Heterogeneous integrated waveguide-based high-speed electro-optical modulator and preparation method thereof

Abstract

The invention discloses a high-speed electro-optical modulator based on a heterogeneous integrated waveguide and a preparation method thereof, and belongs to the technical field of planar optical waveguide optical modulators and preparation thereof. The sensor is composed of a silicon substrate, a silicon dioxide oxide layer, a lead zirconate titanate flat plate layer, a polymer flat plate layer, a first grounding electrode, a signal electrode, a second grounding electrode and a polymer strip-shaped layer from bottom to top in sequence. The polymer strip-shaped layer and the polymer flat plate layer are made of the same material, and the refractive index of the polymer strip-shaped layer is lower than that of the lead zirconate titanate flat plate layer. The polymer flat plate layer prevents direct contact between lead zirconate titanate and the electrode, so that the loss of the modulator is greatly reduced. When an electric field is externally applied, the electric field is uniformly distributed between the signal electrode and the grounding electrode, and the thickness of the polymer flat plate layer and the size of the polymer strip-shaped layer are designed, so that more light fields are controlled in the lead zirconate titanate flat plate layer, and the electro-optical modulation efficiency is further improved. The manufacturing process is simplified, and the method has the advantages of low production cost, high efficiency and the like.

Description

Technical Field

[0001] This invention belongs to the field of planar optical waveguide modulators and their fabrication technology, specifically relating to a high-speed electro-optic modulator based on heterogeneous integrated waveguides and its fabrication method. Background Technology

[0002] With the rapid development of technologies such as the Internet, big data, and cloud computing, global data traffic is experiencing explosive growth, and the demand for data transmission rates will continue to increase in the future. In particular, the widespread adoption of technologies such as artificial intelligence places higher demands on information interconnection technologies. As a core component of optical interconnects, the performance of electro-optic modulators directly affects the operating efficiency and data transmission capabilities of data centers. Therefore, electro-optic modulators need to continuously improve their performance to achieve more efficient and faster electro-optic signal conversion.

[0003] To achieve high-performance electro-optic modulators, various integrated electro-optic platforms have been reported and developed, mainly including silicon-based platforms, thin-film lithium niobate (LNOI) platforms, organic electro-optic polymer platforms, and lead zirconate titanate (PZT) platforms. Silicon-based electro-optic modulators have matured over many years, but their high power consumption and slow modulation speed prevent them from meeting the current demands of optical communication. Thin-film lithium niobate is currently the most widely used crystalline thin-film electro-optic material; however, its electro-optic coefficient limits the modulation efficiency, and the complex waveguide fabrication and etching processes slow its development. In contrast, organic electro-optic polymers can be fabricated using spin-coating methods, providing a flexible and scalable alternative for integrated electro-optic modulation. However, electro-optic polymer materials are complex to fabricate and have low stability, leading to some degradation in their electro-optic performance, posing significant challenges in the field of electro-optic modulation.

[0004] PZT material has a large electro-optic coefficient, which significantly improves the modulation efficiency of PZT electro-optic modulators, thus attracting widespread attention and rapid development in the industry. However, the current PZT waveguide fabrication process requires dry etching, which greatly increases the device's fabrication complexity and cost. Summary of the Invention

[0005] To further improve the modulation efficiency of the modulator and simplify the manufacturing process, this invention proposes a high-speed electro-optic modulator based on heterogeneous integrated waveguides and its fabrication method.

[0006] This invention uses a lead zirconate titanate (PZT) thin film and its associated polymer planar and polymer strip layers as the waveguide core layer. This eliminates the need for PZT etching. By designing the dimensions of the polymer planar and polymer strip layers, the position of the light field is controlled, ensuring that most of the light field is distributed within the PZT thin film. This invention significantly reduces the complexity of the manufacturing process and improves the electro-optic overlap integral factor of the modulator. It fully utilizes the high electro-optic coefficient of lead zirconate titanate, resulting in modulators with high modulation efficiency and broad application prospects for high-speed, high-capacity data transmission. Furthermore, the use of polymer materials as part of the waveguide core layer leverages the ease of processing and compatibility with semiconductor processes, giving the device significant practical application value.

[0007] As attached Figure 1 As shown (for) Figure 2 (Cross-sectional view at position A-A') The high-speed electro-optic modulator based on heterogeneous integrated waveguide described in this invention comprises, from bottom to top, a silicon substrate 31, a silicon dioxide oxide layer 32 deposited on the upper surface of the substrate, an unetched lead zirconate titanate plate layer 33 spin-coated on the upper surface of the silicon dioxide oxide layer 32, a polymer plate layer 34 spin-coated on the upper surface of the lead zirconate titanate plate layer 33, a first ground electrode 36, a signal electrode 35, and a second ground electrode 37 evaporated on the upper surface of the polymer plate layer 34, and a polymer strip layer spin-coated on the upper surface of the polymer plate layer 34; the polymer strip layer and the polymer plate layer 34 are made of the same material.

[0008] The silicon substrate 31 has a thickness of 480~520 μm, the silicon dioxide oxide layer 32 has a thickness of 1~5 μm, the lead zirconate titanate plate layer 33 has a thickness of 0.25~0.35 μm, the polymer plate layer 34 has a thickness h2 of 0.1~2 μm, the first ground electrode 36, the signal electrode 35, and the second ground electrode 37 have the same thickness h3 of 0.5~5 μm, and the polymer strip layer has a thickness h1 of 0.1~2 μm; the signal electrode 35 has a width of 10~40 μm, the first ground electrode 36 and the second ground electrode 37 have the same width of 100~200 μm, and the gap between the first ground electrode 36, the second ground electrode 37 and the signal electrode is equal to 3~15 μm.

[0009] As attached Figure 2As shown, the polymer strip layer of a high-speed electro-optic modulator based on heterogeneous integrated waveguides according to the present invention comprises, from left to right, an input straight waveguide 1, an input tapered waveguide 2, a first rectangular multimode interference waveguide 3 for beam splitting, a first beam-splitting output tapered waveguide 4, a second beam-splitting output tapered waveguide 5, a first beam-splitting output curved waveguide 6, a second beam-splitting output curved waveguide 7, a first beam-splitting connecting tapered waveguide 8, a second beam-splitting connecting tapered waveguide 9, a first modulation straight waveguide 10, a second modulation straight waveguide 11, a first beam-combining connecting tapered waveguide 12, a second beam-combining connecting tapered waveguide 13, and a first beam-combining input. The system comprises a curved waveguide 14, a second beam-combining input curved waveguide 15, a first beam-combining input tapered waveguide 16, a second beam-combining input tapered waveguide 17, a second rectangular multimode interference waveguide 18 for beam combining, an output tapered waveguide 19, and an output straight waveguide 20; a first ground electrode 36, a signal electrode 35, and a second ground electrode 37 are located together on the polymer planar layer 34, with the first ground electrode 36 located outside the first modulation straight waveguide 10, the signal electrode 35 located between the first modulation straight waveguide 10 and the second modulation straight waveguide 11, and the second ground electrode 37 located outside the second modulation straight waveguide 11;

[0010] The first beam-splitting output tapered waveguide 4 and the second beam-splitting output tapered waveguide 5, the first beam-splitting output bent waveguide 6 and the second beam-splitting output bent waveguide 7, the first beam-splitting connecting tapered waveguide 8 and the second beam-splitting connecting tapered waveguide 9, the first modulation straight waveguide 10 and the second modulation straight waveguide 11, the first beam-combining connecting tapered waveguide 12 and the second beam-combining connecting tapered waveguide 13, the first beam-combining input bent waveguide 14 and the second beam-combining input bent waveguide 15, the first beam-combining input tapered waveguide 16 and the second beam-combining input tapered waveguide 17, the first ground electrode 36 and the second ground electrode 37 have the same structure and size, and are along the input straight... The signal light propagation directions in waveguide 1 and output straight waveguide 20 are symmetrically arranged; the first beam-splitting output tapered waveguide 4, the first beam-splitting output curved waveguide 6, the first beam-splitting connecting tapered waveguide 8, the first modulation straight waveguide 10, the first beam-combining connecting tapered waveguide 12, the first beam-combining input curved waveguide 14, and the first beam-combining input tapered waveguide 16 are connected in sequence; the second beam-splitting output tapered waveguide 5, the second beam-splitting output curved waveguide 7, the second beam-splitting connecting tapered waveguide 9, the second modulation straight waveguide 11, the second beam-combining connecting tapered waveguide 13, the second beam-combining input curved waveguide 15, and the second beam-combining input tapered waveguide 17 are connected in sequence.

[0011] The first rectangular multimode interference waveguide 3 has one input end and two output ends. The input straight waveguide 1 and the input tapered waveguide 2 are connected in sequence to serve as the input end of the first rectangular multimode interference waveguide 3. The first beam-splitting output tapered waveguide 4 and the second beam-splitting output tapered waveguide 5 serve as the two output ends of the first rectangular multimode interference waveguide 3, respectively. The second rectangular multimode interference waveguide 18 has two input ends and one output end. The first beam-combining input tapered waveguide 16 and the second beam-combining input tapered waveguide 17 serve as the two input ends of the second rectangular multimode interference waveguide 18, respectively. The output tapered waveguide 19 and the output straight waveguide 20 are connected in sequence to serve as the output end of the second rectangular multimode interference waveguide 18.

[0012] The input straight waveguide 1 and output straight waveguide 20 have the same structure and dimensions, with equal lengths L1 ranging from 100 to 5000 μm; the input tapered waveguide 2, the first beam-splitting output tapered waveguide 4, the second beam-splitting output tapered waveguide 5, the first beam-combining input tapered waveguide 16, the second beam-combining input tapered waveguide 17, and the output tapered waveguide 19 have the same structure and dimensions, with equal lengths Lt ranging from 10 to 100 μm; the first rectangular multimode interference waveguide 3 and the second rectangular multimode interference waveguide 18 have the same structure and dimensions, with equal lengths Lmmi ranging from 100 to 200 μm; the first beam-splitting output curved waveguide 6, the second beam-splitting output curved waveguide 7, the first beam-combining input curved waveguide 14, and the second beam-combining input curved waveguide 15 have the same structure and dimensions, with equal lengths a ranging from 300 to 600 μm. μm; the first beam splitter connected tapered waveguide 8, the second beam splitter connected tapered waveguide 9, the first beam combiner connected tapered waveguide 12, and the second beam combiner connected tapered waveguide 13 have the same structure and size, and their lengths Lc are equal, ranging from 100 to 200 μm; the lengths L of the first ground electrode 36, the signal electrode 35, the second ground electrode 37, the first modulation straight waveguide 10, and the second modulation straight waveguide 11 are equal, ranging from 1000 to 6000 μm; the center position of the connection between the first beam splitter output tapered waveguide 4, the second beam splitter output tapered waveguide 5 and the first rectangular multimode interference waveguide 3 is 1 to 3 μm away from the upper and lower edges of the first rectangular multimode interference waveguide 3; the center position of the connection between the first beam combiner input tapered waveguide 16, the second beam combiner input tapered waveguide 17 and the second rectangular multimode interference waveguide 18 is 1 to 3 μm away from the upper and lower edges of the second rectangular multimode interference waveguide 18.

[0013] The widths of the input straight waveguide 1, the initial width of the input tapered waveguide 2, the termination widths of the first beam-splitting output tapered waveguide 4 and the second beam-splitting output tapered waveguide 5, the widths of the first beam-splitting output curved waveguide 6 and the second beam-splitting output curved waveguide 7, the initial widths of the first beam-splitting connecting tapered waveguide 8 and the second beam-splitting connecting tapered waveguide 9, the termination widths of the first beam-combining connecting tapered waveguide 12 and the second beam-combining connecting tapered waveguide 13, the widths of the first beam-combining input curved waveguide 14 and the second beam-combining input curved waveguide 15, the initial widths of the first beam-combining input tapered waveguide 16 and the second beam-combining input tapered waveguide 17, the termination width of the output tapered waveguide 19, and the width x2 of the output straight waveguide 20 are all equal to 2~4 μm; the widths xmmi of the first rectangular multimode interference waveguide 3 and the second rectangular multimode interference waveguide 18 are all equal to 10~20. μm; the termination width of the input tapered waveguide 2, the starting width of the first beam-splitting output tapered waveguide 4 and the second beam-splitting output tapered waveguide 5, the termination width of the first beam-combining input tapered waveguide 16 and the second beam-combining input tapered waveguide 17, and the starting width xt of the output tapered waveguide 19 are all equal to 3~6 μm; the projection distance b between the termination position and the starting position of the first beam-splitting output curved waveguide 6 and the second beam-splitting output curved waveguide 7 along the direction perpendicular to the signal light propagation is all equal to 5~20 μm; the projection distance b between the starting position and the termination position of the first beam-combining input curved waveguide 14 and the second beam-combining input curved waveguide 15 along the direction perpendicular to the signal light propagation is all equal to 5~20 μm; the termination width of the first beam-splitting connecting tapered waveguide 8 and the second beam-splitting connecting tapered waveguide 9, the width of the first modulation straight waveguide 10 and the second modulation straight waveguide 11, and the starting width x1 of the first beam-combining connecting tapered waveguide 12 and the second beam-combining connecting tapered waveguide 13 are all equal to 1~3 μm. μm, and xt>x2>x1;

[0014] The present invention discloses a method for fabricating a high-speed electro-optic modulator based on heterogeneous integrated waveguides, such as... Figure 3 As shown, the steps are as follows:

[0015] A: Lead zirconate titanate wafer cleaning

[0016] First, the lead zirconate titanate wafer surface, composed of silicon substrate 31, silicon dioxide oxide layer 32 and lead zirconate titanate plate layer 33, is cleaned 2-3 times in sequence with acetone, methanol and isopropanol, and then dried with nitrogen to ensure that the lead zirconate titanate wafer surface is clean.

[0017] B: Polymer Flat Sheet Layer Preparation

[0018] A polymer sheet material (which includes a series of materials such as polyimide (PI), polymethyl methacrylate (PMMA), SU-8 2002, SU-8 2005, EpoCore, and EpoClad, etc., with a refractive index lower than that of the lead zirconate titanate sheet) was coated onto the clean surface of the lead zirconate titanate sheet 33 using a spin coating process. The spin coating speed was 1000~8000 rpm, and the sheet was baked at 100~500 ℃ for 20~50 minutes and then cooled to room temperature to obtain a polymer sheet 34 with a thickness of 0.1~2 μm.

[0019] C. Preparation of polymer strip layers

[0020] A polymer strip layer material (the same material as the polymer planar layer) is coated onto the prepared polymer planar layer 34 using a spin-coating process at a spin speed of 1000-6000 rpm to obtain a polymer film 10'. Then, pre-baking is performed, i.e., heating at 80 ℃-140 ℃ for 3-20 minutes, followed by cooling to 50 ℃-80 ℃. Next, photolithography is performed on the polymer film 10', i.e., alignment photolithography is performed under ultraviolet light with a wavelength of 300-400 nm. The waveguide mask has a shape consistent with the polymer strip layer to be prepared (e.g., ...). Figure 2 (As shown) a complementary structure, with an exposure time of 3-30 seconds, so that the polymer film 10' within the polymer strip layer structure to be prepared is exposed to ultraviolet light; after photolithography, it is heated at 70-130 °C for 3-30 minutes, and then cooled to 20-30 °C; then development is performed, that is, first wet etching in the developer corresponding to the polymer strip layer material for 10-60 seconds to remove the unexposed polymer film 10', then immersing it in isopropanol solution and deionized water respectively to wash away the residual polymer film 10' and developer, and finally drying it with nitrogen gas; after development, post-baking hardening is performed, that is, heating at 120-160 °C for 30-60 minutes, thereby preparing a polymer strip layer with a thickness of 0.1-2 μm (in Figure 3 The positions correspond to the first modulation straight waveguide 10 and the second modulation straight waveguide 11).

[0021] D: Preparation of modulation electrode

[0022] A 0.5–5 µm thick electrode layer 35' (materials Al, Au, or Cr) is evaporated onto the upper surfaces of the polymer planar layer 34 and the polymer strip layer using vacuum evaporation. Then, photoresist BP212 is spin-coated onto the electrode layer 35' surface using a spin-coating process at 1000–8000 rpm, resulting in a BP212 thickness of 1–10 μm. The spin-coated device is baked at 50–300 °C for 10–50 minutes, followed by room temperature photolithography. The mask structure is identical to the electrode structure to be prepared. The device is exposed to a 300–500 nm UV lamp for 10–20 seconds to expose the photoresist in areas other than the electrodes. The device is then immersed in a 2–5‰ NaOH solution for 5–20 minutes to remove the exposed photoresist, rinsed with deionized water, and dried with nitrogen. The device is then heated at 80–300 °C. After baking the device at ℃ for 5-40 minutes, it is cooled to room temperature; then the obtained device is placed in a special developing solution for 5-15 minutes to remove the electrode layer 35' that is not covered by photoresist; finally, the entire device is exposed for 2-5 seconds, and then the device is immersed in ethanol for 1-8 minutes to remove the remaining photoresist, obtaining the first ground electrode 36, signal electrode 35 and second ground electrode 37 of the required structure, then rinsed with deionized water and dried with nitrogen gas, thereby obtaining the high-speed electro-optic modulator based on heterogeneous integrated waveguide described in this invention.

[0023] Compared with existing device structures and technologies, the advantages of this invention are as follows: This invention uses an etch-free lead zirconate titanate (LZT) plate as part of the core layer, which has a larger electro-optic coefficient compared to lithium niobate, thus resulting in a modulator with higher modulation efficiency. Simultaneously, the introduced polymer plate layer prevents direct contact between LZT and the electrodes, significantly reducing modulator losses. When an external electric field is applied, the electric field is uniformly distributed between the signal electrode and the ground electrode. Furthermore, through the design of the polymer plate layer and polymer strip layer dimensions, the optical field is more effectively controlled within the LZT plate layer, further improving electro-optic modulation efficiency. In addition, compared with etched LZT electro-optic modulators, this invention greatly simplifies the fabrication process, reduces the difficulty of device fabrication, and offers advantages such as low production cost and high efficiency. Attached Figure Description

[0024] Figure 1 : Figure 2 Schematic diagram of the A-A' section of the modulator;

[0025] Figure 2 : Schematic diagram of the polymer strip layer in a high-speed electro-optic modulator based on heterogeneous integrated waveguide;

[0026] Figure 3 Flowchart of fabrication process for high-speed electro-optic modulator based on heterogeneous integrated waveguide;

[0027] Figure 4 (a): Figure 2 Light field distribution diagram of section A-A';

[0028] Figure 4 (b): Figure 2 Electric field distribution diagram of section A-A';

[0029] Figure 5 (a): Contour plot of half-wave voltage length product of electro-optic modulator as a function of gap and h1;

[0030] Figure 5 (b): Contour plot of electro-optic modulator loss as a function of gap and h1;

[0031] Figure 5 (c): Contour plot of the half-wave voltage-length product of the electro-optic modulator as a function of x1 and h2;

[0032] Figure 5 (d): Contour plot of electro-optic modulator loss as a function of x1 and h2;

[0033] Figure 6 The curves showing the variation of the modulator's reflection and transmission coefficients with frequency; the reflection coefficient is shown in the figure as S. 11 The curve, with the transmission coefficient S in the figure. 21 The curve corresponds to the left vertical axis in the graph.

[0034] Figure 1 For the modulator cross section ( Figure 2 The schematic diagram (Cross section A-A') shows the following components: silicon substrate 31, silicon dioxide oxide layer 32 deposited on the upper surface of silicon substrate 31, unetched lead zirconate titanate plate layer 33 spin-coated on the upper surface of silicon dioxide oxide layer 32, polymer plate layer 34 spin-coated on the upper surface of lead zirconate titanate plate layer 33, first ground electrode 36, signal electrode 35 and second ground electrode 37 evaporated on the upper surface of polymer plate layer 34, and polymer strip layer spin-coated on the upper surface of polymer plate layer 34 (at this time, the polymer strip layer is the first modulation straight waveguide 10 and the second modulation straight waveguide 11).

[0035] Figure 2This is a schematic diagram of the polymer strip layer structure in a high-speed electro-optic modulator based on heterogeneous integrated waveguides. The names of each part are as follows: input straight waveguide 1, input tapered waveguide 2, first rectangular multimode interference waveguide 3, first beam splitting output tapered waveguide 4, second beam splitting output tapered waveguide 5, first beam splitting output bent waveguide 6, second beam splitting output bent waveguide 7, first beam splitting connecting tapered waveguide 8, second beam splitting connecting tapered waveguide 9, first modulation straight waveguide 10, second modulation straight waveguide 11, first beam combining connecting tapered waveguide 12, second beam combining connecting tapered waveguide 13, first beam combining input bent waveguide 14, second beam combining input bent waveguide 15, first beam combining input tapered waveguide 16, second beam combining input tapered waveguide 17, second rectangular multimode interference waveguide 18, output tapered waveguide 19, output straight waveguide 20, first ground electrode 36, signal electrode 35, and second ground electrode 37.

[0036] Figure 3 This is a process flow diagram for fabricating a high-speed electro-optic modulator based on heterogeneous integrated waveguides. The names of each part are: silicon substrate 31, silicon dioxide oxide layer 32, lead zirconate titanate plate layer 33, polymer plate layer 34, electrode layer 35', and polymer film 10' prepared by spin coating process.

[0037] Figure 4 (a) For high-speed electro-optic modulators based on heterogeneous integrated waveguides Figure 2 Simulation diagram of fundamental mode optical field distribution in waveguide with cross section A-A'; it can be seen from the figure that the optical field is mostly distributed in the lead zirconate titanate planar layer waveguide, which ensures effective light transmission while increasing the overlap area of ​​the optical field and electric field and improving modulation efficiency.

[0038] Figure 4 (b) For high-speed electro-optic modulators based on heterogeneous integrated waveguides Figure 2 Simulated electric field distribution of the fundamental mode in the waveguide with cross section A-A'; the grayscale in the figure represents the electric field distribution. It can be seen that the electric field distribution is uniform in the lead zirconate titanate plate, and the electric field is larger at the edge of the electrode.

[0039] like Figure 5As shown, this is a contour plot showing the electro-optic modulation efficiency and loss of a high-speed electro-optic modulator based on a heterogeneous integrated waveguide structure as a function of relevant waveguide size parameters; among them, (a) is a contour plot showing the half-wave voltage length product of the electro-optic modulator in Example 1 as a function of the gap between the signal electrode 35 and the first ground electrode 36 (second ground electrode 37) and the thickness h1 of the polymer strip layer. It can be seen that as the electrode gap increases, the half-wave voltage length product of the modulator increases, the modulation efficiency decreases, and h1 has little effect on the modulation efficiency; (b) is a contour plot showing the loss of the electro-optic modulator in Example 1 as a function of gap and h1. It can be seen that as the electrode gap increases, the loss of the modulator decreases, and h1 has little effect on the loss; (c) (d) is a contour plot showing the variation of the half-wave voltage length product of the electro-optic modulator in Example 1 with the width x1 of the first modulation straight waveguide 10 (second modulation straight waveguide 11) and the thickness h2 of the polymer plate layer 34. It can be seen that as the thickness h2 of the polymer plate increases, the half-wave voltage length product of the modulator increases, and the modulation efficiency decreases. The width x1 of the first modulation straight waveguide 10 (second modulation straight waveguide 11) has little effect on the modulation efficiency.

[0040] like Figure 6 The figure shows the modulator characteristic curves under the electrode structure of Example 1 of the high-speed electro-optic modulator based on a heterogeneous integrated waveguide structure. From the curve showing the relationship between the transmission coefficient and frequency, it can be seen that the transmission coefficient is low in the high-frequency region and high in the low-frequency region, and the device bandwidth can reach 131.55 GHz (when the S21 parameter (transmission coefficient) decreases to -6.41 dB at DC, the frequency value at this point is called the electrical bandwidth of the modulator). From the curve showing the relationship between the reflection parameter and frequency, it can be seen that the reflection parameter is relatively small. Detailed Implementation

[0041] Example 1

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] As attached Figure 1 As shown (for) Figure 2The cross-sectional view at position A-A' shows a cross-sectional view of a high-speed electro-optic modulator based on heterogeneous integrated waveguides. From bottom to top, it consists of a silicon substrate 31, a silicon dioxide oxide layer 32 deposited on the upper surface of the substrate, an unetched lead zirconate titanate plate layer 33 spin-coated on the upper surface of the silicon dioxide layer, a polymer plate layer 34 spin-coated on the upper surface of the lead zirconate titanate plate layer 33, a first ground electrode 36, a signal electrode 35, and a second ground electrode 37 evaporated on the upper surface of the polymer plate layer 34, and a polymer strip layer (first modulation straight waveguide 10 and second modulation straight waveguide 11) spin-coated on the upper surface of the polymer plate layer 34. The polymer plate layer 34 and the polymer strip layer are made of the same material. The silicon substrate 31 has a thickness of 500 μm, the silicon dioxide oxide layer 32 has a thickness of 4 μm, the lead zirconate titanate plate layer 33 has a thickness of 0.3 μm, the polymer plate layer 34 has a thickness of 0.1 μm, the first ground electrode 36, the signal electrode 35, and the second ground electrode 37 all have a thickness of 0.8 μm, and the polymer strip layer above the polymer plate layer 34 has a thickness of 0.3 μm; the signal electrode 35 has a width of 20 μm, the first ground electrode 36, the second ground electrode 37 and the signal electrode have an equal gap of 5 μm, and the first ground electrode 36 and the second ground electrode 37 have the same width of 100 μm.

[0044] As attached Figure 2The diagram shows a schematic of the polymer strip layer in a high-speed electro-optic modulator based on heterogeneous integrated waveguides according to the present invention. From left to right along the optical signal propagation direction in the input straight waveguide 1 and the output straight waveguide 20, the structure consists of the following layers in sequence: input straight waveguide 1, input tapered waveguide 2, first rectangular multimode interference waveguide 3, first beam-splitting output tapered waveguide 4, second beam-splitting output tapered waveguide 5, first beam-splitting output curved waveguide 6, second beam-splitting output curved waveguide 7, first beam-splitting connecting tapered waveguide 8, second beam-splitting connecting tapered waveguide 9, and first modulation straight waveguide 10. The system comprises: a second modulation straight waveguide 11, a first bundled tapered waveguide 12, a second bundled tapered waveguide 13, a first bundled input bent waveguide 14, a second bundled input bent waveguide 15, a first bundled input tapered waveguide 16, a second bundled input tapered waveguide 17, a second rectangular multimode interference waveguide 18, an output tapered waveguide 19, an output straight waveguide 20, a signal electrode 35, a first ground electrode 36, and a second ground electrode 37. The input straight waveguide 1 and the output straight waveguide 20 have the same structure and dimensions, and their lengths L1 are equal at 4000. μm; The input tapered waveguide 2, the first beam splitter output tapered waveguide 4, the second beam splitter output tapered waveguide 5, the first beam combiner input tapered waveguide 16, the second beam combiner input tapered waveguide 17, and the output tapered waveguide 19 have the same structure and dimensions, and their lengths Lt are equal at 40 μm; The first rectangular multimode interference waveguide 3 and the second rectangular multimode interference waveguide 18 have the same structure and dimensions, and their lengths Lmmi are equal at 150 μm; The first beam splitter output curved waveguide 6, the second beam splitter output curved waveguide 7, the first beam combiner input curved waveguide 14, and the second beam combiner input curved waveguide 15 have the same structure and dimensions, and their lengths a are equal at 500 μm; The first beam splitter connecting tapered waveguide 8, the second beam splitter connecting tapered waveguide 9, the first beam combiner connecting tapered waveguide 12, and the second beam combiner connecting tapered waveguide 13 have the same structure and dimensions, and their lengths Lc are equal at 170 μm. μm; the length L of the signal electrode 35, the first ground electrode 36 and the second ground electrode 37, the first modulation straight waveguide 10 and the second modulation straight waveguide 11 are all equal to 4000 μm; the distance between the center position of the connection between the first beam splitter output tapered waveguide 4 and the second beam splitter output tapered waveguide 5 and the first rectangular multimode interference waveguide 3 and the upper and lower edges of the first rectangular multimode interference waveguide 3, and the distance delta between the center position of the connection between the first beam combiner input tapered waveguide 16 and the second beam combiner input tapered waveguide 17 and the second rectangular multimode interference waveguide 18 and the upper and lower edges of the second rectangular multimode interference waveguide 18 are all equal to 1.5 μm;

[0045] The widths of the input straight waveguide 1, the initial width of the input tapered waveguide 2, the termination widths of the first beam-splitting output tapered waveguide 4 and the second beam-splitting output tapered waveguide 5, the widths of the first beam-splitting output curved waveguide 6 and the second beam-splitting output curved waveguide 7, the initial widths of the first beam-splitting connecting tapered waveguide 8 and the second beam-splitting connecting tapered waveguide 9, the termination widths of the first beam-combining connecting tapered waveguide 12 and the second beam-combining connecting tapered waveguide 13, the widths of the first beam-combining input curved waveguide 14 and the second beam-combining input curved waveguide 15, the initial widths of the first beam-combining input tapered waveguide 16 and the second beam-combining input tapered waveguide 17, the termination width of the output tapered waveguide 19, and the width x2 of the output straight waveguide 20 are all equal to 3 μm; the widths xmmi of the first rectangular multimode interference waveguide 3 and the second rectangular multimode interference waveguide 18 are all equal to 15. μm; the termination width of the input tapered waveguide 2, the starting width of the first beam-splitting output tapered waveguide 4 and the second beam-splitting output tapered waveguide 5, the termination width of the first beam-combining input tapered waveguide 16 and the second beam-combining input tapered waveguide 17, and the starting width xt of the output tapered waveguide 19 are all equal to 4 μm; the projection distance b between the termination position and the starting position of the first beam-splitting output curved waveguide 6 and the second beam-splitting output curved waveguide 7 along the direction perpendicular to the signal light propagation is all equal to 10 μm; the projection distance b between the starting position and the termination position of the first beam-combining input curved waveguide 14 and the second beam-combining input curved waveguide 15 along the direction perpendicular to the signal light propagation is all equal to 10 μm; the termination width of the first beam-splitting connecting tapered waveguide 8 and the second beam-splitting connecting tapered waveguide 9, the width of the first modulation straight waveguide 10 and the second modulation straight waveguide 11, and the starting width x1 of the first beam-combining connecting tapered waveguide 12 and the second beam-combining connecting tapered waveguide 13 are all equal to 2 μm.

[0046] Under the above parameters, the modulation efficiency of the modulator is calculated to be 0.23 V·cm, the loss is 3.8 dB / cm, and the extinction ratio reaches 38.7 dB using the simulation software Comsol Multiphysics. The RF performance of the modulator is simulated using HFSS software, such as... Figure 5 As shown, the transmission parameter (S) 12 and S 21 The reflection parameter (S) is relatively large. 11 and S 22 The reflectivity is relatively small. The results show that the traveling wave electrode of this structure has low reflectivity and high transmittance over a wide frequency range of 0~120 GHz.

[0047] The fabrication method of the high-speed electro-optic modulator based on heterogeneous integrated waveguides described in this invention comprises the following steps:

[0048] (1) Cleaning of lead zirconate titanate wafer: First, use acetone, methanol and isopropanol to clean the surface of lead zirconate titanate wafer (which can be purchased directly, and the lead zirconate titanate wafer is composed of silicon substrate 31, silicon dioxide oxide layer 32 and lead zirconate titanate plate layer 33) three times in sequence, and then blow it dry with nitrogen gas to ensure that the surface of lead zirconate titanate wafer is clean, and obtain silicon substrate 31, silicon dioxide oxide layer 32 and lead zirconate titanate plate layer 33;

[0049] (2) Preparation of polymer plate layer: The polymer plate layer material (EpoCore, whose refractive index is lower than that of lead zirconate titanate plate layer) was coated on the clean surface of lead zirconate titanate plate layer 33 by spin coating process. The rotation speed was 5000 rpm, and the plate layer was baked at 400 ℃ for 30 minutes and then cooled to room temperature to obtain a polymer plate layer 34 with a thickness of 0.1 μm.

[0050] (3) Preparation of polymer strip layer: The polymer material (EpoCore) is coated onto the prepared polymer plate layer 34 using a spin coating process at a speed of 5000 rpm; then the prepared polymer film 10' is pre-baked, i.e., heated at 120℃ for 10 minutes, and then cooled to 60℃; the polymer film 10' is photolithographically lithographically lithographically lithographically lithographically under ultraviolet light with a wavelength of 365 nm, and the waveguide mask has the same shape as the polymer strip layer to be prepared (e.g., ...). Figure 2 (As shown) Complementary structures are used, and the exposure time is 6 seconds to expose the polymer film 10' to be prepared to ultraviolet light. After photolithography, the film is heated at 85 °C for 10 minutes and then cooled to 25 °C. Then, development is performed, i.e., wet etching is first performed in the developer corresponding to the polymer film 10' for 40 seconds to remove the unexposed polymer film 10', and then the film is washed with isopropanol solution and deionized water respectively to remove the residual polymer film 10' and developer. Finally, the film is dried with nitrogen. After development, post-baking hardening is performed by heating at 120 °C for 40 minutes to prepare a polymer strip layer with a thickness of 0.3 μm.

[0051] (4) Preparation of modulation electrodes: A 0.8 µm thick electrode layer 35' (material Au) was evaporated on the surface of the polymer plate layer 34 and the polymer strip layer using vacuum evaporation. Then, photoresist BP212 was spin-coated onto the surface of electrode layer 35' using a spin-coating process at a speed of 6000 rpm, resulting in a BP212 thickness of 1.5 μm. The device with spin-coated photoresist BP212 was baked at 87 °C for 10 minutes, and then cooled to room temperature for mask photolithography. The structure of the mask was the same as that of the electrode to be prepared. It was exposed under a 365 nm UV lamp for 2 s to expose the photoresist in areas other than the electrodes. The device was placed in a 5‰ NaOH solution for 5 minutes to remove the exposed photoresist, then rinsed with deionized water and dried with nitrogen. After baking the device at ℃ for 10 minutes, it was cooled to room temperature. Then, the sample was placed in a gold developer (the developer is iodine and potassium iodide in a mass ratio of 1:8) and developed for 8 minutes to remove the electrode layer 35' that was not covered by the photoresist. Finally, the entire device was exposed for 3 seconds, and then the device was immersed in ethanol for 3 minutes to remove the remaining photoresist, obtaining the signal electrode 35, the first ground electrode 36, and the second ground electrode 37 of the required structure. The device was then rinsed with deionized water and dried with nitrogen gas to obtain the high-speed electro-optic modulator based on heterogeneous integrated waveguide.

[0052] This results in the fabrication of a high-speed electro-optic modulator based on heterogeneous integrated waveguides that meets the requirements. It should be noted that while this invention contains descriptions of many details, it should not be construed as limiting the scope or possible claims of any disclosed technology, but rather as a description of features specific to particular embodiments that may be specific to the disclosed technology. The invention can also be modified in many ways, such as using electro-optic materials like barium titanate or lithium niobate. What those skilled in the art can derive from the explicit disclosure of this invention or from the written description herein without objection falls within the scope of protection of this invention.

Claims

1. A high-speed electro-optic modulator based on heterogeneous integrated waveguides, characterized in that: The structure consists of, from bottom to top, a silicon substrate (31), a silicon dioxide oxide layer (32) deposited on the upper surface of the substrate, an unetched lead zirconate titanate plate layer (33) spin-coated on the upper surface of the silicon dioxide oxide layer (32), a polymer plate layer (34) spin-coated on the upper surface of the lead zirconate titanate plate layer (33), a first ground electrode (36), a signal electrode (35), and a second ground electrode (37) evaporated on the upper surface of the polymer plate layer (34), and a polymer strip layer spin-coated on the upper surface of the polymer plate layer (34). The polymer strip layer and the polymer plate layer (34) are made of the same material, and their refractive index is lower than that of the lead zirconate titanate plate layer. The polymer strip layer, from left to right, consists of an input straight waveguide (1), an input tapered waveguide (2), a first rectangular multimode interference waveguide for beam splitting (3), a first beam-splitting output tapered waveguide (4), a second beam-splitting output tapered waveguide (5), a first beam-splitting output curved waveguide (6), a second beam-splitting output curved waveguide (7), a first beam-splitting connecting tapered waveguide (8), a second beam-splitting connecting tapered waveguide (9), a first modulation straight waveguide (10), a second modulation straight waveguide (11), a first beam-combining connecting tapered waveguide (12), a second beam-combining connecting tapered waveguide (13), a first beam-combining input curved waveguide (14), and a second beam-combining input curved waveguide. The waveguide consists of a first beam-combining input tapered waveguide (15), a second beam-combining input tapered waveguide (16), a second beam-combining input tapered waveguide (17), a second rectangular multimode interference waveguide (18) for beam combining, an output tapered waveguide (19), and an output straight waveguide (20); a first ground electrode (36), a signal electrode (35), and a second ground electrode (37) are located together on the polymer planar layer (34), with the first ground electrode (36) located outside the first modulation straight waveguide (10), the signal electrode (35) located between the first modulation straight waveguide (10) and the second modulation straight waveguide (11), and the second ground electrode (37) located outside the second modulation straight waveguide (11); The first beam-splitting output tapered waveguide (4) and the second beam-splitting output tapered waveguide (5), the first beam-splitting output curved waveguide (6) and the second beam-splitting output curved waveguide (7), the first beam-connecting tapered waveguide (8) and the second beam-connecting tapered waveguide (9), the first modulation straight waveguide (10) and the second modulation straight waveguide (11), the first beam-combining connecting tapered waveguide (12) and the second beam-combining connecting tapered waveguide (13), the first beam-combining input curved waveguide (14) and the second beam-combining input curved waveguide (15), the first beam-combining input tapered waveguide (16) and the second beam-combining input tapered waveguide (17), the first ground electrode (36) and the second ground electrode (37) have the same structure and size, and are along the input straight... The signal light propagation directions in waveguide (1) and output straight waveguide (20) are symmetrically arranged; the first beam-splitting output tapered waveguide (4), the first beam-splitting output curved waveguide (6), the first beam-splitting connecting tapered waveguide (8), the first modulation straight waveguide (10), the first beam-combining connecting tapered waveguide (12), the first beam-combining input curved waveguide (14), and the first beam-combining input tapered waveguide (16) are connected in sequence; the second beam-splitting output tapered waveguide (5), the second beam-splitting output curved waveguide (7), the second beam-splitting connecting tapered waveguide (9), the second modulation straight waveguide (11), the second beam-combining connecting tapered waveguide (13), the second beam-combining input curved waveguide (15), and the second beam-combining input tapered waveguide (17) are connected in sequence; The first rectangular multimode interference waveguide (3) has one input end and two output ends. The input straight waveguide (1) and the input tapered waveguide (2) are connected in sequence to serve as the input end of the first rectangular multimode interference waveguide (3). The first beam splitting output tapered waveguide (4) and the second beam splitting output tapered waveguide (5) serve as the two output ends of the first rectangular multimode interference waveguide (3), respectively. The second rectangular multimode interference waveguide (18) has two input ends and one output end. The first beam combining input tapered waveguide (16) and the second beam combining input tapered waveguide (17) serve as the two input ends of the second rectangular multimode interference waveguide (18), respectively. The output tapered waveguide (19) and the output straight waveguide (20) are connected in sequence to serve as the output end of the second rectangular multimode interference waveguide (18).

2. The high-speed electro-optic modulator based on heterogeneous integrated waveguide as described in claim 1, characterized in that: The thickness of the silicon substrate (31) is 480~520 μm, the thickness of the silicon dioxide oxide layer (32) is 1~5 μm, the thickness of the lead zirconate titanate plate layer (33) is 0.25~0.35 μm, the thickness h2 of the polymer plate layer (34) is 0.1~2 μm, the thickness h3 of the first ground electrode (36), the signal electrode (35) and the second ground electrode (37) is the same as 0.5~5 μm, and the thickness h1 of the polymer strip layer is 0.1~2 μm.

3. The high-speed electro-optic modulator based on heterogeneous integrated waveguide as described in claim 1, characterized in that: The input straight waveguide (1) and the output straight waveguide (20) have the same structure and size, and their lengths L1 are equal, ranging from 100 to 5000 μm; the input tapered waveguide (2), the first beam-splitting output tapered waveguide (4), the second beam-splitting output tapered waveguide (5), the first beam-combining input tapered waveguide (16), the second beam-combining input tapered waveguide (17), and the output tapered waveguide (19) have the same structure and size, and their lengths Lt are equal, ranging from 10 to 100 μm; the first rectangular multimode interference waveguide (3) and the second rectangular multimode interference waveguide (18) have the same structure and size, and their lengths Lmmi are equal, ranging from 100 to 200 μm; the first beam-splitting output curved waveguide (6), the second beam-splitting output curved waveguide (7), the first beam-combining input curved waveguide (14), and the second beam-combining input curved waveguide (15) have the same structure and size, and their lengths a are equal, ranging from 300 to 600 μm. μm; the first beam splitter connected tapered waveguide (8), the second beam splitter connected tapered waveguide (9), the first beam combiner connected tapered waveguide (12), and the second beam combiner connected tapered waveguide (13) have the same structure and size, and their lengths Lc are equal, ranging from 100 to 200 μm; the lengths L of the first ground electrode (36), the signal electrode (35), the second ground electrode (37), the first modulation straight waveguide (10), and the second modulation straight waveguide (11) are equal, ranging from 1000 to 6000 μm; the center position of the connection between the first beam splitter output tapered waveguide (4), the second beam splitter output tapered waveguide (5) and the first rectangular multimode interference waveguide (3) is equal to the distance delta between the upper and lower edges of the first rectangular multimode interference waveguide (3), ranging from 1 to 3. μm, the center position of the connection between the first beam-combining input tapered waveguide (16), the second beam-combining input tapered waveguide (17) and the second rectangular multimode interference waveguide (18) is equal to the distance delta between the upper and lower edges of the second rectangular multimode interference waveguide (18), which is 1~3 μm.

4. A high-speed electro-optic modulator based on heterogeneous integrated waveguides as described in claim 1, characterized in that: The width of the input straight waveguide (1), the starting width of the input tapered waveguide (2), the ending width of the first beam-splitting output tapered waveguide (4) and the second beam-splitting output tapered waveguide (5), the width of the first beam-splitting output curved waveguide (6) and the second beam-splitting output curved waveguide (7), the starting width of the first beam-splitting connecting tapered waveguide (8) and the second beam-splitting connecting tapered waveguide (9), the ending width of the first beam-combining connecting tapered waveguide (12) and the second beam-combining connecting tapered waveguide (13), the width of the first beam-combining input curved waveguide (14) and the second beam-combining input curved waveguide (15), the starting width of the first beam-combining input tapered waveguide (16) and the second beam-combining input tapered waveguide (17), the ending width of the output tapered waveguide (19), and the width of the output straight waveguide (20) are all equal to 2~4. μm; the widths xmmi of the first rectangular multimode interference waveguide (3) and the second rectangular multimode interference waveguide (18) are equal to 10~20 μm; the termination width of the input tapered waveguide (2), the starting widths of the first beam splitting output tapered waveguide (4) and the second beam splitting output tapered waveguide (5), the termination widths of the first beam combining input tapered waveguide (16) and the second beam combining input tapered waveguide (17), and the starting width xt of the output tapered waveguide (19) are equal to 3~6 μm; the projection distance b between the termination and starting positions of the first beam splitting output curved waveguide (6) and the second beam splitting output curved waveguide (7) along the direction perpendicular to the signal light propagation is equal to 5~20 μm; the projection distance b between the starting and ending positions of the first beam combining input curved waveguide (14) and the second beam combining input curved waveguide (15) along the direction perpendicular to the signal light propagation is equal to 5~20 μm. μm; the termination width of the first beam-connecting tapered waveguide (8) and the second beam-connecting tapered waveguide (9), the width of the first modulation straight waveguide (10) and the second modulation straight waveguide (11), and the starting width x1 of the first beam-connecting tapered waveguide (12) and the second beam-connecting tapered waveguide (13) are equal to 1~3 μm, and xt>x2>x1; the width of the signal electrode (35) is 10~40 μm, the width of the first ground electrode (36) and the second ground electrode (37) are the same as 100~200 μm, and the gap between the first ground electrode (36), the second ground electrode (37) and the signal electrode is equal to 3~15 μm.

5. A high-speed electro-optic modulator based on heterogeneous integrated waveguides as described in claim 1, characterized in that: The polymer plate layer material is one of polyimide, polymethyl methacrylate, SU-8 2002, SU-8 2005, EpoCore, and EpoClad; the materials of the first ground electrode (36), signal electrode (35), and second ground electrode (37) are Al, Au, or Cr.

6. A method for fabricating a high-speed electro-optic modulator based on heterogeneous integrated waveguides as described in any one of claims 1 to 5, comprising the following steps: A: Lead zirconate titanate wafer cleaning First, the surface of the lead zirconate titanate wafer, which consists of a silicon substrate (31), a silicon dioxide oxide layer (32), and a lead zirconate titanate plate layer (33), is cleaned 2-3 times in sequence with acetone, methanol, and isopropanol, and then dried with nitrogen gas to ensure that the surface of the lead zirconate titanate wafer is clean. B: Polymer Flat Sheet Layer Preparation The polymer plate layer material was coated onto the clean lead zirconate titanate plate layer (33) using a spin coating process. The spin speed was 1000~8000 rpm. The plate layer was baked at 100~500 ℃ for 20~50 minutes and then cooled to room temperature to obtain the polymer plate layer (34). C. Preparation of polymer strip layers A polymer strip layer material was coated onto the prepared polymer plate layer (34) using a spin coating process at a speed of 1000~6000 rpm to obtain a polymer film (10'). Pre-baking was then performed, i.e., heating at 80 ℃~140 ℃ for 3~20 minutes, followed by cooling to 50 ℃~80 ℃. Photolithography was then performed on the polymer film (10'), i.e., photolithography under ultraviolet light with a wavelength of 300~400 nm. The waveguide mask had a structure complementary to the polymer strip layer to be prepared, and the exposure time was 3~30 seconds, allowing the polymer film (10') within the structure of the polymer strip layer to be prepared to be exposed to ultraviolet light. After photolithography, the film was heated at 70~130 ℃ for 3~30 minutes, followed by cooling to 20~30 ℃. ℃; then development is performed, that is, wet etching is first performed in the developer corresponding to the polymer strip layer material for 10~60 seconds to remove the unexposed polymer film (10'), and then the residual polymer film (10') and developer are washed away in isopropanol solution and deionized water respectively, and finally dried with nitrogen gas; After development, a post-bake hardening process is performed, which involves heating at 120~160 ℃ for 30~60 minutes to prepare a polymer strip layer with a thickness of 0.1~2 μm. D: Preparation of modulation electrode Electrode layers (35') were evaporated on the upper surfaces of the polymer flat layer (34) and the polymer strip layer using a vacuum evaporation method; then, photoresist BP212 was spin-coated onto the surface of the electrode layer (35') using a spin coating process at a speed of 1000~8000 rpm, resulting in a BP212 thickness of 1~10 μm. Devices coated with spin-coated BP212 photoresist are baked at 50–300 °C for 10–50 minutes, then cooled to room temperature for mask photolithography. The mask structure is the same as the electrode structure to be prepared. The device is exposed to a 300–500 nm UV lamp for 10–20 seconds to expose the photoresist in areas other than the electrodes. The device is then immersed in a 2–5‰ NaOH solution for 5–20 minutes to remove the exposed photoresist. It is then rinsed with deionized water and dried with nitrogen. The device is baked at 80–300 °C for 5–40 minutes and then cooled to room temperature. The resulting device is then developed in a dedicated developer for 5–15 minutes to remove the electrode layers not covered by the photoresist (35'). Finally, the entire device is exposed for 2–5 seconds. Then, immerse the device in ethanol for 1-8 minutes to remove the remaining photoresist and obtain the first ground electrode (36), signal electrode (35), and second ground electrode (37) of the required structure. Rinse with deionized water and dry with nitrogen to obtain a high-speed electro-optic modulator based on heterogeneous integrated waveguide.

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