A lithium niobate thin film modulator based on upper and lower traveling wave electrodes

Abstract

The application discloses a lithium niobate thin film modulator based on upper and lower layer traveling wave electrodes, which comprises a substrate, a silicon oxide layer and a lithium niobate thin film, the silicon oxide layer is located on one side of the substrate, and the lithium niobate thin film is located on the side of the silicon oxide layer away from the substrate, and the lithium niobate thin film is provided with a plurality of protruding ridge-shaped waveguide structures; the ridge-shaped waveguide structure comprises a first modulation arm and a second modulation arm, and the first modulation arm and the second modulation arm are provided with a silicon oxide cover layer on the side away from the silicon oxide layer; the silicon oxide cover layer is provided with a GSG traveling wave electrode and a plurality of upper and lower layer electrodes on the side away from the lithium niobate thin film. The lithium niobate thin film modulator based on upper and lower layer traveling wave electrodes can effectively solve the problems of impedance mismatch, large electric signal reflection, large microwave loss and the like, and improve the modulator bandwidth.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology, specifically relating to a lithium niobate thin film modulator based on upper and lower traveling wave electrodes. Background Technology

[0002] With the rapid development of optical communication technology, efficient, compact, and broadband optical modulators have become increasingly important in optical signal processing. Thin-film lithium niobate modulators, as an important optoelectronic device, are widely used in optical communication systems to modulate optical signals for signal transmission and processing in optical communication.

[0003] Traveling-wave electrode modulators based on lithium niobate thin films typically consist of an optical waveguide load and traveling-wave electrodes. Electromagnetic waves propagate between the traveling-wave electrodes, while optical carrier waves propagate within the load waveguide. During the propagation of the optical carrier and electromagnetic waves, the interaction between the electromagnetic waves and the optical carrier causes a phase change in the optical carrier, thus modulating the electrical signal into an optical signal. The traveling-wave electrode structure is a crucial component of the modulator. Careful design of the electrode structure can better achieve impedance matching, ensuring effective signal transmission, modulation, and control, thereby improving device performance.

[0004] When designing traveling-wave electrodes for optical modulators, three factors typically need to be considered: first, the microwave loss of the traveling-wave electrode; second, refractive index matching, meaning that the electrical signal of the traveling-wave electrode and the optical signal have similar transmission rates; and third, impedance matching, meaning that the characteristic impedance of the traveling-wave electrode needs to be compatible with the standard port impedance in the microwave system to reduce reflection loss.

[0005] Currently, the refractive index matching of microwave and light waves in electro-optic modulator electrodes and the impedance matching between traveling wave electrodes and terminal loads are not high enough. At present, metal buffer layers are usually used to improve the refractive index matching of microwave and light waves and the impedance matching between traveling wave electrodes and terminal loads, but this will increase transmission loss.

[0006] Therefore, further improvements will be made to address the aforementioned issues. Summary of the Invention

[0007] The main objective of this invention is to provide a lithium niobate thin-film modulator based on upper and lower traveling wave electrodes, which can effectively solve problems such as impedance mismatch, large electrical signal reflection, and large microwave loss, thereby improving the modulator bandwidth.

[0008] To achieve the above objectives, the present invention provides a lithium niobate thin-film modulator based on upper and lower traveling-wave electrodes, comprising a substrate, a silicon oxide layer, and a lithium niobate thin film, wherein:

[0009] The silicon oxide layer is located on one side of the substrate and the lithium niobate film is located on the side of the silicon oxide layer away from the substrate. The lithium niobate film is provided with several protruding ridge waveguide structures.

[0010] The ridge waveguide structure includes a first modulation arm and a second modulation arm, and a silicon oxide top cover layer is provided on the side of the first modulation arm and the second modulation arm away from the silicon oxide layer.

[0011] The silicon oxide capping layer has a GSG traveling wave electrode and several upper and lower layer electrodes on the side away from the lithium niobate film. The GSG traveling wave electrode includes a first ground transmission electrode, a second ground transmission electrode, and a signal transmission electrode disposed between the first ground transmission electrode and the second ground transmission electrode. The first ground transmission electrode, the signal transmission electrode, and the second ground transmission electrode are arranged in parallel. The upper and lower layer electrodes include several upper and lower structures with the same H-shape when viewed from above, and the upper and lower structures form a mutual inductance structure. The upper and lower structures are used to change the inductance value per unit length of the GSG traveling wave electrode. There is a distance between the upper and lower structures, and the upper structure is located on the side of the lower structure away from the silicon oxide capping layer.

[0012] As a further preferred embodiment of the above technical solution, the upper structure includes a plurality of first upper structures, second upper structures, third upper structures and fourth upper structures, and the lower structure includes a plurality of first lower structures, second lower structures, third lower structures and fourth lower structures. The first upper structure and the first lower structure correspond one-to-one, the second upper structure and the second lower structure correspond one-to-one, the third upper structure and the third lower structure correspond one-to-one, and the fourth upper structure and the fourth lower structure correspond one-to-one.

[0013] As a further preferred embodiment of the above technical solution, the first upper structure and the first lower structure are distributed on the side of the first ground transmission electrode close to the signal transmission electrode.

[0014] The second upper structure and the second lower structure are distributed on the side of the signal transmission electrode close to the first ground transmission electrode;

[0015] The third upper structure and the third lower structure are distributed on the side of the second ground transmission electrode close to the signal transmission electrode;

[0016] The fourth upper layer structure and the fourth lower layer structure are distributed on the side of the signal transmission electrode close to the second ground transmission electrode.

[0017] As a further preferred embodiment of the above technical solution, the upper and lower layer electrodes are configured as periodically varying electrodes along the extension direction of the ridge waveguide structure.

[0018] As a further preferred embodiment of the above technical solution, the upper and lower electrodes include at least one middle layer structure with an H-shape that is the same as the upper and lower layers when viewed from above, and the middle layer structure is located between the upper and lower layers (the upper, middle and lower positions in this invention are relative).

[0019] The beneficial effects of this invention are as follows:

[0020] 1. This invention proposes a thin-film lithium niobate modulator based on an upper and lower traveling-wave electrode structure. The inductance of the required additional inductor structure is determined by the difference between the actual impedance value of the lithium niobate thin-film electro-optic modulator and the value required for impedance matching. By setting upper and lower electrodes spaced a certain distance apart between the signal transmission electrode and the ground transmission electrode, the inductance per unit length of the traveling-wave electrode is changed, achieving impedance matching of the lithium niobate thin-film electro-optic modulator, reducing signal reflection, and increasing bandwidth.

[0021] 2. The periodic distribution of upper and lower metal electrodes in the radio frequency transmission direction allows for adjustment of the microwave refractive index, better matching the optical speed.

[0022] 3. The use of an H-shaped upper and lower electrode structure in top view can greatly improve the design freedom of electrode parameters, significantly increasing its adjustable range compared to existing electrodes. This provides greater optimization space for the traveling wave electrode and makes it easier to effectively adjust the electrode impedance and refractive index to meet the expected requirements.

[0023] 4. The silicon oxide capping layer in this invention can reduce the absorption loss of waveguide modes by the metal. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a lithium niobate thin-film modulator based on upper and lower traveling wave electrodes according to the present invention.

[0025] Figure 2 This is a cross-sectional view of a lithium niobate thin-film modulator based on upper and lower traveling wave electrodes according to the present invention.

[0026] Figure 3 This is a top view of a lithium niobate thin-film modulator based on upper and lower traveling wave electrodes according to the present invention.

[0027] Figure 4 This is a cross-sectional view of a lithium niobate thin-film modulator based on upper and lower traveling wave electrodes according to the present invention.

[0028] Figure 5 This is a radio frequency transmission loss diagram of a lithium niobate thin film modulator based on upper and lower traveling wave electrodes according to the present invention.

[0029] Figure 6This is a port impedance diagram of a lithium niobate thin-film modulator based on upper and lower traveling wave electrodes according to the present invention.

[0030] Figure 7 This is a port RF refractive index diagram of a lithium niobate thin-film modulator based on upper and lower traveling wave electrodes according to the present invention.

[0031] Figure 8 This is a simulation result diagram showing the relationship between the optical waveguide depth, electrode spacing, and VπL of an optical waveguide based on a lithium niobate thin-film modulator with upper and lower traveling wave electrodes according to the present invention.

[0032] The reference numerals in the figures include: 100, substrate; 200, silicon oxide layer; 300, lithium niobate thin film; 310, ridge waveguide structure; 400, silicon oxide capping layer; 500, GSG traveling wave electrode; 510, first ground transmission electrode;

[0033] 520, Second ground transmission electrode; 530, Signal transmission electrode; 600, Upper and lower layer electrodes; 610, Upper layer structure; 611, First upper layer structure; 612, Second upper layer structure; 613, Third upper layer structure; 614, Fourth upper layer structure; 620, Lower layer structure; 621, First lower layer structure; 622, Second lower layer structure; 623, Third lower layer structure; 624, Fourth lower layer structure; 630, Middle layer structure. Detailed Implementation

[0034] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0035] In the preferred embodiments of the present invention, those skilled in the art should note that the substrates and the like involved in the present invention can be considered as prior art.

[0036] Preferred embodiment.

[0037] like Figure 1-8 As shown, this invention discloses a lithium niobate thin-film modulator based on upper and lower traveling-wave electrodes, comprising a substrate 100, a silicon oxide layer 200, and a lithium niobate thin film 300, wherein:

[0038] The silicon oxide layer 200 is located on one side of the substrate 100 and the lithium niobate film 300 is located on the side of the silicon oxide layer 200 away from the substrate 100. The lithium niobate film 300 is provided with a plurality of protruding ridge waveguide structures 310.

[0039] The ridge waveguide structure 310 includes a first modulation arm and a second modulation arm, and a silicon oxide capping layer 400 is provided on the side of the first modulation arm and the second modulation arm away from the silicon oxide layer 200.

[0040] The silicon oxide capping layer 400 has a GSG traveling wave electrode 500 and several upper and lower layer electrodes 600 disposed on the side away from the lithium niobate film 300; the GSG traveling wave electrode 500 includes a first ground transmission electrode 510, a second ground transmission electrode 520, and a signal transmission electrode 530 disposed between the first ground transmission electrode 510 and the second ground transmission electrode 520, and the first ground transmission electrode 510, the signal transmission electrode 530, and the second ground transmission electrode 520 are arranged in parallel; the upper and lower layer electrodes 600 include several The upper structure 610 and the lower structure 620 are of the same H shape when viewed from above, and a mutual inductance structure is formed between the upper structure 610 and the lower structure 620 (the adjustable range of its inductance is greater than the self-inductance formed by a single inductor structure). The upper structure 610 and the lower structure 620 are used to change the inductance value per unit length of the GSG traveling wave electrode 500. There is a distance between the upper structure 610 and the lower structure 620, and the upper structure 610 is located on the side of the lower structure 620 away from the silicon oxide capping layer 400.

[0041] Specifically, the upper structure 610 includes a plurality of first upper structures 611, second upper structures 612, third upper structures 613 and fourth upper structures 614, and the lower structure 620 includes a plurality of first lower structures 621, second lower structures 622, third lower structures 623 and fourth lower structures 624. The first upper structure 611 and the first lower structure 621 correspond one-to-one, the second upper structure 612 and the second lower structure 622 correspond one-to-one, the third upper structure 613 and the third lower structure 623 correspond one-to-one, and the fourth upper structure 614 and the fourth lower structure 624 correspond one-to-one.

[0042] More specifically, the first upper structure 611 and the first lower structure 621 are distributed on the side of the first ground transmission electrode 510 near the signal transmission electrode 530.

[0043] The second upper structure 612 and the second lower structure 622 are distributed on the side of the signal transmission electrode 530 near the first ground transmission electrode 510;

[0044] The third upper structure 613 and the third lower structure 623 are distributed on the side of the second ground transmission electrode 520 near the signal transmission electrode 530;

[0045] The fourth upper structure 614 and the fourth lower structure 624 are distributed on the side of the signal transmission electrode 530 near the second ground transmission electrode 520.

[0046] Furthermore, the upper and lower layer electrodes 600 are configured as periodically varying electrodes along the extension direction of the ridge waveguide structure 310.

[0047] Furthermore, the upper and lower electrode layers 600 include at least one middle layer structure 630 with the same H-shape as the upper layer structure 610 and the lower layer structure 620 when viewed from above. The middle layer structure 630 is located between the upper layer structure 610 and the lower layer structure 620. (The upper, middle, and lower positions in this invention are relative. In the case of upper and lower metal electrode structures that are respectively arranged at a certain distance on the inner side of the first / second ground transmission electrode and on both sides of the signal transmission electrode, it is not limited to only upper and lower layers that are separated by a certain distance; it can also be configured as an upper, middle, and lower layer structure that is separated by a certain distance, such as...) Figure 4 (As shown).

[0048] Preferably, the ridge waveguide structure is located between the first upper (lower) layer structure and the second upper (lower) layer structure, or between the third upper (lower) layer structure and the fourth upper (lower) layer structure.

[0049] For the present invention:

[0050] 1. By setting upper and lower metal electrodes spaced a certain distance apart on the inner side of the first / second ground transmission electrode and on both sides of the signal transmission electrode, the inductance per unit length of the traveling wave electrode is changed, thereby achieving impedance matching of the lithium niobate thin-film electro-optic modulator, reducing electrical signal reflection, and increasing bandwidth.

[0051] 2. A mutual inductance structure is formed between the upper and lower layers, and its inductance adjustment range is greater than that of the self-inductance formed by a single inductance structure.

[0052] 3. The use of an H-shaped upper and lower electrode structure in top view can greatly improve the design freedom of electrode parameters, and make it easier to effectively adjust the electrode impedance and refractive index to achieve the expected requirements.

[0053] The working principle of this invention is as follows:

[0054] To reduce signal reflection, improve modulation bandwidth, and enhance modulator performance, the traveling wave electrodes need to be designed to achieve impedance matching.

[0055] The expression for the characteristic impedance Z is:

[0056]

[0057] Where K is the proportionality coefficient, and L and C are the inductance and capacitance values ​​per unit length, respectively.

[0058] It can be seen that the impedance is related to the inductance and capacitance per unit length of the traveling wave electrode. The inductance per unit length can be changed by adding an inductor structure to the traveling wave electrode, thereby improving impedance matching, reducing electrical signal reflection, and increasing bandwidth.

[0059] The size of the inductor is determined by the difference between the actual impedance value of the modulator and the value used to achieve impedance matching of the modulator.

[0060] This invention changes the inductance per unit length of the traveling wave electrode by setting upper and lower electrodes spaced a certain distance apart on the inner side of the ground transmission electrode and on both sides of the signal transmission electrode.

[0061] The upper and lower electrodes have the same structure, forming a mutual inductance structure between the two layers.

[0062] The inductor structure is generally sheet-like, and its top view shows an H-shape.

[0063] The thin-film lithium niobate modulator was modeled and simulated using HFSS software. RF transmission loss, RF refractive index, and port impedance parameters of the thin-film lithium niobate modulator with upper and lower traveling-wave electrodes were calculated. Simulation results showed that the thin-film lithium niobate modulator with upper and lower electrodes achieved port impedance matching close to 50Ω, as well as microwave and optical refractive index matching. Figure 5 , 6 As shown in Figure 7. VπL can be calculated through electrostatic field simulation, as shown in Figure 7. Figure 8 As shown.

[0064] It is worth mentioning that the technical features such as the substrate involved in this patent application should be regarded as prior art. The specific structure, working principle and possible control methods and spatial arrangement of these technical features can be conventionally selected in the field and should not be regarded as the inventive point of this patent. This patent will not be further elaborated in detail.

[0065] For those skilled in the art, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A lithium niobate thin-film modulator based on upper and lower traveling-wave electrodes, characterized in that, It includes a substrate, a silicon oxide layer, and a lithium niobate thin film, wherein: The silicon oxide layer is located on one side of the substrate and the lithium niobate film is located on the side of the silicon oxide layer away from the substrate. The lithium niobate film is provided with several protruding ridge waveguide structures. The ridge waveguide structure includes a first modulation arm and a second modulation arm, and a silicon oxide top cover layer is provided on the side of the first modulation arm and the second modulation arm away from the silicon oxide layer. The silicon oxide capping layer has a GSG traveling wave electrode and several upper and lower layer electrodes on the side away from the lithium niobate film. The GSG traveling wave electrode includes a first ground transmission electrode, a second ground transmission electrode, and a signal transmission electrode disposed between the first ground transmission electrode and the second ground transmission electrode. The first ground transmission electrode, the signal transmission electrode, and the second ground transmission electrode are arranged in parallel. The upper and lower layer electrodes include several upper and lower structures with the same H-shape when viewed from above, and the upper and lower structures form a mutual inductance structure. The upper and lower structures are used to change the inductance value per unit length of the GSG traveling wave electrode. There is a distance between the upper and lower structures, and the upper structure is located on the side of the lower structure away from the silicon oxide capping layer.

2. The lithium niobate thin-film modulator based on upper and lower traveling-wave electrodes according to claim 1, characterized in that, The upper structure includes a plurality of first upper structure, second upper structure, third upper structure and fourth upper structure, and the lower structure includes a plurality of first lower structure, second lower structure, third lower structure and fourth lower structure. The first upper structure and the first lower structure correspond one-to-one, the second upper structure and the second lower structure correspond one-to-one, the third upper structure and the third lower structure correspond one-to-one, and the fourth upper structure and the fourth lower structure correspond one-to-one.

3. A lithium niobate thin-film modulator based on upper and lower traveling wave electrodes according to claim 2, characterized in that: The first upper structure and the first lower structure are distributed on the side of the first ground transmission electrode close to the signal transmission electrode; The second upper structure and the second lower structure are distributed on the side of the signal transmission electrode that is close to the first ground transmission electrode; The third upper structure and the third lower structure are distributed on the side of the second ground transmission electrode close to the signal transmission electrode; The fourth upper layer structure and the fourth lower layer structure are distributed on the side of the signal transmission electrode close to the second ground transmission electrode.

4. A lithium niobate thin-film modulator based on upper and lower traveling-wave electrodes according to claim 1, characterized in that, The upper and lower layer electrodes are configured as periodic electrodes that vary periodically along the extension direction of the ridge waveguide structure.

5. A lithium niobate thin-film modulator based on upper and lower traveling-wave electrodes according to claim 1, characterized in that, The upper and lower electrodes include at least one middle layer structure with the same H-shape as the upper and lower layers when viewed from above, the middle layer structure being located between the upper and lower layers.

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