Polarization converter and preparation method thereof

Abstract

The invention discloses a polarization converter and a preparation method thereof. The polarization converter comprises a silicon dioxide substrate, a silicon core waveguide, a zinc oxide supporting layer, an asymmetric silver layer and a silicon dioxide substrate, the silicon core waveguide and the zinc oxide supporting layer are attached to the silicon dioxide substrate to form a substrate structure; the asymmetric silver layer is attached to the silicon dioxide substrate to form a silver film structure; the silver film structure is connected with the substrate structure through the zinc oxide supporting layer, and the asymmetric silver layer is located over the silicon core waveguide and does not make contact with the silicon core waveguide. Through a non-contact structure of the asymmetric silver layer and the silicon core waveguide, air is introduced as a low-refractive-index medium to construct a hollow mixed plasmon waveguide structure, so that the transmission loss is effectively reduced, and meanwhile, based on introduction of the asymmetric silver layer, the high integration level and the high conversion rate of the polarization converter are effectively guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polarization converters, in particular to a polarization converter and a preparation method thereof. BACKGROUND

[0002] Currently, to support the rapid development of 5G / 6G, data center interconnection, ultra-large bandwidth, high-speed optical communication systems, higher requirements are put forward for the performance of core devices. As the key carrier of optical signal transmission, the integration, miniaturization and compactness of optical waveguide devices have become one of the important trends in scientific research and industrial application.

[0003] To adapt to the integration demand, researchers have proposed new structures such as photonic crystal waveguide and surface plasmon waveguide, aiming to balance the miniaturization and transmission performance of the device. Among them, waveguide devices with high integration and low loss have attracted widespread attention.

[0004] However, in the above-mentioned technology, the transmission distance of the traditional hybrid plasmonic waveguide is only tens to hundreds of microns. Since its structure depends on the metal structure, the metal has inherent high loss which easily leads to rapid attenuation of optical signals. Although the dielectric-based waveguide has no metal loss, it introduces insertion loss due to the edge effect of the dielectric, making it difficult to achieve high conversion rate deflection conversion in long transmission distance. SUMMARY

[0005] The present application provides a polarization converter and a preparation method thereof, which solves the technical problem that the transmission distance of the traditional hybrid plasmonic waveguide is only tens to hundreds of microns. Since its structure depends on the metal structure, the metal has inherent high loss which easily leads to rapid attenuation of optical signals. Although the dielectric-based waveguide has no metal loss, it introduces insertion loss due to the edge effect of the dielectric, making it difficult to achieve high conversion rate deflection conversion in long transmission distance.

[0006] The polarization converter provided by the present application comprises a silicon dioxide substrate, a silicon core waveguide, a zinc oxide support layer, an asymmetric silver layer and a silicon dioxide substrate;

[0007] The silicon core waveguide and the zinc oxide support layer are attached to the silicon dioxide substrate to form a substrate structure;

[0008] The asymmetric silver layer is attached to the silicon dioxide substrate to form a silver film structure;

[0009] The silver film structure and the substrate structure are connected through the zinc oxide support layer, and the asymmetric silver layer is located directly above the silicon core waveguide and has no contact with the silicon core waveguide.

[0010] Optionally, the zinc oxide support layer is located on both sides of the silicon core waveguide.

[0011] The length of the zinc oxide supporting layer is equal to the length of the silver film structure.

[0012] Optionally, the silicon core waveguide is attached to the silica substrate along the transmission direction of the optical signal.

[0013] The asymmetric silver layer is placed in the same direction as the silicon core waveguide.

[0014] Optionally, the silicon core waveguide is a cuboid, and the total length is equal to the length of the silica substrate.

[0015] The silicon core waveguide includes an input waveguide segment, an output waveguide segment, and a plurality of polarization waveguide segments of different lengths.

[0016] Optionally, the length of the asymmetric silver layer is the sum of the lengths of the output waveguide segment and the plurality of polarization waveguide segments.

[0017] Optionally, the length of the substrate structure is greater than the length of the silver film structure.

[0018] The difference between the length of the substrate structure and the length of the silver film structure is the length of the output waveguide segment.

[0019] Optionally, the polarization waveguide segment includes a first conversion waveguide segment, a second conversion waveguide segment, and a third conversion waveguide segment connected in sequence.

[0020] The asymmetric silver layer is of an asymmetric structure.

[0021] The asymmetric silver layer includes an input segment, a first adjustment segment, a second adjustment segment, and an output segment.

[0022] The initial width of the input segment is a first size, which increases proportionally along the transmission direction of the optical signal until reaching a second size, the length of the input segment is equal to that of the first conversion waveguide segment, and the second size is smaller than the width of the second conversion waveguide segment.

[0023] The width of the first adjustment segment is the second size, and the length of the first adjustment segment is equal to that of the second conversion waveguide segment.

[0024] The initial width of the second adjustment segment is the second size, which increases proportionally along the transmission direction of the optical signal until reaching a third size, and the length of the second adjustment segment is equal to that of the third conversion waveguide segment.

[0025] The width of the output segment is the third size, which is equal to the width of the output waveguide segment, and the length of the output segment is equal to that of the output waveguide segment.

[0026] Optionally, the length of the second conversion waveguide section > the length of the first conversion waveguide section > the length of the third conversion waveguide section > the length of the input waveguide section > the length of the output waveguide section.

[0027] Optionally, the thickness of the silicon dioxide substrate is greater than the thickness of the silicon dioxide substrate.

[0028] The application further provides a preparation method of the polarization converter, comprising:

[0029] A silicon thin film layer and a positive photoresist layer are sequentially deposited on the surface of the silicon dioxide substrate;

[0030] After the mask plate is transferred to the positive photoresist layer by mask alignment technology, an exposure operation and a development operation are performed to form a photoresist mask; the mask plate is drawn with a waveguide contour pattern;

[0031] After a silicon thin film layer is deposited on the photoresist mask as a silicon core waveguide, the positive photoresist layer is peeled off;

[0032] A pre-prepared zinc oxide support layer is moved to a support position of the silicon dioxide substrate by layer transfer method to form a substrate structure; the support position is a boundary on both sides of the silicon core waveguide as the center;

[0033] After a cavity structure processing is performed on the silicon dioxide substrate, a silver metal layer is deposited on the surface of the silicon dioxide substrate by a magnetron sputtering process;

[0034] The deposited silver metal layer is etched according to a polarization conversion contour by a reactive ion etching technology to obtain a silver film structure;

[0035] The silver film structure is transferred to the substrate structure and encapsulated to obtain the polarization converter; wherein the silver film structure and the silicon core waveguide are not in contact.

[0036] As can be seen from the above technical solutions, the application has the following advantages:

[0037] The application provides a polarization converter and a preparation method thereof, the polarization converter comprising a silicon dioxide substrate, a silicon core waveguide, a zinc oxide support layer, an asymmetric silver layer and a silicon dioxide substrate; the silicon core waveguide and the zinc oxide support layer are attached to the silicon dioxide substrate to form a substrate structure; the asymmetric silver layer is attached to the silicon dioxide substrate to form a silver film structure; the silver film structure and the substrate structure are connected through the zinc oxide support layer, and the asymmetric silver layer is located directly above the silicon core waveguide and is not in contact with the silicon core waveguide. By introducing air as a low refractive index medium to construct a hollow type hybrid plasmonic waveguide structure through the non-contact structure of the asymmetric silver layer and the silicon core waveguide, the transmission loss is effectively reduced, and based on the introduction of the asymmetric silver layer, the high integration and high conversion rate of the polarization converter are effectively guaranteed.

[0038] A silicon thin film layer and a positive photoresist layer are sequentially deposited on the surface of a silicon dioxide substrate; after a mask plate is transferred to the positive photoresist layer by using a mask alignment technology, an exposure operation and a development operation are performed to form a photoresist mask; the mask plate is drawn with a waveguide contour pattern; after a silicon thin film layer is deposited on the photoresist mask as a silicon core waveguide, the positive photoresist layer is stripped; a pre-prepared zinc oxide support layer is moved to a support position of the silicon dioxide substrate by using a layer transfer method to form a substrate structure; the support position is a boundary on both sides of the silicon core waveguide as the center; after a cavity structure processing is performed on the silicon dioxide substrate, a silver metal layer is deposited on the surface of the silicon dioxide substrate by using a magnetron sputtering process; the deposited silver metal layer is etched according to a polarization conversion contour by using a reactive ion etching technology to obtain a silver film structure; the silver film structure is transferred to the substrate structure and packaged to obtain a polarization converter; and the silver film structure is in contact with the silicon core waveguide. Through modular operation, precise integration of heterogeneous materials is realized, and excellent process compatibility is exhibited, especially in three-dimensional laminated construction. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0040] Figure 1 A structure schematic diagram of a polarization converter provided by the embodiment of the present application;

[0041] Figure 2 A cross-sectional structure schematic diagram of a polarization converter provided by the embodiment of the present application in the output direction;

[0042] Figure 3 A top view structure schematic diagram of a silicon core waveguide and an asymmetric silver layer in a polarization converter provided by the embodiment of the present application;

[0043] Figure 4 A real part schematic diagram of an effective mode refractive index of an input-output waveguide provided by the embodiment of the present application;

[0044] Figure 5 An electric field distribution evolution diagram of a TE-TM mode conversion process provided by the embodiment of the present application;

[0045] Figure 6 A whole process schematic diagram of polarization conversion provided by the embodiment of the present application;

[0046] Figure 7A performance performance diagram of a polarization converter under different wavelengths provided by the embodiment of the present application is provided.

[0047] Figure 8 A step flow chart of a preparation method of a polarization converter provided by the embodiment of the present application is provided.

[0048] Figure 9 A process diagram of a preparation method of a polarization converter provided by the embodiment of the present application is provided. DETAILED DESCRIPTION

[0049] The embodiment of the present application provides a polarization converter and a preparation method thereof, and is used for solving the technical problems that the transmission distance of a traditional hybrid plasmonic waveguide is only dozens to hundreds of microns, the light signal is easily attenuated due to the inherent high loss of metal which is dependent on the metal structure, and the high conversion rate deflection conversion under long transmission distance is difficult to realize due to the insertion loss caused by the edge effect of the medium.

[0050] In order to make the purpose, characteristics and advantages of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the following described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0051] Please refer to Figures 1-2 , Figure 1 A structural diagram of a polarization converter provided by the embodiment of the present application is provided. Figure 2 A cross-sectional structural diagram of a polarization converter provided by the embodiment of the present application in an output direction is provided.

[0052] The polarization converter provided by the present application comprises a silicon dioxide substrate, a silicon core waveguide, a zinc oxide support layer, an asymmetric silver layer and a silicon dioxide substrate;

[0053] The silicon core waveguide and the zinc oxide support layer are attached to the silicon dioxide substrate to form a substrate structure.

[0054] The asymmetric silver layer is attached to the silicon dioxide substrate to form a silver film structure.

[0055] The silver film structure and the substrate structure are connected through the zinc oxide support layer, and the asymmetric silver layer is located directly above the silicon core waveguide and has no contact between the silicon core waveguide.

[0056] The silicon dioxide substrate ( The substrate is a basic supporting component of the polarization converter, made of silica material, with good insulation and optical stability. In the device, it mainly undertakes the physical bearing function, provides a stable attachment platform for the core functional structures such as the silicon core waveguide and the zinc oxide supporting layer, and ensures that the structure of the whole device does not deviate or be damaged during the working process. At the same time, its stable optical properties can avoid additional interference to the input / output optical signal, and ensure the initial state of the optical signal stable before polarization conversion, laying a foundation for subsequent mode conversion.

[0057] The silicon core waveguide refers to an optical waveguide structure made of silicon as the core material, which is the core channel of optical signal transmission and polarization mode conversion in the device. Its core function is to realize the input of TE mode optical signal and the output of TM mode optical signal. At the same time, the silicon core waveguide directly affects the effective refractive index of the hybrid plasmonic waveguide through width change, and the regulation of the effective refractive index is the key prerequisite for realizing the phase matching of TE mode and TM mode. Only when the phase matching condition is met, can the polarization conversion be efficiently carried out. In addition, in this embodiment, the silicon core waveguide also adopts a segmented design, which completes the gradual conversion from TE mode to TM mode and signal shaping through the cooperation of different functional segments.

[0058] The zinc oxide supporting layer (ZnO supporting layer) is made of zinc oxide material, which has good mechanical strength and optical compatibility, and will not react adversely with other structural materials, nor will it cause significant loss to the optical signal. In this embodiment, it functions as a connecting structure. On the one hand, it is attached to both sides of the silica substrate, supporting the top silica substrate and the asymmetric silver layer. On the other hand, through its height design, it ensures that the asymmetric silver layer can be stably positioned directly above the silicon core waveguide without direct contact between them, providing support for the formation of the hollow structure in the device, while avoiding the loss of optical signal caused by structural contact.

[0059] The asymmetric silver layer refers to a silver thin film structure processed by a reactive ion etching process to match the polarization conversion profile. As a metal material, it has surface plasmon characteristics and can interact with optical signals to realize polarization mode regulation of optical signals. In this embodiment, the asymmetric silver layer is a gradually changing structure, with its width increasing from the initial first size to the second size in proportion, and maintaining the second size within a certain length, and then increasing to the same width as the waveguide output segment of the silicon core waveguide. Figure 2 and Figure 3 Through this gradually changing structure, the polarization direction of the TE mode optical signal is smoothly rotated and gradually converted from TE mode to TM mode. Among them, Figure 2 h m is the thickness of the asymmetric silver layer, h air is the distance between the asymmetric silver layer and the silicon core waveguide, i.e. the thickness of the air medium.Si and w Si are the thickness and width of the silicon core waveguide, respectively.

[0060] The material of the silica substrate is the same as that of the silica substrate, which serves as an auxiliary carrier for the asymmetric silver layer, provides a flat and stable surface for the asymmetric silver layer, ensures that the asymmetric silver layer does not fall off or deform during processing (such as magnetron sputtering deposition) and working process; at the same time, it cooperates with the zinc oxide support layer, and is fixedly connected through the zinc oxide support layer, further ensuring the positional accuracy between the asymmetric silver layer and the silicon core waveguide, avoiding the decline of polarization conversion effect caused by positional deviation, and protecting the stability and reliability of the entire device structure.

[0061] In this embodiment, the polarization converter belongs to a hollow hybrid plasmonic waveguide polarization converter, which adopts a three-dimensional laminated hollow structure with a silica substrate-intermediate hollow area-silica substrate as the core framework. The bottom layer forms a substrate structure based on a silica substrate, with a silicon core waveguide attached in the middle. The silicon core waveguide is designed in five sections, including an input waveguide section, a first polarization conversion waveguide section A, a second polarization conversion waveguide section B, a third polarization conversion waveguide section C, and an output waveguide section D. Zinc oxide support layers are attached to the two side boundaries of the silica substrate. The upper layer forms a silver film structure with a silica substrate as a carrier combined with an asymmetric silver layer. The lower surface of the silica substrate is made into an asymmetric silver layer through magnetron sputtering and then reaction ion etching. The asymmetric silver layer is a gradient structure, and is equal in width to the silicon core waveguide at the output end. The silver film structure is fixedly connected with the substrate structure through the zinc oxide support layers on both sides, so that the asymmetric silver layer is accurately located directly above the silicon core waveguide without contact between them, thereby forming a hollow area with air as the low refractive index medium in the middle. Through this structure, TE mode optical signals can be input from the input waveguide, guided by the gradient asymmetric silver layer in each polarization conversion waveguide section to complete polarization conversion, and then output as TM mode optical signals from the output waveguide. At the same time, it has high conversion rate and low loss characteristics, can be directly bonded or monolithically integrated with miniature elements such as silicon photon waveguide and CMOS sensor, realizes on-chip polarization regulation, reduces the size of the optical system by 1-2 orders of magnitude, and maintains high performance.

[0062] The polarization converter is used to convert transverse electric wave mode optical signals into transverse magnetic wave mode optical signals.

[0063] Transverse electric wave mode (TE mode) refers to the electric field vector being completely in the plane perpendicular to the direction of light signal transmission, i.e. the component of the electric field in the transmission direction is zero, only the transverse component perpendicular to the transmission direction is reserved, which is the basic transmission mode of the silicon photon waveguide in the optical communication system.

[0064] Transverse Magnetic Mode (TM mode) refers to the magnetic field vector (H) is completely located in the horizontal plane perpendicular to the optical signal transmission direction, that is, the component of the magnetic field in the transmission direction is zero, only the transverse component perpendicular to the transmission direction is reserved; and the electric field vector can contain transverse component and longitudinal component in the transmission direction, the overall field distribution presents the characteristic of "no longitudinal component of the magnetic field".

[0065] In the embodiment, the optical signal input into the polarization converter is in TE mode, the asymmetric silver layer in the polarization converter induces a strong electromagnetic field through the gradually changing asymmetric structure of the asymmetric silver layer, and the TE mode optical field in the silicon core waveguide is coupled to gradually push the electric field vector to rotate; before the output waveguide segment, the optical signal is completely converted from TE mode to TM mode, and then is stably output after being shaped by the output waveguide segment, and the whole process relies on the throughness of the silicon core waveguide and the collaborative design of each layer structure to realize low-loss and high-conversion-rate mode conversion.

[0066] In an example of the present application, the zinc oxide support layer is located at the boundary of the silicon core waveguide-centered silicon dioxide substrate on both sides;

[0067] The length of the zinc oxide support layer is equal to the length of the silver film structure.

[0068] As shown in Figure 1 and Figure 2 The zinc oxide support layer is specifically located at the boundary of the silicon core waveguide-centered silicon dioxide substrate on both sides, and the length of the zinc oxide support layer is equal to the length of the silver film structure, the silver film structure is fixedly connected with the substrate structure through the zinc oxide support layers on both sides with equal length, so that the asymmetric silver layer is accurately located above the silicon core waveguide without contact, thereby forming a hollow region with air as the low refractive index medium in the middle.

[0069] The thickness of the silicon dioxide substrate is greater than that of the silicon dioxide substrate.

[0070] In an example of the present application, the silicon core waveguide is attached to the silicon dioxide substrate along the transmission direction of the optical signal;

[0071] The asymmetric silver layer is placed in the same direction as the silicon core waveguide.

[0072] In the embodiment, the silicon core waveguide is linearly and continuously attached to the middle region of the upper surface of the silicon dioxide substrate along the horizontal transmission direction of the optical signal from the input end to the output end of the device, and the overall extension trajectory is completely coincident with the preset transmission path of the optical signal without any directional deviation, so that the TE mode optical signal can be continuously transmitted along the fixed path in the silicon core waveguide after entering from the input waveguide, avoiding optical signal leakage or transmission path bending caused by waveguide directional deviation.

[0073] From the device input end to the output end, the asymmetric silver layer extends synchronously with the extension path of the silicon core waveguide, is located directly above the silicon core waveguide and is in contact with the silicon core waveguide throughout the journey. At the same time, the width change direction of the asymmetric silver layer is synchronized with the light signal transmission direction of the silicon core waveguide, ensuring that the width of the asymmetric silver layer can match the polarization conversion requirement of the light signal in the silicon core waveguide at each stage of light signal transmission. Relying on the surface plasmon characteristics of metal silver to guide the conversion of TE mode to TM mode, the co-directional placement enables the asymmetric silver layer to continuously act on the light signal in the silicon core waveguide throughout the entire path of light signal transmission, so that the light signal gradually adapts to the polarization change with the width change of the asymmetric silver layer, thereby ensuring that the TM mode completes mode field shaping before output, avoiding mode field distortion caused by directional deviation, and ensuring that the TM mode is output in a low-loss, symmetric and stable state.

[0074] In an example of the present application, the silicon core waveguide is a cuboid, and the total length is equal to the length of the silicon dioxide substrate.

[0075] The silicon core waveguide includes an input waveguide segment, an output waveguide segment and a plurality of polarization waveguide segments of different lengths.

[0076] As shown in Figure 1 and Figure 3 , the silicon core waveguide is in a standard cuboid structure, and its cross section is a rectangle with fixed dimensions, and the length and width dimensions are adapted to the light signal transmission requirement, and the thickness direction is perpendicular to the surface of the silicon dioxide substrate, ensuring effective restriction of the light signal inside the silicon core. There is no shape distortion or size mutation along the light signal transmission direction, maintaining the continuity and integrity of the cuboid structure.

[0077] The total length of the silicon core waveguide is equal to the length of the silicon dioxide substrate, so that the silicon core waveguide completely covers the middle region of the silicon dioxide substrate along the transmission direction, and the side surface of the cuboid is parallel to the edge of the silicon dioxide substrate and forms a uniform spacing with the zinc oxide support layer on both sides, and the overall structure is symmetrically distributed on the silicon dioxide substrate. Through the regular boundary of this structure, the difference in refractive index between the silicon material and the surrounding medium (air, silicon dioxide) forms a stable lateral restriction on the light signal, avoiding leakage of the light signal outside the waveguide and reducing the transmission loss of the light signal. At the same time, the length setting avoids structural suspension or unevenness, effectively improving the overall mechanical stability of the polarization converter. In addition, the silicon core waveguide is divided into an input waveguide segment, an output waveguide segment and a plurality of polarization waveguide segments of different lengths to adapt to the width change of the subsequent asymmetric silver layer, so that the mode conversion rate and the polarization conversion rate can reach the peak value.

[0078] Optionally, the length of the asymmetric silver layer is the sum of the lengths of the output waveguide segment and the plurality of polarization waveguide segments.

[0079] As shown in Figure 1 and Figure 3As shown, the asymmetric silver layer covers the output waveguide segment and multiple polarization waveguide segments of the silicon core waveguide. The input waveguide segment of the silicon core waveguide is used to introduce TE mode optical signals, in which case polarization modulation is not required. To avoid unnecessary interaction between the etched silver layer and the optical signal in the non-conversion region and to reduce additional insertion loss, its length and placement are limited to the output waveguide segment and multiple polarization waveguide segments. The conversion of the optical signal is achieved by covering the polarization waveguide segments. At the same time, the coverage of the output waveguide segment assists in the mode field shaping of the optical signal in TM mode, ensuring stable output of the converted signal.

[0080] Optionally, the length of the substrate structure is greater than the length of the silver film structure;

[0081] The difference between the length of the substrate structure and the length of the silver film structure is the length of the output waveguide segment.

[0082] Optionally, the polarization waveguide segment includes a first conversion waveguide segment, a second conversion waveguide segment, and a third conversion waveguide segment connected in sequence;

[0083] The asymmetric silver layer has an asymmetric structure;

[0084] The asymmetric silver layer includes an input segment, a first adjustment segment, a second adjustment segment, and an output segment;

[0085] The initial width of the input segment is a first dimension, which is increased proportionally along the transmission direction of the optical signal until it reaches a second dimension. The length of the input segment is equal to that of the first conversion waveguide segment, and the second dimension is smaller than the width of the second conversion waveguide segment.

[0086] The width of the first adjustment segment is the second dimension, and the length of the first adjustment segment is equal to that of the second conversion waveguide segment;

[0087] The initial width of the second adjustment segment is the second dimension, and it increases proportionally along the transmission direction of the optical signal until it reaches the third dimension. The length of the second adjustment segment is equal to that of the third conversion waveguide segment.

[0088] The width of the output segment is the third dimension, which is equal to the width of the output waveguide segment, and the length of the output segment is equal to the length of the output waveguide segment.

[0089] like Figure 3 As shown, the silicon core waveguide includes a length of L Si The input waveguide segment and polarization waveguide segment include a first conversion waveguide segment A, a second conversion waveguide segment B, and a third conversion waveguide segment C connected in sequence, with lengths L and L respectively. A L B L C The length of the output waveguide segment is LD .

[0090] Meanwhile, the silver strip is etched into an asymmetrically tapered silver strip, which has an asymmetric distribution of width variation trajectory and edge profile relative to the central axis of the silicon core waveguide, and the width variation rate on one side is different from that on the other side, forming an asymmetric strip structure. The width is proportionally widened from the first size w to the second size w m The width variation of the input section can guide the preliminary rotation of the electric field vector of the TE mode in the first conversion waveguide section; the second size is fixed in the width design in the first adjustment section, and the stable metal surface plasmon effect is used to promote the key rotation of the electric field vector of the TE mode to realize the complete conversion to the TM mode; the second adjustment section proportionally widens the second size to the third size, i.e., the third conversion waveguide section, so as to realize the mode field shaping of the TM mode and make the field distribution gradually tend to be symmetric; and the width of the output section is kept at the third width to keep the symmetric field distribution of the TM mode in the output waveguide section, so as to ensure the stable output of the optical signal and effectively reduce the transmission loss.

[0091] Optionally, the length of the second conversion waveguide section > the length of the first conversion waveguide section > the length of the third conversion waveguide section > the length of the input waveguide section > the length of the output waveguide section.

[0092] In the embodiment, one end of the input waveguide section is connected to an external optical signal input device, and the other end is connected to the first conversion waveguide section to receive and stably transmit the TE mode optical signal; the end of the first conversion waveguide section away from the input waveguide section is connected to the second conversion waveguide section to provide space for the preliminary polarization adjustment of the TE mode; the second conversion waveguide section is the core area of the polarization conversion and is connected to the first conversion waveguide section and the third conversion waveguide section at both ends and is the key carrier for the complete conversion of the TE mode to the TM mode; the other end of the third conversion waveguide section is connected to the output waveguide section to perform mode field shaping on the converted TM mode; and the output waveguide section is finally connected to an external receiving device to complete the output of the TM mode. Meanwhile, the length relationship is precisely matched with the segmented structure of the asymmetric silver layer (input section, first adjustment section, second adjustment section, and output section) - the lengths of the sections of the asymmetric silver layer are consistent with the lengths of the corresponding waveguide sections, so that the polarization regulation function of the asymmetric silver layer can be differentially used according to the length difference of the waveguide sections.

[0093] In the embodiment, as shown in Figure 4 The width of the effective refractive index silicon core waveguide of the polarization converter varies, and phase matching needs to be performed on the input TE mode optical signal and the output TM mode optical signal to effectively realize the mode conversion function.

[0094] In addition, to show the effectiveness of the function of the polarization converter provided in the embodiment of the application, please refer toFigure 5 (a) and Figure 5 (b) of FIG. 6 show the process of TE mode light signal dissipation and TM mode light signal formation when the polarization converter is working. As shown in Figure 5 (a) of FIG. 6, it shows that the TE mode light signal gradually disappears in the propagation direction after entering the polarization converter, while Figure 5 (b) of FIG. 6 shows the gradual generation of TM mode light signal in the propagation direction. At the same time, the time domain analysis further shows that the exponential decay of TE mode and the enhancement of TM mode are consistent with the theory of polarization conversion.

[0095] As shown in Figure 6 (a) of FIG. 6, Figure 6 (d) of FIG. 6, based on the three-dimensional full vector field calculation method, quantitatively shows the dynamic process of TE-TM mode conversion in the polarization converter, which includes the cross-sectional electromagnetic field distribution characteristics at different positions along the waveguide axis. Figure 6 (a) of FIG. 6-6 (d) shows the cross-sectional view of the device at different positions along the propagation direction. Figure 6 (a) of FIG. 6 shows the mode field distribution and electric field vector arrow of the input waveguide TE mode, and the typical TE mode field distribution and electric field vector arrow distribution can be observed at the position of the silicon core waveguide. Figure 6 (b) of FIG. 6 shows that the metal silver strip is introduced and placed above the silicon core waveguide to realize polarization conversion, and the field distribution characteristics and electric field vector arrow distribution show that the TE mode has begun to change to TM mode, but the vector rotation has not been completed. Figure 6 (c) of FIG. 6 shows a typical TM mode field distribution and electric field vector arrow distribution, indicating that the effective conversion from TE mode to TM mode has been basically completed. Figure 6 (d) of FIG. 6 shows the complete TM mode field distribution and electric field vector arrow distribution at the output waveguide, indicating that the converted TM mode has formed a good symmetric distribution characteristic through effective mode field distribution shaping.

[0096] Exemplarily, the present application proposes a specific parameter design based on the above-mentioned polarization converter. In the present polarization converter, the polarization conversion of the filter is realized under the premise of the following two conditions: the phase matching of TE mode and TM mode can complete the polarization conversion; the TM mode can be output with extremely low loss. In order to ensure the complete conversion of TE mode to TM mode, the designed waveguide length is as follows: the input waveguide segment length L Si =1μm, the polarization conversion segment length L A =2µm, L B =3.5µm, L C =1.2µm, the output waveguide segment length L D=0.8µm, the width w of the silver layer introduced in the polarization conversion section A is 100nm, the width w of the silver layer in the polarization conversion section B is 155nm, and the performance of the polarization converter under the above parameters in different wave bands (1450-1650nm) is shown in (a) and (b) of FIG. 6. m Figure 7 Figure 7 Figure 7 Figure 7

[0097] The embodiment of the present application provides a polarization converter, which comprises a silicon dioxide substrate, a silicon core waveguide, a zinc oxide support layer, an asymmetric silver layer and a silicon dioxide substrate; the silicon core waveguide and the zinc oxide support layer are attached to the silicon dioxide substrate to form a substrate structure; the asymmetric silver layer is attached to the silicon dioxide substrate to form a silver film structure; the silver film structure is connected to the substrate structure through the zinc oxide support layer, and the asymmetric silver layer is located directly above the silicon core waveguide and has no contact with the silicon core waveguide. Through the non-contact structure of the asymmetric silver layer and the silicon core waveguide, air is introduced as a low refractive index medium to construct a hollow hybrid plasmonic waveguide structure, so that the transmission loss is effectively reduced, and meanwhile, based on the introduction of the asymmetric silver layer, the high integration and high conversion rate of the polarization converter are effectively ensured.

[0098] FIG. 6 shows a step flow chart of a preparation method of the polarization converter in the embodiment of the present application. Figure 8 Figure 8 FIG. 6 shows a step flow chart of a preparation method of the polarization converter in the embodiment of the present application.

[0099] The embodiment of the present application further provides a preparation method of a polarization converter, which comprises the following steps:

[0100] Step 801: depositing a silicon film layer and a positive photoresist layer on the surface of a silicon dioxide substrate in sequence;

[0101] Step 802: transferring a mask plate to the positive photoresist layer by using a mask alignment technology, and then performing exposure operation and development operation to form a photoresist mask; the mask plate is drawn with a waveguide contour pattern;

[0102] ​​​​​​Mask alignment technology is a key technology in the lithography process to ensure the precise positioning of the mask pattern and the existing pattern on the substrate. It is mainly used to transfer the design pattern from the mask to the specified area of the substrate, ensuring the overlay accuracy of multi-layer structure. In specific implementation, the mask plate carrying the pattern and the substrate coated with photoresist are fixed on the alignment table of the lithography machine respectively. The alignment marks on the mask and the substrate are identified by an optical imaging system (such as a microscope). The relative position of the two (including translation, rotation, scaling) is adjusted by using a piezoelectric drive or a precision mechanical adjustment mechanism. The marks are completely overlapped (alignment accuracy can reach microns to nanometers). After alignment, the relative position is kept stable. The mask pattern is transferred to the photoresist by UV exposure.

[0103] In this embodiment, a thin film deposition process is used to uniformly deposit a silicon thin film layer on the clean upper surface of the silicon dioxide substrate. After the silicon thin film layer is solidified and stable, a positive photoresist layer is deposited on its surface. This layer needs to completely cover the silicon thin film layer to provide a processable medium layer for subsequent waveguide profile transfer. Then, the mask plate pattern is accurately attached to the surface of the positive photoresist layer through mask alignment technology, ensuring that the waveguide profile on the mask plate completely overlaps with the preset position of the subsequent silicon core waveguide. After alignment, the exposure operation is performed, causing the part of the photoresist layer irradiated by the light-transmitting area of the mask plate to change in chemical properties. Then, through the development operation, the changed photoresist is removed, and the photoresist in the unexposed area is retained, finally forming a photoresist mask on the surface of the silicon thin film layer consistent with the mask plate pattern. The mask plate is drawn with the waveguide and device profile pattern.

[0104] Step 803: After depositing a silicon thin film layer as a silicon core waveguide on the photoresist mask, the positive photoresist layer is peeled off.

[0105] After obtaining the photoresist mask, it is used as a shield to deposit a silicon thin film layer again using the thin film deposition process on the mask and the exposed area of the silicon thin film layer not covered by the mask. At this time, the second deposited silicon thin film will fill the pattern gap of the photoresist mask. After deposition, the remaining photoresist mask on the surface is removed by photoresist peeling process (such as using special peeling liquid or plasma cleaning), only the silicon core waveguide structure is retained. This waveguide will be directly attached to the silicon dioxide substrate, becoming the core channel for optical signal transmission and polarization conversion.

[0106] Step 804: The pre-prepared zinc oxide support layer is moved to the support position of the silicon dioxide substrate by layer transfer method to form a substrate structure. The support position is the boundary on both sides of the silicon core waveguide as the center.

[0107] Layer transfer is a technique for transferring a pre-fabricated thin-layer material (such as a semiconductor thin film or oxide layer) from a virgin substrate to a target substrate. Its core principle is to achieve controllable separation of the material layer from the virgin substrate and stable bonding with the target substrate. The specific process typically includes: preparing a high-quality thin-layer material on the virgin substrate through epitaxial growth or deposition processes; and then using ion implantation (such as...) A weak bonding interface is created between the material layer and the original substrate by methods such as injection to form a release layer or chemical etching. The thin layer material is then aligned and bonded to the target substrate. The thin layer is separated from the original substrate by thermal annealing, mechanical peeling or chemical treatment. Finally, the thin layer and the target substrate are tightly bonded by low-temperature bonding (such as plasma-activated bonding) or pressure curing process. This method is suitable for the integration of heterogeneous materials and the fabrication of flexible electronic devices.

[0108] The pre-prepared zinc oxide support layer is precisely moved to the support position on the silicon dioxide substrate—that is, the two sides centered on the silicon core waveguide, ensuring that the support layers on both sides are symmetrically distributed and do not contact the silicon core waveguide. After the zinc oxide support layer and the silicon dioxide substrate are stably bonded, the substrate structure is obtained.

[0109] Step 805: After processing the cavity structure of the silicon dioxide substrate, a silver metal layer is deposited on the surface of the silicon dioxide substrate using a magnetron sputtering process.

[0110] Step 806: Using reactive ion etching technology, the deposited silver metal layer is etched according to the polarization conversion profile to obtain the silver film structure;

[0111] Magnetron sputtering is a physical vapor deposition technique that uses a magnetic field to confine the movement of electrons in a plasma, increasing the probability of collisions with the sputtering gas (usually Ar) and improving plasma density to efficiently sputter target atoms and deposit them on the substrate surface to form a thin film. Specifically, in a vacuum sputtering chamber, the target (the material to be deposited) is connected to the negative electrode, and the substrate is connected to the positive electrode or grounded. After low-pressure Ar gas is introduced, the Ar gas is ionized under the action of a radio frequency or DC power supply to form plasma. Electrons undergo helical motion under the combined influence of the magnetic and electric fields, bombarding the target material in large numbers. Ions, making High-speed impact on the target surface causes target atoms to be sputtered out and move toward the substrate, eventually depositing a uniform thin film on the substrate surface. By controlling the sputtering power, gas pressure, time, and the distance between the target and the substrate, the film thickness and composition can be precisely controlled.

[0112] Reactive ion etching (RIE) is a dry etching technique that combines chemical etching and physical sputtering. It involves introducing a reactive gas (such as...) into a vacuum chamber... , (etc.) The method utilizes radio frequency power to generate plasma, in which active free radicals react chemically with the material to be etched to produce volatile products. At the same time, high-energy ions bombard the material surface under the acceleration of the electric field to enhance the etching effect, thereby achieving high-precision patterning of the material. In specific implementation, the substrate covered with a patterned photoresist mask is first placed in the cavity. After evacuation, a specific proportion of reactive gas is introduced. The radio frequency power and gas pressure are adjusted to stabilize the plasma generation. By controlling the etching time and plasma parameters, the areas not protected by the mask are selectively etched, and finally, micro-nano structures with steep edges and precise dimensions are obtained.

[0113] Simultaneously, the silver film structure can be fabricated. First, a silicon dioxide substrate of the same material as the silicon dioxide substrate is selected. A cavity structure is fabricated on the silicon dioxide substrate to reduce its thickness and avoid excessive weight. A silver metal layer is deposited on the fabricated silicon dioxide substrate using magnetron sputtering, ensuring high purity, uniform thickness, and tight adhesion to the substrate. Then, reactive ion etching is used to etch the deposited silver metal layer according to the polarization conversion profile, obtaining the silver film structure. This polarization conversion profile is similar to that described above. Figures 1-3 The contours of the asymmetric silver layers within the silicon waveguide are identical, ensuring that the etched asymmetric silver layers precisely correspond to the functional segments of the silicon waveguide, thus obtaining the silver film structure. Specifically, the silver metal layer is etched to form the aforementioned asymmetric silver layer.

[0114] Step 807: Transfer the silver film structure onto the substrate structure and encapsulate it to obtain the polarization converter; wherein, there is no contact between the silver film structure and the silicon core waveguide.

[0115] Finally, the silver film structure is transferred onto the substrate structure, ensuring that the asymmetric silver layer is relatively isolated from the silicon core waveguide and is located directly above the silicon core waveguide without contact, thus forming a hollow air dielectric region. After the transfer is completed, the device is packaged, such as with insulating materials or in vacuum, to ensure the stability of the internal structure and to prevent interference from the external environment, resulting in a polarization converter.

[0116] like Figure 9 As shown, to facilitate user understanding, this embodiment provides a schematic diagram of a method for fabricating a polarization converter.

[0117] In this embodiment, the preparation method includes the following process:

[0118] (a) depositing a silicon thin film and a positive photoresist (PR) layer on the surface of a SiO2 substrate in sequence; (b) completing photoresist exposure and development processes through mask alignment; (c) implementing secondary deposition of the silicon layer; (d) performing photoresist stripping process; (e) constructing a ZnO support layer stack structure by using layer transfer method; (f) selecting a SiO2 substrate to process a cavity structure; (g) depositing a silver metal layer on the surface of the SiO2 by using a magnetron sputtering process; (h) forming a transducer profile on the silver layer by using a reactive ion etching technology; (i) finally completing transfer and packaging of the silver film structure. The process flow realizes precise integration of heterogeneous materials through modular operation, and especially exhibits excellent process compatibility in three-dimensional stack construction.

[0119] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for some technical features thereof; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A polarization converter, characterized in that, The substrate structure comprises a silica substrate, a silicon core waveguide, a zinc oxide support layer, an asymmetric silver layer and a silica substrate sheet; The silicon core waveguide and the zinc oxide support layer are attached to the silica substrate to form a substrate structure; The asymmetric silver layer is attached to the silica substrate sheet to form a silver film structure; The silver film structure is connected to the substrate structure through the zinc oxide support layer, and the asymmetric silver layer is located directly above the silicon core waveguide without contact between them.

2. The polarization converter of claim 1, wherein, The zinc oxide support layer is located on both sides of the silica substrate boundary centered on the silicon core waveguide; The length of the zinc oxide support layer is equal to the length of the silver film structure.

3. The polarization converter of claim 1, wherein, The silicon core waveguide is attached to the silica substrate along the transmission direction of the optical signal; The asymmetric silver layer is placed in the same direction as the silicon core waveguide.

4. The polarization converter of claim 1, wherein, The silicon core waveguide is a cuboid with a total length equal to the length of the silica substrate; The silicon core waveguide comprises an input waveguide segment, an output waveguide segment and a plurality of polarization waveguide segments of different lengths.

5. The polarization converter of claim 4, wherein, The length of the asymmetric silver layer is the sum of the lengths of the output waveguide segment and the plurality of polarization waveguide segments.

6. The polarization converter of claim 4, wherein, The length of the substrate structure is greater than the length of the silver film structure; The difference between the length of the substrate structure and the length of the silver film structure is the length of the output waveguide segment.

7. The polarization converter of claim 4, wherein, The polarization waveguide segment comprises a first conversion waveguide segment, a second conversion waveguide segment and a third conversion waveguide segment connected in sequence; The asymmetric silver layer is of an asymmetric structure; The asymmetric silver layer comprises an input segment, a first adjustment segment, a second adjustment segment and an output segment; The initial width of the input segment is a first size, which increases proportionally along the transmission direction of the optical signal until it reaches a second size, the length of the input segment is equal to that of the first conversion waveguide segment, and the second size is smaller than the width of the second conversion waveguide segment; The width of the first adjustment segment is the second size, and the length of the first adjustment segment is equal to that of the second conversion waveguide segment; The initial width of the second adjustment segment is the second size, which increases proportionally along the transmission direction of the optical signal until it reaches a third size, and the length of the second adjustment segment is equal to that of the third conversion waveguide segment; The width of the output segment is the third size, which is equal to the width of the output waveguide segment, and the length of the output segment is equal to that of the output waveguide segment.

8. The polarization converter of claim 7, wherein, The length of the second conversion waveguide segment > the length of the first conversion waveguide segment > the length of the third conversion waveguide segment > the length of the input waveguide segment > the length of the output waveguide segment.

9. The polarization converter of claim 1, wherein, The thickness of the silica substrate is greater than that of the silica substrate sheet.

10. A method of making a polarization converter, the method comprising: The method comprises: Depositing a silicon thin film layer and a positive photoresist layer on the surface of the silica substrate in sequence; After transferring the mask plate to the positive photoresist layer using mask alignment technology, performing exposure and development operations to form a photoresist mask; The mask plate is drawn with a waveguide contour pattern; After depositing a silicon thin film layer as a silicon core waveguide on the photoresist mask, stripping the positive photoresist layer; The pre-prepared zinc oxide supporting layer is moved to a supporting position of the silica substrate by layer transfer method to form a substrate structure; the supporting position is a boundary on both sides of the silica core waveguide as a center; After the silica substrate is processed into a cavity structure, a silver metal layer is deposited on the surface of the silica substrate by a magnetron sputtering process; The deposited silver metal layer is etched according to a polarization conversion profile by a reactive ion etching technology to obtain a silver film structure; The silver film structure is transferred to the substrate structure and encapsulated to obtain a polarization converter; and the silver film structure is not in contact with the silica core waveguide.

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