Amorphous silicon-lithium niobate hybrid integrated electro-optical modulator and preparation method thereof

Abstract

The present invention belongs to the field of optical modulators and discloses an amorphous silicon-lithium niobate hybrid integrated electro-optical modulator and a preparation method thereof. The waveguide layer in the electro-optical modulator device layer includes, from left to right, a thin-film lithium niobate input waveguide, a first thin-film lithium niobate optical beam splitting structure, two parallel amorphous silicon-lithium niobate hybrid optical waveguides, a second thin-film lithium niobate optical beam splitting structure, and a thin-film lithium niobate output waveguide. The metal electrode layer in the electro-optical modulator device layer also includes a plurality of T-structure electrodes connected by longitudinal arms to the metal signal electrode and the metal ground electrode on the side facing the amorphous silicon-lithium niobate hybrid optical waveguide. The present invention adapts a thin-film lithium niobate hybrid waveguide deposited with amorphous silicon to a metal electrode layer improved based on a T-structure metal electrode, thereby increasing the group refractive index of the lightwave signal and thereby matching it with the effective refractive index of the microwave signal, thereby enabling the integrated electro-optical modulator to have the performance of wide bandwidth and low driving voltage.

Description

Technical Field

[0001] The present invention belongs to the technical field related to optical modulators, and more specifically, relates to an amorphous silicon-lithium niobate hybrid integrated electro-optical modulator and a preparation method thereof. Background Art

[0002] The rapid development of cutting-edge technologies such as 5G, artificial intelligence, big data, and the Internet of Things (IoT) has ushered in a new chapter in the information age. The convergence of these technologies has triggered more innovative application scenarios for businesses (B2B) and consumers (B2C), driving the trend of ever-increasing data volumes. Against this backdrop of rapid development, high-bandwidth communications have become a core requirement for driving information transmission. Optical modules are a crucial component of data center communication systems, and optical modulators are one of their core components.

[0003] Currently, silicon-based optoelectronic integration technology, using silicon as a substrate, has achieved remarkable development due to its low cost and compatibility with CMOS processes. However, due to the centrosymmetric crystal structure of silicon, which lacks a linear electro-optical effect, its modulators are based on the plasma dispersion effect. This involves applying an external electric field to alter the carrier concentration in the PN junction, thereby changing the refractive index of silicon and thereby modulating the optical signal. However, silicon-based modulators based on the plasma dispersion effect also alter the loss of the silicon waveguide while changing the refractive index of silicon, significantly increasing the loss of the modulator. Furthermore, the plasma dispersion effect is a nonlinear process, making the linearity of silicon-based modulators far inferior to that of lithium niobate modulators.

[0004] Currently, there are two main approaches to achieving wide-bandwidth, low-drive-voltage thin-film lithium niobate modulators: (a) Silicon-based thin-film lithium niobate electro-optical modulators utilize periodic capacitive load electrodes and hollow out portions of the silicon substrate to reduce the effective refractive index of the microwave signal to match the group refractive index of the light wave, thereby reducing microwave losses and achieving better modulation performance. (b) Quartz substrates employ periodic capacitive load electrodes and are replaced with quartz. Quartz substrates have low microwave losses, which can improve the matching of the effective refractive index of microwaves with the group refractive index of light waves, achieving low microwave losses and, consequently, excellent modulation. However, approach (a) suffers from complex manufacturing processes, potentially requiring complex fabrication procedures and increasing production difficulties. Furthermore, device stability may be insufficient, potentially limiting its reliability in practical applications. Approach (b) is incompatible with traditional CMOS processes and silicon-based integration, limiting its application in large-scale integrated circuits and increasing manufacturing difficulties. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides an amorphous silicon-lithium niobate hybrid integrated electro-optical modulator, the purpose of which is to improve the group refractive index of the light wave signal and match it with the effective refractive index of the microwave signal by depositing a thin film lithium niobate hybrid waveguide with amorphous silicon, and adapting it to the metal electrode layer improved based on the T-shaped structure metal electrode, thereby achieving efficient speed matching between microwaves and light waves. At the same time, by setting a periodic capacitive load electrode, the distance between the electrode and the hybrid waveguide is reduced, thereby achieving better electric field modulation, thereby achieving the performance of large bandwidth and low driving voltage.

[0006] To achieve the above objectives, according to one aspect of the present invention, an amorphous silicon-lithium niobate hybrid integrated electro-optical modulator is provided, wherein the integrated electro-optical modulator comprises, from bottom to top, a silicon substrate layer, a buried oxide layer, and an electro-optical modulation device layer;

[0007] The electro-optical modulation device layer includes a waveguide layer, a buffer layer and a metal electrode layer in order from bottom to top;

[0008] The waveguide layer includes, from left to right, a thin-film lithium niobate input waveguide, a first thin-film lithium niobate optical beam splitting structure, two parallel amorphous silicon-lithium niobate hybrid optical waveguides, a second thin-film lithium niobate optical beam splitting structure, and a thin-film lithium niobate output waveguide, wherein the first thin-film lithium niobate optical beam splitting structure and the second thin-film lithium niobate optical beam splitting structure are both connected to the two parallel amorphous silicon-lithium niobate hybrid optical waveguides via the thin-film lithium niobate waveguides; wherein the amorphous silicon-lithium niobate hybrid optical waveguide is formed by depositing amorphous silicon on the thin-film lithium niobate waveguide;

[0009] The metal electrode layer includes a traveling wave signal electrode, two traveling wave ground electrodes and a plurality of T-structure electrodes; the projection position of the traveling wave signal electrode on the waveguide layer is set between two parallel amorphous silicon-lithium niobate hybrid optical waveguides; the projection positions of the two traveling wave ground electrodes on the waveguide layer are respectively set on the outsides of the two parallel amorphous silicon-lithium niobate hybrid optical waveguides; the T-structure electrode is connected to the side of the traveling wave signal electrode and the traveling wave ground electrode facing the amorphous silicon-lithium niobate hybrid optical waveguide through a longitudinal arm.

[0010] As a preferred embodiment of the present invention, the waveguide layer further comprises two amorphous silicon wedge-shaped waveguide optical mode conversion structures, which are respectively arranged at the input end and the output end of the amorphous silicon-lithium niobate hybrid optical waveguide and connected to the thin film lithium niobate waveguide;

[0011] The amorphous silicon wedge-shaped waveguide optical mode conversion structure is formed by depositing an amorphous silicon layer on a thin-film lithium niobate waveguide, and the width of the amorphous silicon wedge-shaped waveguide optical mode conversion structure gradually increases along the direction connecting the amorphous silicon-lithium niobate hybrid optical waveguide until the width of the amorphous silicon wedge-shaped waveguide optical mode conversion structure is consistent with the width of the connection surface of the amorphous silicon-lithium niobate hybrid optical waveguide.

[0012] As a preferred embodiment of the present invention, the T-structure electrode includes an equal number of positive T-shaped electrodes and inverted T-shaped electrodes;

[0013] The positive T-type electrode and the inverted T-type electrode are respectively arranged on the side surfaces of the traveling wave signal electrode and the traveling wave ground electrode on both sides of the amorphous silicon-lithium niobate hybrid optical waveguide through longitudinal arms, so that the positive T-type electrode and the inverted T-type electrode are symmetrically arranged between the traveling wave signal electrode and the traveling wave ground electrode based on the lithium niobate hybrid optical waveguide.

[0014] As a preferred embodiment of the present invention, the thickness of the amorphous silicon is 30-70 nm;

[0015] The buffer layer is selected from a medium with a refractive index less than 2 and has a thickness of 0.1-3 μm.

[0016] As a preferred embodiment of the present invention, the thin film lithium niobate waveguide is formed based on half etching of a thin film lithium niobate layer; wherein the thin film lithium niobate layer is located on the upper layer of the buried oxide layer, and the thickness of the thin film lithium niobate layer is 360-600 nm.

[0017] As a preferred embodiment of the present invention, the thickness of the metal electrode layer is 0.2-1.4 μm;

[0018] The width of the traveling wave signal electrode is 30-40 μm;

[0019] The traveling wave ground electrode has a width of 50-100 μm;

[0020] The distance between the traveling wave signal electrode and the traveling wave ground electrode is 10-25 μm.

[0021] As a preferred embodiment of the present invention, the horizontal arm length of the T-structure electrode is 40-45 μm, and the width is 1-5 μm.

[0022] As a preference of the present invention, the traveling wave signal electrode and the traveling wave ground electrode are coplanar traveling wave distributed electrode structures.

[0023] As a preferred embodiment of the present invention, the amorphous silicon-lithium niobate hybrid optical waveguide is formed by evaporating amorphous silicon on a thin film lithium niobate waveguide;

[0024] Alternatively, the amorphous silicon-lithium niobate hybrid optical waveguide is formed by depositing amorphous silicon on the thin film lithium niobate waveguide and then performing photolithography etching; wherein the photolithography etching is full etching.

[0025] As a preferred embodiment of the present invention, the thin film lithium niobate optical beam splitting structure is a Y-type splitter, an MMI-type splitter or a directional coupler-type splitter.

[0026] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0027] (1) The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator of the present invention deposits amorphous silicon thin film lithium niobate hybrid waveguide and adapts it to the metal electrode layer improved based on the T-structure electrode, thereby increasing the group refractive index of the light wave signal and matching it with the effective refractive index of the microwave signal, thereby achieving efficient speed matching between microwaves and light waves. At the same time, by setting a periodic capacitive load electrode, the distance between the electrode and the hybrid waveguide is reduced, thereby achieving better electric field modulation, thereby achieving the performance of large bandwidth and low driving voltage.

[0028] (2) Preferably, the present invention provides an amorphous silicon wedge-shaped waveguide optical mode conversion structure at both ends of the amorphous silicon-lithium niobate hybrid optical waveguide connected to the thin-film lithium niobate waveguide. The amorphous silicon wedge-shaped waveguide optical mode conversion structure is formed by depositing and photolithographically etching the thin-film lithium niobate waveguide and the amorphous silicon layer. The width of the amorphous silicon layer pattern structure gradually changes from narrow to wide, causing the effective refractive index of the optical waveguide to change slowly, which is beneficial for maintaining low-loss transmission of optical signals.

[0029] (3) As a preferred embodiment, the present invention uses periodic capacitive load electrodes to reduce microwave loss in the electro-optical modulator. While ensuring that the impedance of the metal traveling wave signal electrode matches the impedance of the terminal load, by increasing the width of the traveling wave signal electrode and the spacing between the traveling wave signal electrode and the traveling wave ground electrode, the conduction current along the transmission line is reduced, which is beneficial for reducing microwave loss. While ensuring low optical waveguide transmission loss, the smaller the spacing between the T-shaped structure electrodes, the smaller the product of the half-wave voltage and the length.

[0030] (4) Preferably, the thin-film lithium niobate layer of the present invention has a thickness of 360-600 nm. Using a half-etching scheme, the thickness of the thin-film lithium niobate ridge waveguide is half the thickness of the thin-film lithium niobate layer, and the thickness of the amorphous silicon layer is 30-70 nm. By controlling the thickness of the thin-film lithium niobate layer, the thickness of the ridge waveguide, and the thickness of the amorphous silicon layer, the group refractive index of the optical waveguide is matched to the effective refractive index of the microwave signal, achieving efficient speed matching between microwaves and light waves.

[0031] (5) The integration and application scope of the electro-optical modulator are improved. The existing use of quartz or the partial hollowing of the silicon substrate is to match the microwave effective refractive index to the optical waveguide. The present invention uses silicon as the substrate, which is compatible with the CMOS process, broadens the application scenarios of this electro-optical modulator structure, solves the problems of complex process and poor device stability of silicon-based thin film lithium niobate high-bandwidth electro-optical modulator, and the incompatibility of quartz-based high-bandwidth electro-optical modulator with traditional CMOS process and silicon-based integration. While achieving large bandwidth and low driving voltage, there is no need to change the substrate to quartz or to partially hollow out the silicon substrate. Partial hollowing of the silicon substrate will greatly reduce the stability of the device. Specifically, when the device vibrates or bumps violently, the hollowed-out structure - the cantilever arm waveguide may break, causing damage to the device; in the optical coupling packaging process, wiping the chip edge and surface, and mechanically fixing and positioning, these operations will generate stress and also pose a risk of damaging the device.

[0032] In summary, the amorphous silicon-lithium niobate hybrid integrated electro-optic modulator of the present invention does not require substrate processing. It forms a hybrid waveguide by combining amorphous silicon and thin-film lithium niobate, and combines it with an improved metal electrode layer to increase the group refractive index of the light wave signal, thereby achieving wide bandwidth and low driving voltage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 is a top view of an overall device of an amorphous silicon-lithium niobate hybrid integrated electro-optical modulator according to an example of the present invention;

[0034] Figure 2 1 is a cross-sectional view of an amorphous silicon-lithium niobate hybrid integrated electro-optical modulator device according to an example of the present invention at a lithium niobate hybrid optical waveguide;

[0035] Figure 3 This is a flow chart of a method for preparing a lithium niobate hybrid integrated electro-optical modulator according to an example of the present invention;

[0036] Figure 4 is a partial diagram of a periodic capacitive load electrode according to an embodiment of the present invention;

[0037] Figure 5 1 is a schematic top view of a silicon wedge-shaped waveguide optical mode conversion structure and a lithium niobate hybrid optical waveguide structure according to an embodiment of the present invention;

[0038] Figure 6 This is a comparison diagram of the group refractive index of microwaves and light waves in an amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to an embodiment of the present invention;

[0039] Figure 7This is a microwave loss diagram of an amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to an embodiment of the present invention;

[0040] Figure 8 This is an electro-optic bandwidth diagram of an amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to an embodiment of the present invention.

[0041] Throughout the drawings, like reference numerals are used to denote like structures, wherein:

[0042] 1-Silicon substrate, 2-Buried oxide layer, 3-Thin film lithium niobate layer, 4-Thin film lithium niobate optical waveguide, 5-Amorphous silicon layer, 6-Buffer layer, 7-Thin film lithium niobate input waveguide, 8-Thin film lithium niobate output waveguide, 9-Thin film lithium niobate optical beam splitting structure, 10-Amorphous silicon wedge-shaped waveguide optical mode conversion structure, 11-Amorphous silicon-lithium niobate hybrid optical waveguide, 12-Traveling wave signal electrode, 13-Traveling wave ground electrode, 14-T structure electrode. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0044] like Figure 1 and Figure 2 As shown, an amorphous silicon-lithium niobate hybrid integrated electro-optic modulator of the present invention comprises, from bottom to top, a silicon substrate layer 1, a buried oxide layer 2, and an electro-optic modulation device layer;

[0045] The electro-optical modulation device layer includes a waveguide layer, a buffer layer 6 and a metal electrode layer from bottom to top;

[0046] The waveguide layer includes: a thin film lithium niobate input waveguide 7, a thin film lithium niobate waveguide 4, two thin film lithium niobate optical beam splitting structures 9, two parallel amorphous silicon-lithium niobate hybrid optical waveguides 11, and a thin film lithium niobate output waveguide 8;

[0047] The thin-film lithium niobate input waveguide 7 is connected to the input end of the first thin-film lithium niobate optical beam splitting structure 9. The output end of the first thin-film lithium niobate optical beam splitting structure 9 is connected to the input ends of two parallel amorphous silicon-lithium niobate hybrid optical waveguides 11 through thin-film lithium niobate waveguides 4. The output end of the amorphous silicon-lithium niobate hybrid optical waveguide 11 is connected to the input end of the second thin-film lithium niobate optical beam splitting structure 9 through the thin-film lithium niobate waveguide 4. The output end of the second thin-film lithium niobate optical beam splitting structure 9 is connected to the thin-film lithium niobate output waveguide 8.

[0048] The metal electrode layer includes a traveling wave signal electrode 12, two traveling wave ground electrodes 13 and a plurality of T-structure electrodes 14;

[0049] Among them, the projection position of the traveling wave signal electrode 12 on the waveguide layer is in the middle of the two parallel amorphous silicon-lithium niobate hybrid optical waveguides 11; the projection position of the two traveling wave ground electrodes 13 on the waveguide layer is on the outside of the two parallel amorphous silicon-lithium niobate hybrid optical waveguides 11; the T-structure electrode 14 is connected to the side of the metal traveling wave signal electrode and the metal traveling wave ground electrode facing the amorphous silicon-lithium niobate hybrid optical waveguide through a longitudinal arm.

[0050] The thin film lithium niobate layer referred to in the present invention is a lithium niobate layer with a thickness between 180nm and 1000nm.

[0051] In some embodiments, the waveguide layer further includes an amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 , which is provided with an input end and an output end of the amorphous silicon-lithium niobate hybrid optical waveguide 11 and is connected to the thin film lithium niobate waveguide 4 ;

[0052] The width of the amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 gradually widens along the direction of connection to the amorphous silicon-lithium niobate hybrid optical waveguide 11, until the width of the amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 matches the width of the connecting surface of the amorphous silicon-lithium niobate hybrid optical waveguide 11. The length of the amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 was determined using the finite time-domain difference method. This method simulates and calculates the transmission efficiency of the thin-film lithium niobate waveguide through the amorphous silicon wedge-shaped waveguide optical mode conversion structure and the amorphous silicon-lithium niobate hybrid optical waveguide to determine the length of the amorphous silicon wedge-shaped waveguide optical mode conversion structure.

[0053] The amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 and the amorphous silicon-lithium niobate hybrid optical waveguide 11 are both formed by depositing an amorphous silicon layer 5 on a thin-film lithium niobate waveguide. The thin-film lithium niobate waveguide is formed by half-etching the thin-film lithium niobate layer 3. The resulting thin-film lithium niobate waveguide has a tilt angle of 60°. In this embodiment, after depositing the amorphous silicon layer 5 on the thin-film lithium niobate waveguide, a full etching process can be performed, with the tilt angle of the amorphous silicon layer 5 thereon being 90°.

[0054] In some embodiments, a T-shaped electrode 14 for modulating the optical signal within the optical waveguide arm is disposed between the traveling wave signal electrode 12 and the traveling wave ground electrode 13. Specifically, the T-shaped electrode 14 includes an equal number of positive T-shaped electrodes and inverted T-shaped electrodes. The positive T-shaped electrode and the inverted T-shaped electrode are disposed on the side surfaces of the metal signal electrode and the metal ground electrode on either side of the amorphous silicon-lithium niobate hybrid optical waveguide via longitudinal arms, respectively. This allows the positive T-shaped electrode and the inverted T-shaped electrode to be symmetrically disposed between the metal signal electrode and the metal ground electrode relative to the lithium niobate hybrid optical waveguide 11, while also increasing the distance between the electrodes. This allows the periodic capacitive load electrode to change impedance and effective refractive index to match the group refractive index of the amorphous silicon-lithium niobate hybrid optical waveguide 11. Typically, gaps are left between adjacent T-shaped electrodes 14 to account for process tolerances and metal absorption, and a gap is also left between the T-shaped electrode 14 and the amorphous silicon-lithium niobate hybrid optical waveguide 11.

[0055] In some embodiments, the thickness of the silicon substrate 1 is 200-1000 μm, the thickness of the buried oxide layer 2 is 1-6 μm, and the thickness of the thin film lithium niobate layer 3 is 360-600 nm;

[0056] The thickness of the amorphous silicon 5 is 30-70 nm; the material of the buffer layer 6 can be selected from one of the media with a refractive index less than 2, such as silicon dioxide, and the thickness is 0.1-3 μm.

[0057] In some embodiments, the thin film lithium niobate waveguide 4 is formed by half-etching the thin film lithium niobate layer 3; the thin film lithium niobate layer 3 is located between the buried oxide layer 2 and the electro-optical modulation device layer, and the thickness of the thin film lithium niobate layer 3 is 360-600 nm.

[0058] In some embodiments, the thickness of the metal electrode layer is 0.2-1.4 μm, wherein the traveling wave signal electrode 12 and the traveling wave ground electrode 13 are relatively thick, and the T-structure electrode 14 can be relatively thin, or the traveling wave signal electrode 12, the traveling wave ground electrode 13 and the T-structure electrode 14 are all of substantially the same thickness.

[0059] The width of the traveling wave signal electrode 12 is 30-40 μm; the width of the traveling wave ground electrode 13 is 50-100 μm; and the width of the interval between the traveling wave signal electrode 12 and the traveling wave ground electrode 13 is 10-25 μm.

[0060] In some embodiments, the length of the horizontal arm of the T-structure electrode 14 is (45-50)*0.9 μm, and the width is 1-5 μm. When the length of the long arm is designed to be 45 μm, the effect is better.

[0061] The longitudinal arm of the T-structure electrode 14 is used to connect the traveling wave signal electrode 12 and the traveling wave ground electrode 13 , and its length is determined by the spacing between the T-structure electrodes and the spacing between the traveling wave signal electrode and the traveling wave ground electrode.

[0062] In some embodiments, the contact surface between the buffer layer 6 and the metal electrode layer is a flat surface with the same horizontal height. The traveling wave signal electrode 12 and the traveling wave ground electrode 13 are a coplanar traveling wave distributed electrode structure. The traveling wave signal electrode 12, the traveling wave ground electrode 13 and the T-structure electrode 14 together form a periodic capacitive load electrode.

[0063] In some embodiments, the amorphous silicon-lithium niobate hybrid optical waveguide 11 can be formed by evaporating amorphous silicon on a thin-film lithium niobate waveguide, or by depositing amorphous silicon on a thin-film lithium niobate waveguide and then performing full etching by photolithography.

[0064] In some embodiments, the thin film lithium niobate optical beam splitting structure 9 is a Y-type splitter, an MMI-type splitter, or a directional coupler-type splitter.

[0065] Based on any one of the above-mentioned methods for preparing an amorphous silicon-lithium niobate hybrid integrated electro-optical modulator, such as Figure 3 As shown, the following steps are included:

[0066] S1: Using photolithography and etching technology on silicon-based thin-film lithium niobate substrate materials to prepare thin-film lithium niobate optical structures, including thin-film lithium niobate input and output waveguides, thin-film lithium niobate waveguides, and thin-film lithium niobate optical beam splitting structures;

[0067] S2: growing amorphous silicon on the substrate obtained in step S1 using inductively coupled plasma chemical vapor deposition (ICPCVD), and fabricating an amorphous silicon-lithium niobate hybrid optical waveguide using photolithography and etching techniques;

[0068] S3: depositing a buffer layer on the substrate obtained in step S2 by plasma enhanced chemical vapor deposition (PECVD);

[0069] S4: Using a metal lift-off process, a gold electrode is fabricated on the substrate obtained in step S3 to obtain an amorphous silicon-lithium niobate hybrid integrated electro-optic modulator.

[0070] In the above steps, the photolithography methods include: stepper lithography machine, contact lithography machine, projection lithography machine, electron beam direct writing, laser direct writing and other methods; the electrodes can be completed by magnetron sputtering, electron beam evaporation, electroplating and other methods.

[0071] In the step S2, amorphous silicon is grown on the pattern structure that changes from narrow to wide using inductively coupled plasma chemical vapor deposition, and the wedge-shaped waveguide optical mode conversion structure 10 is prepared using photolithography and etching technology.

[0072] Example 1:

[0073] The integrated electro-optic modulator prepared based on the above preparation method comprises, from bottom to top, a silicon substrate layer 1, a buried oxide layer 2, and an electro-optic modulation device layer;

[0074] The electro-optical modulation device layer includes a waveguide layer, a buffer layer 6 and a metal electrode layer from bottom to top;

[0075] The waveguide layer includes: a thin-film lithium niobate input waveguide 7, a thin-film lithium niobate waveguide 4, a thin-film lithium niobate optical beam splitting structure 9, an amorphous silicon wedge-shaped waveguide optical mode conversion structure 10, an amorphous silicon-lithium niobate hybrid optical waveguide 11, and a thin-film lithium niobate output waveguide 8; wherein the thin-film lithium niobate input waveguide 7 is connected to the input end of the thin-film lithium niobate optical beam splitting structure 9, the two output ends of the thin-film lithium niobate optical beam splitting structure 9 are connected to the upper and lower amorphous silicon-lithium niobate hybrid optical waveguides 11 through the amorphous silicon wedge-shaped waveguide optical mode conversion structure 10, the output end of the amorphous silicon-lithium niobate hybrid optical waveguide 11 is connected to the input end of the thin-film lithium niobate optical beam splitting structure 9, and its output end is connected to the thin-film lithium niobate output waveguide 8.

[0076] The metal electrode layer is entirely arranged on the flat surface of the buffer layer and includes: the projection of the traveling wave signal electrode 12 on the waveguide layer is at the middle position relative to the two lithium niobate hybrid optical waveguides 11, and the projections of the two traveling wave ground electrodes 13 on the waveguide layer are respectively at the positions on the opposite sides of the two lithium niobate hybrid optical waveguides 11; and a T-structure electrode 14 for modulating the optical signal in the optical waveguide arm is arranged between the traveling wave signal electrode 12 and the traveling wave ground electrode 13.

[0077] In this embodiment, the substrate 1 is made of silicon material with a thickness of 525 μm; the buried oxide layer 2 is made of thermal oxide silicon dioxide material with a thickness of 3 μm; the thin film lithium niobate layer 3 is 400 nm thick; the thin film lithium niobate optical waveguide 4 is 200 nm thick and has a tilt angle of 60 degrees; the amorphous silicon 5 is 50 nm thick, the silicon dioxide buffer layer 6 is 800 nm thick, and the traveling wave signal electrode 12, the traveling wave ground electrode 13, and the T-structure electrode 14 are 1.1 μm thick.

[0078] In this embodiment, Figure 4Shown is a partial view of a periodic capacitive load electrode, consisting of a traveling wave signal electrode 12, a traveling wave ground electrode 13, and a T-shaped metal electrode 14. The width Ws of the traveling wave signal electrode 12 is 33.7 μm, the width Wg of the traveling wave ground electrode 13 is 60 μm, and the distance Wgap between the traveling wave signal electrode 12 and the traveling wave ground electrode 13 is 13.4 μm. The positive T-shaped metal electrode 14 and the inverted T-shaped metal electrode 14 have the same structure: the transverse arm width s of the T-shaped metal electrode 14 is 2 μm, the transverse arm length r is 45 μm, the longitudinal arm width t is 5 μm, and the longitudinal arm length h is 3.05 μm. The spacing c between adjacent transverse arms of the positive or inverted T-shaped metal electrodes on the same side is 5 μm. The spacing g between the transverse arms of the oppositely positioned positive T-shaped metal electrode and the inverted T-shaped electrode is 3 μm. When a stronger modulation effect is required, the spacing g can be reduced to 1.8 μm, corresponding to a longitudinal arm length h of 3.8 μm.

[0079] In this embodiment, the width of lithium niobate W0 and the width of amorphous silicon W2 in the amorphous silicon-lithium niobate hybrid optical waveguide are calculated according to the group refractive index formula: The width matching the microwave effective refractive index was calculated, and then the optimal value was determined through iterative optimization considering the modulation efficiency. Under current process capabilities, the width of W1 ranges from 70 to 180 nm. The transmission length of the amorphous silicon-lithium niobate hybrid optical waveguide 11 is determined to achieve a half-wave voltage of less than or equal to 3 V. Based on the calculated electro-optical modulation efficiency (the product of the half-wave voltage and the modulation length), the length of the amorphous silicon-lithium niobate hybrid optical waveguide within the modulation region is calculated to be 9 mm.

[0080] Figure 5 Shown is a schematic diagram of an amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 and an amorphous silicon-lithium niobate hybrid optical waveguide 11. The amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 and the amorphous silicon-lithium niobate hybrid optical waveguide 11 are composed of an amorphous silicon waveguide formed by photolithography using a thin-film lithium niobate waveguide 4 and amorphous silicon 5. The thin-film lithium niobate waveguide 4 has a width W0 of 1.5 μm. The tip widths W1 and W2 of the amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 are 120 nm and 1 μm, respectively. The transmission length l of the amorphous silicon wedge-shaped waveguide optical mode conversion structure 10 is 100 nm (determined using the finite time-domain difference method described above).

[0081] By using periodic capacitive load electrodes, when the distance between the traveling-wave signal electrode and the traveling-wave ground electrode is large, the T-shaped metal electrode configuration can reduce the distance between the electrode and the waveguide while reducing microwave losses. This achieves better electric field loading, better modulation of the silicon-lithium niobate hybrid optical waveguide, and lower electro-optical modulation efficiency (half-wave voltage times length product). Furthermore, the periodic capacitive load electrodes reduce the phase velocity of the microwave signal, enabling microwave slow-wave transmission. When matched with the optical wave group velocity, this helps achieve high-bandwidth performance.

[0082] The group refractive index of the amorphous silicon-lithium niobate hybrid optical waveguide is obtained by finite difference characteristic mode solution, and the microwave effective refractive index is obtained by finite element method. Figure 6 As shown, the calculated light group refractive index and the microwave effective refractive index maintain a good match within the microwave signal frequency range of 0-120 GHz.

[0083] By controlling the distance between the traveling wave signal electrode and the traveling wave ground electrode, we can obtain Figure 7 The microwave loss is less than 7dB / cm within 120GHz and less than 5dB / cm within 100GHz. Compared with the microwave loss of conventional thin-film lithium niobate electro-optical modulators, which is basically less than 6.5dB / cm within 100GHz, the present invention effectively reduces microwave loss. Figure 8 As shown, under the conditions of ensuring impedance matching between the periodic capacitive load electrode and the terminal load impedance, matching the effective refractive index of the microwave signal with the refractive index of the optical signal group, low microwave loss, a half-wave voltage of 3V, and a modulator length of 1.1cm, the electro-optical bandwidth calculated based on the traveling-wave modulator frequency response exceeds 100GHz. Compared to conventional thin-film lithium niobate electro-optical modulators with an electro-optical modulation efficiency (half-wave voltage times length product) of less than or equal to 3.3V·cm, the electro-optical bandwidth of the present invention is improved, with a 3dB electro-optical bandwidth roll-off of less than 2dB within 67GHz.

[0084] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An amorphous silicon-lithium niobate hybrid integrated electro-optical modulator, characterized in that: The integrated electro-optic modulator comprises, from bottom to top, a silicon substrate layer (1), a buried oxide layer (2), and an electro-optic modulation device layer; The electro-optical modulation device layer includes, from bottom to top, a waveguide layer, a buffer layer (6) and a metal electrode layer; The waveguide layer includes, from left to right, a thin-film lithium niobate input waveguide (7), a first thin-film lithium niobate optical splitting structure, two parallel amorphous silicon-lithium niobate hybrid optical waveguides (11), a second thin-film lithium niobate optical splitting structure and a thin-film lithium niobate output waveguide (8) connected in sequence, and the first thin-film lithium niobate optical splitting structure and the second thin-film lithium niobate optical splitting structure are both connected to the two parallel amorphous silicon-lithium niobate hybrid optical waveguides (11) through a thin-film lithium niobate waveguide (4); wherein the amorphous silicon-lithium niobate hybrid optical waveguide (11) is formed by depositing amorphous silicon with a thickness of 30-70 nm on the thin-film lithium niobate waveguide; the waveguide layer also includes two amorphous silicon wedge waveguide optical mode conversion structures (10), which are respectively arranged at the input end and the output end of the amorphous silicon-lithium niobate hybrid optical waveguide (11) and are connected to the thin-film lithium niobate waveguide (4); The metal electrode layer includes a traveling wave signal electrode (12), two traveling wave grounding electrodes (13) and a plurality of T-structure electrodes (14); the projection position of the traveling wave signal electrode (12) on the waveguide layer is between two parallel amorphous silicon-lithium niobate hybrid optical waveguides (11); the projection positions of the two traveling wave grounding electrodes (13) on the waveguide layer are respectively outside the two parallel amorphous silicon-lithium niobate hybrid optical waveguides (11); the T-structure electrodes are connected to the side surfaces of the traveling wave signal electrode (12) and the traveling wave grounding electrode (13) facing the amorphous silicon-lithium niobate hybrid optical waveguide (11) through longitudinal arms.

2. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, characterized in that: The amorphous silicon wedge waveguide optical mode conversion structure (10) is formed by depositing an amorphous silicon layer (5) on a thin-film lithium niobate waveguide, and the width of the amorphous silicon wedge waveguide optical mode conversion structure (10) changes from narrow to wide along the direction of connecting the amorphous silicon-lithium niobate hybrid optical waveguide (11), until the width of the amorphous silicon wedge waveguide optical mode conversion structure (10) is consistent with the width of the connection surface of the amorphous silicon-lithium niobate hybrid optical waveguide (11).

3. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, wherein: The T-structure electrode (14) includes an equal number of positive T-shaped electrodes and inverted T-shaped electrodes; The positive T-shaped electrode and the inverted T-shaped electrode are respectively arranged on the side surfaces of the traveling wave signal electrode (12) and the traveling wave ground electrode (13) on both sides of the amorphous silicon-lithium niobate hybrid optical waveguide (11) through longitudinal arms, so that the positive T-shaped electrode and the inverted T-shaped electrode are symmetrically arranged between the traveling wave signal electrode (12) and the traveling wave ground electrode (13) based on the amorphous silicon-lithium niobate hybrid optical waveguide (11).

4. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, wherein: The buffer layer (6) is selected from a medium with a refractive index less than 2 and has a thickness of 0.1-3 μm.

5. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, wherein: The thin film lithium niobate waveguide (4) is formed based on half etching of a thin film lithium niobate layer (3); wherein the thin film lithium niobate layer (3) is located on the upper layer of the buried oxide layer (2), and the thickness of the thin film lithium niobate layer (3) is 360-600 nm.

6. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, wherein: The thickness of the metal electrode layer is 0.2-1.4 μm; The width of the traveling wave signal electrode (12) is 30-40 μm; The traveling wave ground electrode (13) has a width of 50-100 μm; The distance between the traveling wave signal electrode (12) and the traveling wave ground electrode (13) is 10-25 μm.

7. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, wherein: The cross arm length of the T-structure electrode (14) is 40-45 μm, and the width is 1-5 μm.

8. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, wherein: The traveling wave signal electrode (12) and the traveling wave grounding electrode (13) are coplanar traveling wave distributed electrode structures.

9. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, wherein: The amorphous silicon-lithium niobate hybrid optical waveguide (11) is formed by evaporating amorphous silicon on a thin film lithium niobate waveguide; Alternatively, the amorphous silicon-lithium niobate hybrid optical waveguide (11) is formed by depositing amorphous silicon on the thin film lithium niobate waveguide and then performing photolithographic etching; wherein the photolithographic etching is full etching.

10. The amorphous silicon-lithium niobate hybrid integrated electro-optic modulator according to claim 1, characterized in that: The thin film lithium niobate optical beam splitting structure (9) is a Y-type splitter, an MMI-type splitter or a directional coupler-type splitter.

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