CN110161625B - Method for integrating silicon-based lithium niobate thin-film electro-optic modulator array - Google Patents
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Abstract
The invention aims to provide an integration method of a large-scale silicon-based lithium niobate thin-film electro-optical modulator array aiming at the defects of the prior art. The method reduces the difficulty of the preparation process of the lithium niobate crystal layer, reduces the precision requirement of the adhesion of the lithium niobate and silicon, can simultaneously complete the preparation and the adhesion of the large-scale array lithium niobate crystal layer at one time, and greatly improves the production efficiency of the silicon-based lithium niobate thin-film electro-optic modulator array; by structurally designing and optimizing the silicon crystal layer, light can be naturally alternated and mutually transmitted in the silicon waveguide and the lithium niobate waveguide, and the high-performance lithium niobate thin film electro-optic modulation effect is realized. In addition, the method utilizes the maturity advantage of the standardized silicon-based integration technology, and concentrates the complex chip preparation process on the silicon crystal layer, thereby reducing the process error in the chip manufacturing process and ensuring the performance stability of the whole silicon-based lithium niobate thin-film electro-optic modulator array.
Description
Technical Field
The invention relates to the technical field of photoelectron integrated devices, in particular to a method for integrating a silicon-based lithium niobate thin film electro-optic modulator array.
Technical Field
The electro-optical modulator loads the electric signal to the optical signal and is a signal input interface of an optical signal processing system such as optical communication, microwave photon radar and the like. The performance of the photonic device directly determines the performance of an optical signal processing system, and therefore, the photonic device becomes a very important photonic device. In order to realize an integrated electro-optical modulator on a chip, an electro-optical modulator using a standardized silicon-based integration process has been proposed (see document 1: bunjian peak, zhui, yanglin, silicon-based integrated differential electro-optical modulator and a method for manufacturing the same, national patents CN105044931B, 2015). The doped silicon is used as a light guide medium, the effective refractive index of the doped silicon waveguide can be changed through the control of the electrode, phase modulation can be completed, or a two-arm interference structure is formed, and then the phase modulation is converted into intensity modulation. However, the use of doped silicon as a light-guiding medium has several problems: doped silicon has an absorption effect on light, and the insertion loss of the electro-optic modulator can be obviously increased; the modulation efficiency of doped silicon is low, so the designed half-wave voltage is usually high, and the conversion rate of electro-optic modulation is reduced.
In order to overcome the above difficulties, researchers have developed a novel silicon-based lithium niobate hetero-integrated electro-optical modulator by using lithium niobate as a light guide medium (see document 2: m.he, et al, High-performance silicon and lithium niobate Mach-Zehnder modulators for 100Gbit/s and beyond, Nature Photonics, published online:https://doi.org/10.1038/s41566-019-0378-6,2019). According to the technology, silicon crystal is used as a light guide medium in a Y-branch part of an electro-optical modulator, and the efficiency advantage of a standardized production line is fully utilized; the electro-optical effect part adopts lithium niobate crystal as light guide material, and skillfully solves the problem of short doped silicon plate by virtue of the advantages of low loss and high electro-optical efficiency of the lithium niobate crystal. In addition, the lithium niobate crystal also has the advantage of ultra-high bandwidth range, and can be more suitable for the requirements of a future ultra-high-speed optical signal processing system. At present, the lithium niobate thin film and silicon are mixed and integrated, and the method is generally performed by epitaxial growth or bonding. Because of the characteristics of low technical difficulty and high yield of the bonding mode, the bonding mode is mostly adopted. However, the bonding method has the obvious characteristic of low production efficiency, and cannot be applied to the preparation of large-scale silicon-based lithium niobate thin-film electro-optical modulator arrays.
The number of electro-optical modulators required by existing complex photon signal processing systems (see document 3: e.g. multiple channel photon analog-to-digital conversion system: Zhouyu, Yan, Cheng Jian, optical analog-to-digital conversion device based on multi-channel demultiplexing of modulator, national invention patents CN201710401304.2, 2017; see document 4: photonic neural network: Y.Shen, et al, Deep learning with coherent nanophotonic circuits, Nature Photonics, vol.11, pp.441-446,2017, etc.) is growing geometrically. How to carry out large-scale array integration and preparation on the silicon-based lithium niobate thin-film electro-optic modulator with excellent performance is a bottleneck problem of further application of the technology.
Disclosure of Invention
The invention aims to provide a large-scale silicon-based lithium niobate thin film electro-optical modulator array aiming at the defects of the prior art, the difficulty of the preparation process of a lithium niobate crystal layer is reduced through structural design, the precision requirement of bonding of lithium niobate and silicon is reduced, the preparation and bonding of the large-scale array lithium niobate crystal layer can be simultaneously completed at one time, and the production efficiency of the silicon-based lithium niobate thin film electro-optical modulator array is greatly improved; by structurally designing and optimizing the silicon crystal layer, light can be naturally alternated and mutually transmitted in the silicon waveguide and the lithium niobate waveguide, and the high-performance lithium niobate thin film electro-optic modulation effect is realized. In addition, the method utilizes the maturity advantage of the standardized silicon-based integration technology, and concentrates the complex chip preparation process on the silicon crystal layer, thereby reducing the process error in the chip manufacturing process and ensuring the performance stability of the whole silicon-based lithium niobate thin-film electro-optic modulator array.
The technical solution of the invention is as follows:
an integration method of a silicon-based lithium niobate thin film electro-optical modulator array is characterized by comprising the following steps:
1) oxidizing the smooth silicon crystal substrate by a thermal oxidation method to form a silicon oxide film layer;
2) depositing polysilicon with a certain thickness on the silicon oxide thin film layer by using Chemical Vapor Deposition (CVD), and then forming a silicon waveguide layer of a plurality of silicon-based lithium niobate thin film electro-optical modulators with array distribution by dry etching or wet etching, wherein the silicon waveguide layer comprises optical splitters and optical couplers of all the electro-optical modulators with array distribution, the input end of each optical splitter is an incident light port, and the output end of each optical coupler is a modulated light output port; the optical output ports and the optical input ports between the modulators can be connected with each other to form a cascade, parallel and mixed structure;
3) for each electro-optical modulator in the array, performing ion implantation on two sides of a silicon waveguide which needs to be loaded with direct-current voltage, implanting phosphorus ions into one side of the silicon waveguide, and implanting boron ions into the other side of the silicon waveguide to form a PN junction crossing the silicon waveguide;
4) forming a metal layer on the silicon waveguide layer by chemical vapor deposition, removing redundant metal by a dry etching process, forming a metal connecting wire only above the PN junction, and forming a metal wire connected with the outside at the same time to complete a direct current bias electrode layer and a direct current bias input port;
5) etching a wafer-level lithium niobate wafer by using a dry method or a wet method to form a periodic ridge structure so as to finish the preparation of a lithium niobate thin film layer, wherein the lithium niobate thin film layer covers the N silicon waveguide layers distributed in an array manner;
6) aligning ridge structures on the lithium niobate thin film layer with optical couplers distributed on the silicon waveguide layer in an array manner, and bonding the lithium niobate thin film layer with the silicon waveguide layer by using an adhesive;
7) forming a layer of metal on the lithium niobate thin film layer by a chemical vapor deposition method, removing redundant metal by wet etching or dry etching, and only leaving a radio frequency metal electrode of a region needing to be loaded with a radio frequency signal on each electro-optical modulator and a radio frequency electrode metal connecting wire connected with the outside to form a radio frequency electrode layer and a radio frequency signal input port; in the array integrating N electro-optical modulators, a total of 2 × N optical splitters distributed in an array, 2 × N optical couplers distributed in an array, N direct-current voltage input ports and N radio-frequency input ports are provided.
According to one aspect of the invention, the large-scale silicon-based lithium niobate thin film electro-optical modulator array structure comprises a silicon crystal substrate layer, a silicon oxide thin film layer, a silicon waveguide layer and a lithium niobate thin film layer from bottom to top in sequence, wherein an adhesive layer is arranged between the silicon waveguide layer and the lithium niobate thin film layer and is used for bonding the silicon waveguide layer and the lithium niobate thin film layer, a direct current bias electrode layer is arranged in a region where the silicon waveguide layer needs to be loaded with direct current bias, and a radio frequency electrode layer is arranged in a region where the lithium niobate thin film layer needs to be loaded with radio frequency signals.
And a plurality of silicon-based lithium niobate thin-film electro-optic modulators are periodically arranged on the silicon crystal substrate layer, the silicon oxide thin-film layer, the silicon waveguide layer adhesive layer, the lithium niobate thin-film direct-current bias electrode layer and the radio frequency electrode layer.
All the components described are large scale arrays at the wafer (wafer) level. And simultaneously preparing a plurality of periodic structures on each layer at one time, and preparing a large-scale silicon-based lithium niobate thin-film electro-optic modulator array. Because of the periodically repeated structure, the function of each component will be described below through the structure of one of the silicon-based lithium niobate thin-film electro-optical modulators, and the working principle and process thereof will be described.
In the silicon-based lithium niobate thin film electro-optic modulator, the silicon crystal substrate layer provides a substrate material for the integration of the silicon-based lithium niobate thin film electro-optic modulator; performing an oxidation process on the silicon crystal substrate layer to form a silicon oxide film layer, wherein the silicon oxide film layer is used as a lower cladding of the optical waveguide to provide a constraint effect for light in the waveguide; finishing the growth of silicon crystals above the silicon oxide film layer to form a silicon waveguide layer; the silicon waveguide layer is etched by a dry method or a wet method, a waveguide interconnection structure comprising an optical splitter and an optical coupler can be formed, and the layer is used as a core of an optical waveguide and can complete the functions of light splitting, coupling, direct current bias and light guiding of a partial region; the adhesive layer is positioned above the silicon waveguide layer and can be used for bonding the silicon waveguide layer and the lithium niobate thin film layer; the lithium niobate thin film layer is positioned above the adhesive layer, is a complete lithium niobate crystal plate which is subjected to an etching process and is used for light guide and radio frequency signal loading in a partial region. The lithium niobate thin film layer is engraved with a ridge structure and used for enhancing the constraint effect on light during light guiding; the direct current bias electrode layer can load direct current bias voltage, an electric field is formed in a section of the silicon waveguide layer, the effective refractive index of the section is changed, and therefore phase change of light is caused; the radio frequency electrode layer can load radio frequency signals, an electric field is formed in a section of the lithium niobate thin film layer, and the effective refractive index of the section is changed, so that the phase change of light is caused.
The principle and process of the silicon-based lithium niobate thin film electro-optical modulator are described as follows:
each silicon-based lithium niobate thin film electro-optical modulator is provided with 1 optical input port, 1 or 2 optical output ports, 1 direct current voltage input port and 1 radio frequency input port. During modulation, the material used for guiding the light will change in different processes: in the light splitting and direct current bias processes, the light guide material is the silicon waveguide layer; in the process of loading the radio frequency signal, the light guide material is the lithium niobate thin film layer. Light is input from the optical input port, is conducted in the silicon waveguide layer, and is divided into two beams of light with equal intensity through the optical splitter on the silicon waveguide layer to enter two arms of the modulator. And a direct current bias signal is input from the direct current input port and is loaded on the direct current bias electrode layer to form an electric field on the silicon waveguide layer, so that the effective refractive index of the silicon waveguide layer is influenced. When the two beams pass through, phase changes are accumulated, and thus the direct current bias process is completed. After the direct current bias process is finished, the light passes through the optical coupler structure on the silicon waveguide layer, so that the two beams of light enter the lithium niobate thin film layer for conduction. And a radio-frequency signal is input from a radio-frequency input port and loaded on the radio-frequency electrode layer, an electric field is formed in a lithium niobate thin film section through which light passes, and effective refractive index change is caused, so that two beams of light passing through the lithium niobate thin film accumulate different phase differences, and the loading process of the radio-frequency signal is completed. After the radio frequency signal loading process is finished, the light is acted by the optical coupler on the silicon waveguide layer and returns to the silicon waveguide layer for conduction, and under the action of the other optical splitter, two beams of light accumulated with different phase differences interfere to form one beam of light or two beams of light for output. In the interference process, the phase difference is converted into intensity variation of light, thereby completing intensity modulation of light.
The beam splitter can use a multimode interferometer structure or an evanescent wave beam splitting structure.
The optical coupler may use a waveguide grating coupler or an evanescent wave coupler.
The adhesive layer may be benzocyclobutene (BCB).
The arrangement mode of the modulators in the silicon-based lithium niobate thin film electro-optical modulator array can adopt grid arrangement and honeycomb arrangement.
The ridge structure on the lithium niobate thin film layer can be a transverse periodic strip structure or a grid Mach-Zehnder interference structure.
Based on the technical characteristics, the invention has the following advantages:
1. the invention utilizes the standardized silicon-based integration process to realize complex structures such as interconnection among modulators, optical splitters, breakpoints and optical couplers in the silicon waveguide layer. The process precision and the production efficiency of the standardized process are fully utilized, and the functional effectiveness and the stability of the large-scale silicon-based lithium niobate thin-film electro-optic modulator array are ensured.
2. By designing a periodic structure, the large-scale silicon-based lithium niobate thin-film electro-optic modulator array can be simultaneously prepared at one time, the lithium niobate thin-film layer does not need processes such as cutting, the bonding difficulty of the modulator array is consistent with the difficulty of bonding a single modulator, and therefore the provided structure can greatly improve the preparation efficiency of the large-scale silicon-based lithium niobate thin-film electro-optic modulator array and provide a powerful support for a complex photon signal processing system.
3. The invention utilizes the silicon-based lithium niobate thin film electro-optical modulator integration technology to load radio frequency signals on the lithium niobate thin film layer, and exerts the advantages of high electro-optical efficiency, low insertion loss and ultrahigh modulation bandwidth of the lithium niobate. Can play a role in low-power consumption and large-bandwidth microwave photonic applications.
Drawings
Fig. 1 is a schematic structural diagram of an embodiment of a silicon-based lithium niobate thin film electro-optical modulator array of the present invention, wherein (a) is a schematic structural diagram in a top view, (b) is a schematic structural diagram in a longitudinal section, (c) is a schematic structural diagram in a periodic ridge shape of a lithium niobate thin film layer, and (d) is a schematic structural diagram in a grid arrangement manner of a silicon waveguide layer.
Fig. 2 is a schematic structural diagram of a silicon-based lithium niobate thin film electro-optical modulator according to an embodiment of the present invention, wherein (a) is a top view structural diagram, (b) is a longitudinal sectional diagram corresponding to a ridge structure (i.e., an area indicated by an arrow in the figure) of a lithium niobate thin film layer, and (c) is a longitudinal sectional diagram corresponding to a dc bias and rf electrode layer (i.e., an area indicated by an arrow in the figure).
Fig. 3 is a schematic diagram of the optical mode field distribution in the embodiment of the present invention, wherein (a) is a schematic diagram of the optical mode field distribution in the light guiding of the silicon waveguide layer, which corresponds to the cross-sectional view of the region of the dc bias electrode layer (7) in fig. 2(a), and (b) is a schematic diagram of the optical mode field distribution in the light guiding of the lithium niobate thin film layer, which corresponds to the cross-sectional view of the region of the rf electrode layer (8) in fig. 2 (a).
FIG. 4 is a schematic diagram of an optocoupler in accordance with an embodiment of the invention.
Fig. 5 shows a waveguide interconnection structure that can be adopted by the present invention, in which (a) is a cascade structure, (b) is a parallel structure, and (c) is a hybrid structure.
Detailed Description
The technical solution of the present invention is described in detail below with reference to the accompanying drawings and examples, and a detailed embodiment and structure are given, but the scope of the present invention is not limited to the following examples.
Referring to fig. 1, fig. 1 is a schematic partial structural view of an embodiment of a silicon-based lithium niobate thin film electro-optical modulator array of the present invention, and an integration method of the silicon-based lithium niobate thin film electro-optical modulator array of the present invention includes the following steps:
1) oxidizing the smooth silicon crystal substrate 2 by a thermal oxidation method to form a silicon oxide film layer 3;
2) depositing polysilicon with a certain thickness on the silicon oxide thin film layer 3 by using Chemical Vapor Deposition (CVD), and then forming a silicon waveguide layer 4 of a plurality of silicon-based lithium niobate thin film electro-optical modulators 1 with array distribution by dry etching or wet etching, wherein the silicon waveguide layer 4 comprises optical splitters 4.1 and optical couplers 4.2 of all the electro-optical modulators with array distribution, the input end of the optical splitter 4.1 is an incident light port, and the output end of the optical coupler 4.2 is a modulated light output port; the optical output ports and the optical input ports between the modulators can be connected with each other to form a cascade, parallel and mixed structure;
3) for each electro-optical modulator 1 in the array, performing ion implantation on two sides of a silicon waveguide which needs to be loaded with direct-current voltage, implanting phosphorus ions into one side of the silicon waveguide, and implanting boron ions into the other side of the silicon waveguide to form a PN junction crossing the silicon waveguide;
4) forming a metal layer on the silicon waveguide layer 4 by chemical vapor deposition, removing redundant metal by a dry etching process, forming a metal connecting wire only above the PN junction, and forming a metal wire connected with the outside at the same time to complete the DC bias electrode layer 7 and the DC bias input port;
5) etching a wafer-level lithium niobate wafer by using a dry method or a wet method to form a periodic ridge structure so as to finish the preparation of a lithium niobate thin film layer 6, wherein the lithium niobate thin film layer 6 covers the N silicon waveguide layers 4 distributed in an array manner;
6) aligning the ridge structure on the lithium niobate thin film layer 6 with the optical couplers 4.2 distributed in an array manner on the silicon waveguide layer 4, and bonding the lithium niobate thin film layer 6 with the silicon waveguide layer (4) by using a bonding agent 5;
7) forming a layer of metal on the lithium niobate thin film layer 6 by a chemical vapor deposition method, removing redundant metal by wet etching or dry etching, and only leaving a radio frequency metal electrode of a region needing to be loaded with a radio frequency signal on each electro-optical modulator and a radio frequency electrode metal connecting wire connected with the outside to form a radio frequency electrode layer 8 and a radio frequency signal input port; thus, in the array integrating N electro-optical modulators, there are 2 × N optical splitters 4.1 distributed in an array, 2 × N optical couplers 4.2 distributed in an array, N dc voltage input ports, and N rf input ports.
As can be seen from the top view of fig. 1(a), a plurality of lithium niobate silicon thin film electro-optical modulators 1 are simultaneously fabricated on one wafer (wafer). As can be seen from the schematic diagram of the longitudinal section, the silicon-based lithium niobate thin film electro-optic modulator array comprises a silicon crystal substrate layer, a silicon oxide thin film layer, a silicon waveguide layer, an adhesive layer, a lithium niobate thin film layer, a direct current bias electrode layer and a radio frequency electrode layer. All the components described are large scale arrays at the wafer (wafer) level. A plurality of periodic structures are simultaneously prepared on each layer at one time, and a large-scale silicon-based lithium niobate thin film electro-optic modulator array can be simultaneously prepared. Because of the periodically repeated structure, the function of each component will be described below through the structure of one of the silicon-based lithium niobate thin-film electro-optical modulators, and the working principle and process thereof will be described.
Referring to fig. 2, in a silicon-based lithium niobate thin film electro-optical modulator 1 of the present invention, the silicon crystal substrate layer 2 provides a substrate material for the integration of the silicon-based lithium niobate thin film electro-optical modulator 1; a silicon oxide film layer 3 can be formed by performing an oxidation process on the silicon crystal substrate layer 2, and the silicon oxide film layer is used as a lower cladding of the optical waveguide and provides a constraint effect for light in the waveguide; finishing the growth of silicon crystals above the silicon oxide film layer 3 to form a silicon waveguide layer 4; the silicon waveguide layer 4 is etched by a dry method or a wet method, a waveguide interconnection structure comprising the optical splitter 4.1 and the optical coupler 4.2 can be formed, and the layer is used as a core of an optical waveguide and can complete the functions of light splitting, coupling, direct current bias and light guiding of partial regions; the adhesive layer 5 is positioned above the silicon waveguide layer 4 and can be used for bonding the silicon waveguide layer 4 and the lithium niobate thin film layer 6; the lithium niobate thin film layer 6 is positioned above the adhesive layer 5, is a complete lithium niobate crystal slice which is subjected to an etching process and is used for light guide and radio frequency signal loading in a partial region. The lithium niobate thin film layer 6 is provided with a ridge structure (see fig. 1(c)) for enhancing the constraint effect on light during light guiding; the direct current bias electrode layer 7 can load direct current bias voltage, an electric field is formed in a section of the silicon waveguide layer 5, and the effective refractive index of the section is changed, so that the phase change of light is caused; the radio frequency electrode layer 8 can load radio frequency signals, an electric field is formed in a section of the lithium niobate thin film layer 6, and the effective refractive index of the section is changed, so that the phase change of light is caused.
The principle and process of the single silicon-based lithium niobate thin film electro-optical modulator 1 of the invention are described as follows:
each silicon-based lithium niobate thin-film electro-optical modulator 1 has 1 optical input port, 1 optical output port, 1 direct-current voltage input port and 1 radio-frequency input port. During modulation, the material used for guiding the light will change in different processes: referring to fig. 3, in the light splitting and dc bias processes, the light guide material is the silicon waveguide layer 4; in the process of loading the radio frequency signal, the light guide material is the lithium niobate thin film layer 6. Light is input from the optical input port, is conducted in the silicon waveguide layer 4, and is divided into two beams of light with equal intensity through the optical splitter 4.1 on the silicon waveguide layer 4 to enter two arms of the modulator. The beam splitter 4.1 in the embodiment described uses a multimode interferometer structure. A dc bias signal is input from the dc input port and applied to the dc bias electrode layer 7 to form an electric field on the silicon waveguide layer 4, thereby influencing the effective refractive index of the silicon waveguide layer 4. When two beams of light pass through the silicon waveguide layer, phase change is accumulated, so that direct current bias is completed, and after the direct current bias process is finished, the light passes through the optical coupler 4.2 structure on the silicon waveguide layer, so that the two beams of light enter the lithium niobate thin film layer 6 for conduction. The optical coupler in the embodiment is an evanescent wave coupler. Radio frequency signals are input from the radio frequency input port and loaded on the radio frequency electrode layer 8, an electric field is formed in the region of the lithium niobate thin film 6 where light passes through, effective refractive index change is caused, and therefore the two beams of light passing through the lithium niobate thin film 6 accumulate different phase differences to complete the loading process of the radio frequency signals. After the rf signal loading process is finished, the light is acted by the optical coupler 4.2 on the silicon waveguide layer and is conducted back into the silicon waveguide layer 4. In an embodiment, this optical coupler is a grating coupler. Under the action of the further beam splitter 4.1, the two beams of light accumulated with different phase differences are recombined into one beam, and the phase differences are converted into intensity changes of the light, so that the intensity modulation of the light is completed.
The function of the optical coupler 4.2 in the embodiment can be seen in fig. 4.
In the embodiment, benzocyclobutene (BCB) is used as the adhesive layer 5.
In this embodiment, the large-scale silicon-based lithium niobate thin-film electro-optic modulator array is simultaneously prepared at one time according to the large-scale integration method of the silicon-based lithium niobate thin-film electro-optic modulator array.
In the design and preparation of the silicon waveguide layer, wafer-level large-scale silicon waveguide layer design needs to be completed. Since the arrangement positions of the plurality of silicon-based lithium niobate thin-film electro-optical modulators 1 (hereinafter also referred to as "modulators"), the interconnection among the modulators, the optical splitters inside the modulators, and the optical couplers all need to be designed and completed in the silicon waveguide layer, the design of the silicon waveguide layer includes the arrangement mode of the modulators, the waveguide interconnection structure, the optical splitters, and the optical couplers. Referring to fig. 1(d), the modulator arrangement in the embodiment is a grid arrangement. Referring to fig. 5, the waveguide interconnection design may form a plurality of connection modes such as cascade, parallel, mixed connection, etc. of the modulators; inside each modulator, the design of the front and back two optical splitters 4.1 can be seen in fig. 2, and the design of the front and back two optical couplers 4.2 can be seen in fig. 2.
In the design and preparation of the direct current bias electrode layer, the design of the wafer-level large-scale direct current bias electrode 7 needs to be completed. After the design and preparation of the silicon waveguide layer, a direct current bias electrode 7 is added in a silicon waveguide area needing to be loaded with direct current bias. The specific design can be seen in fig. 2. According to the design, a DC bias electrode layer is prepared.
In the design and preparation of the lithium niobate thin film layer, a periodic ridge structure is designed on the wafer-level lithium niobate thin film layer 6 according to the design of a silicon waveguide layer, so that the constraint effect of lithium niobate on light during light guide is enhanced. Because the modulators in the embodiment are arranged in a grid manner, the ridge structures on the lithium niobate thin film layer 6 are designed as periodic stripe structures (see fig. 1(c)) and are vertically aligned with the optical couplers 4.2 on the silicon waveguide layer 4, so that the optical energy can be smoothly coupled from the silicon waveguide layer 4 to the lithium niobate thin film layer 6 and from the lithium niobate thin film layer 6 to the silicon waveguide layer 4.
In the design and preparation of the radio frequency electrode layer, the wafer-level large-scale radio frequency electrode 8 design needs to be completed. After the lithium niobate thin film layer 6 is designed and prepared, a radio frequency electrode 8 is added in the lithium niobate thin film region needing to be loaded with radio frequency signals. The specific design can be seen in fig. 2. The radio frequency electrode layer 8 is prepared as designed.
As can be seen from fig. 2(b), after the silicon waveguide layer 4 completes the dc bias process, the silicon waveguide layer 4 is etched to form an evanescent wave optical coupler 4.2, so that light enters the lithium niobate thin film layer 6 for conduction. After the radio-frequency signal loading is completed in the lithium niobate thin film layer 6, the radio-frequency signal returns to the silicon waveguide layer 4 again for conduction under the action of the waveguide grating coupler 4.2, and then the radio-frequency signal can be connected with other modulators.
Fig. 2(c) shows the layer distribution of the dc bias electrode layer 7 and the rf electrode layer 8 of the present embodiment. In order to achieve a better DC bias effect, the DC bias electrode layer 7 is located above the silicon oxide thin film layer 3 and is located at the same layer as the silicon waveguide layer 4. Thus, the influence of the electric field on the effective refractive index of the silicon waveguide layer 4 can be improved, and the DC bias effect can be further improved. Similarly, in this embodiment, the radio frequency electrode layer 8 is located above the lithium niobate thin film layer 6, so that the influence of the electric field on the effective refractive index of the lithium niobate thin film layer 6 can be improved, and the radio frequency signal loading effect is further improved.
Fig. 3 shows a schematic diagram of the distribution of the optical mode field in different regions. Fig. 3(a) shows that during dc biasing light is confined to the silicon waveguide layer 4 for conduction. Fig. 3(b) shows that light is confined in the lithium niobate thin film layer 6 for conduction during the radio frequency signal loading.
Fig. 4 depicts a schematic diagram of the waveguide optical coupler 4.2 of the present embodiment. After the radio frequency signal loading process is finished, the light conducted in the lithium niobate thin film layer 6 is subjected to the action of the grating coupler 4.2, is diffracted, and enters the silicon waveguide layer 4 to continue conducting.
Claims (5)
1. An integration method of a silicon-based lithium niobate thin film electro-optical modulator array is characterized by comprising the following steps:
1) oxidizing the smooth silicon crystal substrate (2) by a thermal oxidation method to form a silicon oxide film layer (3);
2) depositing polysilicon with a certain thickness on the silicon oxide thin film layer (3) by using Chemical Vapor Deposition (CVD), and then forming a silicon waveguide layer (4) of a plurality of silicon-based lithium niobate thin film electro-optical modulators (1) with array distribution by dry etching or wet etching, wherein the silicon waveguide layer (4) comprises optical splitters (4.1) and optical couplers (4.2) of all the electro-optical modulators with array distribution, the input end of the optical splitter (4.1) is an incident optical port, and the output end of the optical coupler (4.2) is a modulated optical output port; the optical output ports and the optical input ports between the modulators can be connected with each other to form a cascade, parallel and mixed structure;
3) for each electro-optical modulator (1) in the array, performing ion implantation on two sides of a silicon waveguide which needs to be loaded with direct-current voltage, implanting phosphorus ions on one side, and implanting boron ions on the other side to form a PN junction crossing the silicon waveguide;
4) forming a metal layer on the silicon waveguide layer (4) through chemical vapor deposition, removing redundant metal through a dry etching process, forming a metal connecting wire only above the PN junction, and forming a metal wire connected with the outside at the same time to complete the direct current bias electrode layer (7) and the direct current bias input port;
5) etching a wafer-level lithium niobate wafer by using a dry method or a wet method to form a periodic ridge structure, and finishing the preparation of a lithium niobate thin film layer (6), wherein the lithium niobate thin film layer (6) covers the N silicon waveguide layers (4) distributed in an array manner;
6) aligning the ridge structure on the lithium niobate thin film layer (6) with the optical couplers (4.2) distributed on the silicon waveguide layer (4) in an array manner, and bonding the lithium niobate thin film layer (6) with the silicon waveguide layer (4) by using an adhesive (5);
7) forming a layer of metal on the lithium niobate thin film layer (6) by a chemical vapor deposition method, removing redundant metal by wet etching or dry etching, and only leaving a radio frequency metal electrode of a region needing to be loaded with a radio frequency signal on each electro-optical modulator and a radio frequency electrode metal connecting wire connected with the outside to form a radio frequency electrode layer (8) and a radio frequency signal input port; in the array integrating N electro-optical modulators, a total of 2 × N optical splitters (4.1) distributed in an array, 2 × N optical couplers (4.2) distributed in an array, N direct-current voltage input ports and N radio-frequency input ports are provided.
2. The integration method of the silicon-based lithium niobate thin film electro-optic modulator array according to claim 1, wherein the optical splitter (4.1) is a multimode interferometer structure or an evanescent wave optical splitting structure.
3. The method for integrating the silicon-based lithium niobate thin film electro-optic modulator array according to claim 1, wherein the optical coupler (4.2) is a waveguide grating coupler or an evanescent wave coupler.
4. The method of claim 1, wherein the modulators in the silicon-based lithium niobate thin film electro-optic modulator array are arranged in a grid or honeycomb manner.
5. The integration method of the silicon-based lithium niobate thin film electro-optical modulator array according to any one of claims 1 to 4, wherein the ridge structure on the lithium niobate thin film layer is a laterally periodic strip structure or a grid Mach-Zehnder interference structure.
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| WO2021142588A1 (en) * | 2020-01-13 | 2021-07-22 | 华为技术有限公司 | Electro-optical modulator and manufacturing method therefor, and chip |
| CN111276562B (en) * | 2020-02-19 | 2023-07-25 | 上海交通大学 | Photoelectric monolithic integration system based on lithium niobate-silicon nitride wafer |
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| CN111461317B (en) * | 2020-04-03 | 2022-04-01 | 上海交通大学 | Single-chip integrated photon convolution neural network computing system and preparation method thereof |
| CN113777720B (en) * | 2020-06-10 | 2024-05-17 | 青岛海信宽带多媒体技术有限公司 | Optical module |
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