Film lithium niobate waveguide based on coupling extinction and preparation method thereof

Abstract

The invention relates to the technical field of micro-nano photoelectron chips, in particular to a thin-film lithium niobate waveguide based on coupling extinction and a preparation method of the thin-film lithium niobate waveguide. The waveguide comprises lithium niobate, a cladding, a substrate and a metal layer, the cladding layer is arranged on the substrate, one end of the lithium niobate is exposed out of the first side of the cladding layer, the other end of the lithium niobate is embedded into the cladding layer, and the metal layer is arranged at the top of the cladding layer. The substrate is an input port, the waveguide is coupled with the exposed end of the lithium niobate, and the top of the cladding is an output port. According to the thin-film lithium niobate waveguide based on coupling extinction and the preparation method thereof, design is carried out according to coupling conditions, TE and TM mode fields are mainly concentrated on the side wall and the top, so that the TM mode is strongly absorbed by metal after being coupled to the left waveguide, and after the TE mode is coupled, due to the fact that cladding interval absorption of silicon oxide is weak, the TM mode is greatly absorbed by metal. The polarization extinction ratio of the on-chip polarization device can be improved, and the overall loss of the device is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-nano optoelectronic chips, and in particular to a thin-film lithium niobate waveguide based on coupled extinction and a preparation method thereof. Background Art

[0002] Polarization is the degree of freedom of photon encoding information. Polarization control on optoelectronic chips is important for realizing specific functions. Some optoelectronic devices can use the polarization degree of freedom to increase the dimension and speed of information processing, while some optoelectronic devices support single polarization operation. The input of other polarization components will produce crosstalk, which will deteriorate the performance indicators of the device. In order to eliminate the interference of stray polarized light, a single polarization waveguide structure needs to be introduced on the chip. Single polarization waveguide can be realized by designing the geometric dimensions of the waveguide or introducing high-absorption materials such as metal. By adjusting the geometric dimensions of the waveguide, the equivalent refractive index and radiation loss of the TE / TM polarization mode (TE mode, Chinese full name: transverse electric mode, English full name: Transverse Electric mode; TM mode, Chinese full name: transverse magnetic mode, English full name: Transverse Magnetic mode) can be changed; the mode field distribution of the TE / TM mode is different. Introducing high-absorption materials such as metal in the concentrated light field area of ​​the TE / TM mode can introduce additional losses and realize single polarization transmission of another polarization mode. Single polarization waveguide structure has many application scenarios, including electro-optic modulators, on-chip gyroscopes, sensor devices, etc. Its performance indicators mainly include insertion loss, size, and polarization extinction ratio. The most important performance is the polarization extinction ratio. For end-coupled optoelectronic chips, there is an alignment error between the polarization axis of the polarization-maintaining fiber in the end-coupled optical fiber and the crystal direction of the chip, which will excite components of different polarizations in the optical waveguide, which will deteriorate the modulation efficiency or the sensing accuracy of the Sagnac effect in the gyroscope. The previous technical solution mainly ensured the single-polarization operation of the chip through a high-precision six-axis alignment platform combined with a transmission spectrum test, followed by UV curing and packaging.

[0003] Several existing solutions for achieving high polarization extinction ratio lithium niobate waveguides have the following defects and shortcomings: (1) The solution of adjusting the equivalent refractive index by using the waveguide geometry is very dependent on the precision of micro-nano processing, including the electron beam exposure system or the line precision of photolithography in the chip preparation process, which will affect the mode refractive index and thus affect the single polarization working characteristics of the device, and the etching depth error in the subsequent chip etching process will also have an impact. (2) Although the introduction of metal structures directly above the waveguide structure or on the sidewall can increase the polarization extinction ratio, the overlap with the working mode will introduce additional insertion loss. (3) The refractive index contrast of traditional lithium niobate waveguides defined by titanium diffusion or proton exchange is small, and it is difficult to achieve a large equivalent refractive index difference between TE / TM modes. (4) If the device itself cannot achieve a high polarization extinction ratio, a high-precision six-axis alignment platform combined with a transmission spectrum test is required to ensure the single polarization operation of the chip, and then a UV curing packaging method is used. This process is relatively cumbersome and difficult to mass-produce devices. Summary of the invention

[0004] The present invention provides a thin-film lithium niobate waveguide based on coupled extinction and a preparation method thereof, so as to solve the defects of large insertion loss and low polarization extinction ratio in the prior art. By introducing the principles of directional coupling and metal absorption, a single polarization transmission structure is realized by dry etching on a thin-film lithium niobate optoelectronic chip platform. A single structure can realize a TE / TM polarization extinction ratio of more than 20 dB within a propagation length of less than tens of microns, and the insertion loss is less than 1 dB.

[0005] The present invention provides a thin-film lithium niobate waveguide based on coupled extinction, comprising: lithium niobate, a cladding layer, a substrate and a metal layer; The cladding is disposed on the substrate, and one end of the lithium niobate is exposed to the first side of the cladding, the other end of the lithium niobate is embedded in the cladding, and the metal layer is disposed on the top of the cladding; wherein, The substrate is an input port, the waveguide is coupled to an exposed end of the lithium niobate, and the top of the cladding is an output port.

[0006] According to the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention, the lithium niobate includes: a first strip of lithium niobate and a second strip of lithium niobate parallel to each other; the metal layer includes: a first metal layer and a second metal layer, the first metal layer is located on the top of the cladding and at one end of the first strip of lithium niobate embedded in the cladding, and the second metal layer is located on the top of the cladding and at one end of the second strip of lithium niobate embedded in the cladding.

[0007] According to the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention, the lithium niobate also includes: a third strip of lithium niobate, the third strip of lithium niobate passes through the cladding, and one end of the third strip of lithium niobate is exposed to the second side of the cladding, and the other end of the third strip of lithium niobate is exposed to the third side of the cladding.

[0008] According to the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention, the extension direction of the third lithium niobate strip is perpendicular to the extension directions of the first lithium niobate strip and the second lithium niobate strip.

[0009] According to the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention, the cladding and the substrate are an integrated structure.

[0010] According to the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention, the cladding includes a silicon dioxide cladding; and the substrate includes a silicon dioxide substrate.

[0011] According to the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention, the metal layer includes one of metal chromium, metal nickel and metal platinum.

[0012] The present invention also provides a method for preparing a thin-film lithium niobate waveguide based on coupled extinction according to the present invention, comprising: S1. Electron beam lithography exposure is performed on a thin film lithium niobate substrate; S2, depositing a metal layer by magnetron sputtering to be used as a hard mask in subsequent etching; S3, placing the entire chip in a reagent that can wash away the electron beam photoresist, lifting the EB photoresist and the metal layer thereon, and retaining the metal layer with the etching pattern defined thereon; S4, using trifluoromethane and argon as etching gases, and using these two gases to introduce chemical reaction and physical bombardment respectively during etching, thereby achieving a high etching depth-to-width ratio and a smooth waveguide sidewall; using inductively coupled plasma etching to etch through the lithium niobate layer to form a lithium niobate strip waveguide; S5. After the etching is completed, the chip is chemically polished; S6, depositing silicon dioxide; S7, performing electron beam lithography, metal deposition and lift-off to form a metal layer required for single polarization operation at the top of the waveguide; S8, cleaning the chip, and further depositing a chip cladding layer to protect the chip; S9. The end face is polished to produce an end face coupler structure for coupling input and output light.

[0013] According to the method for preparing a thin-film lithium niobate waveguide based on coupled extinction provided by the present invention, FDTD simulation is used to perform parameter scanning to scan the equivalent refractive index and coupling strength of TE / TM, thereby determining the coupling spacing, cladding thickness, substrate thickness and metal layer size.

[0014] According to the method for preparing a thin-film lithium niobate waveguide based on coupled extinction provided by the present invention, after the etching is completed in S5, chemical polishing of the chip specifically includes: After etching is completed, a mixed solution is prepared by using hydrogen peroxide, ammonia water and water in a mass ratio of 2:2:1, and the chip is chemically polished by using a water bath heating method.

[0015] The present invention provides a thin-film lithium niobate waveguide based on coupled extinction, which includes: lithium niobate, a cladding, a substrate and a metal layer. The cladding is arranged on the substrate, and one end of the lithium niobate is exposed to the first side of the cladding, the other end of the lithium niobate is embedded in the interior of the cladding, and the metal layer is arranged on the top of the cladding. The substrate is an input port, the waveguide is coupled to the exposed end of the lithium niobate, and the top of the cladding is an output port. The present invention provides a thin-film lithium niobate waveguide based on coupled extinction and a preparation method thereof, which is designed according to the coupling conditions. Since the mode fields of TE and TM are mainly concentrated on the side walls and the top, the TM mode is strongly absorbed by the metal after being coupled to the left waveguide, while the TE mode is weakly absorbed due to the cladding interval of silicon oxide after coupling, which can improve the polarization extinction ratio of the on-chip polarization device and reduce the overall loss of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a cross-sectional view of the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention.

[0018] Figure 2 It is a top view of the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention.

[0019] Figure 3 This is a light field propagation diagram of the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention under the input TE mode.

[0020] Figure 4 It is a light field propagation diagram of the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention under the input TM mode.

[0021] Figure 5 It is the transmittance of the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention in the TE mode.

[0022] Figure 6 It is the transmittance of the thin-film lithium niobate waveguide based on coupled extinction provided by the present invention in the TM mode.

[0023] Reference numerals: 1: cladding; 2: substrate; 3: metal layer; 41: first strip of lithium niobate; 42: second strip of lithium niobate; 43: third strip of lithium niobate. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] In the description of the present embodiment, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present embodiment and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present embodiment.

[0026] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this embodiment, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0027] In this embodiment, unless otherwise clearly specified and limited, the terms "set", "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in this embodiment can be understood according to specific circumstances.

[0028] In the embodiments of the present invention, unless otherwise clearly specified and limited, the first feature being "above" or "below" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0029] Combine the following Figure 1 and Figure 2 The present invention describes a thin-film lithium niobate waveguide based on coupled extinction. The thin-film lithium niobate waveguide based on coupled extinction comprises: lithium niobate, a cladding layer 1 , a substrate 2 and a metal layer 3 .

[0030] The cladding 1 is disposed on the substrate 2, and one end of the lithium niobate is exposed to the first side of the cladding 1, the other end of the lithium niobate is embedded in the cladding 1, and the metal layer 3 is disposed on the top of the cladding 1. The substrate 2 is an input port, the waveguide is coupled to the exposed end of the lithium niobate, and the top of the cladding 1 is an output port.

[0031] Specifically, the lower side of the waveguide of the present invention (that is, the substrate 2) serves as an input port, and is coupled with the left waveguide (that is, lithium niobate) during propagation. Since the metal has a high refractive index and strong absorption, the polarization components of TE and TM have different coupling strengths, so the absorption intensity of the metal layer 3 deposited above the left waveguide is different, thereby achieving the function of high polarization extinction. The upper side of the waveguide of the present invention (that is, the metal layer 3) serves as an output port after extinction. The present invention mainly designs the waveguide size, coupling spacing, silicon oxide layer thickness, and the size of the chromium metal strip, wherein the waveguide structure is mainly designed for its coupling conditions. Since the mode fields of TE and TM are mainly concentrated on the side walls and the top, the TM mode is strongly absorbed by the metal after coupling to the left waveguide, while the TE mode is weakly absorbed due to the presence of the silicon oxide cladding 1 interval after coupling. This is the working principle of achieving a high polarization extinction ratio in the present invention.

[0032] Specifically, the waveguide structure of the present application is roughly composed of three parts: a lithium niobate device layer, a silicon oxide cladding 1, and a chromium metal strip structure on the top. The structure of the upper layer of the device is the bus waveguide and the coupling waveguide part. The bus waveguide is the input and output port of the device, which can realize single polarization transmission of the working polarization state (TE mode). The coupling waveguide structure and the chromium metal strip above it are auxiliary structures for realizing single polarization on the chip, and do not correspond to the input and output ports. The use of a coupling waveguide plus a metal absorption extinction structure can change the coupling conditions of the TE and TM modes, and couple the TM mode to the coupling waveguide on the left side of the figure. The energy coupled back to the bus waveguide is reduced through metal absorption, thereby realizing TE mode transmission with a high polarization extinction ratio. At the same time, the TE mode is far away from the metal absorption structure, and the insertion loss of the working mode is also small. It can be seen that the working principle of the present application is different from that of the existing single-polarization waveguide device, and single-polarization transmission is achieved through polarization-sensitive directional coupling and metal strips.

[0033] Simulation results of thin-film lithium niobate waveguide based on coupled extinction in this application: The simulation results are as follows Figure 3 , Figure 4 As shown, Figure 3 This is the light field propagation diagram under the input TE mode. It can be seen that the intensity of the TE mode coupled to the left waveguide is low and there is basically no attenuation along the bus waveguide. Figure 4 The TM mode light field shown in the figure is mainly coupled into the left waveguide and absorbed. Figure 5 and Figure 6 The transmittance of TE and TM modes are given respectively, where the two curves are the transmittance of the light field through one group of structures (solid line) and two groups of structures (dashed line) in the 1530~1570nm band, where the lower curve is the transmittance of the two groups of structures and the higher one is the transmittance of the one group of structures. For the TE mode, the insertion loss of the structure is 0.45dB, while that of the TM mode is 23.6dB. A polarization extinction ratio of 23dB can be achieved with an insertion loss of 0.45dB. At the same time, the coupling region is 25 microns long. The small device size and low insertion loss make it possible to cascade multi-layer devices to achieve a higher polarization extinction ratio.

[0034] Generally, the metal layer 3 is made of chromium metal strips, and can also be replaced by metal titanium, metal aluminum, etc.

[0035] Specifically, FDTD simulation is used to perform parameter scanning, mainly scanning the equivalent refractive index and coupling strength of TE / TM, to ensure that the TE mode equivalent refractive index in the bus waveguide and the coupled waveguide is quite different and basically not coupled to the coupled waveguide, while the TM mode equivalent refractive index is close and the coupling strength is high, so as to determine the waveguide size, coupling spacing, silicon oxide layer thickness (thickness of cladding 1 and substrate 2) and chromium metal strip size. The structural size parameters of an embodiment provided are: the left waveguide width is 0.75um, the right side is 0.8um, the etching depth is 0.3um, and the thickness of lithium niobate is 0.4um.

[0036] The present invention provides a thin-film lithium niobate waveguide based on coupled extinction, which includes: lithium niobate, cladding 1, substrate 2 and metal layer 3. Cladding 1 is provided on substrate 2, and one end of lithium niobate is exposed to the first side of cladding 1, the other end of lithium niobate is embedded in cladding 1, and metal layer 3 is provided on the top of cladding 1. Substrate 2 is an input port, the waveguide is coupled to the exposed end of lithium niobate, and the top of cladding 1 is an output port. The present invention provides a thin-film lithium niobate waveguide based on coupled extinction, which is designed for coupling conditions. Since the mode fields of TE and TM are mainly concentrated on the side walls and the top, the TM mode is strongly absorbed by the metal after being coupled to the left waveguide, while the TE mode is weakly absorbed by the cladding 1 interval due to the presence of silicon oxide after coupling, which can improve the polarization extinction ratio of the on-chip polarization device and reduce the overall loss of the device.

[0037] In one embodiment of the present invention, lithium niobate includes: a first strip of lithium niobate 41 and a second strip of lithium niobate 42 parallel to each other; the metal layer 3 includes: a first metal layer 3 and a second metal layer 3, the first metal layer 3 is located on the top of the cladding 1 and at one end where the first strip of lithium niobate 41 is embedded in the cladding 1, and the second metal layer 3 is located on the top of the cladding 1 and at one end where the second strip of lithium niobate 42 is embedded in the cladding 1. In this embodiment, since the cladding 1 wraps the first metal layer 3 and the second metal layer 3, and the cladding 1 provides a gap between the first metal layer 3 and the second metal layer 3, after TE mode coupling, the absorption is weak due to the presence of the cladding 1 gap.

[0038] In one embodiment of the present invention, the lithium niobate further includes: a third strip of lithium niobate 43, the third strip of lithium niobate 43 passes through the cladding 1, and one end of the third strip of lithium niobate 43 is exposed to the second side of the cladding 1, and the other end of the third strip of lithium niobate 43 is exposed to the third side of the cladding 1. Preferably, the extension direction of the third strip of lithium niobate 43 is perpendicular to the extension direction of the first strip of lithium niobate 41 and the second strip of lithium niobate 42, that is, the third strip of lithium niobate 43 is arranged perpendicular to the first strip of lithium niobate 41 and the second strip of lithium niobate 42. Specifically, the width of the first strip of lithium niobate 41 and the second strip of lithium niobate 42 is 0.75um, the width of the third strip of lithium niobate 43 is 0.8um, the etching depth is 0.3um, and the thickness is 0.4um.

[0039] In one embodiment of the present invention, the cladding 1 and the substrate 2 are an integral structure. In this embodiment, the cladding 1 and the substrate 2 can be an integral structure, that is, the bottom of the cladding 1 has the function of the substrate 2. Regardless of whether the cladding 1 or the substrate 2 is an integral structure or a separate structure, the cladding 1 and the substrate 2 can both be made of silicon dioxide, that is, the cladding 1 includes a silicon dioxide cladding 1; the substrate 2 includes a silicon dioxide substrate 2.

[0040] In one embodiment of the present invention, the metal layer 3 includes one of metal chromium, metal nickel and metal platinum. Preferably, the metal layer 3 is made of metal chromium in the shape of a strip of metal chromium.

[0041] The present invention also provides a method for preparing a thin-film lithium niobate waveguide based on coupled extinction according to the above embodiment of the present invention. The preparation method generally comprises the following steps: EBL electron beam lithography-Cr deposition-lift-off-physical and chemical ICP etching-chip cleaning-chemical polishing-silicon dioxide deposition-metal deposition-metal strip etching-end face polishing.

[0042] Specifically, the preparation method comprises: S1, performing electron beam lithography exposure on the thin film lithium niobate substrate 2; S2, depositing a metal layer 3 by magnetron sputtering to be used as a hard mask in subsequent etching; S3, placing the entire chip in a reagent that can wash away the electron beam photoresist, lifting the EB photoresist and the metal layer 3 thereon, and retaining the metal layer 3 with the etching pattern defined thereon; S4, using trifluoromethane and argon as etching gases, and using these two gases to introduce chemical reaction and physical bombardment respectively during etching, thereby achieving a high etching depth-to-width ratio and a smooth waveguide sidewall; using inductively coupled plasma etching to etch through the lithium niobate layer to form a lithium niobate strip waveguide; S5. After the etching is completed, the chip is chemically polished; S6, depositing silicon dioxide; S7, performing electron beam lithography, metal deposition and lift-off to form the metal layer 3 required for single polarization operation at the top of the waveguide; S8, cleaning the chip, and further depositing a cladding layer 1 of the chip to protect the chip; S9. The end face is polished to produce an end face coupler structure for coupling input and output light.

[0043] It can be seen that the method for preparing a thin-film lithium niobate waveguide based on coupled extinction provided in the present application is different from the lithium niobate chip of titanium diffusion and proton exchange, and the entire device is processed by a dry etching process.

[0044] In one embodiment of the present invention, FDTD simulation is used to perform parameter scanning, scanning the equivalent refractive index and coupling strength of TE / TM, so as to determine the coupling spacing, the thickness of cladding 1, the thickness of substrate 2 and the size of metal layer 3. Specifically, FDTD simulation is used to perform parameter scanning, mainly scanning the equivalent refractive index and coupling strength of TE / TM, to ensure that the equivalent refractive index of TE mode in bus waveguide and coupling waveguide is quite different, and basically not coupled to coupling waveguide, while the equivalent refractive index of TM mode is close, and the coupling strength is high. The simulation results after design are Figure 3 and Figure 4 The above effects can also be clearly verified.

[0045] In one embodiment of the present invention, after etching in S5 is completed, chemical polishing of the chip specifically includes: after etching is completed, a mixed solution is prepared using hydrogen peroxide, ammonia water and water in a mass ratio of 2:2:1, and chemical polishing of the chip is performed by water bath heating.

[0046] The present invention provides a specific embodiment of a method for preparing a thin-film lithium niobate waveguide based on coupled extinction: First, electron beam lithography exposure is performed on a cleaned thin-film lithium niobate substrate 2. Then, a Cr layer of about 120 nm is deposited by magnetron sputtering to be used as a hard mask in subsequent etching. In the lift-off process, the chip as a whole is placed in a reagent that can wash away the electron beam photoresist (the cleaning reagent for each photoresist is different, typically acetone, butanone, etc.) to lift off the EB photoresist and the Cr metal layer 3 above, retaining the Cr metal layer 3 with an etching pattern defined. In the physical and chemical ICP step, CHF3 and Ar are used as etching gases. These two working gases can introduce chemical reactions and physical bombardment in etching, respectively, while achieving high etching depth-to-width ratio and smooth waveguide sidewalls. The 400 nm thick lithium niobate layer is etched through using an inductively coupled plasma etching device to form a lithium niobate strip waveguide. During the etching process, it is necessary to select appropriate parameters such as gas ratio, gas pressure, temperature and etching time. After etching is completed, the chip is chemically polished with a mixed solution of hydrogen peroxide, ammonia and water in a ratio of 2:2:1 and heated in a water bath at 80 degrees for 1 hour. This step can clean the small amount of reaction products left on the side wall, reducing the roughness and scattering loss of the side wall. After PECVD deposits 200nm thick silicon oxide, EBL overlay, metal deposition and lift-off are performed to produce the metal chromium strip required for single polarization operation at the top of the waveguide. After cleaning the contaminants on the surface of the chip, the chip's cladding 1 silicon oxide is further deposited to protect the chip. After the end face is polished to produce the end face coupler structure for coupling input-output light, the entire chip can be obtained.

[0047] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, i.e., they may be located in one place, or they may be distributed over multiple units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present embodiment. Those of ordinary skill in the art may understand and implement the present invention without creative effort.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A thin-film lithium niobate waveguide based on coupled extinction, characterized in that: include: Lithium niobate, cladding (1), substrate (2) and metal layer (3); The cladding (1) is arranged on the substrate (2), and one end of the lithium niobate is exposed to the first side of the cladding (1), and the other end of the lithium niobate is embedded in the cladding (1), and the metal layer (3) is arranged on the top of the cladding (1); wherein: The substrate (2) is an input port, the waveguide is coupled to the exposed end of the lithium niobate, and the top of the cladding (1) is an output port.

2. The thin-film lithium niobate waveguide based on coupled extinction according to claim 1, characterized in that: The lithium niobate comprises: a first strip-shaped lithium niobate (41) and a second strip-shaped lithium niobate (42) which are parallel to each other; the metal layer (3) comprises: a first metal layer (3) and a second metal layer (3), the first metal layer (3) being located at the top of the cladding (1) and at one end where the first strip-shaped lithium niobate (41) is embedded in the cladding (1), and the second metal layer (3) being located at the top of the cladding (1) and at one end where the second strip-shaped lithium niobate (42) is embedded in the cladding (1).

3. The thin-film lithium niobate waveguide based on coupled extinction according to claim 2, characterized in that: The lithium niobate further comprises: a third strip of lithium niobate (43), wherein the third strip of lithium niobate (43) passes through the cladding (1), and one end of the third strip of lithium niobate (43) is exposed to the second side of the cladding (1), and the other end of the third strip of lithium niobate (43) is exposed to the third side of the cladding (1).

4. The thin-film lithium niobate waveguide based on coupled extinction according to claim 3, characterized in that: The extension direction of the third strip-shaped lithium niobate (43) is perpendicular to the extension direction of the first strip-shaped lithium niobate (41) and the second strip-shaped lithium niobate (42).

5. The thin-film lithium niobate waveguide based on coupled extinction according to any one of claims 1 to 4, characterized in that: The cladding (1) and the substrate (2) are an integral structure.

6. The thin-film lithium niobate waveguide based on coupled extinction according to any one of claims 1 to 4, characterized in that: The cladding (1) comprises a silicon dioxide cladding (1); and the substrate (2) comprises a silicon dioxide substrate (2).

7. The thin-film lithium niobate waveguide based on coupled extinction according to any one of claims 1 to 4, characterized in that: The metal layer (3) comprises one of metal chromium, metal nickel and metal platinum.

8. A method for preparing a thin-film lithium niobate waveguide based on coupled extinction according to any one of claims 1 to 7, characterized in that: include: S1, performing electron beam lithography exposure on a thin film lithium niobate substrate (2); S2, depositing a metal layer (3) by magnetron sputtering to be used as a hard mask in subsequent etching; S3, placing the entire chip in a reagent capable of washing away the electron beam photoresist, lifting the EB photoresist and the metal layer (3) thereon, and retaining the metal layer (3) having the etching pattern defined thereon; S4, using trifluoromethane and argon as etching gases, and using these two gases to introduce chemical reaction and physical bombardment respectively during etching, thereby achieving a high etching depth-to-width ratio and a smooth waveguide sidewall; using inductively coupled plasma etching to etch through the lithium niobate layer to form a lithium niobate strip waveguide; S5. After the etching is completed, the chip is chemically polished; S6, depositing silicon dioxide; S7, performing electron beam lithography, metal deposition and lift-off to form a metal layer (3) required for single polarization operation at the top of the waveguide; S8, cleaning the chip, and further depositing a chip cladding layer (1) to protect the chip; S9. The end face is polished to produce an end face coupler structure for coupling input and output light.

9. The method for preparing a thin-film lithium niobate waveguide based on coupled extinction according to claim 8, characterized in that: FDTD simulation is used to perform parameter sweeps to scan the equivalent refractive index and coupling strength of TE / TM, thereby determining the coupling spacing, the thickness of the cladding (1), the thickness of the substrate (2) and the size of the metal layer (3).

10. The method for preparing a thin-film lithium niobate waveguide based on coupled extinction according to claim 8 or 9, characterized in that: After the etching in S5 is completed, the chip is chemically polished, which specifically includes: After etching is completed, a mixed solution is prepared by using hydrogen peroxide, ammonia water and water in a mass ratio of 2:2:1, and the chip is chemically polished by using a water bath heating method.

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