Electro-optic modulator and method with ultra-high modulation efficiency based on fin grating waveguide

Abstract

The present invention discloses an electro-optical modulator and method with ultra-high modulation efficiency based on a fin-type grating waveguide. The electro-optical modulator includes a substrate, on which three parallel traveling-wave electrodes are horizontally arranged, with ground electrodes on both sides and a signal electrode in the middle. A strip waveguide is provided on the substrate between the traveling-wave electrodes, and fin-type grating teeth are vertically arranged on the upper surface of the strip waveguide. The refractive index of the fin-type grating teeth is greater than that of the strip waveguide. During the light propagation process, the light in the strip waveguide enters the fin-type grating teeth and scatters, generating a slow-light effect. The present invention mainly utilizes the characteristics of the vertical distribution of the fin-type grating waveguide to reduce the electrode spacing of the grating slow-light modulator, and at the same time uses the fin-type grating teeth with high refractive index to introduce the light in the waveguide into the grating teeth to reduce the group velocity of the light, generating a slow-light effect, and realizing an electro-optical modulator with ultra-high modulation efficiency and more integration.

Description

Technical Field

[0001] The present invention relates to the field of electro-optic modulators, and in particular, to an electro-optic modulator and method with ultra-high modulation efficiency based on fin-type grating waveguides. Background Art

[0002] Thin-film lithium niobate has become a popular electro-optic modulator R & D platform due to its excellent electro-optic modulation performance (such as a strong linear electro-optic coefficient r 33 = 30.8 pm / V, a relatively wide transparent window of 0.35 - 5.2 μm, and a low propagation loss of ~ 0.3 dB / cm). The traditional traveling-wave Mach-Zehnder type thin-film lithium niobate electro-optic modulator has currently achieved a modulation efficiency of 2.2 V∙cm and a modulation zone arm length of 1.5 cm, which cannot meet the requirements of miniaturization and integration of the new generation of optoelectronic devices.

[0003] In order to further reduce the half-wave voltage-length product of the modulator V π L Currently, the mainstream ideas are as follows: 1) Using micro-nano structures to localize the optical field and enhance the light-matter interaction intensity; 2) Using the slow light effect of photonic crystals to reduce the group velocity of light in the waveguide and increase the electro-optic interaction time. Among them, the method based on the slow light effect of photonic crystals can achieve a high degree of freedom in design by adjusting the parameters of the lattice unit cell, so it has greater practical promotion value. Currently, an electro-optic modulator based on a fishbone grating slow light waveguide can achieve a modulation efficiency of about 0.67 V∙cm. Due to the influence of metal absorption, the distance between the general electrode and the waveguide is about 3 μm. The grating teeth of the fishbone waveguide are placed horizontally, and the length of the grating teeth will further increase the electrode distance (usually greater than 5 μm), reducing the electro-optic overlap integral. Moreover, the materials of the waveguide and the fishbone grating teeth must be the same. Therefore, it is challenging to further improve the modulation efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide an electro-optic modulator and method with ultra-high modulation efficiency based on fin-type grating waveguides that can achieve ultra-high modulation efficiency.

[0005] The technical solution adopted by the present invention is as follows:

[0006] Provide an electro-optic modulator with ultra-high modulation efficiency based on fin-type grating waveguides, including a substrate. Three parallel traveling-wave electrodes are horizontally placed on the substrate, with ground electrodes on both sides and a signal electrode in the middle. A strip waveguide is provided on the substrate between the traveling-wave electrodes, and fin-type grating teeth are vertically arranged on the upper surface of the strip waveguide. The refractive index of the fin-type grating teeth is greater than that of the strip waveguide; during the light propagation process, the light in the strip waveguide enters the fin-type grating teeth and scatters, generating a slow light effect.

[0007] Based on the above technical solution, the group refractive index of the fin grating waveguide is changed by adjusting the relative height between the strip waveguide and the fin grating teeth.

[0008] Based on the above technical solution, the duty cycle of the fin grating teeth is 1:1.

[0009] Based on the above technical solution, the materials of the fin grating teeth and the strip waveguide are different.

[0010] Based on the above technical solution, the material of the fin grating teeth is titanium dioxide, and the material of the strip waveguide is X-cut lithium niobate.

[0011] Based on the above technical solution, the widths of the fin grating teeth and the strip waveguide are equal.

[0012] Based on the above technical solution, the material of the traveling-wave electrode is gold.

[0013] Based on the above technical solution, the material of the substrate is silicon dioxide.

[0014] Based on the above technical solution, a cover layer is provided above the entire electro-optic modulator.

[0015] The present invention also provides an electro-optic modulation method with ultra-high modulation efficiency based on a fin grating waveguide. Based on the electro-optic modulator described in the above technical solution, the method includes the following steps:

[0016] Set the refractive index of the fin grating teeth so that the light in the strip waveguide can enter the fin grating teeth during propagation;

[0017] Using simulation software, through the simulation of the photonic crystal unit cell, calculate the photonic crystal energy band diagrams under different relative heights of the fin grating teeth and the strip waveguide, and calculate the variation curves of the group refractive index with the incident light wavelength under different structures;

[0018] Adjust the lattice constant of the fin grating teeth so that the incident light of a specific wavelength has a high group refractive index under the corresponding structure;

[0019] Establish an optoelectronic co-simulation model based on the lattice constant, the relative height between the fin grating teeth and the strip waveguide, scan the electrode spacing to calculate the electro-optic overlap integral factor, and calculate the half-wave voltage-length product;

[0020] Fabricate an electro-optic modulator with ultra-high modulation efficiency according to the structural parameters of the minimum half-wave voltage-length product.

[0021] Based on the above technical solution, through the grating teeth with a high refractive index, the light in the strip waveguide can enter the grating teeth more, reducing the group velocity during propagation and enhancing the slow light effect.

[0022] The beneficial effects produced by the present invention are as follows: The present invention mainly utilizes the characteristics of the fin-type grating waveguide distributed in the vertical direction to reduce the electrode spacing of the grating slow light modulator. At the same time, the fin-type grating teeth with high refractive index are used to introduce the light in the waveguide into the grating teeth to reduce the group velocity of the light, generating the slow light effect and realizing an electro-optic modulator with ultra-high modulation efficiency.

[0023] Furthermore, the light in the strip waveguide can enter the grating teeth more through the grating teeth with high refractive index, reducing the group velocity during propagation and enhancing the slow light effect.

[0024] Of course, it is not necessary for any product implementing the present invention to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1A is a first three-dimensional structure schematic diagram of an electro-optic modulator with ultra-high modulation efficiency based on a fin-type grating waveguide according to an embodiment of the present invention;

[0027] Figure 1B is a three-dimensional structure schematic of an electro-optic modulator with ultra-high modulation efficiency based on a fin-type grating waveguide according to an embodiment of the present invention Figure 2 ;

[0028] Figure 2 is the optical field distribution of light during propagation in a waveguide according to an embodiment of the present invention;

[0029] Figure 3 is the group refractive index at different wavelengths according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] It should be noted that the diagrams provided in the embodiments of the present invention only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape and size of the components in actual implementation. The types, numbers and proportions of the components in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0032] In the present invention, it should also be noted that for terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present application. In addition, for terms such as "first" and "second", they are only used for descriptive and distinguishing purposes and cannot be construed as indicating or implying relative importance.

[0033] In addition, it should also be noted that the features of various embodiments of the present invention can be partially or wholly combined or integrated, and as can be understood by those skilled in the art, they can interact and operate in different ways. Each embodiment can be implemented independently of each other or in an associated relationship.

[0034] Embodiment 1

[0035] As Figure 1A shown, the electro-optic modulator with ultra-high modulation efficiency based on fin grating waveguides in the embodiment of the present invention includes a substrate 10. Three parallel traveling wave electrodes are horizontally placed on the substrate, with ground electrodes 21 and 22 on both sides and a signal electrode 23 in the middle. A strip waveguide 30 is provided on the substrate between the traveling wave electrodes, and fin grating teeth 40 are vertically arranged on the upper surface of the strip waveguide 30. The refractive index of the fin grating teeth 40 is greater than that of the strip waveguide 30, so that the light in the strip waveguide 30 can enter the fin grating teeth 40 more, increasing the structural dispersion of the light in the waveguide and increasing the group refractive index of the waveguide n g , realizing slow light; during the light propagation process, the light in the strip waveguide 30 enters the fin grating teeth 40 and scatters, generating a slow light effect. This embodiment mainly utilizes the characteristics of the vertical distribution of fin grating waveguides. Compared with the horizontal arrangement, it can greatly reduce the electrode spacing of the grating slow light modulator. At the same time, the fin grating teeth with high refractive index are used to introduce the light in the waveguide into the grating teeth to reduce the group velocity of the light to better realize slow light.

[0036] Adjusting the relative height of the strip waveguide 30 and the fin grating teeth 40 can change the group refractive index of the grating waveguide. In the electro-optic modulator composed of slow light waveguides, the product of the half-wave voltage and the length V π L = n eff λg / (2 n 4 f 3 r 33Γ ) n eff is the effective mode refractive index of the waveguide, λ is the wavelength of the incident light, g is the electrode spacing, n is the refractive index of the waveguide material, is the local field factor, n g is the group refractive index of the fin grating waveguide, r 33 is the electro-optic coefficient, Γ is the electro-optic overlap factor, so the modulator composed of the slow light waveguide has a smaller half-wave voltage-length product V π L . Compared with the traditional fishbone grating waveguide, the grating teeth of the fin grating waveguide are in the vertical direction, so the spacing g of the traveling wave electrodes is smaller, the electro-optic overlap integral factor is larger, and the half-wave voltage-length product V π L is smaller.

[0037] In a preferred embodiment of the present invention, the fin grating teeth 40 are located above the strip waveguide 30 and have the same width, and the duty cycle is 1:1, jointly forming the fin grating waveguide. The traveling wave electrode is composed of three strip electrodes arranged in parallel at equal distances, and the fin grating waveguide is provided in the middle of the electrode gap.

[0038] As Figure 1B shown, the materials of the fin grating teeth 40 and the strip waveguide 30 are different. The material of the fin grating teeth 40 can be selected as titanium dioxide (TiO2), the material of the strip waveguide 30 can be selected as X-cut lithium niobate (LiNbO3), the electrode material can be selected as gold (Au), and the substrate material is selected as silicon dioxide (SiO2). Since the fin grating teeth 40 and the strip waveguide 30 of the present invention are in an up-and-down vertical structure, it is very easy to realize the deposition of different materials in the manufacturing process. In the prior art, if the waveguide and grating structures are arranged horizontally, it is very difficult to realize with two different materials in the actual manufacturing process. On the one hand, the manufacturing process is complicated, and on the other hand, defects are likely to occur during the manufacturing process.

[0039] Furthermore, a cover layer 50 is also provided above the entire electro-optic modulator to isolate the external environment and achieve stable protection of the device performance, and its material can be selected as silicon dioxide (SiO2).

[0040] By setting the refractive index of the grating teeth (TiO2) to be greater than that of the strip waveguide (LiNbO3), although the grating tooth material does not have the electro-optic effect, the grating teeth with a higher refractive index can cause more light to enter the grating teeth from the waveguide when propagating in the waveguide, greatly increasing the structural dispersion of the waveguide, reducing the propagation group velocity, enhancing the slow light effect and thus improving the modulation efficiency. By designing the relative height of the grating teeth and the optical waveguide, the magnitude of the group refractive index can be controlled, and by changing the lattice constant, the position of the operating wavelength can be adjusted. Adjusting these two parameters simultaneously can achieve slow light at the operating wavelength of 1550 nm.

[0041] Moreover, the fin-type grating waveguide arranged in parallel and the traveling-wave electrode form a Mach-Zehnder modulator, and the push-pull structure formed by the two modulation arms can double the modulation efficiency.

[0042] Example 2

[0043] This example is based on Example 1, and the main difference lies in the specifically selected parameters. The fin-type grating teeth are made of TiO2 with a thickness of 300 nm, the strip waveguide is made of X-cut LiNbO3 with a thickness of 500 nm, the traveling-wave electrode is made of Au with a thickness of 800 nm, the substrate is made of SiO2 with a thickness of 5 μm, and the width of the strip waveguide is 1.5 μm.

[0044] Furthermore, the middle electrode is the signal electrode, and the two side electrodes are the ground electrodes, which are connected to the external radio frequency signal through GSG probes.

[0045] Furthermore, the lattice constant of the fin-type grating teeth is 383 nm.

[0046] As Figure 2 shown, the optical field distribution propagating in the waveguide in this example is simulated, and it can be seen that the light in the waveguide enters the grating teeth during the propagation process. This is because the refractive index of the titanium dioxide grating teeth is larger, causing the light to tend to enter the grating teeth more.

[0047] As Figure 3 shown, the group refractive index at different wavelengths is scanned. When the wavelength is 1550 nm, the group refractive index can reach 6.76. In addition, the optical field distribution of the device at different electrode spacings g is also scanned, and the modulation efficiency and the transmittance at different wavelengths are calculated.

[0048] Among them, when the electrode spacing is 2.6 μm and the number of periods N is 600, the modulation efficiency V π L of this example is 0.58884 V∙cm, and the transmittance at the wavelength of 1550 nm is 0.70036.

[0049] Example 3

[0050] The present invention also provides an electro-optic modulation method with ultra-high modulation efficiency based on a fin grating waveguide for implementing the electro-optic modulator in the above embodiments. The method includes the following steps:

[0051] S1. Set the refractive index of the fin grating teeth so that the light in the strip waveguide can enter the fin grating teeth during propagation;

[0052] S2. Use simulation software to calculate the photonic crystal energy band diagrams under different relative heights of the grating teeth and the strip waveguide through simulation of the photonic crystal unit cell, and calculate the variation curve of the group refractive index with the incident light wavelength under different structures;

[0053] S3. Adjust the lattice constant of the fin grating teeth so that the incident light of a specific wavelength has a high group refractive index under the corresponding structure (the group refractive index of the present invention can reach more than 5), and the specific wavelength can be selected as 1550 nm;

[0054] S4. Establish an optoelectronic co-simulation model according to the lattice constant and the relative height of the grating teeth and the strip waveguide, scan the electrode spacing g calculate the electro-optic overlap integral factor Γ and calculate the half-wave voltage-length product according to the formula V π L ;

[0055] S5. Fabricate an electro-optic modulator with ultra-high efficiency according to the structural parameters of the minimum half-wave voltage-length product V π L .

[0056] In summary, the present invention mainly utilizes the characteristics of the fin grating waveguide distributed in the vertical direction to reduce the electrode spacing of the grating slow-light modulator. At the same time, the fin grating teeth with high refractive index are used to introduce the light in the waveguide into the grating teeth to reduce the group velocity of the light, generating a slow-light effect and realizing an electro-optic modulator with ultra-high modulation efficiency.

[0057] It should be noted that according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0058] The magnitudes of the sequence numbers of the steps in the above embodiments do not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0059] It should be understood that those of ordinary skill in the art can make improvements or modifications based on the above description, and all such improvements and modifications shall fall within the protection scope of the appended claims of the present invention.

Claims

1. An electro-optic modulator with ultra-high modulation efficiency based on fin grating waveguides, characterized in that It includes a substrate, on which three parallel traveling-wave electrodes are horizontally placed. The ground electrodes are on both sides and the signal electrode is in the middle. A strip waveguide is provided on the substrate between the traveling-wave electrodes, and fin-type grating teeth are vertically arranged on the upper surface of the strip waveguide. The refractive index of the fin-type grating teeth is greater than that of the strip waveguide. During the light propagation process, the light in the strip waveguide enters the fin-type grating teeth and scatters, generating a slow light effect.

2. The electro-optic modulator with ultra-high modulation efficiency based on fin grating waveguides according to claim 1, wherein The group refractive index of the fin-type grating waveguide is changed by adjusting the relative height between the strip waveguide and the fin-type grating teeth.

3. The electro-optic modulator with ultra-high modulation efficiency based on a fin grating waveguide according to claim 1, characterized in that The duty cycle of the fin-type grating teeth is 1:

1.

4. The electro-optic modulator with ultra-high modulation efficiency based on fin grating waveguides according to claim 1, characterized in that The materials of the fin-type grating teeth and the strip waveguide are different.

5. The electro-optic modulator with ultra-high modulation efficiency based on fin grating waveguides according to claim 4, characterized in that, The material of the fin-type grating teeth is titanium dioxide, and the material of the strip waveguide is X-cut lithium niobate.

6. The electro-optic modulator with ultra-high modulation efficiency based on a fin grating waveguide according to claim 1, characterized in that The widths of the fin-type grating teeth and the strip waveguide are equal.

7. The electro-optic modulator with ultra-high modulation efficiency based on fin-shaped grating waveguides according to claim 1, characterized in that, The material of the traveling-wave electrode is gold, and the material of the substrate is silica.

8. The electro-optic modulator with ultra-high modulation efficiency based on fin grating waveguides according to claim 1, characterized in that, A cover layer is provided above the entire electro-optic modulator.

9. An electro-optic modulation method with ultra-high modulation efficiency based on a fin grating waveguide, characterized in that, The method is based on the electro-optic modulator with ultra-high modulation efficiency based on the fin-type grating waveguide described in any one of claims 1-8, and includes the following steps: Set the refractive index of the fin-type grating teeth so that the light in the strip waveguide can enter the fin-type grating teeth during the propagation process. Use simulation software to calculate the photonic crystal energy band diagram under different relative heights of the fin-type grating teeth and the strip waveguide through the simulation of the photonic crystal unit cell, and calculate the change curve of the group refractive index with the incident light wavelength under different structures. Adjust the lattice constant of the fin-type grating teeth so that the incident light of a specific wavelength has a high group refractive index under the corresponding structure. Establish an optoelectronic co-simulation model according to the lattice constant, the relative height between the fin-type grating teeth and the strip waveguide, scan the electrode spacing to calculate the electro-optic overlap integral factor, and calculate the half-wave voltage-length product. Fabricate an electro-optic modulator with ultra-high modulation efficiency according to the structural parameters of the minimum half-wave voltage-length product.

10. The electro-optic modulation method with ultra-high modulation efficiency based on a fin-type grating waveguide according to claim 9, characterized in that, The high refractive index grating teeth enable more light in the strip waveguide to enter the grating teeth, reduce the group velocity during propagation, and enhance the slow light effect.

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