阅读说明：本技术 模场转换系统 (Mode field conversion system ) 是由 龙跃金 韦琪 张峰 陆海龙 苏习明 陆众 于 2020-12-22 设计创作，主要内容包括：本发明实施例公开了一种模场转换系统,其包括：入射光纤,包括入射端,所述入射端耦合至大模场尺寸波导,所述大模场尺寸波导连接至外部光学器件；出射光纤,包括出射端,所述出射端耦合至小模场尺寸波导；以及过渡光纤,连接所述入射光纤和所述出射光纤,用于将来自所述入射端的光传输至所述出射端,所述过渡光纤包括若干段熔接的光纤段,所述过渡光纤分别熔接至所述入射光纤和所述出射光纤；其中光纤芯径自所述入射光纤至所述出射光纤递减。(The embodiment of the invention discloses a mode field conversion system, which comprises: an input optical fiber comprising an input end coupled to a large mode field size waveguide connected to external optics; an exit fiber comprising an exit end coupled to a small mode field size waveguide; the transition optical fiber is connected with the incident optical fiber and the emergent optical fiber and used for transmitting the light from the incident end to the emergent end, the transition optical fiber comprises a plurality of fused optical fiber sections, and the transition optical fiber is respectively fused to the incident optical fiber and the emergent optical fiber; wherein the core diameter of the optical fiber decreases from the incident optical fiber to the emergent optical fiber.)

1. A mode field conversion system, comprising:

an input optical fiber comprising an input end coupled to a large mode field size waveguide connected to external optics;

an exit fiber comprising an exit end coupled to a small mode field size waveguide;

the transition optical fiber is connected with the incident optical fiber and the emergent optical fiber and used for transmitting light from the incident end to the emergent end, the transition optical fiber comprises a plurality of fused optical fiber sections, and two ends of the transition optical fiber are respectively fused to the incident optical fiber and the emergent optical fiber; wherein the core diameter of the optical fiber decreases from the incident optical fiber to the emergent optical fiber.

2. The mode field conversion system of claim 1, wherein the large mode field size waveguide is a single mode fiber and the external optical device is a laser emitter.

3. The mode-field conversion system of claim 1, wherein said small-mode-field waveguide is a lithium niobate thin film waveguide.

4. The mode field conversion system of claim 1, wherein the optical fiber comprises a core, a cladding, and a coating, the cladding having a refractive index lower than the refractive index of the core.

5. The mode field conversion system of claim 1, wherein said core is made of a quartz material, said cladding is made of a germanium-doped quartz material, and said coating is a resin coating.

6. The mode field conversion system according to claim 1, wherein the incident end comprises a first coupling unit, the first coupling unit comprises a first exposed portion and a first micro-processed end, the incident end forms the first exposed portion after removing the outer coating layer, and an axial end of the first exposed portion forms the first micro-processed end.

7. The mode field conversion system according to claim 1, wherein the exit end comprises a second coupling unit, the second coupling unit comprises a second exposed portion and a second micro-processing end, the second exposed portion is formed by removing the outer periphery of the exit end from the coating layer, and the second micro-processing end is formed at an axial end of the second exposed portion.

8. The mode field conversion system of claim 1, wherein said first micro-machined end is a conical or tetrahedral structure.

9. The mode field conversion system according to claim 1 or 8, wherein the second micro-machined end is a double curvature tetrahedral structure.

10. The mode field conversion system according to claim 1, wherein the core diameter of the entrance end fiber is in the range of 9-400 μm and the core diameter of the exit end fiber is in the range of 3-5 μm.

Technical Field

The invention relates to the field of integrated optics, in particular to a mode field conversion system.

Background

At present, coupling of a light spot of a large mode field into a small mode field is always a key point and a difficulty point of the communication and laser processing industry, and for optical mode field coupling, low loss and high coupling efficiency are always a pursuit target of the industry. Currently, optical fiber is a mode with minimum loss in the field of laser transmission, so that the mode of coupling the laser light into the small mode field waveguide by using the optical fiber is a very suitable mode. For example, the method is applied to the scene of optical coupling of a lithium niobate thin film, the lithium niobate thin film is a typical small mode field waveguide, the lithium niobate crystal is a multifunctional photoelectric material, and the lithium niobate crystal has many excellent physical properties such as acousto-optic, electro-optic, nonlinear optics, piezoelectricity, pyroelectricity, ferroelectric and the like, and has good stability, wide wavelength light transmission range and large intrinsic bandwidth.

In recent years, a single crystal lithium niobate thin film has been produced, and such a thin film material has physical properties that can be close to those of a crystal material. And because of the high refractive index ratio between the lithium niobate crystal and the silicon dioxide isolating layer, various thin film photoelectric devices manufactured by taking the lithium niobate crystal as the substrate have better light limiting capability and smaller cross section size, and can realize higher-density integration. A series of photoelectric devices with excellent performance, such as frequency converters, electro-optical modulators, second harmonic generators and the like, are manufactured by utilizing lithium niobate thin film materials.

The coupling between the optical fiber and the lithium niobate device is an important research direction of integrated optics and has important application value. However, mode field mismatch between the single mode fiber and the lithium niobate thin film causes coupling between the fiber and the small mode field waveguide to be difficult, so how to improve the coupling efficiency between the fiber and the thin film waveguide becomes an important and difficult problem to solve.

Disclosure of Invention

To solve the above technical problem, an embodiment of the present invention provides a mode-field conversion system, which includes:

an input optical fiber comprising an input end coupled to a large mode field size waveguide connected to external optics;

an exit fiber comprising an exit end coupled to a small mode field size waveguide;

the transition optical fiber is connected with the incident optical fiber and the emergent optical fiber and used for transmitting the light from the incident end to the emergent end, the transition optical fiber comprises a plurality of fused optical fiber sections, and the transition optical fiber is respectively fused to the incident optical fiber and the emergent optical fiber; wherein the core diameter of the optical fiber decreases from the incident optical fiber to the emergent optical fiber.

Further, the large mode field size waveguide is a single mode fiber, and the external optical device is a laser transmitter.

Further, the small mode field waveguide is a lithium niobate thin film waveguide.

Further, the optical fiber includes a core, a cladding having a refractive index lower than that of the core, and a coating layer.

Furthermore, the fiber core is made of quartz material, the cladding is made of germanium-doped quartz material, and the coating layer is a resin coating.

Further, the incident end comprises a first coupling unit, the first coupling unit comprises a first exposed portion and a first micro-processing end, the first exposed portion is formed after the outer periphery of the incident end is removed from the coating layer, and a first micro-processing end is formed at the axial end of the first exposed portion.

Further, the exit end comprises a second coupling unit, the second coupling unit comprises a second exposed portion and a second micro-processing end, the second exposed portion is formed after the outer periphery of the exit end is removed from the coating layer, and a second micro-processing end is formed at the axial end of the second exposed portion.

Further, the first micro-processing end is in a conical or tetrahedral structure.

Further, the second micro-processing end is of a double-curvature four-side structure.

Further, the core diameter range of the incident end optical fiber is 9-400 μm, and the core diameter range of the emergent end optical fiber is 3-5 μm.

Further, the transition optical fiber is a cascade optical fiber.

The mode field conversion system provided by the embodiment of the invention has the advantages of small volume, simple structure and high reliability, and can improve the coupling efficiency with the adjacent mode field by changing the optical fiber combination type and the end surface micromachining process according to the application occasion.

Drawings

FIG. 1 is a schematic structural diagram of a mode-field conversion system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of an optical fiber configuration of the mode field conversion system of FIG. 1;

FIG. 3 is a front view of the incident end of the field switching system of FIG. 1;

FIG. 4 is a side view of the incident end of FIG. 3;

FIG. 5 is a top view of the incident end of FIG. 3;

FIG. 6 is a front view of the exit end of the field conversion system of FIG. 1;

FIG. 7 is a side view of the exit end of FIG. 5;

fig. 8 is a top view of the exit end of fig. 5.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, a mode field conversion system according to an embodiment of the present invention includes an incident fiber 1, an exit fiber 2, and a transition fiber 3, where the incident fiber 1 includes an incident end 11, the incident end 11 is coupled to a large mode field size waveguide, and the large mode field size waveguide is connected to an external optical device.

In this embodiment, the large mode field size waveguide is a single mode fiber, and the external optical device is a laser transmitter or a chip. Wherein the core diameter of the single mode fiber configured as a large mode field size waveguide is 8-10 μm.

Wherein the exit fiber 2 comprises an exit end 21, said exit end 21 being coupled to the small mode field size waveguide. The small mode field waveguide in this embodiment is a lithium niobate thin film waveguide, in which the thickness of the lithium niobate thin film is about 0.5 μm.

The transition fiber 3 in this embodiment is used to connect the incident fiber 1 and the exit fiber 2, and is used to transmit the light from the incident end 11 to the exit end 21.

The transition optical fiber 3 has a fiber core diameter between the fiber core diameters of the incident optical fiber 1 and the emergent optical fiber 2, the transition optical fiber 3 includes a plurality of fiber segments 31 welded together, the transition optical fiber 3 of the embodiment of the present invention includes a plurality of fiber segments, wherein the transition optical fiber 3 may be a combination of fiber segments of any type and length.

By providing several or a plurality of combined fiber segments 31, it is ensured that the light travels slowly through the fiber segments 31 of different core diameters while propagating in the transition fiber 3 in the form of a basement membrane or a small number of higher order modes.

Further, the large core diameter end of the transition optical fiber 3 is welded to the incident optical fiber 1, and the small core diameter end of the transition optical fiber 3 is welded to the exit optical fiber 2; wherein the fiber core diameter decreases from the entrance fiber 1 to the exit fiber 2.

Referring to fig. 2, all of the incident optical fiber 1, the exit optical fiber 2, and the transition optical fiber 3 in the present embodiment include a core 4, a cladding 5, and a coating layer 6, which are sequentially disposed from inside to outside, wherein the refractive index of the cladding 5 is lower than that of the core 4.

Specifically, the fiber core 4 is made of a quartz material with a high refractive index, the cladding 5 is made of a germanium-doped quartz material with a low refractive index, and the coating layer 6 is a resin coating. Wherein the light 7 can travel long distances only in the core 4.

As shown in fig. 3 to 5, the incident end 11 according to the embodiment of the present invention includes a first coupling unit coupled to a single mode optical fiber, and the first coupling unit includes a first bare portion 12 and a first micro-processed end 13, wherein the incident end 11 forms the first bare portion 12 exposing the cladding 5 after removing the outer periphery of the coating layer 6, and an axial end of the first bare portion 12 is processed to form the first micro-processed end 13.

Specifically, as shown in fig. 3, the first micro-processing end 13 in the embodiment of the present invention is a conical structure with a curvature at the shaft end, but it may also be a four-sided structure, in which the axial end of the first exposed portion 12 can be formed by an angular processing method such as etching and grinding, and a thermal processing method such as a cone drawing machine firing and a welding machine discharging. The first micro-processing end 13 is mainly configured to couple with a mode field of a transmission spot of a laser transmitter.

As an alternative embodiment, the incident end 11 may not be micro-machined.

Similarly, as shown in fig. 6 to 8, the exit end 21 according to the embodiment of the present invention includes a second coupling unit coupled to the lithium niobate thin film waveguide, the second coupling unit includes a second bare portion 22 and a second micro-processing end 23, the second bare portion 22 of the bare cladding 5 is formed after the outer periphery of the exit end 21 is removed from the coating layer 6, and the second micro-processing end 23 is formed by processing an axial end portion of the second bare portion 22.

Specifically, as shown in fig. 6, the second micro-processing end 23 in the embodiment of the present invention has a double curvature four-sided structure. The axial end part of the second exposed part can form a double-curvature four-side structure by combining the angle processing modes such as corrosion, grinding and the like and the heat processing modes such as firing of a fire head of a tapering machine, discharging of a welding machine and the like. Similarly, the second micro-processing terminal 23 is mainly configured to couple with the emission spot mode field of the lithium niobate thin film waveguide.

In the embodiment of the invention, the core diameter range of the incident optical fiber 1 is 9-400 μm, the core diameter of the incident optical fiber is larger and is mainly used for receiving laser emitted from a laser or other equipment, and the core diameter range of the emergent optical fiber 2 is 3-5 μm.

The mode field conversion system of the embodiment of the invention has small volume, simple structure and high reliability, and can improve the coupling efficiency with the adjacent mode field by changing the optical fiber combination type and the end surface micromachining process according to the application occasion.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.