CN116643417A - Film lithium niobate optical isolator based on acousto-optic scattering and preparation method thereof - Google Patents
Film lithium niobate optical isolator based on acousto-optic scattering and preparation method thereof Download PDFInfo
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title claims abstract description 118
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- 239000013078 crystal Substances 0.000 claims description 14
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 12
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 12
- 229910052804 chromium Inorganic materials 0.000 claims description 12
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- 238000004519 manufacturing process Methods 0.000 claims description 9
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- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 8
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- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 4
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- 229910052581 Si3N4 Inorganic materials 0.000 claims description 3
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 3
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 3
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 2
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 5
- 238000000149 argon plasma sintering Methods 0.000 description 4
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- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 1
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 1
- -1 aluminum scandium nitrogen Chemical compound 0.000 description 1
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- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 1
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/11—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/11—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves
- G02F1/125—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves in an optical waveguide structure
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The application belongs to the technical field of integrated optics, and discloses a thin film lithium niobate optical isolator based on acousto-optic scattering and a preparation method thereof, wherein the thin film lithium niobate optical isolator sequentially comprises a substrate (1), an acoustic isolation layer, a thin film lithium niobate layer (3) and a fan-shaped electroacoustic interdigital transducer (4) from bottom to top; a mode multiplexer, a mode demultiplexer and a bus ridge waveguide (6) are arranged in the thin film lithium niobate layer (3); the interdigital of the sector electroacoustic interdigital transducer (4) is distributed along an arc line and is sector as a whole. The application improves the structure of the active device, adopts a thin film lithium niobate layer integrated with a bus ridge waveguide and a pair of mode (de) multiplexers, is matched with a sector electroacoustic interdigital transducer, and interacts with an optical field through a sound field excited by an electrode of the sector electroacoustic interdigital transducer, so that the direction of the sound field and the acousto-optic phase matching condition can be accurately regulated, unidirectional phase matching is realized, and a nonreciprocal optical isolation function is achieved.
Description
Technical Field
The application belongs to the technical field of integrated optics, and particularly relates to a thin film lithium niobate optical isolator based on acousto-optic scattering and a preparation method thereof.
Background
In recent years, the thin film lithium niobate is widely applied to integrated optical devices because of the large second-order nonlinear coefficient, the electro-optic coefficient, the piezoelectric response and the wide optical transparent window, is hopeful to become a monolithic integrated optical chip platform integrating an active optical device and a passive optical device, and attracts wide attention of domestic and foreign scientific researchers. Along with research hot trend caused by interaction of optical field and sound field in integrated optics, the thin film lithium niobate has more excellent piezoelectric performance compared with other piezoelectric thin film materials such as aluminum nitride and gallium arsenide; meanwhile, the ultra-low optical loss (less than 0.2 dB/m) of the thin film lithium niobate also makes the thin film lithium niobate stand out in a plurality of material systems. Therefore, the low optical loss and high-efficiency electroacoustic conversion make the thin film lithium niobate an ideal material for manufacturing high-performance acousto-optic devices.
In the acousto-optic scattering effect, the optical modes can be classified into intra-mode scattering and inter-mode scattering according to their phase matching process. For the inter-mode scattering process in which phonons participate, a larger phonon wave vector propagating along the waveguide direction is required to meet the phase matching of different optical modes. Therefore, the wave vector size and propagation direction of the applied sound field need to be precisely controlled to realize complete intermodal scattering phase matching. The scattering between the acousto-optic modes can directly realize energy conversion and frequency conversion between modes, can be widely applied to frequency shift and nonreciprocal light transmission, is a very significant research direction, and how to realize higher-efficiency acousto-optic scattering efficiency and more accurate phase matching is a target needing important research.
The manufacturing process of the thin film lithium niobate waveguide is one of the difficulties, and the etching ratio of the common photoresist mask to lithium niobate is not very high due to the characteristics of the lithium niobate material, so that the line manufacturing precision is ensured, and meanwhile, the larger etching depth is difficult to obtain. Therefore, the manufacture of the low-loss optical waveguide is also a key difficulty in manufacturing high-performance acousto-optic devices.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the application aims to provide a film lithium niobate optical isolator based on acousto-optic scattering and a preparation method thereof, wherein the structure of the active device is improved, a film lithium niobate layer integrated with a bus ridge waveguide and a pair of mode (de) multiplexers is adopted, a sector electroacoustic interdigital transducer is matched, an acoustic field excited by an electrode of the sector electroacoustic interdigital transducer interacts with an optical field, the direction of the acoustic field and an acousto-optic phase matching condition can be accurately regulated, unidirectional phase matching is realized, and a nonreciprocal optical isolation function is achieved. In addition, the preparation process of the device is optimized, so that the low-loss thin film lithium niobate waveguide can be obtained, and the performance of the device is further improved.
In order to achieve the above object, according to one aspect of the present application, there is provided a thin film lithium niobate optical isolator based on acousto-optic scattering, which is characterized by comprising a substrate (1), an acoustic isolation layer, a thin film lithium niobate layer (3) and a sector electroacoustic interdigital transducer (4) in this order from bottom to top; wherein, the liquid crystal display device comprises a liquid crystal display device,
a mode multiplexer, a mode demultiplexer and a bus ridge waveguide (6) are arranged in the thin film lithium niobate layer (3), and the bus ridge waveguide (6) is mutually coupled with the mode multiplexer and the mode demultiplexer and is used for multiplexing different light field modes into the bus ridge waveguide (6) or demultiplexing different light field modes from the bus ridge waveguide (6);
the fingers of the fan-shaped electroacoustic interdigital transducer (4) are distributed along an arc, and the arc length corresponding to the outermost group of fingers is longer than that corresponding to the innermost group of fingers, so that the whole fan-shaped electroacoustic interdigital transducer is formed; and the diverging direction of the sector is towards the bus ridge waveguide (6);
the fan-shaped electroacoustic interdigital transducer (4) is used for exciting a sound field in the thin film lithium niobate layer (3) under the drive of an externally applied radio frequency signal, so that different optical field modes unidirectionally transmitted in the bus ridge waveguide (6) can interact with the sound field, and finally, different optical field modes can be routed from different ports of the mode multiplexer and the mode demultiplexer, and an optical isolator for unidirectional optical transmission is realized.
As a further preferred aspect of the application, the total divergence angle of the sector-shaped electroacoustic interdigital transducer (4) is 0.1 ° to 10 °.
As a further preferable mode of the application, an included angle is formed between the central emergent direction of the excitation sound field of the fan-shaped electroacoustic interdigital transducer (4) and the cross section of the bus ridge waveguide (6), and the included angle is recorded as theta;
the total divergence angle of the fan-shaped electroacoustic interdigital transducer (4) is recorded as 2 alpha;
and then, the included angle theta' between the emission angle of the sector electroacoustic interdigital transducer (4) and the cross section of the bus ridge waveguide (6) is an interval [ theta-alpha, theta+alpha ].
As a further preferred aspect of the present application, the thin film lithium niobate layer (3) has a total thickness of 300 nm to 1000 nm, and the mode multiplexer, the mode demultiplexer and the bus ridge waveguide (6) provided therein are formed by etching to a depth of 150 nm to 500 nm;
the bus ridge waveguide (6) is of a trapezoid section, and the inclination angle of the side wall of the waveguide is 50-70 degrees; the bus ridge waveguide (6) is a multimode waveguide, and the upper width of the trapezoid section is 1800-5000 nanometers.
As a further preferable mode of the application, the metal material selected by the fan-shaped electroacoustic interdigital transducer (4) is gold, copper or aluminum, and the thickness is 50-1000 nanometers;
the number of the sector electroacoustic interdigital transducers (4) is multiple, and an electrode contact plate is shared between two adjacent sector electroacoustic interdigital transducers (4); preferably, the bus ridge waveguide (6) is folded in a U shape, the number of the fan-shaped electroacoustic interdigital transducers (4) is even, the fan-shaped divergence direction of half of the total number of the fan-shaped electroacoustic interdigital transducers (4) faces one side of the U shape of the bus ridge waveguide (6), and the fan-shaped divergence direction of the other half of the total number of the fan-shaped electroacoustic interdigital transducers (4) faces the other side of the U shape of the bus ridge waveguide (6);
the output aperture of the single fan-shaped electroacoustic interdigital transducer (4) is more than 10 micrometers, the period length is equal to the ridge width of the bus waveguide (6), and the period number is more than 2.
As a further preferred mode of the application, when the thin film lithium niobate layer (3) adopts X-cut lithium niobate crystals, the emergent direction of the sound field center of the sector interdigital transducer (4) forms an included angle of positive 30 degrees with the Y axis of the crystals;
when the thin film lithium niobate layer (3) adopts Y-cut lithium niobate crystals, the emergent direction of the sound field center of the sector interdigital transducer (4) forms an included angle of plus or minus 45 degrees with the Z axis of the crystals;
when the thin film lithium niobate layer (3) adopts Z-cut lithium niobate crystals, the emergent direction of the sound field center of the sector interdigital transducer (4) forms an included angle of 0 degree or plus or minus 60 degrees with the Y axis of the crystals.
As a further preferred aspect of the present application, the acoustic isolation layer is an oxygen buried layer (2), and the acoustic field mode excited by the fan-shaped electroacoustic interdigital transducer (4) in the thin film lithium niobate layer (3) is a surface acoustic wave;
or the acoustic isolation layer is an air layer, and the sound field mode excited by the fan-shaped electroacoustic interdigital transducer (4) in the thin film lithium niobate layer (3) is a lamb sound wave.
As a further preferred aspect of the present application, the mode multiplexer has the same structure as the mode demultiplexer, wherein the mode multiplexer has an upper port and a lower port for inputting a fundamental mode and a higher order mode, respectively, and the optical coupling into the upper port or the lower port is a vertical coupling or a horizontal coupling.
As a further preferred aspect of the present application, the upper cladding layer of the thin film lithium niobate optical isolator based on acousto-optic scattering is an air upper cladding layer;
or the thin film lithium niobate optical isolator based on acousto-optic scattering is also manufactured with an upper cladding layer, and the upper cladding layer is made of silicon oxide, silicon nitride or hydrogen silsesquioxane polymer HSQ type photoresist.
According to another aspect of the application, the application provides a preparation method of the thin film lithium niobate optical isolator based on acousto-optic scattering, which is characterized by comprising the following steps:
preparing a substrate which is respectively a substrate (1), an acoustic isolation layer and a thin film lithium niobate from bottom to top, and growing metal chromium with the thickness of 80-160 nanometers on the substrate by adopting electron beam evaporation;
spin-coating electron beam glue on the chromeplated substrate, wherein the thickness of the electron beam glue is 300-500 nanometers, and placing the chromeplated substrate on a heating plate with the temperature of preset heating temperature for standing after spin-coating; wherein the preset heating temperature is 150-180 ℃, and the standing time is not shorter than 1 minute;
step three, exposing the substrate by an electron beam exposure system, developing and fixing, and removing the developed residual glue by using oxygen plasma to obtain a waveguide pattern;
step four, etching the substrate by adopting chlorine-based inductively coupled plasma etching, and removing residual electron beam glue to obtain a chromium layer pattern;
step five, etching the substrate by adopting fluorine-based ICP, and removing residual metal chromium to obtain a thin film lithium niobate layer provided with a mode multiplexer, a mode demultiplexer and a bus ridge waveguide (6);
step six, cleaning the substrate;
step seven, carrying out thermal annealing on the substrate, specifically, heating the substrate from normal temperature to preset heat preservation temperature at the rate of 1-5 ℃ per minute under the condition of oxygen atmosphere and normal pressure, and preserving the heat for more than 1 hour; gradually cooling from the maintained temperature to normal temperature at a cooling rate of 0.5-2 ℃ per minute; wherein the preset heat preservation temperature is between 500 ℃ and 1100 ℃;
step eight, spin-coating electron beam glue on the substrate, wherein the thickness of the electron beam glue is 300-500 nanometers, and placing the substrate on a heating plate with the temperature of preset heating temperature for standing after spin-coating; wherein the preset heating temperature is 100-200 ℃, and the standing time is not shorter than 1 minute; then, exposing the substrate by an electron beam exposure system, developing and fixing, and removing the developing residual glue by using oxygen plasma to obtain a sector electroacoustic interdigital transducer pattern;
step nine, placing the substrate in an electron beam evaporation system, depositing metal of a fan-shaped electroacoustic interdigital transducer, and removing the rest of electron beam glue and a metal film by adopting a stripping process, thereby obtaining a film lithium niobate optical isolator based on acousto-optic scattering;
preferably, in the second step, the electron beam glue is ARP6200;
in the third step, the electron beam exposure system is a VISTEC EBPG 5000PES;
in the sixth step, the substrate is specifically cleaned by placing the substrate in a solution of ammonia water, hydrogen peroxide and deionized water according to a ratio of 1:1:5, standing the mixed solution obtained by mixing the mixed solution in a volume ratio for 1 to 15 minutes at a temperature of 60 to 80 ℃; wherein the concentration of the ammonia water solution is 25-28 wt%, and the concentration of the hydrogen peroxide solution is 30wt%.
Compared with the prior art, the thin film lithium niobate optical isolator based on acousto-optic scattering is characterized in that the bus ridge waveguide, the mode multiplexer and the demultiplexer are arranged in the thin film lithium niobate layer, the fan-shaped electroacoustic interdigital transducer is arranged above the thin film lithium niobate layer, the electroacoustic interdigital transducer is driven by an externally applied radio frequency signal to excite a sound field in the thin film lithium niobate layer through a piezoelectric effect, finally, the acousto-optic interaction of direction dependence is realized in the low-loss waveguide of the thin film lithium niobate layer, and the (de) multiplexing of different light field modes is realized through the mode (de) multiplexer, so that the effect of optical isolation of light in a specific direction is realized. Due to the acousto-optic scattering effect, the bus ridge waveguide supports different modes to be transmitted therein and to be input and output from different ports. Taking the mode (de) multiplexer of the conventional port, lower port design as an example, the function of non-reciprocal optical isolation can be achieved when using two specific ports. And the sector electroacoustic transducer is used for realizing phase matching more easily by means of angle optimization and divergent emission sound field.
Unlike the prior art design of heterogeneous integration scheme in which the optical waveguide and the piezoelectric film are divided into two layers (taking the earlier-stage achievements of the subject group of chinese patent application CN114815332a as an example, silicon is adopted as the optical waveguide, and the generation of the sound field depends on the piezoelectric material aluminum scandium nitrogen layer, and the guidance of the sound field and the light field is divided into two different materials, which are relatively complex heterogeneous integration schemes), the acousto-optic interaction strength is limited. The application can improve the intensity of acousto-optic interaction in the same material system by utilizing the film lithium niobate. The thin film lithium niobate layer is provided with the bus ridge waveguide, the mode multiplexer and the demultiplexer, can be used as an optical waveguide for guiding light, can actively generate a sound field under the action of an electrode, and has high acousto-optic interaction strength.
The application can precisely regulate and control the direction of the sound field and the acousto-optic phase matching condition by the sector design of the sector electroacoustic interdigital transducer, realizes unidirectional phase matching and achieves the nonreciprocal optical isolation function. The application utilizes the sector design of the sector electroacoustic interdigital transducer, and the emergent angle of the sector electroacoustic interdigital transducer exciting sound field and the cross section of the bus ridge waveguide in the thin film lithium niobate layer form a certain included angle range (namely the section [ theta-alpha, theta+alpha ] which is expanded in the later embodiment, instead of the traditional included angle fixed value), and because the longitudinal wave vector component of the sound field along the waveguide direction should meet the difference between the fundamental mode transmitting light in the bus ridge waveguide and the longitudinal propagation constant of the high-order optical mode after the acousto-optic scattering as much as possible, the emergent included angle range of the sector sound field in the application can enable the phase matching of different light field modes in the acousto-optic scattering process to be easier. If a traditional electroacoustic interdigital transducer (not fan-shaped, the interdigital transducer is distributed along a straight line segment), an emergent direction of an excitation sound field of the electroacoustic interdigital transducer and the cross section of the bus ridge waveguide form a fixed included angle (namely theta), so that a longitudinal component of a sound wave vector meets the difference of longitudinal propagation constants of a fundamental mode transmission light and a high-order optical mode after acousto-optic scattering in the bus ridge waveguide, quasi-phase matching of different optical field modes in the acousto-optic scattering process is realized (that is, the size of the included angle is determined by the difference of longitudinal propagation constants of the fundamental mode transmission light and the high-order optical mode after the acousto-optic scattering, which is input into the bus ridge waveguide, and is used for compensating phase mismatch of different optical field modes in the acousto-optic scattering process), but the difference of the constants is fluctuated due to the deviation of geometric parameters of the waveguide caused by the process error in the process of preparing the waveguide by etching an actual thin film lithium niobate layer, and quasi-phase matching is affected.
Furthermore, the total divergence angle of the sector electroacoustic interdigital transducer can be controlled to be 0.1-10 degrees, so that errors of a waveguide preparation process can be compensated, sound field energy dissipation caused by an overlarge sound field divergence angle is avoided, the efficiency of sound and light scattering is influenced, the requirement of sound and light scattering quasi-phase matching on process manufacturing is reduced, and the manufacturing yield of the device is improved. The application preferably uses the electrode contact plate shared by the multi-sector electroacoustic interdigital transducers and is arranged on the two sides of the U-shaped waveguide vertically, thereby greatly prolonging the acousto-optic interaction length and overcoming the problem that the output aperture of a single electroacoustic interdigital transducer is limited by technological preparation and electrical impedance matching.
In addition, the application also optimizes the preparation method of the device, adopts electron beam glue (such as ARP 6200.13) to be matched with electron beam exposure, ensures the line precision of the thin film lithium niobate waveguide through a double-layer mask etching process, has good side wall morphology, and can obtain the thin film lithium niobate waveguide with low loss. And after the waveguide is manufactured, performing exposure and manufacture of the electrode pattern, thereby finally obtaining the target device.
In conclusion, the single-side band acousto-optic scattering is realized by electrically driving the film lithium niobate, so that the optical isolator element with low transmission loss and high isolation can be realized, and the optical isolator element has important application in integrated optics.
Drawings
FIG. 1 is a three-dimensional model diagram of a thin film lithium niobate optical isolator structure provided by the application.
Fig. 2 is a schematic diagram of a forward transmission operating principle of an acousto-optic scattering optical isolator according to an embodiment of the present application.
Fig. 3 is a schematic diagram of a reverse transmission working principle of an acousto-optic scattering optical isolator according to an embodiment of the present application.
Fig. 4 is a diagram of unidirectional acousto-optic scattering wave vector matching in an embodiment of the present application.
Fig. 5 is a schematic diagram of the working principle of a sector electroacoustic interdigital transducer according to an embodiment of the present application.
Fig. 6 is a transmission spectrum of the thin film lithium niobate optical waveguide resonator prepared in example 1.
Fig. 7 is a graph comparing performance of a conventional interdigital transducer (non-sector) and a sector electroacoustic interdigital transducer.
The meaning of the reference numerals in fig. 1 is as follows: a 1-silicon substrate, a 2-buried oxide layer, a 3-thin film lithium niobate layer, a 4-sector electroacoustic interdigital transducer, a 5-mode (de) multiplexer, a 6-bus ridge waveguide (i.e., a thin film lithium niobate bus ridge waveguide).
Detailed Description
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application. In addition, the technical features of the embodiments of the present application described below may be combined with each other as long as they do not collide with each other.
Example 1
The three-dimensional structure diagram of the thin film lithium niobate optical isolator device provided by the application is shown in figure 1, and comprises a silicon substrate 1, an oxygen buried layer 2, a thin film lithium niobate layer 3 and a fan-shaped electroacoustic interdigital transducer 4; wherein the thin film lithium niobate layer 3 comprises a pair of mode (de) multiplexers 5 (hereinafter denoted first mode (de) multiplexer and second mode (de) multiplexer, respectively, for input, and de-multiplexer for output, similar to conventional ones), and bus ridge waveguides 6. The refractive index of the material of the thin film lithium niobate layer is larger than that of the oxygen-buried layer and the air cladding layer, so that the optical field mode is limited in the lithium niobate waveguide.
The thin film lithium niobate optical isolator in this embodiment is prepared by the following steps:
step one, preparing a substrate of a silicon substrate 1, an oxygen burying layer 2 and a thin film lithium niobate respectively from bottom to top, and growing metal chromium with the thickness of 160 nanometers on the substrate by adopting electron beam evaporation;
spin-coating electron beam glue on the chromeplated substrate, wherein the thickness of the electron beam glue is 500 nanometers, and placing the chromeplated substrate on a heating plate with the temperature of preset heating temperature for standing after spin-coating; wherein the preset heating temperature is 150 ℃, and the standing time is 1 minute;
step three, exposing the substrate by an electron beam exposure system, developing and fixing, and removing the developed residual glue by using oxygen plasma to obtain a waveguide pattern;
step four, etching the substrate by adopting chlorine-based inductively coupled plasma etching, and removing residual electron beam glue to obtain a chromium layer pattern;
step five, etching the substrate by adopting fluorine-based ICP, and removing residual metal chromium to obtain a thin film lithium niobate layer provided with a mode multiplexer, a mode demultiplexer and a bus ridge waveguide;
step six, cleaning the substrate;
step seven, carrying out thermal annealing on the substrate, specifically, heating the substrate from normal temperature to a preset heat preservation temperature at a rate of 1 ℃ per minute under the condition of oxygen atmosphere and normal pressure, and preserving the heat for 2 hours; then gradually cooling from the maintained temperature to normal temperature at a cooling rate of 2 ℃ per minute; wherein the preset heat preservation temperature is 500 ℃;
the load Q value of the low-loss micro-ring optical waveguide resonant cavity prepared by the steps one to seven can reach 1.1X10 6 As shown in fig. 6, the corresponding waveguide linear loss can be calculated to be about 0.2dB/cm.
Step eight, carrying out electron beam lithography operation from the step two to the step three on the substrate again, and performing alignment to form a sector electroacoustic interdigital transducer pattern, specifically: spin-coating electron beam glue on the substrate, wherein the thickness of the electron beam glue is 500 nanometers, and placing the substrate on a heating plate with the temperature of preset heating temperature for standing after spin-coating; wherein the preset heating temperature is 150 ℃, and the standing time is 1 minute; then, exposing the substrate by an electron beam exposure system, developing and fixing, and removing the developing residual glue by using oxygen plasma to obtain a sector electroacoustic interdigital transducer pattern;
step nine, placing the substrate in an electron beam evaporation system, depositing metal of a fan-shaped electroacoustic interdigital transducer, and removing the rest of electron beam glue and a metal film by adopting a stripping process, thereby obtaining a film lithium niobate optical isolator based on acousto-optic scattering;
in the second step, the electron beam glue is ARP6200.13;
in the third step, the electron beam exposure system is a VISTEC EBPG 5000PES;
in the sixth step, the substrate is specifically cleaned by placing the substrate in a solution of ammonia water, hydrogen peroxide and deionized water according to a ratio of 1:1:5, standing the mixed solution obtained by mixing the mixed solution in a volume ratio for 10 minutes at 60 ℃; wherein the concentration of the ammonia water solution is 25-28 wt%, and the concentration of the hydrogen peroxide solution is 30wt%.
Under the drive of an external electric signal, the periodic structure of the sector electroacoustic interdigital transducer can form a periodic electric field in the film lithium niobate, so that an excitation sound field is generated by a piezoelectric effect, the excitation sound field is emitted from the vicinity of an electrode and is conducted into the film lithium niobate waveguide, finally, an acousto-optic scattering process is realized in the film lithium niobate waveguide, and different light field modes are multiplexed or demultiplexed through different ports of a mode (de) multiplexer, so that the unidirectional transmission optical isolation characteristic can be formed between specific input and output ports.
In the selection of the acoustic field mode, the low-order mode energy of the surface acoustic wave is mainly concentrated in the thin film lithium niobate layer; the lamb sound wave is released through an acoustic isolation layer (air layer), the energy is completely limited to a thin film lithium niobate layer in the propagation process, and the sound field energy can be effectively utilized to carry out sound and light scattering in a lithium niobate waveguide.
In this embodiment, the forward transmission light and the backward transmission light participating in acousto-optic scattering to realize optical isolation are embodied as different optical field modes in the thin film lithium niobate waveguide, that is, the forward input light is a fundamental mode (TE 00 ) Whereas the backward transmitted light is converted into a first order mode (TE) of transverse electric mode in the waveguide by acousto-optic scattering process 10 ). In this embodiment, a forward transmission schematic diagram, a reverse transmission schematic diagram and an acoustic wave vector matching diagram of an optical isolator based on intermode acoustic-optical scattering operation are shown in fig. 2, 3 and 4, respectively. When the optical field is input from the upper port of the first mode multiplexer, the mode entering the thin film lithium niobate waveguide is the fundamental mode TE 00 As shown in fig. 2. At this time, the sound field excited by the external radio frequency signal in the fan-shaped electroacoustic transducer is consistent with the transmission direction of the light field in the waveguide, and is represented by the dispersion curve (fig. 4) of the light field mode, the longitudinal propagation constants of the fundamental mode and the first-order mode have obvious differences, and the phase matching condition of the sound-light scattering between modes cannot be satisfied when the external radio frequency signal and the light field co-propagate in the sound field mode. Thus, the forward propagating fundamental mode light field does not interact with the electrode excited acoustic field, but is normally transmitted to the second modeAfter the (de) multiplexer, the output is from its upper port. When the optical field is input from the upper port of the second mode multiplexer (i.e. reflected back), as shown in fig. 3, since the back-transmitted fundamental mode and the first-order mode satisfy the phase matching of inter-mode scattering after the back-transmitted acoustic field is interposed (fig. 4), the fundamental mode TE 00 Can be fully converted into first order mode TE 10 The mode, the first order mode obtained in the acousto-optic scattering process is not output from the upper port when reaching the first mode (de) multiplexer in the reverse direction, but is mainly output from the lower port, namely, the function of optical isolation during the optical reverse transmission is realized.
In this embodiment, at the preset optical wavelength of 1550nm, the refractive index of the material of the X-cut thin film lithium niobate waveguide layer exhibits birefringence, the refractive indexes of the in-plane lithium niobate crystal in the Y-direction and the Z-direction are 2.21 and 2.14, respectively, and the refractive index of the material of the silicon dioxide oxygen-buried layer is 1.45, so that the optical field mode can be confined in the lithium niobate waveguide. The total thickness of the sections of the thin film lithium niobate waveguide, the first mode (de) multiplexer and the second mode (de) multiplexer is 600 nanometers, the etching depth is 300 nanometers, and the widths of the multimode waveguide and the single-mode waveguide ridge are 2200 nanometers and 900 nanometers respectively. The thickness of the silicon dioxide buried oxide layer is 2 microns.
In this embodiment, the materials of the sector electroacoustic interdigital transducers are all aluminum, the thicknesses are all 100 nanometers, the period lengths are all 2200 nanometers, the period numbers are respectively 20 pairs of finger strips, and the output aperture (i.e. the length of the radiation to the waveguide) of each interdigital transducer is 200 micrometers. The included angle θ between the center emission angle of the fan-shaped and the vertical direction of the bus ridge waveguide is 5.5 degrees, as shown in fig. 5, and the total divergence angle 2α of the fan-shaped is about 2.0 degrees, so that the included angle θ ' between the emission angle of the fan-shaped electroacoustic interdigital transducer and the vertical direction of the bus ridge waveguide is the interval [ θ - α, θ+α ], θ ', that is, the total sound field emission range (correspondingly, the total sound field emission range θ ' is 4.5 degrees to 6.5 degrees in the embodiment; because the longitudinal wave vector component of the sound field along the waveguide direction should satisfy the difference between the longitudinal propagation constants of the high-order optical mode after the fundamental mode transmission light and the acousto-optic scattering in the bus ridge waveguide as much as possible, the fan-shaped design in the application can effectively cover the fluctuation of the difference between the optical mode propagation constants due to the process error in the preparation of the bus ridge waveguide. In the surface of the X-cut film lithium niobate, the emergent angle direction of the central sound field of the fan-shaped electroacoustic interdigital transducer can form an angle of 30 degrees with the Y axis of the crystal so as to obtain the maximum electromechanical coupling coefficient. When the radio frequency signal driving frequency of the interdigital transducer is near 3GHz, stronger sound waves can be excited, stronger strain is generated in the thin film lithium niobate waveguide, and a better acousto-optic scattering effect is obtained.
Example 2
The three-dimensional structure diagram of the thin film lithium niobate optical isolator device provided by the application is shown in figure 1, and comprises a silicon substrate 1, an oxygen buried layer 2, a thin film lithium niobate layer 3 and a fan-shaped electroacoustic interdigital transducer 4; wherein the thin film lithium niobate layer 3 comprises a pair of mode (de) multiplexers 5 (hereinafter denoted first mode (de) multiplexer and second mode (de) multiplexer, respectively, for input, and de-multiplexer for output, similar to conventional ones), and bus ridge waveguides 6. The refractive index of the material of the thin film lithium niobate layer is larger than that of the oxygen-buried layer and the air cladding layer, so that the optical field mode is limited in the lithium niobate waveguide.
The thin film lithium niobate optical isolator in this embodiment is prepared by the following steps:
step one, preparing a substrate of a silicon substrate 1, an oxygen burying layer 2 and a thin film lithium niobate respectively from bottom to top, and growing metal chromium with the thickness of 80 nanometers on the substrate by adopting electron beam evaporation;
spin-coating electron beam glue on the chromeplated substrate, wherein the thickness of the electron beam glue is 300 nanometers, and placing the chromeplated substrate on a heating plate with the temperature of preset heating temperature for standing after spin-coating; wherein the preset heating temperature is 180 ℃, and the standing time is 1 minute;
step three, exposing the substrate by an electron beam exposure system, developing and fixing, and removing the developed residual glue by using oxygen plasma to obtain a waveguide pattern;
step four, etching the substrate by adopting chlorine-based inductively coupled plasma etching, and removing residual electron beam glue to obtain a chromium layer pattern;
step five, etching the substrate by adopting fluorine-based ICP, and removing residual metal chromium to obtain a thin film lithium niobate layer provided with a mode multiplexer, a mode demultiplexer and a bus ridge waveguide;
step six, cleaning the substrate;
step seven, carrying out thermal annealing on the substrate, specifically, heating the substrate from normal temperature to preset heat preservation temperature at the rate of 5 ℃ per minute under the condition of oxygen atmosphere and normal pressure, and preserving the heat for 1 hour; gradually cooling from the maintained temperature to normal temperature at a cooling rate of 0.5 ℃ per minute; wherein the preset heat preservation temperature is 1100 ℃;
step eight, carrying out electron beam lithography operation from the step two to the step three on the substrate again, and performing alignment to form a sector electroacoustic interdigital transducer pattern, specifically: spin-coating electron beam glue on the substrate, wherein the thickness of the electron beam glue is 300 nanometers, and placing the substrate on a heating plate with the temperature of a preset heating temperature for standing after spin-coating; wherein the preset heating temperature is 180 ℃, and the standing time is 1 minute; then, exposing the substrate by an electron beam exposure system, developing and fixing, and removing the developing residual glue by using oxygen plasma to obtain a sector electroacoustic interdigital transducer pattern;
step nine, placing the substrate in an electron beam evaporation system, depositing metal of a fan-shaped electroacoustic interdigital transducer, and removing the rest of electron beam glue and a metal film by adopting a stripping process, thereby obtaining a film lithium niobate optical isolator based on acousto-optic scattering;
in the second step, the electron beam glue is ARP6200.13;
in the third step, the electron beam exposure system is a VISTEC EBPG 5000PES;
in the sixth step, the substrate is specifically cleaned by placing the substrate in a solution of ammonia water, hydrogen peroxide and deionized water according to a ratio of 1:1:5, standing the mixed solution obtained by mixing the mixed solution in a volume ratio for 1 minute at 80 ℃; wherein the concentration of the ammonia water solution is 25-28 wt%, and the concentration of the hydrogen peroxide solution is 30wt%.
Comparative example 1
To further illustrate the design advantages of a sector-shaped electroacoustic interdigital transducer, based on the above-described embodiment 1, the inventors also simulated the theoretical acousto-optic scattering efficiency of a conventional non-sector-shaped interdigital transducer and a sector-shaped electroacoustic interdigital transducer designed in accordance with the present application. The fixed angles of the non-sector electroacoustic interdigital transducer are 4.5 degrees, 5.5 degrees and 6.5 degrees respectively, while the divergence angle of the sector electroacoustic interdigital transducer is not fixed, and θ' is 4.5 degrees to 6.5 degrees. As shown in fig. 7, it can be found that the non-fanned electroacoustic interdigital transducer is greatly affected by a fixed angle, and the peak efficiency of the other two angles is far away from the optical communication C-band except that the sound field emergence angle of 5.5 degrees just satisfies that the peak modulation efficiency is in 1550nm band of interest. The fan-shaped electroacoustic interdigital transducer designed based on the application has higher and flat efficiency in the whole wave band, and the efficiency is higher by nearly 8 dB in 1550nm wave band than that of a non-fan-shaped interdigital transducer with fixed angles of 4.5 degrees and 6.5 degrees.
The above-described embodiments are merely examples, and the cladding material of the optical waveguide in the present application is not limited to the air cladding, and may be a material such as silicon oxide, silicon nitride, or HSQ photoresist, as long as it has no adverse effect on optical field transmission.
The electrode configuration of the fan-shaped electroacoustic transducer in the present application is not limited to the three-electrode contact plate configuration in the embodiment, that is, the ground-signal-ground (GSG) configuration, but may be a five-electrode contact plate GSGSG configuration or a seven-electrode contact plate GSGSGSG configuration, etc., so long as the condition that a plurality of interdigital transducers are connected in parallel is satisfied.
In addition, the above embodiment takes the acoustic isolation layer between the substrate and the thin film lithium niobate layer as an example, and at this time, the acoustic field mode excited by the fan-shaped electroacoustic interdigital transducer 4 in the thin film lithium niobate layer 3 is a surface acoustic wave; similar to other prior art, the acoustic isolation layer may be an air layer (i.e., the thin film lithium niobate layer is suspended) in addition to the oxygen-buried layer, and in this case, the acoustic field mode excited by the fan-shaped electroacoustic interdigital transducer 4 in the thin film lithium niobate layer 3 is a lamb acoustic wave.
In addition, besides the mode (de) multiplexer shown in fig. 1 being located on the same side of the device and the bus ridge waveguide being in a U-folded design, the mode (de) multiplexer may be located on two sides of the device, respectively, left and right, and the bus ridge waveguide may be in a straight-line design (in this case, the sector electroacoustic interdigital transducer may only remain facing the bus ridge waveguide). The number of the fan-shaped electroacoustic interdigital transducers can also be changed and can be more than or equal to 1, and the electrode configuration of the corresponding fan-shaped electroacoustic interdigital transducer can also be flexibly changed (for example, when the number of the fan-shaped electroacoustic interdigital transducers is 1, the electrode configuration of the fan-shaped electroacoustic transducer shown in fig. 1 is taken as a three-electrode contact plate configuration as an example, besides 2 PADs are connected with interdigital transducers, 1 PAD can be suspended), and of course, the greater the number of the parallel fan-shaped electroacoustic interdigital transducers is, the longer the length of an acousto-optic action area in a film lithium niobate waveguide is, and the efficiency of mode conversion generated in the waveguide can be improved to a certain extent, so that the performance of the nonreciprocal optical isolator is further improved.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the application and is not intended to limit the application, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the application are intended to be included within the scope of the application.
Claims (10)
1. The film lithium niobate optical isolator based on acousto-optic scattering is characterized by comprising a substrate (1), an acoustic isolation layer, a film lithium niobate layer (3) and a fan-shaped electroacoustic interdigital transducer (4) from bottom to top in sequence; wherein, the liquid crystal display device comprises a liquid crystal display device,
a mode multiplexer, a mode demultiplexer and a bus ridge waveguide (6) are arranged in the thin film lithium niobate layer (3), and the bus ridge waveguide (6) is mutually coupled with the mode multiplexer and the mode demultiplexer and is used for multiplexing different light field modes into the bus ridge waveguide (6) or demultiplexing different light field modes from the bus ridge waveguide (6);
the fingers of the fan-shaped electroacoustic interdigital transducer (4) are distributed along an arc, and the arc length corresponding to the outermost group of fingers is longer than that corresponding to the innermost group of fingers, so that the whole fan-shaped electroacoustic interdigital transducer is formed; and the diverging direction of the sector is towards the bus ridge waveguide (6);
the fan-shaped electroacoustic interdigital transducer (4) is used for exciting a sound field in the thin film lithium niobate layer (3) under the drive of an externally applied radio frequency signal, so that different optical field modes unidirectionally transmitted in the bus ridge waveguide (6) can interact with the sound field, and finally, different optical field modes can be routed from different ports of the mode multiplexer and the mode demultiplexer, and an optical isolator for unidirectional optical transmission is realized.
2. Thin film lithium niobate optical isolator device based on acousto-optic scattering according to claim 1, characterized in that the total divergence angle of the fan-shaped electro-acoustic interdigital transducer (4) is 0.1 ° to 10 °.
3. The thin-film lithium niobate optical isolator based on acousto-optic scattering according to claim 1, wherein the central emergent direction of the excitation sound field of the fan-shaped electroacoustic interdigital transducer (4) forms an included angle with the cross section of the bus ridge waveguide (6), and the included angle is denoted as θ;
the total divergence angle of the fan-shaped electroacoustic interdigital transducer (4) is recorded as 2 alpha;
and then, the included angle theta' between the emission angle of the sector electroacoustic interdigital transducer (4) and the cross section of the bus ridge waveguide (6) is an interval [ theta-alpha, theta+alpha ].
4. The thin film lithium niobate optical isolator device based on acousto-optic scattering according to claim 1, wherein the thin film lithium niobate layer (3) has a total thickness of 300 nm to 1000 nm, and the mode multiplexer, the mode demultiplexer and the bus ridge waveguide (6) provided therein are formed by etching to a depth of 150 nm to 500 nm;
the bus ridge waveguide (6) is of a trapezoid section, and the inclination angle of the side wall of the waveguide is 50-70 degrees; the bus ridge waveguide (6) is a multimode waveguide, and the upper width of the trapezoid section is 1800-5000 nanometers.
5. The thin film lithium niobate optical isolator based on acousto-optic scattering as claimed in claim 1, wherein the metal material selected for the fan-shaped electroacoustic interdigital transducer (4) is gold, copper or aluminum, and the thickness is 50nm to 1000 nm;
the number of the sector electroacoustic interdigital transducers (4) is multiple, and an electrode contact plate is shared between two adjacent sector electroacoustic interdigital transducers (4); preferably, the bus ridge waveguide (6) is folded in a U shape, the number of the fan-shaped electroacoustic interdigital transducers (4) is even, the fan-shaped divergence direction of half of the total number of the fan-shaped electroacoustic interdigital transducers (4) faces one side of the U shape of the bus ridge waveguide (6), and the fan-shaped divergence direction of the other half of the total number of the fan-shaped electroacoustic interdigital transducers (4) faces the other side of the U shape of the bus ridge waveguide (6);
the output aperture of the single fan-shaped electroacoustic interdigital transducer (4) is more than 10 micrometers, the period length is equal to the ridge width of the bus waveguide (6), and the period number is more than 2.
6. The thin film lithium niobate optical isolator based on acousto-optic scattering as claimed in claim 1, wherein when the thin film lithium niobate layer (3) adopts an X-cut lithium niobate crystal, the outgoing direction of the sound field center of the sector interdigital transducer (4) forms a positive 30-degree included angle with the Y axis of the crystal;
when the thin film lithium niobate layer (3) adopts Y-cut lithium niobate crystals, the emergent direction of the sound field center of the sector interdigital transducer (4) forms an included angle of plus or minus 45 degrees with the Z axis of the crystals;
when the thin film lithium niobate layer (3) adopts Z-cut lithium niobate crystals, the emergent direction of the sound field center of the sector interdigital transducer (4) forms an included angle of 0 degree or plus or minus 60 degrees with the Y axis of the crystals.
7. The thin film lithium niobate optical isolator device based on acousto-optic scattering according to claim 1, wherein the acoustic isolation layer is an oxygen buried layer (2), and the acoustic field mode excited by the fan-shaped electroacoustic interdigital transducer (4) in the thin film lithium niobate layer (3) is a surface acoustic wave;
or the acoustic isolation layer is an air layer, and the sound field mode excited by the fan-shaped electroacoustic interdigital transducer (4) in the thin film lithium niobate layer (3) is a lamb sound wave.
8. The acousto-optic scattering based thin film lithium niobate optical isolator device of claim 1, wherein the mode multiplexer is of the same construction as the mode demultiplexer, wherein the mode multiplexer has an upper port and a lower port for inputting a fundamental mode and a higher order mode, respectively, and the optical coupling into the upper port or the lower port is either a vertical coupling or a horizontal coupling.
9. The acousto-optic scattering based thin film lithium niobate optical isolator device of claim 1, wherein the upper cladding of the acousto-optic scattering based thin film lithium niobate optical isolator device is an air upper cladding;
or the thin film lithium niobate optical isolator based on acousto-optic scattering is also manufactured with an upper cladding layer, and the upper cladding layer is made of silicon oxide, silicon nitride or hydrogen silsesquioxane polymer HSQ type photoresist.
10. The method for manufacturing a thin film lithium niobate optical isolator based on acousto-optic scattering according to any of claims 1 to 9, comprising the steps of:
preparing a substrate which is respectively a substrate (1), an acoustic isolation layer and a thin film lithium niobate from bottom to top, and growing metal chromium with the thickness of 80-160 nanometers on the substrate by adopting electron beam evaporation;
spin-coating electron beam glue on the chromeplated substrate, wherein the thickness of the electron beam glue is 300-500 nanometers, and placing the chromeplated substrate on a heating plate with the temperature of preset heating temperature for standing after spin-coating; wherein the preset heating temperature is 150-180 ℃, and the standing time is not shorter than 1 minute;
step three, exposing the substrate by an electron beam exposure system, developing and fixing, and removing the developed residual glue by using oxygen plasma to obtain a waveguide pattern;
step four, etching the substrate by adopting chlorine-based inductively coupled plasma etching, and removing residual electron beam glue to obtain a chromium layer pattern;
step five, etching the substrate by adopting fluorine-based ICP, and removing residual metal chromium to obtain a thin film lithium niobate layer provided with a mode multiplexer, a mode demultiplexer and a bus ridge waveguide (6);
step six, cleaning the substrate;
step seven, carrying out thermal annealing on the substrate, specifically, heating the substrate from normal temperature to preset heat preservation temperature at the rate of 1-5 ℃ per minute under the condition of oxygen atmosphere and normal pressure, and preserving the heat for more than 1 hour; gradually cooling from the maintained temperature to normal temperature at a cooling rate of 0.5-2 ℃ per minute; wherein the preset heat preservation temperature is between 500 ℃ and 1100 ℃;
step eight, spin-coating electron beam glue on the substrate, wherein the thickness of the electron beam glue is 300-500 nanometers, and placing the substrate on a heating plate with the temperature of preset heating temperature for standing after spin-coating; wherein the preset heating temperature is 100-200 ℃, and the standing time is not shorter than 1 minute; then, exposing the substrate by an electron beam exposure system, developing and fixing, and removing the developing residual glue by using oxygen plasma to obtain a sector electroacoustic interdigital transducer pattern;
step nine, placing the substrate in an electron beam evaporation system, depositing metal of a fan-shaped electroacoustic interdigital transducer, and removing the rest of electron beam glue and a metal film by adopting a stripping process, thereby obtaining a film lithium niobate optical isolator based on acousto-optic scattering;
preferably, in the second step, the electron beam glue is ARP6200;
in the third step, the electron beam exposure system is a VISTEC EBPG 5000PES;
in the sixth step, the substrate is specifically cleaned by placing the substrate in a solution of ammonia water, hydrogen peroxide and deionized water according to a ratio of 1:1:5, standing the mixed solution obtained by mixing the mixed solution in a volume ratio for 1 to 15 minutes at a temperature of 60 to 80 ℃; wherein the concentration of the ammonia water solution is 25-28 wt%, and the concentration of the hydrogen peroxide solution is 30wt%.
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