MZ electro-optic modulator and manufacturing method therefor

Abstract

Provided in the present invention are an MZ electro-optic modulator and a manufacturing method therefor. The MZ 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 which are located on two opposite sides, and two or more modulation arms which are respectively connected to the beam splitter and the beam combiner and oppositely extend to corresponding coupling areas; a silicon nitride strip waveguide of the silicon nitride waveguide layer and the lithium niobate film layer located above same form a mixed waveguide that serves as an active modulation arm; the thickness of the second isolation layer located between the silicon nitride waveguide layer and the lithium niobate film layer is less than 50 nm. The present invention helps to improve the performance of the modulator and reduces transmission loss, and also helps to simplify the manufacturing process therefor and reduce manufacturing costs, thus facilitating large-scale popularization and application thereof.

Description

MZ type electro-optical modulator and its manufacturing method 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 a carrier for information transmission, offering advantages such as high speed, high bandwidth, low latency, and low power consumption. By integrating modulators, detectors, and various functional passive components to achieve on-chip optical interconnection, it is widely applicable in fields such as high-performance computing and optical communications. Furthermore, due to its compatibility with complementary metal oxide semiconductor (CMOS) manufacturing processes, it is expected to enable the mass production of highly integrated chips using low-cost manufacturing processes. Electro-optic modulators, which convert electrical signals into optical signals, are one of the core components of silicon photonics technology.

[0003] Multilayer SiN-on-SOI platforms, where one or more SiN waveguide layers are deposited on a Si photonic layer, can simultaneously utilize the advantages of a complete 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. 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 (LNbO) is widely used in high-speed modulation due to its wide transparency window and large electro-optic coefficient. Existing LNbO hybrid integrated modulators are generally categorized as silicon nitride-LNbO hybrid and silicon-LNbO hybrid. However, each type of modulator presents distinct challenges. For example, the silicon-LNbO hybrid integrated platform suffers from high transmission loss, while the silicon nitride-LNbO heterogeneous integrated platform, while offering lower transmission loss than the silicon-LNbO heterogeneous platform, 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 merely intended to provide a clear and complete description of the technical solutions of this application and facilitate understanding by those skilled in the art. Simply because these solutions are described in the background technology section of this application, it should not be assumed that the above technical solutions are well known to those skilled in the art.

[0006] Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the object of the present invention is to provide an MZ type electro-optical modulator and a preparation method thereof, which are used 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.

[0008] To achieve the above objectives and other related objectives, the present invention provides an MZ electro-optical modulator, comprising, 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 thin 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 includes 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. The silicon nitride waveguide layer comprises a ridge hybrid waveguide formed by a silicon nitride strip waveguide and a lithium niobate thin film layer located above it, serving as an active modulation arm. The thickness of the second isolation layer located between the silicon nitride waveguide layer and the lithium niobate thin film layer is less than 50 nm.

[0009] Optionally, the MZ type electro-optic modulator further includes an upper cladding layer covering the metal layer.

[0010] 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 their respective adjacent waveguide layers.

[0011] Optionally, 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.

[0012] 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.

[0013] More optionally, 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.

[0014] Optionally, the material of the metal layer includes several of aluminum, silver, copper, gold and platinum.

[0015] Optionally, a groove is formed in a region of the substrate layer corresponding to the silicon waveguide.

[0016] The present invention also provides a method for preparing an MZ-type electro-optical modulator as described in any of the above solutions, 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 that of the silicon waveguide layer and then bonded to the silicon nitride waveguide layer.

[0017] Optionally, the method for preparing a silicon waveguide layer on a substrate layer includes providing an SOI wafer, and performing photolithography etching on a top silicon layer of the SOI wafer to obtain a silicon waveguide layer having patterned silicon waveguides and unit devices.

[0018] Optionally, after preparing a silicon waveguide layer on a substrate layer, a first isolation layer, a silicon nitride waveguide layer, and a second isolation layer are sequentially prepared 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. The substrate of the second bonded wafer is then 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.

[0019] As described above, the MZ electro-optic modulator and its preparation method provided by the present invention have the following beneficial effects: This embodiment creatively prepares an MZ electro-optic modulator having a silicon-silicon nitride-lithium niobate three-layer waveguide and carefully designs the position and thickness of each structural layer. Therefore, it can fully utilize the excellent electro-optic modulation performance of the lithium niobate material and the low-light property of the silicon nitride material with lower transmission loss compared to silicon, which can effectively reduce transmission loss and avoid etching processing of the lithium niobate material. At the same time, the non-modulation arm region is made of silicon material, taking advantage of the active capabilities of silicon material and the potential for monolithic integration with other active devices such as germanium silicon detectors, thereby achieving on-chip integration of the modulator and detector, which helps to simplify its preparation process, reduce preparation costs, and promote its large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a schematic diagram showing an exemplary planar structure of an MZ electro-optical modulator provided by the present invention.

[0021] FIG. 2 is a schematic cross-sectional view of FIG. 1 along a direction perpendicular to the transmission direction of the optical waveguide in a single modulation arm.

[0022] FIG3 is a schematic diagram showing the optical mode field distribution in a SiN-LN (lithium niobate) hybrid waveguide.

[0023] FIG4 is a schematic diagram showing the electrostatic field distribution in a single modulation arm.

[0024] FIG5 is a schematic diagram showing the variation of the characteristic impedance of the transmission line with the width and thickness of the signal electrode.

[0025] FIG6 is a schematic diagram showing the variation of the transmission line attenuation coefficient with the width of the signal electrode and the thickness of the electrode.

[0026] FIG7 is a schematic diagram showing the variation of the microwave effective refractive index of the transmission line with the width and thickness of the signal electrode.

[0027] FIG8 is a diagram showing the electro-optical response curves of the electro-optical modulator corresponding to different modulation region lengths, that is, a schematic diagram showing the relationship between optical power and electrical signal frequency.

[0028] FIG9 shows an optical mode transmission diagram of the optimized silicon-SiN / LN interlayer coupler, wherein the abscissa is the position of the structure corresponding to the x-axis, and the ordinate is the position corresponding to the z-axis.

[0029] FIG10 shows a transmission spectrum of the optimized Si-SiN / LN interlayer coupler, where the horizontal axis is the wavelength of light and the vertical axis is the optical power intensity received by the monitor (the total amount is 1).

[0030] FIG11 is a schematic diagram showing the preparation process of the MZ electro-optic modulator provided by the present invention. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention through specific examples. 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. 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 views showing the device structure will not be partially enlarged according to the general proportion, and the schematic views are only examples, 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.

[0032] For convenience, spatially relative terms such as "under," "below," "below," "below," "above," and "on" may be used herein to describe the relationship of one element or feature to other elements or features illustrated in the drawings. It will be understood that these spatially relative terms are intended to encompass orientations of the device in use or operation in addition to the orientation depicted in the drawings. Additionally, 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.

[0033] In the context of the present application, a structure described as a first feature being "above" a second feature may include embodiments where the first and second features are formed in direct contact, and may also include embodiments where an additional feature is formed between the first and second features, such that the first and second features may not be in direct contact.

[0034] It should be noted that the diagrams provided in this embodiment are merely schematic illustrations of the basic concept of the present invention. Therefore, the diagrams only show components relevant to the present invention and are not drawn to the exact number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be varied arbitrarily, and the component layout may be more complex. To minimize the illustrations, not all structures are labeled in the drawings.

[0035] As shown in FIG1 and FIG2 , the present invention provides an MZ 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.

[0036] 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 layer 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. 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 composite structural layer composed of a silicon wafer layer and a silicon oxide layer mentioned above, which makes the MZ type electro-optical modulator provided by the present invention more compatible with the CMOS process. In a further example, the substrate layer 11 is formed with a groove in the area 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 insulating layer may be provided on the surface of the substrate layer 11 or the surface of the groove.

[0037] The silicon waveguide layer 12 forms a silicon waveguide structure, for example, including 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 region, that is, on opposite sides of the coupling region), and two or more modulation arms 123 respectively connected to the beam splitter 121 and the beam combiner 122 and extending toward the corresponding coupling regions. In this embodiment, two silicon modulation arms 123 are used as an example.

[0038] The hybrid waveguide formed by the silicon nitride strip waveguide in the silicon nitride waveguide layer 14 and the lithium niobate (LN) waveguide layer located above it serves as the active modulation arm. Each isolation layer is used to isolate adjacent waveguide layers. The second isolation layer 15 located between the silicon nitride waveguide layer 14 and the lithium niobate thin film layer 16 has a thickness of less than 50 nm. Due to the structural improvements, the modulator of this embodiment eliminates RF loss issues, allowing the thickness of the second isolation layer 15 to be very small or even completely removed, achieving higher modulation efficiency.

[0039] The silicon waveguide layer 12 is the passive region of the electro-optical modulator and is the area that implements the routing, splitting, and combining of the optical path. It should be noted that although the beam splitter 121 shown in Figure 1 is on the left side of the modulation region and the beam combiner 122 is on the right side, the silicon waveguide structure in the silicon waveguide layer 12 is symmetrically distributed. Therefore, the left side can also be considered as the beam combiner 122 and the right side as the beam splitter 121, depending on the direction of light transmission. The silicon waveguide layer 12 has a coupling region (as shown by the dotted line in Figure 1). Light transmitted in the silicon waveguide layer 12 can be coupled into the SIN-LN hybrid waveguide via the coupling region on the left side of Figure 1. Light modulated in the hybrid waveguide can be coupled back into the silicon waveguide layer 12 via the coupling region on the right side of Figure 1. To improve coupling efficiency, the silicon waveguide layer 12 has a tapered structure corresponding to the coupling region. That is, in this coupling region, the width of the silicon waveguide layer 12 varies linearly along the direction of light transmission. For example, the width of the coupling region on the left side of FIG. 1 gradually decreases along the light transmission direction, while the width of the coupling region on the right side of FIG. 1 gradually increases along the light transmission direction.

[0040] Lithium niobate has the characteristic that its 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 thin film layer 16, the refractive index of the lithium niobate thin film layer 16 can be changed, thereby changing the propagation characteristics of light and achieving phase modulation. The ridge-type hybrid waveguide (the rib is a silicon nitride waveguide and the slab is a lithium niobate material) composed of a silicon nitride waveguide layer 14 with a refractive index different from that of lithium niobate and a lithium niobate thin film layer 16 can enhance the waveguide structure's ability to confine the light field, reduce optical loss, and improve modulation efficiency. Of course, in some other examples, the lithium niobate thin film layer 16 can be replaced by other electro-optical material layers with linear electro-optic effects, such as lithium tantalate, lithium titanium tantalate, barium titanate, lead zirconate titanate (PZT), or some electro-optic polymers. However, relatively speaking, lithium niobate has been fully demonstrated to have excellent electro-optical, acousto-optical, and optical nonlinear effects, and its preparation process is relatively more mature.

[0041] 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.

[0042] The exemplary working principle of the MZ electro-optical modulator provided in this embodiment is that light emitted by a device such as a laser enters the grating coupler of the silicon waveguide layer 12, i.e., the beam splitter 121, from the input optical fiber 20, is split by the 1*2 MMI (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 optical coupling region of the silicon waveguide layer 12 and the silicon nitride / lithium niobate hybrid waveguide, i.e., enters the active modulation arm region for propagation, and then also passes through the interlayer coupler (i.e., the beam splitter 121) back to the silicon waveguide layer 12, is combined by the 1*2 MMI of the silicon waveguide layer, and finally is coupled to the output optical fiber 20 by the silicon grating and transmitted via the optical fiber 20 to a detector such as a silicon germanium detector.

[0043] This invention creatively fabricates an MZ electro-optic modulator with a silicon-silicon nitride-lithium niobate three-layer waveguide and meticulously designs the position and thickness of each structural layer. This fully leverages the excellent electro-optic modulation performance of lithium niobate and the low-light properties of silicon nitride, which exhibits lower transmission loss compared to silicon. This effectively reduces transmission loss and avoids etching of the lithium niobate. Furthermore, the non-modulation arm regions utilize silicon, leveraging its active capabilities and potential for monolithic integration with other active devices, such as silicon-germanium detectors. This allows for on-chip integration of the modulator and detector, simplifying the fabrication process, reducing costs, and facilitating large-scale application.

[0044] In some examples, the MZ electro-optic modulator further includes an upper cladding layer 19 covering the metal layer 18. The upper cladding layer 19 is typically an insulating material layer 111, which not only prevents oxidation contamination of the metal layer 18 but also reduces the distribution range of the evanescent field, thereby further improving modulator performance. The upper cladding layer 19 can be, for example, any of an inorganic material such as a silicon oxide layer, a silicon oxynitride layer, or a silicon nitride layer. In other examples, the upper cladding layer 19 can also be an organic material layer such as a polyimide layer.

[0045] To ensure modulator performance, the refractive index of the first, second, and third isolation layers 13, 15, 17, and upper cladding layer 19 is preferably less than that of their respective adjacent waveguide layers. The materials of the first, second, and third isolation layers 13, 15, 17, and upper cladding layer 19 can be the same or different. In this embodiment, since the first waveguide layer is made of silicon, the second waveguide layer is made of silicon nitride, and the third waveguide layer is made of lithium niobate, to simplify the fabrication process and improve the interface properties between the different material layers, the first, second, and third isolation layers 13, 15, 17, and upper cladding layer 19 are preferably silicon dioxide layers, or alternatively, silicon oxynitride layers. When using silicon oxynitride layers, their refractive index can be adjusted by adjusting the oxygen content and / or oxygen content of the silicon oxynitride layer to better match that of the adjacent waveguide layer. Alternatively, in some examples, when silicon oxynitride layers are used as the isolation layers, the isolation layers can have a gradient refractive index.

[0046] The metal layer 18 must be made of a material with good electrical conductivity. For example, the metal layer 18 can be made of aluminum, silver, copper, gold, and platinum. In other words, the metal layer 18 can be made of a single metal or an alloy. To improve compatibility with CMOS manufacturing processes, the metal layer 18 in this embodiment is preferably made of aluminum or copper.

[0047] The thickness of each material layer significantly impacts the electro-optical modulation performance and transmission loss of the electro-optic modulator. Therefore, the thickness of each material layer must be carefully designed; neither too thick nor too thin is acceptable. Extensive experiments have revealed that the thicknesses of each material layer are preferably as follows: the silicon waveguide layer 12 has a thickness of 200 nm to 250 nm (the numerical ranges in this embodiment are inclusive unless otherwise specified); the first isolation layer 13 has a thickness of 120 nm to 150 nm; the silicon nitride waveguide layer 14 has a thickness of 350 nm to 450 nm; the second isolation layer 15 has a thickness of 10 nm to 45 nm; the lithium niobate thin film layer 16 has a thickness of 350 nm to 450 nm; the third isolation layer 17 has a thickness of 150 nm to 250 nm; the metal layer 18 has a thickness of 0.5 μm to 1.5 μm; and the upper cladding layer 19 has a thickness of 1.5 μm to 2.5 μm. It should be noted that, because the thickness of each material layer is not necessarily the same at all locations, the above values ​​refer to the thickness of the corresponding material layer at its maximum thickness. In one specific example, the thickness of the silicon waveguide layer 12 is 220 nm, the thickness of the first isolation layer 13 is 140 nm, the thickness of the silicon nitride waveguide layer 14 is 400 nm, the thickness of the second isolation layer 15 is 30 nm, the thickness of the lithium niobate thin film layer 16 is 400 nm, the thickness of the third isolation layer 17 is 200 nm, the thickness of the metal layer 18 is 1 μm, and the thickness of the upper cladding layer 19 is 2 μm.

[0048] In some examples, the MZ electro-optic modulator may also be provided with a reflector (not shown). The reflector may be arranged along the light transmission path, 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 may be, for example, a Bragg reflector or a metal reflector. The provision of the reflector helps further improve device performance.

[0049] In some examples, the silicon waveguide layer 12 has an array structure, i.e., 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 layer can be provided between two silicon modulator arms 123. The isolation material layer can be, for example, an insulating material layer having photochromic properties, thereby preventing crosstalk between light leaking from different optical waveguides.

[0050] In order 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-optical bandwidth of more than 130GHz and a half-wave voltage-length product of 2.58Vcm in the TE (Transverse Electric) mode at a wavelength of 1550nm was achieved. The optical mode field and electrostatic field distribution in the simulated single-ended modulation arm 123 are shown in Figures 3 and 4 respectively; the port characteristics of the coplanar electrode transmission line, including the characteristic impedance, attenuation coefficient, and microwave effective refractive index as a function of the width and thickness of the signal electrode, are shown in Figures 5 to 7 respectively; the calculated electro-optical response curves of the electro-optic modulator corresponding to different modulation zone lengths after optimization are shown in Figure 8; 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 Figure 9, and the transmission spectrum at 1500-1600nm is shown in Figure 10. These simulation results show that the performance of the electro-optic modulator provided by this embodiment is comparable to that of the existing silicon-lithium niobate hybrid integrated platform and silicon-lithium niobate heterogeneous platform, while also having the advantages of low transmission loss of the silicon nitride-lithium niobate heterogeneous integrated platform and the ability of the silicon-lithium niobate hybrid integrated platform to be integrated with active devices such as germanium silicon detectors.

[0051] The present invention also provides a method for preparing an MZ electro-optic modulator, which can be used to prepare an MZ electro-optic modulator as described in any of the above-mentioned solutions. Therefore, the above-mentioned introduction to the MZ electro-optic modulator can be quoted in its entirety here and will not be repeated for the sake of brevity. The method for preparing the MZ electro-optic modulator provided in this embodiment includes the steps of preparing a silicon waveguide layer 12 on a substrate layer 11, and then sequentially preparing 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, a metal layer 18, and an upper cladding layer 19, wherein the lithium niobate thin film layer 16 is prepared on a substrate different from the silicon waveguide layer 12 and then bonded to the top of the silicon nitride waveguide layer 14. That is, 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. This can avoid etching 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.

[0052] In a preferred embodiment, the method for preparing a silicon waveguide layer on the substrate layer 11 includes providing an SOI wafer and photolithographically etching the top silicon layer of the SOI wafer to obtain a silicon waveguide layer 12 having patterned silicon waveguides and unit devices. Of course, in other embodiments, the process for preparing the silicon waveguide layer 12 on the substrate layer 11 may also involve first providing a base layer. If the base layer is a wafer made of a semiconductor material such as silicon, germanium, silicon germanium, or gallium arsenide, after providing the base layer, an insulating structural layer such as an oxide layer is first formed on the base layer. A polysilicon layer is then formed on the insulating structural layer using a process including but not limited to chemical vapor deposition. The polysilicon layer is then 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. However, relatively speaking, using an SOI wafer and photolithographically etching the top silicon layer of the SOI wafer to obtain the silicon waveguide layer 12 helps simplify the preparation process.

[0053] The preparation method of this embodiment will be described in more detail below with reference to FIG11. 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 to this.

[0054] As shown in FIG11 , the process of preparing the MZ electro-optic modulator in this embodiment is as follows:

[0055] 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, photolithographically etching the top silicon layer of the SOI wafer to obtain a silicon waveguide layer 12, the bottom silicon layer of the SOI wafer forming a substrate layer 11, and the insulating layer of the SOI wafer forming an insulating material layer 111 on the substrate layer 11;

[0056] 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;

[0057] 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 photolithographically etched to obtain a silicon nitride waveguide layer 14;

[0058] 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;

[0059] The preparation process of the second bonded wafer is, for example, as follows: providing a substrate, which is also a silicon wafer with a silicon dioxide layer formed on the surface, but is not limited thereto, and may also be a glass substrate or an organic material substrate;

[0060] A second bonded wafer is obtained by forming a lithium niobate thin film layer 16 on the substrate layer using, but not limited to, a sol-gel method, and then directly bonding the first wafer to the second bonded wafer, wherein the lithium niobate thin film layer 16 and the second isolation layer 15 are bonded to each other;

[0061] Next, the substrate of the second bonded wafer is thinned, for example, by grinding away the silicon substrate of the second bonded wafer and thinning the lithium niobate material layer to a predetermined thickness, and then forming a third isolation layer 17 on the lithium niobate thin film layer 16;

[0062] 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 .

[0063] In summary, this embodiment creatively prepares an MZ-type electro-optical modulator with a silicon-silicon nitride-lithium niobate three-layer waveguide and carefully designs the position and thickness of each structural layer. Therefore, it can fully utilize the excellent electro-optical modulation performance of the lithium niobate material and the low-light property of the silicon nitride material with lower transmission loss compared to silicon, which can effectively reduce transmission loss and avoid etching of the lithium niobate material. At the same time, the non-modulation arm area uses silicon material, utilizing the active capabilities of silicon material and the potential for monolithic integration with other active devices such as germanium silicon detectors, 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 the various shortcomings of the existing technology and has high industrial utilization value.

[0064] 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 skilled in 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 one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to 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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