CN115407532A

CN115407532A - Coupling structure on lithium niobate sheet based on heterogeneous integrated thin film, preparation method and optical device

Info

Publication number: CN115407532A
Application number: CN202211167513.2A
Authority: CN
Inventors: 蔡鑫伦; 张仙
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2022-09-23
Filing date: 2022-09-23
Publication date: 2022-11-29

Abstract

The invention relates to the technical field of optical devices, and provides a coupling structure on a lithium niobate sheet based on a heterogeneous integrated thin film, a preparation method and an optical device. The optical waveguide comprises a thin film lithium niobate photonic chip, wherein a III-V active waveguide layer is integrated on the thin film lithium niobate photonic chip through a heterogeneous integration wafer bonding technology; the thin-film lithium niobate photonic chip is provided with a lithium niobate waveguide layer, and the output end of the lithium niobate waveguide layer is vertically evanescent wave coupled with the input end of the III-V active waveguide layer; the III-V active waveguide layer is covered with an N-type metal electrode and a P-type metal electrode. The invention integrates the III-V active waveguide layer on the lithium niobate photonic chip by the heterogeneous integrated wafer bonding technology, thereby realizing the function of optical detection on the thin-film lithium niobate platform sheet. The III-V active waveguide layer and the thin-film lithium niobate photonic chip are optically interconnected in a vertical evanescent wave coupling mode through an optimally designed III-V/LN mode spot converter, so that high-efficiency coupling between the III-V active waveguide layer and the lithium niobate waveguide is realized.

Description

Coupling structure on lithium niobate sheet based on heterogeneous integrated thin film, preparation method and optical device

Technical Field

The invention relates to the technical field of optical devices, in particular to a lithium niobate on-chip coupling structure based on a heterogeneous integrated thin film, a preparation method and an optical device.

Background

Lithium niobate materials have been receiving attention from researchers due to their high electro-optic effect, and recently the advent of high performance thin film lithium niobate modulators brings the lithium niobate platform on insulator (LNOI) to the researchers' view, and Thin Film Lithium Niobate (TFLN) -based large scale Photonic Integrated Circuits (PICs) are becoming a promising technology for achieving high speed and high capacity optical interconnects. Because LN materials lack the ability to efficiently generate and detect light at telecommunications wavelengths, in order to implement a practical lithium niobate optical I/O chip, an electrically pumped light source and detector must be incorporated.

At present, the main modes for integrating active devices on thin-film lithium niobate are micro-transfer printing, end face butt coupling and wafer bonding. The micro-transfer printing technology needs Flip-chip equipment with high alignment precision, the coupling efficiency between devices is low due to the alignment error of the equipment, and the problems of long time consumption and high cost exist in the placement of a single device. The end-to-end coupling technique is relatively simple but has the disadvantage that two devices of different dimensions or materials must be aligned to sub-micron accuracy to achieve effective coupling when the devices are packaged, is time consuming and inefficient and is not the optimal choice for high volume manufacturing. The integration of III-V materials on lithium niobate photonic chips by wafer bonding is a very efficient technique, and active devices (e.g., lasers and amplifiers) as well as detectors can be integrated on the same chip using a single chip-to-wafer bonding step, where the III-V layer provides efficient light generation, amplification and detection, and the high index contrast LNOI allows optical functionality to be achieved with low footprint. However, the problems of low integration level and coupling efficiency still exist in the prior art of integrating III-V materials on a lithium niobate photonic chip by a wafer bonding technology.

Disclosure of Invention

The invention provides a coupling structure on a lithium niobate chip based on a heterogeneous integration thin film, a preparation method and an optical device, aiming at overcoming the defects of low integration level and coupling efficiency in the prior art of integrating III-V materials on the lithium niobate photonic chip by a wafer bonding technology.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a coupling structure on a thin film lithium niobate chip based on heterogeneous integration comprises a thin film lithium niobate photonic chip, wherein a III-V active waveguide layer is integrated on the thin film lithium niobate photonic chip through a heterogeneous integration wafer bonding technology; a lithium niobate waveguide layer is arranged on the thin-film lithium niobate photonic chip, and the output end of the lithium niobate waveguide layer is vertically evanescent-wave-coupled with the input end of the III-V active waveguide layer; the III-V active waveguide layer is covered with an N-type metal electrode and a P-type metal electrode.

In the technical scheme, reverse voltage is applied to the N-type metal electrode and the P-type metal electrode, light input to the thin-film lithium niobate photonic chip is detected, and photocurrent output is generated. The III-V active waveguide layer is integrated on the lithium niobate photonic chip by a heterogeneous integrated wafer bonding technology, so that the function of optical detection on the thin-film lithium niobate chip is realized; the output end of the lithium niobate waveguide layer is vertically coupled with the input end of the III-V active waveguide layer by evanescent waves, so that the high-efficiency coupling between the III-V active waveguide layer and the lithium niobate waveguide layer is realized.

Preferably, the III-V active waveguide layer includes an N-type metal layer, a multiple quantum well layer, a P-type cladding layer, and a P-type metal layer, which are sequentially disposed from bottom to top.

Preferably, the III-V active waveguide layer is a double-layer cascade tapered waveguide structure.

As a preferred scheme, the lithium niobate waveguide layer comprises a grating coupler, a lithium niobate straight waveguide and a lithium niobate tapered waveguide which are sequentially connected, and the grating coupler is coupled with an external single-mode optical fiber; the III-V active waveguide layer further comprises a III-V group tapered waveguide, and the lithium niobate tapered waveguide and the III-V group tapered waveguide form a III-V/LN optical mode spot converter and keep mode matching.

The output end of the lithium niobate waveguide layer is vertically coupled with the input end of the III-V active waveguide layer through the III-V/LN mode spot converter, so that high-efficiency coupling between the III-V active waveguide layer and the lithium niobate waveguide layer is realized.

Preferably, a silicon oxide layer and a BCB curing layer are arranged between the III-V active waveguide layer and the thin-film lithium niobate photonic chip.

Furthermore, the invention also provides a preparation method of the coupling structure on the lithium niobate chip based on the heterogeneous integrated thin film, which is used for preparing the coupling structure on the chip provided by any technical scheme. Which comprises the following steps:

s1, preparing a grating coupler, a lithium niobate straight waveguide and a lithium niobate tapered waveguide on a thin-film lithium niobate photonic chip;

s2, depositing a silicon oxide layer on the thin-film lithium niobate photonic chip obtained in the step S1 by using a thin-film deposition technology, and then polishing and flattening the silicon oxide layer to a thickness of not more than 50nm by using a chemical mechanical polishing technology;

s3, after a BCB curing layer with the thickness of less than 70nm is spin-coated on the thin film lithium niobate photonic chip obtained in the step S2, bonding the III-V active waveguide layer to the thin film lithium niobate photonic chip by utilizing a heterogeneous integration wafer bonding technology; the output end of the thin-film lithium niobate photonic chip is vertically evanescent-wave-coupled with the input end of the III-V active waveguide layer, and the lithium niobate tapered waveguide is mode-matched with the III-V group tapered waveguide in the III-V active waveguide layer;

and S4, covering and arranging an N-type metal electrode and a P-type metal electrode on the III-V active waveguide layer of the lithium niobate photonic chip obtained in the step S3.

The invention further provides an optical device, and particularly provides an optical detector, which comprises a thin film lithium niobate photonic chip, wherein the thin film lithium niobate photonic chip is integrated with the coupling structure on the thin film lithium niobate chip based on heterogeneous integration, which is provided by any technical scheme.

The thin-film lithium niobate photonic chip is integrated with a III-V group photodetector by a heterogeneous integrated wafer bonding technology; a grating coupler prepared by a lithium niobate waveguide, a lithium niobate straight waveguide and a lithium niobate tapered waveguide are arranged on the thin-film lithium niobate photonic chip, and the lithium niobate tapered waveguide and the III-V group tapered waveguide arranged at the bottom of the III-V group optical detector form an III-V/LN optical mode spot converter and keep mode matching; the III-V group optical detector is covered with an N-type metal electrode and a P-type metal electrode and is used for applying reverse voltage to detect light input to the thin-film lithium niobate photonic chip and generate photocurrent output.

Preferably, the III-V group photodetector is of a multi-quantum well structure and comprises an N-type region, an intrinsic region and a P-type region which are sequentially arranged from bottom to top; the N-type region comprises an N-type metal layer, the intrinsic region comprises a multi-quantum well layer, and the P-type region comprises a P-type cladding layer and a P-type metal layer.

Preferably, a silicon oxide layer and a BCB curing layer are arranged between the III-V group photodetector and the lithium niobate photonic chip.

As a preferred scheme, the lithium niobate photonic chip comprises a silicon substrate, a silicon dioxide layer, a lithium niobate waveguide layer and a silicon oxide layer which are sequentially arranged from bottom to top; the lithium niobate waveguide layer comprises a grating coupler, a lithium niobate straight waveguide and a lithium niobate tapered waveguide.

Compared with the prior art, the technical scheme of the invention has the beneficial effects that: the invention integrates the III-V active waveguide layer on the lithium niobate photonic chip by the heterogeneous integrated wafer bonding technology, thereby realizing the function of optical detection on the thin-film lithium niobate platform sheet. The III-V active waveguide layer is optically interconnected with the lithium niobate photonic chip in a vertical evanescent wave coupling mode through the III-V/LN mode spot converter, and high-efficiency coupling between the III-V active waveguide layer and the lithium niobate waveguide is realized. The wafer bonding adopts a bonding mode from a small-sized III-V active waveguide layer to a large-sized lithium niobate photonic chip, has the characteristics of high integration level, cost saving and contribution to mass production, and is favorable for realizing a high-performance on-chip integrated optical detector.

Drawings

Fig. 1 is a schematic structural diagram of a coupling structure on a lithium niobate sheet based on a hetero-integrated thin film in embodiment 1.

Fig. 2 is a schematic diagram of the structure of the III-V active waveguide layer of example 1.

Fig. 3 is a flowchart of a method for fabricating a heterointegrated thin-film lithium niobate on-chip coupling structure according to embodiment 2.

Fig. 4 is a schematic diagram of the structure of the photodetector based on the hetero-integrated thin film lithium niobate wafer of example 3.

FIG. 5 is a cross-sectional view of a photodetector on a hetero-integrated thin film lithium niobate based sheet of example 3.

Fig. 6 is a schematic diagram of the on-chip wavelength response of example 3.

The photonic chip comprises a 100-lithium niobate photonic chip, a 110-lithium niobate waveguide layer, a 111-grating coupler, a 112-lithium niobate straight waveguide, a 113-lithium niobate tapered waveguide, a 120-silicon substrate, a 130-silicon dioxide layer, a 200-III-V active waveguide layer, a 201-N type metal layer, a 202-multi-quantum well layer, a 203-P type cladding layer, a 204-P type metal layer, a 205-III-V group tapered waveguide, a 300-N type metal electrode, a 400-P type metal electrode, a 500-silicon oxide layer and a 600-BCB curing layer.

Detailed Description

The drawings are for illustrative purposes only and are not to be construed as limiting the patent;

for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product;

it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.

Example 1

The present embodiment provides a coupling structure on a lithium niobate chip based on a hetero-integrated thin film, as shown in fig. 1, which is a schematic structural diagram of the coupling structure on a lithium niobate chip based on a hetero-integrated thin film according to the present embodiment.

The coupling structure on the lithium niobate chip based on the heterogeneous integration thin film provided by the embodiment comprises a thin film lithium niobate photonic chip 100, wherein a III-V active waveguide layer 200 is integrated on the thin film lithium niobate photonic chip 100 through a heterogeneous integration wafer bonding technology.

The thin-film lithium niobate photonic chip 100 of this embodiment is provided with a lithium niobate waveguide layer 110, and an output end of the lithium niobate waveguide layer 110 is vertically evanescent-wave-coupled with an input end of the III-V active waveguide layer 200.

The III-V active waveguide layer 200 is covered with an N-type metal electrode 300 and a P-type metal electrode 400, and is used for applying a reverse voltage to the on-chip coupling structure, so as to detect light input to the thin-film lithium niobate photonic chip 100 and generate photocurrent output.

In this embodiment, the III-V active waveguide layer 200 is integrated on the thin-film lithium niobate photonic chip 100 by the hetero-integrated wafer bonding technology, so as to realize the function of optical detection on the lithium niobate chip. The III-V active waveguide layer 200 is optically interconnected with the thin film lithium niobate photonic chip 100 in a vertical evanescent coupling manner to achieve high efficiency coupling between the III-V active waveguide layer 200 and the lithium niobate waveguide. The wafer bonding adopts a bonding mode from a small-sized III-V active waveguide layer 200 to a large-sized thin film lithium niobate photonic chip 100, has the characteristics of high integration level, cost saving and contribution to mass production, and is favorable for realizing a high-performance on-chip integrated optical detector.

In an alternative embodiment, the III-V active waveguide layer 200 includes an N-type metal layer 201, a mqw layer 202, a P-type cladding layer 203, and a P-type metal layer 204, which are sequentially disposed from bottom to top.

Fig. 2 is a schematic structural diagram of a III-V active waveguide layer 200 according to this embodiment.

The III-V active waveguide layer 200 is a double-layer cascaded tapered waveguide structure. The absorption layer 202 of the multiple quantum well layer of the III-V active waveguide layer 200 is used for detecting incident light to generate electron-hole pairs, and under the action of a reverse bias, the electron-hole pairs move to two stages respectively to generate photocurrent.

In an optional embodiment, the lithium niobate waveguide layer 110 includes a grating coupler 111, a lithium niobate straight waveguide 112 and a lithium niobate tapered waveguide 113, which are connected in sequence, where the grating coupler 111 is coupled with an external single-mode fiber; the III-V active waveguide layer 200 also includes a III-V tapered waveguide 205, the lithium niobate tapered waveguide 112 and the III-V tapered waveguide 205 forming a III-V/LN optical mode spot converter and maintaining mode matching.

In this embodiment, the III-V/LN optical mode spot converter is composed of the lithium niobate tapered waveguide 113 and the III-V tapered waveguide 205, wherein the III-V tapered waveguide 205 is an N-type metal layer 201 waveguide, and the III-V tapered waveguide 205 and the N-type metal layer 201 in the III-V active waveguide layer 200 are integrated waveguide layers.

In a specific implementation process, incident light input by an external single mode fiber is coupled into the lithium niobate straight waveguide 111 and the lithium niobate tapered waveguide 113 by the grating coupler 110, and the lithium niobate tapered waveguide 113 couples an optical signal into the III-V group tapered waveguide 205 and further into the N-type metal layer 201 in the III-V active waveguide layer 200; then, light is gradually coupled into the multiple quantum well layer 202 through the III-V active waveguide layer 200, the multiple quantum well layer 202 generates stimulated radiation after receiving photons, electron hole pairs are generated, and under the action of reverse bias, the electron holes respectively move to two stages to generate photocurrent, thereby realizing the detection of incident light.

Further, in an optional embodiment, the grating coupler 111 is a lithium niobate one-dimensional coupling grating, so as to implement high-efficiency coupling between the thin-film lithium niobate photonic chip 100 and an external single-mode optical fiber.

Further, in an optional embodiment, a silicon oxide layer 500 and a BCB cured layer 600 are disposed between the III-V active waveguide layer 200 and the lithium niobate photonic chip 100.

In this embodiment, the III-V active waveguide layer 200 is integrated on the lithium niobate photonic chip 100 by a hetero-integrated wafer bonding technique, wherein the hetero-integrated bonding method adopts an adhesive bonding method, specifically, BCB (benzocyclobutene) is used as an intermediate layer, and the III-V active waveguide layer 200 is integrated with the thin film lithium niobate photonic chip 100 by BCB curing, which has the characteristics of high integration level, cost saving, and benefit for mass production.

Example 2

This embodiment provides a method for preparing a coupling structure on a lithium niobate substrate based on a hetero-integrated thin film, which is used to prepare the coupling structure on a lithium niobate substrate based on a hetero-integrated thin film provided in embodiment 1.

Fig. 3 is a flowchart of a method for manufacturing a coupling structure on a lithium niobate substrate based on a hetero-integrated thin film according to this embodiment.

The preparation method of the coupling structure on the lithium niobate chip based on the heterogeneous integrated thin film provided by the embodiment comprises the following steps:

s1, preparing a grating coupler 111, a lithium niobate straight waveguide 112 and a lithium niobate tapered waveguide 113 on a lithium niobate photonic chip 100.

S2, depositing a silicon oxide layer 500 on the thin-film lithium niobate photonic chip 100 obtained in the step S1 by using a thin-film deposition technology, and then polishing and flattening the silicon oxide layer 500 to a thickness not greater than 50nm by using a chemical mechanical polishing technology.

And S3, after a BCB solidified layer 600 with the thickness of less than 70nm is spin-coated on the thin film lithium niobate photonic chip 100 obtained in the step S2, bonding a III-V active waveguide layer 200 to the thin film lithium niobate photonic chip 100 by utilizing a heterogeneous integrated wafer bonding technology, wherein the output end of the thin film lithium niobate photonic chip 100 is in vertical evanescent wave coupling with the input end of the III-V active waveguide layer 200, and the lithium niobate tapered waveguide 113 is in mode matching with the III-V group tapered waveguide 205 in the III-V active waveguide layer 200.

And S4, covering the III-V active waveguide layer 200 of the lithium niobate photonic chip 100 obtained in the step S3 with an N-type metal electrode 300 and a P-type metal electrode 400.

In an optional embodiment, the thin-film lithium niobate photonic chip 100 includes a silicon substrate 120 and a silicon dioxide layer 130 sequentially disposed from bottom to top, and in the step S1, a grating coupler 111, a lithium niobate straight waveguide 112, and a lithium niobate tapered waveguide 113 are prepared on the silicon dioxide layer 130 in the thin-film lithium niobate photonic chip 100, so as to obtain the lithium niobate waveguide layer 110.

In this embodiment, a hetero-integrated wafer bonding technique is used to integrate the III-V active waveguide layer 200 onto the thin-film lithium niobate photonic chip 100, and the obtained thin-film lithium niobate photonic chip 100 has a function of optical detection on a lithium niobate chip. In addition, the III-V active waveguide layer 200 of this embodiment is used as a III-V/LN mode spot converter to couple with the vertical evanescent wave of the lithium niobate waveguide layer 110, so as to realize high-efficiency coupling between the III-V active waveguide layer 200 and the lithium niobate waveguide.

Example 3

The embodiment provides an optical device, and particularly, the optical device provided by the embodiment is a photodetector based on a hetero-integrated thin film lithium niobate sheet. As shown in fig. 4 and 5, the structure of the photodetector on the lithium niobate sheet based on hetero-integrated thin film of this embodiment is schematically illustrated (the N-type metal electrode 300, the P-type metal electrode 400, and the BCB cured layer 600 are omitted in fig. 4).

The optical device provided in this embodiment includes a thin-film lithium niobate photonic chip 100, and the thin-film lithium niobate photonic chip 100 integrates the coupling structure based on the hetero-integrated thin-film lithium niobate chip provided in embodiment 1.

Wherein, the thin film lithium niobate photonic chip 100 is integrated with a III-V group photodetector by a hetero-integrated wafer bonding technique.

The thin-film lithium niobate photonic chip 100 is provided with a grating coupler 111, a lithium niobate straight waveguide 112 and a lithium niobate tapered waveguide 113, and the lithium niobate tapered waveguide 113 and a III-V group tapered waveguide 205 arranged at the bottom of the III-V group optical detector form a III-V/LN optical mode spot converter and keep mode matching.

The III-V group optical detector is covered with an N-type metal electrode 300 and a P-type metal electrode 400, and is used for applying reverse voltage to detect light input to the thin-film lithium niobate photonic chip and generate photocurrent output.

In a specific implementation process, the grating coupler 111 is connected to an external single-mode optical fiber, incident light input by the external single-mode optical fiber is coupled by the grating coupler 111 and transmitted to the lithium niobate tapered waveguide 113 of the optical speckle converter through the lithium niobate straight waveguide 112, and the lithium niobate tapered waveguide 113 couples an optical signal to the III-V optical detector. Meanwhile, the III-V group photodetector detects the input light, and by applying reverse voltages to the N-type metal electrode 300 and the P-type metal electrode 400, the electron holes respectively move to two stages under the action of a reverse bias voltage, and generate a photocurrent, thereby realizing the detection of the light.

Fig. 6 is a schematic diagram of on-chip wavelength response of the photodetector based on the hetero-integrated thin film lithium niobate sheet of the present embodiment. As can be seen from the figure, the waveguide coupling effect of the photodetector based on the hetero-integrated thin film lithium niobate chip provided by the embodiment on the condition of applying a reverse voltage of 5V on the input wavelength light of 1550nm and 1560nm can reach 0.52A/W and 0.48A/W respectively.

In this embodiment, the III-V optical detector is integrated on the thin-film lithium niobate photonic chip 100 by the heterogeneous integrated wafer bonding technology, so as to realize the optical detection function on the lithium niobate chip. The III-V group optical detector is coupled with the lithium niobate tapered waveguide 113 through a vertical evanescent wave, so that high-efficiency coupling between the III-V group optical detector and the lithium niobate waveguide is realized, and the III-V group optical detector has the characteristics of high integration level, cost saving and contribution to mass production.

In an optional embodiment, the III-V group photodetector is a multi-quantum well structure, and includes an N-type region, an intrinsic region, and a P-type region sequentially arranged from bottom to top; wherein the N-type region includes an N-type metal layer 201, the intrinsic region includes a multi-quantum well layer 202, and the P-type region includes a P-type cladding layer 203 and a P-type metal layer 204.

The multiple quantum well layer 202 of the III-V group photodetector generates stimulated radiation after receiving photons to generate electron-hole pairs, and the electron-hole pairs move to two stages respectively under the action of reverse bias to generate photocurrent.

In an alternative embodiment, a silicon oxide layer 500 and a BCB cured layer 600 are disposed between the thin-film lithium niobate photonic chips 100.

Further, in an optional embodiment, the thin-film lithium niobate photonic chip 100 includes a silicon substrate 120, a silicon dioxide layer 130, a lithium niobate waveguide layer 110, and a silicon oxide layer 140, which are sequentially disposed from bottom to top; the lithium niobate waveguide layer 110 includes a grating coupler 111 made of a lithium niobate waveguide, a lithium niobate straight waveguide 112, and a lithium niobate tapered waveguide 113.

The same or similar reference numerals correspond to the same or similar parts;

the terms describing positional relationships in the drawings are for illustrative purposes only and are not to be construed as limiting the patent;

it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. The coupling structure on the lithium niobate chip based on the heterogeneous integration thin film is characterized by comprising a thin film lithium niobate photonic chip (100), wherein a III-V active waveguide layer (200) is integrated on the thin film lithium niobate photonic chip (100) through a heterogeneous integration wafer bonding technology;

a lithium niobate waveguide layer (110) is arranged on the thin-film lithium niobate photonic chip (100), and the output end of the lithium niobate waveguide layer (110) is vertically evanescently coupled with the input end of the III-V active waveguide layer (200); the III-V active waveguide layer (200) is covered with an N-type metal electrode (300) and a P-type metal electrode (400).

2. The hetero-integrated thin-film lithium niobate-based on-chip coupling structure of claim 1, wherein the III-V active waveguide layer (200) comprises an N-type metal layer (201), a multi-quantum well layer (202), a P-type cladding layer (203) and a P-type metal layer (204) which are sequentially arranged from bottom to top.

3. The hetero-integrated thin-film lithium niobate-based on-chip coupling structure of claim 2, wherein the III-V active waveguide layer (200) is a double-layer cascaded tapered waveguide structure.

4. The coupling structure on the lithium niobate substrate based on the hetero-integrated thin film according to claim 1, wherein the lithium niobate waveguide layer (110) comprises a grating coupler (111), a lithium niobate straight waveguide (112) and a lithium niobate tapered waveguide (113) which are connected in sequence, and the grating coupler (111) is coupled with an external single-mode fiber; the III-V active waveguide layer (200) further comprises a III-V tapered waveguide (205), and the lithium niobate tapered waveguide (113) and the III-V tapered waveguide (205) form a III-V/LN optical mode spot converter and maintain mode matching.

5. The hetero-integration thin-film lithium niobate-based on-chip coupling structure according to any one of claims 1 to 4, wherein a silicon oxide layer (500) and a BCB cured layer (600) are arranged between the III-V active waveguide layer (200) and the thin-film lithium niobate photonic chip (100).

6. The preparation method based on the coupling structure on the hetero-integrated thin film lithium niobate chip is used for preparing the coupling structure on the hetero-integrated thin film lithium niobate chip according to any one of claims 1 to 5, and comprises the following steps:

s1, preparing a grating coupler (111), a lithium niobate straight waveguide (112) and a lithium niobate tapered waveguide (113) on a thin-film lithium niobate photonic chip (100);

s2, depositing a silicon oxide layer (500) on the thin-film lithium niobate photonic chip (100) obtained in the step S1 by using a thin-film deposition technology, and then polishing and flattening the silicon oxide layer (500) by using a chemical mechanical polishing technology until the thickness is not more than 50nm;

s3, after a BCB curing layer (600) with the thickness of less than 70nm is spin-coated on the thin-film lithium niobate photonic chip (100) obtained in the step S2, bonding the III-V active waveguide layer (200) to the thin-film lithium niobate photonic chip (100) by utilizing a heterogeneous integration wafer bonding technology; wherein the output end of the thin-film lithium niobate photonic chip (100) is vertically evanescently coupled with the input end of the III-V active waveguide layer (200), and the lithium niobate tapered waveguide (113) is mode-matched with a III-V group tapered waveguide (205) in the III-V active waveguide layer (200);

and S4, covering and arranging an N-type metal electrode (300) and a P-type metal electrode (400) on the III-V active waveguide layer (200) of the thin-film lithium niobate photonic chip (100) obtained in the step S3.

7. An optical device comprising a thin film lithium niobate photonic chip (100), the thin film lithium niobate photonic chip (100) having integrated thereon a heterointegration-based thin film lithium niobate on-chip coupling structure of any one of claims 1 to 5, wherein:

the thin-film lithium niobate photonic chip (100) is integrated with a III-V group optical detector through a heterogeneous integrated wafer bonding technology;

a grating coupler (111) prepared by a lithium niobate waveguide, a lithium niobate straight waveguide (112) and a lithium niobate tapered waveguide (113) are arranged on the thin-film lithium niobate photonic chip (100), and the lithium niobate tapered waveguide (113) and a III-V group tapered waveguide (205) arranged at the bottom of the III-V group optical detector form a III-V/LN optical mode spot converter and keep mode matching;

the III-V group optical detector is covered with an N-type metal electrode (300) and a P-type metal electrode (400) and is used for applying reverse voltage to detect light input to the thin-film lithium niobate photonic chip (100) and generate photocurrent output.

8. The optical device according to claim 7, wherein the group III-V photodetector is a multiple quantum well structure comprising an N-type region, an intrinsic region, and a P-type region sequentially disposed from bottom to top; wherein the N-type region comprises an N-type metal layer (201), the intrinsic region comprises a multi-quantum well layer (202), and the P-type region comprises a P-type cladding layer (203) and a P-type metal layer (204).

9. The optical device according to claim 7, wherein a silicon oxide layer (500) and a cured layer of BCB (600) are disposed between the group III-V photodetector and the thin film lithium niobate photonic chip (100).

10. The optical device according to any one of claims 7 to 9, wherein the thin-film lithium niobate photonic chip (100) comprises a silicon substrate (120), a silicon dioxide layer (130), a lithium niobate waveguide layer (110) and a silicon oxide layer (140) which are arranged in sequence from bottom to top; the lithium niobate waveguide layer (110) comprises a grating coupler (111), a lithium niobate straight waveguide (112) and a lithium niobate tapered waveguide (113).