Film lithium niobate modulator based on stacked double-layer capacitive electrode

Abstract

The invention provides a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode, and belongs to the technical field of thin-film lithium niobate electro-optical modulators. The modulator sequentially comprises a silicon substrate layer, a silicon dioxide lower cladding, a lithium niobate waveguide layer, a ridge-shaped optical waveguide layer, a silicon dioxide thin cover layer, a thin accumulation type double-layer capacitive electrode structure, a thick ground-signal-ground traveling wave electrode and a silicon dioxide upper cladding from bottom to top, wherein the ridge-shaped optical waveguide layer, the silicon dioxide thin cover layer, the thin accumulation type double-layer capacitive electrode structure, the thick ground-signal-ground traveling wave electrode and the silicon dioxide upper cladding are formed by etching the upper surface of the lithium niobate layer. The ground-signal-ground traveling wave electrode is composed of a first ground transmission electrode, a signal transmission electrode and a second ground transmission electrode. The stacked double-layer capacitive electrode structure comprises a periodic metal electrode with a stacked structure in a top view and a stepped metal electrode in a side view. The thin film lithium niobate modulator of the stacked double-layer capacitive electrode can realize refractive index matching, better impedance matching, low microwave loss and ultra-large electro-optical bandwidth.

Description

Technical Field

[0001] The present invention provides a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode, belonging to the technical field of electro-optic modulation. Background Art

[0002] As one of the core devices of a microwave photonic radio frequency front-end chip, the performance of an electro-optic modulator directly affects the performance indicators of the entire system. The main function of an electro-optic modulator is to modulate an electrical signal onto an optical signal to achieve the conversion between a microwave signal and an optical wave signal, serving as a bridge connecting microwaves and optical waves. Electro-optic modulators are widely used in systems or devices such as fiber optic communication, free-space optical communication, optical sensing, optical information processing, and high-power pulsed lasers.

[0003] In a traveling-wave electrode modulator, the main performance evaluation indicators are the electro-optic bandwidth and the half-wave voltage. There are three main factors affecting the electro-optic bandwidth: one is microwave loss; the second is the matching between its microwave group velocity and the optical carrier group velocity; and the third is impedance matching.

[0004] In recent years, Mach-Zehnder modulators based on LNOI have received extensive attention due to their advantages such as high modulation bandwidth, low insertion loss, high extinction ratio, and high modulation efficiency. Among them, a periodically capacitively loaded traveling-wave electrode is the best choice to achieve high performance of such modulators. However, this electrode structure still has problems such as velocity mismatch and substrate leakage loss.

[0006] Therefore, in view of the above problems, further improvements are made. Summary of the Invention

[0005] To solve the problems existing in the background art, the present invention provides a lithium niobate thin-film electro-optic modulator with a stacked double-layer capacitive electrode structure, which is suitable for mass production, achieves perfect group velocity matching, and breaks the voltage-bandwidth trade-off limitation of TFLN EO MZM. To achieve the above object, the present invention provides a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode, which includes a silicon substrate layer (1), a silicon dioxide lower cladding layer (2), a lithium niobate waveguide layer (3), ridge waveguide layers (301, 302) in a Mach-Zehnder structure, a silicon dioxide thin capping layer (4), a thin stacked double-layer capacitive electrode structure (501), a thick ground-signal-ground traveling-wave electrode (502, 503, 504), and a silicon dioxide upper cladding layer (6) from bottom to top. The ground-signal-ground traveling-wave electrode is composed of a first ground transmission electrode, a signal transmission electrode, and a second ground transmission electrode. The stacked double-layer capacitive electrode structure includes a periodic metal electrode with a stacked shape in a top view and a stepped metal electrode in a side view. The thick electrodes (502, 503, 504) are the main electrodes with a thickness of 1.4 μm, and the thin electrode (501) is partially stacked with a thickness of 0.2 μm. By adjusting four parameters of the stacked length and width, the characteristic impedance and velocity are matched.

[0007] Among them, the stacked double-layer capacitive electrode structure is composed of two strip electrodes with different lengths stacked from long to short, and the number is not limited. It can also be stacked by three or more strip electrodes.

[0008] Among them, the metal electrodes are regularly distributed in the traveling-wave electrode transmission direction, forming a periodic capacitance between the signal transmission electrode and the ground transmission electrode.

[0009] Among them, the first ground electrode (502), the first signal electrode (503), and the second ground electrode (504) are arranged in parallel and are stacked and aligned left and right in space.

[0010] Among them, the thickness of the lithium niobate waveguide layer (3, 301, 302) is 0.5 μm, and the height of the lithium niobate ridge waveguide (301, 302) is 0.25 μm, the upper width is 1.5 μm, and the angle is 67°.

[0011] Among them, the gap between two opposite stacked double-layer capacitive electrodes is 3 - 5 μm.

[0012] Among them, the thickness of the silicon dioxide lower cladding layer (2) between the silicon substrate layer (1) and the lithium niobate waveguide layer (3) is 4.7 μm.

[0013] Among them, the silicon dioxide thin capping layer (4) is covered between the lithium niobate waveguide layer (3, 301, 302) and the ground-signal-ground traveling-wave electrode, and the thickness is 0.25 μm.

[0014] Among them, the silicon dioxide capping layer (6) is covered above the ground-signal-ground traveling-wave electrode, and the thickness is 0.8 μm.

[0015] A thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention has the following significant advantages and effects:

[0016] The periodic stacked double-layer capacitive electrode structure forms a slow-wave effect in the RF transmission direction, which can increase the microwave refractive index, thereby achieving wave velocity matching.

[0017] The gap between two opposite stacked metal electrodes is very small. Therefore, a high degree of overlap between the strong electric field and the optical field can be obtained between the stacked electrode and the waveguide, improving the electro-optic modulation efficiency of the modulator, alleviating current crowding, and thus reducing microwave loss.

[0018] The stacked double-layer capacitive electrode structure between the electrodes has three different spacings, and the spacing ratio will affect the magnitude of the half-wave voltage and thus affect the modulation efficiency. By flexibly designing various parameters such as the period, duty cycle, electrode spacing, and electrode width that affect the electromagnetic wave propagation speed, a higher modulation bandwidth can be achieved.

[0019] Thick metal main electrodes (502, 503, 504) are used to reduce the RF index, and the stacked thin metal electrodes of low-inductance electrodes expand the signal-ground gap, reducing microwave loss. The thick main electrodes (502, 503, 504) are far from the lithium niobate waveguide, avoiding the plasma effect caused by optical field coupling and significantly reducing the optical loss of the device. At the same time, the combination of the thick main electrodes (502, 503, 504) and the stacked thin electrode (501) structure avoids current aggregation caused by the skin effect of high-frequency electromagnetic fields, reduces the equivalent resistance, makes the ohmic loss decrease, and thus improves the electro-optic bandwidth. Description of the Drawings

[0020] Figure 1 is a three-dimensional view of a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention.

[0021] Figure 2 is a side view of a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention.

[0022] Figure 3 is a top view of a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention.

[0023] Figure 4 is a derivative top view of a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention.

[0024] Figure 5 is a curve of the S parameter varying with frequency in the simulation experiment of a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention.

[0025] Figure 6It is the curve of the microwave loss varying with frequency in the simulation experiment of a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention.

[0026] Figure 7 It is the curve of the radio frequency refractive index varying with frequency in the simulation experiment of a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention.

[0027] Figure 8 It is the curve of the port impedance varying with frequency in the simulation experiment of a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode of the present invention. Specific implementation manners

[0028] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. The above are only the preferred embodiments of the present invention and do not limit the present invention. Any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention defined by the appended claims shall be included within the protection scope of the present invention.

[0029] The present invention provides a thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode: including a silicon substrate layer (1), a silicon dioxide lower cladding layer (2), a lithium niobate waveguide layer (3) and ridge waveguide layers (301, 302) of a Mach-Zehnder structure, a silicon dioxide thin capping layer (4), a thin stacked double-layer capacitive electrode structure (501) and a thick ground-signal-ground traveling-wave electrode (502, 503, 504) and a silicon dioxide upper cladding layer (6), and the ground-signal-ground traveling-wave electrode is composed of a first ground transmission electrode (502), a signal transmission electrode (503), and a second ground transmission electrode (504).

[0030] In the embodiment, as Figure 1 、 2As shown in FIGS. 2 and 3, the stacked double-layer capacitive electrode structure includes periodic metal electrodes with a stacked top-view structure and a stepped side-view structure. The thick electrodes (502, 503, 504) are the main electrodes with a thickness h4 = 1.4 um, and the thin electrode (501) is partially stacked with a thickness h5 = 0.2 um. The thickness of the lithium niobate waveguide layer (3, 301, 302) is 0.5 um. The height h1 of the lithium niobate ridge waveguide (301, 302) is 0.25 um, the upper width w1 is 1.5 um, and the angle is 67°. The gap GAP between two opposite stacked double-layer capacitive electrodes is 3 um - 5 um. The thickness of the silicon dioxide lower cladding (2) between the silicon substrate layer (1) and the lithium niobate waveguide layer (3) is 4.7 um. The silicon dioxide thin capping layer (4) with a thickness h3 = 0.25 um covers the lithium niobate waveguide layer (3, 301, 302) and the ground-signal-ground traveling wave electrode. The silicon dioxide capping layer (6) with a thickness h6 = 0.6 um covers the ground-signal-ground traveling wave electrode. In the stacked double-layer capacitive electrode structure (501), the widths of the long and short strip electrodes are 3 um and 1 um respectively, and the lengths are 50 um and 15 um respectively. The distance between two stacked double-layer capacitive electrodes is 6 um.

[0031] Secondly, as Figure 4 shown, the stacked double-layer capacitive electrode structure derived from Figure 3 is formed by stacking three strip electrodes with different lengths from long to short. In this thin-film lithium niobate modulator, the periodic stacked double-layer capacitive electrode structure (501) forms a slow-wave effect in the RF transmission direction, which can increase the microwave refractive index, thereby achieving wave velocity matching. The gap between two opposite stacked metal electrodes is very small, so a high degree of overlap between the strong electric field and the optical field can be obtained between the stacked electrodes and the waveguide, improving the electro-optic modulation efficiency of the modulator, alleviating current crowding, and thus reducing the RF transmission loss.

[0032] At the same time, thick metal main electrodes (502, 503, 504) are used to reduce the RF index, and the stacked thin metal electrodes with low inductance expand the signal-ground gap to reduce the microwave loss. The thick main electrodes (502, 503, 504) are far from the lithium niobate waveguide, avoiding the plasma effect caused by optical field coupling and significantly reducing the optical loss of the device. At the same time, the combination of the thick main electrodes (502, 503, 504) and the stacked thin electrode (501) structure avoids the current aggregation caused by the skin effect of the high-frequency electromagnetic field, reduces the equivalent resistance, makes the ohmic loss decrease, and thus improves the electro-optic bandwidth.

[0033] In addition, the stacked double-layer capacitive electrode structure between the electrodes has three different spacings, and the spacing ratio will affect the magnitude of the half-wave voltage and thus affect the modulation efficiency. By flexibly designing various parameters that affect the electromagnetic wave propagation speed, such as the period, duty cycle, electrode spacing, and electrode width, a higher modulation bandwidth can be achieved.

[0034] Use HFSS software to perform three-dimensional modeling and simulation on the thin-film lithium niobate modulator, and calculate parameters such as the S-parameters, microwave loss, radio frequency refractive index, and port impedance of the thin-film lithium niobate modulator assisted by the stacked double-layer capacitive electrode. Through simulation calculations, as Figures 5 - 8 shown, the S-parameters, microwave loss, radio frequency refractive index, and port impedance all reach ideal values, with low loss, achieving impedance matching and velocity matching.

[0035] The above-disclosed are only one or more preferred embodiments of the present application, and the scope of rights of the present application cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present application still fall within the scope covered by the present application.

Claims

1. A thin film lithium niobate modulator based on a stacked double-layer capacitive electrode, characterized in that: From bottom to top, there are silicon substrate layer (1), silicon dioxide lower cladding layer (2), lithium niobate waveguide layer (3), ridge waveguide layer (301, 302) of Mach-Zehnder structure, silicon dioxide thin cap layer (4), thin stacked double-layer capacitive electrode structure (501), thick ground-signal-ground traveling wave electrode (502, 503, 504) and silicon dioxide upper cladding layer (6), and the ground-signal-ground traveling wave electrode is composed of a first ground transmission electrode, a signal transmission electrode and a second ground transmission electrode.

2. A thin film lithium niobate modulator based on a stacked double-layer capacitive electrode according to claim 1, characterized in that: The stacked double-layer capacitive electrode structure comprises a metal electrode with a periodic top view structure being a stacked shape, and a side view structure being a stepped metal electrode. The thick electrode part (502, 503, 504) is a main electrode with a thickness of 1.4um, and the thin electrode part (501) is a stack with a thickness of 0.2um. By adjusting the stacked structure parameters, characteristic impedance matching and speed matching are achieved.

3. The thin film lithium niobate modulator based on stacked double-layer capacitive electrodes according to claim 1, characterized in that: The stacked double-layer capacitive electrode structure is composed of two strip electrodes of different lengths stacked from long to short, and the number is not limited. It can also be composed of three or more strip electrodes stacked.

4. The thin film lithium niobate modulator based on stacked double-layer capacitive electrodes according to claim 2, characterized in that: The metal electrodes are regularly distributed in the transmission direction of the traveling wave electrode, and a periodic capacitor is formed between the signal transmission electrode and the ground transmission electrode.

5. The thin film lithium niobate modulator based on stacked double-layer capacitive electrodes according to claim 1, characterized in that: The first ground electrode (502), the first signal electrode (503) and the second ground electrode (504) are arranged in parallel and are stacked and aligned in space.

6. The thin film lithium niobate modulator based on stacked double-layer capacitive electrodes according to claim 1, characterized in that: The thickness of the lithium niobate waveguide layer (3, 301, 302) is 0.5um, the lithium niobate ridge waveguide (301, 302) is 0.25um in height, 1.5um in width on the top and 67° in angle.

7. The thin film lithium niobate modulator based on stacked double-layer capacitive electrodes according to claim 1, characterized in that: The gap between two opposite stacked double-layer capacitive electrodes is 3-5um.

8. According to the thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode as described in claim 1, the thickness of the silicon dioxide lower cladding layer (2) between the silicon substrate layer (1) and the lithium niobate waveguide layer (3) is 4.7 um.

9. The thin-film lithium niobate modulator based on a stacked double-layer capacitive electrode according to claim 1, characterized in that: The silicon oxide thin cap layer (4) is covered between the lithium niobate waveguide layer (3, 301, 302) and the ground-signal-ground traveling wave electrode, and has a thickness of 0.25 um.

10. The thin film lithium niobate modulator based on stacked double-layer capacitive electrodes according to claim 1, characterized in that: The ground-signal-ground traveling wave electrode is covered with the silicon oxide cap layer (6) with a thickness of 0.8 um.

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