive coupling device based on the crystal electro-optic effect. The space light is coupled to the focal point after passing through the self-focusing lens to compress the beam waist, and the coupled light spot falls on the end face of the multimode fiber in the front section of the trapezoidal fiber. The signal light coupled to the multimode fiber is transitioned through the few-mode fiber to reduce the mode loss, and finally output through the single-mode fiber. According to the corresponding algorithm, the potential of each potential point can be adjusted, thereby optimizing parameters such as the focusing constant of the self-focusing lens in real time, and improving the coupling efficiency of space light.

The above is a space light adaptive coupling device based on the crystal electro-optic effect and its realization method, which has a wide application prospect in the fields of fiber laser, space optical communication and astronomical observation.

It should be noted that, in this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any relationship between these entities or operations. any such actual relationship or sequence exists. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass non-exclusive inclusion such that a process, method, article or terminal device that includes a list of elements includes not only those elements, but also a non-exclusive list of elements. other elements, or also include elements inherent to such a process, method, article or terminal equipment. Without further limitation, an element defined by the phrase "comprises..." or "comprises..." does not preclude the presence of additional elements in the process, method, article, or terminal device that includes the element. In addition, in this text, "greater than", "less than", "exceeds" and the like are understood as not including the number; "above", "below", "within" and the like are understood as including the number.

Although the above embodiments have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic inventive concept, so the above is only the implementation of the present invention For example, it does not limit the scope of patent protection of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly used in other related technical fields, are similarly included in this document. The invention is within the scope of patent protection.

Claims (6)

1. A space light self-adaptive coupling device based on a crystal electro-optic effect is characterized by comprising a self-focusing lens, a supporting platform and a trapezoidal optical fiber, wherein the diameter of an optical fiber core of the trapezoidal optical fiber is gradually reduced from a front section to a tail section, the trapezoidal optical fiber comprises at least three sections of optical fibers, the front section is a multimode optical fiber, the tail section is a single-mode optical fiber, the front end of the multimode optical fiber is located at the focus of the self-focusing lens, and the trapezoidal optical fiber is arranged on the supporting platform.

2. The crystal electro-optic effect-based spatial light adaptive coupling device according to claim 1, wherein the middle section of the trapezoidal optical fiber is a multimode optical fiber and/or a few-mode optical fiber.

3. The crystal electro-optic effect-based spatial light adaptive coupling device according to claim 1, wherein the front section of the trapezoidal optical fiber is a multimode optical fiber, the middle section is a few-mode optical fiber, and the tail section is a single-mode optical fiber.

4. The spatial light adaptive coupling device based on the crystal electro-optic effect as claimed in claim 3, wherein the trapezoidal optical fiber is provided with a cladding radius of 125 μm, a core diameter of a multimode optical fiber of 100 μm, a core diameter of a single mode optical fiber of 10 μm, and a core diameter of a few-mode optical fiber of 20-80 μm.

5. The crystal electro-optic effect-based space optical adaptive coupling device according to claim 1, wherein the self-focusing lens adopts LiNbO₃And (5) preparing crystals.

6. The crystal electro-optic effect-based spatial light adaptive coupling device according to claim 1, wherein the LiNbO₃A plurality of potential points are densely distributed on the crystal, and different potential values can be applied to the potential points.

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