Thin-film lithium niobate electro-optical modulator

Abstract

The invention discloses a thin-film lithium niobate electro-optical modulator, and relates to the technical field of electro-optical modulators, and the thin-film lithium niobate electro-optical modulator comprises a substrate layer bonded with a thin-film lithium niobate layer, and a lumped electrode and a topological photonic crystal structure which are arranged on the substrate layer. The topological photonic crystal structure comprises a first topological photonic crystal and a second topological photonic crystal which is in mirror symmetry with the first topological photonic crystal; the first topological photonic crystal and the second topological photonic crystal form a topological interface state on the thin-film lithium niobate layer by a symmetry plane; the lumped electrodes are distributed on the two sides of the topological photonic crystal structure. According to the thin-film lithium niobate electro-optical modulator, the first topological photonic crystal structure and the second topological photonic crystal structure are in mirror symmetry, and the lumped electrodes are arranged on the two sides of the topological photonic crystal structures, so that the overall size of the thin-film lithium niobate electro-optical modulator can be reduced while the modulation speed is kept.

Description

Technical Field

[0001] The present application relates to the technical field of electro-optic modulators, and in particular to a thin-film lithium niobate electro-optic modulator. Background Art

[0002] With the development of thin-film lithium niobate (TFLN) photonics, TFLN electro-optic modulators have become an important optoelectronic interconnect device and are widely used in current optical communication systems.

[0003] In the prior art, various electro-optic modulators with various structures and performances have been demonstrated using the Pockels effect of lithium niobate. Conventional Mach-Zehnder interferometer (MZI) modulators based on thin-film lithium niobate have been able to operate at voltages compatible with CMOS. In order to reduce the size of the device, technicians have proposed many structures, such as folded MZI waveguides, slow light waveguides, and various resonant cavities. Among them, thin-film lithium niobate microring modulators help reduce the size of the device and usually have a specific path length or racetrack ring required for sufficient phase accumulation. However, the anisotropic properties of TFLN make its waveguide bending not as easy to achieve as other materials. Therefore, in order to achieve waveguide bending, new structures such as Fabry-Perot (FP) structure and photonic crystal (PC) structure have been developed, which can further reduce the size and enhance the bandwidth. On a thin-film lithium niobate platform loaded with silicon nitride, a high-speed electro-optic modulator with a one-dimensional lattice topological interface state can be developed. However, in the above structure, there are limitations in bandwidth and size.

[0004] Therefore, based on the deficiencies of the prior art, there is an urgent need to provide a new thin-film lithium niobate electro-optic modulator that can reduce the overall size of the thin-film lithium niobate electro-optic modulator while maintaining the modulation speed. Summary of the invention

[0005] The purpose of the present application is to provide a thin film lithium niobate electro-optic modulator, so as to reduce the overall size of the thin film lithium niobate electro-optic modulator while maintaining the modulation speed.

[0006] To achieve the above objectives, this application provides the following solutions:

[0007] The present application provides a thin-film lithium niobate electro-optic modulator, comprising: a substrate layer bonded with a thin-film lithium niobate layer, and a lumped electrode and a topological photonic crystal structure arranged on the substrate layer;

[0008] The topological photonic crystal structure comprises: a first topological photonic crystal and a second topological photonic crystal which is mirror-symmetrical to the first topological photonic crystal; the first topological photonic crystal and the second topological photonic crystal form a topological interface state on a thin-film lithium niobate layer with a symmetric plane;

[0009] The lumped electrodes are distributed on both sides of the topological photonic crystal structure.

[0010] Optionally, the first topological photonic crystal and the second topological photonic crystal both include: a plurality of photonic crystals with a period of 454 nm.

[0011] Optionally, the periodic duty cycle of the photonic crystal is 0.5.

[0012] Optionally, the photonic crystal includes: a first medium with a waveguide width of 900 nm and a second medium with a waveguide width of 400 nm.

[0013] Optionally, the thin film lithium niobate layer has a thickness of 400 nm and is etched to 200 nm by Ar+ ICP-RIE dry etching.

[0014] Optionally, the base layer is silicon dioxide.

[0015] Optionally, the lumped electrode includes: a lumped signal electrode and a lumped ground electrode;

[0016] The lumped signal electrode and the lumped ground electrode are arranged oppositely on two sides of the topological photonic crystal structure.

[0017] Optionally, the lumped electrode includes: a titanium layer and a gold layer.

[0018] Optionally, the lumped electrode is processed by a lift-off process, and an electron beam evaporation technique and a lift-off process are sequentially used to generate a titanium layer and a gold layer.

[0019] Optionally, the thin-film lithium niobate electro-optic modulator further comprises: an input grating, an input optical waveguide, an output optical waveguide and an output grating;

[0020] The input grating is connected to the input optical waveguide; the input grating and the input optical waveguide are used to couple the modulated light and transmit it to the thin-film lithium niobate electro-optic modulator;

[0021] The output optical waveguide is connected to the input optical waveguide via a topological photonic crystal structure;

[0022] The output grating is connected to the output optical waveguide; the output grating and the output optical waveguide are used to output modulated light after resonance by the topological photonic crystal.

[0023] According to the specific embodiments provided in this application, this application has the following technical effects:

[0024] The present application provides a thin-film lithium niobate electro-optic modulator, comprising: a substrate layer bonded to a thin-film lithium niobate layer, and a lumped electrode and a topological photonic crystal structure arranged on the substrate layer; the topological photonic crystal structure comprises: a first topological photonic crystal and a second topological photonic crystal that is mirror-symmetrical to the first topological photonic crystal; the first topological photonic crystal and the second topological photonic crystal form a topological interface state on the thin-film lithium niobate layer with a symmetry plane; the lumped electrode is distributed on both sides of the topological photonic crystal structure, and by arranging the first topological photonic crystal structure and the second topological photonic crystal structure to be mirror-symmetrical and arranging the lumped electrode on both sides of the topological photonic crystal structure, the overall size of the thin-film lithium niobate electro-optic modulator is reduced while maintaining the modulation speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A three-dimensional diagram of a thin-film lithium niobate electro-optic modulator in an embodiment of the present application;

[0027] Figure 2 A top view of a topological photonic crystal structure provided in one embodiment of the present application;

[0028] Figure 3 A side view of a photonic crystal provided in one embodiment of the present application;

[0029] Figure 4 is a schematic diagram of the energy band distribution of the photonic crystal; Figure 4 Part (a) is the energy band diagram of the first medium (medium A) of the photonic crystal. Figure 4 Part (b) is the energy band diagram of the second medium (medium B) of the photonic crystal;

[0030] Figure 5 A schematic diagram of a topological photonic crystal transmission spectrum provided in an embodiment of the present application;

[0031] Figure 6 A lumped electrode electric field diagram provided for another embodiment of the present application.

[0032] Reference numerals:

[0033] 1-input grating, 2-input optical waveguide, 3-topological photonic crystal structure, 4-output optical waveguide, 5-output grating, 6-lumped signal electrode, 7-lumped ground electrode. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0036] In an exemplary embodiment, Figure 1 As shown, a thin-film lithium niobate electro-optic modulator is provided, which includes: a substrate layer bonded with a thin-film lithium niobate layer, and a lumped electrode and a topological photonic crystal structure 3 arranged on the substrate layer.

[0037] The topological photonic crystal structure 3 includes: a first topological photonic crystal and a second topological photonic crystal that is mirror-symmetrical to the first topological photonic crystal; the first topological photonic crystal and the second topological photonic crystal form a topological interface state on a thin-film lithium niobate layer with a symmetric plane.

[0038] Among them, the topological photonic crystal structure 3 not only has the excellent light confinement and light flow control capabilities of photonic crystals, and can achieve tight confinement of the light field, thereby improving the modulation efficiency of the thin-film lithium niobate electro-optical modulator, but also has better optical robustness, can suppress backscattering, reduce light loss, and make its optical properties not changed by some small disturbances. These unique characteristics of the topological photonic crystal structure 3 make it have potential application value in electro-optical modulators.

[0039] The lumped electrodes are distributed on both sides of the topological photonic crystal structure 3 .

[0040] In a specific embodiment, an electric signal is applied to the lumped electrode, and the changing electric field passes through the modulation region of the thin film lithium niobate electro-optic modulator, and the electric field distribution is as follows: Figure 6 As shown. Due to the excellent electro-optical properties of thin-film lithium niobate, the changing electric field causes the refractive index of the thin-film lithium niobate electro-optical modulator to change, causing the resonance peak of the topological photonic crystal structure 3 to shift. When the wavelength of the modulated light is constant, the optical power changes with the change of the electrical signal, thereby converting the electrical signal into an optical signal. The topological protection mechanism of the topological photonic crystal structure 3 enables it to be free from the influence of material defects and impurities, achieving stable electro-optical modulation.

[0041] like Figure 2As shown, the first topological photonic crystal and the second topological photonic crystal both include: a plurality of photonic crystals with a period of 454 nm.

[0042] Specifically, the periodic duty cycle of the photonic crystal is 0.5.

[0043] like Figure 3 As shown, the photonic crystal includes: a first medium (medium A) with a waveguide width of 900 nm and a second medium (medium B) with a waveguide width of 400 nm.

[0044] Specifically, the thickness of the thin film lithium niobate layer is 400 nm, and is etched by 200 nm through Ar+ ICP-RIE dry etching.

[0045] In a specific embodiment, the modulator is fabricated on a commercial X-cut lithium niobate on insulator (NanoLN) wafer having a 400 nm thick TFLN (Thin Film Lithium Niobate) layer etched 200 nm by Ar+ ICP-RIE dry etching.

[0046] In a specific embodiment, the topological photonic crystal structure 3 is composed of a photonic crystal with a periodic structure, which is formed by connecting the photonic crystal BA on the left side of the symmetry plane and the photonic crystal AB on the right side. The period of the photonic crystal is 454nm, and the period duty ratio of the AB medium is 0.5. The waveguide widths of the AB medium are 400nm and 900nm respectively. At this time, the energy band distribution and transmission spectrum of the photonic crystal are as follows: Figure 4 and Figure 5 As shown, the modulated light is input into the modulator through the input grating 1 and the input waveguide, and then resonates between the two photonic crystals, generating a topological boundary state at the connection point. The transmitted light passes through the output waveguide and the output grating 5 at the other end, and a topological resonance peak can be observed.

[0047] With the topological photonic crystal structure 3 having a compact device size, under the action of the peak enhancement effect, the bandwidth of the thin-film lithium niobate electro-optic modulator can be easily achieved to over 110 GHz.

[0048] Specifically, the base layer is silicon dioxide.

[0049] like Figure 1 As shown, the lumped electrode includes: a lumped signal electrode 6 and a lumped ground electrode 7;

[0050] The lumped signal electrode 6 and the lumped ground electrode 7 are arranged oppositely on two sides of the topological photonic crystal structure 3 .

[0051] Specifically, the lumped electrode includes: a titanium layer and a gold layer. In a specific embodiment, the lumped electrode is composed of two layers: one layer is 20 nanometers thick titanium (Ti), and the other layer is 400 nanometers thick gold (Au).

[0052] The lumped electrode is processed by a lift-off process, and the titanium layer and the gold layer are generated by electron beam evaporation technology and a lift-off process in sequence.

[0053] In an exemplary embodiment, Figure 1 As shown, the thin film lithium niobate electro-optic modulator further includes: an input grating 1 , an input optical waveguide 2 , an output optical waveguide 4 and an output grating 5 .

[0054] The input grating 1 is connected to the input optical waveguide 2; the input grating 1 and the input optical waveguide 2 are used to couple the modulated light and transmit it to the thin-film lithium niobate electro-optic modulator.

[0055] The output optical waveguide 4 is connected to the input optical waveguide 2 via a topological photonic crystal structure 3 .

[0056] The output grating 5 is connected to the output optical waveguide 4; the output grating 5 and the output optical waveguide 4 are used to output modulated light after resonance by the topological photonic crystal.

[0057] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0058] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A thin film lithium niobate electro-optic modulator, characterized in that: The thin-film lithium niobate electro-optic modulator comprises: a substrate layer bonded with a thin-film lithium niobate layer, and a lumped electrode and a topological photonic crystal structure arranged on the substrate layer; The topological photonic crystal structure comprises: a first topological photonic crystal and a second topological photonic crystal which is mirror-symmetrical to the first topological photonic crystal; the first topological photonic crystal and the second topological photonic crystal form a topological interface state on a thin-film lithium niobate layer with a symmetric plane; The lumped electrodes are distributed on both sides of the topological photonic crystal structure.

2. A thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The first topological photonic crystal and the second topological photonic crystal both include: a plurality of photonic crystals with a period of 454 nm.

3. A thin film lithium niobate electro-optic modulator according to claim 2, characterized in that: The periodic duty cycle of the photonic crystal is 0.

5.

4. A thin film lithium niobate electro-optic modulator according to claim 2, characterized in that: The photonic crystal comprises: a first medium with a waveguide width of 900 nm and a second medium with a waveguide width of 400 nm.

5. The thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The thickness of the thin film lithium niobate layer is 400 nm, and is etched by 200 nm by Ar+ ICP-RIE dry etching.

6. The thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The base layer is silicon dioxide.

7. The thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The lumped electrode comprises: a lumped signal electrode and a lumped ground electrode; The lumped signal electrode and the lumped ground electrode are arranged oppositely on two sides of the topological photonic crystal structure.

8. The thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The lumped electrode comprises a titanium layer and a gold layer.

9. The thin film lithium niobate electro-optic modulator according to claim 8, characterized in that: The lumped electrode is processed by a lift-off process, and an electron beam evaporation technique and a lift-off process are sequentially used to generate a titanium layer and a gold layer.

10. The thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The thin-film lithium niobate electro-optic modulator further comprises: an input grating, an input optical waveguide, an output optical waveguide and an output grating; The input grating is connected to the input optical waveguide; the input grating and the input optical waveguide are used to couple the modulated light and transmit it to the thin-film lithium niobate electro-optic modulator; The output optical waveguide is connected to the input optical waveguide via a topological photonic crystal structure; The output grating is connected to the output optical waveguide; the output grating and the output optical waveguide are used to output modulated light after resonance by the topological photonic crystal.

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