A thin film barium titanate electro-optic switch cell based on a composite electrode and an array thereof

Abstract

A thin film barium titanate electro-optical switch unit and array based on composite electrode. The optical switch unit comprises a first waveguide fiber coupling module, a second waveguide fiber coupling module, an optical beam splitting module, an electro-optical phase shift region, an optical beam combining module, a third waveguide fiber coupling module and a fourth waveguide fiber coupling module. The composite electrode of the electro-optical phase shift region is composed of a metal electrode and a transparent conductive layer. The transparent characteristic of the transparent conductive material makes the electrode closer to the waveguide, effectively enhances the coupling of the optical field and the electric field, and improves the extinction ratio. At the same time, the barium titanate thin film with high electro-optical coefficient is used as the waveguide material, which further optimizes the performance, so that the electro-optical switch unit has the excellent characteristics of low voltage driving, high extinction ratio, low insertion loss and small size.

Description

Technical Field

[0001] This invention relates to the fields of optical communication and optoelectronics, specifically to a thin-film barium titanate electro-optical switch unit and its array based on composite electrodes, which is particularly suitable for optical path switching and control in core optical network equipment such as optical add-drop multiplexers, optical cross-connect devices, and optical routers. Background Technology

[0002] Optical switches, as key components in optical add-drop multiplexers, optical cross-connect devices, and optical routers, directly impact the system's response capability, integration density, and energy consumption. However, single electro-optical switch units generally face the constraint of balancing modulation efficiency and optical loss: reducing electrode spacing to improve modulation efficiency often results in significant metal absorption losses, limiting further optimization of the switching extinction ratio and driving voltage. Furthermore, the intrinsic electro-optic coefficients of traditional electro-optic materials such as lithium niobate are limited, making it difficult to achieve efficient optical field modulation under low voltage and short modulation lengths, thus restricting the miniaturization of switch units and the expansion of array size.

[0003] Patent CN120447240A discloses a thin-film lithium niobate electro-optic modulator with stepped electrodes, which attempts to alleviate the contradiction between efficiency and loss by optimizing the electrode structure. However, due to the limitations of the material system and electrode design, it is still difficult to break through to a higher level of performance.

[0004] Patent CN120559922A discloses an 8×8 lithium niobate array optical switch, attempting to construct a low-loss, highly integrated array optical switch by optimizing the waveguide structure and electrode drive. However, this patent is still limited to traditional lithium niobate, and the modulation efficiency of the electro-optic switch unit is limited, requiring a relatively long modulation length, which makes it difficult to meet the small size requirements of large-scale optical switch arrays. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a thin-film barium titanate electro-optic switch unit and its array based on composite electrodes. By employing a low-loss composite electrode that can be closely attached to the optical waveguide and a thin-film barium titanate with a high electro-optic coefficient, the modulation efficiency of the electro-optic switch unit is significantly improved, the modulation length is shortened, the extinction ratio is increased, and a highly integrated electro-optic switch array can be constructed.

[0006] This invention is achieved through the following technical solutions:

[0007] A thin-film barium titanate electro-optic switch unit based on a composite electrode, characterized in that it includes:

[0008] Substrate layer;

[0009] The buried oxide layer located above the substrate layer;

[0010] A waveguide layer located above the buried oxide layer, the waveguide layer being composed of a barium titanate thin film and having a first waveguide and a second waveguide formed thereon;

[0011] A buffer layer covering the barium titanate optical waveguide layer;

[0012] A composite electrode located above the buffer layer, the composite electrode being used to apply a modulation electric field to the first waveguide and / or the second waveguide;

[0013] The composite electrode has a stepped structure, including a metal main electrode and a transparent conductive secondary electrode. The transparent conductive secondary electrode is located between the metal main electrode and the buffer layer, and the lower surface of the transparent conductive secondary electrode is in direct contact with the upper surface of the buffer layer. The width of the transparent conductive secondary electrode in the transverse cross section perpendicular to the light transmission direction is smaller than the width of the metal main electrode in the same cross section, so that the transparent conductive secondary electrode forms a stepped structure protruding towards the first waveguide and / or the second waveguide on the buffer layer.

[0014] Furthermore, the composite electrode also includes a first ground electrode, a signal electrode, and a second ground electrode arranged in parallel along the lateral direction, forming a GSG coplanar waveguide arrangement structure of ground electrode-signal electrode-ground electrode; the first waveguide is located in the lateral direction between the first ground electrode and the signal electrode, and the second waveguide is located in the lateral direction between the signal electrode and the second ground electrode to form a push-pull modulation structure.

[0015] Furthermore, the thickness of the transparent conductive secondary electrode is 50 nm to 200 nm, and the thickness of the metal primary electrode is 0.8 μm to 2 μm.

[0016] Furthermore, the material of the metal main electrode is Au, Al, or Cu; the material of the transparent conductive secondary electrode is a transparent conductive oxide, metal nanowires / mesh, transparent conductive polymer, carbon nanotubes, or graphene.

[0017] Furthermore, the transparent conductive oxide is ITO, AZO, or GAO.

[0018] Furthermore, the first waveguide and the second waveguide are direct-etched waveguides, loaded hybrid waveguides, substitution waveguides, or hybrid silicon integrated waveguides.

[0019] Furthermore, it also includes:

[0020] The output end of the optical beam splitter is optically connected to the input end of the first waveguide and the input end of the second waveguide, respectively.

[0021] The input end of the optical beam combining module is optically connected to the output end of the first waveguide and the output end of the second waveguide, respectively.

[0022] The output end of the first waveguide fiber coupling module is optically connected to the first input end of the optical beam splitter module.

[0023] The output end of the second waveguide fiber coupling module is optically connected to the second input end of the optical beam splitter module.

[0024] The third waveguide fiber coupling module has its input end optically connected to the first output end of the optical beam combining module;

[0025] The fourth waveguide fiber coupling module has its input end optically connected to the second output end of the optical beam combining module.

[0026] Furthermore, each waveguide fiber coupling module is used to achieve efficient optical mode coupling between the fiber and the waveguide, aiming to improve the optical mode field conversion efficiency between the fiber and the waveguide, and realize optical signal input / output (I / O) between the fiber and the on-chip waveguide, which can be end face coupling, grating coupling or evanescent coupling.

[0027] Furthermore, the optical beam splitter and optical beam combiner are directional couplers, Y-type beam splitters, and multimode interference couplers (MMIs).

[0028] Furthermore, an upper cladding layer is provided above the composite electrode.

[0029] Secondly, the present invention also provides a thin-film barium titanate electro-optic switch array based on composite electrodes, characterized in that: it is formed by interconnecting multiple thin-film barium titanate electro-optic switch units based on composite electrodes as described above according to a preset network topology, thereby forming an N×M optical switch array with N optical input ports and M optical output ports.

[0030] Furthermore, the network topology is Benes or a modified Benes, PILOSS, Butterfly, DLN or a modified DLN, Crossbar.

[0031] Compared with existing technologies, the advantages of this invention are as follows: The electro-optic unit, by employing composite electrodes, especially a transparent conductive layer, can be close to the optical waveguide with low absorption loss, thereby reducing the electrode spacing and significantly enhancing the overlap between the optical and electric fields. By introducing a barium titanate thin-film waveguide with an ultra-high electro-optic coefficient, the same phase modulation can be achieved at a shorter modulation distance, ultimately significantly reducing the driving voltage and increasing the extinction ratio. This results in a small-size, highly integrated optical switch array. Attached Figure Description

[0032] Figure 1 This is a topological block diagram of a thin-film barium titanate electro-optic switch unit based on a composite electrode according to Embodiment 1 of the present invention.

[0033] Figure 2This is a cross-sectional view of the thin-film barium titanate electro-optic switch unit based on composite electrodes according to Embodiment 1 of the present invention, along the light propagation direction.

[0034] Figure 3 This is a comparison diagram of the half-wave voltage-length product Vπ*L between the thin-film barium titanate electro-optic switch unit based on composite electrodes and the barium titanate electro-optic switch unit based on traditional gold electrodes of the present invention.

[0035] Figure 4 This is a comparison chart showing the loss of the thin-film barium titanate electro-optic switch unit based on composite electrodes of the present invention and the traditional electro-optic switch unit based on composite electrodes.

[0036] Figure 5 This is a schematic diagram of the architecture of a thin-film barium titanate electro-optic switch array based on composite electrodes according to Embodiment 2 of the present invention.

[0037] In the figure: 1-First waveguide fiber coupling module, 2-Second waveguide fiber coupling module, 3-Optical beam splitter module, 4-First waveguide, 5-Second waveguide, 6-First ground electrode, 7-Signal electrode, 8-Second ground electrode, 9-Optical beam combining module, 10-Third waveguide fiber coupling module, 11-Fourth waveguide fiber coupling module, 12-Substrate layer, 13-Buried oxide layer, 14-Waveguide layer, 15-Buffer layer, 16-Composite electrode, 161-Main electrode, 162-Secondary electrode, 17-Upper cladding layer. Detailed Implementation

[0038] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings. This embodiment is implemented under the premise of the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0039] Example 1:

[0040] Please see Figure 1 , Figure 1This invention provides a thin-film barium titanate electro-optic switch unit based on a composite electrode, as shown in the figure. The unit employs a Mach-Zehnder interferometer structure and includes: a first waveguide fiber coupling module 1, a second waveguide fiber coupling module 2, an optical beam splitter module 3, an electro-optic phase-shifting region, an optical beam combiner module 9, a third waveguide fiber coupling module 10, and a fourth waveguide fiber coupling module 11. The electro-optic phase-shifting region serves as the modulation region, integrating a first waveguide 4 and a second waveguide 5 arranged in parallel, as well as a composite electrode structure for applying a modulation electric field. Specifically, the composite electrode structure includes a first ground electrode 6, a signal electrode 7, and a second ground electrode 8, arranged in a GSG coplanar waveguide configuration of ground electrode-signal electrode-ground electrode. The first waveguide 4 is located between the first ground electrode 6 and the signal electrode 7, and the second waveguide 5 is located between the signal electrode 7 and the second ground electrode 8, achieving push-pull modulation. The output port of the first waveguide fiber coupling module 1 is connected to the input port of the optical beam splitter module 3, and the output port of the optical beam splitter module 3 is connected to the input ports of the first waveguide 4 and the second waveguide 5. The output ports of the first waveguide 4 and the second waveguide 5 are connected to the input ports of the optical beam combining module 9, and the output ports of the optical beam combining module 9 are connected to the input ports of the third waveguide fiber coupling module 10 and the fourth waveguide fiber coupling module 11.

[0041] The workflow of optical signals is as follows:

[0042] The input light enters the optical beam splitter module 3 (in this embodiment, a 3dB multimode interference coupler, MMI) via the first waveguide fiber coupling module 1 or the second waveguide fiber coupling module 2, and is split into two paths, entering the first waveguide 4 and the second waveguide 5 respectively. The two waveguides extend parallel to each other, with a first ground electrode 6, a signal electrode 7, and a second ground electrode 8 arranged sequentially on both sides. When the signal electrode 7 receives a modulation signal, it generates electric fields in opposite directions in the regions of the first waveguide 4 and the second waveguide 5. Utilizing the linear electro-optic effect of barium titanate, the refractive index of the two waveguides is changed, thereby introducing a phase difference between the two optical signals. These two beams then interfere in the optical beam combiner module 9 (also using a 3dB MMI) and are output by the third waveguide fiber coupling module 10 and the fourth waveguide fiber coupling module 11. By controlling the presence or magnitude of the modulation voltage, the interference result can be precisely controlled to be constructive or destructive, thus achieving the switching of the optical signal between the "on" and "off" states at the output end.

[0043] Please see Figure 2 , Figure 2The figure shows a cross-sectional view of an embodiment of the thin-film barium titanate electro-optic switch unit based on a composite electrode according to the present invention. From bottom to top, it includes: a substrate layer 12, a buried oxide layer 13, a waveguide layer 14, a buffer layer 15, a composite electrode 16, and an upper cladding layer 17. The composite electrode 16 consists of a main electrode 161 and a secondary electrode 162. The entire composite electrode 16 has a stepped structure, with a high-conductivity conventional metal electrode serving as the thick main electrode 161; while the transparent conductive layer serves as the thin secondary electrode 162, acting as a small step close to the optical waveguide to shorten the electrode spacing, enhance the overlap between the optical and electric fields, improve modulation efficiency, and optimize the extinction ratio of the switch unit.

[0044] In this embodiment, the modulation arm is a barium titanate waveguide. The waveguide structure can be a direct-etched waveguide, a substitutional waveguide, or a loaded waveguide, etc. This example uses a ridge waveguide as an example. The structural parameters such as waveguide thickness s, etching depth h, and ridge waveguide width w should be reasonably configured to limit optical transmission leakage in the operating wavelength band. The main electrode thickness t1 should be reasonably configured, as should the main electrode spacing d1, secondary electrode spacing d2, and buffer layer thickness h. buffer The structural parameters can be determined by considering the loss and extinction ratio requirements of the electro-optical switch. Furthermore, these structural parameters can be flexibly designed and adjusted according to different process conditions; this embodiment does not impose any limitations on this.

[0045] In this invention, the main electrode material is primarily a high-conductivity metal, including Au, Al, and Cu electrodes, with a gold electrode as an example. The secondary electrode is primarily a transparent conductive material, including transparent conductive oxides ITO, AZO, and GAO, metal nanowires / mesh, transparent conductive polymers, carbon nanotubes, and graphene, with an ITO electrode as an example. The composite electrode utilizes the transparency of the secondary electrode to reduce the impact of waveguide-derived electromagnetic waves on the free electrons of the electrode material, thus reducing losses. Therefore, it can be positioned closer to the waveguide than traditional electrodes, effectively reducing the driving voltage and improving the extinction ratio while keeping losses at a reasonable level.

[0046] This example uses barium titanate as the waveguide material. However, other waveguides can also be integrated using a mixture of barium titanate and lithium niobate, or a mixture of barium titanate and silicon nitride. The key is to utilize the high electro-optic coefficient of barium titanate while also considering process compatibility.

[0047] Please see Figure 3-4 , Figure 3 The image shows a comparison of the Vπ*L values ​​of the thin-film barium titanate electro-optic switch unit based on composite electrodes and the barium titanate electro-optic switch unit based on traditional gold electrodes according to the present invention. Figure 4This is a loss comparison diagram of the thin-film barium titanate electro-optic switch unit based on composite electrodes of this invention and the traditional lithium niobate electro-optic switch unit based on composite electrodes. All three switch units are 2×2MHz type electro-optic switches. In this invention, as the experimental group, the main electrode of the composite electrode is made of gold, the secondary electrode is made of ITO, and the waveguide is made of thin-film barium titanate. Figure 3 The control group used a conventional gold electrode, and the waveguide used the same thin-film barium titanate material as the present invention. Figure 4 The control group used the same composite electrode as the present invention, and the waveguide used was a traditional thin-film lithium niobate material. Simulation results show that the electro-optic switch unit of the present invention effectively utilizes the advantages of short electrode spacing and high electro-optic coefficient, achieving a half-wave voltage-length product as low as 0.07 V·cm, which is far superior to traditional electro-optic switches in terms of driving voltage and loss. This superior modulation efficiency allows the optical switch unit to have a low driving voltage while requiring only one-tenth the modulation size of the original traditional electro-optic switch unit, and also possesses the characteristics of low insertion loss, small size, and high extinction ratio, demonstrating the superiority of the electro-optic switch unit of the present invention.

[0048] Example 2:

[0049] Based on the aforementioned Embodiment 1, this embodiment provides a thin-film barium titanate electro-optic switch array based on composite electrodes. This array consists of multiple 2×2 electro-optic switch units as basic components, interconnected according to a specific network topology to achieve large-scale optical path switching functionality.

[0050] Please see Figure 5 , Figure 5 This is a schematic diagram of the architecture of a thin-film barium titanate electro-optic switch array based on composite electrodes, as shown in Embodiment 2 of the present invention. The present invention supports N×M scale optical switch arrays; this embodiment uses a Benes network topology to illustrate an 8×8 array optical switch. In the figure, S... NM This invention represents a thin-film barium titanate electro-optic switch unit based on composite electrodes. This array optical switch based on composite electrodes enables arbitrary interconnection from eight input ports to eight output ports. The Benes network consists of multiple levels of 2×2 optical switch units, exhibiting strictly non-blocking characteristics, meaning that the connection between any input / output pair is not affected by other established connections. Each electro-optic switch can be connected to an external optical fiber via a waveguide fiber coupling module. The electrodes of the electro-optic switch unit can be linked via pins, and the optical coupling path from the input port to the output port can be controlled by dynamically adjusting the electrode voltage. This 8×8 array electro-optic switch, based on the traditional Benes network, combines the high-efficiency modulation and low-loss advantages of composite electrodes. The array has a size approximately one-tenth that of the original traditional electro-optic switch unit, possessing the potential for large-scale integration and providing a key optical routing solution for next-generation optical communication and optical computing systems.

[0051] Besides gold, low-resistance metals such as aluminum and copper can also be used for the main metal electrode. Transparent conductive secondary electrodes, besides ITO, can also be made of AZO, GAO, graphene, or metal nanowire meshes. The topology of the large-scale array is not limited to Benes networks; depending on application requirements, structures such as PILOSS, Butterfly, DLN, or Crossbar can also be selected. Substrate materials, besides silicon, can also be made of quartz, magnesium oxide, etc.; cladding and buffer layer materials, besides silicon dioxide, can also be made of materials with different dielectric constants, such as magnesium fluoride, aluminum oxide, or silicon nitride, to further optimize the high-frequency response characteristics of the electrodes. These variations and alternatives should all be considered to fall within the scope of protection of this invention.

[0052] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of this patent. Any equivalent changes and simple modifications made by those skilled in the art based on the claims of this invention should still fall within the scope of this patent.

Claims

1. A thin-film barium titanate electro-optic switch unit based on a composite electrode, characterized in that, include: Substrate (12); Buried oxide layer (13) located above the substrate layer (12); A waveguide layer (14) is located above the buried oxide layer (13). The waveguide layer (14) is made of a barium titanate film and has a first waveguide (4) and a second waveguide (5). A buffer layer (15) covering the barium titanate waveguide layer (14); A composite electrode (16) is located above the buffer layer (15), the composite electrode (16) being used to apply a modulation electric field to the first waveguide (4) and / or the second waveguide (5); The composite electrode (16) has a stepped structure, including a metal main electrode and a transparent conductive secondary electrode. The transparent conductive secondary electrode is located between the metal main electrode and the buffer layer (15), and the lower surface of the transparent conductive secondary electrode is in direct contact with the upper surface of the buffer layer (15). The width of the transparent conductive secondary electrode in the transverse cross section perpendicular to the light transmission direction is smaller than the width of the metal main electrode in the same cross section, so that the transparent conductive secondary electrode forms a stepped structure protruding towards the first waveguide (4) and / or the second waveguide (5) on the buffer layer (15).

2. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to claim 1, characterized in that, The composite electrode (16) also includes a first ground electrode (6), a signal electrode (7), and a second ground electrode (8) arranged in parallel along the lateral direction to form a GSG coplanar waveguide arrangement structure of ground electrode-signal electrode-ground electrode; the first waveguide (4) is located between the first ground electrode (6) and the signal electrode (7) in the lateral direction, and the second waveguide (5) is located between the signal electrode (7) and the second ground electrode (8) in the lateral direction to form a push-pull modulation structure.

3. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to claim 1, characterized in that, The thickness of the transparent conductive secondary electrode (162) is 50 nm to 200 nm, and the thickness of the metal main electrode (161) is 0.8 μm to 2 μm.

4. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to claim 1, characterized in that, The material of the metal main electrode is Au, Al or Cu; the material of the transparent conductive secondary electrode is transparent conductive oxide, metal nanowire / mesh, transparent conductive polymer, carbon nanotube or graphene.

5. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to claim 4, characterized in that, The transparent conductive oxide is ITO, AZO, or GAO.

6. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to claim 1, characterized in that, The first waveguide and the second waveguide are direct-etched waveguides, loaded hybrid waveguides, substitution waveguides, or hybrid silicon integrated waveguides.

7. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to any one of claims 1-6, characterized in that, Also includes: The output end of the optical beam splitter module (3) is optically connected to the input end of the first waveguide (4) and the input end of the second waveguide (5), respectively. The input end of the optical beam combining module (9) is optically connected to the output end of the first waveguide (4) and the output end of the second waveguide (5), respectively. The output end of the first waveguide fiber coupling module (1) is optically connected to the first input end of the optical beam splitter module (3); The output end of the second waveguide fiber coupling module (2) is optically connected to the second input end of the optical beam splitter module (3); The input end of the third waveguide fiber coupling module (10) is optically connected to the first output end of the optical beam combining module (9); The fourth waveguide fiber coupling module (11) has its input end optically connected to the second output end of the optical beam combining module (9).

8. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to claim 7, characterized in that, Each waveguide fiber coupling module is used to achieve efficient optical mode coupling between the fiber and the waveguide, aiming to improve the optical mode field conversion efficiency between the fiber and the waveguide, and realize optical signal input / output between the fiber and the on-chip waveguide, which can be end face coupling, grating coupling or evanescent coupling.

9. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to claim 7, characterized in that, The optical beam splitter module (3) and the optical beam combiner module (9) are directional couplers, Y-type beam splitters, or multimode interference couplers (MMI).

10. The thin-film barium titanate electro-optic switch unit based on composite electrodes according to claim 1, characterized in that, An upper cladding layer (17) is also provided above the composite electrode (16).

11. A thin-film barium titanate electro-optic switch array based on composite electrodes, characterized in that: The optical switch array is formed by interconnecting multiple thin-film barium titanate electro-optical switch units based on composite electrodes as described in any one of claims 1-10 according to a preset network topology, thereby forming an N×M optical switch array with N optical input ports and M optical output ports.

12. The thin-film barium titanate electro-optic switch array based on composite electrodes as described in claim 11, characterized in that: The network topology is Benes or a modified Benes, PILOSS, Butterfly, DLN or a modified DLN, Crossbar.

Images