Laminated conductor type thin film lithium niobate electro-optical modulator

Abstract

The invention relates to the field of photoelectric integrated devices, in particular to a laminated conductor type thin film lithium niobate electro-optical modulator which comprises a substrate, a lower cladding, a lithium niobate thin film, a ridge type optical waveguide, an upper cladding and a Ground-signal-ground electrode (GSG). The GSG electrode comprises a central signal electrode, a first grounding electrode and a second grounding electrode, the first grounding electrode and the second grounding electrode are arranged on the two sides of the central signal electrode at intervals, the signal electrode, the first grounding electrode and the second grounding electrode are each of a laminated structure of silicon dioxide and a gold conductor and are all formed on a lithium niobate film, and upper wrapping layers are arranged on the tops and the side faces of the lithium niobate film. The ridge-type optical waveguides comprise a first ridge-type optical waveguide and a second ridge-type optical waveguide which are both formed on the lithium niobate film, the first ridge-type optical waveguide is formed between the central electrode and the first grounding electrode, the second ridge-type optical waveguide is formed between the central electrode and the second grounding electrode, the lithium niobate film is located on the lower wrapping layer, and the lower wrapping layer is located on the substrate.

Description

Technical Field

[0001] The invention relates to the fields of optical communication and optoelectronic integrated devices, and in particular to a laminated conductor type thin film lithium niobate electro-optic modulator structure. Background Art

[0002] Light, as an electromagnetic wave, is widely used to carry information for broadcasting and television, mobile communications, and large-scale data network access, and forms the main architecture of modern broadband Internet through optical fiber. Electro-optic modulators are a reliable means of information modulation, which can quickly control the amplitude, phase, and frequency of optical broadband signals. Currently, the largest application area that needs to improve electro-optic modulators is the termination of millions of optical fibers in telecommunications and data center optical networks. The initial lead in data transmission capacity after the invention of optical fiber has been overshadowed by the continuous development of electronic bandwidth following Moore's Law. The urgent need for integrated electro-optic modulators in optical communications is to reduce power consumption while operating at high speeds and maintaining excellent signal-to-noise ratio.

[0003] The requirement of low-cost large-scale integration has led to the rapid development of silicon photonics. With the mature complementary metal oxide semiconductor manufacturing infrastructure, silicon has become the main commercial photonic platform in addition to III-V and traditional lithium niobate platforms. However, although silicon photonics is expected to achieve excellent low-cost integration, its lack of inherent second-order nonlinearity poses great challenges to achieving the bandwidth and power consumption required for future high-data-volume systems. The high-speed electro-optical effect of silicon relies on electron doping, which faces a difficult trade-off between voltage, bandwidth and optical loss. Therefore, various heterogeneous approaches are introduced to introduce newer and better solutions for silicon devices.

[0004] The thin-film lithium niobate platform may become a practical solution for the next generation of electro-optical integrated circuits. With the latest technological advances in thin-film material processing and device design, thin-film lithium niobate has enabled modulator performance to reach previously unattainable levels and demonstrated great integration potential. In practical applications, one of the main factors affecting the modulator bandwidth is the microwave loss in the voltage transmission line, which causes the driving voltage to decay with the electrode length. The microwave electrode loss of thin-film lithium niobate modulators is mainly the ohmic conductor loss caused by the finite resistivity of the metal. This is because the electrode gap in thin-film lithium niobate modulators is usually only a few microns, that is, the modulation efficiency is improved by reducing the half-wave voltage-length product, but the skin effect increases the resistance of the electrode and greatly increases the ohmic loss. Summary of the invention

[0005] The problem to be solved by the present invention is to provide a structure of a stacked conductor thin film lithium niobate electro-optic modulator in view of the deficiencies existing in the above-mentioned technology, which can significantly improve the voltage bandwidth performance of the thin film lithium niobate modulator and reduce the ohmic loss, while retaining key material advantages such as linear response, high extinction ratio, and low optical loss.

[0006] The solution of the present invention to the above-mentioned problem is: a laminated conductor thin film lithium niobate electro-optic modulator. It includes a substrate, a lower cladding, a lithium niobate thin film, a ridge optical waveguide, an upper cladding, and a Ground-signal-ground electrode (GSG); the GSG electrode includes a central signal electrode and a first and a second grounding electrode arranged at intervals on both sides, the signal electrode and the first and the second grounding electrodes are all laminated structures of silicon dioxide and gold conductors, the signal electrode and the first and the second grounding electrodes are all formed on the lithium niobate thin film, and there is a silicon dioxide upper cladding on the top and both sides, the ridge optical waveguide includes a first and a second ridge optical waveguide, both of which are formed on the lithium niobate thin film, the first ridge optical waveguide is formed between the central electrode and the first grounding electrode, the second ridge optical waveguide is formed between the central electrode and the second grounding electrode, the lithium niobate thin film is located on the lower cladding, and the lower cladding is located on the silicon substrate.

[0007] Furthermore, the substrate is made of silicon, which provides support for the lower cladding layer, lithium niobate film, etc. at the bottom and has a thickness of 450 microns.

[0008] Furthermore, the material of the lower cladding layer is silicon dioxide, which provides a higher relative refractive index and enhances the confinement effect on the mode in the lithium niobate ridge optical waveguide, and has a thickness of 2 microns.

[0009] Furthermore, the lithium niobate film has a thickness of 0.3-0.4 microns.

[0010] Furthermore, the material of the first ridge type optical waveguide and the second ridge type optical waveguide is lithium niobate, which can well confine the waveguide mode, has a thickness of 0.2-0.3 microns, a top width of 1-1.5 microns, and a side wall inclination angle of 70-85 degrees.

[0011] Furthermore, the signal electrode is made of gold and silicon dioxide, that is, three layers of silicon dioxide with a thickness of 0.02-0.06 microns and four layers of gold with a thickness of 0.18-0.21 microns are alternately stacked, with a width of 10-20 microns, and the intervals with the first and second ground electrodes are both 3-8 microns.

[0012] Furthermore, the materials of the first and second grounding electrodes are gold and silicon dioxide, that is, three layers of silicon dioxide with a thickness of 0.02-0.06 microns and four layers of gold with a thickness of 0.18-0.21 microns are alternately stacked.

[0013] Furthermore, the material of the upper cladding layer is silicon dioxide, which protects the device from external damage and prevents current leakage and interference, and has a thickness of 0.2-1.6 microns.

[0014] The present application also provides a method for preparing a laminated conductor type thin film lithium niobate electro-optic modulator, which is used to prepare the laminated conductor type thin film lithium niobate electro-optic modulator in the above embodiment. The method for preparing the laminated conductor type thin film lithium niobate electro-optic modulator comprises the following steps:

[0015] S1. Immerse the silicon glass wafer in acetone for ultrasonic cleaning. Use anhydrous alcohol to ultrasonically clean the wafer. Use isopropyl alcohol to ultrasonically clean the wafer to prevent the wafer from being contaminated by particles in the air. In each ultrasonic cleaning, the temperature is 50°C and the washing time is 5 minutes. Finally, the wafer is spun, rinsed and dried.

[0016] S2, making all the laminated layers have the same pattern by photolithography, specifically, spin coating the photoresist on the substrate, and then exposing the photoresist under the mask of the laminated structure. Finally, developing the photoresist to obtain the pattern;

[0017] S3, deposition of laminated layers, wherein the gold layer is deposited by evaporation and the silicon dioxide layer is prepared by plasma enhanced chemical vapor deposition;

[0018] S4. Perform a stripping process to remove the photoresist and obtain a laminated conductor.

[0019] Compared with the prior art, the stacked conductor thin-film lithium niobate electro-optic modulator provided by the present invention significantly improves the voltage bandwidth performance of the thin-film lithium niobate modulator by making GSG electrodes with overlapping silicon dioxide and gold on the lithium niobate film, reduces ohmic losses, and retains key material advantages such as linear response, high extinction ratio, and low optical loss.

[0020] The concept, specific structure and technical effect of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the electro-optic modulator of the present invention.

[0022] Figure 2 This is a diagram of the electric field distribution between electrodes on both sides of a single ridge-type optical waveguide of the present invention.

[0023] Figure 3 This is the light field distribution diagram of a single ridge-type optical waveguide of the present invention.

[0024] Among them, 1. substrate, 2. lower cladding, 3. lithium niobate film, 4. first ridge type optical waveguide, 5. second ridge type optical waveguide, 6. first ground electrode, 7. signal electrode, 8. second ground electrode, 9. upper cladding. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention with reference to the drawings in the specification to make the technical content clearer and easier to understand. The present invention can be implemented through many different forms of examples, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0026] In the drawings, components with the same functions are indicated by the same numerical reference numerals. The size of each component shown in the drawings is arbitrarily shown, and the present invention does not limit the size. In order to make the illustration clearer, the size and thickness of some components in the drawings are appropriately exaggerated.

[0027] like Figure 1 As shown, this embodiment uses silicon material as a substrate, specifically, the thickness of the substrate 1 is 450 microns. There is a lower cladding 2 on the substrate 1, and a lithium niobate film 3 is arranged on the lower cladding 2. The lower cladding 2 specifically uses silicon dioxide as an oxidized insulating layer. Preferably, the thickness of the lower cladding 2 is 2 microns. (Lithium niobate film material) The thickness of the lithium niobate film 3 is 0.3-0.4 microns. Based on the lithium niobate film 3, a first ridge-type optical waveguide 4 and a second ridge-type optical waveguide 5 are constructed, and the material thereof is lithium niobate, with a thickness of 0.2-0.3 microns, a top width of 1-1.5 microns, and a side wall inclination angle of 70-85 degrees. A first grounding electrode 6 and a signal electrode 7 are arranged on both sides of the first ridge-type optical waveguide 4. Preferably, the material of the first ground electrode 6 is gold and silicon dioxide. Specifically, four layers of gold with a thickness of 0.18-0.21 microns are overlapped with three layers of silicon dioxide with a thickness of 0.02-0.06 microns, that is, gold-silicon dioxide-gold-silicon dioxide-gold-silicon dioxide-gold. The material and structure of the signal electrode 7 are the same as those of the first ground electrode 6, and the only difference is the width. Specifically, the width is 10-20 microns. The second ground electrode 8 and the signal electrode 7 are arranged on both sides of the second ridge optical waveguide 5. Preferably, the material and size of the second ground electrode 8 are exactly the same as those of the first ground electrode 6. An upper cladding layer 9 is deposited on the portion without components above the lithium niobate film 3, the first ridge optical waveguide 4, the second ridge optical waveguide 5, the first ground electrode 6, the center electrode 7 and the second ground electrode 8. Preferably, the material of the upper cladding layer 9 is silicon dioxide.

[0028] In practical applications, one of the main factors affecting the bandwidth of the modulator is the microwave loss in the voltage transmission line, which causes the driving voltage to decay with the electrode length. The microwave electrode loss of the thin-film lithium niobate modulator is mainly the ohmic conductor loss caused by the finite resistivity of the metal. This is because the electrode gap in the thin-film lithium niobate modulator is usually only a few microns, which improves the modulation efficiency and reduces the half-wave voltage-length product (Vπ·L). However, the skin effect increases the resistance of the electrode and greatly increases the ohmic loss.

[0029] The present invention introduces the laminated conductor technology used for coaxial cables into the coplanar waveguide of a thin-film lithium niobate modulator. The metal signal line and the ground line are both changed into laminated conductors, realizing a low-loss, wide-bandwidth laminated coplanar waveguide. Since the effective skin depth of the laminated coplanar waveguide is larger than that of the solid coplanar waveguide, the ohmic loss of the laminated coplanar waveguide is much smaller than that of the solid coplanar waveguide, and the ohmic loss of the laminated coplanar waveguide with multi-layer insulators is even lower. In addition, replacing the solid conductor with the laminated conductor has almost no effect on the characteristic impedance, phase constant and dielectric attenuation of the coplanar waveguide. In order to reduce the ohmic loss of the coplanar waveguide, a laminated conductor is used instead of a traditional solid conductor. The laminated conductor is formed by alternating the conductor layer of gold and the insulating layer of silicon dioxide. The total thickness of the laminated conductor is equal to the thickness of the solid conductor. The insulating layer of the laminated conductor is not less than one layer.

[0030] Therefore, the present invention can significantly improve the voltage bandwidth performance of the thin film lithium niobate modulator and reduce ohmic loss, while retaining key material advantages such as linear response, high extinction ratio, and low optical loss.

[0031] Figure 2 The light and dark in the figure represent the electric field intensity near the ridge optical waveguide. Figure 3 It shows the ability of ridge optical waveguide to confine the guided wave mode.

Claims

1. A laminated conductor thin-film lithium niobate electro-optic modulator. It comprises a substrate, a lower cladding, a lithium niobate thin film, a ridge optical waveguide, an upper cladding, and a Ground-signal-ground electrode (GSG); the GSG electrode comprises a central signal electrode and first and second ground electrodes arranged at intervals on both sides, the signal electrode and the first and second ground electrodes are all laminated structures of silicon dioxide and gold conductors, the signal electrode and the first and second ground electrodes are all formed on the lithium niobate thin film, and there are upper claddings on the top and both sides thereof, the ridge optical waveguide comprises first and second ridge optical waveguides, both of which are formed on the lithium niobate thin film, the first ridge optical waveguide is formed between the central electrode and the first ground electrode, the second ridge optical waveguide is formed between the central electrode and the second ground electrode, the lithium niobate thin film is located on the lower cladding, and the lower cladding is located on the substrate.

2. The stacked conductor thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The substrate is made of silicon and has a thickness of 450 micrometers.

3. The stacked conductor thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The material of the lower cladding layer is silicon dioxide, and the thickness is 2 microns.

4. The stacked conductor thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The thickness of the lithium niobate film is 0.3-0.4 microns.

5. The stacked conductor thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The materials of the first ridge type optical waveguide and the second ridge type optical waveguide are lithium niobate, with a thickness of 0.2-0.3 microns, a top width of 1-1.5 microns, and a side wall inclination angle of 70-85 degrees.

6. The stacked conductor thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The signal electrode is made of gold and silicon dioxide, that is, three layers of silicon dioxide with a thickness of 0.02-0.06 microns and four layers of gold with a thickness of 0.18-0.21 microns are alternately stacked, with a width of 10-20 microns, and the intervals with the first and second ground electrodes are both 3-8 microns.

7. The stacked conductor thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The materials of the first and second grounding electrodes are gold and silicon dioxide, that is, three layers of silicon dioxide with a thickness of 0.02-0.06 microns and four layers of gold with a thickness of 0.18-0.21 microns are alternately stacked.

8. The stacked conductor thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The material of the upper cladding layer is silicon dioxide, and the thickness is 0.2-1.6 microns. S1. Immerse the silicon glass wafer in acetone for ultrasonic cleaning. Use anhydrous alcohol to ultrasonically clean the wafer. Use isopropyl alcohol to ultrasonically clean the wafer to prevent the wafer from being contaminated by particles in the air. In each ultrasonic cleaning, the temperature is 50°C and the washing time is 5 minutes. Finally, the wafer is spun, rinsed and dried. S2, making all the laminated layers have the same pattern by photolithography, specifically, spin coating the photoresist on the substrate, and then exposing the photoresist under the mask of the laminated structure. Finally, developing the photoresist to obtain the pattern; S3, deposition of laminated layers, wherein the gold layer is deposited by evaporation and the silicon dioxide layer is prepared by plasma enhanced chemical vapor deposition; S4. Perform a stripping process to remove the photoresist and obtain a laminated conductor.

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