A thin film lithium niobate electro-optic modulator

Abstract

The application discloses a thin-film lithium niobate electro-optic modulator, and relates to the technical field of electro-optic modulators.The thin-film lithium niobate electro-optic modulator comprises a substrate layer for bonding a thin-film lithium niobate layer, lumped electrodes 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-symmetric to the first topological photonic crystal.The first topological photonic crystal and the second topological photonic crystal form a topological interface state with a symmetry plane on the thin-film lithium niobate layer.The lumped electrodes are distributed on both sides of the topological photonic crystal structure.By arranging the first topological photonic crystal structure and the second topological photonic crystal structure to be mirror-symmetric and arranging the lumped electrodes on both sides of the topological photonic crystal structure, the overall size of the thin-film lithium niobate electro-optic modulator can be reduced while the modulation speed is maintained.

Description

TECHNICAL FIELD

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

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

[0003] In the prior art, various structures and performance electro-optical modulators have been demonstrated using the Pockels effect of lithium niobate. Traditional 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 micro-ring modulators help to reduce the size of the device and usually have a specific path length or racetrack-shaped ring required for sufficient phase accumulation. However, the anisotropic properties of TFLN make it less easy to implement waveguide bends than other materials. Therefore, in order to be able to implement waveguide bends, new structures such as Fabry-Perot (FP) structures and photonic crystal (PC) structures have been developed, which can further reduce the size and enhance the bandwidth. On a silicon nitride-loaded thin-film lithium niobate platform, a high-speed electro-optical modulator with a one-dimensional lattice topological interface state has been demonstrated. However, in the above structures, there are limitations in terms of bandwidth and size.

[0004] Therefore, based on the deficiencies of the prior art, it is necessary to provide a new thin-film lithium niobate electro-optical modulator to be able to reduce the overall size of the thin-film lithium niobate electro-optical modulator while maintaining the modulation speed. SUMMARY

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

[0006] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0007] The present application provides a thin-film lithium niobate electro-optical modulator, comprising: a substrate layer bonded to a thin-film lithium niobate layer, and a lumped electrode and a topological photonic crystal structure disposed 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-symmetric 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;

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

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

[0011] Optionally, the photonic crystal has a period duty cycle of 0.5.

[0012] Optionally, 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.

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

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

[0015] Optionally, the lumped electrodes comprise a lumped signal electrode and a lumped ground electrode.

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

[0017] Optionally, the lumped electrodes comprise a titanium layer and a gold layer.

[0018] Optionally, the lumped electrodes are processed by a Lift-off process, and the titanium layer and the gold layer are generated in sequence by an electron beam evaporation technology and a stripping process.

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

[0020] The input grating is connected with the input optical waveguide; the input grating and the input optical waveguide are used for coupling and transmitting the modulated light into the thin film lithium niobate electro-optical modulator.

[0021] The output optical waveguide is connected with the input optical waveguide through the topological photonic crystal structure.

[0022] The output grating is connected with the output optical waveguide; the output grating and the output optical waveguide are used for outputting the modulated light after resonance of the topological photonic crystal.

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

[0024] The application provides a thin-film lithium niobate electro-optical modulator, comprising: a substrate layer bonding 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-symmetric 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, by arranging the first topological photonic crystal structure and the second topological photonic crystal structure mirror-symmetrically and arranging the lumped electrode on both sides of the topological photonic crystal structure, the overall size of the thin-film lithium niobate electro-optical modulator is reduced while the modulation speed is maintained. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort.

[0026] Figure 1 FIG. 1 is a perspective view of a thin-film lithium niobate electro-optical modulator according to an embodiment of the present application;

[0027] Figure 2 FIG. 2 is a top view of a topological photonic crystal structure according to an embodiment of the present application;

[0028] Figure 3 FIG. 3 is a side view of a photonic crystal according to an embodiment of the present application;

[0029] Figure 4 FIG. 4 is a band diagram of a photonic crystal according to an embodiment of the present application; wherein, Figure 4 part (a) of FIG. 4 is a band diagram of a first medium (A medium) of the photonic crystal, Figure 4 part (b) of FIG. 4 is a band diagram of a second medium (B medium) of the photonic crystal;

[0030] Figure 5 FIG. 5 is a transmission spectrum diagram of a topological photonic crystal according to an embodiment of the present application;

[0031] Figure 6 FIG. 6 is an electric field diagram of a lumped electrode according to another embodiment of the present application.

[0032] Reference signs:

[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 technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0035] In order to make the above-mentioned purposes, features and advantages of the present application more apparent and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0036] In one exemplary embodiment, as shown in Figure 1 A thin-film lithium niobate electro-optic modulator is provided, which includes a substrate layer bonding a thin-film lithium niobate layer, and a lumped electrode and a topological photonic crystal structure 3 disposed on the substrate layer.

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

[0038] The topological photonic crystal structure 3 not only has excellent beam confinement and light flow control ability as the photonic crystal has, can realize tight confinement of the optical field, thereby improving the efficiency of the thin-film lithium niobate electro-optic modulator, but also has more excellent optical robustness, can suppress backscattering and reduce optical loss, so that its optical properties are not changed by some small disturbances. These unique characteristics of the topological photonic crystal structure 3 make it have potential application value in electro-optic modulators.

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

[0040] In one specific embodiment, an electrical signal is applied to the lumped electrode, and a varying electric field passes through the modulation region of the thin-film lithium niobate electro-optic modulator, and the electric field distribution is as shown in Figure 6 Due to the excellent electro-optic properties of the thin-film lithium niobate, the varying electric field causes the refractive index of the thin-film lithium niobate electro-optic modulator to change, so that the resonance peak of the topological photonic crystal structure 3 shifts. 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 makes it immune to material defects and impurities, and realizes stable electro-optic modulation.

[0041] As shown in Figure 2As shown, the first topological photonic crystal and the second topological photonic crystal each comprise a plurality of photonic crystals with a period of 454 nm.

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

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

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

[0045] In one embodiment, the modulator is manufactured on a commercial X-cut lithium niobate on insulator (NanoLN) wafer. The wafer has a 400-nanometer-thick TFLN (thin film lithium niobate) layer, and 200 nanometers is etched by Ar+ ICP-RIE dry etching.

[0046] In one embodiment, the topological photonic crystal structure 3 is composed of a periodic photonic crystal, which is connected by 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 454 nm, and the duty cycle of the AB medium is 0.5. The waveguide width of the AB medium is 400 nm and 900 nm, respectively. At this time, the band distribution and transmission spectrum of the photonic crystal are as shown in Figure 4 and Figure 5 As shown, the modulated light is input to 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, and the transmission light can be observed to have a topological resonance peak through the output waveguide and the output grating 5 on the other end.

[0047] The topological photonic crystal structure 3 can easily achieve a bandwidth of more than 110 GHz for the thin film lithium niobate electro-optic modulator under the action of the peak enhancement effect while having a compact device size.

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

[0049] As shown, Figure 1 The lumped signal electrode 6 and the lumped ground electrode 7 are oppositely arranged on both sides of the topological photonic crystal structure 3.

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

[0051] Specifically, the lumped electrode comprises 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 titanium layer and the gold layer are generated by using the lift-off process, the electron beam evaporation technology and the stripping process in sequence.

[0053] In an exemplary embodiment, as shown in Figure 1 The thin film lithium niobate electro-optical modulator further comprises 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 with the input optical waveguide 2; the input grating 1 and the input optical waveguide 2 are used for coupling and transmitting the modulated light into the thin film lithium niobate electro-optical modulator.

[0055] The output optical waveguide 4 is connected with the input optical waveguide 2 through the topological photonic crystal structure 3.

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

[0057] The technical features of the above embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, however, as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present application.

[0058] The principles and implementation modes of the present application are described by using specific examples in the present application, and the above embodiment descriptions are only used to help understand the method and its core idea of the present application; meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range can be changed. In conclusion, the content of the present application should not be understood as a limitation.

Claims

1. A thin film lithium niobate electro-optic modulator, characterized in that: The thin-film lithium niobate electro-optic modulator comprises: a base layer bonded with a thin-film lithium niobate layer, and a lumped electrode and a topological photonic crystal structure arranged on the base layer; The topological photonic crystal structure 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; The lumped electrodes are distributed on both sides of the topological photonic crystal structure; The first topological photonic crystal and the second topological photonic crystal both include: a plurality of photonic crystals with a period of 454 nm; The periodic duty cycle of the photonic crystal is 0.5; 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.

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

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

4. The thin film lithium niobate electro-optic modulator according to claim 1, characterized in that: The lumped electrode includes: 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.

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

6. The thin film lithium niobate electro-optic modulator according to claim 5, characterized in that: The lumped electrode is processed by a lift-off process, and a titanium layer and a gold layer are sequentially generated by an electron beam evaporation technique and a lift-off process.

7. 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-optical 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 the topological photonic crystal resonates.

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