CN113325612A - Thin film lithium niobate electro-optic modulator and preparation method thereof - Google Patents
Thin film lithium niobate electro-optic modulator and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a thin-film lithium niobate electro-optic modulator and a preparation method thereof, wherein the thin-film lithium niobate electro-optic modulator comprises a silicon substrate, an oxygen-buried layer and a lithium niobate layer which are arranged from bottom to top, and a thin-film lithium niobate optical waveguide is formed by etching the upper surface of the lithium niobate layer; the thin film lithium niobate optical waveguide comprises a Mach-Zehnder structure; a traveling wave signal electrode and a traveling wave grounding electrode are respectively arranged on two sides of each optical waveguide arm of the Mach-Zehnder structure, and a capacitance load type T structure electrode for modulating optical signals in the optical waveguide arms is arranged between the traveling wave signal electrode and the traveling wave grounding electrode; hollow isolation structures used for reducing the effective refractive index of microwave signals are arranged on the two sides and below each optical waveguide arm of the Mach-Zehnder structure. The thin-film lithium niobate electro-optical modulator realizes ultra-low driving voltage, ultra-low microwave loss and ultra-large electro-optical bandwidth under a silicon substrate, and is convenient for realizing ultra-high speed and ultra-low energy consumption electro-optical modulation in the fields of optical communication, optical sensing, optical integration and the like in the future.
Description
Technical Field
The invention belongs to the fields of optical communication, optical sensing and optical integration, and particularly relates to a thin-film lithium niobate electro-optic modulator and a preparation method thereof.
Background
With the continuous development of the information age, a large number of novel information-oriented industries are continuously approaching to the daily life of people, such as 5G, cloud computing, big data processing, artificial intelligence and the like, and the novel technologies bring great convenience to the daily life of people, and simultaneously, the requirements of the data processing and transmission technologies with high speed, large bandwidth and low power consumption are continuously strengthened. Taking a data center, which is a typical application in short-distance optical communication, as an example, the network traffic of a simple data center is greatly accelerated, the data capacity in the whole data center reaches a higher degree, and the power consumption pressure is continuously increased, so that how to effectively solve the problem of high-capacity and low-power-consumption data transmission becomes a very urgent need to be solved in the optical communication industry at present.
At present, silicon-based optoelectronic integration technology using silicon as a substrate has been developed rapidly due to its advantages of low cost, excellent passive performance, CMOS compatibility, and the like. However, since silicon itself does not have an electro-optic effect, electro-optic modulation can be achieved only by using an electro-absorption F-K effect or a carrier injection type effect or other methods, and the modulation rate cannot reach a very high speed (ns magnitude). Besides the modulation rate can not reach very high speed, the bandwidth of pure silicon-based electro-optical modulation can only reach about 40GHz at present, so that the modulation rate requirements of 100G, 400G and even 1.6T in the future cannot be met. Therefore, thin film lithium niobate-based electro-optic modulators with large bandwidth, low power consumption, low insertion loss, and high speed have gained widespread attention in recent years.
With the continuous temperature rise of the research on the thin-film lithium niobate electro-optical modulator, in 2018, the first thin-film lithium niobate electro-optical modulator driven by the CMOS is provided in Nature by the subject group of Harvard university, and the thin-film lithium niobate electro-optical modulator with the driving voltage of 1.4V, the electro-optical bandwidth of 45GHz and high bandwidth and low power consumption is realized. After one year, the subject group provides the first silicon-based hetero-integrated thin-film lithium niobate electro-optic modulator on Nature Photonics, and the driving voltage is 5.1V, the electro-optic bandwidth is up to 70GHz, so that the feasibility of realizing hetero-integration of the thin-film lithium niobate electro-optic modulator on silicon is proved. However, in the current high-speed optical communication field, the modulation rate has been shifted from 100G to 400G in general, and it is highly probable that the modulation rate is directly advanced to 1.6T in the future.
Disclosure of Invention
The purpose of the invention is as follows: the first purpose of the invention is to provide a silicon-based thin-film lithium niobate electro-optical modulator; the second purpose of the invention is to provide a preparation method of the silicon-based thin film lithium niobate electro-optic modulator.
The technical scheme is as follows: the invention relates to a thin-film lithium niobate electro-optical modulator which comprises a substrate, an oxygen-buried layer and a lithium niobate layer which are arranged from bottom to top, wherein the upper surface of the lithium niobate layer is etched to form a thin-film lithium niobate optical waveguide; the thin film lithium niobate optical waveguide comprises a Mach-Zehnder structure; the substrate is made of silicon, a traveling wave signal electrode and a traveling wave grounding electrode are respectively arranged on two sides of each optical waveguide arm of the Mach-Zehnder structure, and a capacitance load type T structure electrode for modulating optical signals in the optical waveguide arms is arranged between the traveling wave signal electrode and the traveling wave grounding electrode; hollow isolation structures used for reducing the effective refractive index of microwave signals are arranged on the two sides and below each optical waveguide arm of the Mach-Zehnder structure.
Preferably, the hollowed-out isolation structure comprises isolation layers continuously arranged on two sides of the optical waveguide arm and grooves arranged below the optical waveguide arm, and the bottom of each isolation layer is communicated with the corresponding groove.
Furthermore, a plurality of supporting structures connected with the two sides of the isolating layer are arranged in the isolating layer on the two sides of the optical waveguide arm.
Preferably, the traveling wave signal electrode and the traveling wave grounding electrode are in a coplanar traveling wave distributed electrode structure.
Furthermore, the width of the traveling wave signal electrode is 70-78um, and the distance between each group of traveling wave grounding electrodes and the traveling wave signal electrode is 30-40 um.
Preferably, the capacitance load type T-structure electrode includes a plurality of positive T-shaped electrodes and the same number of inverted T-shaped electrodes, the positive T-shaped electrodes and the inverted T-shaped electrodes are symmetrically arranged, the longitudinal arm end of the positive T-shaped electrode is connected with the traveling wave signal electrode, the longitudinal arm end of the inverted T-shaped electrode is connected with the traveling wave grounding electrode, and the cross arm of the positive T-shaped electrode and the cross arm of the inverted T-shaped electrode are respectively located on two sides of one optical waveguide arm of the mach-zehnder structure.
Furthermore, the distance between the positive T-shaped electrode cross arm and the reverse T-shaped electrode cross arm which are oppositely arranged is 1.5-2 um.
Furthermore, small holes are formed between adjacent positive T-shaped electrodes or negative T-shaped electrodes positioned on the same side, grooves are formed below the optical waveguide arms and are formed in the surface of the substrate, and the small holes penetrate through the cladding layer, the oxygen buried layer and the lithium niobate layer and are communicated with the grooves. The length of the section of the small hole perpendicular to the axial direction is 20-100um, the width is 3-50um, the depth of the groove is 5-50um, the edge of the section of the groove perpendicular to the axial direction is arc-shaped, and the radius can adopt 25-40 um. The grooves are typically machined into the substrate upper surface because the depth of the grooves exceeds the buried oxide thickness. When the technical scheme that the small holes are formed between adjacent positive T-shaped electrodes or reverse T-shaped electrodes located on the same side is adopted, materials below the longitudinal arm of the T-shaped electrode serve as a supporting structure and are used for supporting the optical waveguide arm and surrounding materials, and the small holes evenly distributed on the two sides of the optical waveguide arm are used for hollowing and isolating the two sides of the optical waveguide arm.
Furthermore, the width s of a cross arm of the positive T-shaped electrode or the reverse T-shaped electrode is 1-5um, the length r of the cross arm is 30-200um, the width T of a longitudinal arm is 1-5um, and the length h of the longitudinal arm is 5-50 um; the distance c between the positive T-shaped electrode or the negative T-shaped electrode positioned on the same side and the adjacent cross arm is 1-10 um; the distance between the positive T-shaped electrode cross arm and the inverted T-shaped electrode cross arm which are oppositely arranged is as small as possible in design requirements, but is larger than the width of the optical waveguide arm, and the width of the optical waveguide arm is generally 1.5 um.
Preferably, the thin film lithium niobate optical waveguide further comprises an input grating, a 1 x 2 beam splitter, a 2 x 1 beam combiner and an output grating; the input grating is connected with the input end of the 1X 2 beam splitter, the output end of the 1X 2 beam splitter is connected with the input end of the 2X 1 beam combiner through the Mach-Zehnder structure, and the output end of the 2X 1 beam combiner is connected with the output grating.
Preferably, the oxygen burying layer is made of silicon dioxide materials and is 1-6um thick. The lithium niobate layer is made of lithium niobate material, the inclination angle of the waveguide of the thin film lithium niobate is 60-70 degrees, the total thickness is 200-600nm, and the etching thickness is 100-300 nm. The cladding is arranged on the upper surface of the lithium niobate layer and covers the thin-film lithium niobate optical waveguide, and the cladding is made of a silicon dioxide material and has the thickness of 0.1-3 um.
Furthermore, the traveling wave signal electrode and the traveling wave grounding electrode are both arranged on the surface of the cladding, and the two optical waveguide arms of the Mach-Zehnder structure are symmetrically distributed on two sides of the traveling wave signal electrode. The traveling wave grounding electrode, the traveling wave signal electrode and the capacitance load type T structure electrode are not necessarily positioned above the optical waveguide arm, and on the premise of modulating an optical signal in the optical waveguide arm, the relative positions of the traveling wave grounding electrode, the traveling wave signal electrode and the capacitance load type T structure electrode and the optical waveguide arm in the vertical direction can be adjusted according to design requirements.
The preparation method of the thin film lithium niobate electro-optical modulator comprises the following steps: the method comprises the following steps:
(a) depositing and forming an oxygen burying layer on the upper surface of the silicon substrate;
(b) preparing a lithium niobate layer on the upper surface of the oxygen burying layer;
(c) preparing a thin film lithium niobate optical waveguide on the upper surface of the lithium niobate layer;
(d) depositing a cladding layer on the lithium niobate layer;
(e) plating a first layer of thin metal on the cladding to form a capacitance load type T structure electrode, a traveling wave signal electrode bottom structure and a traveling wave grounding electrode bottom structure;
(f) plating a second layer of thick metal on the surfaces of the bottom layer structure of the traveling wave signal electrode and the bottom layer structure of the traveling wave grounding electrode to form a top layer structure of the traveling wave signal electrode and a top layer structure of the traveling wave grounding electrode;
(g) preparing small holes between adjacent T-shaped electrodes on the same side;
(h) and etching the substrate by using the small hole as a channel to form a groove, thereby finishing the preparation of the device.
Preferably, the specific steps of processing and forming the thin-film lithium niobate optical waveguide in the step 3 are as follows:
and preparing a micro-nano pattern on the lithium niobate layer by utilizing a photoetching or electron beam exposure mode, and preparing the thin film lithium niobate optical waveguide by utilizing an etching mode on the basis of the micro-nano pattern.
Preferably, the first layer of thin metal plating and the second layer of thick metal plating in the steps e and f are performed by sputtering or evaporation.
Preferably, the specific steps of processing and forming the small holes in the step g are as follows:
and preparing a small hole pattern at a set position on the cladding by utilizing a photoetching mode, and etching the cladding, the lithium niobate layer and the oxygen buried layer in sequence by utilizing an etching mode to form a small hole.
Preferably, the specific steps of processing and forming the groove in the step h are as follows:
and etching the substrate silicon through the small holes by utilizing isotropic etching to form grooves.
When the thin-film lithium niobate electro-optical modulator works, light waves enter from the input grating, the light waves are divided into two beams through the 1 x 2 beam splitter, one beam passes through the upper light waveguide arm of the Mach-Zehnder structure 13, and the other beam passes through the lower light waveguide arm of the Mach-Zehnder structure 13. And high-frequency signals are loaded on the traveling wave signal electrode and the traveling wave grounding electrode through the GSG triangular probe. Because the signal loading mode of the traveling wave electrode is a push-pull mode, the refractive indexes of the lithium niobate optical waveguides of the upper optical waveguide arm and the lower optical waveguide arm of the Mach-Zehnder structure are changed to be opposite phases, a certain phase difference is generated between the upper arm and the lower arm after a certain distance, the upper arm and the lower arm are combined into a waveguide through a 2-to-1 beam combiner, and finally, the waveguide is output through an output grating, so that electro-optical modulation is realized.
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:
1. the integratability and applicability of the electro-optic modulator are improved. Silicon is selected as a substrate material, so that the silicon can be very effectively integrated with a silicon-based optoelectronic platform compatible with CMOS, the application scene of the electro-optical modulator structure is widened, and meanwhile, the electro-optical modulator structure is applied to a silicon-based heterogeneous integrated platform, so that the feasibility of applying the electro-optical modulator to other fields such as optical communication and the like is also improved.
2. The microwave loss of the electro-optical modulator is greatly reduced. The thin-film lithium niobate electro-optical modulator increases the width of a traveling wave signal electrode, increases the distance between the traveling wave signal electrode and a traveling wave grounding electrode, and reduces the surface resistance of the traveling wave signal electrode by using the larger width of the traveling wave signal electrode under the condition of ensuring that the impedance of the traveling wave electrode is matched with the impedance of a terminal load, thereby reducing the microwave loss mainly caused by the traveling wave electrode. Capacitive load type T-shaped structure electrodes are introduced between the traveling wave signal electrodes and the traveling wave grounding electrodes, so that the distance between each group of oppositely arranged T-shaped electrodes is ensured to be as small as possible, the product of extremely small half-wave voltage and length can be obtained, meanwhile, the microwave field is limited in a small range due to the extremely small electrode distance, and the radiation loss caused by the substrate under the high-frequency condition is greatly reduced.
3. And the high-efficiency speed matching of the microwave and the optical wave is realized. When the substrate is made of silicon, the effective refractive index of microwave signals is high due to the fact that the dielectric constant of the silicon is high, group refraction of microwaves and light waves is not matched, and the electro-optic bandwidth of the modulator is affected. Therefore, the substrate is hollowed to form a groove, substrate silicon with high dielectric constant is removed, the effective refractive index of microwave signals is reduced, and the slow wave effect caused by the capacitance load type T-shaped structure electrode is reduced, so that efficient microwave and light wave speed matching is realized. The isolation layers on the two sides of the optical waveguide arm can be obtained by dry etching, and in the aspect of a processing technology, the isolation layers can provide a channel for processing a groove; in the aspect of working principle, the isolation layers on the two sides of the waveguide arm can also reduce the effective refractive index of microwave signals, and high-efficiency speed matching of microwaves and light waves is realized.
4. The drive circuit has the characteristics of low-voltage drive and high bandwidth. The thin-film lithium niobate electro-optical modulator realizes the electro-optical bandwidth of more than 120GHz under the condition of ultralow driving voltage of 2V on a silicon-based substrate.
Drawings
FIG. 1 is a top view of the integral device of the thin film lithium niobate electro-optic modulator of the present invention;
FIG. 2 is a flow chart of a method for fabricating a thin film lithium niobate electro-optic modulator of the present invention;
FIG. 3 is a sectional view of the structure obtained in step 1 of the production method of the present invention.
FIG. 4 is a sectional view of the structure obtained in step 2 of the production method of the present invention.
FIG. 5 is a sectional view of the structure obtained in step 3 of the production method of the present invention.
FIG. 6 is a sectional view of the structure obtained in step 4 of the production method of the present invention.
FIG. 7 is a cross-sectional view of the structure obtained in step 5 of the production method of the present invention.
Fig. 8 is a sectional view of the structure obtained in step 6 in the production method of the present invention.
Fig. 9 is a sectional view of the structure obtained in step 7 in the production method of the present invention.
FIG. 10 is a cross-sectional view of the structure obtained in step 8 of the production method of the present invention.
FIG. 11 shows the group refractive index contrast between microwave and optical waves of the thin-film lithium niobate electro-optic modulator of the present invention.
FIG. 12 is a graph of microwave loss comparison of the inventive structure with a conventional thin film lithium niobate electro-optic modulator.
FIG. 13 is a comparison graph of the electro-optic bandwidth of the inventive structure and a conventional thin-film lithium niobate electro-optic modulator at the same driving voltage.
Fig. 14 is a partial view of a capacitive load type T-structure electrode in the present invention.
Detailed Description
The technical solution of the present invention is further described in detail with reference to the accompanying drawings and examples.
As shown in fig. 1 and 10, a thin-film lithium niobate electro-optic modulator includes a substrate 1, a buried oxide layer 2 and a lithium niobate layer 3, which are sequentially arranged from bottom to top, wherein a thin-film lithium niobate optical waveguide 4 is formed by etching the upper surface of the lithium niobate layer, and a cladding 5 is arranged on the upper surface of the lithium niobate layer and covers the thin-film lithium niobate optical waveguide; the thin film lithium niobate optical waveguide comprises an input grating 11, a 1 × 2 beam splitter 12, a Mach-Zehnder structure 13, a 2 × 1 beam combiner 14 and an output grating 15; the input grating is connected with the input end of the 1X 2 beam splitter, the output end of the 1X 2 beam splitter is connected with the input end of the 2X 1 beam combiner through the Mach-Zehnder structure, and the output end of the 2X 1 beam combiner is connected with the output grating.
In this embodiment, the substrate is made of a silicon material; the oxygen burying layer is made of silicon dioxide materials and is 3um thick; the lithium niobate layer is made of lithium niobate materials, and the total thickness is 400 nm; the thickness of the thin film lithium niobate optical waveguide is 200nm, and the inclination angle is 60 degrees; the cladding is made of silicon dioxide material and has a thickness of 0.9 um.
In this embodiment, the traveling wave signal electrode 7 and the traveling wave ground electrode 8 are in a coplanar traveling wave distributed electrode structure, the traveling wave signal electrode and the traveling wave ground electrode are both arranged on the surface of the cladding, two optical waveguide arms of the mach-zehnder structure are symmetrically distributed on two sides of the traveling wave signal electrode, and two groups of traveling wave ground electrodes are symmetrically distributed on two sides of the traveling wave signal electrode; and a traveling wave signal electrode and a group of traveling wave grounding electrodes are respectively arranged on two sides of each optical waveguide arm.
The width of increase travelling wave signal electrode is to 75um, increases the interval between travelling wave signal electrode and the travelling wave earthing electrode and is to 35.8um, under the circumstances that guarantees travelling wave electrode impedance and terminal load impedance match, bigger travelling wave signal electrode width can reduce travelling wave signal electrode surface resistance, reduces mainly the microwave loss that arouses by the travelling wave electrode.
In this embodiment, a capacitive load type T-structure electrode 6 is disposed in a gap between the two sets of traveling wave ground electrodes and the traveling wave signal electrode, and two ends of the capacitive load type T-structure electrode are respectively connected to the traveling wave signal electrode and the traveling wave ground electrode. Each group of capacitance load type T-shaped structure electrodes comprises a plurality of positive T-shaped electrodes 16 and a same number of inverted T-shaped electrodes 17, the positive T-shaped electrodes and the inverted T-shaped electrodes which are oppositely arranged are symmetrically arranged, the end parts of the longitudinal arms of the positive T-shaped electrodes are connected with a traveling wave signal electrode, the end parts of the longitudinal arms of the inverted T-shaped electrodes are connected with a traveling wave grounding electrode, and the cross arms of the positive T-shaped electrodes and the cross arms of the inverted T-shaped electrodes are respectively positioned on two sides of one optical waveguide arm of the Mach-Zehnder structure.
The positive T-shaped electrode and the inverted T-shaped electrode have the same structure and are both T-shaped electrodes, the width s of a transverse arm of each T-shaped electrode is 2 micrometers, the length r of the transverse arm is 47 micrometers, the width T of a longitudinal arm is 5 micrometers, and the length h of the longitudinal arm is 15 micrometers; the distance c between the positive T-shaped electrode or the negative T-shaped electrode positioned on the same side and the adjacent cross arm is 3 um; the distance between the positive T-shaped electrode cross arm and the reverse T-shaped electrode cross arm which are oppositely arranged is 1.8 um.
The distance between the positive T-shaped electrode cross arm and the inverted T-shaped electrode cross arm which are oppositely arranged is as small as possible in design requirements, but is larger than the width of the optical waveguide arm, and the width of the optical waveguide arm is generally 1.5 um. The small distance between the positive T-shaped electrode cross arm and the inverted T-shaped electrode cross arm which are oppositely arranged can obtain the product of the half-wave voltage and the length, and meanwhile, the microwave field is limited in a small range due to the small electrode distance, so that the radiation loss caused by the substrate under the high-frequency condition can be greatly reduced.
In this embodiment, small holes 9 are formed between adjacent positive T-shaped electrodes or negative T-shaped electrodes on the same side, grooves 10 are formed below the optical waveguide arms, and the small holes on both sides of each optical waveguide arm in the mach-zehnder structure and the grooves 10 below the small holes jointly isolate the optical waveguide arms in a hollow manner, so that the effective refractive index of microwave signals is reduced.
The axial cross-section length 39um is perpendicular to the aperture, and is wide 9.3um, and the recess degree of depth is 39.65um, and the axial cross-section edge is approximately arc perpendicularly to the recess, and the radius can adopt 35 um. Because the depth of the groove exceeds the thickness of the buried oxide layer, the groove is generally processed on the upper surface of the substrate; the bottom of the small hole is communicated with the groove, and the surrounding of the hollow structure on the two sides and the bottom of the optical waveguide arm can be realized. The hollow isolation structures around each optical waveguide arm can reduce the effective refractive index of microwave signals and slow down the slow wave effect caused by the capacitance load type T-shaped structure electrode, so that efficient speed matching of microwaves and optical waves is realized.
As shown in fig. 2, a method for preparing a thin-film lithium niobate electro-optic modulator is characterized in that: the method comprises the following steps:
(a) depositing a silicon dioxide oxygen burying layer on the silicon substrate, as shown in figure 3;
(b) preparing a lithium niobate layer on the upper surface of the oxygen burying layer, as shown in fig. 4;
(c) forming a thin film lithium niobate waveguide on the lithium niobate layer by dry etching, as shown in fig. 5;
(d) depositing a silica cladding on the lithium niobate layer by using a plasma chemical vapor deposition method, wherein the silica cladding covers the thin-film lithium niobate waveguide at the same time, as shown in fig. 6;
(e) preparing a micro-nano pattern of a first layer of metal electrode by using a photoetching or electron beam exposure mode, plating the first layer of metal electrode on the cladding 5 by using an evaporation or electroplating mode, and forming a capacitance load type T-shaped structure electrode 6, a traveling wave signal electrode bottom layer structure and a traveling wave grounding electrode bottom layer structure as shown in fig. 7;
(f) preparing a micro-nano pattern of a second layer of metal by using a photoetching or electron beam exposure mode, and plating a second layer of metal electrode by using an evaporation or electroplating mode to form a traveling wave signal electrode top layer structure and a traveling wave grounding electrode top layer structure, as shown in fig. 8;
(g) preparing a micro-nano pattern of a small hole at a set position on the cladding by using a photoetching or electron beam exposure mode, etching the small hole by using a dry etching mode, and sequentially etching the cladding, the lithium niobate layer and the oxygen buried layer to form the small hole, as shown in fig. 9;
(h) and hollowing the substrate silicon by using the isotropic etching mode through the small holes to form grooves, and finishing the preparation of the device, as shown in fig. 10.
In this embodiment, the lithography can be performed by using a stepper, a contact lithography machine, an electron beam direct writing method, a laser direct writing method, and the like, the etching can be performed by using isotropic etching, dry etching, such as ICP, RIE, and the like, and wet etching, and the electrode can be performed by using magnetron sputtering, electron beam evaporation, electroplating, and the like.
Through tests, the thin-film lithium niobate electro-optical modulator can keep good speed matching within the microwave signal of 0-100GHz, as shown in figure 11. Because this application has adopted the width that increases travelling wave signal electrode structurally, increases the interval between travelling wave signal electrode and the travelling wave earthing electrode, sets up capacitive load type T structure electrode and sets up fretwork isolation structure around the optical waveguide arm, compares with conventional film lithium niobate electro-optical modulator, the microwave loss of electro-optical modulator greatly reduces in this application, controls at lower level, as shown in fig. 12. The electro-optic modulator in the application realizes that the electro-optic bandwidth is up to more than 120GHz under the condition of ultralow driving voltage of 2V on a silicon substrate, and as shown in figure 13, compared with the conventional thin-film lithium niobate electro-optic modulator, the bandwidth is improved by 90GHz under the same driving voltage.
In conclusion, the thin-film lithium niobate electro-optic modulator in the application solves the performance bottleneck of the current commercial bulk material lithium niobate electro-optic modulator and the conventional thin-film lithium niobate electro-optic modulator, and realizes the novel silicon-based thin-film lithium niobate electro-optic modulator with ultra-large bandwidth and ultra-low power consumption by introducing the capacitance load type T-structure electrode and a new hollowing process mode.
Claims (10)
1. A thin-film lithium niobate electro-optical modulator comprises a substrate (1), an oxygen buried layer (2) and a lithium niobate layer (3) which are arranged from bottom to top, wherein a thin-film lithium niobate optical waveguide (4) is formed on the upper surface of the lithium niobate layer (3) through etching; the thin-film lithium niobate optical waveguide (4) comprises a Mach-Zehnder structure (13); the method is characterized in that: the substrate (1) is made of silicon, a traveling wave signal electrode (7) and a traveling wave grounding electrode (8) are respectively arranged on two sides of each optical waveguide arm of the Mach-Zehnder structure (13), and a capacitance load type T structure electrode (6) used for modulating optical signals in the optical waveguide arms is arranged between the traveling wave signal electrode (7) and the traveling wave grounding electrode (8); hollow isolation structures used for reducing the effective refractive index of microwave signals are arranged on the two sides and below each optical waveguide arm of the Mach-Zehnder structure (13).
2. The thin film lithium niobate electro-optic modulator of claim 1, wherein: the hollow isolation structure comprises isolation layers continuously arranged on two sides of the optical waveguide arm and a groove (10) arranged below the optical waveguide arm, and the bottom of each isolation layer is communicated with the groove (10).
3. The thin film lithium niobate electro-optic modulator of claim 2, wherein: and a plurality of supporting structures connected with the two sides of the isolating layer are arranged in the isolating layer on the two sides of the optical waveguide arm.
4. The thin film lithium niobate electro-optic modulator of claim 1, wherein: the traveling wave signal electrode (7) and the traveling wave grounding electrode (8) are in a coplanar traveling wave distributed electrode structure.
5. The thin film lithium niobate electro-optic modulator of claim 4, wherein: the width of the traveling wave signal electrode (7) is 70-78um, and the distance between the traveling wave grounding electrode (8) and the traveling wave signal electrode (7) is 30-40 um.
6. The thin film lithium niobate electro-optic modulator of claim 1, wherein: the capacitance load type T-shaped structure electrode (6) comprises a plurality of positive T-shaped electrodes (16) and a same number of symmetrically arranged reverse T-shaped electrodes (17), the end part of the longitudinal arm of each positive T-shaped electrode (16) is connected with the traveling wave signal electrode (7), the end part of the longitudinal arm of each reverse T-shaped electrode (17) is connected with the traveling wave grounding electrode (8), and the cross arm of each positive T-shaped electrode (16) and the cross arm of each reverse T-shaped electrode (17) are respectively positioned on two sides of one optical waveguide arm of the Mach-Zehnder (13) structure.
7. The thin film lithium niobate electro-optic modulator of claim 6, wherein: the distance between the cross arm of the positive T-shaped electrode (16) and the cross arm of the reverse T-shaped electrode (17) which are oppositely arranged is 1.5-2 um.
8. The thin film lithium niobate electro-optic modulator of claim 6, wherein: and small holes (9) are formed between adjacent positive T-shaped electrodes (16) or reverse T-shaped electrodes (17) positioned on the same side, grooves (10) are formed below the optical waveguide arms, the grooves (10) are formed in the surface of the substrate (1), and the small holes (9) penetrate through the cladding layer (5), the oxygen buried layer (2) and the lithium niobate layer (3) and are communicated with the grooves (10).
9. A preparation method of a thin-film lithium niobate electro-optical modulator is characterized by comprising the following steps: the method comprises the following steps:
(a) depositing and forming a buried oxide layer (2) on the upper surface of the silicon substrate (1);
(b) preparing a lithium niobate layer (3) on the upper surface of the oxygen embedding layer (2);
(c) preparing a thin-film lithium niobate optical waveguide (4) on the upper surface of the lithium niobate layer (3);
(d) depositing a cladding (5) on the lithium niobate layer (3);
(e) plating a first layer of thin metal on the cladding (5) to form a bottom layer structure of a capacitance load type T-shaped structure electrode (6), a traveling wave signal electrode (7) and a bottom layer structure of a traveling wave grounding electrode (8);
(f) plating a second layer thick metal on the upper surfaces of the bottom layer structure of the traveling wave signal electrode (7) and the bottom layer structure of the traveling wave grounding electrode (8) to form a top layer structure of the traveling wave signal electrode (8) and a top layer structure of the traveling wave grounding electrode (8);
(g) preparing a small hole (9) between adjacent T-shaped electrodes on the same side;
(h) and etching the substrate (1) by using the small hole (9) as a channel to form a groove (10) so as to finish the preparation of the electro-optical modulator.
10. The method for preparing the thin-film lithium niobate electro-optical modulator according to claim 9, wherein: the concrete steps of processing and forming the small hole (9) in the step g and the groove (10) in the step h are as follows:
preparing a small hole pattern at a set position on the cladding (5) by utilizing a photoetching mode, and sequentially etching the cladding (5), the lithium niobate layer (3) and the oxygen buried layer (2) by utilizing a dry etching mode to form a small hole (9); and etching the substrate silicon by utilizing an isotropic etching mode to form the groove (10).
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