Thin film lithium niobate electro-optical modulator based on inclined electrode structure

Abstract

The invention discloses a thin-film lithium niobate electro-optical modulator based on an inclined electrode structure, and belongs to the technical field of communication, and the thin-film lithium niobate electro-optical modulator is provided with a groove. The structure is sequentially composed of a silicon substrate layer, a silicon dioxide lower cladding, a lithium niobate waveguide, a silicon dioxide buffer layer, a metal inclined electrode and a silicon dioxide upper cladding from bottom to top, the electrode is wrapped between the silicon dioxide upper cladding and the silicon dioxide buffer layer, and the thin film lithium niobate ridge waveguide is wrapped between the silicon dioxide buffer layer and the lower cladding; the inclined electrode ground-signal-ground traveling wave electrode is adopted in the metal electrode structure, an electric field is concentrated through point discharge, the electric field intensity in lithium niobate is increased, the photoelectric modulation efficiency can be effectively enhanced, the thin silicon dioxide buffer layer is additionally arranged between the lithium niobate film and the metal inclined electrode, and the photoelectric modulation efficiency is improved. Absorption of transmission light in the lithium niobate ridge waveguide by the metal electrode is weakened, and waveguide loss is effectively reduced; speed matching and impedance matching can be promoted by adjusting the inclination angles of different metal electrodes, the half-wave voltage can be effectively reduced, the modulation efficiency is improved, and the light absorption loss is reduced.

Description

Technical Field

[0001] The present invention relates to the field of lithium niobate communication technology, and in particular to a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure and with a groove design, which is similar to the principle of a T-electrode, increases the conductor area and improves the modulation efficiency. Background Art

[0002] With the rapid development of network technologies such as optical communication, optical interconnection, and 5G, the application demand for photonic devices continues to increase, and at the same time, the requirements for their indicators are getting higher and higher. In order to meet people's demand for high quality and high speed, it is urgent to develop new modulation technologies to reduce signal loss and increase modulation rate. Among the common modulator manufacturing materials, thin-film lithium niobate materials have excellent electro-optical properties far exceeding indium phosphide, and have a larger waveguide refractive index difference than ordinary lithium niobate bulk materials, which makes them have stronger mode restrictions. The electrodes can be closer to the waveguide to achieve high-speed optical signal modulation; its large bandwidth characteristics can meet the growing demand for bandwidth in today's high-speed communications. Modulators made according to the characteristics of thin-film lithium niobate materials are easier to achieve high modulation bandwidth, low half-wave voltage, and low insertion loss than silicon bulk materials. It has great potential application value for the future integration of optical communication technology.

[0003] The present invention discloses a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure. The metal electrode adopts an inclined electrode plus a groove structure. Compared with the traditional type, the tip discharge effect is obvious. The inclination angle of the inclined electrode will promote the concentration of the electric field, thereby increasing the electric field strength inside the lithium niobate and enhancing the electric field induced at the waveguide. Under the same light transmission loss and working stability, a stronger electric field is generated at the ridge waveguide, and the electrode is not close to the lithium niobate waveguide, which will not increase the light absorption loss. Summary of the invention

[0004] The object of the present invention is to provide a thin film lithium niobate electro-optic modulator based on an inclined electrode structure, so as to reduce the half-wave voltage, improve the modulation efficiency and reduce the waveguide loss.

[0005] To achieve the above-mentioned purpose, the present invention provides a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure, which is composed of a silicon substrate layer (1), a silicon dioxide lower cladding layer (2), a lithium niobate waveguide layer (3), a silicon dioxide buffer layer (4), an inclined electrode (5), and a silicon dioxide upper cladding layer (6) from bottom to top; the silicon dioxide lower cladding layer (2) is located above the silicon substrate layer (1), the silicon dioxide buffer layer (4) is between the lithium niobate waveguide layer (3) and the inclined electrode (5), the lithium niobate waveguide layer (3) is located between the silicon dioxide buffer layer (4) and the silicon dioxide lower cladding layer (2), and the inclined electrode (5) is located between the silicon dioxide buffer layer (4) and the silicon dioxide upper cladding layer (6). In addition, there is a spacing between the left and right sides of the inclined electrodes, and the silicon dioxide buffer layer (4) and the silicon dioxide upper cladding layer (6) are connected through the inclined electrode spacing.

[0006] Wherein, the thickness H of the silicon substrate layer (1) is Si It is 525um, the refractive index is 3.49, and the relative dielectric constant is 11.9.

[0007] Wherein, the thickness of the silicon dioxide lower cladding layer (2) is It is 4.7um.

[0008] Wherein, the thickness H of the lithium niobate waveguide layer (3) is slab is 0.5um, and the ridge waveguide height H rib 0.25um, width W rib The thickness is 1.5um and the angle is 67°.

[0009] Wherein, the thickness of the silicon dioxide buffer layer (4) is It is 0.2um.

[0010] Wherein, the thickness H of the inclined electrode (5) is Au It is 1.4um and the inclination angle α is 30°.

[0011] The lithium niobate thin film layer has an extraordinary light refractive index of ne=2.1376, an ordinary light refractive index of no=2.2111, and relative dielectric constants of se=27.9 and so=44.3.

[0012] The present invention adds a silicon oxide dielectric buffer layer between the lithium niobate film and the inclined electrode, which helps to weaken the metal electrode's absorption of light transmitted in the lithium niobate ridge waveguide and effectively reduce waveguide loss; by adjusting different metal electrode inclination angles, speed matching and impedance matching can be promoted, which can effectively reduce the half-wave voltage, improve modulation efficiency, and reduce light absorption loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1It is a stereoscopic diagram of a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure of the present invention.

[0014] Figure 2 It is a top view of a metal electrode of a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure of the present invention.

[0015] Figure 3 It is a front view of a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure of the present invention.

[0016] Figure 4 It is a side view of a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure of the present invention.

[0017] Figure 5 The present invention discloses a curve diagram showing the variation of electrode spacing, half-wave voltage and light absorption loss of a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure.

[0018] Figure 6 The present invention is a curve diagram showing the variation of the tilt angle, half-wave voltage and light absorption loss of a thin-film lithium niobate electro-optic modulator based on a tilted electrode structure.

[0019] Figure 7 The present invention is a curve diagram showing the change in thickness of a silicon dioxide buffer layer, half-wave voltage and light absorption loss of a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure.

[0020] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0021] The present invention provides a thin-film lithium niobate electro-optic modulator based on an inclined electrode structure, comprising a silicon substrate (1), silicon dioxide layers (2, 4, 6), a lithium niobate waveguide (3), and a metal electrode (5). DETAILED DESCRIPTION

[0022] According to this specific embodiment, the silicon dioxide lower cladding layer (2) is located above the silicon substrate layer (1), the silicon dioxide buffer layer is between the lithium niobate waveguide layer (3) and the inclined electrode (5), the lithium niobate waveguide layer (3) is located between the silicon dioxide buffer layer (4) and the silicon dioxide lower cladding layer (2), and the inclined electrode (5) is located between the silicon dioxide buffer layer (4) and the silicon dioxide upper cladding layer (6). In addition, there is a gap between the left and right sides of the inclined electrodes, and the silicon dioxide buffer layer (4) and the silicon dioxide upper cladding layer (6) are connected through the inclined electrode gap. The metal electrode adopts an inclined electrode structure. Compared with the traditional type, the tip discharge effect is obvious. The inclination angle of the inclined electrode will promote the concentration of the electric field, thereby increasing the electric field strength inside the lithium niobate, and at the same time enhancing the electric field induced at the waveguide. Under the same light transmission loss and working stability, a stronger electric field is generated at the ridge waveguide, and the electrode is not close to the lithium niobate waveguide and will not increase the light absorption loss. A thin silicon dioxide buffer layer is added between the lithium niobate film and the metal inclined electrode, which is beneficial to weaken the metal electrode's absorption of the light transmitted in the lithium niobate ridge waveguide, effectively reducing the waveguide loss.

[0023] Then, if Figure 3 As shown, the thickness of the substrate (1) is 525um. The thickness of the silicon dioxide lower cladding layer (2) is 4.7um. The thickness of the lithium niobate layer (3) is 0.5um, wherein the width of the ridge waveguide is 0.25um, the width of the ridge waveguide is 1.5um, and the angle is 67°. The thickness of the silicon dioxide buffer layer (4) is 0.2um. The thickness of the silicon dioxide upper cladding layer (6) is 0.8-2um.

[0024] Secondly, the cladding thickness mentioned above remains unchanged, and the inclination angle of the metal inclined electrode layer (5) and the distance between the electrodes are changed by design, and the relationship between the angle and distance of the metal electrodes and the half-wave voltage and light absorption loss is observed. Figure 5 As shown in the figure, a curve of the electrode spacing, half-wave voltage and light absorption loss of a thin-film lithium niobate electro-optic modulator based on a tilted electrode structure shows that as the metal electrode spacing increases, the half-wave voltage decreases, while the light absorption loss increases. However, since the electrode spacing is too close, the electric field distribution will be distorted, causing the output signal to be distorted. At the same time, the capacitive coupling will increase, resulting in increased crosstalk between signals, reducing the signal isolation of the modulator, affecting the performance of the modulator at high frequencies, limiting its operating bandwidth, and easily causing breakdown, resulting in short circuits. It can be seen that, weighing the half-wave voltage and light absorption loss, the metal electrode spacing is designed to be around 2.5um, which can achieve better half-wave voltage and light absorption loss effects. Figure 6As shown in the figure, the curve of the tilt angle, half-wave voltage and light absorption loss of a thin-film lithium niobate electro-optic modulator based on a tilted electrode structure shows that as the tilt angle of the metal electrode continues to increase, the light absorption loss curve fluctuates, but generally continues to increase; and as the tilt angle of the metal electrode increases, its half-wave voltage decreases. It can be seen that, weighing the half-wave voltage and light absorption loss, the tilt angle α of the metal electrode is designed to be around 20° to 60°, and the half-wave voltage and light absorption loss effects are better. Figure 7 As shown, a curve change diagram of the silicon dioxide buffer layer, half-wave voltage, and light absorption loss of a thin-film lithium niobate electro-optic modulator based on a tilted electrode structure shows that as the thickness of the silicon dioxide buffer layer increases, the light absorption loss curve fluctuates slightly, but generally decreases; and as the thickness of the silicon dioxide buffer layer increases, its half-wave voltage continues to increase; it can be seen that, weighing the half-wave voltage and light absorption loss, the thickness of the silicon dioxide buffer layer is designed to be around 0.2um, and the half-wave voltage and light absorption loss effects are better. As described above, the present invention provides a thin-film lithium niobate electro-optic modulator based on a tilted electrode structure, which effectively reduces the half-wave voltage, improves the modulation efficiency, and reduces the light absorption loss, and considers the design parameters of the metal tilt angle and the electrode spacing as follows: the tilt angle α of the metal electrode is designed to be between 20° and 60°, the metal electrode spacing is designed to be around 2.5um, and the thickness of the silicon dioxide buffer layer is designed to be around 0.2um, so as to achieve the best effect.

[0025] A thin-film lithium niobate electro-optic modulator based on an inclined electrode structure is used in this example. The metal electrode structure in the present invention adopts an inclined electrode ground-signal-ground traveling wave electrode, which concentrates the electric field through tip discharge, increases the electric field strength inside the lithium niobate, and can effectively enhance the photoelectric modulation efficiency. A thin silicon dioxide buffer layer is added between the lithium niobate film and the metal inclined electrode, which is conducive to weakening the metal electrode's absorption of the light transmitted in the lithium niobate ridge waveguide, effectively reducing the waveguide loss; by adjusting different metal electrode inclination angles, speed matching and impedance matching can be promoted, which can effectively reduce the half-wave voltage, improve the modulation efficiency, and reduce light absorption loss.

[0026] What is disclosed above is only one or more preferred embodiments of the present application, and cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiments and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A thin-film lithium niobate electro-optic modulator based on an inclined electrode structure, characterized in that: From bottom to top, it is composed of a silicon substrate layer (1), a silicon dioxide lower cladding layer (2), a lithium niobate waveguide layer (3), a silicon dioxide buffer layer (4), an inclined electrode (5), and a silicon dioxide upper cladding layer (6); the silicon dioxide lower cladding layer (2) is located above the silicon substrate layer (1), the silicon dioxide buffer layer (4) is between the lithium niobate waveguide layer (3) and the inclined electrode (5), the lithium niobate waveguide layer (3) is located between the silicon dioxide buffer layer (4) and the silicon dioxide lower cladding layer (2), and the inclined electrode (5) is located between the silicon dioxide buffer layer (4) and the silicon dioxide upper cladding layer (6). In addition, there is a spacing between the left and right sides of the inclined electrode, and the silicon dioxide buffer layer (4) and the silicon dioxide upper cladding layer (6) are connected through the inclined electrode spacing.

2. The thin-film lithium niobate electro-optic modulator based on the inclined electrode structure as described in claim 1, wherein the extraordinary light refractive index of the thin-film lithium niobate layer is ne=2.1376, the ordinary light refractive index is no=2.2111, and the relative dielectric constants are se=27.9 and so=44.

3.

3. The thin-film lithium niobate electro-optic modulator based on the inclined electrode structure according to claim 1, characterized in that: The thickness of the lithium niobate waveguide layer (3) is 0.5um, the ridge waveguide height is 0.25um, the upper side width is 1.5um and the angle is 67°.

4. The thin-film lithium niobate electro-optic modulator based on the inclined electrode structure according to claim 1, characterized in that: The thickness of the silicon dioxide buffer layer (4) is 0.2 um.

5. The thin-film lithium niobate electro-optic modulator based on the inclined electrode structure according to claim 1, characterized in that: The thickness of the inclined electrode (5) is 1.4 um, the distance between the two electrodes is 2.5 um, and the inclination angle α is 30°.

6. The thin-film lithium niobate electro-optic modulator based on the inclined electrode structure according to claim 1, characterized in that: The thickness of the silicon dioxide lower cladding layer (6) is 4.7 um.

7. The thin-film lithium niobate electro-optic modulator based on the inclined electrode structure according to claim 1, characterized in that: The ground-signal-ground traveling wave electrode is covered with a silicon oxide cap layer.

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