A composite cladding electro-optic modulator with high modulation efficiency

Abstract

The present invention discloses a composite cladding electro-optical modulator with high modulation efficiency. The modulator comprises: a substrate layer; a buried oxide layer; a waveguide core layer; a composite cladding layer disposed on the waveguide core layer; and a set of electrodes for applying an electrical signal and modulating the waveguide. The present invention utilizes a multi-layer composite dielectric cladding structure to improve the modulation efficiency of the electro-optical modulator.

Description

Technical Field

[0001] The present invention relates to the field of integrated optics, and in particular to a composite cladding electro-optic modulator with high modulation efficiency. Background Art

[0002] With the continuous development of new technologies such as 5G, big data, and artificial intelligence, the demand for information transmission is increasing. Due to their enormous communication capacity, optical fiber communication networks bear the primary responsibility for information transmission. Electro-optical modulators, as key components for converting electrical and optical signals in optical communication systems, significantly impact the performance of communication systems. Therefore, the development of modulators with high modulation rates, low loss, and high integration is crucial for high-speed optical communications. In terms of materials, silicon, lithium niobate, or polymers are primarily used for modulation. Silicon-based EO modulators mostly rely on the free-carrier plasma dispersion effect. Under the influence of an applied electric field, free carriers in the waveguide diffuse or drift, thereby changing the waveguide's refractive index. Both lithium niobate and polymer EO modulators rely on the inherent electro-optical effect of the material. Under the influence of an applied electric field, their refractive index changes with the electric field. In short, the strength of the applied electric field is crucial to the modulation efficiency of modulators of various material platforms. The stronger the electric field applied to the waveguide per unit voltage, the higher the modulation efficiency. The traditional single-dielectric cladding structure electro-optic modulator has a limited electric field strength in the waveguide region, which makes the half-wave voltage-length product large and limits the modulation efficiency of the modulator. Summary of the Invention

[0003] In view of the above problems, the present invention mainly proposes a composite cladding electro-optic modulator with high modulation efficiency, which utilizes a multi-layer composite dielectric cladding structure to improve the modulation efficiency of the electro-optic modulator.

[0004] For a composite cladding electro-optic modulator, comprising:

[0005] substrate layer;

[0006] a buried oxide layer disposed on the substrate layer;

[0007] a waveguide core layer disposed on the buried oxide layer;

[0008] A composite cladding is provided outside the waveguide core layer, wherein the equivalent refractive index of the composite cladding material is smaller than the equivalent refractive index of the waveguide core material, and is used to achieve a large refractive index difference between the waveguide core layer and the cladding, thereby confining the light field in the waveguide for transmission;

[0009] A first cladding layer, a second cladding layer, and possibly more outer cladding layers are provided outside the waveguide core layer. After the first cladding layer is deposited, a second cladding layer having a dielectric constant greater than that of the first cladding layer is deposited thereon to increase the electric field strength at the interface between the first cladding layer and the second cladding layer. According to different requirements, a third, fourth, or more cladding layers having a larger dielectric constant may be deposited to increase the electric field strength at the interface between two adjacent cladding layers;

[0010] A set of electrodes used to apply an electrical signal and modulate the waveguide.

[0011] The present invention introduces a composite dielectric cladding structure by introducing a dielectric cladding composed of two or more cladding materials. This composite dielectric cladding structure can enhance the electric field strength in dielectrics with low dielectric constants. Furthermore, near the interface between different dielectric cladding layers, the electric field within the waveguide experiences a steep rise from low to high, manifesting as a new peak in electric field strength. This increases the electric field strength at that location, thereby reducing the modulator's half-wave voltage and improving the modulator's modulation efficiency.

[0012] In addition, the core waveguide and modulation electrode distribution structure of the electro-optical modulator according to the above embodiment of the present invention may also have the following additional technical features:

[0013] Furthermore, in an embodiment of the present invention, the waveguide core layer material may be a thin film lithium niobate material, which is used to transmit light and modulate optical signals.

[0014] Furthermore, in one embodiment of the present invention, a group of electrodes for applying an electrical signal and modulating the waveguide are loaded in a vertical direction of the waveguide core layer, are respectively arranged outside the composite cladding and inside the substrate, and apply an electric field in the vertical direction;

[0015] Furthermore, in one embodiment of the present invention, a group of electrodes for applying an electrical signal and modulating the waveguide are loaded in the horizontal direction of the waveguide core layer, are arranged inside or outside the composite cladding, and apply an electric field in the horizontal direction;

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] Previous electro-optic modulators typically had only one cladding structure. When voltage was applied to perform electro-optical modulation, the electric field strength applied to the optical waveguide was limited, resulting in insufficient modulation efficiency. The present invention employs a composite cladding structure, adding layers of other materials to the cladding of the previous modulator. Because composite cladding structures can increase the electric field strength in dielectrics with low dielectric constants, adding a second cladding with a larger dielectric constant to the first cladding can increase the electric field strength in the first cladding. Furthermore, the field strength generates an electric field peak at the interface between the two dielectrics. Therefore, by simply designing the cladding structures appropriately, the electric field strength around the modulated waveguide can be increased, thereby increasing modulation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of a high modulation efficiency Z-cut LNOI electro-optical modulator according to an embodiment of the present invention;

[0019] Figure 2 Schematic diagram of the structure of a high modulation efficiency X-cut LNOI electro-optical modulator according to an embodiment of the present invention;

[0020] Figure 3 The refractive index distribution of the waveguide of the single-clad Z-cut LNOI electro-optic modulator;

[0021] Figure 4 The refractive index distribution of the composite cladding Z-cut LNOI electro-optic modulator waveguide;

[0022] Figure 5 This is the electric field diagram of the single-clad Z-cut LNOI electro-optic modulator;

[0023] Figure 6 The electric field diagram of the composite cladding Z-cut LNOI electro-optic modulator;

[0024] Figure 7 This is the electric field diagram of the single-clad X-cut LNOI electro-optic modulator;

[0025] Figure 8 This is the electric field diagram of the composite cladding X-cut LNOI electro-optic modulator;

[0026] In the figure, 1 is the Si substrate, 2 is the SiO2 insulating layer, 3 is the waveguide core layer, 4 is the material 1 cladding, 5 is the material 2 cladding, 6 is the material 3 cladding, 7 is the signal electrode, 8 is the ground electrode, 9 is the Si substrate, 10 is the SiO2 insulating layer, 11 is the LN waveguide core layer, 12 is the material 1 cladding, 13 is the material 3 cladding, 14 is the signal electrode, and 15 is the ground electrode. DETAILED DESCRIPTION

[0027] The waveguide core layer described in the present invention has a ridge shape, which is achieved by etching. The waveguide core layer is made of lithium niobate, the substrate is a silicon substrate, the insulating layer is SiO2, the cladding layer of material 2 is made of a material with a greater dielectric constant than material 1, and the cladding layer of material 3 is made of a material with a greater dielectric constant than material 2. The signal electrode and ground electrode are made of gold.

[0028] Example 1

[0029] like Figure 1 As shown, this embodiment provides a high modulation efficiency Z-cut LNOI electro-optical modulator, including a Si substrate 1, a SiO2 insulating layer 2, a waveguide core layer 3, an upper cladding layer 4, an upper cladding layer 5, an upper cladding layer 6, a signal electrode 7, and a ground electrode 8.

[0030] Atop the Si substrate 1 is a SiO2 insulating layer 2, and above this is a LN thin film. Etching creates a ridge-shaped waveguide core 3 (i.e., the LN waveguide core). Atop this waveguide core 3 is an upper cladding layer 4 (i.e., the Material 1 cladding). Due to the significant refractive index difference between the waveguide core 3 and the upper cladding 4, light is effectively confined within the waveguide core for transmission. Deposited on the upper cladding 4 is an upper cladding layer 5 (i.e., the Material 2 cladding), which has a dielectric constant greater than that of Material 1. Because the composite dielectric cladding structure enhances the electric field strength in dielectrics with lower dielectric constants, a peak in electric field intensity occurs at the interface between the two cladding layers. This effectively increases the electric field strength at the interface between the upper cladding layers 4 and 5, thereby enhancing modulation efficiency. Due to the high height of the Z-cut lithium niobate waveguide core, an upper cladding layer 6 (i.e., the Material 3 cladding), with a dielectric constant greater than that of Material 2, is added to the Material 2 cladding. This effectively enhances the electric field strength at the top of the waveguide, further increasing modulation efficiency. The selection of materials 1, 2, and 3 is sufficient as long as they meet the aforementioned conditions. In this example, SiO2 is selected as material 1, Al2O3 as material 2, and Si3N4 as material 3. A signal electrode 7 is formed on the upper side of the upper cladding layer 6 at the position corresponding to the optical waveguide, and a ground electrode 8 is formed on the corresponding position of the substrate. The electric field is oriented along the optical axis of the Z-cut LN material. This maximizes the material's electro-optic coefficient, helping to enhance device performance. Figure 3 The waveguide refractive index distribution of the Z-cut LNOI electro-optic modulator with only SiO2 cladding is shown in Figure 2. Figure 4 The refractive index distribution diagram of the Z-cut LNOI electro-optic modulator waveguide is a composite cladding structure with Al2O3 and Si3N4 cladding added on the basis of single cladding. It can be seen that when the composite cladding is added, the refractive index of the waveguide is significantly reduced compared with the single cladding structure. Figure 5 is the electric field diagram of the single-clad Z-cut LNOI electro-optic modulator, Figure 6This is the electric field diagram of the composite cladding Z-cut LNOI electro-optical modulator. By comparing the electric field distribution diagrams of the two structures, it can be seen that when the SiO2-Al2O3-Si3N4 composite cladding structure is used, the electric field intensity at the junction of each cladding is significantly increased, which can effectively improve the modulation efficiency of the modulator.

[0031] Example 2

[0032] like Figure 2 As shown, this embodiment provides a high modulation efficiency X-cut LNOI electro-optical modulator, including a Si substrate 9, a SiO2 insulating layer 10, a waveguide core layer 11, an upper cladding layer 12, an upper cladding layer 13, a signal electrode 14, and a ground electrode 15.

[0033] On the Si substrate 9 is a SiO2 insulating layer 10, and above that is a LN thin film layer. A waveguide core layer 11 is fabricated on the LN thin film by etching. A SiO2 cladding layer 12 is applied near the optical waveguide. The large refractive index difference between the SiO2 cladding layer and the lithium niobate waveguide enhances the waveguide's ability to confine the light field. Signal electrodes 14 and ground electrodes 15 are placed on both sides of the optical waveguide to align the electric field with the Z-axis of the lithium niobate crystal, thereby utilizing the material's maximum electro-optical coefficient. Finally, a cladding layer 13 (i.e., Material 3 cladding) with a dielectric constant greater than that of SiO2 is deposited on the device. The Material 3 used in the experiment is Si3N4. The introduction of the composite dielectric layer increases the electric field strength within the waveguide at the interface between the cladding 12 and cladding 13, thereby increasing the modulation efficiency of the modulator and improving various device performances. Figure 7 This is the electric field distribution diagram obtained by simulation when there is only SiO2 cladding. Figure 8 This is the electric field distribution diagram obtained by simulation when another layer of Si3N4 cladding is added on the SiO2 cladding. By comparing the two figures, it can be seen that the composite cladding structure can indeed increase the electric field strength at the junction of the two claddings and improve the modulation efficiency of the modulator.

Claims

1. An electro-optic modulator for a composite cladding, characterized in that include: substrate layer; a buried oxide layer disposed on the substrate layer; a waveguide core layer disposed on the buried oxide layer; a composite cladding layer disposed on the waveguide core layer; a set of electrodes for applying an electrical signal and modulating the waveguide; The composite cladding structure is centered on the waveguide core layer and extends outward to form multiple cladding layers. The number of cladding materials is greater than or equal to two. The cladding layers from the inner side of the waveguide core layer to the outer side are respectively called the first cladding layer, the second cladding layer, ..., and so on. The dielectric constant of the first cladding material is smaller than the dielectric constant of the second cladding material, the dielectric constant of the second cladding material is smaller than the dielectric constant of the third cladding material, and so on.

2. The composite cladding electro-optic modulator according to claim 1, characterized in that: The group of electrodes are loaded in the vertical direction of the waveguide core layer and are respectively arranged inside or outside the composite cladding and the substrate to apply an electric field in the vertical direction.

3. The electro-optic modulator of composite cladding according to claim 1, characterized in that: The group of electrodes is loaded in the horizontal direction of the waveguide core layer, is arranged inside or outside the composite cladding, and applies an electric field in the horizontal direction.

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