CN118963009A

CN118963009A - Suspended waveguide matrix thin film lithium niobate acousto-optic modulator

Info

Publication number: CN118963009A
Application number: CN202411276061.0A
Authority: CN
Inventors: 张维佳; 李佳琦; 罗雪婷
Original assignee: Tianjin University of Science and Technology
Current assignee: Tianjin University of Science and Technology
Priority date: 2024-09-12
Filing date: 2024-09-12
Publication date: 2024-11-15

Abstract

The invention provides a novel suspension waveguide matrix film lithium niobate acousto-optic modulator, which belongs to the technical field of acousto-optic modulation and comprises a bulk lithium niobate substrate and a plurality of suspension waveguide layers which are laminated from bottom to top, wherein each suspension waveguide layer comprises a bulk lithium niobate substrate, an etched silicon dioxide buffer layer, a lithium niobate film, an optical waveguide, an interdigital electrode, an etched silicon dioxide buffer layer and an electromagnetic shielding layer which are laminated from bottom to top, all optical waveguides of each waveguide layer correspond to two-dimensional coordinates related to the positions of the optical waveguides, all the two-dimensional coordinates form a waveguide matrix, working parameters of the optical waveguides corresponding to elements in the waveguide matrix are recorded respectively, and each waveguide layer is sequentially prepared according to the lamination sequence. The invention can comprise a plurality of available optical waveguides, can modulate laser with various optical wavelengths and has multiband compatibility: the suspended waveguide structure can be suitable for modulating optical signals in different wave bands such as visible light, infrared light and the like, so that the suspended waveguide structure has wider application range.

Description

Suspension waveguide matrix film lithium niobate acousto-optic modulator

Technical Field

The invention belongs to the technical field of acousto-optic modulation, and relates to a suspension waveguide matrix film lithium niobate acousto-optic modulator.

Background

With the continuous development of optoelectronic integration technology, the integration of an acousto-optic modulator is gradually becoming a research hot spot. The integration technology realizes miniaturization, high performance and low power consumption of devices by integrating a plurality of photoelectric devices on the same chip. For the acousto-optic modulator, the integration technology not only can improve the modulation rate and modulation depth of the modulator, but also can reduce the power consumption and cost of the device. In the design of integrated acousto-optic modulators, a number of factors need to be considered, such as the choice of acousto-optic materials, the coupling efficiency of acoustic and light waves, the heat dissipation properties of the device, etc. In order to obtain better performance, researchers are continually exploring novel acousto-optic materials and novel device structures, such as high-performance materials of thin film lithium niobate, chalcogenide glass and the like, and novel device structures of suspension reinforced structures, one-dimensional photonic crystal nano-beams and the like.

A suspended waveguide, or suspended waveguide, is a special waveguide structure that is characterized primarily by suspended lower boundaries of the waveguide. The structure has important application in various fields of optics, microwave communication, photonics and the like. The suspended waveguide is mainly used for end face coupling of silicon light and optical fibers, the suspended structure can prevent the light field from leaking to the substrate silicon layer, and meanwhile, the suspended waveguide structure can be used for widening the light field, so that low-refractive-index-difference waveguides can be formed, and coupling loss with the optical fibers is further reduced.

The invention creates a novel preparation method of the prepared suspended waveguide, the area below the waveguide is corroded after the waveguide is prepared, but a suspended area is reserved when the silicon dioxide buffer layer is prepared, the waveguide of a liquid phase epitaxial growth technology is bonded, and finally the redundant lithium niobate is stripped by utilizing a smart-cut technology to form the thin film lithium niobate. Versatility and versatility of the modulator are achieved in a matrix-integrated manner.

Disclosure of Invention

In view of the above background desire for an acousto-optic modulator, a suspended waveguide matrix thin film lithium niobate acousto-optic modulator based on a lithium niobate thin film is proposed to solve the above problems. The modulator structure adopts a matrix multi-layer stacked thin film lithium niobate waveguide structure to form a matrix waveguide, and the integration level of the acousto-optic modulator is completed. The novel suspension structure and the liquid phase epitaxial growth technology are introduced to prepare the suspension waveguide, so that energy loss can be reduced, and modulation efficiency is improved.

The invention is realized by the following technical scheme:

The suspended waveguide matrix film lithium niobate acousto-optic modulator comprises a bulk lithium niobate substrate and a plurality of waveguide layers which are laminated from bottom to top, wherein each waveguide layer comprises an etched silicon dioxide buffer layer, a lithium niobate film, a suspended optical waveguide, an interdigital electrode, an etched silicon dioxide buffer layer and an electromagnetic shielding layer which are laminated from bottom to top, all optical waveguides of each waveguide layer correspond to two-dimensional coordinates related to the positions of the optical waveguides, all the two-dimensional coordinates form a waveguide matrix, working parameters of the optical waveguides corresponding to each element in the waveguide matrix are recorded respectively, optical fibers with different wavelengths can be coupled to the optical waveguides at the corresponding positions according to requirements, grooves matched with the interdigital electrode and suspended waveguide areas are etched on the bottom surface of the etched silicon dioxide buffer layer, the standby waveguide layers are sequentially prepared according to the lamination sequence, the electromagnetic shielding layer is made of carbon nano materials, and the optical waveguides are manufactured on the lithium niobate film layer by adopting a liquid phase epitaxial growth technology.

Further, the operating parameters include a band and a frequency of the optical waveguides, each of the optical waveguides having a different frequency.

Further, the preparation step of the optical waveguide includes:

9. The preparation (liquid phase epitaxial growth) step of the optical waveguide comprises:

step S11, cutting the lithium niobate single crystal into thin slices with the size of 35 multiplied by 10 multiplied by 2 mm, and then grinding and polishing;

step S12, preparing a film, namely mixing Li ₂CO₃ 49.0.0 mol%, V ₂O₅ 39.2.2 mol%, nb ₂O₅ 9.8.8 mol% and Cu ₂ O2.0 mol%, and fully and uniformly mixing;

Step S13, liquid phase epitaxial growth conditions: heating to 1180deg.C for eight hours at room temperature, maintaining the temperature for ten hours, cooling to 900 deg.C for four hours, maintaining 900 deg.C for two hours under constant current state, soaking, cooling to 300 deg.C for ten hours, and naturally cooling to room temperature.

And S14, putting the flakes in dilute hydrochloric acid to dissolve out fluxing agents.

Further, the preparation steps of the interdigital electrode comprise:

step S21, sequentially carrying out spin coating and photoetching on the lithium niobate thin film;

S22, coating the sample obtained in the step S21 by adopting an Au material;

and S23, placing the sample obtained in the step S22 into an acetone solution, and removing residual Au in a separation mode to manufacture the required electrode.

Further, the preparation steps of the electromagnetic shielding layer include:

Step S31, adding the multiwall carbon nano powder into a triton solution, soaking and stirring the multiwall carbon nano powder in deionized water after grinding in a grinder, and centrifuging the multiwall carbon nano powder after ultrasonic treatment at intervals of a single second to obtain a uniform and stable multiwall carbon nano tube solution;

Step S32, placing the beaker in a cold water bath, respectively placing Ti3AIC2, liF, deionized water and concentrated hydrochloric acid into the beaker, and magnetically stirring after sealing the beaker;

Step S33, repeatedly washing the suspension subjected to LiF-HCl etching obtained in the step S32 by using ionized water until the pH value of the suspension is close to 6;

Step S34, removing impurities from the solution obtained in the step S33, and performing centrifugal treatment, wherein supernatant is single-layer or less-layer Ti3C2Tx colloidal solution;

And step S35, mixing the carbon nanotube solution and the Ti3C2Tx colloid solution according to different proportions, stirring and carrying out ultrasonic treatment, and preparing the mixed solution into a film by adopting a vacuum suction filtration process to obtain the electromagnetic shielding layer.

Further, the lithium niobate thin film is prepared by adopting Smtr-Cut technology based on H+ ion implantation and SiO2 bonding.

Further, the thickness of the lithium niobate thin film layer is not more than 500nm, and the thickness of the waveguide layer is not more than 4um.

The invention has the following beneficial effects:

1. the adoption of the suspension structure can increase the acousto-optic interaction throwing strength: the suspended waveguide structure enables the sound waves to act on the light waves more effectively by optimizing the interaction path of the sound waves and the light waves, so that the modulation efficiency is improved. This configuration helps to reduce energy losses, so that more acoustic energy is converted into a change in optical energy, thereby improving modulation efficiency. The suspended waveguide structure can more effectively utilize the acoustic energy, so that the driving voltage required by the modulator can be reduced, and the energy consumption is reduced.

2. Reducing mechanical vibrations and disturbances: the suspended waveguide structure realizes the modulation of light waves in a non-contact mode, and avoids mechanical vibration and interference generated by contact in the traditional waveguide structure, thereby improving the performance stability of the modulator.

3. Enhancing environmental adaptability: the suspended waveguide structure has better adaptability to changes of external environment (such as temperature, humidity and the like), so that stable performance can be maintained under wider environmental conditions.

4. And (3) miniaturization design: the suspended waveguide structure generally adopts a micro manufacturing process, so that the modulator is more compact in size, and the miniaturization and integration of equipment are facilitated.

5. And (3) light weight: the miniaturized design also brings the advantage of light weight, so that the modulator has better application prospect in the fields with strict weight requirements such as aerospace, portable equipment and the like.

6. Multiband compatibility: the suspended waveguide structure can be suitable for modulating optical signals in different wave bands such as visible light, infrared light and the like, so that the suspended waveguide structure has wider application range. This is particularly important for application scenarios (e.g., optical imaging, communications, etc.) where multiple optical signals need to be processed.

7. High-precision modulation: because the suspended waveguide structure has higher modulation efficiency and stability, the optical signal modulation with higher precision can be realized, and the application requirement on the modulation precision is met.

8. Flexible configuration: matrix form integration allows flexible configuration of the parameters and functions of the modulator according to the actual requirements. Modulation of optical signals of different wavelengths and different modulation rates can be achieved by adjusting the internal structure of the matrix or increasing/decreasing the number of elements.

9. Easy to expand: with the development of technology and the increase of application demands, the matrix-form integrated acousto-optic modulator can be conveniently expanded and upgraded. The overall performance and range of application of the modulator can be further improved by adding additional matrix modules or optimizing the performance of existing modules.

10. High integration level: matrix form integration enables the acousto-optic modulator to perform more complex functions in a smaller space. This contributes not only to the downsizing and weight saving of the device but also to the improvement of the integration level and reliability of the system.

11. Cost effectiveness: by adopting the matrix form integration, the manufacturing cost can be reduced while the performance is ensured. This is because the design of the matrix structure can optimize material usage, reduce processing steps, reduce testing costs, and the like. In addition, the high integration also contributes to reducing the overall cost and maintenance expense of the system.

Drawings

The invention is described in further detail below with reference to the accompanying drawings.

FIG. 1 is a schematic flow chart of the present invention

Fig. 2 is a schematic cross-sectional view of the present invention.

Fig. 3 is a schematic top view of the present invention.

FIG. 4 is a flow chart of the preparation of the present invention.

FIG. 5 is a schematic diagram of a silicon dioxide buffer layer etched according to a floating structure of the present invention.

Wherein, 1, a bulk lithium niobate substrate; 2. a waveguide layer; 3. a silicon dioxide buffer layer after etching; 4. a lithium niobate thin film; 5. an optical waveguide; 6. interdigital electrodes; 71. a levitation region; 8. an electromagnetic shielding layer.

Detailed Description

As shown in fig. 2, the suspended waveguide matrix film lithium niobate acousto-optic modulator includes a bulk lithium niobate substrate 1 stacked from bottom to top, two waveguide layers 2, the waveguide layers 2 including an etched silica buffer layer 3, a lithium niobate film 4, an optical waveguide 5, an interdigital electrode 6, the etched silica buffer layer 3, and an electromagnetic shielding layer 8 stacked from bottom to top. The optical waveguide 5 extends inwardly from the top surface of the lithium niobate thin film 4. In this embodiment, the two-dimensional coordinates corresponding to the optical waveguide 5 of the waveguide layer 2 positioned below are (1, 1), the two-dimensional coordinates corresponding to the two optical waveguides 5 of the waveguide layer 2 positioned in the middle are (2, 1), the two-dimensional coordinates corresponding to the optical waveguide 5 of the waveguide layer 2 positioned above are (3, 1), the abscissa of the two-dimensional coordinates represents the number of layers of the waveguide layer where the optical waveguide is positioned, the ordinate represents the number of the waveguide layer where the optical waveguide is positioned from left to right, all the two-dimensional coordinates form a waveguide matrix, and the working parameters of the optical waveguide 5 corresponding to the two-dimensional coordinates in the waveguide matrix are recorded respectively.

The thickness of the lithium niobate thin film 4 in this embodiment is about 500nm, the silicon dioxide buffer layer 3 and the electromagnetic shielding layer 8 can also be controlled within the nm level, that is, the thickness of each layer of waveguide layer 2 is only increased to less than 3um except for the bulk lithium niobate substrate 1, and the whole thickness of the existing photoelectric modulator is generally 5mm, so that even if the bulk lithium niobate substrate 1 is designed to be 4mm, 300 more layers of waveguides can be laminated in the rest 1mm, that is, if three hundred available waveguides can be contained in the waveguide matrix at least, compared with the case that one device of the existing photoelectric modulator contains only one waveguide, the universality of the invention is greatly enhanced.

In the existing acousto-optic modulator, the low-frequency device, the intermediate-frequency device and the high-frequency device are all devices, so that the universality is low, and customization is usually required according to the use situation. In this embodiment, the frequencies of the optical waveguides 5 are all different, and by reasonably setting the frequencies of the optical waveguides 5, the acousto-optic modulator of the present invention can cover any frequency bands of low, medium and high simultaneously, thereby completing the breakthrough of bandwidth in another form and achieving ultra-wide bandwidth. In this embodiment, the operating parameters of each optical waveguide 5 are shown in table 1:

TABLE 1

Two-dimensional coordinates	Band/nm	Frequency/Hz
			(1，1，)	1550nm	40Hz
(2，1)	1310nm	10GHz

In the preparation, in order to avoid the influence of metal bonding and grinding technology on the surface evenness and uniformity of the lithium niobate film 4, the Smart-Cut technology based on H+ ion implantation and SiO ₂ bonding is adopted to prepare the lithium niobate film 4.

Since the thickness of the lithium niobate thin film 4 is nano-scale, when the optical waveguide 5 is manufactured, the lithium niobate thin film 4 is required to be stacked on a certain substrate and then the optical waveguide is manufactured, in this embodiment, for the waveguide layer 2 below, the silicon dioxide buffer layer 3 is required to be stacked on the etched suspended area on the lithium niobate substrate 1, then the lithium niobate thin film 4 is required to be stacked on the silicon dioxide buffer layer 3, then the optical waveguide 5 is manufactured according to the following manufacturing process, for the waveguide layer 2 in the middle or the waveguide layer 2 above, the silicon dioxide buffer layer 3 is required to be stacked on the electromagnetic shielding layer 8 of the previous layer and then the suspended structure is required to be etched, then the lithium niobate thin film 4 is stacked on the silicon dioxide buffer layer 3, and then the optical waveguide 5 is manufactured according to the following manufacturing process, namely, each waveguide layer 2 is manufactured sequentially according to the stacking sequence.

The preparation process of the optical waveguide 5 is different from the traditional preparation method of the optical waveguide 5, and the preparation method of the optical waveguide 5 by adopting the liquid phase epitaxial growth technology in the embodiment specifically comprises the following steps:

As shown in fig. 4, the preparation of the electrode includes the following steps:

step S21, sequentially carrying out photoresist homogenizing and photoetching on the lithium niobate thin film 4, wherein the photoetching comprises spin coating photoresist, pre-baking, ultraviolet exposure and development;

Step S22, coating the sample obtained in the step S21 by adopting an Au material, wherein the Au has the advantages of high conductivity, stable chemical property, good ductility, small reflection coefficient and the like;

As shown in fig. 5, the etched silicon dioxide buffer layer 3 is formed according to the shape of the previous electrode, a suspending area matched with the interdigital electrode 6 and a suspending area 71 of the waveguide are formed on the bottom surface of the etched silicon dioxide buffer layer 3, the etching process cleans the substrate, then photo-etching is performed, the silicon dioxide film is etched, then photoresist is removed, and the etched silicon dioxide buffer layer 3 is bonded on the lithium niobate thin film 4, so that leveling can be performed before the next lithium niobate thin film 4 is laminated.

In order to shield the influence of electric fields of other waveguide layers, each waveguide layer 2 needs to be provided with an electromagnetic shielding layer 8, and electromagnetic wave frequency band isolation can be realized based on the high conductivity of the carbon nano tube and the special microstructure of the conductive network, so that synchronous absorption of electromagnetic waves in a long wave band and a short wave band can be realized, the electromagnetic isolation effect is most suitable choice by adopting the carbon nano tube, and the preparation process comprises the following steps:

Step S31, adding the multi-wall carbon nano powder into a triton solution, grinding for 40min in a grinder, soaking and stirring by adopting deionized water, carrying out ultrasonic treatment at intervals of a single second, and centrifuging to obtain a uniform and stable multi-wall carbon nano tube solution;

And step S35, mixing the carbon nanotube solution and the Ti3C2Tx colloid solution according to different proportions, stirring and carrying out ultrasonic treatment, and preparing the mixed solution into a film by adopting a vacuum suction filtration process to obtain the electromagnetic shielding layer 8.

The foregoing description is only illustrative of the preferred embodiments of the present invention and is not to be construed as limiting the scope of the invention, i.e., the invention is not to be limited to the details of the claims and the description, but rather is to cover all modifications which are within the scope of the invention.

Claims

1. A suspended waveguide matrix thin film lithium niobate acousto-optic modulator, characterized in that it comprises a bulk lithium niobate substrate and a plurality of waveguide layers stacked from bottom to top, each waveguide layer comprises a silicon dioxide buffer layer, a lithium niobate thin film, a suspended optical waveguide, an interdigital electrode, an etched silicon dioxide buffer layer and an electromagnetic shielding layer stacked from bottom to top, all optical waveguides of each waveguide layer correspond to two-dimensional coordinates related to their positions, all two-dimensional coordinates form a waveguide matrix, and the working parameters of the optical waveguides corresponding to each element in the waveguide matrix are recorded respectively, and optical fibers of different wavelengths can be coupled to the optical waveguides at corresponding positions as required, the bottom surface of the etched silicon dioxide buffer layer is etched with grooves matching the interdigital electrodes and a reserved suspended waveguide area, each waveguide layer is prepared in sequence according to the stacking order, the electromagnetic shielding layer is made of carbon nanomaterials, and the optical waveguide is made in the lithium niobate thin film layer by using buffered proton exchange technology.

2. The suspended waveguide matrix thin film lithium niobate acousto-optic modulator according to claim 1 is characterized in that the operating parameters include the waveband and frequency of the optical waveguide, and the frequencies of the optical waveguides are different.

3. The suspended waveguide matrix thin film lithium niobate acousto-optic modulator according to claim 6, characterized in that the steps of preparing the optical waveguide (liquid phase epitaxial growth) include:

Step S11, cutting the lithium niobate single crystal into thin slices with a size of 35×10×2 mm, and then grinding and polishing;

Step S12, preparing the film ingredients: 49.0 mol% of Li ₂ Co ₃ , 39.2 mol% of V ₂ O ₅ , 9.8 mol% of Nb ₂ O ₅ , and 2.0 mol% of Cu ₂ O, and mixing them thoroughly;

Step S13, liquid phase epitaxial growth conditions: heat up to 1180°C from room temperature in eight hours and maintain constant temperature for ten hours, cool down to 900°C after four hours, maintain 900°C under constant current state for two hours and then dip the wafer, cool down to 300°C after ten hours and naturally cool down to room temperature.

Step S14: placing the wafer in dilute hydrochloric acid to dissolve the flux.

4. The suspended waveguide matrix thin film lithium niobate acousto-optic modulator according to claim 1, 2 or 3, characterized in that the steps of preparing the interdigital electrodes include:

Step S21, performing coating and photolithography on the lithium niobate film in sequence;

Step S22, using Au material to plate the sample after step S21;

Step S23, placing the sample after step S22 into an acetone solution, removing the remaining Au by separation, thereby manufacturing the desired electrode.

5. The waveguide matrix thin film lithium niobate acousto-optic modulator according to claim 1, 2 or 3, characterized in that the preparation step of the electromagnetic shielding layer comprises:

Step S31, adding multi-walled carbon nanotube powder to a Triton solution, grinding it in a grinder, soaking it in deionized water and stirring it, ultrasonicating it at one-second intervals, and then centrifuging it to obtain a uniform and stable multi-walled carbon nanotube solution;

Step S32, placing a beaker in a cold water bath, respectively putting Ti3AlC2, LiF, deionized water and concentrated hydrochloric acid into the beaker, sealing the beaker and then stirring it magnetically;

Step S33, repeatedly washing the suspension obtained in step S32 after LiF-HCl etching with ionized water until the pH of the suspension is close to 6;

Step S34, the solution obtained in step S33 is centrifuged after impurities are removed, and the upper clear liquid is a single-layer or few-layer Ti3C2Tx colloidal solution;

Step S35, mixing the carbon nanotube solution and the Ti3C2Tx colloidal solution according to different proportions, stirring and ultrasonicating the mixed solution, and then using a vacuum filtration process to prepare the mixed solution into a thin film to obtain an electromagnetic shielding layer.

6. The waveguide matrix thin film lithium niobate acousto-optic modulator according to claim 1, 2 or 3, characterized in that the lithium niobate film is prepared by Smart-Cut technology based on H+ ion implantation and SiO2 bonding.

7. The waveguide matrix thin film lithium niobate acousto-optic modulator according to claim 1, 2 or 3, characterized in that the thickness of the lithium niobate thin film layer is not greater than 500nm, and the thickness of the waveguide layer is not greater than 4um.

8. The suspended waveguide matrix thin film lithium niobate acousto-optic modulator according to claim 8 is characterized in that the notches from bottom to top form a step-like shape that becomes smaller layer by layer.