Triforked structure spot size converter for proton exchange waveguide and preparation method of triforked structure spot size converter

Abstract

The invention discloses a trigeminal structure spot size converter for a proton exchange waveguide and a preparation method. The trigeminal structure spot size converter sequentially comprises a substrate, an insulating layer and a lithium niobate film layer, the lithium niobate film layer comprises a first waveguide part which is used as an input end of the converter; the second waveguide part is connected with one end of the first waveguide part and is positioned on the same plane as the first waveguide part; a third waveguide portion on the second waveguide portion; the proton exchange waveguide is arranged in the third waveguide part, light is transmitted in the first waveguide part, the second waveguide part, the third waveguide part and the proton exchange waveguide in sequence, and the transverse sizes of the second waveguide part, the third waveguide part and the proton exchange waveguide are sequentially increased in the light transmission direction. The silicon oxynitride waveguide guides light waves in the optical fiber to enter the chip, the light waves in the optical fiber are efficiently guided, the light waves are limited in the silicon oxynitride waveguide and enter the lithium niobate waveguide, and loss caused by light wave diffusion is avoided; a conical waveguide structure is adopted, mode mutation is avoided, and coupling loss is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of pattern spot converters, and in particular to a trident structure pattern spot converter for a proton exchange waveguide and a preparation method thereof. Background Art

[0002] With the development of communication technology and modern information technology, the length of traditional microelectronic chips has been gradually reduced to 5nm and 3nm to further reduce power consumption, and it is close to its physical limit. In order to meet people's needs for communication speed and information volume, optical waveguide chips based on optical communication technology are one of the important breakthroughs. Lithium niobate crystals have become an important optical material for electro-optical modulation chips due to their excellent electro-optical properties. Lithium niobate thin film optical waveguides have been widely used due to their low loss, small size and easy integration. Lithium niobate thin film optical waveguides are divided into buried proton exchange waveguides and ridge etched waveguides according to waveguide structure and preparation method. Ridge etched waveguides have better performance and smaller device size, but their process processing is very difficult and is currently mostly used in laboratory research; while the processing technology of proton exchange waveguides is basically stable, and can also show the excellent optoelectronic properties of lithium niobate, and has been used commercially.

[0003] However, the cross-sectional size of the lithium niobate film waveguide is much smaller than the optical mode spot size of the single-mode optical fiber. When light is transmitted from the optical fiber into the lithium niobate waveguide, a large coupling loss is caused due to the mismatch between the mode in the waveguide and the mode in the optical fiber. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a trident structure pattern spot converter for proton exchange waveguide and a preparation method. The total length of the device is 225μm, and the simulated device insertion loss is 0.365dB, which is used to solve the problem of large mode mismatch loss between lithium niobate proton exchange waveguide and optical fiber coupling in the prior art.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A trident structure spot converter for a proton exchange waveguide comprises: a substrate; an insulating layer located on the substrate; a lithium niobate film layer located on the insulating layer;

[0007] Wherein, the lithium niobate thin film layer comprises:

[0008] a first waveguide portion, serving as an input end of the converter;

[0009] a second waveguide portion connected to one end of the first waveguide portion and located in the same plane as the first waveguide portion;

[0010] a third waveguide portion, located on the second waveguide portion; and

[0011] a proton exchange waveguide, disposed in the third waveguide portion,

[0012] Light is transmitted in the first waveguide portion, the second waveguide portion, the third waveguide portion and the proton exchange waveguide in sequence, and in the direction of light transmission, the lateral dimensions of the second waveguide portion, the third waveguide portion and the proton exchange waveguide increase in sequence.

[0013] In the present invention, preferably, the first waveguide portion includes a first waveguide, a second waveguide and a third waveguide arranged in parallel, the third waveguide is arranged between the first waveguide and the second waveguide, and the first waveguide and the second waveguide are inclined relative to the third waveguide, and further, in the direction of light transmission, the first waveguide and the second waveguide gradually approach the third waveguide;

[0014] The second waveguide portion is connected to one end of the third waveguide, and a width of one end of the second waveguide portion connected to the third waveguide is equal to a width of the third waveguide.

[0015] In the present invention, preferably, the second waveguide portion and the third waveguide portion are both configured as tapered structures, and the width of the second waveguide portion gradually increases in a direction from the first end to the second end thereof; and the width of the third waveguide portion gradually increases in a direction from the first end to the second end thereof;

[0016] In the vertical direction, the second end of the second waveguide portion is flush with the second end of the third waveguide portion, the width of the first end of the second waveguide portion is equal to the width of the first end of the third waveguide portion, and the width of the second end of the second waveguide portion is greater than the width of the second end of the third waveguide portion.

[0017] In the present invention, preferably, the overall length of the second waveguide portion is greater than the overall length of the third waveguide portion.

[0018] In the present invention, preferably, the proton exchange waveguide is configured as a conical structure, and the width of the proton exchange waveguide gradually increases from the first end of the proton exchange waveguide to the second end thereof, the first end thereof is equal to the width of the first end of the third waveguide portion, the second section of the proton exchange waveguide is smaller than the width of the second end of the third waveguide portion, and in the vertical direction, the two ends of the proton exchange waveguide are flush with the two ends of the third waveguide portion.

[0019] In the present invention, preferably, a silicon oxynitride waveguide is further included, and the silicon oxynitride waveguide covers the first waveguide portion, the first end of the second waveguide portion, the first end of the third waveguide portion, and the first end of the proton exchange waveguide.

[0020] In the present invention, preferably, the insulating layer is a silicon dioxide insulating layer.

[0021] In the present invention, preferably, the thickness of the lithium niobate thin film layer is 600 nm, the total length L3 of the first waveguide portion is 15 μm, the total length L1 of the second waveguide portion is 200 μm, and the total length L2 of the third waveguide portion is 165 μm.

[0022] In the present invention, preferably, the widths of both ends of the first waveguide, the second waveguide and the third waveguide are the same, which are all 0.24 μm, the center distance between the first waveguide, the second waveguide and the center of the third waveguide in the middle is 1.1 μm, and the first waveguide and the second waveguide are inclined at an angle of about 5° to the third waveguide.

[0023] A method for preparing a pattern spot converter comprises the steps of:

[0024] forming an insulating layer on a substrate;

[0025] forming a lithium niobate thin film layer on the insulating layer;

[0026] Etching the lithium niobate thin film layer to form a third waveguide portion;

[0027] Continue etching the lithium niobate thin film layer to form a second waveguide portion and a first waveguide portion;

[0028] forming a proton exchange waveguide in the third waveguide portion by using a proton exchange technique;

[0029] A silicon oxynitride waveguide is deposited in front of the spot converter, and covers the first waveguide portion, the first end of the second waveguide portion, the first end of the third waveguide portion, and the first end of the proton exchange waveguide.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The device of the present invention is end-face coupled with an optical fiber, and the mode field size is changed by using a tapered mode spot converter structure. In order to further reduce the length of the device, a trident waveguide structure is introduced, so that the mode size can be converted into the chip faster and more efficiently;

[0032] The silicon oxynitride waveguide is used to guide the light waves in the optical fiber into the chip. With the characteristics of the silicon oxynitride waveguide and the optical fiber having similar refractive index and size, the light waves in the optical fiber are guided efficiently. In the subsequent propagation, the light waves are confined in the silicon oxynitride waveguide and gradually enter the lithium niobate waveguide to prevent the light waves from diffusing into the air and being lost.

[0033] A tapered waveguide structure is used, which gradually changes from small to large in the lateral direction along the light wave transmission direction, so as to realize the gradual change from the mode in the previous structure to the mode in the next structure, and avoid the mode mutation as small as possible to reduce the coupling loss;

[0034] In summary, the present invention uses a double-layer inverted cone-shaped spot mode converter with a trident structure as a transition method to couple the optical mode field from the optical fiber into the lithium niobate proton exchange waveguide, thereby realizing the spot mode conversion function in a low coupling loss manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic structural diagram of the trident structure spot converter for proton exchange waveguide described in the present invention.

[0036] Figure 2 This is a top view of the trident structure spot converter for proton exchange waveguide described in the present invention.

[0037] In the attached drawings: 1-substrate, 2-insulating layer, 3-lithium niobate thin film layer, 4-first waveguide portion, 5-second waveguide portion, 6-third waveguide portion, 7-proton exchange waveguide, 8-silicon oxynitride waveguide. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the solutions of the present invention, the following will describe the implementation methods of the present invention in detail in conjunction with the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve corresponding technical effects can be fully understood and implemented accordingly. The embodiments of the present invention and the various features in the embodiments can be combined with each other without conflict, and the technical solutions formed are all within the protection scope of the present invention.

[0039] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0040] It should be noted that the terms "include" and "have" in the specification and claims of the present invention and the above drawings and any modifications thereof are intended to cover non-exclusive inclusions.

[0041] Please also see Figure 1 and Figure 2 A preferred embodiment of the present invention provides a trident structure spot converter for proton exchange waveguide, comprising: a substrate 1; an insulating layer 2, located on the substrate 1; a lithium niobate thin film layer 3, located on the insulating layer 2; wherein the lithium niobate thin film layer 3 comprises:

[0042] The first waveguide portion 4 serves as the input end of the converter; the second waveguide portion 5 is connected to one end of the first waveguide portion 4 and is located in the same plane as the first waveguide portion 4; the third waveguide portion 6 is located on the second waveguide portion 5; and the proton exchange waveguide 7 is arranged in the third waveguide portion 6, and light is transmitted in the first waveguide portion 4, the second waveguide portion 5, the third waveguide portion 6 and the proton exchange waveguide 7 in sequence, and in the direction of light transmission, the lateral dimensions of the second waveguide portion 5, the third waveguide portion 6 and the proton exchange waveguide 7 increase in sequence.

[0043] In this embodiment, the first waveguide portion 4 includes a first waveguide, a second waveguide and a third waveguide arranged in parallel, the third waveguide is arranged between the first waveguide and the second waveguide, and the first waveguide and the second waveguide are inclined relative to the third waveguide. Further, in the direction of light transmission, the first waveguide and the second waveguide gradually approach the third waveguide; the second waveguide portion 5 is connected to one end of the third waveguide, and the width of the end of the second waveguide portion 5 connected to the third waveguide is equal to the width of the third waveguide, the widths of the first waveguide, the second waveguide and the third waveguide at both ends are the same, which is 0.24μm, the center distance between the first waveguide, the second waveguide and the center of the third waveguide in the middle is 1.1μm, the first waveguide and the second waveguide are inclined at an angle of about 5° to the third waveguide, and the total length L3 of the first waveguide portion 4 is 15μm.

[0044] In this embodiment, the first waveguide, the second waveguide and the third waveguide are all ridge waveguides, and the inclination angle of the side wall of the ridge waveguide is 80°.

[0045] In this embodiment, the second waveguide portion 5 and the third waveguide portion 6 are both configured as tapered structures, and the width of the second waveguide portion 5 gradually increases from the first end to the second end thereof; and the width of the third waveguide portion 6 gradually increases from the first end to the second end thereof. In the vertical direction, the second end of the second waveguide portion 5 is flush with the second end of the third waveguide portion 6, and the width of the first end of the second waveguide portion 5 is equal to the width of the first end of the third waveguide portion 6, and the width of the second end of the second waveguide portion 5 is greater than the width of the second end of the third waveguide portion 6. Specifically, the total length L1 of the second waveguide portion 5 is 200 μm, and the total length L2 of the third waveguide portion 6 is 165 μm; the first end width w4 of the second waveguide portion 5 and the third waveguide portion 6 is 0.24 μm, the second end width w1 of the second waveguide portion 5 is 5 μm, and the second end width w2 of the third waveguide portion 6 is 4 μm.

[0046] In this embodiment, the proton exchange waveguide 7 is configured as a conical structure, and the width of the proton exchange waveguide 7 gradually increases from the first end to the second end of the proton exchange waveguide 7, and the first end is equal to the width of the first end of the third waveguide portion 6. The second section of the proton exchange waveguide 7 is smaller than the width of the second end of the third waveguide portion 6. In the vertical direction, the two ends of the proton exchange waveguide 7 are flush with the two ends of the third waveguide portion 6. Specifically, the width w3 of the second end of the proton exchange waveguide 7 is 3 μm.

[0047] In this embodiment, a silicon oxynitride waveguide 8 is also included. The silicon oxynitride waveguide 8 covers the first waveguide portion 4, the first end of the second waveguide portion 5, the first end of the third waveguide portion 6, and the first end of the proton exchange waveguide 7. The length L4 of the silicon oxynitride waveguide 8 is 221 μm, the width W5 at both ends is 4 μm, and the thickness is 3 μm. The silicon oxynitride waveguide 8 first receives the light waves from the optical fiber. The refractive index of the silicon oxynitride waveguide 8 is similar to that of the optical fiber, and the structural size of the silicon oxynitride waveguide 8 is also similar to that of the lens optical fiber, which can couple the light waves in the optical fiber into the chip with high coupling efficiency.

[0048] In this embodiment, the insulating layer 2 is a silicon dioxide insulating layer 2 .

[0049] In this embodiment, the thickness of the lithium niobate thin film layer 3 is 600 nm, the total length of the spot converter is 225 μm, and the transmittance obtained after simulation is 0.9193, and the simulated device insertion loss is 0.365 dB, which is relatively small.

[0050] Working principle:

[0051] The light in the optical fiber is first coupled into the front end of the spot converter and then coupled into the silicon oxynitride waveguide 8. Since the size and refractive index of the silicon oxynitride waveguide 8 are similar to those of the optical fiber, the coupling loss of this part can be greatly reduced.

[0052] After entering the silicon oxynitride waveguide 8, it first reaches the first waveguide section 4. Since the lithium niobate waveguide of the first waveguide section 4 is very small, the trident lithium niobate waveguide of the first waveguide section 4 cannot form a waveguide mode. The light wave is mainly transmitted in the silicon oxynitride waveguide 8 diffused in the outer layer. The trident structure formed by the first waveguide section 4 here helps guide the light wave to the lithium niobate and speed up the subsequent light wave to enter the conical lithium niobate structure. Because the refractive index of lithium niobate is larger than that of silicon oxynitride, the light wave tends to propagate to a place with a larger refractive index, and the trident structure has a larger effective area on the convergent light beam than an ordinary single narrow waveguide, which can allow the light beam to enter the subsequent conical waveguide faster.

[0053] Then it enters the double-layer conical structure composed of the second waveguide part 5 and the third waveguide part 6. The double-layer conical structure gradually changes from small to large in the lateral direction along the light wave transmission direction, so as to realize the gradual change of the light wave mode at the structure from not supporting the waveguide mode to supporting single-mode transmission, and avoids mode mutation as small as possible, reduces coupling loss, and allows the light waves in the silicon oxynitride to enter the conical waveguide structure with less loss; the structure of the third waveguide part 6 realizes the size change in the longitudinal direction in the third region, and further limits the light waves in the conical waveguide to avoid diffusion or dissipation due to the formation of multi-mode mode due to the excessive lateral width of the first layer of cone.

[0054] The function of the tapered proton exchange waveguide is the same as that of the tapered waveguide. It gradually changes from small to large in the lateral direction along the light wave transmission direction, realizing the gradual change from the mode supported by the tapered waveguide to the mode supported by the proton exchange waveguide, avoiding mode mutation as small as possible, reducing coupling loss, and allowing the light wave in the tapered waveguide to enter the proton exchange waveguide with less loss.

[0055] A preferred embodiment of the present invention provides a method for preparing the above-mentioned trident structure pattern converter, comprising the steps of:

[0056] forming an insulating layer 2 on a substrate 1;

[0057] forming a lithium niobate thin film layer 3 on the insulating layer 2;

[0058] Etching the lithium niobate thin film layer 3 to form a third waveguide portion 6;

[0059] Continue etching the lithium niobate thin film layer 3 to form a second waveguide portion 5 and a first waveguide portion 4;

[0060] Forming a proton exchange waveguide 7 in the third waveguide portion 6 by using a proton exchange technique;

[0061] A silicon oxynitride waveguide 8 is deposited in front of the spot converter, and covers the first waveguide portion 4 , the first end of the second waveguide portion 5 , the first end of the third waveguide portion 6 and the first end of the proton exchange waveguide 7 .

[0062] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and such combinations should also be regarded as the contents disclosed in the present disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0063] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by technical personnel in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. A trident structure spot converter for proton exchange waveguide, characterized in that: include: Substrate (1); An insulating layer (2) located on the substrate (1); A lithium niobate thin film layer (3) located on the insulating layer (2); Wherein, the lithium niobate thin film layer (3) comprises: A first waveguide portion (4) serving as an input end of the converter; A second waveguide portion (5) connected to one end of the first waveguide portion (4) and located in the same plane as the first waveguide portion (4); a third waveguide portion (6) located on the second waveguide portion (5); and A proton exchange waveguide (7) is arranged in the third waveguide portion (6), Light is transmitted in the first waveguide portion (4), the second waveguide portion (5), the third waveguide portion (6) and the proton exchange waveguide (7) in sequence, and in the direction of light transmission, the lateral dimensions of the second waveguide portion (5), the third waveguide portion (6) and the proton exchange waveguide (7) increase in sequence.

2. The trident structure spot converter for proton exchange waveguide according to claim 1, characterized in that: The first waveguide portion (4) comprises a first waveguide, a second waveguide and a third waveguide arranged in parallel, the third waveguide being arranged between the first waveguide and the second waveguide, and the first waveguide and the second waveguide being inclined relative to the third waveguide, and further, in the direction of light transmission, the first waveguide and the second waveguide gradually approach the third waveguide; The second waveguide portion (5) is connected to one end of the third waveguide, and the width of the end of the second waveguide portion (5) connected to the third waveguide is equal to the width of the third waveguide.

3. The trident structure spot converter for proton exchange waveguide according to claim 2, characterized in that: The second waveguide portion (5) and the third waveguide portion (6) are both arranged to be tapered structures, and the width of the second waveguide portion (5) gradually increases in a direction from the first end to the second end of the second waveguide portion (5); and the width of the third waveguide portion (6) gradually increases in a direction from the first end to the second end of the third waveguide portion (6); In the vertical direction, the second end of the second waveguide portion (5) is flush with the second end of the third waveguide portion (6), the width of the first end of the second waveguide portion (5) is equal to the width of the first end of the third waveguide portion (6), and the width of the second end of the second waveguide portion (5) is greater than the width of the second end of the third waveguide portion (6).

4. The trident structure spot converter for proton exchange waveguide according to claim 3, characterized in that: The overall length of the second waveguide portion (5) is greater than the overall length of the third waveguide portion (6).

5. The trident structure spot converter for proton exchange waveguide according to claim 3, characterized in that: The proton exchange waveguide (7) is configured as a tapered structure. In a direction from the first end of the proton exchange waveguide (7) to the second end thereof, the width of the proton exchange waveguide (7) gradually increases. The first end thereof is equal to the width of the first end of the third waveguide portion (6). The second section of the proton exchange waveguide (7) is smaller than the width of the second end of the third waveguide portion (6). In a vertical direction, the two ends of the proton exchange waveguide (7) are flush with the two ends of the third waveguide portion (6).

6. The trident structure spot converter for proton exchange waveguide according to claim 1, characterized in that: It also includes a silicon oxynitride waveguide (8), which covers the first waveguide portion (4), the first end of the second waveguide portion (5), the first end of the third waveguide portion (6), and the first end of the proton exchange waveguide (7).

7. The trident structure spot converter for proton exchange waveguide according to claim 1, characterized in that: The insulating layer (2) is a silicon dioxide insulating layer.

8. The trident structure spot converter for proton exchange waveguide according to claim 1, characterized in that: The thickness of the lithium niobate thin film layer (3) is 600 nm, the total length L3 of the first waveguide portion (4) is 15 μm, the total length L1 of the second waveguide portion (5) is 200 μm, and the total length L2 of the third waveguide portion (6) is 165 μm.

9. The trident structure spot converter for proton exchange waveguide according to claim 2, characterized in that: The widths of both ends of the first waveguide, the second waveguide and the third waveguide are the same, which are all 0.24 μm. The center distance between the first waveguide, the second waveguide and the center of the third waveguide in the middle is 1.1 μm. The first waveguide and the second waveguide are inclined at an angle of about 5° to the third waveguide.

10. A preparation method for preparing the trident structure spot converter for proton exchange waveguide according to any one of claims 1 to 9, characterized in that: Includes steps: forming an insulating layer (2) on a substrate (1); forming a lithium niobate thin film layer (3) on the insulating layer (2); Etching the lithium niobate thin film layer (3) to form a third waveguide portion (6); Continue etching the lithium niobate thin film layer (3) to form a second waveguide portion (5) and a first waveguide portion (4); forming a proton exchange waveguide (7) in the third waveguide portion (6) by using a proton exchange technique; A silicon oxynitride waveguide (8) is deposited in front of the pattern spot converter, and the silicon oxynitride waveguide (8) covers the first waveguide portion (4), the first end of the second waveguide portion (5), the first end of the third waveguide portion (6), and the first end of the proton exchange waveguide (7).

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