KR20240158178A - Lithium niobate waveguide modulator device and method for manufacturing same - Google Patents

Abstract

The present invention discloses a lithium niobate waveguide modulator and a method for manufacturing the same. The lithium niobate waveguide modulator includes a substrate and a rib waveguide on the substrate. At least a portion of the rib waveguide has a lithium niobate negative domain structure, and electrodes are installed on both sides of the lithium niobate negative domain structure. The method for manufacturing the lithium niobate waveguide modulator includes the steps of combining a substrate having a film coated on its surface and a film lithium niobate, then processing the combined film lithium niobate into a rib waveguide, then fabricating a negative domain structure through a room temperature electric field polarization process, and finally fabricating electrodes on both sides of the rib waveguide. The present invention performs electro-optic modulation by utilizing the domain inversion characteristics of lithium niobate for the first time and manufactures a lithium niobate waveguide modulator, which has a simple manufacturing method, easy implementation, and wide application potential.

Description

Lithium niobate waveguide modulator and method for manufacturing the same {LITHIUM NIOBATE WAVEGUIDE MODULATOR DEVICE AND METHOD FOR MANUFACTURING SAME}

The present invention relates to a waveguide modulator and a method for manufacturing the same, and more particularly, to a lithium niobate waveguide modulator and a method for manufacturing the same.

Optical modulators are key components for high-speed, short-distance optical communications and are one of the most important integrated optical components. Optical modulators can be divided into electro-optical, thermo-optical, acousto-optical, and all-optical types according to their modulation principles. Their basic theories include various forms of electro-optical effects, acousto-optical effects, magneto-optical effects, Franz-Keldysh effects, quantum well Stark effects, and carrier dispersion effects. Among them, electro-optical modulators are components that ultimately control the refractive index, absorption, amplitude, or phase of output light by changing voltage or electric fields, and they are superior to other types of modulators in terms of loss, power consumption, speed, and integration. Optical modulators are used to control the intensity of light in the entire process of emitting, transmitting, and receiving light in optical communications, and their role is very important.

Electro-optic modulators (EOMs) are fabricated by exploiting the electro-optic effect of certain electro-optic crystals, such as lithium niobate (LiNbO ₃ ), gallium arsenide (GaAs), and lithium tantalate (LiTaO ₃ ). Electro-optic modulation is based on the linear electro-optic effect (Pulck effect), which is an effect in which the refractive index of an optical waveguide is proportional to the change in an external electric field. When the refractive index of an optical waveguide in a phase modulator changes linearly due to the electro-optic effect, a phase shift occurs in the optical wave passing through the waveguide, resulting in phase modulation. Simple phase modulation cannot modulate the intensity of light, but a Mach-Zehnder interferometer-type modulator consisting of two phase modulators and two Y-branch waveguides can modulate the intensity of light. How to design a waveguide modulator that exploits the domain inversion properties of lithium niobate for electro-optic modulation is an urgent technical challenge that needs to be solved.

An object of the present invention is to provide a lithium niobate waveguide modulator which performs electric field modulation and generates a waveguide by utilizing the domain inversion characteristics of lithium niobate. An object of the present invention is to provide a method for manufacturing the lithium niobate waveguide modulator.

A lithium niobate waveguide modulator according to the present invention comprises a substrate and a rib waveguide on the substrate, at least some of the rib waveguides having a lithium niobate negative domain structure, and electrodes are provided on both sides of the lithium niobate negative domain structure.

Furthermore, 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 coating material is silicon dioxide, aluminum oxide, titanium oxide, magnesium fluoride or calcium fluoride. The material of the rib waveguide is lithium niobate of the same component, stoichiometric lithium niobate or magnesium-doped lithium niobate. The electrode is a metal electrode, and the electrode material is gold, silver, copper or aluminum.

Furthermore, the electrode completely covers the lithium niobate negative domain structure.

Furthermore, the electrodes on both sides of the lithium niobate negative domain structure are connected to a positive voltage and a negative voltage, respectively. When there is no voltage on the electrode, the refractive index of the negative domain is the same as the refractive index of the waveguide, and the negative domain does not perform any action. When a voltage is applied to the electrode, the refractive index of the negative domain portion increases according to the electro-optical effect, and the negative domain portion forms an effect similar to a lens to converge light. When a plurality of negative domains are cascaded, the convergence effect is strengthened. When the convergence effect reaches a certain level, the light transmitted from the waveguide does not satisfy the waveguide transmission condition, and the intensity of the light transmitted from the waveguide decreases, resulting in an intensity modulation effect.

Furthermore, the pattern of the negative domain structure is circular, arc-shaped or prism-shaped, and preferably, the domain wall of the negative domain structure has a certain degree of curvature, and the pattern is circular or arc-shaped.

The method for manufacturing the above lithium niobate waveguide modulator includes the steps of combining a substrate having a film coated on its surface and a film lithium niobate, then processing the combined film lithium niobate into a rib waveguide, then fabricating a negative domain structure through a room temperature electric field polarization process, and finally fabricating electrodes on both sides of the rib waveguide.

Furthermore, the rib waveguide is processed and obtained by adopting the methods of photolithography, etching and/or focused ion beam, and the electrode is processed and obtained by adopting the methods of photolithography and/or film coating.

The principle of the present invention is as follows. That is, the refractive index principal axis of a lithium niobate crystal changes under the action of an external electric field E according to the electro-optic effect, so that the refractive index in each direction changes. According to the linear electro-optic effect matrix of lithium niobate, when an electric field E is applied in the Z-axis direction, Ex = Ey = 0, Ez = V/w, and the increase in the refractive index is as follows.

… … (1)

Here is the refractive index of e light, is the electro-optic coefficient, is the voltage, is the electric field width.

For single lenses, a simplified form of the lens maker's formula can be followed.

… … (2)

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. Multiple circular negative domains can be produced to enhance the focusing effect. For multiple lenses, the focal length can be calculated according to the following formula.

… … (3)

Compared with the prior art, the present invention has the following significant advantages: that is, for the first time, the domain inversion characteristic of lithium niobate is utilized to perform electro-optic modulation, and a lithium niobate waveguide modulator is manufactured and obtained, the manufacturing method of which is simple, easy to perform, and has wide applicability.

Figure 1 is a structural diagram of a lithium niobate waveguide modulator according to the present invention.
FIG. 2 is a three-dimensional diagram of a lithium niobate waveguide modulator according to the present invention.
FIG. 3 is a cross-sectional view of a lithium niobate waveguide modulator according to the present invention.

Hereinafter, the technical solution of the present invention will be described in more detail with reference to the attached drawings.

Example

As illustrated in FIGS. 1 and 2, the lithium niobate waveguide modulator of the present invention includes a substrate (1) and a rib waveguide (2) on the substrate (1). The rib waveguide (2) has a section of a lithium niobate negative domain structure (3), and the domain wall of the negative domain structure (3) has a certain degree of curvature and a circular pattern. Electrodes are installed on both sides of the lithium niobate negative domain structure (3), and the electrodes (4) completely cover the lithium niobate negative domain structure (3).

In this embodiment, a silicon dioxide film is coated on a silicon wafer, and then a 1 μm thick lithium niobate film is bonded thereto. The bonded lithium niobate film is processed into a rib waveguide (2) having a width of 1 μm, a height of 1 μm, and a length of 10 mm through a focused ion beam process. Thereafter, a circular negative domain structure (3) as shown in Fig. 3 is fabricated through a room temperature electric field polarization process. Finally, a copper metal electrode (4) is processed through photolithography and a film coating method.

The above rib waveguide (2) is coupled through a grating to transmit a 1064 nm linearly polarized laser, and the polarization direction is parallel to the Z-axis (the Z-axis (optical axis) of the lithium niobate waveguide of Fig. 1 is in the ground, the waveguide propagates along the X-direction, and the electric field is parallel to the Y-axis). When there is no 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.

Negative domain structure (3) After applying a positive voltage and a negative voltage of ±0.5 V to the electrodes (4) on both sides, the refractive index of the circular negative domain changes according to the electro-optical effect. Lithium niobate And, according to formula (1), , V=1V, w=1μm by substituting Obtain .

According to formula (2), the radius of curvature of the arc is , and the focal length of a single negative domain is is calculated as . To enhance this effect, 10 negative domains can be connected in series, and according to formula (3), the total focal length is is obtained by

The normally transmitted laser passes through the negative domain and then is spatially modulated by the lens transmission effect of the negative domain, causing focusing, which deviates from the waveguide transmission condition of the rib waveguide. Therefore, the intensity of the transmitted laser decreases, and the higher the applied voltage, the lower the intensity, thereby forming an intensity-modulated waveguide electro-optic modulator.

1: Substrate
2: Rib waveguide
3: Negative domain structure
4: Electrode

Claims (10)

In lithium niobate waveguide modulators,
A lithium niobate waveguide modulator comprising a substrate (1) and a rib waveguide (2) on the substrate, wherein at least a portion of the rib waveguide (2) is a lithium niobate negative domain structure (3), and electrodes (4) are installed on both sides of the lithium niobate negative domain structure (3). In the first paragraph,
A lithium niobate waveguide modulator, characterized in that the material of the above substrate (1) is lithium niobate, sapphire, silicon carbide or silicon dioxide. In the first paragraph,
A lithium niobate waveguide modulator, characterized in that the surface of the substrate (1) is coated with a film, and the film coating material is silicon dioxide, aluminum oxide, titanium oxide, magnesium fluoride or calcium fluoride. In the first paragraph,
A lithium niobate waveguide modulator, characterized in that the material of the above rib waveguide (2) is lithium niobate, stoichiometric lithium niobate or magnesium-doped lithium niobate of the same component. In the first paragraph,
A lithium niobate waveguide modulator, characterized in that the above electrode (4) is a metal electrode and the electrode material is gold, silver, copper or aluminum. In the first paragraph,
A lithium niobate waveguide modulator, characterized in that the above electrode (4) completely covers the lithium niobate negative domain structure (3). In the first paragraph,
A lithium niobate waveguide modulator, characterized in that the electrodes (4) on both sides of the lithium niobate negative domain structure (3) communicate with a positive voltage and a negative voltage, respectively. In the first paragraph,
A lithium niobate waveguide modulator, characterized in that the pattern of the lithium niobate negative domain structure (3) is circular, arc-shaped or prism-shaped. In a method for manufacturing a lithium niobate waveguide modulator according to any one of claims 1 to 8,
The above method is a method for manufacturing a lithium niobate waveguide modulator, characterized in that it includes the steps of combining a substrate (1) having a film coated on its surface and lithium niobate film, then processing the combined lithium niobate film into a rib waveguide (2), then fabricating a negative domain structure (3) through a room temperature electric field polarization process, and finally fabricating electrodes (4) on both sides of the rib waveguide (2). In Article 9,
A method for manufacturing a lithium niobate waveguide modulator, characterized in that the rib waveguide (2) is processed and obtained by adopting a method of photolithography, etching and/or focused ion beam, and the electrode (4) is processed and obtained by adopting a method of photolithography and/or film coating.