Mach-Zehnder modulator based on silicon carbide substrate and preparation method thereof

Abstract

The invention provides a Mach-Zehnder modulator based on a silicon carbide substrate and a preparation method of the Mach-Zehnder modulator. An isolation layer, a waveguide material layer, a Mach-Zehnder structure, a distributed traveling wave electrode and an upper cladding are sequentially formed on the silicon carbide substrate; by utilizing the characteristics that the silicon carbide substrate has low dielectric loss and a dielectric constant capable of being matched with the optical group refractive index in a high-frequency band and optimizing parameters of the distributed traveling wave electrode, the loss of a microwave signal in transmission can be remarkably reduced, and accurate matching of the microwave phase refractive index and the optical group refractive index can be realized; in addition, the heat conductivity coefficient of the silicon carbide substrate is far higher than that of a substrate material such as silicon, so that heat generated by working of a device can be effectively dissipated, interference of a heat effect on modulation performance is avoided, and further, the modulation bandwidth and the modulation efficiency of the Mach-Zehnder modulator are improved. According to the preparation process, the process stability and repeatability are remarkably improved, and feasibility is provided for large-scale integrated manufacturing of devices.

Description

Technical Field

[0001] This invention relates to the field of integrated optoelectronic device technology, and in particular to a Mach-Zehnder modulator based on a silicon carbide substrate and its fabrication method. Background Technology

[0002] In the information technology era, the explosive growth of big data, artificial intelligence, and global interconnectivity demands higher requirements for data processing and transmission capabilities. Traditional microelectronic devices, limited by their physical principles, face significant limitations in improving the size and performance of their fundamental transistor components. Against this backdrop, integrated photonics technology, using photons as information carriers, is considered key to solving these problems due to its inherent advantages, including greater bandwidth, lower loss, higher spectral efficiency, and communication capacity. This is attributed to its more stable and controllable modulation and multiplexing dimensions, such as amplitude, phase, wavelength, polarization state, and mode.

[0003] Microwave photonics, which combines integrated photonics and microwave technology, achieves tightly bound propagation of single-mode optical fields through a high refractive index difference. Using light waves as high-frequency carriers, it receives modulation from microwave signals, achieving up-conversion and thus low-loss microwave propagation. Key technologies for modulating light waves with microwaves include: 1) a 50Ω impedance-matched transmission line structure design to reduce unnecessary reflections of energy transmitted to the microwave generator before the electrodes; 2) a low-loss transmission line structure design in the radio frequency band to reduce electric field losses during microwave transmission; and 3) matching the microwave phase refractive index with the optical group refractive index to improve the actual modulation efficiency accumulated by photoelectric coupling in the modulation working region. To simultaneously meet the above requirements, existing technologies have proposed various on-chip electro-optic modulator solutions. For example, they can achieve the matching of microwave refractive index and optical field group refractive index by designing coplanar waveguide traveling wave electrodes or by using T-shaped capacitive traveling wave electrodes to reduce transmission line loss. However, these solutions require a suspended substrate process to obtain good refractive index matching. In other words, existing technologies have to rely on special microstructure designs for the traveling wave electrodes or the substrate itself to achieve low microwave loss and good refractive index matching. This greatly increases the complexity of the process and the manufacturing cost. It is difficult to guarantee yield and consistency in the process of large-scale on-chip integration, thus hindering industrial applications.

[0004] Furthermore, when designing traveling-wave electrodes for coplanar waveguides, their dimensional parameters significantly impact device performance. Taking Mach-Zehnder modulators as an example, while narrowing the electrode spacing can increase microwave intensity within the optical field, thus improving modulation efficiency, excessively narrow electrode spacing drastically increases the absorption loss of light waves by the metal. Additionally, while shallow etching of the waveguide material layer to reduce waveguide height can increase the channels for microwaves to enter the optical field region, thereby improving modulation efficiency, excessively shallow etching depth weakens the confinement of optical modes, leading to increased optical losses, and in severe cases, even making single-mode transmission unsustainable. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a Mach-Zehnder modulator based on a silicon carbide substrate and its fabrication method, in order to solve the problem that the electro-optic modulators in the prior art can only rely on special microstructure design of traveling wave electrodes or the substrate itself, which leads to high process complexity, high fabrication cost, and difficulty in ensuring yield and consistency.

[0006] To achieve the above and other related objectives, the present invention provides a Mach-Zehnder modulator based on a silicon carbide substrate, comprising a substrate, an optical isolation layer, a waveguide material layer, a Mach-Zehnder structure, distributed traveling-wave electrodes, and an upper cladding layer.

[0007] The substrate, the optical isolation layer, and the waveguide material layer are stacked sequentially, wherein the substrate is a single-crystal silicon carbide substrate;

[0008] The Mach-Zehnder structure is disposed on the surface of the waveguide material layer away from the optical isolation layer, and includes a first optical waveguide, a second optical waveguide, and a coupler. The first optical waveguide and the second optical waveguide are arranged in parallel, and the coupler is disposed at both ends of the first optical waveguide and the second optical waveguide. One end of the coupler is connected to the first optical waveguide and the second optical waveguide respectively through two single-mode waveguides, and the other end of the coupler is also provided with an input waveguide and an output waveguide.

[0009] The distributed traveling-wave electrode is disposed outside the first optical waveguide and the second optical waveguide and in the middle of the first optical waveguide and the second optical waveguide, and is used to apply a microwave field to the Mach-Zehnder structure to achieve electro-optic modulation. The Mach-Zehnder structure and the distributed traveling-wave electrode are covered by the upper cladding.

[0010] Optionally, the crystal system type of the single-crystal silicon carbide substrate includes 3C-SiC, 4H-SiC, 6H-SiC or 15R-SiC, and the thickness of the single-crystal silicon carbide substrate is 0.2 to 1 mm.

[0011] Optionally, the distributed traveling wave electrode includes a first ground electrode, a traveling wave signal electrode, and a second ground electrode, wherein the distance between the first ground electrode, the second ground electrode, and the traveling wave signal electrode is 3~7μm.

[0012] Optionally, the thickness of the traveling wave signal electrode is 0.5~20μm, and the width of the traveling wave signal electrode is 30~80μm.

[0013] Optionally, the material of the distributed traveling wave electrode includes at least one of titanium, gold, silver, copper, niobium, aluminum, and chromium.

[0014] Optionally, the waveguide material layer, the first optical waveguide, and the second optical waveguide are made of one of the following materials: single-crystal silicon, lithium niobate, lithium tantalate, silicon nitride, silicon carbide, barium titanate, lead zirconate titanate, quartz, silicon dioxide, or diamond.

[0015] Optionally, the length of the first optical waveguide is equal to the length of the second optical waveguide, the thickness of the first optical waveguide and the second optical waveguide is 200~1000nm, and the width of the first optical waveguide and the second optical waveguide is 200~2500nm.

[0016] Optionally, the refractive index of the optical isolation layer is less than that of the waveguide material layer, and the material forming the optical isolation layer includes silicon dioxide or quartz, and the thickness of the optical isolation layer is 0.3~20μm.

[0017] The present invention also provides a method for fabricating a Mach-Zehnder modulator based on a silicon carbide substrate, which is used to fabricate the above-mentioned Mach-Zehnder modulator based on a silicon carbide substrate, and includes the following steps:

[0018] A single-crystal silicon carbide substrate is provided, and an optical isolation layer and a waveguide material layer are sequentially formed on the silicon carbide substrate;

[0019] A first photoresist mask layer is formed on the waveguide material layer. The first photoresist mask layer is exposed and developed. The waveguide material layer is then dry-etched to transfer the pattern of the Mach-Zehnder structure into the waveguide material layer. The Mach-Zehnder structure includes a first optical waveguide, a second optical waveguide, and a coupler. The first optical waveguide and the second optical waveguide are arranged in parallel, and the coupler is disposed at both ends of the first optical waveguide and the second optical waveguide. One end of the coupler is connected to the first optical waveguide and the second optical waveguide respectively through two single-mode waveguides. The other end of the coupler is also provided with an input waveguide and an output waveguide.

[0020] Distributed traveling wave electrodes are formed on the waveguide material layer. The distributed traveling wave electrodes are disposed on the outside of the first optical waveguide and the second optical waveguide and in the middle of the first optical waveguide and the second optical waveguide, and are used to apply a microwave field to the Mach-Zehnder structure to achieve electro-optic modulation.

[0021] An upper cladding is formed on the waveguide material layer, the upper cladding covering the Mach-Zehnder structure and the distributed traveling wave electrode.

[0022] Optionally, forming the electrode structure on the photoelectric thin film layer includes the following steps: forming a patterned second photoresist mask layer on the first photoresist mask layer; exposing and developing the second photoresist mask layer to define electrode deposition vias; and depositing a metal layer in the electrode deposition vias to form the distributed traveling wave electrode.

[0023] Optionally, the crystal system type of the single-crystal silicon carbide substrate includes 3C-SiC, 4H-SiC, 6H-SiC or 15R-SiC, and the thickness of the single-crystal silicon carbide substrate is 0.2 to 1 mm.

[0024] As described above, the Mach-Zehnder modulator based on a silicon carbide substrate and its fabrication method of the present invention have the following beneficial effects: The Mach-Zehnder modulator of the present invention utilizes the characteristics of low dielectric loss and dielectric constant that can match the optical group refractive index of the silicon carbide substrate in the high-frequency band. By optimizing the parameters of the distributed traveling wave electrode, it eliminates the need for T-shaped electrodes or substrate hollowing, thereby significantly reducing the loss of microwave signals during transmission and achieving precise matching between the microwave phase refractive index and the optical group refractive index, significantly improving the modulation bandwidth and modulation efficiency of the Mach-Zehnder modulator. In addition, the thermal conductivity of the silicon carbide substrate is much higher than that of substrate materials such as silicon, thereby effectively dissipating the heat generated during device operation and avoiding interference of thermal effects on modulation performance. Furthermore, the fabrication process of the present invention significantly improves process stability and repeatability, providing feasibility for large-scale integrated manufacturing of devices. Attached Figure Description

[0025] Figure 1 The diagram shown is a cross-sectional view of the Mach-Zehnder modulator based on a silicon carbide substrate according to the present invention.

[0026] Figure 2 The diagram shown is a three-dimensional structural schematic of the Mach-Zehnder modulator based on a silicon carbide substrate according to the present invention.

[0027] Figure 3 The diagram shown is a top view of the Mach-Zehnder modulator based on a silicon carbide substrate according to the present invention.

[0028] Figure 4 The diagram shows the microwave energy flow of the Mach-Zehnder modulator based on a silicon carbide substrate according to the present invention.

[0029] Figure 5 The diagram shows the contour plots of optical loss and electro-optic modulation efficiency in the Mach-Zehnder modulator based on silicon carbide substrate of the present invention, representing the changes in etching depth and electrode spacing.

[0030] Figure 6 The diagram shows the single-mode transmission optical field and optical group velocity of the Mach-Zehnder modulator based on a silicon carbide substrate according to the present invention.

[0031] Figure 7 The diagram shows the electric field distribution of the Mach-Zehnder modulator based on a silicon carbide substrate according to the present invention.

[0032] Figure 8 The diagram shows the microwave loss, microwave refractive index, and transmission line characteristic impedance of the Mach-Zehnder modulator based on a silicon carbide substrate according to the present invention.

[0033] Figure 9 The electro-optic response curve and modulation bandwidth diagram of the Mach-Zehnder modulator based on a silicon carbide substrate of the present invention are shown.

[0034] Figure 10 The diagram shows the process flow of the method for fabricating a Mach-Zehnder modulator based on a silicon carbide substrate according to the present invention.

[0035] Figure 11 The diagram shown is a cross-sectional view of the optical isolation layer and waveguide material layer formed in the preparation method of the present invention.

[0036] Figure 12 The diagram shown is a cross-sectional view of the Mach-Zehnder structure formed in the preparation method of the present invention.

[0037] Figure 13 The diagram shown is a cross-sectional view of the structure after the distributed traveling wave electrode is formed in the preparation method of the present invention.

[0038] Figure 14 The diagram shown is a cross-sectional view of the structure after the upper cladding is formed in the preparation method of the present invention.

[0039] Component designation explanation

[0040] 10. Silicon carbide substrate; 11. Optical isolation layer; 12. Waveguide material layer; 131. First optical waveguide; 132. Second optical waveguide; 133. Input waveguide; 134. Output waveguide; 135. Coupler; 136. Single-mode waveguide; 141. First ground electrode; 142. Second ground electrode; 143. Traveling wave signal electrode; 15. Upper cladding; S1~S4, Steps. Detailed Implementation

[0041] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0042] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0043] It should be understood that the use of terms such as "first" and "second" to define the components is merely for the purpose of distinguishing the aforementioned components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0044] Please see Figures 1 to 14 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0045] Example 1

[0046] Please see Figure 1 , Figure 1This is a schematic diagram of a Mach-Zehnder modulator based on a silicon carbide substrate 10 according to an embodiment of the present invention. The Mach-Zehnder modulator based on the silicon carbide substrate 10 includes a substrate, an optical isolation layer 11, and a waveguide material layer 12 stacked sequentially. Specifically, the crystal system of the single-crystal silicon carbide substrate 10 includes one of 3C-SiC, 4H-SiC, 6H-SiC, or 15R-SiC. The silicon carbide substrate 10 is a good thermal conductor with a thermal conductivity exceeding 500 W / (m·K), thereby effectively dissipating the heat accumulated by the device during operation and avoiding interference of thermal effects on modulation performance. Furthermore, single-crystal silicon carbide has low dielectric loss and a dielectric constant that matches the refractive index of the optical group in the high-frequency band, which can improve the electric field strength and enhance the electro-optic modulation efficiency. In this embodiment, the substrate is a wafer-level substrate, such as a 6-inch, 8-inch, or 12-inch wafer-level substrate, or it can be an irregularly shaped substrate. The shape and size of the substrate are not excessively limited here.

[0047] Optionally, the material forming the optical isolation layer 11 includes at least one of silicon dioxide or quartz, that is, the optical isolation layer 11 can be one of them, or it can be a stacked structure composed of two or more of them. The thickness of the optical isolation layer 11 is 0.3~20μm. Silicon dioxide or quartz has good insulation and low dielectric constant, which can effectively prevent mutual interference between different layers, reduce the transmission loss of optical signals, and also reduce the microwave loss of the electro-optic modulator structure.

[0048] Optionally, the material forming the waveguide material layer 12 includes one of single-crystal silicon, lithium niobate, lithium tantalate, silicon nitride, silicon carbide, barium titanate, lead zirconate titanate, quartz, silicon dioxide, or diamond. The refractive index of the waveguide material layer 12 is greater than that of the optical isolation layer 11, and the materials forming the waveguide material layer 12 all have excellent electro-optic effects. Under the action of an external electric field, the refractive index of the materials forming the waveguide material layer 12 will change. Therefore, they are usually used as optical waveguide materials to make optical waveguides. The thickness of the waveguide material layer 12 is 300~1000nm. The thickness of the waveguide material layer 12 can be any value within the above range, which will not be elaborated here.

[0049] like Figure 2As shown, a Mach-Zehnder structure is disposed on the waveguide material layer 12. The Mach-Zehnder structure includes a first optical waveguide 131, a second optical waveguide 132, and a coupler 135. The first optical waveguide 131 and the second optical waveguide 132 are arranged in parallel. The length of the first optical waveguide 131 is equal to the length of the second optical waveguide 132. The thickness of the first optical waveguide 131 and the second optical waveguide 132 is 200~1000nm, and the width of the first optical waveguide 131 and the second optical waveguide 132 is 200~2500nm. In this embodiment, the thickness of the first optical waveguide 131 and the second optical waveguide 132 is 200nm, and the width of the first optical waveguide 131 and the second optical waveguide 132 is 1200nm. The coupler 135 is disposed between the first optical waveguide 131 and the second optical waveguide 132. At both ends of the second optical waveguide 132, one end of the coupler 135 is connected to the first optical waveguide 131 and the second optical waveguide 132 respectively through two single-mode waveguides 136. The other end of the coupler 135 is also provided with an input waveguide 133 and an output waveguide 134 respectively. Specifically, the coupler 135 is of type 1×2. The optical signal is coupled from the input waveguide 133 into the coupler 135, and is split into two optical signals by the 1×2 coupler 135. The two optical signals enter the first optical waveguide 131 and the second optical waveguide 132 respectively for transmission. Finally, the optical signals with phase difference are formed by the electric field modulation generated by the distributed traveling wave electrode. The optical signals with phase difference are then combined by the 1×2 coupler 135 to finally form intensity modulation based on the constructive or destructive interference effect.

[0050] On the side of the waveguide material layer 12 away from the optical isolation layer 11, there are at least two spaced-apart distributed traveling-wave electrodes. These distributed traveling-wave electrodes are located outside the first optical waveguide 131 and the second optical waveguide 132 and between the first optical waveguide 131 and the second optical waveguide 132. Figure 2 Three distributed traveling-wave electrodes are shown. In this embodiment, as... Figure 3As shown, the distributed traveling wave electrode has a coplanar electrode structure. The distributed traveling wave electrode includes a first ground electrode 141, a traveling wave signal electrode 143, and a second ground electrode 142. The traveling wave signal electrode 143 is located in the middle region formed by the first optical waveguide 131 and the second optical waveguide 132. The first ground electrode 141 is located outside the first optical waveguide 131, and the second ground electrode 142 is located outside the second optical waveguide 132. The distance between the first ground electrode 141, the second ground electrode 142, and the traveling wave signal electrode 143 is 3~7μm. Specifically, in this embodiment, the distance between the first ground electrode 141, the second ground electrode 142, and the traveling wave signal electrode 143 is 5μm.

[0051] Optionally, the thickness of the traveling wave signal electrode 143 is 0.5~20μm, the width of the traveling wave signal electrode 143 is 30~80μm, and the material of the distributed traveling wave electrode includes at least one of titanium, gold, silver, copper, niobium, aluminum, and chromium. Specifically, in this embodiment, the first ground electrode 141, the traveling wave signal electrode 143, and the second ground electrode 142 are all titanium / silver / gold electrodes, wherein the thickness of the titanium electrode layer is 30nm, the thickness of the silver electrode layer is approximately 800nm, and the thickness of the gold electrode layer is 50nm.

[0052] An upper cladding layer 15 is also disposed above the waveguide material layer 12. The refractive index of the upper cladding layer 15 is less than that of the waveguide material layer 12, and the material forming the upper cladding layer 15 is one of air, vacuum, silicon dioxide or quartz. Specifically, in this embodiment, the upper cladding layer 15 is a silicon dioxide layer.

[0053] like Figure 4 As shown, it displays the microwave energy flow diagram of the Mach-Zehnder modulator based on silicon carbide substrate 10 of the present invention. According to the simulation results of HFSS software, the microwave energy is confined in the gap between the first ground electrode 141 and the traveling wave signal electrode 143 and the second ground electrode 142 and the traveling wave signal electrode 143, and highly overlaps with the regions where the first optical waveguide 131 and the second optical waveguide 132 are located. Moreover, the microwave energy attenuates with the distance of propagation.

[0054] like Figure 5As shown, this is a contour plot illustrating the optical loss and electro-optic modulation efficiency variations in the etching depth and electrode spacing of the Mach-Zehnder modulator based on a silicon carbide substrate 10 according to the present invention. The geometric parameters of the first optical waveguide 131 and the second optical waveguide 132, as well as the geometric parameters of the first ground electrode 141, the traveling wave signal electrode 143, and the second ground electrode 142 in the Mach-Zehnder modulator, all have a strong impact on the device performance. For the Mach-Zehnder modulator, narrowing the spacing between the first ground electrode 141, the traveling wave signal electrode 143, and the second ground electrode 142 can increase the microwave intensity within the optical field range and improve modulation efficiency. However, excessively narrow spacing will drastically increase the absorption loss of light waves by the metal. Furthermore, while shallow etching of the waveguide material layer 12 to reduce the height of the first optical waveguide 131 and the second optical waveguide 132 can increase the channel for the microwave field to enter the optical field region, thereby improving modulation efficiency, excessively shallow etching depth will weaken the confinement ability of the optical mode, leading to increased optical loss, and in severe cases, even making it impossible to maintain single-mode transmission. Figure 5 The results show that when the distance between the first ground electrode 141, the traveling wave signal electrode 143, and the second ground electrode 142 is 5 μm, and the height of the first optical waveguide 131 and the second optical waveguide 132 is 200 nm, the modulation bandwidth and modulation efficiency of the Mach-Zehnder modulator can be significantly improved without increasing optical loss.

[0055] like Figure 6 As shown, it displays the single-mode transmission optical field and optical group velocity diagram of the Mach-Zehnder modulator based on silicon carbide substrate 10 of the present invention. As can be seen from the figure, when the optical signal is transmitted by the electro-optic modulator described in this embodiment, the optical signal is transmitted in TE single mode with a group refractive index of 2.14, and most of the optical field is tightly confined in the first optical waveguide 131 and the second optical waveguide 132.

[0056] like Figure 7 As shown, it is an electric field distribution diagram of the Mach-Zehnder modulator based on silicon carbide substrate 10 of the present invention. As can be seen from the figure, the electric field formed in the electro-optic modulator is a microwave field that propagates from traveling wave signal electrode 143 to the first ground electrode 141 and the second ground electrode 142, and its microwave phase refractive index is 2.2.

[0057] like Figure 8The figure shows the microwave loss, microwave refractive index, and transmission line characteristic impedance of the Mach-Zehnder modulator based on silicon carbide substrate 10 according to the present invention. As can be seen from the figure, the microwave loss of the first ground electrode 141, traveling wave signal electrode 143, and second ground electrode 142 is 4.8 dB / cm@50 dB; the microwave refractive index of the first ground electrode 141, traveling wave signal electrode 143, and second ground electrode 142 converges to 2.12, thus matching the refractive index of the optical group; the characteristic impedance of the ports of the first ground electrode 141, traveling wave signal electrode 143, and second ground electrode 142 converges to 50 Ω, which can reduce unnecessary reflections of energy transmitted to the microwave generator inside the electrodes. Figure 8 As can be seen from the microwave loss curve shown, when faced with the trade-off between modulation efficiency and modulation bandwidth, the silicon carbide substrate 10 has the characteristics of low dielectric loss and suitable dielectric constant in the high-frequency band, which can significantly reduce the loss of microwave signal in transmission and achieve efficient matching between microwave phase refractive index and optical group refractive index, thus significantly improving the modulation bandwidth and modulation efficiency of electro-optic modulator.

[0058] like Figure 9 As shown, the electro-optic response curve and modulation bandwidth diagram of the Mach-Zehnder modulator based on silicon carbide substrate 10 of the present invention are displayed. As can be seen from the figure, its modulation efficiency is 2.85 V·cm and the -1.2dB electro-optic modulation bandwidth is about 300 GHz.

[0059] Example 2

[0060] This embodiment provides a method for fabricating a Mach-Zehnder modulator based on a silicon carbide substrate 10, such as... Figure 10 The diagram shown is a process flow chart of the fabrication method of the Mach-Zehnder modulator based on silicon carbide substrate 10, including the following steps:

[0061] S1: A single-crystal silicon carbide substrate 10 is provided, and an optical isolation layer 11 and a waveguide material layer 12 are sequentially formed on the silicon carbide substrate 10;

[0062] S2: A first photoresist masking layer is formed on the waveguide material layer 12. The first photoresist masking layer is exposed and developed. The waveguide material layer 12 is dry etched to transfer the pattern of the Mach-Zehnder structure into the waveguide material layer 12. The Mach-Zehnder structure includes a first optical waveguide 131, a second optical waveguide 132, and a coupler 135. The first optical waveguide 131 and the second optical waveguide 132 are arranged in parallel, and the coupler 135 is disposed at both ends of the first optical waveguide 131 and the second optical waveguide 132. One end of the coupler 135 is connected to the first optical waveguide 131 and the second optical waveguide 132 respectively through two single-mode waveguides 136. The other end of the coupler 135 is also provided with an input waveguide 133 and an output waveguide 134.

[0063] S3: A distributed traveling wave electrode is formed on the waveguide material layer 12. The distributed traveling wave electrode is disposed on the outside of the first optical waveguide 131 and the second optical waveguide 132 and in the middle of the first optical waveguide 131 and the second optical waveguide 132, and is used to apply a microwave field to the Mach-Zehnder structure to achieve electro-optic modulation.

[0064] S4: An upper cladding layer 15 is formed on the waveguide material layer 12, the upper cladding layer 15 covering the Mach-Zehnder structure and the distributed traveling wave electrode.

[0065] The fabrication method of the electro-optic modulator based on the silicon carbide substrate 10 is further described below with reference to the accompanying drawings:

[0066] In step S1, please refer to Figure 11 A single-crystal silicon carbide substrate 10 is provided, on which an optical isolation layer 11 and a waveguide material layer 12 are sequentially formed.

[0067] As an example, the substrate is a single-crystal silicon carbide substrate 10. The crystal system type of the single-crystal silicon carbide substrate 10 includes one of 3C-SiC, 4H-SiC, 6H-SiC, or 15R-SiC. As a good thermal conductor, the silicon carbide substrate 10 has a thermal conductivity exceeding 500 W / (m·K), which can effectively dissipate the heat accumulated by the device during operation and avoid interference of thermal effects on modulation performance. Furthermore, single-crystal silicon carbide has the characteristics of low dielectric loss and a dielectric constant that can match the refractive index of optical groups in the high-frequency band. The substrate can be a wafer-level substrate, such as a 6-inch, 8-inch, or 12-inch wafer-level substrate. No excessive restrictions are placed on the morphology and size of the substrate here.

[0068] In some embodiments, the thickness of the single-crystal silicon carbide substrate 10 ranges from 0.2 to 1 mm, but this is not limited here.

[0069] Specifically, in this embodiment, the thickness of the single-crystal silicon carbide substrate 10 is 0.5 mm, which can ensure the mechanical strength of the electro-optic modulator structure, while avoiding the problem of increased light loss during propagation due to the large thickness of the single-crystal silicon carbide substrate 10.

[0070] As an example, an optical isolation layer 11 and a waveguide material layer 12 are sequentially formed on the silicon carbide substrate 10. Specifically, the optical isolation layer 11 is formed on one side surface of the silicon carbide substrate 10 by physical vapor deposition or chemical vapor deposition.

[0071] In some embodiments, the material forming the optical isolation layer 11 includes at least one of silicon dioxide or quartz. Silicon dioxide or quartz has good insulation and low dielectric constant, which can effectively prevent mutual interference between different layers and reduce the transmission loss of optical signals.

[0072] In some embodiments, the thickness of the optical isolation layer 11 is 0.3~20μm, but this is not limited here.

[0073] Specifically, in this embodiment, the optical isolation layer 11 is a silicon dioxide layer with a thickness of 2 μm. By setting the above thickness range, not only can the microwave loss of the electro-optic modulator structure be reduced, but also the interaction between different layers can be avoided.

[0074] Specifically, the steps for forming the waveguide material layer 12 are as follows: providing an ion-implanted optical waveguide wafer, flip-bonding the optical waveguide wafer to the optical isolation layer 11, and then performing a high-temperature annealing process to form the waveguide material layer 12 on the optical isolation layer 11.

[0075] In this embodiment, the optical waveguide wafer is a lithium tantalate wafer, and the size of the lithium tantalate wafer is equal to the size of the substrate.

[0076] Specifically, ions are implanted into the lithium tantalate wafer using ion implantation. The lithium tantalate wafer is then sequentially divided into a residual layer, a separation layer, and a lithium tantalate thin film layer. The lithium tantalate wafer is flip-chip bonded to the optical isolation layer 11, followed by a high-temperature annealing process, specifically annealing at 550°C for 6 hours. The residual layer is then separated from the lithium tantalate thin film layer, and a waveguide material layer 12 is formed on the optical isolation layer 11. The waveguide material layer 12 is then chemically and mechanically polished to reduce its roughness.

[0077] In other embodiments, the material forming the waveguide material layer 12 may also be one of single-crystal silicon, lithium niobate, silicon nitride, silicon carbide, barium titanate, lead zirconate titanate, quartz, silicon dioxide, or diamond. All of the above materials have excellent electro-optic effects. Under the action of an external electric field, the refractive index of the above materials will change. The refractive index of the waveguide material layer 12 is greater than that of the optical isolation layer 11. The thickness of the waveguide material layer 12 is 300~1000nm, which is not limited here.

[0078] The thickness of the waveguide material layer 12 can be adjusted by adjusting the ion implantation depth. The greater the ion implantation depth, the greater the thickness of the prepared waveguide material layer 12; conversely, the smaller the ion implantation depth, the smaller the thickness of the prepared waveguide material layer 12. Specifically, in this embodiment, the thickness of the waveguide material layer 12 is 300 nm.

[0079] In step S2, please refer to Figure 12 A first photoresist masking layer is formed on the waveguide material layer 12. The first photoresist masking layer is exposed and developed. The waveguide material layer 12 is dry etched to transfer the pattern of the Mach-Zehnder structure into the waveguide material layer 12. The Mach-Zehnder structure includes a first optical waveguide 131, a second optical waveguide 132, and a coupler 135. The first optical waveguide 131 and the second optical waveguide 132 are arranged in parallel, and the coupler 135 is disposed at both ends of the first optical waveguide 131 and the second optical waveguide 132. One end of the coupler 135 is connected to the first optical waveguide 131 and the second optical waveguide 132 respectively through two single-mode waveguides 136. The other end of the coupler 135 is also provided with an input waveguide 133 and an output waveguide 134.

[0080] In this embodiment, a first photoresist mask layer is formed on the waveguide material layer 12. The first photoresist mask layer is then subjected to drying, exposure, and development processes to form a patterned first photoresist layer. Using the patterned first photoresist layer as a mask, the waveguide material layer 12 is dry-etched to form a Mach-Zehnder structure in the waveguide material layer 12. The Mach-Zehnder structure includes a first optical waveguide 131, a second optical waveguide 132, and a coupler 135. The first optical waveguide 131 and the second optical waveguide 132... The first optical waveguide 131 and the second optical waveguide 132 are arranged in parallel, with a thickness of 200 nm. The first optical waveguide 131 and the second optical waveguide 132 are ridge waveguides. The coupler 135 is disposed at both ends of the first optical waveguide 131 and the second optical waveguide 132. One end of the coupler 135 is connected to the first optical waveguide 131 and the second optical waveguide 132 respectively through two single-mode waveguides 136. The other end of the coupler 135 is also provided with an input waveguide 133 and an output waveguide 134 respectively.

[0081] Specifically, the dry etching method for the waveguide material layer 12 includes ion beam etching, reactive ion etching, or inductively coupled plasma etching. Preferably, in this embodiment, the dry etching method for the waveguide material layer 12 is reactive ion etching.

[0082] In step S3, please refer to Figure 13 Distributed traveling wave electrodes are formed on the waveguide material layer 12. The distributed traveling wave electrodes are disposed on the outside of the first optical waveguide 131 and the second optical waveguide 132 and in the middle of the first optical waveguide 131 and the second optical waveguide 132, and are used to apply a microwave field to the Mach-Zehnder structure to achieve electro-optic modulation.

[0083] As an example, forming a distributed traveling wave electrode on the waveguide material layer 12 includes the following steps: forming a patterned second photoresist mask layer on the first photoresist mask layer; exposing and developing the second photoresist mask layer to define electrode deposition vias; and depositing a metal layer in the electrode deposition vias to form the distributed traveling wave electrode.

[0084] Specifically, after performing step S2, the patterned first photoresist layer formed on the waveguide material layer 12 can be left unremoved, and the patterned second photoresist masking layer can be grown immediately afterwards. The method for forming the patterned second photoresist masking layer is a photoresist coating, drying, exposure, and development process, which will not be described in detail here.

[0085] In this embodiment, using a patterned second photoresist masking layer as a mask, the first photoresist layer is photolithographically etched to form electrode deposition vias. The bottom of the electrode deposition vias exposes the top of the waveguide material layer 12. A metal layer is deposited in the electrode deposition vias using electron beam evaporation to form the distributed traveling wave electrodes. Optionally, before depositing the metal layer in the electrode deposition vias using electron beam evaporation, the first photoresist layer and the second photoresist masking layer need to be removed.

[0086] In this embodiment, the distributed traveling-wave electrode is disposed outside the first optical waveguide 131 and the second optical waveguide 132 and in the middle of the first optical waveguide 131 and the second optical waveguide 132, for applying a microwave field to the Mach-Zehnder structure to achieve electro-optic modulation. Specifically, the distributed electrode includes a first ground electrode 141, a traveling-wave signal electrode 143, and a second ground electrode 142, wherein the traveling-wave signal electrode 143 is located in the middle region formed by the first optical waveguide 131 and the second optical waveguide 132, the first ground electrode 141 is located outside the first optical waveguide 131, the second ground electrode 142 is located outside the second optical waveguide 132, and the distance between the first ground electrode 141, the second ground electrode 142, and the traveling-wave signal electrode 143 is 3~7μm.

[0087] Optionally, the material forming the distributed electrode includes at least one of titanium, gold, silver, copper, niobium, aluminum, and chromium. Specifically, in this embodiment, titanium / silver / gold electrodes are sequentially deposited in the electrode deposition via using electron beam evaporation technology. The thickness of the titanium metal layer is 30 nm, the thickness of the silver metal layer is approximately 800 nm, and the thickness of the gold metal layer is 50 nm. During the deposition process, the deposition rate and thickness are controlled in real time using a film thickness monitor to ensure the uniformity and conductivity of each metal layer. After deposition, chemical mechanical polishing (CMP) is used to planarize the metal layers. By selecting appropriate polishing fluid and polishing pads, and adjusting the polishing pressure and polishing time, the surface flatness of the distributed electrode is reduced.

[0088] In step S4, please refer to Figure 14 An upper cladding layer 15 is formed on the waveguide material layer 12, and the upper cladding layer 15 covers the Mach-Zehnder structure and the distributed traveling wave electrode.

[0089] As an example, the refractive index of the upper cladding 15 is less than that of the waveguide material layer 12, and the material forming the upper cladding 15 is one of air, vacuum, silicon dioxide or quartz.

[0090] In some embodiments, a low-refractive-index upper cladding layer 15 is formed on the electrode structure and the optical modulation structure using plasma-enhanced chemical vapor deposition (PECVD). Optionally, the refractive index of the upper cladding layer 15 is lower than that of the waveguide material layer 12, and the material forming the upper cladding layer 15 is one of air, vacuum, silicon dioxide, or quartz. During the deposition process, the growth rate and refractive index of the upper cladding layer 15 are controlled by adjusting the power of the RF power supply, the gas flow ratio, and the cavity pressure to reduce optical loss.

[0091] In summary, the Mach-Zehnder modulator based on a silicon carbide substrate and its fabrication method of the present invention utilize the low dielectric loss and dielectric constant of silicon carbide substrates in the high-frequency band, which can match the optical group refractive index. Through optimization of the distributed traveling-wave electrode parameters, it eliminates the need for T-shaped electrodes or substrate hollowing, significantly reducing microwave signal loss during transmission and achieving precise matching between the microwave phase refractive index and the optical group refractive index. This significantly improves the modulation bandwidth and modulation efficiency of the Mach-Zehnder modulator. Furthermore, the thermal conductivity of silicon carbide substrates is much higher than that of substrate materials such as silicon, effectively dissipating the heat generated during device operation and avoiding thermal interference with modulation performance. Moreover, the fabrication process of the present invention significantly improves process stability and repeatability, providing feasibility for large-scale integrated manufacturing of the device. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0092] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A Mach-Zehnder modulator based on a silicon carbide substrate, characterized in that, The substrate, the optical isolation layer, and the waveguide material layer are sequentially stacked, wherein the substrate is a single crystal silicon carbide substrate. The Mach-Zehnder structure is arranged on the surface of the waveguide material layer away from the optical isolation layer, and includes a first optical waveguide, a second optical waveguide, and a coupler. The distributed traveling wave electrode is arranged outside and in the middle of the first optical waveguide and the second optical waveguide, and is used to apply a microwave field to the Mach-Zehnder structure to realize electro-optic modulation. The crystal system type of the single crystal silicon carbide substrate includes 3C-SiC, 4H-SiC, 6H-SiC, or 15R-SiC, and the thickness of the single crystal silicon carbide substrate is 0.2-1 mm.

2. The silicon carbide substrate-based Mach-Zehnder modulator of claim 1, wherein: The distributed traveling wave electrode includes a first grounding electrode, a traveling wave signal electrode, and a second grounding electrode, wherein the distance between the first grounding electrode, the second grounding electrode, and the traveling wave signal electrode is 3-7 μm.

3. The silicon carbide substrate-based Mach-Zehnder modulator of claim 1, wherein: The thickness of the traveling wave signal electrode is 0.5-20 μm, and the width of the traveling wave signal electrode is 30-80 μm.

4. The silicon carbide substrate-based Mach-Zehnder modulator of claim 3, wherein: The material of the distributed traveling wave electrode includes at least one of titanium, gold, silver, copper, niobium, aluminum, chromium.

5. The silicon carbide substrate-based Mach-Zehnder modulator of claim 1, wherein: The material of the waveguide material layer, the first optical waveguide, and the second optical waveguide includes one of single crystal silicon, lithium niobate, lithium tantalate, silicon nitride, silicon carbide, barium titanate, lead zirconium titanate, quartz, silicon dioxide, or diamond.

6. The silicon carbide substrate-based Mach-Zehnder modulator of claim 1, wherein: The length of the first optical waveguide is equal to the length of the second optical waveguide, the thickness of the first optical waveguide and the second optical waveguide is 200-1000 nm, and the width of the first optical waveguide and the second optical waveguide is 200-2500 nm.

7. The silicon carbide substrate-based Mach-Zehnder modulator of claim 1, wherein: The refractive index of the optical isolation layer is less than the refractive index of the waveguide material layer, and the material forming the optical isolation layer includes silicon dioxide or quartz, and the thickness of the optical isolation layer is 0.3-20 μm.

8. The silicon carbide substrate-based Mach-Zehnder modulator of claim 1, wherein: The method includes the following steps:

9. A method for manufacturing a Mach-Zehnder modulator based on a silicon carbide substrate, for manufacturing the Mach-Zehnder modulator based on a silicon carbide substrate according to any one of claims 1 to 8, characterized by, A single crystal silicon carbide substrate is provided, and an optical isolation layer and a waveguide material layer are sequentially formed on the silicon carbide substrate. ​ forming a first photoresist mask layer on the waveguide material layer, exposing and developing the first photoresist mask layer, and dry etching the waveguide material layer to transfer a pattern of a Mach-Zehnder structure into the waveguide material layer, the Mach-Zehnder structure including a first optical waveguide, a second optical waveguide, and a coupler, wherein the first optical waveguide and the second optical waveguide are arranged in parallel, and the coupler is arranged at both ends of the first optical waveguide and the second optical waveguide, one end of the coupler is connected to the first optical waveguide and the second optical waveguide through two single-mode waveguides, respectively, and the other end of the coupler is further provided with an input waveguide and an output waveguide, respectively; forming a distributed row wave electrode on the waveguide material layer, the distributed row wave electrode being arranged outside the first optical waveguide and the second optical waveguide and in the middle of the first optical waveguide and the second optical waveguide, for applying a microwave field to the Mach-Zehnder structure to realize electro-optic modulation; forming an upper cladding layer on the waveguide material layer, the upper cladding layer covering the Mach-Zehnder structure and the distributed row wave electrode.

10. The method of producing a silicon carbide based electro-optic modulator according to claim 9, wherein: forming the electrode structure on the photoelectric thin film layer includes the following steps: forming a patterned second photoresist mask layer on the first photoresist mask layer, exposing and developing the second photoresist mask layer to define an electrode deposition through hole, and depositing a metal layer in the electrode deposition through hole to form the distributed row wave electrode.

11. The method of producing a silicon carbide based electro-optic modulator according to claim 9, wherein: The crystal system type of the single crystal silicon carbide-based substrate includes 3C-SiC, 4H-SiC, 6H-SiC, or 15R-SiC, and the thickness of the single crystal silicon carbide-based substrate is 0.2-1 mm.

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