Ultrahigh-modulation-efficiency electro-optical modulator based on fin-type grating waveguide and method

Abstract

The electro-optical modulator comprises a substrate, three parallel traveling wave electrodes are horizontally arranged on the substrate, ground electrodes are arranged on the two sides of the substrate, a signal electrode is arranged in the middle of the substrate, strip-shaped waveguides are arranged on the portions, between the traveling wave electrodes, of the substrate, and the strip-shaped waveguides are arranged on the portions, between the traveling wave electrodes, of the substrate. Fin type grating teeth are vertically arranged on the upper surface of the strip-shaped waveguide, and the refractive index of the fin type grating teeth is larger than that of the strip-shaped waveguide. In the light propagation process, light in the strip-shaped waveguide enters the fin-type grating teeth to be scattered, and the slow light effect is generated. The characteristic that the fin type grating waveguide is distributed in the vertical direction is mainly utilized, the electrode distance of the grating slow light modulator is reduced, meanwhile, the fin type grating teeth with the high refractive index are utilized to introduce light in the waveguide into the grating teeth, the group velocity of the light is reduced, the slow light effect is generated, and the electro-optical modulator which is ultrahigh in modulation efficiency and more integrated is achieved.

Description

Technical Field

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

[0002] Thin-film lithium niobate has excellent electro-optic modulation properties (such as extremely strong linear electro-optic coefficient r 33 = 30.8 pm / V, a wide transparent window of 0.35 - 5.2 μm and low propagation loss of ~ 0.3 dB / cm), has become a popular electro-optic modulator research and development platform. The traditional traveling-wave Mach-Zehnder 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 needs 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 , the current mainstream ideas are: 1) using the localized light field of micro-nano structures to enhance the intensity of light-matter interaction; 2) using the slow light effect of photonic crystals to reduce the group velocity of light in the waveguide and increase the electro-optical 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 cells, so it has greater practical promotion value. At present, the electro-optic modulator based on the 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 electrode and the waveguide is generally about 3 μm, and the grating teeth of the fishbone waveguide are placed in the horizontal direction. The length of the grating teeth will further increase the electrode spacing (often greater than 5 μm), reduce the electro-optic overlap integral, and the materials of the waveguide and the fishbone grating teeth must also be the same, so further improving the modulation efficiency faces challenges. Summary of the invention

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

[0005] The technical solution adopted by the present invention is: Provided is an electro-optic modulator with ultra-high modulation efficiency based on a fin-type grating waveguide, comprising a substrate, on which three parallel traveling wave electrodes are horizontally placed, with ground electrodes on both sides and a signal electrode in the middle, a strip waveguide is arranged 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 being greater than the refractive index of the strip waveguide; during light propagation, light in the strip waveguide enters the fin-type grating teeth and is scattered, thereby generating a slow light effect.

[0006] Following the above technical solution, the group refractive index of the fin grating waveguide is changed by adjusting the relative height of the strip waveguide and the fin grating teeth.

[0007] According to the above technical solution, the duty cycle of the fin-type grating teeth is 1:1.

[0008] According to the above technical solution, the fin-type grating teeth and the strip waveguide are made of different materials.

[0009] According to 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.

[0010] According to the above technical solution, the widths of the fin-type grating teeth and the strip waveguide are equal.

[0011] According to the above technical solution, the material of the traveling wave electrode is gold.

[0012] According to the above technical solution, the material of the substrate is silicon dioxide.

[0013] Following the above technical solution, a cover layer is provided above the entire electro-optic modulator.

[0014] The present invention also provides an electro-optical modulation method with ultra-high modulation efficiency based on a fin-type grating waveguide, which is based on the electro-optical modulator described in the above technical solution, and the method comprises the following steps: Setting 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 propagation; The simulation software is used to simulate the photonic crystal cell, calculate the photonic crystal band diagram under different relative heights of the fin grating teeth and the strip waveguide, and calculate the curve of the group refractive index under different structures with the wavelength of the incident light; The lattice constant of the fin grating teeth is adjusted so that incident light of a specific wavelength has a high group refractive index under the corresponding structure; An optoelectronic co-simulation model is established based on the lattice constant, the relative height of the fin grating teeth and the strip waveguide, the electro-optical overlap integral factor is calculated by scanning the electrode spacing, and the half-wave voltage-length product is calculated; An electro-optic modulator with ultra-high modulation efficiency is manufactured based on the structural parameters of the minimum half-wave voltage-length product.

[0015] According to the above technical solution, the grating teeth with high refractive index allow more light in the strip waveguide to enter the grating teeth, thereby reducing the group velocity during propagation and enhancing the slow light effect.

[0016] The beneficial effects of the present invention are as follows: the present invention mainly utilizes the characteristics of the fin-type grating waveguide being distributed in the vertical direction to reduce the electrode spacing of the grating slow light modulator, and at the same time utilizes the high-refractive-index fin-type grating teeth to introduce the light in the waveguide into the grating teeth to reduce the group velocity of the light, thereby generating a slow-light effect and realizing an electro-optic modulator with ultra-high modulation efficiency.

[0017] Furthermore, the grating teeth with high refractive index enable more light in the strip waveguide to enter the grating teeth, thereby reducing the group velocity during propagation and enhancing the slow light effect.

[0018] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1A Schematic diagram 1 of the three-dimensional structure 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 1B Schematic diagram of the three-dimensional structure 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 ; Figure 2 is the light field distribution of light in the waveguide during the propagation process of light in one embodiment of the present invention; Figure 3 is the group refractive index of an embodiment of the present invention at different wavelengths. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying 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.

[0022] It should be noted that the illustrations provided in the embodiments of the present invention are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout type may also be more complicated.

[0023] In the present invention, it is also necessary to explain that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, if the terms "first" and "second" appear, they are only used for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0024] In addition, it should be noted that the features of the various embodiments of the present invention may be combined or combined in part or in whole, and may interact and operate in different ways as will be appreciated by those skilled in the art. Each embodiment may be implemented independently of one another, or in an associated relationship.

[0025] Example 1 like Figure 1A As shown, an electro-optic modulator with ultra-high modulation efficiency based on a fin-type grating waveguide according to an embodiment of the present invention comprises a substrate 10, on which three parallel traveling wave electrodes are horizontally placed, 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 a fin-type grating tooth 40 is vertically arranged on the upper surface of the strip waveguide 30, the refractive index of the fin-type grating tooth 40 is greater than the refractive index of the strip waveguide 30, so that more light in the strip waveguide 30 can enter the fin-type grating tooth 40, thereby increasing the structural dispersion of 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-type grating teeth 40 and is scattered, producing a slow light effect. This embodiment mainly utilizes the characteristics of the fin-type grating waveguide being distributed in the vertical direction. Compared with the horizontal arrangement, the electrode spacing of the grating slow light modulator can be greatly reduced. At the same time, the high-refractive-index fin-type grating teeth 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.

[0026] Adjusting the relative height of the strip waveguide 30 and the fin-type grating teeth 40 can change the group refractive index of the grating waveguide. In the electro-optic modulator composed of the slow light waveguide, the half-wave voltage-length product V π L = n eff λg / (2 n 4 f 3 r 33 Γ ), neff is the effective mode index of the waveguide, λ is the wavelength of 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-optical overlap factor, so the modulator composed of 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 of the traveling wave electrodes is g Smaller, larger electro-optical overlap integration factor, half-wave voltage-length product V π L Smaller.

[0027] In a preferred embodiment of the present invention, the fin grating teeth 40 are located above the strip waveguide 30 and have equal widths, a duty ratio of 1:1, and together form a fin grating waveguide. The traveling wave electrode is composed of three strip electrodes arranged in parallel and equidistantly, and a fin grating waveguide is provided in the middle of the electrode gap.

[0028] like Figure 1B As shown, the fin-type grating teeth 40 and the strip waveguide 30 are made of different materials. The material of the fin-type grating teeth 40 can be titanium dioxide (TiO2), the material of the strip waveguide 30 can be X-cut lithium niobate (LiNbO3), the electrode material can be gold (Au), and the substrate material can be silicon dioxide (SiO2). Since the fin-type grating teeth 40 and the strip waveguide 30 of the present invention are vertical structures, it is easy to achieve the deposition of different materials in the manufacturing process. If the waveguide and grating structure in the prior art are arranged in a horizontal direction, it is difficult to achieve this through two different materials in the actual preparation process. On the one hand, the manufacturing process is complicated, and on the other hand, defects are prone to occur during the manufacturing process.

[0029] Furthermore, a cover layer 50 is provided on the entire electro-optic modulator to isolate the external environment and achieve stable protection of the device performance, and the material thereof can be silicon dioxide (SiO2).

[0030] 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 an electro-optical effect, the grating teeth with a higher refractive index can allow more light to enter the grating teeth from the waveguide when propagating in the waveguide, greatly improving the structural dispersion of the waveguide, reducing the group velocity of propagation, improving the slow light effect and thus improving the modulation efficiency. The size of the group refractive index can be controlled by designing the relative height of the grating teeth and the optical waveguide, and the position of the operating wavelength can be adjusted by changing the lattice constant. Adjusting these two parameters at the same time can achieve slow light with an operating wavelength of 1550 nm.

[0031] The parallel arranged fin grating waveguide and traveling wave electrode form a Mach-Zehnder modulator, and the push-pull structure composed of two modulation arms can double the modulation efficiency.

[0032] Example 2 This embodiment is based on Embodiment 1, and the main difference lies in the specific selected parameters. The fin 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 strip waveguide width is 1.5 μm.

[0033] Furthermore, the middle electrode is a signal electrode, and the electrodes on both sides are ground electrodes, which are connected to an external radio frequency signal through a GSG probe.

[0034] Furthermore, the lattice constant of the fin grating teeth is 383 nm.

[0035] like Figure 2 As shown, this embodiment simulates the distribution of the light field propagating in the waveguide, 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, making the light more inclined to enter the grating teeth.

[0036] like Figure 3 As shown in the figure, the group refractive index at different wavelengths is scanned, and the group refractive index can reach 6.76 when the wavelength is 1550 nm. In addition, different electrode spacings are also scanned. g The optical field distribution of the device is analyzed and the modulation efficiency and transmittance at different wavelengths are calculated.

[0037] When the electrode spacing is 2.6 μm and the number of cycles N is 600, the modulation efficiency of this embodiment is V π L =0.58884 V∙cm, and the transmittance at 1550 nm is 0.70036.

[0038] Example 3 The present invention also provides an electro-optical modulation method with ultra-high modulation efficiency based on a fin-type grating waveguide, which is used to implement the electro-optical modulator of the above embodiment, and the method comprises the following steps: S1, setting 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 propagation; S2. Use simulation software to simulate photonic crystal cells, calculate the photonic crystal band diagram under different relative heights of grating teeth and strip waveguides, and Calculate the curves of group refractive index changing with the wavelength of incident light under different structures; S3, adjusting the lattice constant of the fin-type grating teeth so that 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 5 or more), and the specific wavelength can be selected as 1550 nm; S4. According to the lattice constant and the relative height of the grating teeth and the strip waveguide, an optoelectronic joint simulation model is established to scan the electrode spacing. g Calculating the Electro-Optic Overlap Integration Factor Γ , calculate the half-wave voltage-length product according to the formula V π L ; S5, according to the minimum half-wave voltage length product V π L The structural parameters of the device are used to produce an ultra-high efficiency electro-optic modulator.

[0039] In summary, 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 utilizes the high-refractive index fin-type grating teeth to introduce the light in the waveguide into the grating teeth to reduce the group velocity of the light, thereby generating a slow-light effect and realizing an electro-optic modulator with ultra-high modulation efficiency.

[0040] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and 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.

[0041] The order of execution of each step in the above embodiment does not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0042] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

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

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

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

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

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

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

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

9. An electro-optical modulation method with ultra-high modulation efficiency based on a fin-type grating waveguide, characterized in that: The method is based on the ultra-high modulation efficiency electro-optical modulator based on the fin-type grating waveguide according to any one of claims 1 to 8, and comprises the following steps: Setting 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 propagation; The simulation software is used to simulate the photonic crystal cell, calculate the photonic crystal band diagram under different relative heights of the fin grating teeth and the strip waveguide, and calculate the curve of the group refractive index under different structures with the wavelength of the incident light; The lattice constant of the fin grating teeth is adjusted so that incident light of a specific wavelength has a high group refractive index under the corresponding structure; An optoelectronic co-simulation model is established based on the lattice constant, the relative height of the fin grating teeth and the strip waveguide, the electro-optical overlap integral factor is calculated by scanning the electrode spacing, and the half-wave voltage-length product is calculated; An electro-optic modulator with ultra-high modulation efficiency is manufactured based on the structural parameters of the minimum half-wave voltage-length product.

10. The electro-optical modulation method with ultra-high modulation efficiency based on fin-type grating waveguide according to claim 9, characterized in that: The high refractive index grating teeth allow more light in the strip waveguide to enter the grating teeth, thereby reducing the group velocity during propagation and enhancing the slow light effect.

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