Runway micro-ring electro-optical switch structure based on lithium niobate

Abstract

The invention discloses a runway micro-ring electro-optical switch structure based on lithium niobate, and belongs to the technical field of optical waveguides and optical switches. The lithium niobate-based runway micro-ring structure realizes an optical switch function of electro-optical modulation, and comprises an upper bus waveguide, a lower bus waveguide and an optical loop cascaded with a runway micro-ring resonator in the middle; the optical loop comprises an upper bus waveguide, a runway micro-ring resonator, a motor set, an air groove in a left-right bending shape and a lower bus waveguide, a micro-ring runway is clamped between the two bus waveguides, and all the structures are combined to form the runway micro-ring electro-optical switch structure. A group of independently-controlled gold material electrodes are arranged at the position of a directional coupler composed of an upper bus and a runway micro-ring, voltage signals are applied to the electrodes through the electro-optical effect of a lithium niobate material to regulate and control optical signals, and the optical signals are output from a specific port at different powers, for example, the optical signals are output from a downloading end in a passive state. And the active state is output from the straight-through end, so that the function of multidirectional controllable transmission of optical signals is realized, and the reconfiguration of the optical switch is realized. According to the invention, a reconfigurable optical switch network can be constructed, high-speed, low-loss and low-crosstalk switching of an optical switch state is realized by adopting an electro-optical modulation signal based on an excellent electro-optical coefficient of a lithium niobate material, a free spectral range in a certain range is realized, and a certain filtering function is realized; the method is suitable for manufacturing a large-scale optical switch array and is applied to an on-chip integrated system.

Description

Technical Field

[0001] The present invention relates to the technical field of optical switches and optical waveguides, and in particular to a racetrack micro-ring electro-optical switch structure based on lithium niobate, which can be applied to the fields of optoelectronic interconnection, optical network, optical communication and the like. Background Art

[0002] With the rapid growth of big data demand and the increasing performance requirements of Internet companies and large data centers, they increasingly rely on optoelectronic interconnection to provide key communication connections between many servers, among which chip performance and communication capacity need further research and solution. At the same time, in order to achieve faster information processing speed and higher information transmission capacity, optical switches and optical switch networks that are compatible with complementary metal semiconductor (CMOS) processes, have fast response, low loss, and high reliability have begun to be widely studied. Because the original electronic chips and their interconnection technologies are gradually unable to meet the requirements of computing and storage systems for high-speed data transmission and high energy efficiency, they have become a bottleneck restricting the performance improvement of data centers and high-performance computers. Optical interconnection technology has become one of the solutions for short-distance interconnection in integrated circuit chips. Compared with electrical interconnection, optical interconnection has the characteristics of large bandwidth, low latency, good electromagnetic interference resistance, high integration density, and low power consumption. Moreover, as an important component of optoelectronic integrated chips, it is the core component in optical interconnection networks, affecting the performance and reliability of optoelectronic chips. The new challenges of multi-directional, controllable, and high-speed optical switches and optical networks under the new generation of information technology have broad research prospects.

[0003] Optical switches are important components for high-speed and high-capacity information exchange for servers and data centers. Optical switches based on optical waveguides include SiC, silicon dioxide waveguides, lithium niobate, polymers and other types of materials. Lithium niobate (LN) material has excellent optical properties, excellent linear electro-optical effect (Purkes effect), and stable physical and chemical properties. It is one of the materials with good performance in all aspects and is widely used in electro-optic modulators. The good linear electro-optical properties of lithium niobate can be used to achieve fast and low-power conversion of optical switch states under the regulation of electric and optical fields. The processing and manufacturing process of lithium niobate materials is mature. The commonly used manufacturing processes mainly include titanium diffusion method, proton exchange method, femtosecond laser etching method, chemical vapor deposition method, etc. The optical waveguide based on lithium niobate materials is easy to make and easy to integrate, and has become a research hotspot for electro-optical switches. The application of many excellent properties of lithium niobate crystals in microring structures has been one of the main research directions of researchers in recent years. Its application scenarios are wide, especially in the fields of electro-optical modulation. Optical waveguide microrings play a vital role in integrated optical waveguide switches and optical networks. They are basic devices for electro-optical sensors, filters, and nonlinear optical devices, and have broad application prospects in optical communications, optical sensing, and optical networks.

[0004] The present invention is achieved through the following technical solutions:

[0005] A racetrack microring electro-optical switch structure based on lithium niobate, wherein the function of the multi-directional controllable electro-optical switch is realized based on the racetrack microring, and the optical circuit comprises a racetrack-type microring and two optical waveguides for uploading and downloading; the optical circuit comprises a racetrack-type microring, an upper waveguide and a lower waveguide outside the microring area, wherein the upper waveguide and the lower waveguide are placed in parallel to sandwich the racetrack-type microring inside, forming two groups of optical paths for uploading straight through and downloading reversely, thereby forming an optical circuit; two metal electrodes are respectively arranged on both sides of the upper waveguide and the upper waveguide of the racetrack microring; the cross section of the optical waveguide constituting the optical switch structure is suitable for all integrated optical waveguide structures, and at least comprises: a strip waveguide, a ridge waveguide, and a multilayer waveguide; the structure constituting the electro-optical switch is provided with a silicon substrate and a quartz substrate, and a silicon dioxide protective layer is arranged on the optical waveguide layer made of lithium niobate thin film material, and the silicon dioxide protective layer is in a uniform rectangular shape and is spread on the lithium niobate thin film material, and the refractive index of the protective layer material is less than the refractive index of the lithium niobate thin film material. The high electro-optic coefficient r33 of lithium niobate material is used to achieve high-speed and high-modulation efficiency electro-optical modulation.

[0006] The micro-ring resonance principle used is based on the phase matching condition using the following formula:

[0007] neff*L=mλ, where neff is the effective refractive index of the waveguide, L is the circumference of the micro-ring track, m is a positive integer, and λ is the wavelength of the optical signal.

[0008] In the above technical solution, the electro-optical switch structure utilizes an upper waveguide and a straight waveguide in the upper part of the racetrack microring to form a passive waveguide area for electro-optical modulation. Two parallel rectangular gold material electrodes are placed at a certain distance from both sides of the above two waveguides. The length is consistent with the two optical waveguides to be modulated, and the height is slightly higher than the optical waveguide.

[0009] In the above technical solution, the racetrack micro-ring part is composed of two 180-degree curved waveguides on the left and 180-degree curved waveguides on the right with the same bending radius and curvature, and two straight optical waveguides with the same length sandwiched in the middle, forming a closed micro-ring racetrack structure.

[0010] In the above technical solution, the upper and lower waveguides a and b are sandwiched between the upper and lower sides of the micro-ring racetrack, and their structural cross-section is consistent with the optical waveguide of the micro-ring, but their length is greater than the length of the two straight waveguides of the micro-ring racetrack.

[0011] The present invention has the following beneficial effects:

[0012] The present invention is a lithium niobate-based racetrack micro-ring electro-optical switch structure that can change the propagation direction of the optical signal in the original optical waveguide, and use the electric field under the application of a reasonable voltage to regulate the optical field, so as to realize the function that the optical signal can be output from the designated port (through port or download port) with different power ratios and reverse transmission (download port output), and realize the function that the optical signal can be transmitted in multiple directions in a controllable manner. The present invention is based on lithium niobate thin film materials, has a good electro-optical coefficient, can realize low-power and high-speed transmission, and realizes high quality factor and filtering function under a certain free spectrum range, and has a large tunable range.

[0013] The present invention is conducive to constructing an optical network structure based on a multi-directional controllable optical switch, realizing a reconfigurable function, and realizing a high-speed and low-power optical switch structure design, thereby providing flexibility and practicality for making large-scale optical switch arrays and optical interconnection networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the overall structure of the racetrack micro-ring electro-optical switch based on lithium niobate and the transmission direction of the optical signal of a straight-through port of the present invention;

[0015] Figure 2 It is a schematic diagram of the overall structure of the racetrack micro-ring electro-optical switch based on lithium niobate and the transmission direction of the optical signal of one download port of the present invention;

[0016] Figure 3 It is a schematic cross-sectional view of the electro-optic modulation region of the racetrack micro-ring electro-optic switch based on lithium niobate in the present invention, including cross-sections of structures 1, 2, and 5;

[0017] Figure 4 Schematic diagram of a cross section of an air groove and a 180-degree bending portion of a lithium niobate bending waveguide in the present invention;

[0018] Figure 5 It is a schematic diagram of the 180-degree Euler bending structure on the left side of the racetrack micro-ring structure in the present invention; DETAILED DESCRIPTION

[0019] The present invention is further described in detail below by specific implementation modes in conjunction with the accompanying drawings. The present application can be implemented in a variety of different forms and is not limited to the implementation modes described in this embodiment. The purpose of providing the following specific implementation modes is to facilitate a clearer and more thorough understanding of the content of the invention of the present invention.

[0020] like Figure 1As shown, the overall structure of a racetrack microring electro-optical switch based on lithium niobate and the working condition of the optical signal transmission direction of a straight-through port, including an upper bus waveguide 1, an upper waveguide 2 of a racetrack microring, a 180-degree curved waveguide 3 on the right, and a 180-degree curved waveguide 4 on the left, a gold material electrode group 5 placed on both sides of the waveguides 1 and 2, a right air groove 6 and a left air groove 7 with the same curvature radius as the curved waveguide, a lower waveguide 8 of the racetrack microring, and a lower bus waveguide 9. Among them, waveguide 1 and waveguide 2, waveguide 8 and 9 are spaced at a certain distance and are equal, the spacing distance is micron-level, and the length is about 1 micron; air grooves 6, 7 and curved waveguides 3, 4 are spaced at a certain distance and are equal, the spacing distance is micron-level, and the length is about 2 microns; the gold material electrode group 5 and waveguides 1, 2 are spaced at an equal distance, the spacing distance is micron-level, and the length is about 2 microns; the connection between waveguides 2, 8 and curved waveguides 3, 4 uses the same length of lateral offset distance to connect the ports, the lateral offset distance is micron-level, and the length is about 0.5 microns. The left port of waveguide 1 is the input port port1 and the right port is the straight port port2, the left port of waveguide 9 is the download port port3 and the right port is port4, and waveguides 2, 3, 8, 4 form a complete racetrack microring structure. The parallel straight waveguides are waveguides 1, 2, 8, 9, and the metal electrode group 5 is also placed in parallel. According to the above method, the structure of the racetrack microring electro-optical switch can be formed.

[0021] When working, along the direction of the white arrow in the figure, the optical signal is input from the input port port1, and the optical signal is directly transmitted without coupling in the symmetrical directional coupler composed of waveguide 2 and waveguide 1, and is transmitted along waveguide 1, and finally output from the output port port2. At this time, the electrode group 5 applies a 25V voltage to regulate the optical signal, that is, when the electrode group 5 works actively, the refractive index of the modulation area material of waveguides 1 and 2 is changed, thereby changing the effective refractive index of the mode, changing the coupling coefficient, and realizing the above working conditions. The above working conditions are based on the resonance principle of the micro-ring runway, that is, the length of the waveguide 2 is designed to be equal to the length of the directional coupler in the range of 8000 microns, and the spacing distance is designed to be about 1 micron, so that the optical signal input to port1 is cross-transmitted in the directional coupler composed of waveguide 2 and waveguide 1 when the electrode group 5 is not working passively, and is directly transmitted when the motor group 5 works actively, as shown in the figure, without optical path conversion, and finally output from port2. At this time, if the wavelength of the optical signal input to port1 does not meet the formula of micro-ring resonance, it will be directly transmitted to port2 at this length distance.

[0022] like Figure 2 As shown in the figure, the overall structure of a racetrack micro-ring electro-optical switch based on lithium niobate and the working status of the optical signal output direction of one download port. Figure 1The above situations are consistent, and the same structural components and structural parameters are used. In this working condition, along the direction of the white arrow on the way, light enters from Port 1, and in the directional coupler composed of waveguide 2 and waveguide 1, when the electrode group 5 is not working and passive, the light is output from the cross end of the directional coupler, that is, the right side of waveguide 2, and the light is output from the right side of waveguide 2 along the 180-degree curved waveguide 3 on the right side, and then transmitted to waveguide 8. In the directional coupler composed of waveguide 8 and waveguide 9, the optical signal is coupled and output from port 3 at the cross end. At this time, the critical coupling state of the microring is reached, the principle of microring resonance is satisfied, the coupling efficiency is reached to the highest state, and the reconfigurable transmission function of the optical signal is realized at the same time.

[0023] like Figure 3 As shown, the cross section of the electro-optic modulation area of ​​the racetrack micro-ring electro-optic switch based on lithium niobate is a cross section including structures 1, 2, and 5, including the cross section of the lithium niobate LN dual waveguide directional coupler, the cross section of the SiO2 upper cladding above the waveguide, the structural cross section of the motor group 5, the cross section of the SiO2 buried layer, and the cross section of the Si substrate. Among them, the Si, SiO2, LN, and AU indicated by the black straight line are the names of the materials of the structure, HAU and WAU are the height and width of the AU gold electrode, Hrib, Hslab, and WLN are the ridge height and plate height of the ln lithium niobate waveguide and the waveguide width, Gap is the slit width between the dual waveguides, and Hsio2 is the height of the SiO2 upper cladding. The above are all double arrows to indicate the distance of the corresponding structure. The material properties and light wavelength of the waveguide, the single-mode polarized light field determine the structural parameters of the waveguide, the thickness of the SiO2 cladding, and the length and width of the electrode are determined by the required optimal electro-optic modulation efficiency, minimum loss, and minimum footprint.

[0024] like Figure 4 As shown, the figure shows the cross-section of the air groove and the 180-degree curved part of the lithium niobate curved waveguide, including the cross-section of waveguides 4, 7 and 3, 6, including the cross-section of the lithium niobate waveguide and the sio2 upper cladding. The air groove at a certain distance to the left of the lithium niobate waveguide is etched in the lithium niobate planar waveguide and is labeled with LN, AIR, sio2. Among them, the black double arrow L of the air groove indicates the width of the air groove, Hslab is the height of the air groove, the white arrow indicates that the structure is sio2 material, and gap is the length of the waveguide from the air groove. Among them, the width of the air groove and the distance gap are determined by the minimum light transmission loss in the curved waveguide.

[0025] like Figure 5As shown, the 180-degree Euler bending structure on the left side of the racetrack micro-ring structure includes waveguide structures 4, 7, and 2. The black straight line indicates that waveguides 4 and 2 are made of lithium niobate materials, and waveguide 7 is an air groove. The black double arrow indicates the distance between the air groove and waveguide 4. The lateral offset between waveguides 2 and 7 is applied in the area shown in the figure. Reff and Rmin in the circular area are two radii of the Euler bending structure. Reff indicates the radius corresponding to the bending arc at the connection between waveguides 2 and 4, and Rmin indicates the radius corresponding to the rear middle point of the Euler bending radius, where Rmin*1.38=Reff, and the curvature of the 90-degree bending arc changes linearly with the long-range bending arc. The Euler bending structure is applied to the air groove and the curved waveguide, so that the etching tracks of the two are consistent and the spacing remains unchanged. The Reff and Rmin of the Euler bending need to meet the needs of the micro-ring phase change and the minimum loss.

[0026] The above is only a preferred specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be covered within the protection scope of the present invention.

Claims

1. The present invention proposes a racetrack micro-ring electro-optical switch structure based on lithium niobate, characterized in that: The electro-optical switch structure is realized based on a racetrack microring resonator on a lithium niobate platform, and includes an optical circuit cascaded by two upper and lower bus waveguides and a middle racetrack microring resonator; the optical circuit includes an upper bus waveguide 1, a racetrack microring resonator (waveguides 2, 3, 8, 4), a motor group 5, air grooves 6, 7, and a lower bus waveguide 9. All of the above structures are combined to form a racetrack microring electro-optical switch structure.

2. The lithium niobate-based racetrack micro-ring electro-optical switch structure according to claim 1, characterized in that: The cross-section of the waveguides 1, 2 and the motor group 5 constituting the structure is defined by the parameters of the cross-sectional diagram shown in FIG3, including the height HAU and width WAU of the electrode group 5, the ridge height Hrib of the two lithium niobate waveguides separated by a gap, the plate height Hslab, the waveguide width WLN, the shape and thickness Hsio2 of the SiO2 cladding strip covering the lithium niobate waveguide, and the SiO2 buried layer and Si substrate below. The cross-section of the micro-ring bending part 4, 3 and the air groove structure 7, 6 is defined by the parameters shown in FIG4, including the structural parameters of a lithium niobate waveguide consistent with FIG3, the height Hsio2 and shape structure of the SiO2 cladding, the gap between the lithium niobate waveguide and the air groove, the width L and height Hslab of the air groove, and the SiO2 buried layer and Si substrate below. The top view of the air groove 7, curved waveguide 4, and straight waveguide 2 constituting the Euler bending structure of the microring is shown in FIG5, including the gap between the air groove 7 and the curved waveguide 4, the lateral offset between the straight waveguide 2 and the curved waveguide 4, and the radius Reff and Rmin of the input end and the middle point of the curved waveguide, wherein the curved waveguide and the air groove are designed according to the principle of Euler bending. The above structural parameters are applicable to the racetrack microring resonator.

3. The lithium niobate based racetrack micro-ring electro-optical switch structure and its structural parameters according to claims 1 and 2, characterized in that: Through the critical coupling condition of the racetrack microring resonator, a wide range of FSR filtering effects are achieved, a large optical transparency window is created, and the light field signal is modulated by switching the electrode group, and the absorption of light is changed to change the switching state of the light signal. By adding an air groove structure and a lateral offset between the straight waveguide and the curved waveguide, and using an Euler curved structure to reduce the transmission loss of the optical signal, a high-speed, low-loss multi-directional controllable switching function is achieved.

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