Method for improving nonlinear coefficient of strip waveguide, strip waveguide and optical device

Abstract

The application relates to the technical field of optical waveguides, and provides a method for improving the nonlinear coefficient of a strip waveguide, a strip waveguide and an optical device, the method comprising the following steps: preparing a strip waveguide, wherein the strip waveguide comprises a silicon-based layer, a silicon dioxide layer and a monocrystalline silicon layer which are sequentially stacked; and preparing a nonlinear enhancement layer on the surface of the silicon dioxide layer and on the side away from the silicon-based layer, so that the nonlinear coefficient of the strip waveguide in TM mode shows an overall upward trend with the increase of the thickness of the nonlinear enhancement layer. The strip waveguide also comprises a nonlinear enhancement layer arranged on the surface of the silicon dioxide layer and on the side away from the silicon-based layer, and the nonlinear coefficient of the strip waveguide in TM mode shows an overall upward trend with the increase of the thickness of the nonlinear enhancement layer. The application solves the problem of low nonlinear effect of the strip waveguide in TM mode by designing a nonlinear polymer to enhance the interaction between the evanescent wave optical field and the nonlinear polymer.

Description

Technical Field

[0001] This application relates to the field of optical waveguide technology, and in particular provides a method for improving the nonlinear coefficient of a strip waveguide, a strip waveguide, and an optical device. Background Technology

[0002] Optical nonlinearity is essential for high-performance computing and high-speed all-optical signal processing in optical communications. Highly nonlinear silicon photonic integrated devices (SIPs) have attracted much attention due to their compact structure, high integration density, low power consumption, and compatibility with CMOS processes. In silicon-based integrated optoelectronic systems, silicon waveguides play a crucial role as signal transmission media. Common silicon waveguide structures include strip waveguides, ridge waveguides, photonic crystal waveguides, and single-groove waveguides. Among them, the strip waveguide, as the basic structure for guiding the optical field in SOI-based integrated optoelectronic device systems, is compact in size. However, the accompanying strong optical field confinement and the high third-order nonlinear coefficient of the material itself can cause certain nonlinear damage to the high-speed optical signals transmitted within it. Strip waveguide nonlinear devices mainly operate in the TE mode and higher-order modes of the TE mode. Compared to the TE mode, the evanescent field of the TM mode is stronger on the waveguide surface. If transmission is directly in TM mode, the strip waveguide will suffer even greater losses, which greatly limits the nonlinearity of the waveguide device and the utilization rate of the waveguide's TM mode.

[0003] Patent application number 202110316133.X discloses a nonlinear slit waveguide, its fabrication method, and its applications. It reveals a fabrication technique for adding a nonlinear enhancement layer to the surface of a conventional slit waveguide to obtain a highly nonlinear slit waveguide. This process is easily controllable, and the fabricated nonlinear enhancement layer is of high quality and stable, thus ensuring the stability of the nonlinear enhancement effect of the nonlinear slit waveguide. However, further research revealed that in this patented technology, the nonlinear coefficient of the device generally decreases with the increase of the silicon waveguide width. This means that the application of the nonlinear enhancement layer in waveguide devices is affected by the silicon waveguide width, and for wider waveguides, it faces the dilemma of difficulty in improving the nonlinear performance of the device.

[0004] In summary, improving the nonlinear effect of strip waveguide devices in TM mode has become a pressing technical problem that needs to be solved. Summary of the Invention

[0005] The purpose of this application is to provide a method, a strip waveguide, and an optical device for improving the nonlinear coefficient of a strip waveguide. The aim is to utilize the strong evanescent wave at the strip waveguide interface in TM mode and enhance the interaction between the evanescent wave optical field and the nonlinear polymer by designing a nonlinear polymer, thereby solving the problem of low nonlinear effect of the strip waveguide in TM mode.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0007] A method for improving the nonlinear coefficient of a strip waveguide, the method comprising the following steps:

[0008] Prepare a strip waveguide, the strip waveguide comprising a silicon substrate, a silicon dioxide layer and a single crystal silicon layer stacked sequentially;

[0009] A nonlinear enhancement layer is prepared on the surface of the silicon dioxide layer and on the side opposite to the silicon substrate, so that the nonlinear coefficient of the waveguide in TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer.

[0010] Optionally, the nonlinear enhancement layer is applied to the monocrystalline silicon layer by a spraying or spin coating process.

[0011] Optionally, the nonlinear reinforcement layer is a discontinuous layered structure that does not completely cover the surface of the silicon dioxide layer, or a continuous layered structure that completely covers the surface of the silicon dioxide layer.

[0012] Optionally, the nonlinear enhancement layer covers the upper surface of the silicon dioxide layer and encapsulates the monocrystalline silicon layer.

[0013] Optionally, the thickness of the nonlinear enhancement layer is 200 nm to 1 μm.

[0014] Optionally, the nonlinear coefficient of the waveguide is 1500W. -1 m -1 ~2000W -1 m -1 .

[0015] This application also provides a strip waveguide, which includes a silicon substrate, a silicon dioxide layer, and a single crystal silicon layer stacked sequentially. The strip waveguide also includes a nonlinear enhancement layer disposed on the surface of the silicon dioxide layer and on the side away from the silicon substrate. The nonlinear coefficient of the strip waveguide in TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer.

[0016] Optionally, the thickness of the single-crystal silicon layer is 200nm to 260nm.

[0017] Optionally, the width of the single-crystal silicon layer is 200nm to 300nm.

[0018] This application also provides an optical device, which includes the aforementioned strip waveguide.

[0019] This application utilizes the fact that strip waveguides in TM mode have a significant amount of optical field leakage into the air. By adding a nonlinear enhancement layer to the surface of the strip waveguide, part of the electric field leaking into the air is combined with the nonlinear polymer to improve the overall nonlinear effect of the strip waveguide device.

[0020] This application utilizes the strong evanescent wave at the waveguide interface in the TM mode to enhance the interaction between the evanescent wave optical field and the nonlinear enhancement layer by setting a nonlinear enhancement layer of appropriate thickness. This results in a waveguide in which the nonlinear coefficient in the TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer, thereby improving the overall nonlinear effect of the device. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram illustrating the steps of the method for improving the nonlinear coefficient of a strip waveguide in this embodiment;

[0023] Figure 2 This is a schematic diagram of the waveguide structure in this embodiment;

[0024] Figure 3 The curves show how the nonlinear coefficient of the strip waveguide with different top silicon thickness varies with the thickness of the nonlinear reinforcement layer.

[0025] Figures 4(a) to 4(e) The graph shows the variation of the nonlinear coefficient of strip waveguides with different top silicon thicknesses as a function of the silicon waveguide width.

[0026] Figure 5 Comparative test diagrams of slit waveguides of different sizes and specifications and the strip waveguide of this embodiment;

[0027] The following are the labeling elements in the figure:

[0028] 10. Silicon waveguide body; 101. Silicon substrate; 102. Silicon dioxide layer; 103. Monocrystalline silicon layer; 20. Nonlinear enhancement layer. Detailed Implementation

[0029] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0030] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0031] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0032] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0033] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0034] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0035] Please see Figures 1-3 This embodiment provides a method for improving the nonlinear coefficient of a strip waveguide, the method including the following steps:

[0036] Prepare a strip-shaped silicon waveguide body 10. The silicon waveguide body 10 includes a silicon substrate 101, a silicon dioxide layer 102 and a single crystal silicon layer 103 stacked sequentially.

[0037] A nonlinear enhancement layer 20 is prepared on the surface of the silicon dioxide layer 102 and on the side opposite to the silicon substrate 101, so that the nonlinear coefficient of the strip waveguide in TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer 20.

[0038] As one possible implementation of this embodiment, the nonlinear enhancement layer 20 can be fabricated using micro / nano fabrication processes. Optionally, the nonlinear enhancement layer 20 can be applied to the single-crystal silicon layer 103 using a spray coating or spin coating process. For example, the method for improving the nonlinear coefficient of the strip waveguide in this embodiment can be specifically as follows:

[0039] S1. Prepare the silicon waveguide body 10 for the strip waveguide;

[0040] S2. Spin-coat MEH-PPV nonlinear polymer on the surface of silicon dioxide layer 102 and on the side opposite to silicon substrate 101 to form nonlinear reinforcement layer 20.

[0041] As one possible implementation method, the fabrication method of the strip waveguide micro / nano in this embodiment may specifically include the following steps:

[0042] S1 Prepares a silicon waveguide body 10, which includes a silicon substrate 101, a silicon dioxide layer 102, and a single-crystal silicon layer 103 stacked sequentially.

[0043] S1.1 The waveguide was cleaned successively with acetone, isopropanol, and pure water:

[0044] S1.2 Spin-coating photoresist onto the surface of the single-crystal silicon layer 103;

[0045] S1.3 Perform electron beam lithography according to the waveguide layout;

[0046] S1.4 Develops and fixes the etched strip waveguide pattern;

[0047] S1.5 Next, the strip waveguide pattern is etched using an etching machine to obtain the strip waveguide structure;

[0048] S1.6 Use acetone, isopropanol and pure water in sequence to clean away the residual photoresist on the waveguide;

[0049] S2 places the entire waveguide on a spin coater to spin coat MEH-PPV nonlinear polymer to form a nonlinear reinforcement layer 20, thus obtaining a high nonlinear silicon-based polymer waveguide suitable for TM mode in this embodiment. The nonlinear coefficient of this waveguide in TM mode generally increases with the increase of the thickness of the nonlinear reinforcement layer 20.

[0050] It should be noted that in all embodiments of this application, TM mode and TE mode refer to transverse magnetic field mode and transverse electric field mode, respectively. T is an abbreviation for transverse, which literally means "lateral". In the mode, it specifically refers to "the direction perpendicular to the transmission direction". For example, if the electromagnetic wave transmission direction in the waveguide is the z-direction, then the transverse direction is the x and y directions in the rectangular coordinate system; or the rho and phi directions in the cylindrical coordinate system. TE mode means "all electric field components are perpendicular to the transmission direction", that is, "there is no electric field component in the transmission direction"; TM mode means "all magnetic field components are perpendicular to the transmission direction", that is, "there is no magnetic field component in the transmission direction".

[0051] Similarly, in all embodiments of this application, the nonlinear coefficient of the strip waveguide in TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer 20. The general upward trend refers to the following: the nonlinear enhancement layer 20 of any feasible thickness is processed on the surface of the strip waveguide, and all feasible thickness values ​​constitute the thickness range of the nonlinear enhancement layer 20. Within this thickness range, when the nonlinear enhancement layer 20 reaches the maximum thickness threshold, the nonlinear coefficient of the strip waveguide will increase to the maximum and tend to saturate, which is to obtain the maximum nonlinear coefficient of the waveguide. Furthermore, the nonlinear coefficient obtained by the strip waveguide when the nonlinear enhancement layer 20 is relatively thick is generally greater than the nonlinear coefficient obtained by the strip waveguide when the nonlinear enhancement layer 20 is relatively thin. Within this thickness range, there are individual smaller sub-ranges in which the nonlinear coefficient obtained by the strip waveguide when the nonlinear enhancement layer 20 is relatively thick is smaller than the nonlinear coefficient obtained by the strip waveguide when the nonlinear enhancement layer 20 is relatively thin.

[0052] Compared to the previously reported patent application number 202110316133.X, which proposed a slit waveguide filled with a nonlinear enhancement layer 20 in TE mode, the effect of the thickness of the nonlinear enhancement layer 20 on the nonlinear performance of the device is exactly the opposite of the effect of the thickness of the nonlinear enhancement layer 20 on the nonlinear performance of the slit waveguide in this embodiment. The principle is fundamentally different from the embodiment of this application. Specifically, in the slit waveguide filled with a nonlinear enhancement layer 20 in TE mode, as the silicon width increases, the nonlinear coefficient of the device gradually decreases and tends to saturate. This is because, in TE operating mode, increasing the thickness of the nonlinear enhancement layer 20 leads to an increase in the effective mode field area, thereby reducing the overall nonlinear coefficient of the device. For the previously reported scheme of filling the nonlinear enhancement layer 20 in the slit waveguide under TE mode, it is required that the thickness of the nonlinear enhancement layer 20 is exactly equal to or slightly higher than the slit height. Obviously, this requires precise control of the thickness of the nonlinear enhancement layer 20 during fabrication, which places high demands on the precision processing of the high nonlinear enhancement layer 20 of this type of waveguide, making the manufacturing difficulty of this type of high nonlinear waveguide more difficult.

[0053] This embodiment reveals that the nonlinear coefficient of the strip waveguide in TM mode generally increases with the thickness of the nonlinear enhancement layer 20. This is because in TM mode, the optical field is distributed along the longitudinal boundary of the strip waveguide. The greater the thickness of the nonlinear enhancement layer 20, the more contact it has with the optical field, and the more optical power can interact with the material of the nonlinear enhancement layer 20. Meanwhile, the effective mode area changes relatively little, hence the increasing nonlinear coefficient of the strip waveguide device. Since the nonlinear coefficient of the strip waveguide in TM mode generally increases with the thickness of the nonlinear enhancement layer 20, the requirements for the thickness of the nonlinear enhancement layer 20 in the fabrication process of the optical waveguide device in this embodiment are more lenient. This simplifies the fabrication of high-nonlinearity devices while ensuring high nonlinearity in the strip waveguide.

[0054] Optionally, the nonlinear reinforcement layer 20 can be a discontinuous layered structure that does not completely cover the surface of the silicon dioxide layer 102, or a continuous layered structure that completely covers the surface of the silicon dioxide layer 102. It is understood that a discontinuous layered structure refers to a shape formed by the outline of the nonlinear reinforcement layer 20 that is not integral, such as a number of scattered point-like or block-like structures on the upper surface of the silicon dioxide layer 102; a continuous layered structure refers to a shape formed by the outline of the nonlinear reinforcement layer 20 that is integral, such as an integral planar reinforcement layer covering the surface of the silicon dioxide layer 102.

[0055] Optionally, the nonlinear enhancement layer 20 covers the upper surface of the silicon dioxide layer 102 and encapsulates the monocrystalline silicon layer 103. That is, the thickness of the nonlinear enhancement layer 20 is greater than or equal to the thickness of the monocrystalline silicon layer 103. To facilitate processing and ensure the nonlinearity improvement effect, this embodiment can be further designed such that the four edges of the nonlinear enhancement layer 20 are aligned and coincide with the four edges of the contact surface of the silicon dioxide layer 102, that is, the width of the nonlinear enhancement layer 20 is consistent with the width of the silicon dioxide layer 102; at the same time, the thickness of the silicon dioxide layer 102 remains flush with the top surface of the monocrystalline silicon layer 103. Of course, the nonlinear enhancement layer 20 can also be designed to completely cover the silicon dioxide layer 102 and encapsulate the entire outer peripheral surface of the monocrystalline silicon layer 103. In this way, the nonlinear coefficient of the waveguide in this embodiment is maximized.

[0056] Optionally, the thickness of the nonlinear enhancement layer 20 is 200 nm to 1 μm. Devices with this specification have a high tolerance for fabrication errors in the nonlinear enhancement layer 20, significantly reducing the difficulty of nonlinear layer fabrication. Furthermore, this embodiment demonstrates that for a typical strip waveguide with a top silicon width of 300 nm and a top silicon thickness of 200 nm to 260 nm, when the thickness of the nonlinear enhancement layer 20 exceeds 500 nm, the nonlinearity tends to saturate and stabilizes at 1600 W. -1 m -1Approximately. For narrow strip waveguides with a top silicon width of 200nm and a top silicon thickness of 200nm–260nm, when the thickness of the nonlinear enhancement layer exceeds 700nm, the nonlinearity tends to saturate and stabilizes at 1800W. -1 m -1 ~2000W -1 m -1 about.

[0057] For common strip waveguide structures, the required nonlinearity can be obtained by controlling the nonlinear enhancement layer 20 to a reasonable thickness. This embodiment demonstrates that for strip waveguides of any size, a nonlinear enhancement layer 20 of a certain thickness (e.g., 100nm to 1000nm) on its surface can achieve the desired nonlinear effect.

[0058] Please refer to Tables 1 and 2. In this embodiment, nonlinear layers of different thicknesses are fabricated for strip waveguides of different sizes and specifications. In the tables, h_NP represents the thickness of the nonlinear enhancement layer, and h_si represents the thickness of the single-crystal silicon layer. For a conventional strip waveguide with a top silicon width of 300nm and a top silicon thickness of 200nm, the nonlinear coefficient is only 14W during TM mode transmission. -1 m -1 By adding a 240nm thick nonlinear enhancement layer 20, its nonlinear coefficient will be increased to 254.02W. -1 m -1 ; By further increasing the thickness of the nonlinear enhancement layer to 1000 nm, the nonlinear coefficient of this waveguide will reach as high as 1756.58 W. -1 m -1 For example, for a conventional strip waveguide with a top silicon width of 300nm and a top silicon thickness of 220nm, the nonlinear coefficient is only 25.03W during TM mode transmission. -1 m -1 By adding a 280nm thick nonlinear enhancement layer 20, its nonlinear coefficient will be increased to 1019.8W. -1 m -1 By further increasing the thickness of the nonlinear enhancement layer to 1000 nm, the nonlinear coefficient of this waveguide will reach as high as 1943.21 W. -1 m -1 .

[0059] Table 1. Conventional strip waveguides with a top silicon width of 300nm

[0060]

[0061] Table 2 Narrow strip waveguides with a top silicon width of 200nm

[0062]

[0063] When the silicon waveguide width is 300nm, its TM mode nonlinearity coefficient is generally larger than that of the TE mode, and the device maintains a high nonlinearity coefficient over a wide range of polymer thicknesses. Specifically, the nonlinearity coefficient is 1500W. -1 m -1 At the above parameters, the nonlinear coefficient is more than four times that of the TE mode of a conventional strip waveguide, and more than twice that of the TE mode of the strip waveguide after spin-coating the nonlinear enhancement layer 20. The nonlinear effect of the strip waveguide device reaches its maximum at this size mode. In summary, the nonlinear enhancement layer 20 designed in this embodiment significantly improves the nonlinearity of the strip waveguide, which will help improve the utilization rate of waveguide modes in related waveguide devices.

[0064] This application innovatively proposes a highly nonlinear silicon-based waveguide suitable for TM mode. Utilizing the strong evanescent wave at the waveguide interface in TM mode, and by incorporating a nonlinear enhancement layer 20 of appropriate thickness, the interaction between the evanescent wave optical field and the nonlinear enhancement layer 20 is enhanced, thereby improving the overall nonlinear effect of the device. Under the same structure, the nonlinear coefficient of the device operating in TM mode is significantly higher than that in TE mode. This application effectively improves the utilization rate of waveguide modes and has significant application potential in multimode optical communication and mode-multiplexed optical signal processing.

[0065] Optionally, according to Tables 1 and 2, this embodiment can adaptively set a nonlinear enhancement layer 20 of a certain thickness to maintain the nonlinear coefficient of the strip waveguide at 1500W. -1 m -1 ~2000W -1 m -1 The strip waveguide equipped with the nonlinear enhancement layer 20 has a nonlinear coefficient much larger than that of a conventional strip waveguide. Furthermore, for strip waveguides of any size, the nonlinear coefficient can be maintained within a specific required range by designing the nonlinear enhancement layer 20. Experiments in this embodiment have shown that the thickness of the nonlinear enhancement layer 20 can maintain a high nonlinear coefficient for the device even within a large dynamic range.

[0066] Please see Figure 5 This embodiment also conducted comparative tests on slot waveguides of different sizes. When the slot waveguide transmits in TM mode, it can be seen that even when the slot width is 50nm, the silicon width is 340nm, and the nonlinearity is at its strongest, the nonlinearity coefficient of the slot waveguide can only reach 559W. -1 m -1 As can be seen from the left and right, it is far inferior to the nonlinearity of the waveguide in the embodiment of this application under the same parameters.

[0067] Since the nonlinear coefficient of the device at this size specification is less affected by the thickness of the nonlinear enhancement layer 20, the solution disclosed in this embodiment can also fabricate the aforementioned nonlinear enhancement layer 20 with a dynamic thickness range according to actual needs, thus making the fabrication process of the nonlinear enhancement layer 20 of the waveguide device easier to realize, while also ensuring that the high nonlinear coefficient of the device can reach up to 2000W. -1 m -1 .

[0068] In this embodiment, the material of the nonlinear reinforcement layer 20 is any one or more of MEH-PPV and DDMEBT. The Chinese name of MEH-PPV is poly(2-methoxy,5-(2'-ethylhexyloxy)-1,4-phenylene vinylene) (English name: poly(2-methoxy,5-(2'-ethylhexyloxy)-1,4-phenylene vinylene)); the Chinese name of the nonlinear polymer DDMEBT is ([2-[4-(dimethylamino)phenyl]-3-([4-(dimethylamino)phenyl]ethynyl)buta-1,3-diene-1,1,4,4-tetracarbonitrile]) (English name: (2-[4-dimethylamino)phenyl]-3-{[4-(dimethylamino)phenyl]ethynyl}buta-1,3-diene-1,1,4,4-tetracarbonitrile)).

[0069] It is worth noting that if other nonlinear polymers have a higher nonlinear Kerr coefficient than the polymer used in this application, and the light loss generated by passing through the polymer is within an acceptable range, the new nonlinear polymer can replace the polymer used in this application. Since the nonlinear coefficient of a waveguide is related to its material properties, structure, and size, the properties of the polymer, such as its nonlinear Kerr coefficient and refractive index, need to be understood before replacement. Then, based on the properties of the waveguide and polymer cladding, the nonlinear coefficients under different waveguide structures and sizes are simulated to find the optimal nonlinear structural dimensions. Finally, the fabrication, testing, and application are carried out.

[0070] The aforementioned embodiments of this application utilize the fact that a significant amount of optical field leakage into the air occurs in strip waveguides under TM mode. By adding a nonlinear enhancement layer 20 to the silicon waveguide layer of the strip waveguide, the portion of the electric field leaking into the air interacts with highly nonlinear polymers such as MEH-PPV, thereby improving the overall nonlinear effect of the device. In contrast to existing slit waveguides containing a nonlinear enhancement layer 20, in the TM optical field of slit waveguides, most of the optical field energy leaks into the oxide layer under TM mode, with only a small portion enhancing nonlinearity in the polymer. These slit waveguides with a nonlinear enhancement layer 20 still suffer from significant losses due to scintillation losses caused by the uneven sidewalls, resulting in substantial light loss during propagation in the slit. However, the embodiments of this application innovatively incorporate a highly nonlinear enhancement layer 20 on the surface of the strip waveguide. Because light propagates on the surface of the strip waveguide, a large amount of energy interacts with the polymer, resulting in lower waveguide device losses and significantly improving the nonlinearity of the strip waveguide device.

[0071] Please see Figures 2-3 This embodiment also provides a strip waveguide, which includes a silicon substrate 101, a silicon dioxide layer 102 and a single crystal silicon layer 103 stacked sequentially. The strip waveguide also includes a nonlinear enhancement layer 20 disposed on the surface of the silicon dioxide layer 102 and on the side away from the silicon substrate 101. The nonlinear coefficient of the strip waveguide in TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer 20.

[0072] This embodiment innovatively applies nonlinear enhancement technology to strip waveguides in TM mode, achieving the opposite effect to applying nonlinear enhancement technology to slot waveguides. This overcomes the primary technical bottleneck currently hindering the development of highly nonlinear waveguides, making the fabrication of highly nonlinear waveguide devices simpler and easier to implement. This embodiment utilizes devices where the evanescent field of the TM mode strongly interacts with the cladding material to maximize performance, enhancing the nonlinear performance of the strip waveguide TM mode. It also improves the sensitivity of integrated evanescent field sensors and enhances the performance of some nonlinear waveguide cladding-based nonlinear applications.

[0073] Optionally, according to Tables 1 and 2, when the thickness of the single-crystal silicon layer 103 is between 200 nm and 260 nm, the waveguide nonlinear coefficient generally shows an increasing trend with the increase of thickness. Furthermore, when the thickness of the single-crystal silicon layer 103 is between 220 nm and 260 nm, the waveguide nonlinear coefficient can obtain a stable and relatively large value.

[0074] Optionally, the width of the single-crystal silicon layer 103 is designed to be 200nm–300nm. For strip waveguides of this size, designing a nonlinear enhancement layer 20 on the strip waveguide can achieve an optimal nonlinear coefficient, and the improvement in nonlinearity compared to narrow strip waveguides is more significant than the improvement compared to wide strip waveguides. Please refer to [link / reference]. Figures 4(a) to 4(b)In this embodiment, strip waveguides with different widths of single-crystal silicon layers were tested, wherein the thickness of the nonlinear enhancement layer was 320nm. The test revealed that the nonlinear coefficient of the strip waveguide containing the nonlinear enhancement layer 20 of this embodiment was greater than that of the corresponding TE mode. Furthermore, as the thickness of the nonlinear enhancement layer 20 increased, the nonlinear coefficients of both the TM mode and the TE mode tended to saturate.

[0075] This embodiment also reveals that when the thickness of the monocrystalline silicon layer 103 and the thickness of the nonlinear enhancement layer 20 are constant, the nonlinear coefficient of the strip waveguide in TM mode generally increases as the width of the monocrystalline silicon layer 103 decreases. That is, the nonlinear coefficient of a relatively narrow strip waveguide in TM mode is greater than that of a relatively wide strip waveguide.

[0076] For the strip waveguide with a single-crystal silicon layer 103 with a width of 200nm to 300nm in this embodiment, the nonlinear coefficient of the strip waveguide device operating in TM mode is much higher than that in TE mode under the same structure. This scheme effectively improves the utilization rate of the strip waveguide TM mode and has great application potential in multimode optical communication and mode-multiplexed optical signal processing.

[0077] This embodiment also provides an optical device, which includes the aforementioned strip waveguide. The optical device can be any one of an optical nonlinear device, an all-optical logic operation device, a code conversion device, a wavelength conversion device, and a demultiplexer.

[0078] Since this embodiment utilizes the fact that the nonlinear coefficient of the strip waveguide in TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer 20, the thickness of the nonlinear enhancement layer 20 is gradually increased to obtain the target nonlinear coefficient of the strip waveguide. When the strip waveguide of this embodiment is applied to an optical device system, it can significantly reduce the requirements for input signal power, improve the conversion efficiency of nonlinear signal processing and the output power of the converted signal, while also taking into account the simple fabrication of high strip waveguides.

[0079] This embodiment innovatively proposes a highly nonlinear silicon-based waveguide suitable for TM mode. Utilizing the strong evanescent wave at the waveguide interface in TM mode, and by incorporating a nonlinear enhancement layer 20 of appropriate thickness, the interaction between the evanescent wave optical field and the nonlinear enhancement layer 20 is enhanced, thereby improving the overall nonlinear effect of the device. Under the same structure, the nonlinear coefficient of the device operating in TM mode is significantly higher than that in TE mode. This embodiment effectively improves the utilization rate of waveguide modes and has significant application potential in multimode optical communication and mode-multiplexed optical signal processing.

[0080] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method of increasing the nonlinear coefficient of a slab waveguide, comprising: The method comprises the following steps: preparing a strip waveguide comprising a silicon-based layer, a silicon dioxide layer and a monocrystalline silicon layer arranged in sequence; preparing a nonlinear enhancement layer on the surface of the silicon dioxide layer and on the side away from the silicon-based layer, so that the nonlinear coefficient of the strip waveguide in TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer, the material of the nonlinear enhancement layer being any one or several of MEH-PPV and DDMEBT; the nonlinear enhancement layer covers the upper surface of the silicon dioxide layer and wraps the monocrystalline silicon layer, the thickness of the nonlinear enhancement layer being greater than or equal to the thickness of the monocrystalline silicon layer; the edges of the nonlinear enhancement layer are aligned with the edges of the contact surface of the silicon dioxide layer, and the thickness of the silicon dioxide layer remains flush with the top surface of the monocrystalline silicon layer.

2. The method of claim 1, wherein: The nonlinear enhancement layer is arranged on the monocrystalline silicon layer by a spraying process or a spin coating process.

3. The method of claim 1, wherein: The nonlinear enhancement layer is a discontinuous layered structure incompletely covering the surface of the silicon dioxide layer or a continuous layered structure completely covering the surface of the silicon dioxide layer.

4. The method of claim 1, wherein: The thickness of the nonlinear enhancement layer is 200 nm to 1 μm.

5. The method of claim 1, wherein: The nonlinear coefficient of the slab waveguide is 1500 W -1 m -1 ~2000 W -1 m -1 .

6. A slab waveguide comprising a silicon-based layer, a silicon dioxide layer, and a single-crystal silicon layer disposed in a stack, characterized in that: The strip waveguide further comprises a nonlinear enhancement layer arranged on the surface of the silicon dioxide layer and on the side away from the silicon-based layer, so that the nonlinear coefficient of the strip waveguide in TM mode generally increases with the increase of the thickness of the nonlinear enhancement layer, the material of the nonlinear enhancement layer being any one or several of MEH-PPV and DDMEBT; the nonlinear enhancement layer covers the upper surface of the silicon dioxide layer and wraps the monocrystalline silicon layer, the thickness of the nonlinear enhancement layer being greater than or equal to the thickness of the monocrystalline silicon layer; the edges of the nonlinear enhancement layer are aligned with the edges of the contact surface of the silicon dioxide layer, and the thickness of the silicon dioxide layer remains flush with the top surface of the monocrystalline silicon layer.

7. The slab waveguide of claim 6, wherein: The thickness of the monocrystalline silicon layer is 200 nm to 260 nm.

8. The slab waveguide of claim 6, wherein: The width of the monocrystalline silicon layer is 200 nm to 300 nm.

9. An optical device, characterized by The optical device comprises the strip waveguide according to any one of claims 6-8.

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