Fast exchange ferroelectric domain switch for visible light communication and array thereof

Abstract

The invention discloses a fast switching ferroelectric domain switch for visible light communication and an array thereof, and belongs to the technical field of electro-optical switches. The switch is a 2 * 2 MZI switch unit and is composed of a silicon-based substrate, a lower cladding, a flat plate layer, a waveguide core layer and an upper cladding in sequence. The waveguide core layer is composed of two input straight waveguides, an input 2 * 2 MMI, two input S bent waveguides, two modulation straight waveguides, two output S bent waveguides, an output 2 * 2 MMI and two output straight waveguides. The outer sides and the inner sides of the two modulation straight waveguides are respectively provided with two grounding metal electrodes and one signal metal electrode. The switch array is composed of six 2 * 2 MZI switch units and two crossed waveguide units, and each crossed waveguide unit is of a central symmetry structure and is composed of a first transmission waveguide and a second transmission waveguide which are perpendicular to each other; the structure disclosed by the invention has the advantages of high integration level, low crosstalk, low insertion loss and the like, and is suitable for a large-scale photon integrated circuit.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electro-optical switches, and particularly relates to a ferroelectric domain switch for fast switching of visible light communication and an array thereof. BACKGROUND

[0002] Optical communication technology plays an important role in frontier fields such as quantum information, high-speed optical interconnection and programmable photon chips. In particular, in quantum computing systems, the visible light band has become the core band for manipulating ion traps, color centers and other quantum bits, and the accuracy, efficiency and fidelity of optical routing directly determine the upper limit of the performance of the entire system. Therefore, developing an optical switch array capable of realizing high-speed, low-loss and reconfigurable manipulation in the visible light band has become a core challenge to promote the development of related technologies.

[0003] Current traditional optical switch technologies are difficult to meet the above comprehensive performance requirements. Although the switch technology based on thermal light effect is relatively mature, its millisecond-level response speed and high power consumption cannot adapt to high-speed application scenarios. Although the electro-optical switch based on silicon material has a relatively fast response speed, it will introduce too high loss in the visible light band, resulting in serious attenuation of the optical signal, which greatly limits its application feasibility in high-fidelity systems such as quantum communication; and the optical switch based on micro-electro-mechanical system has inherent challenges in long-term reliability and large-scale integration.

[0004] In recent years, ferroelectric material systems represented by lithium niobate and lead zirconium titanate have attracted widespread attention due to their excellent linear electro-optic effect. The material has high transparency and fast electro-optic response characteristics in the visible light band, which theoretically provides an ideal platform for constructing low-loss and high-speed optical switches. Although the ferroelectric material itself has significant advantages, how to integrate it based on a silicon-based heterogeneous platform and design a low-voltage, high-extinction-ratio and scalable switch array structure suitable for the visible light band is still a core problem that has not been completely solved in the current technical direction. In particular, further technical breakthroughs are still needed in electrode structure design, modulation efficiency optimization, crosstalk control and large-scale integration process. SUMMARY

[0005] The purpose of the application is to provide a ferroelectric domain switch for fast switching of visible light communication.

[0006] The ferroelectric domain switch for fast switching of visible light communication according to the application is a 2x2 MZI switch unit, which is composed of a silicon substrate (16), a lower cladding layer (17), a flat plate layer (18), a waveguide core layer and an upper cladding layer (19) from bottom to top. Figure 1As shown, the waveguide core layer is composed of a first input straight waveguide (1), a second input straight waveguide (2), an input 2x2 MMI (Multimode Interference, Multimode Interference Coupler) (3), a first input S curved waveguide (4), a second input S curved waveguide (5), a first modulation straight waveguide (6), a second modulation straight waveguide (7), a first output S curved waveguide (11), a second output S curved waveguide (12), an output 2x2 MMI (13), a first output straight waveguide (14) and a second output straight waveguide (15); the first input straight waveguide (1) and the second input straight waveguide (2), the first modulation straight waveguide (6) and the second modulation straight waveguide (7), the first output straight waveguide (14) and the second output straight waveguide (15) have the same structure and size and are arranged in parallel to each other, and the centers of symmetry of the three pairs of straight waveguides are collinear; a first ground metal electrode (8), a second ground metal electrode (9) and a signal metal electrode (10) are arranged in parallel to each other outside the first modulation straight waveguide (6), outside the second modulation straight waveguide (7) and between the first modulation straight waveguide (6) and the second modulation straight waveguide (7); the first input S curved waveguide (4) and the second input S curved waveguide (5), the first output S curved waveguide (11) and the second output S curved waveguide (12) are symmetrically arranged on the left and right sides of the centers of symmetry of the three pairs of straight waveguides; the input 2x2 MMI (3) and the output 2x2 MMI (13) have the same structure and size, are left-right symmetrical structures about the center of symmetry of the three pairs of straight waveguides, and the input 2x2 MMI (3) and the output 2x2 MMI (13) are arranged symmetrically about the front and back of the signal metal electrode (10).

[0007] The structure of the input 2x2 MMI (3) according to the application is as shown in Figure 3(a) as shown, by the input 2x2 MMI first input straight waveguide (20), the input 2x2 MMI second input straight waveguide (21), the input 2x2 MMI first input wedge waveguide (22), the input 2x2 MMI second input wedge waveguide (23), the input 2x2 MMI multimode interference region (24), the input 2x2 MMI first output wedge waveguide (25), the input 2x2 MMI second output wedge waveguide (26), the input 2x2 MMI first output straight waveguide (27) and the input 2x2 MMI second output straight waveguide (28); the input 2x2 MMI first input straight waveguide (20) and the input 2x2 MMI first input wedge waveguide (22) are connected as the input 2x2 MMI first input end (input channel 1), the input 2x2 MMI second input straight waveguide (21) and the input 2x2 MMI second input wedge waveguide (23) are connected as the input 2x2 MMI second input end (input channel 2), the input 2x2 MMI first output wedge waveguide (25) and the input 2x2 MMI first output straight waveguide (27) are connected as the input 2x2 MMI first output end (output channel 1), and the input 2x2 MMI second output wedge waveguide (26) and the input 2x2 MMI second output straight waveguide (28) are connected as the input 2x2 MMI second output end (output channel 2); the four wedge waveguides are completely the same in structure and size, and along the input light direction, the input 2x2 MMI first input wedge waveguide (22) and the input 2x2 MMI second input wedge waveguide (23) are changed from narrow to wide, and the input 2x2 MMI first output wedge waveguide (25) and the input 2x2 MMI second output wedge waveguide (26) are changed from wide to narrow.

[0008] The structure of the output 2x2 MMI (4) described in the application is as follows Figure 3(b) is shown, consisting of an output 2x2 MMI first input straight waveguide (20'), an output 2x2 MMI second input straight waveguide (21'), an output 2x2 MMI first input wedge waveguide (22'), an output 2x2 MMI second input wedge waveguide (23'), an output 2x2 MMI multimode interference region (24'), an output 2x2 MMI first output wedge waveguide (25'), an output 2x2 MMI second output wedge waveguide (26'), an output 2x2 MMI first output straight waveguide (27'), and an output 2x2 MMI second output straight waveguide (28'); the output 2x2 MMI first input straight waveguide (20') and the output 2x2 MMI first input wedge waveguide (22') are connected as an output 2x2 MMI first input end (input channel 1'), the output 2x2 MMI second input straight waveguide (21') and the output 2x2 MMI second input wedge waveguide (23') are connected as an output 2x2 MMI second input end (input channel 2'), the output 2x2 MMI first output wedge waveguide (25') and the output 2x2 MMI first output straight waveguide (27') are connected as an output 2x2 MMI first output end (output channel 1'), and the output 2x2 MMI second output wedge waveguide (26') and the output 2x2 MMI second output straight waveguide (28') are connected as an output 2x2 MMI second output end (output channel 2'); the four wedge waveguides are completely the same in structure and size, and along the input light direction, the output 2x2 MMI first input wedge waveguide (22') and the output 2x2 MMI second input wedge waveguide (23') become wider from narrower, and the output 2x2 MMI first output wedge waveguide (25') and the output 2x2 MMI first output straight waveguide (27') become narrower from wider.

[0009] The first input straight waveguide (1) is connected with the input 2x2 MMI first input straight waveguide (20), the second input straight waveguide (2) is connected with the input 2x2 MMI second input straight waveguide (21), the input 2x2 MMI first output straight waveguide (27) is connected with the first input S-bent waveguide (4), and the input 2x2 MMI second output straight waveguide (28) is connected with the second input S-bent waveguide (5); the first output S-bent waveguide (11) is connected with the output 2x2 MMI first input straight waveguide (20'), the second output S-bent waveguide (12) is connected with the output 2x2 MMI second input straight waveguide (21'), the output 2x2 MMI first output straight waveguide (27') is connected with the first output straight waveguide (14), and the output 2x2 MMI second output straight waveguide (28') is connected with the second output straight waveguide (15).

[0010] Figure 2 (a) and Figure 2 (b) are respectivelyFigure 1 The cross-sectional schematic view of the positions of a-a' and b-b'. Figure 2 As shown in (a), no electrode is provided at the position, and the device is composed of a silicon-based substrate (16), a lower cladding layer (17), a slab layer (18), a waveguide core layer, and an upper cladding layer (19) from bottom to top, and the waveguide core layer is a first input straight waveguide (1) and a second input straight waveguide (2) which are separated and parallel. Figure 2 As shown in (b), an electrode is provided at the position, and the device is composed of a silicon-based substrate (16), a lower cladding layer (17), a slab layer (18), a waveguide core layer, a metal electrode layer, and an upper cladding layer (19) from bottom to top. Figure 2 As shown in (c), the metal electrode layer is composed of a metal adhesion layer (34) and a main electrode layer (35) from bottom to top. Figure 2 As shown in (b), an electrode is provided at the position, and the device is composed of a silicon-based substrate (16), a lower cladding layer (17), a slab layer (18), a waveguide core layer, a metal electrode layer, and an upper cladding layer (19) from bottom to top. Figure 1 As shown in (c), the metal electrode layer is composed of a metal adhesion layer (34) and a main electrode layer (35) from bottom to top.

[0011] The switch array refers to an array built by switches through a certain architecture. Different architectures, including BENES, SAS, PILOSS, etc., are required in different application scenarios. Figure 9 As shown in (a), the switch array is composed of 6 2x2 MZI (Mach-Zehnder Interferometer) switch units and 2 crossing waveguide units, has four input ends and four output ends, i.e., a first input end (Input1), a second input end (Input2), a third input end (Input3), a fourth input end (Input4), and a first output end (Output1), a second output end (Output2), a third output end (Output3), and a fourth output end (Output4) of the switch array.

[0012] The crossing waveguide unit (crossing) described in the present application is as shown in (b). Figure 6As shown. The cross waveguide unit is a centrally symmetric structure, consisting of a first transmission waveguide and a second transmission waveguide that are perpendicular to each other; wherein, the first transmission waveguide is composed of a first waveguide (D1) and a third waveguide (D3) with collinear symmetry centers, and the second transmission waveguide is composed of a second waveguide (D2) and a fourth waveguide (D4) with collinear symmetry centers; the first waveguide (D1), the third waveguide (D3), the second waveguide (D2), and the fourth waveguide (D4) have the same structure and size, and are connected from the outside to the inside by a wedge-shaped waveguide (29) and a multimode interference waveguide (30) to reduce the transmission loss at the crossover point. The width of the wedge-shaped waveguide (29) near the multimode interference waveguide (30) is greater than the width of the wedge-shaped waveguide (29) away from the multimode interference waveguide (30). Its width gradually changes linearly along the direction of light propagation. This is used to achieve optical field mode matching between the conventional straight waveguide (the straight waveguide connected to the port of the cross waveguide unit) and the multimode interference waveguide (30), thereby reducing coupling loss. The multimode interference waveguide (30) is a rectangular structure. Its length and width are designed so that when light is input from any input port (such as Port1), it can couple to its diagonal output port (Port3) with extremely low crosstalk and insertion loss, and effectively suppress light coupling to adjacent cross ports (Port2 and Port4).

[0013] The ferroelectric domain switching array for fast switching in visible light communication described in this invention is as follows: Figure 9 As shown, it is composed of a first 2×2 MZI switching unit (S11), a second 2×2 MZI switching unit (S12), a third 2×2 MZI switching unit (S13), a fourth 2×2 MZI switching unit (S21), a fifth 2×2 MZI switching unit (S22), a sixth 2×2 MZI switching unit (S23), a first cross waveguide unit (C1), and a second cross waveguide unit (C2). Each 2×2 MZI switching unit has a first input port (I1) and a second input port (I2), as well as a first output port (O1) and a second output port (O2), which correspond to... Figure 1 The cross waveguide unit comprises a first input straight waveguide (1), a second input straight waveguide (2), a first output straight waveguide (14), and a second output straight waveguide (15); each cross waveguide unit has four ports: Port1, Port2, Port3, and Port4, corresponding to... Figure 6Port1, Port2, Port3, and Port4.The first output port (O1) of the first 2×2 MZI switching unit (S11) is connected to the first input port (I1) of the second 2×2 MZI switching unit (S12). The first output port (O1) of the second 2×2 MZI switching unit (S12) is connected to the first input port (I1) of the third 2×2 MZI switching unit (S13). The second output port (O2) of the fourth 2×2 MZI switching unit (S21) is connected to the second input port (I2) of the fifth 2×2 MZI switching unit (S22). The second output port (O2) of the fifth 2×2 MZI switching unit (S22) is connected to the second input port (I2) of the sixth 2×2 MZI switching unit (S23). Port1 of the first cross waveguide unit (C1) is connected to the first output port (O1) of the fourth 2×2 MZI switching unit (S21). Port2 of the first cross waveguide unit (C1) is connected to the first input port (I1) of the fifth 2×2 MZI switching unit (S12). The first input port (I1) of the MZI switching unit (S22) is connected; the Port3 port of the first cross waveguide unit (C1) is connected to the second input port (I2) of the second 2×2 MZI switching unit (S12); the Port4 port of the first cross waveguide unit (C1) is connected to the second output port (O2) of the first 2×2 MZI switching unit (S11); the Port1 port of the second cross waveguide unit (C2) is connected to the first output port (O1) of the fifth 2×2 MZI switching unit (S22); the Port2 port of the second cross waveguide unit (C2) is connected to the first input port (I1) of the sixth 2×2 MZI switching unit (S23); the Port3 port of the second cross waveguide unit (C2) is connected to the second input port (I2) of the third 2×2 MZI switching unit (S13); and the Port4 port of the second cross waveguide unit (C2) is connected to the second output port (O2) of the second 2×2 MZI switching unit (S12). The first input port (I1) and the second input port (I2) of the MZI switching unit (S11) serve as the first input terminal (Input1) and the second input terminal (Input2) of the switching array, respectively. The first input port (I1) and the second input port (I2) of the fourth 2×2 MZI switching unit (S21) serve as the third input terminal (Input3) and the fourth input terminal (Input4) of the switching array, respectively. The first output port (O1) and the second output port (O2) of the third 2×2 MZI switching unit (S13) serve as the first output terminal (Output1) and the second output terminal (Output2) of the switching array, respectively. The first output port (O1) and the second output port (O2) of the sixth 2×2 MZI switching unit (S23) serve as the third output terminal (Output3) and the fourth output terminal (Output4) of the switching array, respectively.

[0014] The working principle of the ferroelectric domain switch and its array for fast switching in visible light communication described in this invention is as follows: For a single 2×2 MZI switch unit, light is input from one port (first input straight waveguide (1) or second input straight waveguide (2)) and then split into two paths with equal success rate by the input 2×2 MMI (3). The paths pass through the first modulation straight waveguide (6) and the second modulation straight waveguide (7) respectively. The first ground metal electrode (8) and the second ground metal electrode (9) are connected to the ground wire respectively. When a voltage is applied to the signal metal electrode (10), opposite electric field directions are formed on the first modulation straight waveguide (6) and the second modulation straight waveguide (7). Due to the Pockels effect, the first modulation straight waveguide (6) and the second modulation straight waveguide (7) have a refractive index difference, which ultimately leads to a phase difference in the light in the two modulation straight waveguides. When a light source is input from one port of a 2×2 MZI switching unit (such as the first input straight waveguide (1)), if no voltage is applied to the signal metal electrode (10), the light will be output from the output port (such as the second output straight waveguide (15)) on the different side from the input port, i.e., the switch is in a cross state; if a voltage of 2.6V is applied to the signal metal electrode (10), the light will be output from the output port (such as the first output straight waveguide (14)) on the same side as the input port (such as the first input straight waveguide (1)), i.e., the switch is in a bar state. For a switching array integrated with multiple of the above 2×2 MZI switching units and cross waveguide units, the reconfigurable optical routing function from any input port to any output port can be realized by coordinating the working state (bar or cross) of each switching unit in the array.

[0015] The innovation of this invention compared with the prior art lies in: 1. This invention is the first to apply ferroelectric materials such as lithium niobate and lead zirconate titanate (used to prepare planar layers and waveguide core layers) to optical switch arrays in the visible light band. The high linear electro-optic effect (Pokkers effect) of these materials can achieve high-speed, low-loss optical modulation in the visible light band, effectively overcoming the problems of high absorption loss and high driving voltage of traditional semiconductor materials in the visible light band; 2. This invention proposes a switch array structure for heterogeneous integrated ferroelectric waveguides on a silicon substrate. Through optimized design of 2×2 MZI switch units and cross-waveguide units, a reconfigurable optical routing architecture of 4×4 BENES is achieved. This structure possesses advantages such as high integration, low crosstalk, and low insertion loss, making it suitable for large-scale photonic integrated circuits. 3. The present invention designs a symmetrical coplanar metal electrode structure (including two ground metal electrodes and one signal metal electrode) on both sides of the 2×2 MZI modulation arm. By applying a low voltage to the signal metal electrode, a reverse electric field can be formed on the dual modulation arm. The Pockels effect is used to achieve efficient and fast refractive index modulation, which significantly reduces the driving voltage and improves the modulation efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the 2×2 MZI switching unit structure described in this invention; Figure 2 This is a schematic cross-sectional view of the 2×2 MZI switching unit described in this invention. Figure 2 (a) is Figure 1 A schematic diagram of the cross-section at position a-a'. Figure 2 (b) is Figure 1 A schematic diagram of the cross-section at position b-b'; Figure 3 (a) and Figure 3 (b) are schematic diagrams of the input 2×2 MMI and output 2×2 MMI of the present invention, respectively; Figure 4 When the input channel 1 of the 2×2 MMI described in this invention is used as the input terminal, the transmission optical field patterns of output channel 1 and output channel 2 are as follows: Figure 5 The transmission spectrum of output channel 1 and output channel 2 when the input channel 1 of the 2×2 MMI described in this invention is used as the input terminal; Figure 6 This is a schematic diagram of the cross-waveguide unit structure described in this invention; Figure 7 This is a transmission optical field diagram of the cross waveguide unit when light is input from Port1 according to the present invention; Figure 8 The output spectra of ports 2, 3, and 4 when Port1 of the cross waveguide unit described in this invention is used as input; Figure 9 This is a schematic diagram of the 4×4 BENES switch array structure described in this invention; Figure 10 This is a graph showing the change in optical transmission loss of the 2×2 MZI switching unit described in this invention as a function of the voltage applied to the signal metal electrode; Figure 11 (a) and Figure 11 (b) Output spectra of the cross state and bar state when the first input port (I1) and the second input port (I2) of the 2×2 MZI switch unit described in this invention are inputs, respectively; Figure 12 (a) Figure 12 (b) Figure 12 (c) Figure 12 (d) is the output spectrum of the switch array from the first output terminal (Output1) to the fourth output terminal (Output4) of the open-parallel array when the light is input from the first input terminal (Input1) to the fourth input terminal (Input4) of the open-parallel array in the "all-bar" state. Figure 12 (e) Figure 12 (f) Figure 12 (g) Figure 12 (h) is the output spectrum of the switch array described in this invention from the first output terminal (Output1) to the fourth output terminal (Output4) of the open-parallel array when light is input from the first input terminal (Input1) to the fourth input terminal (Input4) of the open-parallel array in the "all-cross" state. Figure 13 This is a flowchart illustrating the fabrication process of the visible light ferroelectric domain switch array described in this invention. Detailed Implementation

[0017] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The embodiments described below are not exhaustive; all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0018] Example 1 The switch and its array proposed in this invention are applicable to visible light bands such as 405nm, 532nm, and 655nm. For ease of explanation, the following embodiments will all use 655nm as an example.

[0019] like Figure 1 As shown, the direction of the input light in the first input straight waveguide (1) or the second input straight waveguide (2) is defined as the length direction, and the direction perpendicular to the input light is defined as the width direction. The width of the first ground metal electrode (8) and the second ground metal electrode (9) is 100μm, the width of the signal metal electrode (10) is 40μm, and the length of both is 5000μm; the width of the first modulation straight waveguide (6) and the width of the second modulation straight waveguide (7) are 1μm and the length is 5000μm; the structural dimensions of the first input S-bend waveguide (4), the second input S-bend waveguide (5), the first output S-bend waveguide (11), and the second output S-bend waveguide (12) are exactly the same, with a width of 1μm, a lateral length (horizontal distance between the center of the input end and the center of the output end) of 200μm, and a longitudinal length (vertical distance between the center of the input end and the center of the output end) of 20.5μm.

[0020] As attached Figure 2 As shown, the silicon substrate (16) can be either silicon or silicon nitride, with a thickness of 500~800 μm. In this embodiment, silicon with a thickness of 600 μm is selected as the substrate. The lower cladding layer (17) and the upper cladding layer (19) are made of silicon dioxide or polymers (such as polymethyl methacrylate, polyethylene, polyester, polystyrene, etc.) with low refractive indices, with a thickness range of 2~4 μm. In this embodiment, silicon dioxide is selected, with a refractive index of 1.4564 at a wavelength of 655 nm. The thickness of both the upper and lower cladding layers is 3 μm. The planar layer (18) and the waveguide core layer are made of the same material, using one of the ferroelectric domain materials such as lithium niobate (LN), lead zirconate titanate (PZT), and lanthanum-modified lead zirconate titanate (PLZT). The thickness of the planar layer (18) ranges from 0.2 to 0.5 μm. In this embodiment, lithium niobate is selected as the planar layer (18) and the waveguide core layer, with a refractive index of 1.4564 at a wavelength of 655 nm. and The thickness of the planar layer (18) is 0.35 μm; the waveguide core layer is located above the planar layer (18), with a height range of 0.2~0.5 μm and an etching angle of 70~80°. In this embodiment, the height of the waveguide core layer is 0.35 μm and the etching angle is 74°. The optical field mode is distributed between the waveguide core layer and the planar layer (18) and is mainly confined to the waveguide core layer and its adjacent planar region for transmission. The first ground metal electrode (8), the second ground metal electrode (9) and the signal metal electrode (10) are composed of a metal adhesion layer (34) and a main electrode layer (35) from bottom to top. The metal adhesion layer (34) can be one of titanium, chromium and tantalum, with a thickness range of 5~15 nm. In this embodiment, titanium is selected as the metal adhesion layer (34), and its thickness is 10 nm. The main electrode layer (35) can be made of aluminum, gold, silver, tungsten, or titanium, with a thickness ranging from 300 to 500 nm. In this embodiment, gold is selected as the main electrode layer (35), with a thickness of 400 nm.

[0021] The lengths of the first input straight waveguide (20), the second input straight waveguide (21), the first output straight waveguide (27), and the second output straight waveguide (28) of the 2×2 MMI are 10 μm and the widths are 1 μm. The distance between the centers of symmetry of the first input straight waveguide (20) and the second input straight waveguide (21) of the 2×2 MMI is 4 μm, and the distance between the centers of symmetry of the first output straight waveguide (27) and the second output straight waveguide (28) of the 2×2 MMI is 4 μm. The length of the wedge waveguide is 10 μm, and the widths of the first input wedge waveguide (22) and the second input wedge waveguide (23) of the 2×2 MMI change linearly from 1 μm to 2 μm. The widths of the first output wedge waveguide (25) and the second output wedge waveguide (28) of the 2×2 MMI are 10 μm and 1 μm respectively. The width of the second output wedge waveguide (26) of the MMI is linearly varied from 2 μm to 1 μm; the distance between the centers of symmetry of the first input wedge waveguide (22) and the second input wedge waveguide (23) of the input 2×2 MMI is 4 μm, and the distance between the centers of symmetry of the first output wedge waveguide (25) and the second output wedge waveguide (26) of the input 2×2 MMI is 4 μm; the length of the multimode interference region (24) of the input 2×2 MMI is 220 μm and the width is 6 μm. The structure and dimensions of the output 2×2 MMI (13) are exactly the same as those of the input 2×2 MMI (3).

[0022] like Figure 4 The image shows the transmission optical field diagrams of output channel 1 and output channel 2 of the 2×2 MMI used in this invention at a wavelength of 655nm. Figure 5 The transmission spectrum shown indicates that at 655nm, the two channels of output channel 1 and output channel 2 exhibit uniform spectral dispersion.

[0023] like Figure 6 As shown, each wedge-shaped waveguide (29) has a length of 5 μm and a width that linearly changes from 1 μm to 2 μm or from 2 μm to 1 μm. The sum of the lengths of the first waveguide (D1) and the third waveguide (D3) is 24 μm, and the sum of the lengths of the second waveguide (D3) and the fourth waveguide (D4) is 24 μm.

[0024] like Figure 7 As shown, combined with Figure 8 The transmission spectrum shown in the figure indicates that the crosstalk is less than -85dB, which means that the cross waveguide can perform its function well at 655nm.

[0025] like Figure 9As shown, the switch architecture can be either BENES or PILOSS; this embodiment uses the BENES architecture. This embodiment uses a 4×4 switch array, but it can also be expanded to 8×8, 16×16, and larger-scale switch arrays.

[0026] like Figure 10 As shown, when a voltage of 0V is applied to the signal metal electrode (10), the switch is in the cross state; when a voltage of 2.6V is applied to the signal metal electrode (10), the switch is in the bar state, and the extinction ratio is greater than 50dB.

[0027] like Figure 11 (a) and Figure 11 As shown in (b), the extinction ratio is greater than 50dB at a wavelength of 655nm, indicating that the switching unit has excellent switching performance. The figure shows three curves because: when the first input port (I1) is used as the input, the spectrum output from the first output port (O1) in the bar state completely overlaps with the spectrum output from the second output port (O2) in the cross state; when the second output port (I2) is used as the input, the spectrum output from the second output port (O2) in the bar state completely overlaps with the spectrum output from the first output port (O1) in the cross state. The overlap of these two sets of curves proves that this MZI switching unit has perfect structural and functional symmetry, meaning that regardless of which input port the light enters from, the spectrum of the through output port in the bar state is always consistent with the spectrum of the cross output port in the cross state.

[0028] like Figure 12 (a) Figure 12 (b) Figure 12 (c) Figure 12 As shown in (d), the extinction ratio is greater than 25dB when the wavelength is 655nm, indicating that the switch array can achieve the expected optical routing function in both states.

[0029] like Figure 13 As shown, the method for fabricating the electro-optic switch array of the present invention is as follows: 1) This embodiment is based on a silicon substrate (16), on which a 3μm thick silicon dioxide lower cladding layer (17) and a 700nm thick lithium niobate film are deposited sequentially. The lithium niobate film serves as the subsequent planar layer (18) and waveguide core layer (31, 31'). Subsequently, a 100nm layer of metallic chromium (32) is deposited by electron beam evaporation as a hard mask for subsequent dry etching. Photoresist (33) is spin-coated on the metallic chromium (32), and the mask pattern with the same structure as the waveguide core layer is transferred onto the photoresist (33) by ultraviolet lithography and development. 2) Next, inductively coupled plasma (ICP) is used to perform dry etching on the chromium metal (32) to transfer the waveguide core layer pattern on the photoresist onto the chromium metal (32) to form a mask; the photoresist is removed, and then the exposed lithium niobate film is etched using ICP dry etching technology with the chromium layer as a mask. The etching depth is precisely controlled to be 350nm, so as to form the required waveguide core layer structure (31, 31') on the lithium niobate film. At this time, the height of the waveguide core layer is 350nm, and the remaining 350nm thick lithium niobate layer is the planar layer (18). 3) After the waveguide core layer is fabricated, a 3μm thick silicon dioxide layer is deposited on the chip surface as an upper cladding layer using plasma enhanced chemical vapor deposition (PECVD) (19); then, the electrode window opening process is performed: spin-coating photoresist (33), forming a mask pattern complementary to the metal electrode area by photolithography (i.e., photoresist covering the non-electrode area), and then using ICP dry etching to etch silicon dioxide to expose the planar layer below which the metal electrode needs to be fabricated (18). 4) Finally, the metal electrodes are fabricated: photoresist (33) is spin-coated on the chip surface, and an electrode window pattern consistent with the shape of the metal electrode is formed by photolithography; a 10 nm thick titanium metal adhesion layer and a 400 nm thick gold main electrode layer are deposited sequentially by electron beam evaporation; finally, the photoresist and the metal above it are removed by a stripping process, and the required electrode structure (8, 10, 9) is formed in the electrode window. The residual photoresist is removed, and the device fabrication is completed.

Claims

1. A ferroelectric domain switch for fast switching in visible light communication, characterized in that: It is a 2×2 MZI switching unit, which consists of a silicon substrate (16), a lower cladding (17), a planar layer (18), a waveguide core layer, and an upper cladding (19) from bottom to top; the waveguide core layer consists of a first input straight waveguide (1), a second input straight waveguide (2), an input 2×2 MMI (3), a first input S-bend waveguide (4), a second input S-bend waveguide (5), a first modulation straight waveguide (6), a second modulation straight waveguide (7), a first output S-bend waveguide (11), a second output S-bend waveguide (12), and an output 2×2 MZI switch. The system consists of an MMI (13), a first output straight waveguide (14), and a second output straight waveguide (15); the first input straight waveguide (1) and the second input straight waveguide (2), the first modulation straight waveguide (6) and the second modulation straight waveguide (7), the first output straight waveguide (14) and the second output straight waveguide (15) have the same structure and size and are arranged in parallel to each other, and the three pairs of straight waveguides are collinear in symmetry; a first grounding metal electrode (8), a second grounding metal electrode (9) and a signal metal electrode (10) are respectively provided on the outside of the first modulation straight waveguide (6), the outside of the second modulation straight waveguide (7), and between the first modulation straight waveguide (6) and the second modulation straight waveguide (7); the first input S-bend waveguide (4) and the second input S-bend waveguide (5), the first output S-bend waveguide (11) and the second output S-bend waveguide (12) are symmetrically arranged on the left and right sides of the symmetry center of the three pairs of straight waveguides; the input 2×2 MMI (3) and the output 2×2 The MMI (13) has the same structure and size, and is a left-right symmetrical structure about the center of symmetry of three pairs of straight waveguides. The input 2×2 MMI (3) and output 2×2 MMI (13) are symmetrically arranged about the front and back of the signal metal electrode (10). The first input straight waveguide (1) is connected to the first input straight waveguide (20) of the input 2×2 MMI, the second input straight waveguide (2) is connected to the second input straight waveguide (21) of the input 2×2 MMI, the first output straight waveguide (27) of the input 2×2 MMI is connected to the first input S-bend waveguide (4), the second output straight waveguide (28) of the input 2×2 MMI is connected to the second input S-bend waveguide (5), the first output S-bend waveguide (11) is connected to the first input straight waveguide (20') of the output 2×2 MMI, and the second output S-bend waveguide (12) is connected to the output 2×2 The second input straight waveguide (21') of the MMI is connected, the first output straight waveguide (27') and the first output straight waveguide (14) of the 2×2 MMI are connected, and the second output straight waveguide (28') and the second output straight waveguide (15) of the 2×2 MMI are connected.

2. A ferroelectric domain switch for fast switching in visible light communication as described in claim 1, characterized in that: The input 2×2 MMI (3) is composed of the input 2×2 MMI first input straight waveguide (20), the input 2×2 MMI second input straight waveguide (21), the input 2×2 MMI first input wedge waveguide (22), the input 2×2 MMI second input wedge waveguide (23), the input 2×2 MMI multimode interference region (24), the input 2×2 MMI first output wedge waveguide (25), the input 2×2 MMI second output wedge waveguide (26), the input 2×2 MMI first output straight waveguide (27), and the input 2×2 MMI second output straight waveguide (28); the input 2×2 MMI first input straight waveguide (20) and the input 2×2 MMI first input wedge waveguide (22) are connected as the input 2×2 MMI first input terminal (input channel 1), and the input 2×2 MMI second input straight waveguide (21) and the input 2×2 MMI second input wedge waveguide (23) are connected as the input 2×2 MMI second input wedge waveguide (23). The second input terminal of the MMI (input channel 2) is connected to the first output wedge waveguide (25) and the first output straight waveguide (27) of the 2×2 MMI as the first output terminal of the 2×2 MMI (output channel 1), and the second output wedge waveguide (26) and the second output straight waveguide (28) of the 2×2 MMI as the second output terminal of the 2×2 MMI (output channel 2). The four wedge waveguides have the same structure and size. Along the direction of the input light, the first input wedge waveguide (22) and the second input wedge waveguide (23) of the 2×2 MMI become wider, and the first output wedge waveguide (25) and the second output wedge waveguide (26) of the 2×2 MMI become narrower.

3. A ferroelectric domain switch for fast switching in visible light communication as described in claim 1, characterized in that: The output 2×2 MMI (3) is composed of the first input straight waveguide (20'), the second input straight waveguide (21'), the first input wedge waveguide (22'), the second input wedge waveguide (23'), the multimode interference region (24'), the first output wedge waveguide (25'), the second output wedge waveguide (26'), the first output straight waveguide (27'), and the second output straight waveguide (28'); the first input straight waveguide (20') and the first input wedge waveguide (22') are connected as the first input terminal (input channel 1') of the output 2×2 MMI, and the second input straight waveguide (21') and the output 2×2 MMI are connected as the first input terminal (input channel 1'). The second input wedge waveguide (23') of the MMI is connected as the second input terminal of the output 2×2 MMI (input channel 2'). The first output wedge waveguide (25') and the first output straight waveguide (27') of the output 2×2 MMI are connected as the first output terminal of the output 2×2 MMI (output channel 1'). The second output wedge waveguide (26') and the second output straight waveguide (28') of the output 2×2 MMI are connected as the second output terminal of the output 2×2 MMI (output channel 2'). The four wedge waveguides have the same structure and size. Along the input light direction, the first input wedge waveguide (22') and the second input wedge waveguide (23') of the output 2×2 MMI become wider, and the first output wedge waveguide (25') and the first output straight waveguide (27') of the output 2×2 MMI become narrower.

4. A ferroelectric domain switch for fast switching in visible light communication as described in claim 1, characterized in that: The silicon substrate (16) is one of silicon or silicon nitride, with a thickness of 500~800 μm; the lower cladding layer (17) and the upper cladding layer (19) are one of silicon dioxide, polymethyl methacrylate, polyethylene, polyester, or polystyrene with a low refractive index, with a thickness range of 2~4 μm; the planar layer (18) and the waveguide core layer are made of the same material, one of lithium niobate, lead zirconate titanate, or lanthanum-modified lead zirconate titanate, with a thickness range of 0.2~0.5 μm; the waveguide core layer is located above the planar layer (18), with a height range of 0.2~0.5 μm and an etching angle of 70~80°; the first ground metal electrode (8), the second ground metal electrode (9), and the signal metal electrode (10) are composed of a metal adhesion layer (34) and a main electrode layer (35) from bottom to top, with the metal adhesion layer (34) being one of titanium, chromium, or tantalum, with a thickness range of 5~15 μm. nm; the main electrode layer (35) is one of aluminum, gold, silver, tungsten, and titanium, with a thickness range of 300~500 nm.

5. A ferroelectric domain switching array for fast switching in visible light communication, characterized in that: The switch array is composed of 2×2 MZI switch units as described in any one of claims 1 to 5 and 2 cross waveguide units; the cross waveguide unit is a centrally symmetrical structure, consisting of a first transmission waveguide and a second transmission waveguide that are perpendicular to each other; wherein, the first transmission waveguide is composed of a first waveguide (D1) and a third waveguide (D3) with collinear symmetry centers, and the second transmission waveguide is composed of a second waveguide (D2) and a fourth waveguide (D4) with collinear symmetry centers; the first waveguide (D1), the third waveguide (D3), the second waveguide (D2), and the fourth waveguide (D4) have the same structure and size, and are connected from the outside to the inside by a wedge-shaped waveguide (29) and a multimode interference waveguide (30); the width of the wedge-shaped waveguide (29) near the multimode interference waveguide (30) is greater than the width of the wedge-shaped waveguide (29) away from the multimode interference waveguide (30), and its width gradually changes linearly along the direction of light propagation; the multimode interference waveguide (30) is a rectangular structure.

6. A ferroelectric domain switching array for fast switching in visible light communication as described in claim 5, characterized in that: It is composed of a first 2×2 MZI switching unit (S11), a second switching unit (S12), a third 2×2 MZI switching unit (S13), a fourth 2×2 MZI switching unit (S21), a fifth 2×2 MZI switching unit (S22), a sixth 2×2 MZI switching unit (S23), a first cross waveguide unit (C1), and a second cross waveguide unit (C2); Each 2×2 MZI switch unit has a first input port (I1) and a second input port (I2), as well as a first output port (O1) and a second output port (O2), corresponding to the first input straight waveguide (1), the second input straight waveguide (2), the first output straight waveguide (14), and the second output straight waveguide (15) in Figure 1, respectively; each cross waveguide unit has four ports: Port1, Port2, Port3, and Port4, corresponding to Port1, Port2, Port3, and Port4 in Figure 6, respectively; The first output port (O1) of the first 2×2 MZI switching unit (S11) is connected to the first input port (I1) of the second 2×2 MZI switching unit (S12). The first output port (O1) of the second 2×2 MZI switching unit (S12) is connected to the first input port (I1) of the third 2×2 MZI switching unit (S13). The second output port (O2) of the fourth 2×2 MZI switching unit (S21) is connected to the second input port (I2) of the fifth 2×2 MZI switching unit (S22). The second output port (O2) of the fifth 2×2 MZI switching unit (S22) is connected to the second input port (I2) of the sixth 2×2 MZI switching unit (S23). Port1 of the first cross waveguide unit (C1) is connected to the first output port (O1) of the fourth 2×2 MZI switching unit (S21). Port2 of the first cross waveguide unit (C1) is connected to the first input port (I1) of the fifth 2×2 MZI switching unit (S12). The first input port (I1) of the MZI switching unit (S22) is connected; the Port3 port of the first cross waveguide unit (C1) is connected to the second input port (I2) of the second 2×2 MZI switching unit (S12); the Port4 port of the first cross waveguide unit (C1) is connected to the second output port (O2) of the first 2×2 MZI switching unit (S11); the Port1 port of the second cross waveguide unit (C2) is connected to the first output port (O1) of the fifth 2×2 MZI switching unit (S22); the Port2 port of the second cross waveguide unit (C2) is connected to the first input port (I1) of the sixth 2×2 MZI switching unit (S23); the Port3 port of the second cross waveguide unit (C2) is connected to the second input port (I2) of the third 2×2 MZI switching unit (S13); and the Port4 port of the second cross waveguide unit (C2) is connected to the second output port (O2) of the second 2×2 MZI switching unit (S12). The first input port (I1) and the second input port (I2) of the MZI switching unit (S11) serve as the first input terminal (Input1) and the second input terminal (Input2) of the switching array, respectively. The first input port (I1) and the second input port (I2) of the fourth 2×2 MZI switching unit (S21) serve as the third input terminal (Input3) and the fourth input terminal (Input4) of the switching array, respectively. The first output port (O1) and the second output port (O2) of the third 2×2 MZI switching unit (S13) serve as the first output terminal (Output1) and the second output terminal (Output2) of the switching array, respectively. The first output port (O1) and the second output port (O2) of the sixth 2×2 MZI switching unit (S23) serve as the third output terminal (Output3) and the fourth output terminal (Output4) of the switching array, respectively.

7. The ferroelectric domain switching array for fast switching in visible light communication as described in claim 5, characterized in that: The width of the first ground metal electrode (8) and the second ground metal electrode (9) is 100 μm, the width of the signal metal electrode (10) is 40 μm, and the length of both is 5000 μm; the width of the first modulation straight waveguide (6) and the second modulation straight waveguide (7) is 1 μm and the length is 5000 μm; the structural dimensions of the first input S-bend waveguide (4), the second input S-bend waveguide (5), the first output S-bend waveguide (11), and the second output S-bend waveguide (12) are exactly the same, the width is 1 μm, the horizontal length, i.e. the horizontal distance between the center of the input end and the center of the output end, is 200 μm, and the vertical length, i.e. the vertical distance between the center of the input end and the center of the output end, is 20.5 μm.

8. A ferroelectric domain switching array for fast switching in visible light communication as described in claim 5, characterized in that: The lengths of the first input straight waveguide (20), the second input straight waveguide (21), the first output straight waveguide (27), and the second output straight waveguide (28) of the 2×2 MMI are 10 μm and the width is 1 μm; the distance between the centers of symmetry of the first input straight waveguide (20) and the second input straight waveguide (21) of the 2×2 MMI is 4 μm, and the distance between the centers of symmetry of the first output straight waveguide (27) and the second output straight waveguide (28) of the 2×2 MMI is 4 μm; the lengths of the first input wedge waveguide (22) and the second input wedge waveguide (23) of the 2×2 MMI are 10 μm, and the widths gradually change from 1 μm to 2 ... The length of the first output wedge waveguide (25) of the MMI and the second output wedge waveguide (26) of the input 2×2 MMI are 10 μm, and the width gradually changes from 2 μm to 1 μm. The distance between the centers of symmetry of the first input wedge waveguide (22) of the input 2×2 MMI and the second input wedge waveguide (23) of the input 2×2 MMI is 4 μm, and the distance between the centers of symmetry of the first output wedge waveguide (25) of the input 2×2 MMI and the second output wedge waveguide (26) of the input 2×2 MMI is 4 μm. The length of the multimode interference region (24) of the input 2×2 MMI is 220 μm and the width is 6 μm. The structure and size of the output 2×2 MMI (13) are exactly the same as those of the input 2×2 MMI (3).

9. The ferroelectric domain switching array for fast switching in visible light communication as described in claim 5, characterized in that: Each wedge waveguide (29) has a length of 5 μm and a width that linearly changes from 1 μm to 2 μm or from 2 μm to 1 μm. The sum of the lengths of the first waveguide (D1) and the third waveguide (D3) is 24 μm, and the sum of the lengths of the second waveguide (D3) and the fourth waveguide (D4) is 24 μm.

Images