A lithium niobate electro-optic modulator and a preparation method and application thereof

Abstract

This invention relates to a lithium niobate electro-optic modulator, its fabrication method, and its application. The lithium niobate electro-optic modulator, from bottom to top, comprises a ground electrode, a substrate layer, a buried oxide layer, a lithium niobate waveguide, and a high-dielectric-constant cladding. Symmetrically distributed optical isolation trenches are arranged on both sides of the lithium niobate waveguide. The high-dielectric-constant cladding includes a first cladding and a second cladding from the inside out, wherein the dielectric constant of the first cladding is less than that of the second cladding. The number of high-dielectric-constant cladding layers is ≥2. The lithium niobate electro-optic modulator also includes a signal electrode embedded within the high-dielectric-constant cladding and located above the optical isolation trenches. The synergistic effect of the optical isolation trenches and the high-dielectric-constant cladding in this invention enables the lithium niobate electro-optic modulator to possess not only high modulation efficiency but also high bandwidth. Furthermore, the lithium niobate electro-optic modulator of this invention exhibits excellent power tolerance.

Description

Technical Field

[0001] This application relates to the field of integrated optical technology, and in particular to a lithium niobate electro-optic modulator, its fabrication method, and its application. Background Technology

[0002] Electro-optic modulators are crucial components in high-speed photonic communication, serving as a "bridge" between fiber optic transmission and data centers. They transmit information by modulating the phase and amplitude of optical signals. The performance of the electro-optic modulator itself determines the system's data transmission capability. Lithium niobate (LiNbO3, LN) has become a popular material for electro-optic modulators due to its excellent electro-optic coefficient and broad-spectral transparency. The lithium niobate waveguide in electro-optic modulators has strong light confinement capabilities, allowing for a reduction in device size while lowering the modulation voltage.

[0003] Driven by emerging technologies such as 5G communication, artificial intelligence, and quantum computing, optical communication networks are undergoing a leapfrog upgrade from 400G to 800G / 1.6T ultra-high-speed optical modules. This development trend places more stringent requirements on electro-optic modulators in terms of bandwidth and modulation efficiency.

[0004] The patent with publication number CN115268122A provides a high modulation efficiency composite cladding electro-optic modulator, which improves the modulation efficiency of the electro-optic modulator by using a composite cladding, but does not focus on bandwidth.

[0005] Therefore, there is an urgent need to develop lithium niobate electro-optic modulators with high modulation efficiency and high bandwidth to meet current market demands. Summary of the Invention

[0006] The primary objective of this invention is to overcome the problems of low modulation efficiency and low bandwidth of existing lithium niobate electro-optic modulators, and to provide a lithium niobate electro-optic modulator.

[0007] A further objective of this invention is to provide a method for fabricating a lithium niobate electro-optic modulator.

[0008] Another object of the present invention is to provide the application of the above-mentioned lithium niobate electro-optic modulator in the fabrication of high-speed optical communication devices or integrated photonic chips.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution:

[0010] A lithium niobate electro-optic modulator, comprising, from bottom to top, a ground electrode, a substrate layer, a buried oxide layer, a lithium niobate waveguide, and a high dielectric constant cladding;

[0011] Symmetrically distributed optical isolation slots are provided on both sides of the lithium niobate waveguide.

[0012] The high dielectric constant cladding includes a first cladding and a second cladding from the inside out, wherein the dielectric constant of the first cladding is less than the dielectric constant of the second cladding.

[0013] The number of layers of the high dielectric constant cladding is ≥2;

[0014] The lithium niobate electro-optic modulator also includes a signal electrode, which is embedded in a high dielectric constant cladding and located above the optical isolation trench.

[0015] The inventors of this invention have discovered that the synergistic effect of the optical isolation trench and the high dielectric constant cladding in this invention enables the lithium niobate electro-optic modulator of this invention to not only have high modulation efficiency, but also high bandwidth.

[0016] The principle is as follows: a high-dielectric-constant cladding with a gradient dielectric constant (the dielectric constant of the first cladding is less than that of the second cladding) can reduce the phase mismatch between the microwave signal and the optical wave. Meanwhile, the optical isolation trench can confine the optical field to the waveguide core, and in conjunction with the embedded signal electrode, it can shorten the distance between the signal electrode and the bottom electrode, guiding the microwave electric field to be more concentrated in the optical waveguide region. The synergy of these two factors significantly improves the bandwidth of the lithium niobate electro-optic modulator. Simultaneously, the high-dielectric-constant cladding design with a gradient dielectric constant not only regulates the distribution of the optical field but also optimizes the electric field distribution. Furthermore, the optical isolation trench avoids parasitic capacitance effects in the non-modulated region by reducing electric field distortion at the signal electrode edges, thereby synergistically improving the modulation efficiency of the lithium niobate electro-optic modulator (reducing the half-wave voltage).

[0017] Furthermore, the inventors have discovered that the lithium niobate electro-optic modulator of the present invention has excellent power tolerance. The principle is that the optical isolation trench restricts the outward diffusion of the optical field, and the high dielectric cladding enhances the electric field utilization efficiency and suppresses microwave loss. The combined effect of these two factors can improve the power tolerance of the lithium niobate electro-optic modulator of the present invention.

[0018] Preferably, the optical isolation groove contains a medium.

[0019] More preferably, the refractive index of the medium is lower than that of lithium niobate, the refractive index of the first cladding material is lower than that of the lithium niobate waveguide, and the refractive index of the second cladding material is lower than that of the first cladding material.

[0020] Optical isolation trenches are introduced on both sides of the lithium niobate waveguide, and the refractive index of the medium contained in the optical isolation trenches is lower than that of the lithium niobate waveguide itself. This change in lateral refractive index effectively limits the lateral diffusion of the optical field and reduces crosstalk between adjacent waveguides. Simultaneously, by setting a refractive index gradient between the materials of the first and second cladding layers in the vertical direction, vertical leakage of the optical field can be effectively suppressed, achieving a perfect match between the optical field mode and the waveguide structure. The synergistic effect of these two methods enables the lithium niobate electro-optic modulator of this invention to suppress optical field crosstalk and thus reduce losses.

[0021] Preferably, the medium is at least one of silicon dioxide, air, or magnesium fluoride.

[0022] Preferably, the medium contains embedded nanomaterials. Embedding nanomaterials into the medium can enhance the electric field at the edge of the optical isolation trench through localized surface plasmon resonance, thereby reducing the driving voltage of the device.

[0023] More preferably, the nanomaterials are embedded in the medium in an array.

[0024] More preferably, the nanomaterial is at least one of titanium dioxide or aluminum oxide.

[0025] More preferably, the morphology of the nanomaterial is at least one of nanoparticles or nanowires.

[0026] More preferably, the average diameter of the nanoparticles is 10~150 nm.

[0027] More preferably, the average diameter of the cross-section of the nanowire is 10~50 nm, and the aspect ratio is ≥5:1.

[0028] More preferably, when the morphology of the nanomaterial in the optical isolation groove is nanoparticles, the volume ratio of the nanomaterial to the medium is (1~6):(4~9); when the morphology of the nanomaterial in the optical isolation groove is nanowires, the nanomaterial is embedded on the surface of the medium in a two-dimensional distribution, and the density of the nanomaterial is 10. 6 ~10 9 wires / cm 2 .

[0029] Preferably, the cross-section of the optical isolation groove is rectangular.

[0030] Preferably, the optical isolation groove has a depth of 0.5~5 μm and a width of 0.5~20 μm.

[0031] Preferably, the ratio of the maximum width of the cross-section of the lithium niobate waveguide to the width of the optical isolation trench is 1:(1~5).

[0032] Preferably, the high dielectric constant cladding has 2 to 4 layers.

[0033] Preferably, the dielectric constant of the first cladding layer is ≥7.5.

[0034] More preferably, the dielectric constant of the first cladding layer is 7.5 to 80.

[0035] Preferably, the difference in dielectric constant between the first cladding layer and the second cladding layer is ≥5.

[0036] Preferably, the refractive indices of the first cladding material and the second cladding material are independently ≤2.2.

[0037] Preferably, the difference in refractive index between the materials of the first cladding layer and the second cladding layer is ≥0.1.

[0038] Preferably, the thickness of the first cladding layer is 10~80 nm.

[0039] Preferably, the thickness of the second cladding layer is 10~80 nm.

[0040] Preferably, the materials of the first cladding layer and the second cladding layer are independently at least one of aluminum nitride, hafnium oxide, aluminum oxide, titanium oxide, lanthanum fluoride, or silicon nitride.

[0041] Preferably, the lithium niobate electro-optic modulator further includes a titanium oxide layer located above the high dielectric constant cladding, the titanium oxide layer covering only the non-optical field region.

[0042] Adding a titanium oxide layer can further optimize the distribution of the optical and electric fields, thereby improving the performance of the lithium niobate electro-optic modulator.

[0043] More preferably, the thickness of the titanium oxide layer is 10~50 nm.

[0044] Preferably, the thickness of the high dielectric constant cladding is 50~150 nm.

[0045] Preferably, the horizontal distance between the center of the lithium niobate waveguide and the center of the adjacent signal electrode is 1~10μm.

[0046] Preferably, the cross-section of the signal electrode is trapezoidal or T-shaped.

[0047] Preferably, the signal electrode includes a side extension structure, the width of which increases outward along the lithium niobate waveguide, with an increase of 20~50 nm / μm.

[0048] Preferably, the signal electrode consists of an adhesive layer and a conductive layer from bottom to top.

[0049] More preferably, the material of the adhesive layer is at least one of chromium or titanium.

[0050] More preferably, the conductive layer is made of at least one of gold, copper, aluminum, indium tin oxide, or graphene.

[0051] More preferably, the thickness of the conductive layer is 200~1000 nm, the thickness of the adhesive layer is 10~50 nm, and the width of the adhesive layer is 1~5 μm.

[0052] Preferably, the substrate layer is made of at least one of Si, Al2O3, quartz, or lithium niobate.

[0053] Preferably, the thickness of the substrate layer is 250~600 μm.

[0054] Preferably, the material of the buried oxide layer is at least one of SiO2, BCB or Si3N4.

[0055] Preferably, the thickness of the buried oxide layer is 1~5 μm.

[0056] Preferably, the lithium niobate waveguide has a height of 50~1000 nm and a width of 0.2~5 μm.

[0057] Preferably, the lithium niobate waveguide is a ridge waveguide or a strip waveguide.

[0058] More preferably, the cross-sectional shape of the strip waveguide is rectangular.

[0059] Preferably, the ground electrode consists of a conductive layer and an adhesive layer from bottom to top.

[0060] More preferably, the material of the adhesive layer is at least one of chromium or titanium.

[0061] More preferably, the conductive layer is made of at least one of gold, copper, aluminum, indium tin oxide, or graphene.

[0062] More preferably, the thickness of the conductive layer is 200~1000 nm, and the thickness of the adhesive layer is 10~50 nm.

[0063] A method for fabricating a lithium niobate electro-optic modulator includes the following steps:

[0064] S1. Etch the lithium niobate thin film layer of a wafer on which a buried oxide layer and a lithium niobate thin film layer are sequentially disposed on a substrate to form a lithium niobate waveguide and an optical isolation trench;

[0065] S2. Fill the optical isolation groove with a medium;

[0066] S3. A high dielectric constant cladding is formed above the lithium niobate waveguide;

[0067] S4. Prepare the signal electrode and the ground electrode to obtain the lithium niobate electro-optic modulator.

[0068] Preferably, the thickness of the lithium niobate thin film layer is 100~900 nm.

[0069] Preferably, the specific process of step S2 is as follows: coating photoresist on the lithium niobate thin film layer, exposing the photoresist to form a lithium niobate waveguide pattern and an optical isolation trench pattern, and etching the lithium niobate waveguide pattern and the optical isolation trench pattern to form a lithium niobate waveguide and an optical isolation trench.

[0070] Preferably, the etching process is at least one of dry etching, wet etching, or femtosecond laser etching.

[0071] More preferably, the etching power is 100~400 W and the bias voltage is 50~400 V.

[0072] Preferably, the specific process of step S2 is as follows: growing a medium in an optical isolation tank by atomic layer deposition.

[0073] More preferably, the growth temperature is 100~300℃.

[0074] Preferably, the process further includes a step of embedding nanomaterials into the medium after filling the medium.

[0075] More preferably, the embedding method is magnetron sputtering or sol-gel method.

[0076] More preferably, the conditions for the magnetron sputtering method include: sputtering power of 100~400 W, gas pressure of 1~5 mTorr, and an inert gas atmosphere.

[0077] Preferably, the specific process of step S3 is as follows: a first cladding and a second cladding are prepared on the lithium niobate waveguide by selected area atomic layer deposition or plasma-enhanced atomic layer deposition.

[0078] This invention also protects the application of the above-mentioned lithium niobate electro-optic modulator in the fabrication of high-speed optical communication devices or integrated photonic chips.

[0079] Compared with the prior art, the beneficial effects of the present invention are:

[0080] The synergistic effect of the optical isolation trench and the high dielectric constant cladding in this invention enables the lithium niobate electro-optic modulator of this invention to not only have high modulation efficiency, but also high bandwidth.

[0081] Furthermore, the lithium niobate electro-optic modulator of the present invention has excellent power tolerance. Attached Figure Description

[0082] Figure 1This is a schematic diagram of the structure of the lithium niobate electro-optic modulator in Example 1.

[0083] Figure 2 This is a SEM image of the lithium niobate electro-optic modulator of Example 1.

[0084] Figure 3 A diagram of the instrumentation used to test insertion loss.

[0085] Figure 4 This is a diagram of the instruments and equipment used for testing bandwidth.

[0086] In the figure, 1 is the ground electrode, 2 is the substrate layer, 3 is the buried oxide layer, 4 is the lithium niobate waveguide, 5 is the optical isolation trench, 6 is the dielectric, 7 is the nanomaterial, 81 is the first cladding layer, 82 is the second cladding layer, 9 is the titanium oxide layer, and 10 is the signal electrode. Detailed Implementation

[0087] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0088] Example 1

[0089] This embodiment provides a lithium niobate electro-optic modulator, such as Figure 1 As shown, from bottom to top, the structure includes a ground electrode 1, a substrate layer 2, a buried oxide layer 3, a lithium niobate waveguide 4, and a high-dielectric-constant cladding layer 8. Optical isolation trenches 5 are symmetrically arranged on both sides of each lithium niobate waveguide, each containing a dielectric material 6 embedded with nanomaterials 7. The high-dielectric-constant cladding layer 8 includes a first cladding layer 81 and a second cladding layer 82 covering the structure from the inside out. The high-dielectric-constant cladding layer 8 has two layers, and a titanium oxide layer 9 covers the non-optical field region of each high-dielectric-constant cladding layer 8. The lithium niobate electro-optic modulator also includes a signal electrode 10 embedded in the high-dielectric-constant cladding layer 8 and located above the optical isolation trenches 5.

[0090] The substrate layer 2 has a thickness of 450 μm, the buried oxide layer 3 has a thickness of 2.7 μm, the first cladding layer 81 has a thickness of 40 nm, the second cladding layer 82 has a thickness of 40 nm, and the titanium oxide layer has a thickness of 50 nm. The lithium niobate waveguide 4 has a rectangular cross-section with a width a of 1 μm and a height b of 500 nm. The optical isolation trench 5 has a rectangular cross-section with a width c of 2 μm and a depth d of 0.5 μm. The horizontal distance e between the center of the lithium niobate waveguide 4 and the center of the adjacent signal electrode 10 is 3 μm.

[0091] The substrate 2 is made of silicon, the buried oxide layer 3 is made of silicon dioxide, the dielectric 6 is made of silicon dioxide with a refractive index of 1.44; the first cladding layer 81 is made of aluminum nitride with a refractive index of 2.1 and a dielectric constant of 9; the second cladding layer 82 is made of hafnium oxide with a refractive index of 2.0 and a dielectric constant of 22; the titanium oxide layer 9 has a refractive index of 2.5 and a dielectric constant of 80; the lithium niobate waveguide 4 has a refractive index of 2.2; the nanomaterial 7 is titanium dioxide nanoparticles with a volume ratio of 4:6 to dielectric 6 and an average diameter of 80 nm.

[0092] The signal electrode has a trapezoidal cross-section. From bottom to top, the signal electrode consists of an adhesion layer and a conductive layer. The adhesion layer is made of chromium, and the conductive layer is made of gold. The adhesion layer is 50 nm thick and 1 μm wide, while the conductive layer is 800 nm thick. The ground electrode also consists of a conductive layer and an adhesion layer. The adhesion layer is made of chromium, and the conductive layer is made of gold. The adhesion layer is 50 nm thick, and the conductive layer is 800 nm thick.

[0093] The fabrication method of the lithium niobate electro-optic modulator in this embodiment includes the following steps:

[0094] (1) Take an X-cut LNOI wafer with a lithium niobate thin film thickness of 600 nm and a buried oxide layer of 2.7 μm, perform RCA standard cleaning to remove surface contaminant particles and organic matter. Then, spin-coat a layer of electron beam photoresist on the surface of the lithium niobate thin film, and use electron beam exposure to form waveguide patterns and optical isolation trench patterns.

[0095] (2) The waveguide pattern and optical isolation trench pattern obtained in step (1) are etched by wet etching to form a lithium niobate waveguide and an optical isolation trench; wherein the etching power is 300 W and the bias voltage is 100 V.

[0096] (3) Silicon dioxide was grown in an optically isolated tank by atomic layer deposition (the precursors of the growth material were SiH2Cl2 and H2O, and the growth temperature was 200℃). After growth, titanium dioxide nanoparticles (average diameter of 80 nm) were embedded into the silicon dioxide by magnetron sputtering (the conditions for magnetron sputtering included sputtering power of 200 W and Ar pressure of 4 mTorr).

[0097] (4) A first cladding layer is fabricated on the lithium niobate waveguide using selected area atomic layer deposition (SALD). Next, a second cladding layer is fabricated on the first cladding layer using plasma-enhanced atomic layer deposition (PEALD) to form a high-dielectric-constant cladding layer. Then, a titanium oxide layer is fabricated on top of the high-dielectric-constant cladding layer using PALD. Finally, another high-dielectric-constant cladding layer and another titanium oxide layer are fabricated, resulting in a total of two high-dielectric-constant cladding layers and two titanium oxide layers.

[0098] (5) Preparation of signal electrode and ground electrode. The surfaces of the signal electrode and ground electrode are planarized by polishing with silica gel, removing 500 nm of silica gel, and the surface roughness is less than 1 nm.

[0099] Example 2

[0100] This embodiment provides a lithium niobate electro-optic modulator, which differs from Embodiment 1 in that the first cladding layer 81 is made of aluminum oxide, and the second cladding layer 82 is made of lanthanum fluoride. The aluminum oxide has a refractive index of 1.76 and a dielectric constant of 9.8; the lanthanum fluoride has a refractive index of 1.6 and a dielectric constant of 10.

[0101] The method for fabricating the lithium niobate electro-optic modulator in this embodiment differs from that in Example 1 in that:

[0102] Accordingly, adjust the materials used in step (3) to prepare the first and second cladding layers.

[0103] Example 3

[0104] This embodiment provides a lithium niobate electro-optic modulator, which differs from Embodiment 1 in that the first cladding layer 81 is made of silicon nitride, and the second cladding layer 82 is made of aluminum oxide. Specifically, silicon nitride has a refractive index of 2.0 and a dielectric constant of 7.5; aluminum oxide has a refractive index of 1.76 and a dielectric constant of 9.8.

[0105] The method for fabricating the lithium niobate electro-optic modulator in this embodiment differs from that in Example 1 in that:

[0106] Accordingly, adjust the materials used in step (3) to prepare the first and second cladding layers.

[0107] Comparative Example 1

[0108] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that: the optical isolation trench 5 is not provided, and the high dielectric constant cladding 8 is replaced with a silicon dioxide cladding. The thickness of the single-layer silicon dioxide cladding is equal to the thickness of the high dielectric constant cladding in Example 1.

[0109] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0110] Step (1) is changed to: spin-coating a layer of electron beam photoresist on the surface of the lithium niobate thin film layer and forming a waveguide pattern by electron beam exposure;

[0111] Step (2) is changed to: using wet etching to etch the waveguide pattern obtained in step (1) to form a lithium niobate waveguide;

[0112] Step (3) is not performed.

[0113] Step (4) is changed to: a silicon dioxide cladding is prepared on the lithium niobate waveguide by selective area atomic layer deposition (SALD), and then a titanium oxide layer is prepared on the silicon dioxide cladding by plasma-enhanced atomic layer deposition (PEAD). Then, one silicon dioxide cladding layer and one titanium oxide layer are prepared to make the number of silicon dioxide cladding layers 2 and the number of titanium oxide layers 2.

[0114] Comparative Example 2

[0115] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that the material of the first cladding 81 is hafnium oxide (i.e., the high dielectric constant cladding is a hafnium oxide cladding).

[0116] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0117] Step (4) involves: fabricating a first cladding (hafnium oxide cladding) on ​​the lithium niobate waveguide using selected area atomic layer deposition (SALD). Next, a second cladding (hafnium oxide cladding) is fabricated on the first cladding using plasma-enhanced atomic layer deposition (PEALD) to form a high-dielectric-constant cladding. Then, a titanium oxide layer is fabricated on top of the high-dielectric-constant cladding using PALD. Finally, another high-dielectric-constant cladding and a titanium oxide layer are fabricated, resulting in a total of two high-dielectric-constant cladding layers and two titanium oxide layers.

[0118] Comparative Example 3

[0119] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that it does not have an optical isolation slot 5.

[0120] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0121] Step (1) is changed to: spin-coating an electron beam photoresist layer on the surface of the lithium niobate thin film layer and forming a waveguide by electron beam exposure;

[0122] Step (2) is changed to: using wet etching to form a lithium niobate waveguide pattern obtained in step (1);

[0123] Step (3) is not performed.

[0124] Comparative Example 4

[0125] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that the high dielectric constant cladding 8 is replaced with a silicon dioxide cladding, and the thickness of the single silicon dioxide cladding is equal to the thickness of the high dielectric constant cladding in Example 1.

[0126] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0127] Step (4) is changed to: a silicon dioxide cladding is prepared on the lithium niobate waveguide by selective area atomic layer deposition (SALD), and then a titanium oxide layer is prepared on the silicon dioxide cladding by plasma-enhanced atomic layer deposition (PEAD). Then, one silicon dioxide cladding layer and one titanium oxide layer are prepared to make the number of silicon dioxide cladding layers 2 and the number of titanium oxide layers 2.

[0128] Comparative Example 5

[0129] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that the first cladding layer 81 is made of hafnium oxide and the second cladding layer 82 is made of aluminum nitride.

[0130] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0131] Accordingly, adjust the materials used in step (3) to prepare the first and second cladding layers.

[0132] Performance testing

[0133] 1. Testing of insertion loss, half-wave voltage, and bandwidth

[0134] The insertion loss, half-wave voltage, and bandwidth of the lithium niobate electro-optic modulator in the test example and the comparative lithium niobate electro-optic modulators in each example are shown in Table 1.

[0135] Among them, the following are adopted Figure 3 The benchtop optical power meter shown is used to test insertion loss. The formula for calculating insertion loss is as follows: In the formula, P out P represents the output power of the lithium niobate electro-optic modulator. in The input power of the lithium niobate electro-optic modulator. The test steps for the half-wave voltage are as follows: (1) Apply 0 to V π(2) Fit the optical power-voltage curve to determine the voltage value required for the light intensity change to complete one cycle. This invention uses half-wave voltage as the core evaluation index of modulation efficiency. The physical meaning of half-wave voltage is: the driving voltage required to change the phase of the light wave by π radians (corresponding to the complete switching of light intensity). Generally, the smaller the half-wave voltage, the higher the modulation efficiency (the larger the phase change produced by unit voltage). Using such a linear ramp voltage, the optical power change is recorded synchronously; (3) Fit the optical power-voltage curve to determine the voltage value required for the light intensity change to complete one cycle. Figure 4 The probe station shown is used to test the bandwidth. The bandwidth testing steps are as follows: (1) Connect the modulator to the photoelectric test port of the VNA; (2) Scan the frequency range (10 MHz~40 GHz) and record S. 21 Parameters; (3) Read the value of 3 dB bandwidth through a vector network analyzer.

[0136] 2. Power tolerance

[0137] The highest power that the lithium niobate electro-optic modulator of the test embodiment and the comparative lithium niobate electro-optic modulators of each example can withstand is shown in Table 1. The test steps are as follows: (1) Gradually increase the input optical power and record the output power and temperature rise; (2) When the optical transmission suddenly attenuates and the infrared thermal image shows that the thermoelectric temperature is greater than 150°C, it is determined that a critical failure point has occurred, and the output power corresponding to the critical failure point is the power tolerance.

[0138] Table 1 Test results for each performance aspect

[0139]

[0140] As shown in Table 1, the lithium niobate electro-optic modulators of Examples 1-3 have insertion losses below 1.8 dB, half-wave voltages below 1.5 V, 3 dB bandwidths above 80 GHz, and tolerable power above 3800 mW. This indicates that the lithium niobate electro-optic modulator of the present invention not only has high modulation efficiency, but also high bandwidth, low loss, and excellent power tolerance.

[0141] Compared to the lithium niobate electro-optic modulator of Comparative Example 1, which does not have an optical isolation trench and replaces the high dielectric constant cladding with a low dielectric constant silicon dioxide cladding, it has a low 3 dB bandwidth and low tolerable power, as well as high insertion loss and high half-wave voltage (low modulation efficiency).

[0142] Comparative Example 3 features a high dielectric constant cladding, and Comparative Example 4 features an optical isolation trench. The performance of the lithium niobate electro-optic modulators in Comparative Examples 3 and 4 is improved compared to Comparative Example 1. Example 1 features a high dielectric constant cladding and an optical isolation trench. The performance is not only significantly improved compared to Comparative Example 1, but the degree of improvement is also greater than the sum of the improvement degrees of Comparative Examples 3 and 4 compared to Comparative Example 1. This demonstrates that the high dielectric constant cladding and the optical isolation trench can synergistically improve the performance.

[0143] Comparative Example 2 shows that the high dielectric constant cladding of the lithium niobate electro-optic modulator is not a cladding with a dielectric constant gradient, resulting in a low 3 dB bandwidth and tolerable power, as well as high insertion loss and half-wave voltage (low modulation efficiency).

[0144] Comparative Example 5 shows that the dielectric constant of the cladding in the high dielectric constant lithium niobate electro-optic modulator decreases layer by layer from the inside out. It has a low 3 dB bandwidth and low tolerable power, as well as high insertion loss and high half-wave voltage (low modulation efficiency).

[0145] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A lithium niobate electro-optic modulator, characterized in that, From bottom to top, it includes a ground electrode (1), a substrate layer (2), a buried oxide layer (3), a lithium niobate waveguide (4), and a high dielectric constant cladding layer (8). The lithium niobate waveguide (4) is provided with symmetrically distributed optical isolation grooves (5) on both sides; The high dielectric constant cladding (8) includes a first cladding (81) and a second cladding (82) from the inside out, wherein the dielectric constant of the first cladding (81) is smaller than that of the second cladding (82); The high dielectric constant cladding (8) has ≥2 layers; The lithium niobate electro-optic modulator also includes a signal electrode (10), which is embedded in a high dielectric constant cladding (8) and located above the optical isolation trench (5); The optical isolation groove (5) contains a medium (6), and the medium (6) contains embedded nanomaterials (7), wherein the nanomaterials (7) are at least one of titanium dioxide or aluminum oxide; the morphology of the nanomaterials (7) is at least one of nanoparticles or nanowires. The refractive index of the medium (6) is lower than that of lithium niobate, the refractive index of the material of the first cladding layer (81) is lower than that of the lithium niobate waveguide (4), and the refractive index of the material of the second cladding layer (82) is lower than that of the material of the first cladding layer (81). The dielectric constant of the first cladding layer (81) is ≥7.

5.

2. The lithium niobate electro-optic modulator as described in claim 1, characterized in that, The difference in dielectric constant between the first cladding layer (81) and the second cladding layer (82) is ≥5.

3. The lithium niobate electro-optic modulator as described in claim 1, characterized in that, The ratio of the maximum width of the cross-section of the lithium niobate waveguide (4) to the width of the optical isolation groove (5) is 1:(1~5).

4. The lithium niobate electro-optic modulator as described in claim 1, characterized in that, The materials of the first cladding layer (81) and the second cladding layer (82) are independently at least one of aluminum nitride, hafnium oxide, aluminum oxide, titanium oxide, lanthanum fluoride or silicon nitride.

5. The lithium niobate electro-optic modulator as described in claim 1, characterized in that, The refractive indices of the materials of the first cladding layer (81) and the second cladding layer (82) are independently ≤2.

2.

6. The lithium niobate electro-optic modulator as described in claim 1, characterized in that, The thickness of the high dielectric constant cladding (8) is 50~150 nm.

7. The method for preparing the lithium niobate electro-optic modulator according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Etch the lithium niobate thin film layer of a wafer on which a buried oxide layer and a lithium niobate thin film layer are sequentially disposed on a substrate to form a lithium niobate waveguide and an optical isolation trench; S2. Fill the optical isolation groove with a medium; S3. A high dielectric constant cladding is formed above the lithium niobate waveguide; S4. Prepare the signal electrode and the ground electrode to obtain the lithium niobate electro-optic modulator.

8. The application of the lithium niobate electro-optic modulator according to any one of claims 1 to 6 in the fabrication of high-speed optical communication devices or integrated photonic chips.

Images