MZ type electro-optical modulator and preparation method thereof

Abstract

The invention provides an MZ type electro-optical modulator and a preparation method thereof. The MZ type electro-optical modulator comprises a substrate layer, a silicon waveguide layer, a first isolation layer, a silicon nitride waveguide layer, a second isolation layer, a lithium niobate film layer, a third isolation layer and a metal layer from bottom to top. The surface of the substrate layer is an insulating material layer; the silicon waveguide layer comprises a beam splitter and a beam combiner which are positioned on two opposite sides, and more than two modulation arms which are respectively connected with the beam splitter and the beam combiner and oppositely extend to corresponding coupling areas; a mixed waveguide formed by a silicon nitride strip-shaped waveguide of the silicon nitride waveguide layer and a lithium niobate thin film layer located on the upper layer of the silicon nitride strip-shaped waveguide serves as an active modulation arm, and the thickness of a second isolation layer located between the silicon nitride waveguide layer and the lithium niobate thin film layer is smaller than 50 nm. According to the invention, the performance of the modulator is improved, the transmission loss is reduced, the preparation process is simplified, the preparation cost is reduced, and large-scale popularization and application of the modulator are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, in particular to a silicon optical device, and specifically to an MZ type electro-optical modulator and a preparation method thereof. Background Art

[0002] Silicon photonics (SiPh) technology uses photons as the transmission carrier of information, and has the advantages of high speed, high bandwidth, low latency, and low power consumption. It can be widely used in high-performance computing and optical communications by integrating modulators, detectors, and a variety of functional passive devices to achieve on-chip optical interconnection. At the same time, due to its compatibility with complementary metal oxide semiconductor (CMOS) manufacturing processes, it is expected to achieve the preparation of large-scale high-integration chips through low-cost manufacturing processes. The electro-optic modulator can realize the conversion function from electrical signals to optical signals and is one of the core devices of silicon photonics technology.

[0003] Multilayer SiN-on-SOI platform, that is, one or more SiN waveguide layers are deposited on the Si photonic layer, can simultaneously take advantage of the entire set of optical functional devices on the SOI platform and the ultra-low transmission loss of silicon nitride waveguides. At the same time, SOI or SiN photonic wafers can provide a platform for integrating various other optical materials, and under the requirements of CMOS compatibility, various functional materials can be mixed and integrated with silicon to enhance the functionality of the silicon photonic platform.

[0004] Lithium niobate materials are widely used in high-speed modulation due to their advantages such as wide transparent window and large electro-optic coefficient. Existing lithium niobate hybrid integrated modulators are generally divided into two types: silicon nitride-lithium niobate hybrid integration and silicon-lithium niobate hybrid integration. However, these two types of modulators have different problems. For example, the transmission loss of the silicon-lithium niobate hybrid integration platform is high, and the silicon nitride-lithium niobate heterogeneous integration platform has lower transmission loss than the silicon-lithium niobate heterogeneous platform, but lacks the ability to integrate with active devices such as silicon germanium detectors.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0006] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to provide an MZ type electro-optic modulator and a preparation method thereof, so as to solve the different problems existing in the existing lithium niobate hybrid integrated modulators. For example, the transmission loss of the silicon-lithium niobate hybrid integrated platform is relatively high, and the silicon nitride-lithium niobate heterogeneous integrated platform has lower transmission loss than the silicon-lithium niobate heterogeneous platform, but lacks the ability to be integrated with active devices such as germanium silicon detectors.

[0007] To achieve the above-mentioned purpose and other related purposes, the present invention provides an MZ type electro-optic modulator, which comprises, from bottom to top, a substrate layer, a silicon waveguide layer, a first isolation layer, a silicon nitride waveguide layer, a second isolation layer, a lithium niobate film layer, a third isolation layer and a metal layer; the surface of the substrate layer is an insulating material layer; the silicon waveguide layer comprises a beam splitter and a beam combiner located on opposite sides, and two or more modulation arms respectively connected to the beam splitter and the beam combiner and extending toward each other to corresponding coupling regions; a ridge-type hybrid waveguide composed of a silicon nitride strip waveguide of the silicon nitride waveguide layer and a lithium niobate film layer located on the upper layer thereof serves as an active modulation arm; and a second isolation layer located between the silicon nitride waveguide layer and the lithium niobate film layer has a thickness of less than 50 nm.

[0008] Optionally, the MZ type electro-optic modulator further includes an upper cladding layer covering the metal layer.

[0009] Optionally, the refractive indexes of the first isolation layer, the second isolation layer, the third isolation layer and the upper cladding layer are smaller than the refractive indexes of the respective adjacent waveguide layers.

[0010] Optionally, the substrate layer includes a silicon wafer and a silicon dioxide layer on the silicon wafer, and the first isolation layer, the second isolation layer, the third isolation layer and the upper cladding layer all include a silicon dioxide layer.

[0011] Optionally, the thickness of the silicon waveguide layer is 200nm-250nm, the thickness of the first isolation layer is 120nm-150nm, the thickness of the silicon nitride waveguide layer is 350nm-450nm, the thickness of the second isolation layer is 10nm-45nm, the thickness of the lithium niobate thin film layer is 350nm-450nm, the thickness of the third isolation layer is 150nm-250nm, the thickness of the metal layer is 0.5μm-1.5μm, and the thickness of the upper cladding layer is 1.5μm-2.5μm.

[0012] More optionally, the thickness of the silicon waveguide layer is 220nm, the thickness of the first isolation layer is 140nm, the thickness of the silicon nitride waveguide layer is 400nm, the thickness of the second isolation layer is 30nm, the thickness of the lithium niobate thin film layer is 400nm, the thickness of the third isolation layer is 200nm, the thickness of the metal layer is 1μm, and the thickness of the upper cladding layer is 2μm.

[0013] Optionally, the material of the metal layer includes several of aluminum, silver, copper, gold and platinum.

[0014] Optionally, a groove is formed in a region of the substrate layer corresponding to the silicon waveguide.

[0015] The present invention also provides a method for preparing an MZ type electro-optic modulator as described in any of the above schemes, comprising the steps of preparing a silicon waveguide layer on a substrate layer, and then sequentially preparing a first isolation layer, a silicon nitride waveguide layer, a second isolation layer, a lithium niobate thin film layer, a third isolation layer, a metal layer and an upper cladding layer, wherein the lithium niobate thin film layer is prepared on a substrate different from the silicon waveguide layer and then bonded to the top of the silicon nitride waveguide layer.

[0016] Optionally, the method for preparing a silicon waveguide layer on a substrate layer includes providing an SOI wafer, and photolithographically etching a top silicon layer of the SOI wafer to obtain a silicon waveguide layer having a patterned silicon waveguide and unit devices.

[0017] Optionally, after preparing a silicon waveguide layer on the substrate layer, a first isolation layer, a silicon nitride waveguide layer and a second isolation layer are prepared in sequence to obtain a first bonded wafer, which is then directly bonded to a second bonded wafer having a lithium niobate thin film layer formed thereon, wherein the lithium niobate thin film layer and the second isolation layer are bonded to each other, and then the substrate of the second bonded wafer is thinned, and then a metal layer and an upper cladding layer are prepared on the side of the lithium niobate thin film layer facing away from the silicon nitride waveguide layer.

[0018] As described above, the MZ type electro-optic modulator and its preparation method provided by the present invention have the following beneficial effects: This embodiment creatively prepares an MZ type electro-optic modulator with a three-layer waveguide of silicon-silicon nitride-lithium niobate and carefully designs the position and thickness of each structural layer, so that the excellent electro-optic modulation performance of lithium niobate material and the low light property of silicon nitride material with lower transmission loss compared to silicon can be fully utilized, which can effectively reduce transmission loss and avoid etching of lithium niobate material. At the same time, silicon material is used in the non-modulation arm area, and the active capability of silicon material and the potential for monolithic integration with other active devices such as germanium silicon detectors are utilized, so that on-chip integration of modulators and detectors can be realized, which helps to simplify its preparation process, reduce preparation costs, and contribute to its large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shown is a schematic diagram of an exemplary planar structure of an MZ type electro-optical modulator provided by the present invention.

[0020] Figure 2 Display as Figure 1 Schematic cross-section perpendicular to the optical waveguide transmission direction in a single modulation arm.

[0021] Figure 3 Shown is a schematic diagram of the optical mode field distribution in a SiN-LN (lithium niobate) hybrid waveguide.

[0022] Figure 4 Shown is a schematic diagram of the electrostatic field distribution in a single modulation arm.

[0023] Figure 5 Shown is a schematic diagram of how the characteristic impedance of the transmission line changes with the width of the signal electrode and the thickness of the electrode.

[0024] Figure 6 Shown is a schematic diagram of the transmission line attenuation coefficient changing with the signal electrode width and electrode thickness.

[0025] Figure 7 Shown is a schematic diagram of the variation of the microwave effective refractive index of the transmission line with the width of the signal electrode and the electrode thickness.

[0026] Figure 8 The graph shows the electro-optical response curve of the electro-optical modulator corresponding to different modulation zone lengths, that is, a schematic diagram of the relationship between optical power and electrical signal frequency.

[0027] Fig. 9 Shown is an optical mode transmission diagram of the optimized silicon-SiN / LN interlayer coupler, where the abscissa is the position of the structure corresponding to the x-axis and the ordinate is the position corresponding to the z-axis.

[0028] Fig.10 Shown is the transmission spectrum diagram of the optimized silicon-SiN / LN interlayer coupler, where the horizontal axis is the light wavelength and the vertical axis is the light power intensity received by the monitor (the total amount is 1).

[0029] Fig.11 Shown is a schematic diagram of the preparation process of the MZ type electro-optic modulator provided by the present invention. DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general proportion, and the schematic diagram is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0031] For ease of description, spatially relative terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatially relative terms are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the drawings. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

[0032] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0033] It should be noted that the diagrams provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the diagrams only show the components related to the present invention rather than the number, shape and size of the components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed arbitrarily, and the layout of the components may also be more complicated. In order to make the diagrams as concise as possible, not all structures are marked in the drawings.

[0034] like Figure 1 and Figure 2 As shown, the present invention provides an MZ type electro-optic modulator, which includes, from bottom to top, a substrate layer 11, a silicon waveguide layer 12, a first isolation layer 13, a silicon nitride waveguide layer 14, a second isolation layer 15, a lithium niobate thin film layer 16, a third isolation layer 17 and a metal layer 18.

[0035] The surface of the substrate layer 11 is an insulating material layer 111. For example, in some examples, the substrate layer 11 is a single structural layer, that is, it is made of insulating material as a whole, for example, the substrate layer 11 is quartz glass or other organic material layers such as BCB (benzocyclobutene) with a refractive index lower than the waveguide layer. In some other examples, the substrate layer 11 is a composite structural layer, that is, it is composed of multiple material layers stacked up and down. For example, the substrate layer 11 includes a bottom silicon wafer layer and a silicon dioxide layer located on the upper surface of the silicon wafer layer, and the silicon dioxide layer can be formed on the surface of the silicon wafer layer by a thermal oxidation process and / or a chemical vapor deposition process. The substrate layer 11 in this embodiment is preferably a silicon-based material, for example, the aforementioned composite structural layer composed of a silicon wafer layer and a silicon oxide layer, which makes the MZ type electro-optical modulator provided by the present invention better compatible with the CMOS process. In a further example, a groove is formed in the region of the substrate layer 11 corresponding to the silicon waveguide, so that the silicon waveguide is in a suspended state. This will help reduce or even prevent heat from diffusing outward from the substrate layer 11, help reduce thermal modulation loss, and further improve the electro-optical modulation efficiency of the modulator. In other examples, a heat insulation layer may be provided on the surface of the substrate layer 11 or the surface of the groove.

[0036] The silicon waveguide layer 12 forms a silicon waveguide structure, for example, includes a beam splitter 121 and a beam combiner 122 located on opposite sides (the beam combiner 122 and the beam splitter 121 are located in the phase modulation area, that is, on opposite sides of the coupling area), and more than two modulation arms 123 respectively connected to the beam splitter 121 and the beam combiner 122 and extending toward the corresponding coupling areas. In this embodiment, two silicon modulation arms 123 are taken as an example.

[0037] The hybrid waveguide composed of the silicon nitride strip waveguide of the silicon nitride waveguide layer 14 and the lithium niobate (LN) waveguide layer located on the upper layer thereof serves as an active modulation arm. Each isolation layer is used to isolate adjacent waveguide layers, wherein the thickness of the second isolation layer 15 located between the silicon nitride waveguide layer 14 and the lithium niobate film layer 16 is less than 50 nm. Due to the structural improvement, the modulator of this embodiment does not have the RF loss problem, so that the thickness of the second isolation layer 15 can be made very small, or even completely removed, to obtain higher modulation efficiency.

[0038] The silicon waveguide layer 12 is the passive region of the electro-optic modulator and is the region for realizing the wiring, beam splitting and beam combining of the optical path. Figure 1 The beam splitter 121 shown in the figure is on the left side of the modulation region and the beam combiner 122 is on the right side, but the silicon waveguide structure in the silicon waveguide layer 12 is symmetrically distributed, so the left side can also be considered as the beam combiner 122 and the right side can be considered as the beam splitter 121, depending on the light transmission direction. The silicon waveguide layer 12 has a coupling region (such as Figure 1The light transmitted in the silicon waveguide layer 12 can be transmitted through Figure 1 The coupling region on the left is coupled to the SIN-LN hybrid waveguide. The light modulated in the hybrid waveguide can be transmitted through Figure 1 The coupling region on the right is coupled back to the silicon waveguide layer 12. To improve the coupling efficiency, the silicon waveguide layer 12 has a tapered structure corresponding to the coupling region. That is, in the coupling region, the width of the silicon waveguide layer 12 changes linearly along the transmission direction of the light. Figure 1 The width of the coupling region on the left gradually decreases along the light transmission direction, while Figure 1 The width of the coupling region on the right gradually increases along the light transmission direction.

[0039] Lithium niobate has the characteristic that the refractive index changes in direct proportion to the strength of the applied electric field. Therefore, when an electric field is applied to the lithium niobate film layer 16, the refractive index of the lithium niobate film layer 16 can be changed, thereby changing the propagation characteristics of light to achieve phase modulation. The ridge-type hybrid waveguide (the rib of the ridge is a silicon nitride waveguide, and the slab of the ridge is a lithium niobate material) composed of a silicon nitride waveguide layer 14 and a lithium niobate film layer 16 having a refractive index different from that of lithium niobate can enhance the ability of the waveguide structure to limit the light field, reduce light loss, and improve modulation efficiency. Of course, in some other examples, the lithium niobate film layer 16 can be replaced by other electro-optical material layers with linear electro-optical effects, such as lithium tantalate, lithium titanium tantalate, barium titanate, lead zirconate titanate (PZT for short) or some electro-optical polymers. But relatively speaking, lithium niobate has been fully proven to have excellent electro-optical, acousto-optical and optical nonlinear effects, and its preparation process is relatively more mature.

[0040] The metal layer 18 serves as a metal electrode, and its main function is to transmit microwave signals to the electrode through an external metal probe when the device is working.

[0041] The exemplary working principle of the MZ type electro-optical modulator provided in this embodiment is that the light emitted by a device such as a laser enters the grating coupler of the silicon waveguide layer 12 from the input optical fiber 20, that is, the beam splitter 121, is split by the 1*2MMI (multi-mode interference coupler) of the silicon waveguide layer 12, and then is coupled into the hybrid waveguide through the interlayer coupler composed of the tapered light coupling area of ​​the silicon waveguide layer 12 and the silicon nitride / lithium niobate hybrid waveguide, that is, enters the active modulation arm area for propagation, and then also passes through the interlayer coupler (that is, the beam splitter 121) back to the silicon waveguide layer 12, is combined by the 1*2MMI of the silicon waveguide layer, and finally is coupled to the output optical fiber 20 by the silicon grating, and is transmitted to a germanium silicon detector such as through the optical fiber 20.

[0042] The present invention creatively prepares an MZ-type electro-optic modulator with a three-layer waveguide of silicon-silicon nitride-lithium niobate and carefully designs the position and thickness of each structural layer, so that the excellent electro-optic modulation performance of lithium niobate material and the low-light property of silicon nitride material with lower transmission loss compared to silicon can be fully utilized, which can effectively reduce transmission loss and avoid etching of lithium niobate material. At the same time, silicon material is used in the non-modulation arm area, and the active ability of silicon material and the potential for monolithic integration with other active devices such as germanium silicon detectors are utilized, so that on-chip integration of modulators and detectors can be realized, which helps to simplify its preparation process, reduce preparation costs, and facilitate its large-scale promotion and application.

[0043] In some examples, the MZ type electro-optic modulator further includes an upper cladding layer 19 covering the metal layer 18. The upper cladding layer 19 is usually an insulating material layer 111, which can not only prevent the metal layer 18 from being oxidized and contaminated, but also reduce the distribution range of the light evanescent field, which helps to further improve the performance of the modulator. The upper cladding layer 19 can be, for example, any one of inorganic materials such as a silicon oxide layer, a silicon oxynitride layer, and a silicon nitride layer. In some other examples, the upper cladding layer 19 can also be an organic material layer such as a polyimide layer.

[0044] To ensure the performance of the modulator, the refractive index of the first isolation layer 13, the second isolation layer 15, the third isolation layer 17 and the upper cladding layer 19 is preferably less than the refractive index of the adjacent waveguide layer. The materials of the first isolation layer 13, the second isolation layer 15, the third isolation layer 17 and the upper cladding layer 19 can be the same or different. In this embodiment, since the material of the first waveguide layer is silicon, the material of the second waveguide layer is silicon nitride, and the material of the third waveguide layer is lithium niobate, from the perspective of simplifying the preparation process and improving the interface performance of different material layers, the first isolation layer 13, the second isolation layer 15, the third isolation layer 17 and the upper cladding layer 19 are preferably silicon dioxide layers, or can also be silicon oxynitride layers. When a silicon oxynitride layer is used, its refractive index can be adjusted by adjusting the oxygen content and / or oxygen in the silicon oxynitride layer to better match the adjacent waveguide layer. Or in some examples, when the relevant isolation layer uses a silicon oxynitride layer, the isolation layer can have a gradient refractive index.

[0045] The metal layer 18 needs to be made of a material with good electrical conductivity. For example, the material of the metal layer 18 can be selected from aluminum, silver, copper, gold and platinum. That is, the metal layer 18 can be a single metal material or an alloy. In order to be more compatible with the CMOS manufacturing process, the metal layer 18 in this embodiment is preferably aluminum or copper.

[0046] The thickness of each material layer has a great influence on the electro-optic adjustment performance and transmission loss of the electro-optic modulator, so the thickness of each material layer needs to be carefully designed, and it is not acceptable to be too thick or too thin. Through a large number of experiments, it is found that the thickness of each material layer is preferably as follows: the thickness of the silicon waveguide layer 12 is 200nm-250nm (the numerical range in this embodiment, unless otherwise specified, refers to the end point value), the thickness of the first isolation layer 13 is 120nm-150nm, the thickness of the silicon nitride waveguide layer 14 is 350nm-450nm, the thickness of the second isolation layer 15 is 10nm-45nm, the thickness of the lithium niobate film layer 16 is 350nm-450nm, the thickness of the third isolation layer 17 is 150nm-250nm, the thickness of the metal layer 18 is 0.5μm-1.5μm, and the thickness of the upper cladding layer 19 is 1.5μm-2.5μm. It should be noted that, since the thickness of each material layer is not necessarily the same at each location, the above values ​​refer to the values ​​of the corresponding material layer at the location with the maximum thickness. In a specific example, the thickness of the silicon waveguide layer 12 is 220nm, the thickness of the first isolation layer 13 is 140nm, the thickness of the silicon nitride waveguide layer 14 is 400nm, the thickness of the second isolation layer 15 is 30nm, the thickness of the lithium niobate film layer 16 is 400nm, the thickness of the third isolation layer 17 is 200nm, the thickness of the metal layer 18 is 1μm, and the thickness of the upper cladding layer 19 is 2μm.

[0047] In some examples, the MZ type electro-optic modulator may also be provided with a reflector (not shown), which may be arranged along the transmission path of light, for example, on the side (non-optical coupling surface) of one of the waveguide layers. For example, in one example, the reflector is provided on the side of the silicon waveguide layer. More specifically, the reflector is provided on both sides of the coupling region of the silicon waveguide layer. The reflector is, for example, a Bragg reflector or a metal reflector. Providing a reflector helps to further improve the performance of the device.

[0048] In some examples, the silicon waveguide layer 12 is an array structure, that is, it includes a plurality of silicon waveguides arranged in an array. In this case, an isolation material layer can be provided between adjacent silicon waveguide structures to prevent optical crosstalk. For example, in this embodiment, an isolation material can be provided between two silicon modulation arms 123. The isolation material layer is, for example, an insulating material layer having photochromic properties, thereby preventing light leaking from different optical waveguides from crosstalking.

[0049] To verify the performance of the MZ electro-optic modulator of this embodiment, the inventors conducted a large number of experiments. After simulation optimization, an MZ electro-optic modulator based on a silicon-silicon nitride-lithium niobate hybrid integrated platform with an electro-optic bandwidth of more than 130 GHz and a half-wave voltage length product of 2.58 Vcm was achieved in the TE (Transverse Electric) mode at a wavelength of 1550 nm. The optical mode field and electrostatic field distribution in the simulated single-ended modulation arm 123 are shown as follows: Figure 3 and Figure 4 The port characteristics of the coplanar electrode transmission line, including the characteristic impedance, attenuation coefficient, and microwave effective refractive index, are shown in Figure 2. The changes of the signal electrode width and electrode thickness are shown in Figure 2. Figures 5 to 7 As shown; the electro-optic response curves of the electro-optic modulators corresponding to the different modulation zone lengths after the optimized size are shown as follows Figure 8 As shown; at the same time, the simulation optimization obtained an interlayer coupler structure with an insertion loss of 1dB, and its optical mode transmission diagram is shown in Fig. 9 As shown, the transmission spectrum at 1500-1600nm is as follows Fig.10 These simulation results show that the performance of the electro-optic modulator provided by this embodiment is not inferior to that of the existing silicon-lithium niobate hybrid integrated platform and silicon-lithium niobate heterogeneous platform, but it also has the advantages of low transmission loss of silicon nitride-lithium niobate heterogeneous integrated platform and the ability of silicon-lithium niobate hybrid integrated platform to be integrated with active devices such as germanium silicon detectors.

[0050] The present invention also provides a method for preparing an MZ type electro-optic modulator, which can be used to prepare an MZ type electro-optic modulator as described in any of the above schemes. Therefore, the above introduction to the MZ type electro-optic modulator can be quoted here in its entirety, and will not be repeated for the purpose of brevity. The method for preparing the MZ type electro-optic modulator provided in this embodiment includes the steps of preparing a first isolation layer 13, a silicon nitride waveguide layer 14, a second isolation layer 15, a lithium niobate film layer 16, a third isolation layer 17, a metal layer 18 and an upper cladding layer 19 in sequence after preparing a silicon waveguide layer 12 on a substrate layer 11, wherein the lithium niobate film layer 16 is bonded to the top of the silicon nitride waveguide layer 14 after being prepared on a substrate different from the silicon waveguide layer 12. That is to say, in the preparation method provided in this embodiment, the preparation of the lithium niobate thin film layer 16 is independent of the preparation of the silicon waveguide layer 12 and the silicon nitride waveguide layer 14, which can avoid etching processing of the lithium niobate thin film layer 16, reduce or even avoid damage to the lithium niobate thin film layer 16 during the processing, and ensure its modulation performance.

[0051] In a preferred example, the method for preparing a silicon waveguide layer on the substrate layer 11 includes providing an SOI wafer, and performing photolithography etching on the top silicon layer of the SOI wafer to obtain a silicon waveguide layer 12 having a patterned silicon waveguide and a unit device. Of course, in other examples, the process of preparing the silicon waveguide layer 12 on the substrate layer 11 can also be to first provide a base layer. If the base layer is a wafer of semiconductor materials such as silicon, germanium wafer, germanium silicon, gallium arsenide, etc., then after providing the base layer, an insulating structure layer such as an oxide layer is first formed on the base layer, and then a polysilicon layer is formed on the insulating structure layer using a process including but not limited to chemical vapor deposition, and then the polysilicon layer is photolithographically etched to obtain the silicon waveguide layer 12. If the base layer is an insulating material such as quartz glass, a polysilicon layer can be directly formed on the base layer and then photolithographically etched. But relatively speaking, using an SOI wafer and performing photolithographic etching on the top silicon of the SOI wafer to obtain the silicon waveguide layer 12 helps to simplify the preparation process.

[0052] Next, we will combine the Fig.11 The preparation method of this embodiment is described in more detail. It should be noted that in this embodiment, each isolation layer is a silicon oxide layer, and the metal layer 18 is an aluminum layer, but in actual applications, the materials of each isolation layer and the metal layer 18 are not limited thereto.

[0053] like Fig.11 As shown, the process of preparing the MZ type electro-optic modulator in this embodiment is:

[0054] First, a first bonded wafer and a second bonded wafer are prepared; the preparation process of the first bonded wafer includes: providing an SOI wafer, photolithography and etching the top silicon layer of the SOI wafer to obtain a silicon waveguide layer 12, the bottom silicon layer of the SOI wafer constitutes a substrate layer 11, and the insulating layer of the SOI wafer constitutes an insulating material layer 111 on the substrate layer 11;

[0055] Next, a silicon dioxide layer covering the silicon waveguide layer 12 is formed as a first isolation layer 13 by using a process including but not limited to chemical vapor deposition;

[0056] Then, a silicon nitride material layer is formed on the first isolation layer 13 by using a process including but not limited to chemical vapor deposition, and the silicon nitride material layer is photoetched to obtain a silicon nitride waveguide layer 14;

[0057] Next, a silicon dioxide layer covering the silicon nitride waveguide layer 14 is formed as a second isolation layer 15 by using a process including but not limited to chemical vapor deposition, thereby obtaining a first bonded wafer;

[0058] The preparation process of the second bonding wafer is, for example, providing a substrate, the substrate being, for example, a silicon wafer having a silicon dioxide layer formed on the surface, but not limited thereto, and may also be a glass substrate or an organic material substrate;

[0059] A second bonding wafer is obtained by forming a lithium niobate thin film layer 16 on the substrate layer using a sol-gel method including but not limited to, and then directly bonding the first wafer to the second bonding wafer, wherein the lithium niobate thin film layer 16 and the second isolation layer 15 are bonded to each other;

[0060] Next, the substrate of the second bonded wafer is thinned, for example, the silicon substrate of the second bonded wafer is ground off by a grinding process and the lithium niobate material layer is thinned to a preset thickness, and then a third isolation layer 17 is formed on the lithium niobate thin film layer 16;

[0061] Then, a metal layer 18 and an upper cladding layer 19 are formed on the side of the lithium niobate thin film layer 16 facing away from the silicon nitride waveguide layer 14 , for example, on the third isolation layer 17 .

[0062] In summary, this embodiment creatively prepares an MZ-type electro-optic modulator with a three-layer waveguide of silicon-silicon nitride-lithium niobate and carefully designs the position and thickness of each structural layer, so that the excellent electro-optic modulation performance of lithium niobate material and the low-light property of silicon nitride material with lower transmission loss compared to silicon can be fully utilized, which can effectively reduce transmission loss and avoid etching of lithium niobate material. At the same time, silicon material is used in the non-modulation arm area, and the active ability of silicon material and the potential for monolithic integration with other active devices such as germanium silicon detectors are utilized, so that on-chip integration of modulators and detectors can be achieved, which helps to simplify its preparation process, reduce preparation costs, and facilitate its large-scale promotion and application. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0063] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An MZ type electro-optical modulator, characterized in that: The MZ type electro-optic modulator comprises, from bottom to top, a substrate layer, a silicon waveguide layer, a first isolation layer, a silicon nitride waveguide layer, a second isolation layer, a lithium niobate film layer, a third isolation layer and a metal layer; the surface of the substrate layer is an insulating material layer; the silicon waveguide layer comprises a beam splitter and a beam combiner located on opposite sides, and two or more modulation arms respectively connected to the beam splitter and the beam combiner and extending toward corresponding coupling regions; a hybrid waveguide composed of a silicon nitride strip waveguide of the silicon nitride waveguide layer and a lithium niobate film layer located on the upper layer thereof serves as an active modulation arm; and a second isolation layer located between the silicon nitride waveguide layer and the lithium niobate film layer has a thickness of less than 50 nm.

2. The MZ type electro-optic modulator according to claim 1, characterized in that: The MZ type electro-optic modulator further includes an upper cladding layer covering the metal layer, and the refractive indexes of the first isolation layer, the second isolation layer, the third isolation layer and the upper cladding layer are smaller than the refractive indexes of the respective adjacent waveguide layers.

3. The MZ type electro-optic modulator according to claim 2, characterized in that: The substrate layer includes a silicon wafer and a silicon dioxide layer located on the silicon wafer, and the first isolation layer, the second isolation layer, the third isolation layer and the upper cladding layer all include a silicon dioxide layer.

4. The MZ type electro-optic modulator according to claim 2, characterized in that: The thickness of the silicon waveguide layer is 200nm-250nm, the thickness of the first isolation layer is 120nm-150nm, the thickness of the silicon nitride waveguide layer is 350nm-450nm, the thickness of the second isolation layer is 10nm-45nm, the thickness of the lithium niobate thin film layer is 350nm-450nm, the thickness of the third isolation layer is 150nm-250nm, the thickness of the metal layer is 0.5μm-1.5μm, and the thickness of the upper cladding layer is 1.5μm-2.5μm.

5. The MZ type electro-optic modulator according to claim 4, characterized in that: The thickness of the silicon waveguide layer is 220 nm, the thickness of the first isolation layer is 140 nm, the thickness of the silicon nitride waveguide layer is 400 nm, the thickness of the second isolation layer is 30 nm, the thickness of the lithium niobate thin film layer is 400 nm, the thickness of the third isolation layer is 200 nm, the thickness of the metal layer is 1 μm, and the thickness of the upper cladding layer is 2 μm.

6. The MZ type electro-optic modulator according to claim 1, characterized in that: The material of the metal layer includes several of aluminum, silver, copper, gold and platinum.

7. The MZ type electro-optic modulator according to claim 1, characterized in that: A groove is formed in the substrate layer in a region corresponding to the silicon waveguide.

8. A method for preparing an MZ type electro-optical modulator as claimed in claim 1, characterized in that: The method comprises the steps of preparing a silicon waveguide layer on a substrate layer, and then sequentially preparing a first isolation layer, a silicon nitride waveguide layer, a second isolation layer, a lithium niobate film layer, a third isolation layer and a metal layer, wherein the lithium niobate film layer is prepared on a substrate different from the silicon waveguide layer and then bonded to the silicon nitride waveguide layer.

9. The method for preparing an MZ type electro-optic modulator according to claim 8, characterized in that: The method for preparing a silicon waveguide layer on a substrate layer comprises providing an SOI wafer, and performing photolithography etching on a top silicon layer of the SOI wafer to obtain a silicon waveguide layer having a patterned silicon waveguide and a unit device.

10. The method for preparing an MZ type electro-optic modulator according to claim 8, characterized in that: After preparing a silicon waveguide layer on the substrate layer, a first isolation layer, a silicon nitride waveguide layer and a second isolation layer are prepared in sequence to obtain a first bonded wafer, which is then directly bonded to a second bonded wafer having a lithium niobate film layer formed thereon, wherein the lithium niobate film layer and the second isolation layer are bonded to each other, and then the substrate of the second bonded wafer is thinned, and then a metal layer and an upper cladding layer are prepared on the side of the lithium niobate film layer away from the silicon nitride waveguide layer.

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