Thin film lithium niobate polarizer and manufacturing method therefor

Abstract

A thin film lithium niobate polarizer and a manufacturing method therefor. The thin film lithium niobate polarizer comprises a substrate layer, an optical waveguide layer and an upper cladding layer; the optical waveguide layer comprises a light input port, a light output port, a slab layer and a ridge waveguide layer, the ridge waveguide layer being disposed on the slab layer; the ridge waveguide layer comprises at least one transmission waveguide section, and two ends of the transmission waveguide section are symmetrically connected with connecting waveguide sections; and the transmission waveguide section is used to filter light in a TM mode in a laser signal, and output light in a TE mode in the laser signal by means of the connecting waveguide section at the other end and the light output port, achieving separation of TM and TE components in the input laser signal, to obtain pure TE light, and thereby achieve a polarizing effect. In addition, using a thin film lithium niobate platform helps to reduce the size of a device, facilitating device integration and chip miniaturization. A standard semiconductor process is used, and the process technology is mature, so that costs can be effectively reduced, and the batch production capacity of the device is improved.

Description

A thin film lithium niobate polarizer and its manufacturing method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from the following patent applications:

[0003] (1) A Chinese patent application entitled “A thin film lithium niobate polarizer and its manufacturing method” was submitted to the China Patent Office on January 26, 2024 with application number 202410115237.8. Technical Field

[0004] The present invention relates to the technical field of optical communications, and in particular to a thin-film lithium niobate polarizer and a manufacturing method thereof. Background Art

[0005] Driven by the demand for massive data transmission in data centers, long-distance coherent optical communication technology is gradually spreading to short-distance interconnection applications that are highly sensitive to cost and energy consumption. The use of polarization manipulation technology can effectively reduce the cost and power consumption of short-distance coherent optical communication systems.

[0006] With the vigorous development of optoelectronic integration technology, integration and chipization are important trends in the future development of optical polarization manipulation devices. Traditional polarizers are large in size, which limits the miniaturization of devices and has high manufacturing costs. Lithium niobate materials have advantages such as low insertion loss and high refractive index. Currently, most high-performance polarization manipulation devices are based on lithium niobate crystal materials. However, the optical waveguides prepared in traditional lithium niobate crystals have the disadvantages of small refractive index contrast and weak light field confinement ability, resulting in large device size and difficulty in meeting the development needs of integration. Compared with traditional polarizers, thin-film lithium niobate polarizers are smaller in waveguide size and have stronger light confinement capabilities, which are more conducive to meeting the needs of miniaturization and integration of communications. At present, there is no relatively mature research that can simply and efficiently realize lithium niobate waveguides with high polarization extinction ratios on-chip.

[0007] In view of this, overcoming the defects of the prior art is an urgent problem to be solved in this technical field.

[0008] Application Contents

[0009] The technical problem to be solved by the present invention is how to simply and at low cost realize a waveguide with a high polarization extinction ratio on a thin-film lithium niobate platform.

[0010] The present invention adopts the following technical solutions:

[0011] In a first aspect, a thin-film lithium niobate polarizer is provided, comprising a substrate layer, an optical waveguide layer, and an upper cladding layer, wherein the optical waveguide layer is disposed between the substrate layer and the upper cladding layer;

[0012] The optical waveguide layer includes an optical input port, an optical output port, a slab layer, and a ridge waveguide layer, wherein the ridge waveguide layer is disposed on the slab layer; the ridge waveguide layer includes at least one transmission waveguide segment, and both ends of the transmission waveguide segment are symmetrically connected to a connecting waveguide segment;

[0013] The optical input port is used to receive a laser signal and transmit the laser signal to the transmission waveguide segment through the connecting waveguide segment. The transmission waveguide segment is used to filter the transverse magnetic field (TM) mode light in the laser signal and output the transverse electric field (TE) mode light in the laser signal through another connecting waveguide segment and the optical output port.

[0014] Preferably, the connecting waveguide section includes a straight waveguide section and a tapered waveguide section, the straight waveguide section is connected to the tapered waveguide section, and the tapered waveguide section is connected to the transmission waveguide section;

[0015] The width of one end of the tapered waveguide section matches the width of the straight waveguide section, and the width of the other end of the tapered waveguide section matches the width of the transmission waveguide section.

[0016] Preferably, the polarizer further comprises a buffer layer, and the buffer layer is arranged between the base layer and the optical waveguide layer;

[0017] The buffer layer and the upper cladding layer are made of silicon oxide or silicon dioxide;

[0018] The thickness of the buffer layer and the upper cladding layer is greater than 3 μm.

[0019] Preferably, the polarizer further includes an output waveguide structure, and the transmission waveguide segment is arranged between the output waveguide structures;

[0020] The derivation waveguide structure is used to derivate the TM mode light in the laser signal; the width of the derivation waveguide structure is 0.2um to 0.5um, and the distance between the derivation waveguide structure and the transmission waveguide section is 2um to 3um.

[0021] Preferably, the refractive index of the upper cladding layer is smaller than the refractive index of the optical waveguide layer.

[0022] Preferably, the optical waveguide layer is made of lithium niobate, the slab layer has a thickness ranging from 0.1 um to 5 um, and the ridge waveguide layer has a thickness ranging from 0.1 um to 5 um.

[0023] Preferably, the light input port and the light output port are grating coupling structures.

[0024] In a second aspect, a method for manufacturing a thin-film lithium niobate polarizer is provided, comprising:

[0025] preparing the base layer;

[0026] A buffer layer, an optical waveguide layer and an upper cladding layer are manufactured on the surface of the base layer.

[0027] Preferably, the step of fabricating a buffer layer, an optical waveguide layer, and an upper cladding layer on the surface of the substrate layer comprises:

[0028] forming the buffer layer on the upper surface of the base layer;

[0029] forming an optical waveguide material layer on the buffer layer;

[0030] removing a portion of the optical waveguide material layer by an etching process to form the optical waveguide layer;

[0031] The upper cladding layer is formed to cover the optical waveguide layer.

[0032] Preferably, the etching process includes inductively coupled plasma etching or reactive ion etching.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention receives a laser signal through the optical input port and transmits it to the transmission waveguide segment via the connecting waveguide segment. After the laser signal passes through the transmission waveguide segment, the transmission loss for the TM mode light is very large, while the transmission loss for the TE mode light is small. Therefore, the TM mode light gradually attenuates, while the TE mode light can continue to transmit. This separates the TM and TE components of the input laser signal, producing pure TE mode light, thereby achieving polarization. Furthermore, the use of a thin-film lithium niobate platform facilitates device size reduction, facilitating device integration and chip miniaturization. The use of standard, mature semiconductor processes effectively reduces costs and enhances device mass production capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in 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 only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] FIG1 is a schematic structural diagram of a thin-film lithium niobate polarizer provided by an embodiment of the present invention;

[0037] FIG2 is a schematic cross-sectional view of a thin-film lithium niobate polarizer provided by an embodiment of the present invention;

[0038] FIG3 is another schematic structural diagram of a thin-film lithium niobate polarizer provided by an embodiment of the present invention;

[0039] 4 is a schematic diagram showing the relationship between the extinction ratio of a transmission waveguide segment of a thin-film lithium niobate polarizer and the polarizer provided by an embodiment of the present invention;

[0040] 5 is a schematic diagram showing the relationship between the width of the ridge waveguide layer of a thin-film lithium niobate polarizer provided by an embodiment of the present invention and the loss of light in the TM mode and the light in the TE mode;

[0041] 6 is a schematic diagram of the electric field intensity distribution of the TE mode when the waveguide width of a thin-film lithium niobate polarizer provided by an embodiment of the present invention is 0.4 μm;

[0042] 7 is a schematic diagram of the electric field intensity distribution of the TM mode when the waveguide width of a thin-film lithium niobate polarizer provided by an embodiment of the present invention is 0.4 μm;

[0043] FIG8 is a schematic structural diagram of a connecting waveguide section of a thin-film lithium niobate polarizer provided by an embodiment of the present invention;

[0044] FIG9 is a schematic structural diagram of a lead-out waveguide structure of a thin-film lithium niobate polarizer provided by an embodiment of the present invention;

[0045] FIG10 is a schematic diagram of the specific structure of a thin-film lithium niobate polarizer provided by an embodiment of the present invention;

[0046] FIG11 is a more specific structural diagram of a thin-film lithium niobate polarizer provided by an embodiment of the present invention;

[0047] 12 is a schematic flow chart of a method for manufacturing a thin-film lithium niobate polarizer according to an embodiment of the present invention;

[0048] FIG13 is a schematic diagram of a method for manufacturing a thin-film lithium niobate polarizer according to an embodiment of the present invention;

[0049] FIG14 is a schematic structural diagram of a method for manufacturing a thin-film lithium niobate polarizer provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0051] The terms "first," "second," etc., used in this disclosure are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referenced. Thus, a feature identified with "first," "second," etc., may explicitly or implicitly include one or more of such features. In the description of this disclosure, unless otherwise specified, "plurality" means two or more.

[0052] In the present invention, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium.

[0053] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0054] Example 1:

[0055] Achieving a high polarization extinction ratio (PER) waveguide on a thin-film lithium niobate platform primarily involves optimizing the waveguide design and manufacturing process to improve polarization state control and extinction capabilities. By precisely designing the waveguide's width, height, and shape, the propagation characteristics of the polarization mode can be optimized, thereby enhancing the polarization extinction ratio. Ridge waveguides, by providing a different refractive index contrast, can better control TE (transverse electric) mode light and TM (transverse magnetic) mode light, thereby improving the polarization extinction ratio. The use of high-purity, low-defect materials can reduce scattering and absorption in light wave transmission and improve the polarization extinction ratio. At the same time, precise lithography and etching processes are crucial for manufacturing waveguides with precise dimensions, which can effectively reduce irregularities in the waveguide manufacturing process and improve polarization selectivity.

[0056] Furthermore, temperature fluctuations can affect the optical properties of lithium niobate, so precise temperature control can stabilize the waveguide's polarization performance. Good packaging can protect the waveguide from environmental influences and reduce polarization mode mismatch caused by mechanical stress. Choosing simple and efficient manufacturing processes, such as using standard photolithography and etching techniques, can reduce production costs. Standardizing designs and mass-producing waveguide components can significantly reduce unit costs.

[0057] In this embodiment, a thin-film lithium niobate polarizer is proposed, as shown in FIG1 , comprising a substrate layer, an optical waveguide layer and an upper cladding layer, wherein the optical waveguide layer is arranged between the substrate layer and the upper cladding layer; referring to FIG2 and FIG3 , the optical waveguide layer comprises an optical input port, an optical output port, a slab layer and a ridge waveguide layer, wherein the ridge waveguide layer is arranged on the slab layer; the ridge waveguide layer comprises at least one transmission waveguide segment, and connecting waveguide segments are symmetrically connected at both ends of the transmission waveguide segment; the optical input port is used to receive a laser signal and transmit the laser signal to the transmission waveguide segment through the connecting waveguide segment, and the transmission waveguide segment is used to filter the TM mode light in the laser signal and output the TE mode light in the laser signal through another connecting waveguide segment and the optical output port.

[0058] The substrate layer is the fundamental structure of the polarizer, providing stable support for the entire device. The substrate layer is typically made of materials with good mechanical stability and low optical loss. These materials include elemental semiconductor materials (e.g., silicon, germanium), Group IIIV compound semiconductor materials, Group IIVI compound semiconductor materials, organic semiconductor materials, or other semiconductor materials known in the art. The specific materials are not specifically limited in this embodiment.

[0059] The optical waveguide layer is the core component of the polarizer, positioned between the substrate layer and the upper cladding layer. The upper cladding layer is located above the optical waveguide layer and serves to protect the optical waveguide layer. The upper cladding layer should be made of a material with good light transmittance and an appropriate refractive index. In a preferred embodiment, the refractive index of the upper cladding layer is lower than that of the optical waveguide layer. The basic principle of waveguides is to use the difference in refractive index to restrict light propagation to a specific area. When the refractive index of the optical waveguide layer is higher than that of the surrounding materials (including the upper cladding layer and the substrate layer), light waves are confined to the high-refractive-index region, a phenomenon known as total internal reflection. When light enters a low-refractive-index medium from a high-refractive-index medium, if the angle of incidence is greater than a certain critical angle, the light waves are completely reflected back into the high-refractive-index medium, a phenomenon known as total internal reflection. In an optical waveguide, this total internal reflection ensures that light waves can propagate along the waveguide without leaking into the surrounding low-refractive-index material. This design can greatly improve light transmission efficiency because light waves propagate primarily within the optical waveguide layer, with virtually no energy lost to the upper cladding layer.

[0060] The slab layer, as part of the optical waveguide layer, provides a basic light propagation path and helps maintain stable transmission of light waves. The ridge waveguide layer is arranged on top of the slab layer and generally has a higher refractive index, which is used to precisely control the propagation of light waves. The ridge waveguide layer is used to achieve high-efficiency and high-quality optical waveguide transmission. The constituent materials of the optical waveguide layer include lithium niobate. The thickness of the slab layer ranges from 0.1um to 5um; the thickness of the ridge waveguide layer ranges from 0.1um to 5um. The optical waveguide layer is an etched ridge waveguide with a single crystal structure and an X-cut Y-transmission direction.

[0061] The optical input port is used to receive laser signals, while the optical output port is used to output processed optical signals. The key to the design of the optical input and output ports is to achieve efficient coupling and transmission of optical signals.

[0062] In a preferred embodiment, the light input and output ports are grating coupling structures. A grating coupling structure utilizes a periodic grating structure to couple light waves from free space into a waveguide, or vice versa, through diffraction. This structure effectively enables light wave input and output. The efficiency of a grating coupling structure depends on multiple factors, such as the grating period, depth, and shape, as well as the refractive index of the waveguide. By precisely designing these parameters, coupling efficiency can be optimized.

[0063] The transmission waveguide segment is the main part of the ridge waveguide layer and is used to transmit light waves of a specific polarization mode. It is particularly used to filter light in the TM mode and only allow light in the TE mode to pass through. The connecting waveguide segments are located at both ends of the transmission waveguide segment and are symmetrically connected. The function of these connecting waveguide segments is to transmit the laser signal from the optical input port to the transmission waveguide segment, and to transmit the optical signal from the transmission waveguide segment to the optical output port after processing. It is worth noting that in this embodiment, for ease of explanation, the transmission waveguide segment has only one segment. In a preferred embodiment, the transmission waveguide segment can be designed to have multiple segments, and the more segments the transmission waveguide segment has, the greater the extinction ratio of the polarizer. As shown in Figure 4, n is the number of segments of the transmission waveguide segment, and PER is the extinction ratio of the polarizer.

[0064] When a laser signal enters the optical input port, it is first transmitted through the connecting waveguide segment to the transmission waveguide segment. Within the transmission waveguide segment, specific design (such as the waveguide size, shape, and material refractive index) filters out TM mode light, allowing only TE mode light to be effectively transmitted. The processed laser signal is then transmitted through the connecting waveguide segment at the other end to the optical output port, completing the entire process.

[0065] This design optimizes the polarization selectivity of light, effectively separating light of different polarization states. By precisely controlling the size and shape of the waveguide structure, high-efficiency light transmission and a high polarization extinction ratio can be achieved, which are crucial for optical communications, optical information processing, and various optical sensing applications. This design also improves the bandwidth and signal stability of the optical waveguide, significantly contributing to the performance and reliability of the entire optical system.

[0066] This embodiment receives a laser signal through the optical input port and transmits the laser signal to the transmission waveguide segment via the connecting waveguide segment. After the laser signal passes through the transmission waveguide segment, the transmission loss for the TM mode light is very large, while the transmission loss for the TE mode light is relatively small. Therefore, the TM mode light gradually attenuates, while the TE mode light can continue to transmit. This achieves separation of the TM and TE components in the input laser signal, resulting in pure TE mode light, thereby achieving the polarization effect. The effect of the polarizer is shown in Figures 5, 6, and 7. Figure 5 shows the transmission loss values ​​for the TE and TM modes at different ridge waveguide widths, where W represents the ridge waveguide width and LOSS represents the transmission loss value. Figures 6 and 7 show the electric field intensity distributions for the TE and TM modes, respectively, when the waveguide width is 0.4 μm. The use of a thin-film lithium niobate platform facilitates device size reduction, facilitating device integration and chip miniaturization. The use of standard semiconductor processes with mature process technology can effectively reduce costs and improve the device's mass production capacity.

[0067] In order to facilitate the input of the laser signal into the transmission waveguide section and the output after being processed by the transmission waveguide section, in a preferred embodiment, as shown in Figure 8, the connecting waveguide section includes a straight waveguide section and a tapered waveguide section, the straight waveguide section and the tapered waveguide section are connected, and the tapered waveguide section is connected to the transmission waveguide section; the width of one end of the tapered waveguide section matches the width of the straight waveguide section, and the width of the other end of the tapered waveguide section matches the width of the transmission waveguide section.

[0068] The connecting waveguide segment helps to improve the coupling efficiency of light waves and reduce the transmission loss of light waves between different waveguide segments. Among them, the straight waveguide segment is used to connect the optical input port and the tapered waveguide segment. The main function is to stably transmit light waves and ensure that the light waves smoothly enter the waveguide system from the input port. The design of the straight waveguide segment is usually relatively simple, and parameters such as width and refractive index are optimized to ensure that the light waves can be transmitted efficiently. The main function of the tapered waveguide segment is to serve as a transition structure for connecting the straight waveguide segment and the transmission waveguide segment. This design can reduce the reflection and scattering of light waves caused by sudden changes in waveguide size or shape, thereby improving the transmission efficiency of light waves. The width of one end of the tapered waveguide segment matches that of the straight waveguide segment, while the width of the other end matches that of the transmission waveguide segment. This gradual design can smoothly adjust the propagation mode of the light wave and reduce mode mismatch and loss during transmission between waveguides.

[0069] The laser signal is first transmitted through the straight waveguide section. When the laser signal reaches the tapered waveguide section, the gradual width change of the tapered waveguide section allows the laser signal to smoothly transition from one waveguide geometry to another, which helps reduce reflection and scattering. Within the tapered waveguide section, the propagation mode of the laser signal gradually adjusts to adapt to the geometry of the transmission waveguide section. This smooth transition helps maintain the transmission quality of the laser signal and reduces optical loss. When the laser signal enters the transmission waveguide section from the tapered waveguide section, since the widths of the two have been precisely matched, the laser signal can efficiently enter the transmission waveguide section and continue its transmission process. By reducing the mode mismatch between the waveguides, the coupling efficiency of the laser signal can be improved. The smooth transition design of the tapered waveguide section helps reduce transmission loss between waveguides. Overall, this design helps improve the optical transmission performance of the waveguide.

[0070] In a preferred embodiment, referring to FIG2 , which is a cross-sectional view of FIG1 along dashed line A, the polarizer further comprises a buffer layer disposed between the substrate layer and the optical waveguide layer. The buffer layer and the upper cladding layer are composed of silicon oxide or silicon dioxide. The thickness of each of the buffer layer and the upper cladding layer is greater than 3 μm. The thickness of the buffer layer and the upper cladding layer may be the same or different.

[0071] The buffer layer is disposed between the substrate layer and the optical waveguide layer, primarily to reduce mechanical stress between the two layers. Because different materials may have different coefficients of thermal expansion, the buffer layer can mitigate thermal stress and reduce damage caused by temperature fluctuations. The buffer layer can also help improve the manufacturing quality of the optical waveguide layer by providing a smoother, more uniform foundation, helping to reduce defects and unevenness within the layer. The buffer layer also prevents impurities from the substrate layer from diffusing into the optical waveguide layer, thereby maintaining the high purity and low loss of the optical waveguide layer.

[0072] Silicon oxide (SiO) and silicon dioxide (SiO2) are two commonly used materials for the buffer layer and the upper cladding layer. These materials have low light absorption and good chemical stability, making them suitable for high-performance optical applications.

[0073] When designing such a multilayer structure, it is necessary to consider the thermal expansion coefficients between different materials. If the thermal expansion coefficients are not properly matched, large mechanical stresses may be generated between the materials, thereby affecting the stability and life of the device. The design of the buffer layer and the upper cladding layer is not only for mechanical stability, they can also affect the propagation of light waves. By adjusting the thickness and refractive index of these layers, the mode propagation characteristics of the waveguide can be optimized, such as reducing mode dispersion, improving mode confinement, etc. More specifically, no specific limitations are made in this embodiment. In order to ensure sufficient mechanical strength and optical performance, in a preferred embodiment, the thickness of the buffer layer and the upper cladding layer are both greater than 3 microns, and the choice of thickness depends on the required degree of stress relaxation and the propagation characteristics of the light waves. The thickness of the buffer layer and the upper cladding layer can be the same or different, depending on the specific design requirements, such as different refractive index contrasts, thermal expansion coefficient matching, etc., which are not specifically limited in this embodiment.

[0074] In a preferred embodiment, as shown in Figure 9, the polarizer also includes an export waveguide structure, and the transmission waveguide segment is arranged between the export waveguide structures; the export waveguide structure is used to export the TM mode light in the laser signal; the width of the export waveguide structure is 0.2um~0.5um, and the distance between the export waveguide structure and the transmission waveguide segment is 2um~3um.

[0075] The decoupling waveguide structure is designed to specifically extract or decoupling TM-mode lightwaves from the laser signal. The TM mode refers to a lightwave in which the magnetic field component of the electromagnetic field is primarily aligned along the transverse direction of the waveguide. This design enhances the polarization selectivity of the polarizer, effectively distinguishing and processing lightwaves of different polarization modes. To ensure sufficient optical coupling and avoid unnecessary cross-coupling of lightwaves, the distance between the decoupling waveguide structure and the transmission waveguide segment is set to 2 to 3 microns.

[0076] The derivation waveguide structure is able to derivate TM (transverse magnetic) mode light, primarily due to the waveguide structure's geometric shape and refractive index distribution guiding electromagnetic waves. In a waveguide, the TM mode refers to an electromagnetic wave whose electric field component is primarily aligned along the waveguide's longitudinal direction (propagation direction), while the magnetic field component is primarily in a plane perpendicular to the propagation direction. The following are several key factors that explain why the derivation waveguide structure can derivate TM mode light:

[0077] 1. Waveguide Geometry: A waveguide is composed of layers of materials with different refractive indices. When light waves reflect at the interfaces between these dissimilar materials, their electric and magnetic field distributions change. Specific interface design can optimize the propagation of specific modes, such as the TM mode. The width and height of the waveguide determine the degree of confinement of the light wave within the waveguide, which in turn affects the formation and propagation of the TM mode. Specific dimensions can make the TM mode more stable and efficient.

[0078] 2. Refractive Index Distribution: The refractive index contrast between different material layers determines the degree of light confinement in the waveguide. A higher refractive index contrast helps better confine the TM mode. The refractive index distribution of the waveguide affects the dispersion characteristics of the mode. Proper design can reduce the dispersion of the TM mode and improve its transmission efficiency.

[0079] 3. Polarization dependence:

[0080] The electric field component of the TM mode primarily aligns along the longitudinal direction of the waveguide, so waveguide design must consider how to effectively support and maintain this electric field distribution. The magnetic field component of the TM mode lies in a plane perpendicular to the waveguide propagation direction. The waveguide structure must support this distribution and minimize magnetic field losses.

[0081] 4. Selection of waveguide materials:

[0082] The optical properties of waveguide materials, such as absorption and scattering losses, have a significant impact on the efficiency of the TM mode. Selecting the appropriate material can optimize the light propagation in the TM mode.

[0083] The accuracy of the extraction waveguide structure is crucial for the effective extraction of the TM mode. Any slight dimensional deviation can lead to mode mismatch or increased loss. In summary, through precise design and fabrication, the extraction waveguide structure can effectively extract TM mode light. Furthermore, differences in the materials used to construct the extraction waveguide structure can also affect the extinction ratio of the polarizer. For more details, see the following examples.

[0084] Example 2:

[0085] In Example 1, a thin-film lithium niobate polarizer is proposed. When only one transmission waveguide section is provided, the polarizer's extinction ratio can reach 5.28 dB. Referring to Figure 1 , as the number of iterations of the structure in Example 1 increases, the polarizer's extinction ratio also increases. A plan view of this embodiment is shown in Figure 10 , and a cross-sectional view of the waveguide is the same as that in Example 1, shown in Figure 2 . The structure proposed in this embodiment is a structure obtained by reproducing the structure in Example 1 four times. The polarizer's extinction ratio in this embodiment can reach 21.1 dB.

[0086] The specific structure of the thin film lithium niobate polarizer is shown in Example 1 and will not be described in detail in this embodiment.

[0087] Example 3:

[0088] In Example 2, a structure is proposed, which is a structure obtained by cycling the structure of Example 1 four times. As shown in Figure 11, when the component material of the lead-out waveguide structure is lithium niobate, the width is 0.2 to 0.5 um, the thickness is 0.3 um, and the distance between the bottom end of the lead-out waveguide structure and the top end of the transmission waveguide section is 2 to 3 um, the extinction ratio of the polarizer in this embodiment can reach 27.4 dB.

[0089] When the constituent materials of the export waveguide structure are Au and Ti, which in this embodiment are a 50nm Ti layer and a 1um Au layer, the width of the export waveguide structure is 0.2~0.5um, and the distance between the export waveguide structure and the top of the transmission waveguide section is 2~3um, the extinction ratio of the polarizer in this embodiment can reach 34.4dB.

[0090] The specific structure of the thin-film lithium niobate polarizer is shown in Example 1 and will not be described in detail in this embodiment.

[0091] Example 4:

[0092] In Example 1, a thin-film lithium niobate polarizer is proposed. In this example, a method for manufacturing a thin-film lithium niobate polarizer is proposed. The method for manufacturing the thin-film lithium niobate polarizer is shown in FIG12 and includes:

[0093] Step 101: making the base layer.

[0094] The base layer is made of single-element semiconductor materials (such as silicon, germanium), group IIIV compound semiconductor materials, group IIVI compound semiconductor materials, organic semiconductor materials or other semiconductor materials known in the art.

[0095] Step 102: Fabricate a buffer layer, an optical waveguide layer, and an upper cladding layer on the surface of the substrate layer.

[0096] The buffer layer, the optical waveguide layer, and the upper cladding layer may be fabricated by thin film deposition processes, including but not limited to chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, or a combination thereof.

[0097] The main function of the buffer layer is to provide a good interface and bonding between different material layers to reduce problems caused by material mismatch. Processes such as chemical vapor deposition, plasma-enhanced chemical vapor deposition, or atomic layer deposition can be used to prepare the buffer layer.

[0098] The optical waveguide layer is a critical layer for laser signal transmission, so its preparation requires special attention to ensure stable transmission of the optical signal. Chemical vapor deposition, plasma-enhanced chemical vapor deposition, or atomic layer deposition processes can also be used, depending on the required material properties and layer thickness of the waveguide layer.

[0099] The upper cladding layer covers the optical waveguide layer, protecting the optical waveguide structure and providing additional support and insulation. Chemical vapor deposition, plasma-enhanced chemical vapor deposition, or atomic layer deposition processes can also be used to achieve suitable upper cladding properties and good coverage. The choice of thin film deposition process depends on factors such as the material, properties, and thickness of the desired film. The combination of different processes can be adjusted according to specific design requirements to ensure that the film quality and performance meet the desired level. Specifically, this is not limited in this embodiment.

[0100] Specifically, as shown in FIG13 and FIG14 , step 102 specifically includes:

[0101] Step 1021: forming the buffer layer on the upper surface of the base layer, and forming an optical waveguide material layer on the buffer layer.

[0102] Among them, the buffer layer is mainly used to reduce the mechanical stress between the substrate layer and the optical waveguide layer. Since the thermal expansion coefficients between different materials may be different, the buffer layer can play a role in alleviating thermal stress and reducing damage caused by temperature changes. The buffer layer can also help improve the manufacturing quality of the optical waveguide layer. It provides a smoother and more uniform foundation for the optical waveguide layer, which helps to reduce defects and unevenness in the optical waveguide layer. The buffer layer can also prevent impurities in the substrate layer from diffusing into the optical waveguide layer, thereby maintaining the high purity and low loss of the optical waveguide layer. Silicon oxide (SiO) and silicon dioxide (SiO2) are two commonly used materials used for the buffer layer. These materials have low light absorption and good chemical stability and are suitable for high-performance optical applications.

[0103] This preparation method may involve multiple steps, including coating, deposition, and etching. For example, a buffer layer can be formed on the substrate layer using techniques such as physical vapor deposition or chemical vapor deposition. Subsequently, the optical waveguide material layer is formed on the buffer layer using similar deposition techniques, or using other appropriate processes.

[0104] Step 1022: removing a portion of the optical waveguide material layer by an etching process to form the optical waveguide layer.

[0105] The etching process includes inductively coupled plasma etching or reactive ion etching, and the optical waveguide material layer is removed by the inductively coupled plasma etching or reactive ion etching to form an optical waveguide layer.

[0106] Inductively coupled plasma etching (ICP) uses high-energy ions from an inductively coupled plasma (ICP) to etch the surface of a material. In this process, an electromagnetic field is used to excite a gas to generate a plasma. These ions impact the surface of the optical waveguide material at high speeds, etching away any excess material.

[0107] Reactive ion etching (RIE) involves introducing gases into a vacuum environment and generating ions through ionization. These ions are then used to etch the optical waveguide material. One advantage of RIE is that it can achieve highly selective etching of materials by selecting different gases and process conditions. The specific details are not detailed in this embodiment.

[0108] Step 1023: forming the upper cladding layer covering the optical waveguide layer.

[0109] An upper cladding layer is covered on the optical waveguide layer. The upper cladding layer may be composed of silicon oxide (SiO) and silicon dioxide (SiO2). These materials have low light absorption and good chemical stability and are suitable for high-performance optical applications.

[0110] The specific structure of the thin film lithium niobate polarizer is shown in Example 1 and will not be described in detail in this embodiment.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A thin-film lithium niobate polarizer, characterized in that, It includes a base layer, an optical waveguide layer, and an upper cladding layer, and the optical waveguide layer is disposed between the base layer and the upper cladding layer; The optical waveguide layer includes an optical input port, an optical output port, a flat layer, and a ridge waveguide layer, and the ridge waveguide layer is disposed on the flat layer; the ridge waveguide layer includes at least one transmission waveguide segment, and connecting waveguide segments are symmetrically connected to both ends of the transmission waveguide segment; The optical input port is used to receive a laser signal and transmit the laser signal to the transmission waveguide segment through the connecting waveguide segment, and the transmission waveguide segment is used to filter the TM-mode light in the laser signal and output the TE-mode light in the laser signal through another connecting waveguide segment and the optical output port.

2. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The connecting waveguide segment includes a straight waveguide segment and a tapered waveguide segment, the straight waveguide segment is connected to the tapered waveguide segment, and the tapered waveguide segment is connected to the transmission waveguide segment; The width of one end of the tapered waveguide segment matches the width of the straight waveguide segment, and the width of the other end of the tapered waveguide segment matches the width of the transmission waveguide segment.

3. The thin-film lithium niobate polarizer according to claim 1, wherein The polarizer further includes a buffer layer, and the buffer layer is disposed between the base layer and the optical waveguide layer; The constituent materials of the buffer layer and the upper cladding layer include silicon oxide or silica; The thicknesses of both the buffer layer and the upper cladding layer are greater than 3um.

4. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The polarizer further includes a waveguide structure for exporting, and the transmission waveguide segment is disposed between the waveguide structures for exporting; the waveguide structures for exporting are used to export the TM-mode light in the laser signal; The width of the waveguide structure for exporting is 0.2um - 0.5um, and the distance between the waveguide structure for exporting and the transmission waveguide segment is 2um - 3um.

5. The thin-film lithium niobate polarizer according to claim 4, wherein The constituent material of the waveguide structure for exporting is Au and Ti.

6. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The refractive index of the upper cladding layer is less than the refractive index of the optical waveguide layer.

7. The thin-film lithium niobate polarizer according to claim 1, wherein The constituent material of the optical waveguide layer includes lithium niobate, the thickness range of the flat layer is 0.1um - 5um; the thickness range of the ridge waveguide layer is 0.1um - 5um.

8. The thin-film lithium niobate polarizer according to claim 1, wherein The optical input port and the optical output port are grating coupling structures.

9. The thin-film lithium niobate polarizer according to claim 1, wherein The material of the base layer includes: elemental semiconductor material, III-V compound semiconductor material, II-VI compound semiconductor material, or organic semiconductor material.

10. The thin-film lithium niobate polarizer according to claim 1, characterized in that, The optical waveguide layer is an etched ridge waveguide, having a single crystal structure, with the tangential direction being X-cut and Y-propagation.

11. A manufacturing method of a thin-film lithium niobate polarizer, which is used to manufacture the thin-film lithium niobate polarizer according to any one of claims 1-10, characterized in that, It includes: Fabricating the base layer; Fabricating a buffer layer, an optical waveguide layer, and an upper cladding layer on the surface of the base layer.

12. The manufacturing method of the thin-film lithium niobate polarizer according to claim 11, characterized in that, The fabricating a buffer layer, an optical waveguide layer, and an upper cladding layer on the surface of the base layer includes: Forming the buffer layer on the upper surface of the base layer; Forming an optical waveguide material layer on the buffer layer; Removing part of the optical waveguide material layer through an etching process to form the optical waveguide layer; Forming the upper cladding layer covering the optical waveguide layer.

13. The manufacturing method of the thin-film lithium niobate polarizer according to claim 12, wherein, The etching process includes inductively coupled plasma etching or reactive ion etching.

Images