Broadband thin film lithium niobate electro-optic modulator based on phase compensation and preparation method thereof

Abstract

This invention belongs to the fields of optical fiber communication and integrated photonics, and discloses a broadband thin-film lithium niobate electro-optic modulator based on phase compensation and its fabrication method, comprising: a silicon substrate; a silicon dioxide buried oxide layer disposed on top of the silicon substrate; a lithium niobate optical waveguide disposed on top of the silicon dioxide buried oxide layer for transmitting optical waveguide signals and extending the transmission time of the optical waveguide signals to compensate for phase mismatch of microwave-modulated optical waves; an optical waveguide cladding disposed on the top outer side of the lithium niobate optical waveguide for protecting the lithium niobate optical waveguide and serving as an optical buffer layer to achieve optical buffering between the optical waveguide signals and metal electrodes; and segmented traveling-wave electrodes disposed on top of the lithium niobate optical waveguide and configured in conjunction with the lithium niobate optical waveguide, enabling alternating electro-optic interactions between the microwave signals and the optical waveguide signals through the segmented traveling-wave electrodes. This invention can accurately compensate for the phase mismatch accumulated in the modulation region of a straight waveguide.

Description

Technical Field

[0001] This invention relates to the fields of optical fiber communication and integrated photonics, and particularly to a broadband thin-film lithium niobate electro-optic modulator based on phase compensation and its fabrication method. Background Technology

[0002] Thin-film lithium niobate, with its excellent linear electro-optic coefficient, low optical transmission loss, and good compatibility with CMOS processes, has become the core platform for next-generation high-speed electro-optic modulators. The traveling-wave electrode structure is a classic scheme for achieving broadband modulation, its core being the matching of the phase velocity of microwave and optical signals. When the microwave and optical wave speeds are inconsistent, the phase difference generated during their propagation accumulates, causing the modulation efficiency to drop sharply with increasing frequency, i.e., bandwidth limitation. Especially when the electro-optic modulation region needs to be lengthened to reduce the modulator drive voltage, the bandwidth is significantly reduced. Therefore, there is an urgent need for modulators that can flexibly compensate for velocity mismatch, alleviate the constraint between bandwidth and drive voltage, and achieve high-efficiency, high-bandwidth modulation.

[0003] However, the performance of traditional traveling-wave electrode thin-film lithium niobate electro-optic modulators is often limited by the velocity mismatch between microwaves and light waves. Specifically, when microwaves propagate through the high-dielectric-constant lithium niobate material, their effective refractive index is typically higher than the group refractive index of light waves, leading to phase mismatch during long-distance interaction. This causes the modulation efficiency to decrease sharply with increasing frequency, limiting the device's bandwidth. Furthermore, the complex slow-wave electrode structures designed to overcome this problem often introduce additional microwave losses and are subject to design complexity and small process tolerances.

[0004] Therefore, how to provide a broadband thin-film lithium niobate electro-optic modulator based on phase compensation is an urgent problem to be solved. Summary of the Invention

[0005] This invention provides a broadband thin-film lithium niobate electro-optic modulator based on phase compensation and its fabrication method to solve the above-mentioned technical problems in the prior art.

[0006] According to a first aspect of the present invention, a broadband thin-film lithium niobate electro-optic modulator based on phase compensation is provided.

[0007] In one embodiment, a broadband thin-film lithium niobate electro-optic modulator based on phase compensation includes: a silicon substrate; a silicon dioxide buried oxide layer disposed on top of the silicon substrate; a lithium niobate optical waveguide disposed on top of the silicon dioxide buried oxide layer for transmitting optical waveguide signals and extending the transmission time of optical waveguide signals to compensate for phase mismatch of microwave modulated optical waves; an optical waveguide cladding disposed on the top outer side of the lithium niobate optical waveguide for protecting the lithium niobate optical waveguide and serving as an optical buffer layer to achieve optical buffering between the optical waveguide signals and the metal electrodes; and a segmented traveling-wave electrode disposed on top of the lithium niobate optical waveguide and configured in conjunction with the lithium niobate optical waveguide, through which the microwave signals and the optical waveguide signals alternately undergo electro-optic interaction.

[0008] In one embodiment, the lithium niobate optical waveguide includes: a multimode interference coupler symmetrically disposed at the top of the buried oxide layer of silicon dioxide for splitting or combining optical waveguide signals; a plurality of lithium niobate straight optical waveguides disposed between two sets of multimode interference couplers, wherein the optical waveguide signals in the lithium niobate straight optical waveguides extend in a straight line for electro-optic modulation; and a lithium niobate bent optical waveguide disposed between two adjacent sets of lithium niobate straight optical waveguides for increasing the transmission path length of the optical waveguide signals and compensating for the accumulated phase mismatch between the microwave signals and the optical waveguide signals.

[0009] In one embodiment, the lithium niobate optical bending waveguide has a U-shaped or arc-shaped structure.

[0010] In one embodiment, the bending radius R of the lithium niobate optical bending waveguide ranges from 100µm to 200µm.

[0011] In one embodiment, the segmented traveling-wave electrode includes: a plurality of straight waveguide modulation regions disposed on both sides of the lithium niobate optical straight waveguide, wherein the microwave field and the optical field in the straight waveguide modulation regions interact electro-optically; and a curved waveguide delay compensation region disposed between two adjacent sets of straight waveguide modulation regions, wherein additional time delay accumulation of the optical waveguide signal is achieved in the curved waveguide delay compensation region to compensate for the phase lead generated by the previous straight waveguide modulation region.

[0012] In one embodiment, the geometric path length of the lithium niobate optical curved waveguide is greater than the equivalent path length of microwave signal transmission within the delay compensation region of the curved waveguide.

[0013] In one embodiment, the relationship between the length of the straight waveguide modulation region and the optical delay of the curved waveguide delay compensation region is expressed as follows:

[0014] ;

[0015] In the formula, ΔL represents the optical delay introduced by the delay compensation region of the curved waveguide; v gRepresents the group velocity of light; L represents the length of the modulation region in the straight waveguide; v m This indicates the microwave phase velocity.

[0016] In one embodiment, the curved waveguide delay compensation region is bridged by an air bridge structure to form the vertical distance between the electrode in the curved waveguide delay compensation region and the lithium niobate optical curved waveguide, thereby enabling the separate transmission of microwave signals and optical waveguide signals.

[0017] In one embodiment, the segmented traveling wave electrode is a coplanar waveguide electrode, which includes a central signal electrode and ground electrodes distributed on both sides of the central signal electrode.

[0018] According to a second aspect of the present invention, a method for fabricating a broadband thin-film lithium niobate electro-optic modulator based on phase compensation is provided.

[0019] In one embodiment, the fabrication method of the phase-compensated broadband thin-film lithium niobate electro-optic modulator includes:

[0020] A silicon dioxide buried oxide layer is grown on a silicon substrate by thermal oxidation, and a single-crystal lithium niobate thin film is bonded on the silicon dioxide buried oxide layer by ion beam or wafer bonding process.

[0021] Optical waveguide patterns are defined on lithium niobate thin films using electron beam lithography or deep ultraviolet lithography, and lithium niobate thin films are etched using inductively coupled plasma to form lithium niobate optical waveguides.

[0022] An optical waveguide cladding is applied over a lithium niobate optical waveguide using spin coating or chemical vapor deposition processes.

[0023] Electrodes of the straight waveguide modulation region were covered above the straight waveguide of lithium niobate optical waveguide by photolithography and magnetron sputtering.

[0024] A sacrificial layer material is deposited on top of the bent lithium niobate optical waveguide in the lithium niobate optical waveguide. The sacrificial layer material is then photolithographically lithographically deposited with metal electrodes, and the sacrificial layer is removed by wet etching or dry etching to construct an air bridge structure.

[0025] After the segmented traveling wave electrode is fabricated, a polished end face is made through a grinding and polishing process to form a phase-compensated broadband thin-film lithium niobate electro-optic modulator.

[0026] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0027] 1. This invention employs a segmented traveling-wave electrode structure, alternating between the electric field modulation region and the air bridge bridging region. In the electric field modulation region, corresponding to the straight waveguide region, efficient electro-optic interaction occurs; in the air bridge region, corresponding to the curved waveguide region, the electrodes are bridged by air bridges, and no modulation occurs. This allows the light wave to actively "wait" for the microwave in each air bridge region, ensuring that the light wave and microwave resynchronize phase when entering the next modulation region. The synergistic effect of these two mechanisms enables efficient electro-optic interaction within a finite length, significantly improving modulation efficiency and reducing the half-wave voltage-length product.

[0028] 2. This invention employs a segmented lithium niobate optical waveguide structure, dividing a long electro-optic modulation region into multiple short modulation regions. The accumulated phase difference within each straight short modulation region is small, and the delay region of the curved waveguide is parameterized, enabling precise optical path increment control within a limited chip area while ensuring low bending loss. This periodic modulation, reset, and remodulation structure effectively avoids the continuous accumulation of phase difference, keeping the phase mismatch between microwaves and light waves within a minimal range over the entire device length. This overcomes the speed mismatch limitations of traditional long modulation structures, facilitating the achievement of ultra-wide electro-optic modulation bandwidth.

[0029] 3. This invention eliminates the need for complex slow-wave electrodes or photonic crystal slow waveguide structures, resulting in a simple structure that is compatible with traditional thin-film lithium niobate fabrication processes. Furthermore, this structure avoids the additional microwave and optical transmission losses associated with traditional slow-wave designs. While achieving high modulation efficiency and high bandwidth, it maintains low insertion loss and drive power consumption, effectively resolving the inherent contradiction between modulation efficiency, bandwidth, and loss—key modulator performance metrics that are difficult to balance.

[0030] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0031] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0032] Figure 1 This is a cross-sectional view of the electro-optic interaction region of a phase-compensated broadband thin-film lithium niobate electro-optic modulator according to an exemplary embodiment;

[0033] Figure 2 This is a plan view of a phase-compensated broadband thin-film lithium niobate electro-optic modulator according to an exemplary embodiment;

[0034] Figure 3 This is a schematic flowchart illustrating a method for fabricating a phase-compensated broadband thin-film lithium niobate electro-optic modulator according to an exemplary embodiment.

[0035] Figure label:

[0036] 1. Lithium niobate optical waveguide; 11. Lithium niobate straight optical waveguide; 12. Lithium niobate bent optical waveguide; 2. Segmented traveling wave electrode; 3. Optical waveguide cladding; 4. Multimode interference coupler; 5. Silica buried oxide layer; 6. Silicon substrate. Detailed Implementation

[0037] The following description and accompanying drawings fully illustrate specific embodiments described herein to enable those skilled in the art to practice them. Some portions and features of certain embodiments may be included in or replace portions and features of other embodiments. The scope of the embodiments herein includes the entire scope of the claims and all available equivalents thereof. The various embodiments described herein are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0038] The modules in the apparatus or system of this application can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0039] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0040] Figure 1 and Figure 2 An embodiment of the phase-compensated broadband thin-film lithium niobate electro-optic modulator of the present invention is shown.

[0041] In this optional embodiment, the broadband thin-film lithium niobate electro-optic modulator based on phase compensation includes: a silicon substrate 6; a silicon dioxide buried oxide layer 5 disposed on the top of the silicon substrate 6; a lithium niobate optical waveguide 1 disposed on the top of the silicon dioxide buried oxide layer 5, used to realize the transmission of optical waveguide signals and extend the transmission time of optical waveguide signals to compensate for the phase mismatch of microwave modulated optical waves; an optical waveguide cladding 3 disposed on the top outer side of the lithium niobate optical waveguide 1, used to protect the lithium niobate optical waveguide 1, and the optical waveguide cladding 3 serves as an optical buffer layer to realize the optical buffer between the optical waveguide signal and the metal electrode; and a segmented traveling wave electrode 2 disposed on the top of the lithium niobate optical waveguide 1 and configured in conjunction with the lithium niobate optical waveguide 1, so that the microwave signal and the optical waveguide signal alternately undergo electro-optic interaction through the segmented traveling wave electrode 2.

[0042] In this optional embodiment, the lithium niobate optical waveguide 1 includes: a multimode interference coupler 4, symmetrically disposed at the top of the silicon dioxide buried oxide layer 5, used to split or combine the optical waveguide signal; a plurality of lithium niobate straight optical waveguides 11, disposed between two sets of multimode interference couplers 4, wherein the optical waveguide signal in the lithium niobate straight optical waveguide 11 extends in a straight line, used to realize electro-optic modulation; and a lithium niobate bent optical waveguide 12, disposed between two adjacent sets of lithium niobate straight optical waveguides 11, used to increase the transmission path length of the optical waveguide signal and realize compensation for the cumulative phase mismatch between the microwave signal and the optical waveguide signal.

[0043] In this optional embodiment, the lithium niobate optical bending waveguide 12 has a U-shaped or arc-shaped structure.

[0044] In this optional embodiment, the bending radius R of the lithium niobate optical bending waveguide 12 is in the range of 100um≤R≤200um.

[0045] In this optional embodiment, the segmented traveling wave electrode 2 includes: several straight waveguide modulation regions disposed on both sides of the lithium niobate optical straight waveguide 11, in which the microwave field and the optical field interact electro-optically; and a curved waveguide delay compensation region disposed between two adjacent sets of straight waveguide modulation regions, in which additional time delay accumulation of the optical waveguide signal is achieved to compensate for the phase lead generated by the previous straight waveguide modulation region.

[0046] In this optional embodiment, the geometric path length of the lithium niobate optical curved waveguide 12 is greater than the equivalent path length of microwave signal transmission within the delayed compensation region of the curved waveguide.

[0047] In this optional embodiment, the relationship between the length of the straight waveguide modulation region and the optical delay of the curved waveguide delay compensation region is expressed as follows:

[0048] ;

[0049] In the formula, ΔL represents the optical delay introduced by the delay compensation region of the curved waveguide; v g Represents the group velocity of light; L represents the length of the modulation region in the straight waveguide; v m This indicates the microwave phase velocity.

[0050] In this optional embodiment, the curved waveguide delay compensation region is bridged by an air bridge structure to form the vertical distance between the electrode in the curved waveguide delay compensation region and the lithium niobate optical curved waveguide 12, so as to realize the separate transmission of microwave signals and optical waveguide signals.

[0051] In this optional embodiment, the segmented traveling wave electrode 2 is a coplanar waveguide electrode, which includes a central signal electrode and ground electrodes distributed on both sides of the central signal electrode.

[0052] Figure 3 An embodiment of the fabrication method of the broadband thin-film lithium niobate electro-optic modulator based on phase compensation of the present invention is shown.

[0053] In this optional embodiment, the fabrication method of the broadband thin-film lithium niobate electro-optic modulator based on phase compensation includes:

[0054] Step S101: A silicon dioxide buried oxide layer 5 is grown on a silicon substrate 6 by thermal oxidation process, and a single crystal lithium niobate thin film is bonded on the silicon dioxide buried oxide layer 5 by ion beam or wafer bonding process.

[0055] Step S102: Define the optical waveguide pattern on the lithium niobate thin film using electron beam lithography or deep ultraviolet lithography, and then use inductively coupled plasma etching to form the lithium niobate optical waveguide 1.

[0056] Step S103: Using spin coating or chemical vapor deposition, cover the optical waveguide cladding 3 on top of the lithium niobate optical waveguide 1;

[0057] Step S104: By photolithography and magnetron sputtering, electrodes of the straight waveguide modulation region are covered above the straight waveguide 11 of the lithium niobate optical waveguide 1.

[0058] Step S105: Deposit a sacrificial layer material on the bent lithium niobate optical waveguide 12 in the lithium niobate optical waveguide 1, perform photolithography and deposition of metal electrodes on the sacrificial layer material, and remove the sacrificial layer by wet etching or dry etching to construct an air bridge structure.

[0059] Step S106: After completing the processing of the segmented traveling wave electrode 2, a polished end face is made by grinding and polishing process to form a phase-compensated broadband thin-film lithium niobate electro-optic modulator.

[0060] To facilitate understanding of the above technical solutions of the present invention, the following further explains the above technical solutions of the present invention from the perspective of architecture and principle, as follows:

[0061] It should be further explained that the lithium niobate optical waveguide 1 consists of a lithium niobate waveguide core and a silicon dioxide or polymer cladding, used to realize optical transmission. The required optical waveguide is formed by dry etching or proton exchange process. The multimode interference coupler 4 is used for beam splitting or beam combining of light. In practical applications, the multimode interference coupler 4 can be selected as a 1×2 multimode interference coupler, i.e., 1×2 MMI, for beam splitting or beam combining of light. The input light is split by a 1×2 MMI and enters two modulation arms. After electro-optic modulation and delay-based phase compensation matching, it is then combined and output by another 1×2 MMI. The segmented traveling-wave electrode 2 structure alternately arranges straight waveguide modulation region and curved waveguide delay compensation region along the optical wave propagation direction. That is, the segmented traveling-wave electrode 2 includes a straight waveguide modulation region and a curved waveguide phase compensation region, i.e., a curved waveguide delay compensation region. In the straight waveguide modulation region, the waveguide in the optical waveguide layer extends in a straight line, and the segmented traveling-wave electrode 2 is located on both sides of the waveguide, where the microwave field and the optical field undergo efficient electro-optic interaction. In the curved waveguide phase compensation region, the waveguide in the optical waveguide layer is a curved waveguide segment. In this region, the segmented traveling-wave electrode is connected by an air bridge, and the microwave and optical waves are transmitted separately without electro-optic interaction.

[0062] The curved waveguide segment in the curved waveguide delay compensation region can be a U-shaped, arc-shaped, or other structure to increase the transmission path length of the optical wave within a limited chip area, thereby compensating for the phase mismatch of the microwave-modulated optical wave. The radius of curvature R of the curved waveguide segment satisfies 100um≤R≤200um, enabling precise optical path increment control within a limited chip area while ensuring low bending loss. The optical wave propagates along the curved path, while the microwave propagates along a straight or approximately straight path via an air bridge structure. The two are spatially separated and interact only within the straight waveguide modulation region.

[0063] The segmented traveling wave electrode 2 is a coplanar waveguide electrode, including a central signal electrode and two ground electrodes distributed on both sides of it.

[0064] The length L of the straight waveguide modulation region and the optical delay ΔL introduced by the curved waveguide delay compensation region satisfy the following relationship:

[0065] ;

[0066] Among them, v g v is the group velocity of light. m The microwave phase velocity is such that the extra time delay accumulated by the light wave in each curved waveguide delay compensation region exactly compensates for the phase lead generated in the previous straight waveguide modulation region. Therefore, the light wave and microwave re-synchronize when entering the next straight waveguide modulation region, begin efficient modulation, repeat the above process, and output a microwave-modulated optical signal.

[0067] More specifically, this invention relates to a technique for efficient electro-optic modulation using a straight waveguide modulation region and for compensating for modulation accumulation phase mismatch by utilizing the optical delay of a curved waveguide. The phase mismatch caused by long electro-optic interactions is compensated and canceled through a clever segmented design, resulting in a high-bandwidth, high-efficiency thin-film lithium niobate electro-optic modulator that achieves precise speed matching between microwaves and optical waves, suitable for next-generation high-speed optical communication networks.

[0068] In view of this, one of the main objectives of this invention is to propose a broadband thin-film lithium niobate electro-optic modulator based on phase compensation. The long electro-optic modulator region is segmented, and each segment consists of a straight waveguide and a curved waveguide. High-efficiency electro-optic modulation is performed through the straight waveguide. In the first segment of the straight waveguide modulation region, phase mismatch between microwave and light wave accumulates. Then, the light wave actively waits for the microwave through the subsequent curved waveguide delay compensation region, thereby achieving phase compensation, and then the electro-optic modulation of the next segment is performed.

[0069] The core of this invention lies in dividing the long electro-optic modulation region into multiple straight waveguide modulation regions and curved waveguide delay compensation regions. In each curved waveguide delay compensation region, the optical path is increased to make the light wave actively wait for the microwave, thus accurately compensating for the accumulated phase mismatch between the microwave and the light wave generated in the previous straight waveguide modulation region.

[0070] The segmented waveguide structure is designed with alternating straight waveguide modulation regions and curved waveguide delay regions to achieve an active velocity matching mechanism for optical waves to wait for microwaves.

[0071] Within the straight waveguide modulation region, the optical waveguide extends in a straight line, and the signal electrode of the segmented traveling-wave electrode 2 completely covers this region. The radio frequency modulation signal acts on the lithium niobate waveguide through the cladding, utilizing the linear electro-optic effect of lithium niobate, i.e., the Pockels effect, to modulate the intensity of the light wave.

[0072] Within the curved waveguide delay compensation region, the optical waveguide is a carefully designed curved waveguide, such as a U-shaped or arc-shaped structure, with a curvature radius R satisfying 100µm ≤ R ≤ 200µm, to maximize the optical path length and ensure low loss within a limited area. Simultaneously, the electrodes in this region are connected by air bridges to ensure continuous microwave signal transmission while the underlying optical waveguide remains unaffected by the modulation electric field.

[0073] The principle is based on the assumption that within the modulation region of a straight waveguide, the group velocity v of the light wave is... g Slightly faster than microwave phase velocity v m That is, v g Greater than v m After a length L, the microwave phase lags behind the light wave. In the subsequent curved waveguide delay compensation region, the microwave propagates along a straight, or approximately straight, equivalent path via an air bridge, while the light wave propagates along the curved waveguide segment. Let the geometric path length of the curved waveguide segment be L. delay The microwave equivalent path length corresponding to this region is L.mw It is typically approximately equal to the linear projection length of the region. By designing L... delay >L mw The propagation time t of light waves in this region opt =L delay / v g The transmission time t_ is greater than that of microwaves mv =L_ mw / v_ m The additional time Δt = t opt -t mv Precisely designed to match the phase lead time generated by the previous modulation region, phase compensation is achieved. Therefore, when the light wave exits the curved waveguide delay compensation region and enters the next straight waveguide modulation region, it achieves perfect phase synchronization with the arriving microwave signal. This process repeats, through modulation, reset, and remodulation cycles, ensuring that the light wave actively waits for the microwave in each delay region, maintaining phase compensation throughout the entire device length.

[0074] Preferably, the length L of the straight waveguide modulation region is equal to the optical delay ΔL introduced by the curved waveguide delay compensation region. delay -L mw It needs to be based on the actual measured v g With v m A precise design is required to satisfy the following relationships:

[0075] ;

[0076] The above design enables zero net accumulation of residual velocity mismatch.

[0077] By utilizing the increased transmission time of light waves in a curved path, the light waves actively wait for microwaves, thereby accurately compensating for the phase difference between microwaves and light waves accumulated in the modulation region of a straight waveguide.

[0078] The optical waveguide cladding 3 acts on the lithium niobate optical waveguide 1, alleviating the velocity mismatch between microwaves and light waves. Simultaneously, through the design of the lithium niobate optical bend waveguide 12 within the structure of the lithium niobate optical waveguide 1, the light wave actively waits for the microwave, precisely compensating for the phase advance accumulated in the previous waveguide modulation region. The synergistic effect of these two mechanisms achieves near-perfect velocity matching while effectively reducing modulation power consumption.

[0079] like Figure 1 As shown, a cross-sectional view of the electro-optic interaction region of the broadband thin-film lithium niobate electro-optic modulator based on phase compensation in this embodiment is provided. Figure 2 As shown, a schematic diagram of the modulator in this embodiment is provided.

[0080] A silicon dioxide buried oxide layer 5 is grown on a silicon substrate 6 using a thermal oxidation process. A single-crystal lithium niobate thin film is bonded to the silicon dioxide buried oxide layer 5 using ion beam bonding or wafer bonding. An optical waveguide pattern is defined on the lithium niobate thin film using electron beam lithography or deep ultraviolet lithography, and the lithium niobate thin film is etched using inductively coupled plasma to form a lithium niobate optical waveguide 1. The lithium niobate optical waveguide 1 includes a straight lithium niobate optical waveguide 11 and a bent lithium niobate optical waveguide 12. The radius of curvature R of the bent lithium niobate optical waveguide 12 satisfies 100µm ≤ R ≤ 200µm to ensure low... Bending loss; an optical waveguide cladding 3 is coated on top of the lithium niobate optical waveguide 1 using spin coating or chemical vapor deposition; segmented traveling-wave electrodes 2 are fabricated on top of the optical waveguide cladding 3 using photolithography and magnetron sputtering. The segmented traveling-wave electrodes 2 are alternately arranged along the optical wave propagation direction. In the straight waveguide modulation region, the electrodes cover the lithium niobate straight waveguide 11, and in the bent waveguide delay compensation region, they are bridged by an air bridge structure. The air bridge structure is formed using a sacrificial layer process, ensuring a certain vertical distance between the electrodes in the bent waveguide delay compensation region and the underlying lithium niobate bent waveguide 12. The air bridge structure is formed through the following steps: depositing a sacrificial layer material, such as photoresist or silicon dioxide, on top of the lithium niobate bent waveguide 12, followed by photolithography and deposition of metal electrodes, and finally removing the sacrificial layer by wet etching or dry etching to form the air bridge bridging structure.

[0081] In practical applications, the specific steps for fabricating a broadband thin-film lithium niobate electro-optic modulator based on phase compensation are as follows: Step 1: Deposit an 800nm ​​thick silicon dioxide mask layer on an LNOI wafer using PECVD, and then etch the mask pattern using patterning and dry etching processes; Step 2: Etch LN using an ICP-RIE device, with Ar and CHF3 gases used for etching, and the etching depth is half the film thickness. After dry etching, chemical polishing cleaning is performed using an RCA solution with NH3:H2O2:H2O = 1:1:5 at a solution temperature of 50℃ for 20 minutes to remove residual etching byproducts on the waveguide sidewalls, forming a ridged optical waveguide with smooth sidewalls, containing optical input / output waveguides and a phase-modulated lithium niobate optical straight waveguide. The process includes: Step 3: PECVD deposition of a 1000nm thick silicon dioxide cladding layer for the waveguide, i.e., the optical waveguide cladding layer 3; Photolithography combined with dry etching of silicon dioxide to remove the silicon oxide cladding layer of the segmented traveling wave electrode 2 to be deposited, wherein the silicon oxide cladding layer of the segmented traveling wave electrode 2 across the lithium niobate optical waveguide 12 is retained, so that the overlap area between the electrode and the waveguide forms an air bridge to avoid light absorption loss caused by metal; Step 4: Photolithography to overlay electrode pattern, evaporation of a 50nm thick Ti adhesion layer and a 900nm thick Au electrode by electron beam, and then peeling to form the target pattern electrode; Step 5: The sample obtained in the above steps is polished by grinding and polishing process to form a polished end face, forming a complete phase-compensated electro-optic modulator.

[0082] During operation, a continuous laser is coupled into the lithium niobate optical waveguide 1, where it is split into two beams by a 1×2 MMI. These beams then enter two modulation arms, undergo modulation and delay matching, and are then combined and output through another 1×2 MMI. A high-speed radio frequency (RF) signal is applied to the segmented traveling-wave electrode 2. In the straight waveguide modulation region, the RF electric field acts on the lithium niobate optical waveguide 1 through the waveguide cladding 3, modulating the light wave. Because the waveguide cladding 3 reduces the effective refractive index of the microwave, the propagation speeds of the microwave and light wave become closer. After passing through the straight waveguide modulation region, the microwave phase lags slightly behind the light wave. Subsequently, both enter the curved waveguide delay compensation region. When the light wave emerges from the lithium niobate curved waveguide 12, it resynchronizes with the microwave, which has just arrived via a straight path, and enters the next straight waveguide modulation region for efficient interaction. After multiple such cycles, low-voltage, high-bandwidth modulation of the entire light wave is ultimately achieved.

[0083] In summary, the broadband thin-film lithium niobate electro-optic modulator based on phase compensation includes a segmented lithium niobate optical waveguide 1, a segmented traveling-wave electrode 2, and a 1×2 MMI. The 1×2 MMI is used for beam splitting or combining; the lithium niobate optical waveguide 1 is used for optical signal transmission; the segmented traveling-wave electrode 2 has alternating straight waveguide modulation regions and curved waveguide delay compensation regions along the light propagation direction. In the straight waveguide modulation region, the microwave signal and the light wave undergo efficient electro-optic interaction, but because the light wave travels faster than the microwave wave, a large phase mismatch accumulates between them after a certain modulation length, leading to a decrease in modulation bandwidth. In the curved waveguide delay compensation region, the segmented traveling-wave electrode 2 is bridged by an air bridge structure, preventing electro-optic interaction. Specifically, the geometric path length of the lithium niobate optical curved waveguide 12 is configured to be greater than the equivalent path length of microwave signal transmission within the delay compensation region of the curved waveguide. Utilizing the increased propagation time of the light wave in the curved path, the light wave actively waits for the microwave, thereby accurately compensating for the phase mismatch accumulated in the modulation region of the straight waveguide. This significantly improves the modulation bandwidth while achieving long-distance electro-optical interaction in segments, achieving compatibility between the modulator's wide bandwidth and low driving voltage. The electro-optic modulator of this invention is suitable for next-generation high-speed optical communication networks, especially modulation scenarios in 400G+ coherent communication, data center optical interconnects, and high-end integrated photonic chips.

[0084] This invention is not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this invention is limited only by the appended claims.

Claims

1. A broadband thin-film lithium niobate electro-optic modulator based on phase compensation, characterized in that, include: Silicon substrate (6); A silicon dioxide buried oxide layer (5) is disposed on the top of the silicon substrate (6); A lithium niobate optical waveguide (1) is disposed at the top of the buried oxide layer (5) of silicon dioxide to realize the transmission of optical waveguide signals and extend the transmission time of optical waveguide signals, thereby compensating for the phase mismatch of microwave modulated optical waves. The optical waveguide cladding (3) is disposed on the top outer side of the lithium niobate optical waveguide (1) to protect the lithium niobate optical waveguide (1) and to serve as an optical buffer layer to achieve optical buffering between the optical waveguide signal and the metal electrode; A segmented traveling wave electrode (2) is disposed on the top of the lithium niobate optical waveguide (1) and is configured in conjunction with the lithium niobate optical waveguide (1). The segmented traveling wave electrode (2) enables the microwave signal and the optical waveguide signal to alternately interact electro-optically.

2. The broadband thin-film lithium niobate electro-optic modulator based on phase compensation according to claim 1, characterized in that, The lithium niobate optical waveguide (1) includes: A multimode interference coupler (4) is symmetrically arranged at the top of the buried oxide layer (5) of silicon dioxide to realize the splitting or combining of optical waveguide signals; Several lithium niobate optical straight waveguides (11) are disposed between the two sets of multimode interference couplers (4). The optical waveguide signal in the lithium niobate optical straight waveguides (11) extends in a straight line to realize electro-optic modulation. A lithium niobate optical bend waveguide (12) is disposed between two adjacent sets of lithium niobate optical straight waveguides (11) to increase the transmission path length of the optical waveguide signal and to compensate for the cumulative phase mismatch between the microwave signal and the optical waveguide signal.

3. The broadband thin-film lithium niobate electro-optic modulator based on phase compensation according to claim 2, characterized in that, The lithium niobate optical bending waveguide (12) has a U-shaped or arc-shaped structure.

4. The broadband thin-film lithium niobate electro-optic modulator based on phase compensation according to claim 3, characterized in that, The bending radius R of the lithium niobate optical bending waveguide (12) is in the range of 100um≤R≤200um.

5. The broadband thin-film lithium niobate electro-optic modulator based on phase compensation according to claim 4, characterized in that, The segmented traveling wave electrode (2) includes: Several straight waveguide modulation regions are disposed on both sides of the lithium niobate optical straight waveguide (11), and the microwave field and the optical field in the straight waveguide modulation regions undergo electro-optic interaction; A curved waveguide delay compensation region is set between two adjacent groups of straight waveguide modulation regions. In the curved waveguide delay compensation region, additional time delay accumulation of the optical waveguide signal is achieved to compensate for the phase lead generated by the previous straight waveguide modulation region.

6. The broadband thin-film lithium niobate electro-optic modulator based on phase compensation according to claim 5, characterized in that, The geometric path length of the lithium niobate optical curved waveguide (12) is greater than the equivalent path length of microwave signal transmission within the delay compensation region of the curved waveguide.

7. The broadband thin-film lithium niobate electro-optic modulator based on phase compensation according to claim 6, characterized in that, The relationship between the length of the straight waveguide modulation region and the optical delay of the curved waveguide delay compensation region is expressed as follows: ； In the formula, ΔL represents the optical delay introduced by the curved waveguide delay compensation region; v g Represents the group velocity of light; L represents the length of the straight waveguide modulation region; v m This indicates the microwave phase velocity.

8. The broadband thin-film lithium niobate electro-optic modulator based on phase compensation according to claim 7, characterized in that, The curved waveguide delay compensation region is connected by an air bridge structure to form the vertical distance between the electrode in the curved waveguide delay compensation region and the lithium niobate optical curved waveguide (12), so as to realize the separate transmission of microwave signals and optical waveguide signals.

9. The broadband thin-film lithium niobate electro-optic modulator based on phase compensation according to claim 8, characterized in that, The segmented traveling wave electrode (2) is a coplanar waveguide electrode, which includes a central signal electrode and ground electrodes distributed on both sides of the central signal electrode.

10. A method for fabricating a broadband thin-film lithium niobate electro-optic modulator based on phase compensation, used to realize the fabrication of the broadband thin-film lithium niobate electro-optic modulator based on phase compensation as described in claim 9, characterized in that, The preparation method includes: A silicon dioxide buried oxide layer (5) is grown on a silicon substrate (6) by a thermal oxidation process, and a single-crystal lithium niobate thin film is bonded on the silicon dioxide buried oxide layer (5) by an ion beam or wafer bonding process. The optical waveguide pattern is defined on the lithium niobate thin film by electron beam lithography or deep ultraviolet lithography, and the lithium niobate thin film is etched by inductively coupled plasma to form the lithium niobate optical waveguide (1). Using spin coating or chemical vapor deposition, an optical waveguide cladding (3) is applied over the lithium niobate optical waveguide (1). Electrodes of the straight waveguide modulation region are covered above the straight waveguide (11) of the lithium niobate optical waveguide (1) by photolithography and magnetron sputtering; A sacrificial layer material is deposited on top of the bent lithium niobate optical waveguide (12) in the lithium niobate optical waveguide (1), and the sacrificial layer material is photolithographically lithographically deposited with metal electrodes. The sacrificial layer is then removed by wet etching or dry etching to construct an air bridge structure. After the segmented traveling wave electrode (2) is processed, a polished end face is made by grinding and polishing process to form a phase-compensated broadband thin-film lithium niobate electro-optic modulator.

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