Electro-optical modulator with low driving voltage and preparation method thereof

Abstract

According to the electro-optical modulator with the low driving voltage and the preparation method of the electro-optical modulator, the modulation electrode is prepared by adopting the superconducting material instead of conventional metal, so that the ohmic loss of the modulation electrode can be eliminated in a low-temperature working environment, a microwave modulation signal can be transmitted with extremely low loss, the bandwidth of the electro-optical modulator is remarkably improved, and the performance of the electro-optical modulator is improved. Due to the characteristic of extremely low transmission loss of the superconducting modulation electrode, the interaction between the electrode and a light field is enhanced by adopting a longer electrode design on the premise of not introducing obvious signal attenuation, so that the half-wave voltage can be effectively reduced while the ultra-high modulation bandwidth of the electro-optical modulator can be maintained, and the performance of the electro-optical modulator is improved. Therefore, a millivolt-level weak electric signal can be efficiently responded, and a cross-temperature zone interconnection system with higher energy efficiency can be constructed; besides, by means of the formed high-quality electro-optical thin film layer, waveguide transmission loss is greatly reduced, photorefractive damage is avoided under high optical power, the reliability of the whole optical interconnection core device is remarkably improved, and the service life of the whole optical interconnection core device is remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of integrated optics and superconducting electronics, and in particular to an electro-optic modulator with low driving voltage and its fabrication method. Background Technology

[0002] With the rapid development of superconducting computing and quantum information processing technologies, cryogenic computing systems, represented by superconducting computers, are placing higher demands on the bandwidth and energy efficiency of data transmission across temperature ranges. For example... Figure 1 As shown, the core computing units of cryogenic computing systems typically operate below the liquid helium temperature range (approximately 4 K) (the core processing unit actually operates in the milliKelvin (mK) range; while the peripheral classical readout and control interconnect units are located in the liquid helium temperature range (approximately 4 K)). However, their input / output (I / O) signals are extremely weak, mostly in the millivolt range. Therefore, in order to interconnect with high-speed data networks in room temperature environments, it is necessary to construct a signal interconnection scheme that spans a large temperature difference. An ideal cross-temperature range signal interconnection scheme must simultaneously meet multiple requirements such as extremely low thermal load, ultra-high data throughput, direct millivolt-level signal read / write, and high reliability to match the ultra-high energy efficiency of the core computing units of cryogenic computing systems.

[0003] Traditional electrical interconnection schemes based on metal transmission lines, such as coaxial cables combined with cryogenic amplifiers, are technically mature, but as they develop towards speeds of tens of Gbps and higher, the total power consumption and thermal load of the system are approaching the limits of the cooling system. Furthermore, to meet the ever-increasing I / O demands of superconducting processors, the industry has explored solutions using radio frequency transmission lines for signal relay in cryogenic environments. However, the performance degradation and additional power consumption of high-speed amplifiers at deep cryogenic temperatures still limit their transmission rate and reliability. Photonic interconnect technology is considered a research hotspot for overcoming these challenges. Its basic principle is that optical fibers possess ultra-low thermal conductivity and ultra-high bandwidth potential. Using optical fibers as the transmission medium, superconducting weak electrical signals can be directly converted into optical signals through an electro-optic modulator in the liquid helium temperature range, theoretically solving the aforementioned problems simultaneously. This requires the electro-optic modulator in the core computing unit to simultaneously meet the following key characteristics: 1) Extremely low half-wave voltage (V π 1) ≤50 mV) to directly respond to millivolt-level signals; 2) Sufficiently high modulation bandwidth (generally ≥ 20 Gbps) to support high-speed data communication; 3) Excellent low-temperature operating stability and low optical loss to ensure that the core computing unit can operate reliably for a long time.

[0004] Currently, research on high-performance electro-optic modulators for cryogenic applications mainly focuses on monolithic integrated electro-optic modulator schemes. Among them, integrated modulators based on thin-film lithium niobate have become the mainstream research focus. However, this type of integrated modulator still faces the following key problems that need to be solved in practical applications:

[0005] Power stability: The typical transmission loss of existing thin-film lithium niobate waveguides is about 1 dB / cm. They are prone to photorefractive damage at higher optical power, which affects the long-term reliability of the device at low temperatures.

[0006] High-frequency losses of electrodes: Current electro-optic modulators typically use traveling-wave electrodes made of conventional metals (such as gold), such as... Figure 2 The figure shows the relationship between the modulator bandwidth and half-wave voltage caused by microwave losses in ordinary metals and superconducting materials. As can be seen from the figure, in the microwave band, the ohmic loss of the metal electrode determines that low half-wave voltage and large bandwidth cannot be achieved at the same time, and a trade-off usually needs to be made in the design. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an electro-optic modulator with low driving voltage and its preparation method, which solves the problem that the electro-optic modulator using conventional metals to prepare modulation electrodes in the prior art generates high ohmic loss when transmitting microwave modulation voltage signals in low-temperature environments. This results in a fundamental contradiction between reducing the half-wave voltage and increasing the electrode length and increasing the bandwidth and shortening the electrode, which seriously restricts the improvement of modulation bandwidth.

[0008] To achieve the above and other related objectives, the present invention provides an electro-optic modulator with a low driving voltage, comprising:

[0009] A substrate and an optical isolation layer and an electro-optic thin film layer disposed on the substrate;

[0010] The Mach-Zehnder structure is disposed on the surface of the electro-optic thin film layer away from the optical isolation layer and is covered by the first dielectric layer. The Mach-Zehnder structure includes at least a first optical waveguide, a second optical waveguide, and a coupler. The first optical waveguide and the second optical waveguide are arranged in parallel. The coupler is disposed at both ends of the first optical waveguide and the second optical waveguide. The other end of the coupler is also provided with an input waveguide and an output waveguide, respectively.

[0011] A first dielectric layer is disposed on the electro-optic thin film layer, and the height of the first dielectric layer is greater than the height of the Mach-Zehnder structure to protect the Mach-Zehnder structure.

[0012] A superconducting modulation electrode is disposed on the first dielectric layer and corresponding to the first optical waveguide and the second optical waveguide, and is used to apply a modulation electric field to the Mach-Zehnder structure.

[0013] A second dielectric layer is disposed on the first dielectric layer and is used to cover the superconducting modulation electrode.

[0014] Optionally, the material of the electro-optic thin film layer includes one of lithium tantalate, lithium niobate, barium titanate, strontium titanate, and lead zirconate titanate.

[0015] Optionally, the material of the superconducting modulation electrode includes one of niobium, niobium nitride, titanium niobium nitride, tantalum, aluminum, and yttrium barium copper oxide.

[0016] Optionally, the superconducting modulation electrode includes a first ground electrode, a signal electrode, and a second ground electrode, wherein the lengths of the first ground electrode, the second ground electrode, and the signal electrode are equal and are all 0.1~2m, and the width of the signal electrode is 1~50μm.

[0017] Optionally, the first optical waveguide and the second optical waveguide are either strip waveguides or ridge waveguides, the length of the first optical waveguide is equal to the length of the second optical waveguide, and the width of the first optical waveguide and the second optical waveguide is 1~3μm.

[0018] Optionally, the height of the ridge waveguide is 200~500nm.

[0019] Optionally, the height of the strip waveguide is 400~800nm, and the strip waveguide is a fully etched waveguide.

[0020] Optionally, the refractive index of the optical isolation layer is less than that of the electro-optic thin film layer, and the material forming the optical isolation layer includes silicon dioxide, quartz or sapphire, and the thickness of the optical isolation layer is 0.3~20μm.

[0021] The present invention also provides a method for fabricating a low-drive-voltage electro-optic modulator, which includes the following steps:

[0022] A substrate is provided, on which an optical isolation layer and an electro-optic thin film layer are sequentially formed;

[0023] A first hard mask layer is formed on the electro-optic thin film layer, and a dry etching process is performed on the electro-optic thin film layer based on the first hard mask layer to form a Mach-Zehnder structure on the electro-optic thin film layer. The Mach-Zehnder structure includes at least 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. The other end of the coupler is also provided with an input waveguide and an output waveguide, respectively.

[0024] A first dielectric layer is formed on the electro-optic thin film layer, the height of the first dielectric layer being greater than the height of the Mach-Zehnder structure;

[0025] A superconducting modulation electrode is formed on the first dielectric layer and is disposed corresponding to the first optical waveguide and the second optical waveguide, for applying a modulation electric field to the Mach-Zehnder structure.

[0026] A second dielectric layer is formed on the first dielectric layer, and the second dielectric layer covers the superconducting modulation electrode.

[0027] Optionally, after dry etching the electro-optic thin film layer, the process further includes a step of smoothing the sidewalls of the formed Mach-Zehnder waveguide using a wet etching process.

[0028] As described above, the electro-optic modulator with low driving voltage and its fabrication method of the present invention have the following beneficial effects: The electro-optic modulator of the present invention uses superconducting materials to replace conventional metals to prepare the modulation electrodes, which greatly reduces the ohmic loss of the modulation electrodes in a low-temperature operating environment, enabling microwave modulation signals to be transmitted with extremely low loss, significantly improving the 3dB bandwidth of the electro-optic modulator. Thanks to the extremely low transmission loss characteristic of the superconducting modulation electrodes, a longer electrode design can be used to enhance the interaction between the electrodes and the optical field without introducing significant signal attenuation. This allows the electro-optic modulator to maintain an ultra-high modulation bandwidth while effectively reducing the half-wave voltage, thereby enabling efficient response to weak electrical signals at the millivolt level, which helps to build a more energy-efficient cross-temperature interconnect system. In addition, the high-quality electro-optic thin film layer formed significantly reduces waveguide transmission loss, preventing photorefractive damage even at high optical power, and significantly improving the reliability and service life of the entire optical interconnect core device. Attached Figure Description

[0029] Figure 1 The diagram shows a cross-temperature interconnect architecture based on photonic interconnect technology in the prior art.

[0030] Figure 2 This diagram illustrates the relationship between the modulator's bandwidth and half-wave voltage caused by microwave losses in ordinary metals.

[0031] Figure 3 The diagram shown is a cross-sectional view of the electro-optic modulator with low driving voltage according to the present invention.

[0032] Figure 4 The diagram shows a three-dimensional structure of the electro-optic modulator with low driving voltage according to the present invention.

[0033] Figure 5 The diagram shows the distribution of optical loss and electro-optic modulation efficiency as a function of the first dielectric layer thickness and electrode spacing of the low-drive-voltage electro-optic modulator of the present invention.

[0034] Figure 6The diagram shows the impedance and effective refractive index distribution of the second dielectric layer thickness and signal electrode width of the low-drive-voltage electro-optic modulator of the present invention.

[0035] Figure 7 The diagram shows a process flow chart of the fabrication method of the low-drive-voltage electro-optic modulator of the present invention.

[0036] Figure 8 The diagram shown is a cross-sectional view of the optical isolation layer and the electro-optic thin film layer formed in the preparation method of the present invention.

[0037] Figure 9 The diagram shown is a cross-sectional view of the Mach-Zehnder structure formed in the preparation method of the present invention.

[0038] Figure 10 The diagram shown is a cross-sectional view of the first dielectric layer after it has been formed in the preparation method of the present invention.

[0039] Figure 11 The diagram shown is a cross-sectional view of the superconducting modulation electrode formed in the preparation method of the present invention.

[0040] Figure 12 The diagram shown is a cross-sectional view of the second dielectric layer after it has been formed in the preparation method of the present invention.

[0041] Component designation explanation

[0042] 101. Liquid helium temperature region; 10. Substrate; 11. Optical isolation layer; 12. Electro-optic thin film layer; 131. First optical waveguide; 132. Second optical waveguide; 133. Input waveguide; 134. Output waveguide; 135. Coupler; 141. First ground electrode; 142. Second ground electrode; 143. Traveling wave signal electrode; 15. First dielectric layer; 16. Second dielectric layer; S1~S5. Steps. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Please see Figures 1 to 11 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.

[0047] Example 1

[0048] Please see Figure 3 and Figure 4 , Figure 3 This is a cross-sectional structural schematic diagram of an electro-optic modulator with low driving voltage provided in an embodiment of the present invention. The electro-optic modulator with low driving voltage includes a substrate 10 and an optical isolation layer 11 and an electro-optic thin film layer 12 stacked on the substrate 10. Specifically, the substrate 10 is a silicon substrate 10, a single-crystal silicon carbide substrate 10, a quartz substrate, or a sapphire substrate, and the thickness of the substrate is 0.1mm-1mm. The substrate 10 is a wafer-level substrate 10, such as a 6-inch, 8-inch, or 12-inch wafer-level substrate 10. The morphology and size of the substrate 10 are not excessively limited here.

[0049] 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 these materials, 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, quartz, or sapphire have good insulation and low dielectric constant. Setting an optical isolation layer 11 of appropriate thickness 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.

[0050] Optionally, the material of the electro-optic thin film layer 12 includes one of lithium tantalate, lithium niobate, barium titanate, strontium titanate, and lead zirconate titanate. All of the above-mentioned materials of the electro-optic thin film layer 12 have excellent electro-optic effects, specifically, the refractive index of the above-mentioned materials will change under the action of an external electric field. Therefore, they are usually used as optical waveguide materials to make optical waveguides. In this embodiment, the refractive index of the electro-optic thin film layer 12 is greater than the refractive index of the optical isolation layer 11, and the thickness of the electro-optic thin film layer 12 is 300~1000nm. The thickness of the electro-optic thin film layer 12 can be any value within the above range, which will not be elaborated here.

[0051] As an example, such as Figure 2 As shown, a Mach-Zehnder structure is disposed on the electro-optic thin film 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, and the width of the first optical waveguide 131 and the second optical waveguide 132 is 1~3μm. 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. The other end of the coupler 135 is also provided with an input waveguide 133 and an output waveguide 134.

[0052] In this embodiment, the coupler 135 includes a 1×2 type optical beamsplitter and a 1×2 type optical beam combiner. The optical signal is coupled into the coupler 135 from the input waveguide 133. The 1×2 type optical beamsplitter splits the signal into two optical signals, which are then transmitted into the first optical waveguide 131 and the second optical waveguide 132, respectively. The optical signals are affected by the refractive index changes of the first optical waveguide 131 and the second optical waveguide 132 and modulated by the electric field generated by the distributed traveling wave electrodes, forming optical signals with a phase difference. The optical signals with a phase difference are then combined by the 1×2 type optical beamsplitter, ultimately forming intensity modulation based on constructive or destructive interference effects.

[0053] As an example, a first dielectric layer 15 is disposed on the electro-optic thin film layer 12. The first dielectric layer 15 is a silicon dioxide layer, and the height of the silicon dioxide layer is greater than the height of the Mach-Zehnder structure, serving to protect the electro-optic thin film layer 12 and the Mach-Zehnder structure. In this embodiment, the thickness of the first dielectric layer 15 is 700 nm.

[0054] As an example, a superconducting modulation electrode is disposed on the side of the first dielectric layer 15 away from the electro-optic thin film layer 12. The superconducting modulation 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.

[0055] In this embodiment, as Figure 3 As shown, the superconducting modulation electrode has a coplanar electrode structure. The superconducting modulation 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 lengths of the first ground electrode 141, the second ground electrode 142, and the signal electrode 143 are equal and are all 0.1~2m. The width of the signal electrode 143 is 1~50μm.

[0056] Specifically, in this embodiment, the first grounding electrode 141, the second grounding electrode 142 and the signal electrode 143 have the same length and are all 1m, and the width of the signal electrode 143 is 4.5μm.

[0057] Optionally, the material of the superconducting modulation electrode includes at least one of niobium, niobium nitride, titanium niobium nitride, tantalum, aluminum, and yttrium barium copper oxide. Specifically, in this embodiment, the first ground electrode 141, the traveling wave signal electrode 143, and the second ground electrode 142 are all superconducting niobium electrodes, wherein the thickness of the superconducting niobium electrode is 300 nm.

[0058] A second dielectric layer 16 is further disposed on the first dielectric layer 15. The second dielectric layer 16 is used to cover the superconducting modulation electrode. The refractive index of the second dielectric layer 16 is less than that of the electro-optic thin film layer 12. The second dielectric layer 16 is one of air, vacuum, silicon dioxide or quartz. Specifically, in this embodiment, the second dielectric layer 16 is a silicon dioxide layer and the thickness of the second dielectric layer 16 is 4.6 μm.

[0059] like Figure 5 As shown, it displays an optical loss and electro-optic modulation efficiency distribution diagram with variations in the thickness of the first dielectric layer 15 and the electrode spacing of the low-drive-voltage electro-optic modulator of the present invention. Figure 5 It can be seen that when the thickness of the first dielectric layer 15 is 700nm, and the distance between the first ground electrode 141, the second ground electrode 142 and the signal electrode 143 is 2.4μm, the optical transmission loss of the electro-optic modulator is 5dB / m and the electro-optic modulation efficiency is 2.5V·cm.

[0060] like Figure 6 As shown, it is an impedance and effective refractive index distribution diagram showing the thickness of the second dielectric layer 16 and the width of the signal electrode 143 in the low-drive voltage electro-optic modulator of the present invention. According to Figure 5 It can be seen that when the width of the signal electrode 143 is 4.5μm and the thickness of the second dielectric layer 16 is 4.6μm, its effective refractive index is 2.2 and its impedance is 50Ω, which means that impedance matching and velocity matching can be satisfied at the same time.

[0061] Example 2

[0062] This embodiment provides a method for fabricating an electro-optic modulator with low driving voltage, such as... Figure 7 The diagram shown is a process flow chart of the fabrication method of the low-drive-voltage electro-optic modulator, including the following steps:

[0063] S1: A substrate 10 is provided, and an optical isolation layer 11 and an electro-optic thin film layer 12 are sequentially formed on the substrate 10;

[0064] S2: A first hard mask layer is formed on the electro-optic thin film layer 12. Based on the first hard mask layer, the electro-optic thin film layer 12 is dry etched to form a Mach-Zehnder structure on the electro-optic thin film layer 12. The Mach-Zehnder structure includes at least 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 coupler 135 is disposed at both ends of the first optical waveguide 131 and the second optical waveguide 132. The other end of the coupler 135 is also provided with an input waveguide 133 and an output waveguide 134, respectively.

[0065] S3: A first dielectric layer 15 is formed on the electro-optic thin film layer 12, and the height of the first dielectric layer 15 is greater than the height of the Mach-Zehnder structure.

[0066] S4: A superconducting modulation electrode is formed on the first dielectric layer 15 and is disposed corresponding to the first optical waveguide 131 and the second optical waveguide 132, for applying a modulation electric field to the Mach-Zehnder structure.

[0067] S5: A second dielectric layer 16 is formed on the first dielectric layer 15, and the second dielectric layer 16 covers the superconducting modulation electrode.

[0068] The following is a further description of the low-drive-voltage electro-optic modulator with reference to the accompanying drawings:

[0069] In step S1, please refer to Figure 8 A substrate 10 is provided, on which an optical isolation layer 11 and an electro-optic thin film layer 12 are sequentially formed.

[0070] As an example, the substrate 10 is a silicon substrate 10, a single-crystal silicon carbide substrate 10, a quartz substrate or a sapphire substrate. The substrate 10 can be a wafer-level substrate 10, such as a 6-inch, 8-inch, or 12-inch wafer-level substrate 10. The morphology and size of the substrate 10 are not excessively limited here.

[0071] In some embodiments, the thickness of the substrate 10 ranges from 0.2 to 1 mm, and is not limited here. A suitable substrate 10 thickness can ensure the mechanical strength of the electro-optic modulator structure, while also avoiding the problem of increased light loss during propagation due to a larger substrate 10 thickness.

[0072] As an example, an optical isolation layer 11 and an electro-optic thin film layer 12 are sequentially formed on the substrate 10. Specifically, the optical isolation layer 11 is formed on one side surface of the substrate 10 by physical vapor deposition or chemical vapor deposition.

[0073] 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.

[0074] In some embodiments, the thickness of the optical isolation layer 11 is 0.3~20μm, which is not limited here. By setting an appropriate thickness for the optical isolation layer 11, not only can the microwave loss of the electro-optic modulator structure be reduced, but also the interaction between different layers can be further avoided.

[0075] Specifically, the steps for forming the electro-optic thin film layer 12 are as follows: providing an electro-optic thin film wafer, the electro-optic thin film wafer including a substrate layer and an electro-optic thin film layer 12, flip-bonding the electro-optic thin film wafer to the optical isolation layer 11, and then forming the electro-optic thin film layer 12 on the optical isolation layer 11 by separating the substrate layer and the electro-optic thin film layer 12, wherein the size of the electro-optic thin film wafer is equal to the size of the substrate 10.

[0076] Specifically, ion implantation is performed on the electro-optic thin film wafer to form a damage layer between the substrate layer and the electro-optic thin film layer 12. The implanted ions are H+ and / or He+, and the implantation energy is 50-1000 keV. Then, the damage layer is etched to separate the substrate layer and the electro-optic thin film layer 12. Finally, the electro-optic thin film layer 12 is formed on the optical isolation layer 11, and the electro-optic thin film layer 12 is chemically mechanically polished to reduce the roughness of the electro-optic thin film layer 12 to less than 0.3 nm to meet the requirement of low scattering loss.

[0077] The electro-optic thin film layer 12 is made of one of lithium tantalate, lithium niobate, barium titanate, strontium titanate, or lead zirconate titanate. All of these materials have excellent electro-optic effects. Under the action of an external electric field, the refractive index of these materials will change. The refractive index of the waveguide material layer is greater than that of the optical isolation layer 11. The thickness of the electro-optic thin film layer 12 is 300~1000nm, which is not limited here.

[0078] The thickness of the waveguide material layer can be adjusted by changing the ion implantation depth. The greater the ion implantation depth, the greater the thickness of the prepared waveguide material layer; conversely, the smaller the ion implantation depth, the smaller the thickness of the prepared waveguide material layer.

[0079] In step S2, please refer to Figure 9 A first hard mask layer is formed on the electro-optic thin film layer 12. Based on the first hard mask layer, the electro-optic thin film layer 12 is dry etched to form a Mach-Zehnder structure on the electro-optic thin film layer 12. The Mach-Zehnder structure includes at least 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 coupler 135 is disposed at both ends of the first optical waveguide 131 and the second optical waveguide 132. The other end of the coupler 135 is also provided with an input waveguide 133 and an output waveguide 134, respectively.

[0080] In this embodiment, a first hard mask layer is formed on the electro-optic thin film layer 12, and dry etching is performed on the electro-optic thin film layer 12 based on the first hard mask layer to form a Mach-Zehnder structure on the electro-optic thin film layer 12. The Mach-Zehnder structure includes at least 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 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. The other end of the coupler 135 is also provided with an input waveguide 133 and an output waveguide 134.

[0081] Specifically, the dry etching method for the electro-optic thin film layer 12 includes ion beam etching, reactive ion etching, or inductively coupled plasma etching. Preferably, in this embodiment, reactive ion etching is used to dry etch the electro-optic thin film layer 12. After etching, it is immersed in a solution of potassium hydroxide and hydrogen peroxide at high temperature for about 5 minutes for wet etching, thereby removing the redeposited material generated by dry etching and making the sidewalls of the waveguide forming the Mach-Zehnder structure smoother.

[0082] As an example, the first optical waveguide 131 and the second optical waveguide 132 are either strip waveguides or ridge waveguides, the length of the first optical waveguide 131 is equal to the length of the second optical waveguide 132, and the width of the first optical waveguide 131 and the second optical waveguide 132 is 1~3μm.

[0083] In this embodiment, both the first optical waveguide 131 and the second optical waveguide 132 are ridge waveguides with a height of 200~500nm, meaning that a portion of the electro-optic thin film layer 12 is retained during dry etching of the electro-optic thin film layer 12.

[0084] In other embodiments, the first optical waveguide 131 and the second optical waveguide 132 are both strip waveguides with a height of 400~800nm, and the strip waveguides are fully etched waveguides, that is, the optical isolation layer 11 is exposed when the electro-optic thin film layer 12 is dry etched.

[0085] In step S3, please refer to Figure 10 A first dielectric layer 15 is formed on the electro-optic thin film layer 12, and the height of the first dielectric layer 15 is greater than the height of the Mach-Zehnder structure.

[0086] In some embodiments, a first dielectric layer 15 is formed on the electro-optic thin film layer 12 using plasma-enhanced chemical vapor deposition (PECVD) technology. Optionally, the material of the first dielectric layer 15 is one of air, vacuum, silicon dioxide, or quartz. During the deposition process, the growth rate and refractive index of the first dielectric layer 15 are controlled by adjusting the power of the radio frequency power supply, the gas flow ratio, and the cavity pressure to reduce optical loss.

[0087] In step S4, please refer to Figure 11 A superconducting modulation electrode is formed on the first dielectric layer 15 and is disposed corresponding to the first optical waveguide 131 and the second optical waveguide 132, for applying a modulation electric field to the Mach-Zehnder structure.

[0088] As an example, forming a superconducting modulation electrode on the first dielectric layer 15 includes the following steps: forming a superconducting metal thin film on the first dielectric layer 15 by magnetron sputtering; forming a patterned photoresist layer on the superconducting metal thin film to define the region of the superconducting modulation electrode; using a plasma-enhanced reactive ion etching system with carbon tetrafluoride as the etching gas to transfer the superconducting modulation electrode into the superconducting metal thin film; and removing the photoresist and excess superconducting metal thin film by a wet etching process to form the final superconducting modulation electrode. The superconducting modulation electrode includes a first ground electrode 141, a signal electrode 143, and a second ground electrode 142, wherein the lengths of the first ground electrode 141, the second ground electrode 142, and the signal electrode 143 are equal and are all 0.1~2m, and the width of the signal electrode 143 is 1~50μm.

[0089] In this embodiment, 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.

[0090] Optionally, the material of the superconducting modulation electrode includes one of niobium, niobium nitride, titanium niobium nitride, tantalum, aluminum, and yttrium barium copper oxide. During the process of forming a superconducting metal thin film on the first dielectric layer 15 by magnetron sputtering, the deposition rate and thickness are controlled in real time by a film thickness monitoring instrument to ensure the uniformity and conductivity of the formed superconducting metal thin film. After deposition, chemical mechanical polishing (CMP) technology is used to perform surface smoothing treatment on the metal layer.

[0091] In step S5, please refer to Figure 12 A second dielectric layer 16 is formed on the first dielectric layer 15, and the second dielectric layer 16 covers the superconducting modulation electrode.

[0092] In some embodiments, a first dielectric layer 15 with a low refractive index is formed on the electrode structure and the optical modulation structure using plasma-enhanced chemical vapor deposition (PECVD) technology. Optionally, the material of the first dielectric layer 15 is one of air, vacuum, silica, or quartz. During the deposition process, the growth rate and refractive index of the first dielectric layer 15 are controlled by adjusting the power of the radio frequency power supply, the gas flow ratio, and the cavity pressure to reduce optical loss.

[0093] Example 3

[0094] A cross-sectional structural schematic diagram of a low-drive-voltage electro-optic modulator provided in this embodiment of the invention is shown below. Figure 12 As shown, the substrate 10 is a silicon substrate 10 with a thickness of 500 μm; the optical isolation layer 11 is a silicon dioxide layer with a thickness of 2 μm; the electro-optic thin film layer 12 is made of lithium niobate with a thickness of 300 nm and a surface roughness of less than 0.3 nm; the first waveguide and the second waveguide are ridge-shaped lithium niobate waveguides etched from the electro-optic thin film layer 12, with a thickness of 200 nm; the first dielectric layer 15 is a silicon dioxide layer with a thickness of 0.7 μm; the superconducting modulation electrode is a superconducting niobium electrode, including a first ground electrode 141, a signal electrode 143, and a second ground electrode 142, with a spacing of 2.4 μm between the first ground electrode 141, the signal electrode 143, and the second ground electrode 142, and a width of 4.5 μm for the signal electrode 143; the second dielectric layer 16 is a silicon dioxide layer with a thickness of 4.6 μm; and the length of the first ground electrode 141, the signal electrode 143, and the second ground electrode 142 is 1 m.

[0095] In summary, the low-drive-voltage electro-optic modulator and its fabrication method of this invention utilize superconducting materials instead of conventional metals to fabricate the modulation electrodes. This eliminates ohmic losses in the modulation electrodes under low-temperature operating conditions, enabling microwave modulation signals to be transmitted with extremely low loss. This significantly improves the 3dB bandwidth of the electro-optic modulator. Thanks to the extremely low transmission loss of the superconducting modulation electrodes, a longer electrode design can be used to enhance the interaction between the electrodes and the optical field without introducing significant signal attenuation. This allows the electro-optic modulator to maintain ultra-high modulation bandwidth while effectively reducing the half-wave voltage, thus enabling efficient response to weak electrical signals at the millivolt level. This contributes to the construction of more energy-efficient cross-temperature interconnect systems. Furthermore, the high-quality electro-optic thin film layer significantly reduces waveguide transmission loss, preventing photorefractive damage even at high optical power, and significantly improving the reliability and lifespan of the entire optical interconnect core device. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0096] 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 low-drive-voltage electro-optic modulator, characterized in that, include: Substrate and an optical isolation layer and an electro-optic thin film layer disposed on the substrate; The Mach-Zehnder structure is disposed on the surface of the electro-optic thin film layer away from the optical isolation layer and is covered by the first dielectric layer. The Mach-Zehnder structure includes at least a first optical waveguide, a second optical waveguide, and a coupler. The first optical waveguide and the second optical waveguide are arranged in parallel. The coupler is disposed at both ends of the first optical waveguide and the second optical waveguide. The other end of the coupler is also provided with an input waveguide and an output waveguide, respectively. A first dielectric layer is disposed on the electro-optic thin film layer, and the height of the first dielectric layer is greater than the height of the Mach-Zehnder structure to protect the Mach-Zehnder structure. A superconducting modulation electrode is disposed on the first dielectric layer and corresponding to the first optical waveguide and the second optical waveguide, and is used to apply a modulation electric field to the Mach-Zehnder structure. A second dielectric layer is disposed on the first dielectric layer and is used to cover the superconducting modulation electrode.

2. The low-drive-voltage electro-optic modulator according to claim 1, characterized in that: The material of the electro-optic thin film layer includes one of lithium tantalate, lithium niobate, barium titanate, strontium titanate, and lead zirconate titanate.

3. The low-drive-voltage electro-optic modulator according to claim 1, characterized in that: The superconducting modulation electrode is made of one of the following materials: niobium, niobium nitride, titanium niobium nitride, tantalum, aluminum, and yttrium barium copper oxide.

4. The low-drive-voltage electro-optic modulator according to claim 1, characterized in that: The superconducting modulation electrode includes a first ground electrode, a signal electrode, and a second ground electrode, wherein the lengths of the first ground electrode, the second ground electrode, and the signal electrode are equal and are all 0.1~2m, and the width of the signal electrode is 1~50μm.

5. The low-drive-voltage electro-optic modulator according to claim 1, characterized in that: The first optical waveguide and the second optical waveguide are either strip waveguides or ridge waveguides. The length of the first optical waveguide is equal to the length of the second optical waveguide, and the width of the first optical waveguide and the second optical waveguide is 1~3μm.

6. The low-drive-voltage electro-optic modulator according to claim 5, characterized in that: The height of the ridge waveguide is 200~500nm.

7. The low-drive-voltage electro-optic modulator according to claim 5, characterized in that: The height of the strip waveguide is 400~800nm, and the strip waveguide is a fully etched waveguide.

8. The low-drive-voltage electro-optic modulator according to claim 1, characterized in that: The refractive index of the optical isolation layer is less than that of the electro-optic thin film layer, and the material forming the optical isolation layer includes silicon dioxide, quartz or sapphire, and the thickness of the optical isolation layer is 0.3~20μm.

9. A method for fabricating a low-drive-voltage electro-optic modulator, used to fabricate the low-drive-voltage electro-optic modulator according to any one of claims 1 to 8, characterized in that, Includes the following steps: A substrate is provided, on which an optical isolation layer and an electro-optic thin film layer are sequentially formed; A first hard mask layer is formed on the electro-optic thin film layer, and a dry etching process is performed on the electro-optic thin film layer based on the first hard mask layer to form a Mach-Zehnder structure on the electro-optic thin film layer. The Mach-Zehnder structure includes at least 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. The other end of the coupler is also provided with an input waveguide and an output waveguide, respectively. A first dielectric layer is formed on the electro-optic thin film layer, the height of the first dielectric layer being greater than the height of the Mach-Zehnder structure; A superconducting modulation electrode is formed on the first dielectric layer and is disposed corresponding to the first optical waveguide and the second optical waveguide, for applying a modulation electric field to the Mach-Zehnder structure. A second dielectric layer is formed on the first dielectric layer, and the second dielectric layer covers the superconducting modulation electrode.

10. The method for fabricating a low-drive-voltage electro-optic modulator according to claim 9, characterized in that: After dry etching of the electro-optic thin film layer, the process further includes a step of smoothing the sidewalls of the waveguide formed by the Mach-Zehnder structure using a wet etching process.

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