WO2024007500A1

WO2024007500A1 - Lithium niobate wire-based electro-optic modulator and manufacturing method therefor

Info

Publication number: WO2024007500A1
Application number: PCT/CN2022/131023
Authority: WO
Inventors: 李西军
Original assignee: 西湖大学
Priority date: 2022-07-08
Filing date: 2022-11-10
Publication date: 2024-01-11
Also published as: CN115167016A

Abstract

A lithium niobate wire-based electro-optic modulator and a manufacturing method therefor. The lithium niobate wire-based electro-optic modulator comprises an input mechanism (1), a modulation mechanism (2), and an output mechanism (3) which are connected in sequence. Laser sequentially passes through the input mechanism (1) and the modulation mechanism (2), and then is outputted by means of the output mechanism (3), and at least one of the input mechanism (1), the modulation mechanism (2) or the output mechanism (3) is provided with a waveguide tube (4) having a hexagonal cross-section. The waveguide tube (4) comprising lithium niobate wires (41) and having a hexagonal cross-section is used, shape mismatch between light modes of an optical fiber/laser and the lithium niobate wire-based electro-optic modulator is eliminated by utilizing a light mode close to the Gaussian beam spot shape in the waveguide tube (4), and the coupling efficiency between the optical fiber/laser and the lithium niobate wire-based electro-optic modulator is greatly improved in cooperation with lens coupling. A light guide mode of the lithium niobate wire-based electro-optic modulator and a modulating electric field generated by modulation electrodes around the waveguide tube (4) highly spatially overlap, and the symmetry is close, so that the electro-optic modulation efficiency can be improved.

Description

A lithium niobate wire electro-optical modulator and its preparation method

Technical field

The present disclosure relates to the technical field of modulation equipment, and in particular, to a lithium niobate wire electro-optical modulator and a preparation method thereof.

Background technique

The electro-optical modulator uses microwave signals to modulate continuous light into optical pulses, and uses the ultra-low transmission loss of optical pulses in optical fibers to transmit information. This is the basis of the principle of optical fiber communication. Therefore, the electro-optical modulator is an important component of optical fiber communication, and it is widely used in optical fiber networks and data centers. Lithium niobate material is a modulator whose electro-optical modulation frequency can reach over 100GHz. As early as 2004, Li Xijun, the inventor of this patent, used semiconductor processing technology to develop a high-performance lithium niobate ridge waveguide for the development of integrated nonlinear optical systems. In 2006, he proposed niobate on the insulating layer as an integrated nonlinear optical and nonlinear optical system. Concept of optoelectronic devices. In the past few years, Professor Marko Loncar's research group at Harvard University has developed efficient lithium niobate optoelectronic devices by using nano-niobate films on the insulating layer and semiconductor processing technology. These optical waveguide devices developed using semiconductors all adopt a ridge waveguide structure, as shown in Figure 1. The spatial distribution of the light field propagating in the waveguide is similar to that of a waveguide collision, completely deviating from the circular structure. The optical fiber communication connected to the electro-optical modulator or the spatial distribution of the light spot of the laser is a Gaussian beam spot as shown in Figure 1, which leads to a so-called mode mismatch with low coupling efficiency between the modulator and the laser or optical fiber. Usually the light spot size of the optical fiber output is 8-10 microns, while the light mode size of the lithium niobate ridge waveguide is 1-3 microns. Lens coupling is used, and the light output through the focused fiber is incident on the ridge waveguide at the input end, and the over-amplified modulator is used at the output end to output the spot size, which can reduce the coupling loss. But by carefully analyzing Figure 1, we can find that there is a mode mismatch between the ridge waveguide modulator and the optical fiber or laser coupling. In addition to the optical mode geometric size mismatch, there is also a geometric shape mismatch. Using the above lens coupling, we can only reduce the size mismatch between the fiber/laser optical mode and the modulator waveguide optical mode, but cannot change the shape adaptation of their optical modes. In addition, the spatial overlap of the ridge waveguide optical mode and the electric field distribution of the modulation electrode results in a loss of electro-optical modulation efficiency due to the asymmetry of the optical waveguide mode geometry.

Contents of the invention

In view of this, embodiments of the present disclosure propose a lithium niobate wire electro-optic modulator and a preparation method thereof to solve the problem of reduced electro-optic modulation efficiency caused by size mismatch and shape asymmetry in existing electro-optic modulators.

The present disclosure provides a lithium niobate wire electro-optic modulator, which includes an input mechanism, a modulation mechanism and an output mechanism that are connected in sequence. Laser passes through the input mechanism and the modulation mechanism in sequence and is output through the output mechanism, and the input mechanism, At least one of the modulation mechanism or the output mechanism is provided with a waveguide having a hexagonal cross-section.

In some embodiments, the material of the waveguide includes single crystal lithium niobate material.

In some embodiments, the material of the waveguide includes Z-cut lithium niobate, X-cut lithium niobate or Y-cut lithium niobate.

In some embodiments, the modulation mechanism further includes a modulation electrode structure corresponding to at least one of the waveguides, and the modulation electrode structures are distributed in the Z direction of the corresponding waveguide.

In some embodiments, the waveguide and the modulation electrode structure are both located within a layer of dielectric material.

In some embodiments, the modulation mechanism includes a first modulation arm and a second modulation arm arranged in parallel. Part of the laser light of the input mechanism passes through the first modulation arm and is then input to the output mechanism, and the remaining part of the laser light passes through the first modulation arm. The second modulation arm is then input to the output mechanism, and the modulation direction of the laser by the first modulation arm is opposite to the modulation direction of the laser by the second modulation arm.

In some embodiments, the waveguide includes two relatively interlocked lithium niobate wires, the cross-section of the lithium niobate wire is an isosceles trapezoid, and the angle between the base angles of the isosceles trapezoid is 60°. .

A method for preparing the above-mentioned lithium niobate wire electro-optical modulator, including:

Step S1: Arrange lithium niobate material on the insulating layer and form a lithium niobate wafer;

Step S2: Etch the lithium niobate wafer in S1 to form a lithium niobate line with an inclination angle of 60°;

Step S3: Perform electroplating and/or deposition at a preset position on the peripheral side of the lithium niobate wire to form an electrode;

Step S4: Electroplating a dielectric material on the peripheral side of the lithium niobate wire to form a dielectric material layer;

Step S5: Bond the two lithium niobate wires prepared in step S4 to form a waveguide.

In some embodiments, in step S1, the lithium niobate material is a Z-cut lithium niobate material, and in step S3, electroplating and/or deposition is performed at a preset position on the peripheral side of the lithium niobate wire to form a driving electrode. .

In some embodiments, in step S1, the lithium niobate material is an X-cut lithium niobate material or a Y-cut lithium niobate material, and in step S3, electroplating is performed at a preset position on the peripheral side of the lithium niobate wire. and/or deposited to form modulating electrodes.

The embodiment of the present disclosure uses a lithium niobate wire waveguide with a hexagonal cross-section, and utilizes the light mode in the waveguide that is close to the Gaussian beam spot shape to eliminate the shape adaptation between the above-mentioned optical fiber/laser and the light mode of the electro-optical modulator, and cooperate with Lens coupling greatly improves the coupling efficiency between fiber/laser and electro-optical modulator. The light guide mode of the lithium niobate wire electro-optic modulator disclosed in the present invention is highly spatially coincident with the modulation electric field generated by the modulation electrode around the waveguide. The close symmetry can improve the electro-optic modulation efficiency.

Description of the drawings

In order to explain the embodiments of the present disclosure or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments recorded in this disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting any creative effort.

Figure 1 is a schematic structural diagram of an electro-optical modulator in the prior art;

Figure 2 is a schematic structural diagram of a lithium niobate wire electro-optical modulator according to an embodiment of the present disclosure;

Figure 3 is a schematic structural diagram of an adjustment mechanism whose material is Z-cut lithium niobate according to an embodiment of the present disclosure;

Figure 4 is a preparation process diagram of the adjustment mechanism of Figure 3 according to an embodiment of the present disclosure;

Figure 5 is a schematic structural diagram of an adjustment mechanism in which the material is X-cut lithium niobate or Y-cut lithium niobate according to an embodiment of the present disclosure;

Figure 6 is a diagram of the preparation process of the adjustment mechanism of Figure 4 according to an embodiment of the present disclosure.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are some, but not all, of the embodiments of the present disclosure. Based on the described embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present disclosure.

Unless otherwise defined, technical terms or scientific terms used in this disclosure shall have the usual meaning understood by a person with ordinary skill in the art to which this disclosure belongs. "First", "second" and similar words used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprising" mean that the elements or things appearing before the word include the elements or things listed after the word and their equivalents, without excluding other elements or things. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right", etc. are only used to express relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

In order to keep the following description of the embodiments of the present disclosure clear and concise, the present disclosure omits detailed descriptions of well-known functions and components.

The embodiment of the present disclosure relates to a lithium niobate wire electro-optical modulator as shown in Figures 1 to 6, including an input mechanism 1, a modulation mechanism 2 and an output mechanism 3 connected in sequence. The laser passes through the input mechanism 1 and the modulation mechanism in sequence. Mechanism 2 then outputs through the output mechanism 3, and at least one of the input mechanism 1, the modulation mechanism 2 or the output mechanism 3 is provided with a waveguide 4 with a hexagonal cross-section. The cross-section of this waveguide 4 structure and its circular light pattern are shown in Figure 2. The ground-mode laser spot propagating in the hexagonal cross-section lithium niobate waveguide 4 is close to a circle, which is consistent with the shape of the spatial structure mode of the light output by long-distance optical transmission fibers and commonly used lasers, which improves the coupling between them. Adaptation of the spatial shape of the mode. The optical mode close to the Gaussian beam spot shape shown in Figure 2 can reduce or even eliminate the shape mismatch between the fiber/laser and the electro-optical modulator optical mode. With lens coupling, it can be greatly improved. Coupling efficiency between fiber/laser and electro-optical modulator.

The light guide mode of the lithium niobate wire electro-optic modulator is highly spatially coincident with the modulation electric field generated by the modulation electrode around the waveguide 4, and the close symmetry can improve the electro-optic modulation efficiency. Taking the case of using z-cut lithium niobate material to make a lithium niobate wire electro-optical modulator, an MZ modulator is used, and its structural schematic diagram is shown in Figure 3. At this time, both arms of the MZ modulator have their own modulation electrodes. The modulation electrodes are located directly above and below the modulation arm, as shown in Figure 4. The modulated electric field between the two electrodes of the same modulation arm forms a uniform electric field distribution in the light guide mode space with a circular structure. Because of the high overlap and uniform distribution between the modulating electric field and the modulated light mode, the highest modulation efficiency is achieved. The traveling wave modulation electrodes are distributed on both sides of the two arms of the MZ modulator, and the light guides of both arms are embedded in dielectric materials. The length, width and thickness of the electrodes are simultaneously optimized to microwave impedance within the modulation operating frequency range. is 50 ohms, where the microwaves maintain phase matching with the modulated light waves propagating in the two arms of the MZ. The size of the hexagonal lithium niobate micron nanotubes is between 1um and 10um. The spacing of the modulating electrodes can be controlled between 2um and 15 microns accordingly. The required driving voltage is between 1.5-10V.

Optionally, the material of the waveguide 4 includes single crystal lithium niobate material.

Optionally, the material of the waveguide 4 includes Z-cut lithium niobate, X-cut lithium niobate or Y-cut lithium niobate.

More specifically, the modulation mechanism 2 also includes a modulation electrode structure 5 corresponding to at least one of the waveguides 4 , and the modulation electrode structures 5 are distributed in the corresponding waveguides 4 in the Z direction. The optical waveguide passing through the waveguide 4 is modulated by the modulation electrode structure 5. The modulated optical waveguide is coupled and enters the output mechanism 3 to complete the modulation of the optical waveguide.

In some embodiments, the waveguide 4 and the modulation electrode structure 5 are both located within the dielectric material layer 6 . A lithium niobate waveguide with a hexagonal cross-section is buried in the medium. By selecting and controlling the growth of the dielectric material, the effective refractive index of the ground state light mode in the waveguide can be adjusted, and the optical mode radius can be optimized when coupling with the lens fiber. Coupling; the modulating electrode structure 5 is embedded in a dielectric material. Choosing a suitable dielectric material can greatly optimize the phase adaptation between the microwave propagating on the electrode and the modulated light wave in the waveguide 4; the modulating electrode structure 5 and niobium The lithium acid wires 41 are all buried in dielectric materials, and their heights can be optimized to be the same or similar to ensure that the distribution of the high-frequency electric field between the electrodes and the ground state light mode in the lithium niobate wires 41 are completely consistent in space.

In some embodiments, the modulation mechanism 2 includes a first modulation arm 21 and a second modulation arm 22 arranged in parallel. Part of the laser light of the input mechanism 1 passes through the first modulation arm 21 and is then input to the output mechanism. 3. The remaining part of the laser light is input to the output mechanism 3 after passing through the second modulation arm 22, and the modulation direction of the laser light by the first modulation arm 21 is opposite to the modulation direction of the laser light by the second modulation arm 22. The symmetry of the modulation mechanism 2 is effectively improved, thereby improving the electro-optical modulation efficiency.

In some embodiments, the waveguide 4 includes two relatively interlocked lithium niobate wires 41 , the cross section of the lithium niobate wire 41 is an isosceles trapezoid, and the angle between the base angles of the isosceles trapezoid is is 60°. That is, even if the cross-section of the waveguide 4 is a regular hexagon, the propagating light mode can have a circularly symmetrical shape of a Gaussian beam spot, which can reduce or even eliminate the shape mismatch between the optical fiber/laser and the electro-optical modulator optical mode. Lens coupling greatly improves the coupling efficiency between fiber/laser and electro-optical modulator.

Step S1: Arrange lithium niobate material on the insulating layer and form a lithium niobate wafer (as shown in Figure 4a or Figure 6a);

Step S2: Etch the lithium niobate wafer in S1 to form a lithium niobate line 41 with an inclination angle of 60° (as shown in Figures 4b to 4e or 6b to 6e);

Step S3: Perform electroplating and/or deposition at a preset position on the peripheral side of the lithium niobate wire 41 to form an electrode (as shown in Figures 4f to 4h or as shown in Figures 6f to 6h);

Step S4, electroplating a dielectric material on the peripheral side of the lithium niobate wire 41 to form a dielectric material layer 6 (as shown in Figure 4i or Figure 6i);

Step S5: Bond the two lithium niobate wires 41 prepared in step S4 to form a waveguide 4 (as shown in Figure 4k or Figure 6k).

In some embodiments, as shown in FIGS. 3 and 4 , in step S1 , the lithium niobate material is a Z-cut lithium niobate material, and in step S3 it is at a preset position on the peripheral side of the lithium niobate wire 41 Electroplating and/or deposition are performed to form driving electrodes.

As another embodiment, as shown in Figures 5 and 6, in step S1, the lithium niobate material is an X-cut lithium niobate material or a Y-cut lithium niobate material, and in step S3, the lithium niobate wire is Electroplating and/or deposition are performed at preset positions on the peripheral side of 41 to form modulation electrodes.

Between step S4 and step S5, the substrate and/or the insulating layer also need to be removed (as shown in Figure 4j or Figure 6j).

After step S5, the upper protective slide also needs to be removed (as shown in Figure 4l or Figure 6l).

The embodiment of the present disclosure adopts a hexagonal cross-section lithium niobate wire 41 waveguide 4, and utilizes the light mode close to the Gaussian beam spot shape in the waveguide 4 to eliminate the shape incompatibility between the above-mentioned optical fiber/laser and the electro-optical modulator light mode. With lens coupling, the coupling efficiency between fiber/laser and electro-optical modulator is greatly improved. The light guide mode of the lithium niobate wire electro-optic modulator disclosed in the present invention is highly spatially coincident with the modulation electric field generated by the modulation electrode around the waveguide 4, and the close symmetry can improve the electro-optic modulation efficiency.

The above description is only a description of the preferred embodiments of the present disclosure and the technical principles applied. Those skilled in the art should understand that the disclosure scope involved in the present disclosure is not limited to technical solutions composed of specific combinations of the above technical features, but should also cover solutions composed of the above technical features or without departing from the above disclosed concept. Other technical solutions formed by any combination of equivalent features. For example, a technical solution is formed by replacing the above features with technical features with similar functions disclosed in this disclosure (but not limited to).

Furthermore, although operations are depicted in a specific order, this should not be understood as requiring that these operations be performed in the specific order shown or performed in a sequential order. Under certain circumstances, multitasking and parallel processing may be advantageous. Likewise, although several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of the present disclosure. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are merely example forms of implementing the claims.

Multiple embodiments of the present disclosure have been described in detail above, but the present disclosure is not limited to these specific embodiments. Those skilled in the art can make various variations and modifications to the embodiments based on the concepts of the present disclosure. These variations and modifications All should fall within the scope of protection claimed by this disclosure.

Claims

A lithium niobate wire electro-optical modulator, which is characterized in that it includes an input mechanism, a modulation mechanism and an output mechanism connected in sequence. The laser passes through the input mechanism and the modulation mechanism in sequence and is output through the output mechanism, and the input mechanism At least one of the modulation mechanism or the output mechanism is provided with a waveguide with a hexagonal cross-section.
The lithium niobate wire electro-optic modulator according to claim 1, wherein the material of the waveguide includes single crystal lithium niobate material.
The lithium niobate wire electro-optic modulator according to claim 1, wherein the material of the waveguide includes Z-cut lithium niobate, X-cut lithium niobate or Y-cut lithium niobate.
The lithium niobate wire electro-optical modulator according to claim 3, characterized in that the modulation mechanism further includes a modulation electrode structure, the modulation electrode mechanism corresponds to at least one of the waveguides, and the modulation electrode structure distributed in the corresponding Z direction of the waveguide.
The lithium niobate wire electro-optical modulator according to claim 4, wherein the waveguide and the modulation electrode structure are located in a dielectric material layer.
The lithium niobate wire electro-optical modulator according to claim 1, characterized in that the modulation mechanism includes a first modulation arm and a second modulation arm arranged in parallel, and part of the laser light of the input mechanism passes through the first modulation arm. The arm is input to the output mechanism, and the remaining part of the laser is input to the output mechanism after passing through the second modulation arm, and the modulation direction of the laser by the first modulation arm is consistent with the modulation of the laser by the second modulation arm. In the opposite direction.
The lithium niobate wire electro-optic modulator according to claim 1, wherein the waveguide includes two relatively interlocked lithium niobate wires, the cross section of the lithium niobate wire is an isosceles trapezoid, and the The angle between the base angles of an isosceles trapezoid is 60°.
A method for preparing the lithium niobate wire electro-optical modulator according to any one of claims 1 to 7, characterized in that it includes:

Step S1: Arrange lithium niobate material on the insulating layer and form a lithium niobate wafer;

Step S2: Etch the lithium niobate wafer in S1 to form a lithium niobate line with an inclination angle of 60°;

Step S3: Perform electroplating and/or deposition at a preset position on the peripheral side of the lithium niobate wire to form an electrode;

Step S4: Electroplating a dielectric material on the peripheral side of the lithium niobate wire to form a dielectric material layer;

Step S5: Bond the two lithium niobate wires prepared in step S4 to form a waveguide.
The preparation method according to claim 8, characterized in that, in step S1, the lithium niobate material is a Z-cut lithium niobate material, and in step S3, it is performed at a preset position on the peripheral side of the lithium niobate wire. Electroplating and/or deposition forms the drive electrodes.
The preparation method according to claim 8, characterized in that, in step S1, the lithium niobate material is an X-cut lithium niobate material or a Y-cut lithium niobate material, and in step S3, around the lithium niobate wire Electroplating and/or deposition are performed at preset positions on the side to form modulation electrodes.