A lithium niobate waveguide modulator and a method for manufacturing the same

Abstract

The application discloses a lithium niobate waveguide modulator and a preparation method thereof. The lithium niobate waveguide modulator comprises a substrate and a ridge waveguide on the substrate, at least a part of the ridge waveguide is a lithium niobate negative domain structure, and electrodes are arranged on both sides of the lithium niobate negative domain structure. The preparation method of the lithium niobate waveguide modulator comprises the following steps: bonding a substrate after surface film plating and thin film lithium niobate, processing the bonded thin film lithium niobate into a ridge waveguide, then preparing a negative domain structure through a room temperature electric field polarization process, and finally preparing electrodes on both sides of the ridge waveguide. The application first utilizes the domain inversion characteristics of lithium niobate to perform electro-optic modulation and prepare the lithium niobate waveguide modulator, and the preparation method is simple and easy to implement, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a waveguide modulator and a preparation method thereof, in particular to a lithium niobate waveguide modulator and a preparation method thereof. BACKGROUND

[0002] Optical modulator is a key device for high-speed and short-distance optical communication, and is one of the most important integrated optical devices. According to the modulation principle, the optical modulator can be divided into electro-optic, thermo-optic, acousto-optic, all-optical and the like. The basic theories they rely on are various forms of electro-optic effect, acousto-optic effect, magneto-optic effect, Franz-Keldysh effect, quantum well Stark effect and carrier dispersion effect. Among them, the electro-optic modulator is a device that ultimately controls the refractive index, absorption rate, amplitude or phase of the output light through the change of voltage or electric field. It is superior to other types of modulators in terms of loss, power consumption, speed and integration. In the process of optical emission, transmission and reception of the whole optical communication, the optical modulator is used to control the intensity of light, and its role is very important.

[0003] The electro-optic modulator (EOM) is made of some electro-optic crystals, such as lithium niobate (LiNbO3), gallium arsenide (GaAs) and lithium tantalate (LiTaO3). Electro-optic modulation is based on linear electro-optic effect (Pockels effect), that is, the refractive index of the optical waveguide is proportional to the change of the applied electric field. The linear change of the refractive index of the optical waveguide in the phase modulator caused by the electro-optic effect makes the light wave passing through the waveguide have a phase shift, thereby realizing phase modulation. Pure phase modulation cannot modulate the intensity of light, but the Mach-Zehnder interferometer type modulator composed of two phase modulators and two Y branch waveguides can modulate the intensity of light. How to design a waveguide modulator that utilizes the domain inversion characteristics of lithium niobate for electro-optic modulation is a technical problem to be solved at present. SUMMARY

[0004] The present application aims to provide a lithium niobate waveguide modulator that utilizes the domain inversion characteristics of lithium niobate for electric field modulation and produces a waveguide; and a preparation method of the lithium niobate waveguide modulator.

[0005] Technical scheme: The lithium niobate waveguide modulator provided by the present application comprises a substrate and a ridge waveguide on the substrate, at least a part of the ridge waveguide is a lithium niobate negative domain structure, and electrodes are arranged on both sides of the lithium niobate negative domain structure.

[0006] Further, the material of the substrate is lithium niobate, sapphire, silicon carbide or silicon dioxide; the upper surface of the substrate is coated with a film, and the film material is silicon dioxide, aluminum oxide, titanium oxide, magnesium fluoride or calcium fluoride; the material of the ridge waveguide is homogenous lithium niobate, stoichiometric lithium niobate or magnesium-doped lithium niobate; and the electrode is a metal electrode, and the electrode material is gold, silver, copper or aluminum.

[0007] Further, the electrode completely covers the lithium niobate negative domain structure.

[0008] Further, the electrodes on both sides of the lithium niobate negative domain structure are respectively connected to a positive voltage and a negative voltage. When there is no voltage on the electrode, the refractive index of the negative domain is equal to that of the waveguide, and the negative domain does not play any role. When a voltage is applied to the electrode, according to the electro-optic effect, the refractive index of the negative domain part increases, and the negative domain part forms a lens-like effect to converge light. When a plurality of negative domains are cascaded, the convergence effect is enhanced. When the convergence effect reaches a certain degree, the light transmitted in the waveguide does not meet the waveguide transmission condition, and the light intensity transmitted in the waveguide becomes small, thereby producing an intensity modulation effect.

[0009] Further, the pattern of the negative domain structure is circular, arc-shaped or prismatic; preferably, the domain wall of the negative domain structure has a certain degree of bending, and the pattern is circular or arc-shaped.

[0010] The preparation method of the lithium niobate waveguide modulator comprises the following steps: bonding the substrate after surface coating and thin film lithium niobate, processing the bonded thin film lithium niobate into a ridge waveguide, then making a negative domain structure through a room temperature electric field polarization process, and finally preparing electrodes on both sides of the ridge waveguide.

[0011] Further, the ridge waveguide is processed by using a method of photolithography, etching and / or focused ion beam, and the electrode is processed by photolithography and / or film coating.

[0012] The principle of the present application is that, according to the electro-optic effect, under the action of an external electric field E, the refractive index principal axis of lithium niobate crystal changes, causing the refractive index change in each direction. According to the linear electro-optic effect matrix of lithium niobate, an electric field E is applied along the Z-axis direction, then E x = E y = 0, E z = V / w, and the increase of the refractive index is:

[0013]

[0014] wherein n e is the e light refractive index, γ 33 is the electro-optic coefficient, V is the voltage, and w is the electric field width.

[0015] For a single lens, the simplified form of the formula of the grinder can be:

[0016]

[0017] Calculate the focal length of a single lens, where r is the radius of the circular negative domain or the radius of curvature of the arc. To enhance the focusing effect, multiple circular negative domains can be fabricated. For multiple lenses, the focal length can be calculated using the following formula:

[0018]

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: For the first time, the domain inversion characteristics of lithium niobate are utilized for electro-optic modulation and a lithium niobate waveguide modulator is prepared. The preparation method is simple and easy to implement and has broad application prospects. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the lithium niobate waveguide modulator described in this invention;

[0021] Figure 2 This is a three-dimensional diagram of the lithium niobate waveguide modulator described in this invention;

[0022] Figure 3 This is a cross-sectional view of the lithium niobate waveguide modulator described in this invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0024] The reference numerals in the attached figures are: 1-substrate, 2-ridge waveguide, 3-negative domain structure, 4-electrode.

[0025] Example

[0026] like Figures 1-2 As shown, the lithium niobate waveguide modulator of the present invention includes a substrate 1 and a ridge waveguide 2 on the substrate 1. A section of the ridge waveguide 2 is a lithium niobate negative domain structure 3. The domain walls of the negative domain structure 3 have a certain degree of curvature and a circular pattern. Electrodes are provided on both sides of the lithium niobate negative domain structure 3, and the electrodes 4 completely cover the lithium niobate negative domain structure 3.

[0027] In this embodiment, a silicon dioxide film is deposited on a silicon wafer, and then bonded to a 1μm thick thin film of lithium niobate. The bonded thin film of lithium niobate is then processed into a ridge waveguide 2 with a width of 1μm, a height of 1μm, and a length of 10mm using a focused ion beam process. Then, a room temperature electric field polarization process is used to fabricate... Figure 3 The circular negative domain structure 3 is shown. Finally, the copper metal electrode 4 is fabricated by photolithography and film deposition.

[0028] The aforementioned ridge waveguide 2 is coupled through a grating to transmit 1064nm linearly polarized laser light, with the polarization direction parallel to the Z-axis.Figure 1 The Z axis (optical axis) of the lithium niobate waveguide is in the paper, the waveguide propagates along the X direction, and the electric field is parallel to the Y axis. Without voltage on the electrode 4, the refractive index of the negative domain is the same as that of the waveguide, and the laser is not affected when passing through the negative domain.

[0029] When the electrodes 4 on both sides of the negative domain structure 3 are respectively applied with positive and negative voltages ±0.5V, according to the electro-optic effect, the refractive index of the circular negative domain changes. The γ of lithium niobate is 33 ≈29.5pm / V, according to formula (1), n e =2.15, V=1V, w=1μm, Δn e =1.5E-4.

[0030] According to formula (2) again, the curvature radius of the circular arc is r=0.5μm, and the focal length of a single negative domain is calculated as f=3.7mm. In order to enhance this effect, 10 negative domains can be connected in series, and according to formula (3), the total focal length is f 10 =0.37mm.

[0031] When the normally transmitted laser passes through the above negative domain, it receives the spatial modulation of the lens effect of the negative domain, generates focusing, and thus exceeds the waveguide transmission condition of the ridge waveguide, so the intensity of the transmitted laser decreases, and the higher the voltage is applied, the more the intensity decreases, thereby forming an intensity-modulated waveguide electro-optic modulator.

Claims

1. A lithium niobate waveguide modulator, characterized by, The application relates to a ridge waveguide, which comprises a substrate (1) and a ridge waveguide (2) on the substrate, at least a part of the ridge waveguide (2) being a lithium niobate negative domain structure (3), electrodes (4) being arranged on both sides of the lithium niobate negative domain structure (3); the electrodes (4) on both sides of the lithium niobate negative domain structure (3) are respectively supplied with positive voltage and negative voltage; when the electrodes (4) on both sides of the lithium niobate negative domain structure (3) are supplied with voltage, the refractive index of the lithium niobate negative domain structure (3) changes according to the electro-optic effect.

2. The lithium niobate waveguide modulator of claim 1, wherein, The material of the substrate (1) is lithium niobate, sapphire, silicon carbide or silicon dioxide.

3. The lithium niobate waveguide modulator of claim 1, wherein, The upper surface of the substrate (1) is coated with a film, and the film material is silicon dioxide, aluminum oxide, titanium oxide, magnesium fluoride or calcium fluoride.

4. The lithium niobate waveguide modulator of claim 1, wherein, The material of the ridge waveguide (2) is homogenous lithium niobate, stoichiometric lithium niobate or magnesium-doped lithium niobate.

5. The lithium niobate waveguide modulator of claim 1, wherein, The electrode (4) is a metal electrode, and the electrode material is gold, silver, copper or aluminum.

6. The lithium niobate waveguide modulator of claim 1, wherein, The electrode (4) completely covers the lithium niobate negative domain structure (3).

7. The lithium niobate waveguide modulator of claim 1, wherein, The pattern of the lithium niobate negative domain structure (3) is circular, arc-shaped or prismatic.

8. A method of fabricating a lithium niobate waveguide modulator according to any one of claims 1-7, characterized in that, The method comprises the following steps: bonding the substrate (1) after surface coating and thin-film lithium niobate, processing the bonded thin-film lithium niobate into a ridge waveguide (2), then preparing a lithium niobate negative domain structure (3) through a room-temperature electric field polarization process, and finally preparing electrodes (4) on both sides of the ridge waveguide (2).

9. The method of claim 8, wherein the lithium niobate waveguide modulator is prepared by the steps of: The ridge waveguide (2) is processed through a photolithography, etching and / or focused ion beam method, and the electrode (4) is processed through photolithography and / or film coating. ​

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