A hollow waveguide structure based on anti-resonance effect and a preparation method thereof

Abstract

This invention relates to a hollow waveguide structure based on the anti-resonance effect and its fabrication method, belonging to the field of waveguide optics, and solves the problems of large size, complex manufacturing process, and high cost of traditional hollow anti-resonant optical fibers. The hollow waveguide structure based on the anti-resonance effect includes: a first cladding layer, a core layer, and a second cladding layer stacked sequentially; wherein the core layer includes an air core and a plurality of capillary walls distributed symmetrically to both sides of the air core, wherein the thickness of the capillary walls is determined based on the anti-resonance condition, which is determined by the wavelength of the transmitted light, the effective refractive index of air, and the effective refractive index of the capillary wall material.

Description

Technical Field

[0001] This invention relates to the field of waveguide optics, and in particular to a hollow waveguide structure based on the anti-resonance effect and its fabrication method. Background Technology

[0002] With the rapid development of photonic integrated circuits in data centers, quantum computing, and on-chip optical interconnects, the shift from discrete devices to on-chip integration in traditional optical systems has become an inevitable trend. Ultra-low loss on-chip waveguides, as core components for long-distance optical signal transmission and efficient control in photonic integrated circuits, directly affect the system's power consumption, integration density, and signal integrity.

[0003] Currently, mainstream on-chip waveguides use silicon-based materials or silicon nitride as transmission media. Their transmission loss is limited by intrinsic absorption, surface / interface scattering, and bending radiation loss. In existing technologies, researchers have tried to reduce loss through high-precision electron beam lithography, passivation processes, and optimized waveguide cross-sectional design. However, these methods require high precision in fabrication and still cannot eliminate the intrinsic loss of light propagating in the dielectric material.

[0004] In the field of traditional fiber optics, researchers have proposed hollow-core antiresonant fiber (Hollow Fiber) to overcome intrinsic defects such as nonlinearity, dispersion, and photo-induced damage caused by the matrix material of solid-core optical fibers. core Anti resonant Fiber, HC However, in order to limit mode leakage in the air core and reduce transmission loss, HC-ARF has to adopt a multi-layer complex structure to enhance the anti-resonance effect, which results in its size being larger than that of traditional optical fibers, and its manufacturing process being complex and costly. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a hollow waveguide structure based on the anti-resonance effect and its fabrication method, in order to solve the problems of large size, complex process and high cost of traditional hollow anti-resonant optical fiber.

[0006] In a first aspect, embodiments of the present invention provide a hollow waveguide structure based on the anti-resonance effect, comprising: The first cladding layer, the core layer, and the second cladding layer are stacked sequentially. The core layer includes an air core and a plurality of capillary walls that are centrally symmetrically distributed on both sides of the air core. The thickness of the capillary walls is determined based on an anti-resonance condition, which is determined by the wavelength of the transmitted light, the effective refractive index of air, and the effective refractive index of the material of the capillary walls.

[0007] Based on the further improvement of the hollow waveguide structure described above, the air core is set to be square, and the thickness of the air layer between the capillary walls is a fixed value.

[0008] Based on the further improvement of the above hollow waveguide structure, the thickness of the core layer is 10 to 30 micrometers, and the thickness of the hollow waveguide structure is less than 125 micrometers.

[0009] Based on the further improvement of the above hollow waveguide structure, the first cladding and the second cladding are made of silicon oxide, and the core layer and the capillary wall are made of silicon nitride.

[0010] Based on the further improvement of the hollow waveguide structure described above, the thickness t of the capillary wall is given by the following formula:

[0011] in, Let n be the wavelength of light transmitted in the waveguide, n0 be the effective refractive index of air, n1 be the effective refractive index of the capillary wall material, and m be the resonance order of the anti-resonance condition.

[0012] Secondly, embodiments of the present invention provide a method for fabricating a hollow waveguide structure based on the anti-resonance effect, comprising the following steps: A first cladding layer is formed on the substrate; A core base layer is formed on the first cladding layer; A photoresist film layer is formed on the core base layer; The photoresist film layer is patterned, and the patterned photoresist film layer is used to perform plasma etching on the core layer base layer to form a core layer. The core layer includes an air core and multiple capillary walls distributed symmetrically to both sides of the air core. The thickness of the capillary walls is determined based on an anti-resonance condition, which is determined by the wavelength of the transmitted light, the effective refractive index of air, and the effective refractive index of the capillary wall material. A second cladding layer is formed on the core layer.

[0013] Further improvements to the above preparation method include forming a first cladding layer on the substrate, comprising: A cladding material of a first thickness is deposited on a substrate using plasma-enhanced chemical vapor deposition (PECVD); and A second cladding material of a thickness less than the first thickness is deposited on a cladding material of a first thickness using a low-pressure chemical vapor deposition process.

[0014] Based on further improvements to the above preparation method, forming a core base layer on the first cladding layer includes: A core layer material of a third thickness is deposited on the first cladding layer using a plasma-enhanced chemical vapor deposition process to form the core layer base layer.

[0015] Further improvements to the above preparation method include forming a second cladding layer on the core layer, comprising: A cladding material of the first thickness is deposited on another substrate using a plasma-enhanced chemical vapor deposition process; A low-pressure chemical vapor deposition process is used to deposit a second-thickness cladding material on a first-thickness cladding material, wherein the second thickness is less than the first thickness; The core layer is bonded to the upper surface of the cladding material of the second thickness; and The other substrate was removed using a chemical mechanical polishing process.

[0016] Based on further improvements to the above preparation method, the third thickness is 10 to 30 micrometers, and the total thickness of the first cladding layer, the core layer, and the second cladding layer is less than 125 micrometers.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. The present invention proposes a hollow waveguide structure based on the anti-resonance principle. By integrating optical technology, a hollow waveguide structure based on the anti-resonance effect is constructed on a photonic integrated chip, breaking the large size effect of traditional HC-ARF. The size of the hollow waveguide structure of the present invention can be 15~20 micrometers, realizing on-chip integration and significantly reducing bending loss.

[0018] 2. The hollow waveguide structure proposed in this invention confines the energy of light to the air for transmission through the anti-resonance principle, eliminating the intrinsic losses caused by the dielectric material in traditional on-chip waveguides, including intrinsic material absorption and surface / interface scattering, thus significantly improving transmission efficiency.

[0019] 3. The hollow waveguide structure in this invention is fabricated using a semiconductor process compatible with CMOS (Complementary Metal Oxide Semiconductor), which can significantly improve production efficiency and reduce manufacturing costs.

[0020] 4. The hollow waveguide structure proposed in this invention adopts the standard process of traditional waveguides, which can be realized through three steps: film deposition, plasma etching, and bonding. There are no special process steps, the fabrication is easy, and it can support large-scale mass production.

[0021] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0022] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 A schematic diagram of a hollow waveguide structure based on the anti-resonance effect according to an embodiment of the present invention is shown.

[0023] Figure 2 It shows Figure 1 A schematic diagram of the cross-section of the hollow waveguide structure.

[0024] Figure 3(a) shows Figure 1 The electric field simulation diagram of the hollow waveguide structure under the first-order anti-resonance condition.

[0025] Figure 3(b) shows Figure 1 The electric field simulation diagram of the hollow waveguide structure under the first-order resonance condition.

[0026] Figure 3(c) shows Figure 1 The electric field simulation diagram of the hollow waveguide structure under the second-order anti-resonance condition.

[0027] Figure 3(d) shows Figure 1 A true simulation of the electric field under second-order resonance conditions in a hollow waveguide structure.

[0028] Figure 4 A schematic flowchart of a method for fabricating a hollow waveguide structure based on the anti-resonance effect according to an embodiment of the present invention is shown.

[0029] Figure 5 A schematic flowchart of a method for fabricating a hollow waveguide structure based on the anti-resonance effect according to another embodiment of the present invention is shown. Detailed Implementation

[0030] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0031] According to one aspect of the present invention, a hollow waveguide structure based on the anti-resonance effect is provided. Figure 1A schematic diagram of a hollow waveguide structure based on the anti-resonance effect according to an embodiment of the present invention is shown. Figure 1 As shown, the hollow waveguide structure based on the anti-resonance effect includes: a first cladding layer 2, a core layer 3, and a second cladding layer 4 stacked sequentially on a substrate 1. The core layer 3 includes an air core and multiple capillary walls that are centrally symmetrically distributed on both sides of the air core. Figure 2 It shows Figure 1 A schematic diagram of the cross-section of the hollow waveguide structure. (See diagram below.) Figure 2 As shown, the red dashed box encloses the air core in core layer 3, and the blue dashed box encloses the capillary walls in core layer 3. The dot at the center of the air core represents light. Figure 1 The large circle at the center of the hollow core is also light. Figure 2 There are a total of 6 capillary walls, which are centrally symmetrically distributed with the two sides of the air core.

[0032] exist Figure 2 In the diagram, the thickness of the capillary wall is denoted as t, and the thickness of the air layers b, c, d, and e between the individual capillary walls, as well as the air layers a and f between the capillary wall and the sidewall of the core layer 3, is denoted as l (lowercase L). The thickness of the capillary wall is determined based on the anti-resonance condition, which is determined by the wavelength of the transmitted light, the effective refractive index of air, and the effective refractive index of the capillary wall material.

[0033] In some embodiments, the thickness t of the capillary wall is given by the following formula:

[0034] in, n is the wavelength of light transmitted in the waveguide, n0 is the effective refractive index of air, n1 is the effective refractive index of the capillary wall material, and m is the resonance order of the anti-resonance condition (taken as a positive integer, such as 1 or 2).

[0035] In some embodiments, the air core is configured as a square, and the thicknesses of the air layers a, b, c, d, e, and f between the capillary walls are fixed. It is advantageous to configure the air core as a square to maintain the mode symmetry of light propagation in the waveguide. The thicknesses of a, b, c, d, e, and f are determined empirically.

[0036] In some embodiments, the first cladding layer 2 and the second cladding layer 4 are made of silicon oxide, and the core layer 3 and the capillary wall are made of silicon nitride or thin-film lithium niobate.

[0037] In some embodiments, the thickness of the core layer 3 is 10 to 30 micrometers, and the thickness of the hollow waveguide structure is less than 125 micrometers. In some embodiments, the side length of the square air core can be 15 to 20 micrometers, the thickness of the first cladding layer 2 and the second cladding layer 4 can be 5 micrometers, and the thickness of the entire hollow waveguide structure is only about 30 micrometers, which is a significant reduction compared to the size of traditional HC-ARF (≥125 micrometers).

[0038] Figure 3(a) shows Figure 1 The electric field simulation diagram of the hollow waveguide structure under the first-order anti-resonance condition is shown in Figure 3(b). Figure 1 The electric field simulation diagram of the hollow waveguide structure under the first-order resonance condition is shown in Figure 3(c). Figure 1 The electric field simulation diagram of the hollow waveguide structure under the second-order anti-resonance condition is shown in Figure 3(d). Figure 1 The simulation diagrams of the electric field under the second-order resonance condition of the hollow waveguide structure in Figure 3(a), 3(b), 3(c), and 3(d) are shown. The wavelength of the transmitted light in the simulations is... The wavelength is set to 1550 nm; n0 is set to 1.0; n1 is the effective refractive index of silicon nitride, set to 2.0; when m=1 and 2, the wall thickness t under the anti-resonance condition is 0.38 μm and 1.12 μm, respectively; the thickness l of air layers a, b, c, d, e, and f is set to 3 μm. As shown in Figures 3(a) and 3(b), when the capillary wall thickness t satisfies the first-order and second-order anti-resonance conditions, the electric field modes of the transmitted light can be effectively confined to the hollow waveguide for stable transmission without mode leakage; as shown in Figures 3(c) and 3(d), when the capillary wall thickness t satisfies the first-order and second-order resonance conditions, most modes are leaked into the cladding and cannot achieve normal transmission.

[0039] According to another aspect of the present invention, a method for fabricating a hollow waveguide structure based on the anti-resonance effect is provided. Figure 4 A schematic flowchart illustrating a method for fabricating a hollow waveguide structure based on the anti-resonance effect according to an embodiment of the present invention is shown. Figure 4 As shown, the fabrication method of the hollow waveguide structure based on the anti-resonance effect includes the following steps: Step 401: Form the first cladding layer on the substrate.

[0040] The substrate here can be a silicon-based substrate. The silicon-based substrate is made by dissolving high-purity polycrystalline silicon, pulling single crystals, slicing, and grinding. The thickness of the silicon-based substrate can be adjusted according to the application requirements through chemical mechanical polishing (CMP).

[0041] In this embodiment, a cladding material of a certain thickness can be deposited on the upper surface of the substrate using plasma-enhanced chemical vapor deposition (PECVD) to form a first cladding layer. The cladding material can be silicon oxide. The thickness of the first cladding layer can be 5 micrometers.

[0042] In some embodiments, to ensure the uniformity and density of the cladding, a plasma-enhanced chemical vapor deposition (PECVD) process can be used to deposit a cladding material of a first thickness on the upper surface of the substrate. Then, a low-pressure chemical vapor deposition (LPCVD) process is used to deposit a cladding material of a second thickness on the upper surface of the first thickness cladding material, forming the first cladding. The second thickness is less than the first thickness. Preferably, the first thickness is 4 micrometers and the second thickness is 1 micrometer.

[0043] Step 402: Form a core base layer on the first cladding layer.

[0044] In this embodiment, a third core layer material of a third thickness can be deposited on top of the first cladding layer using a PECVD process to form the core layer base layer. The core layer material can be silicon nitride or lithium niobate waveguide material (correspondingly, thin-film lithium niobate material should also be mentioned earlier; the core layer material for this structure should not be specified as silicon nitride).

[0045] Step 403: Form a photoresist film layer on the core base layer.

[0046] In this embodiment, a photoresist film layer can be formed by applying photoresist to the upper surface of the core base layer using a photoresist coating machine. The thickness of the photoresist film layer can be approximately 3 micrometers. The photoresist film layer can be a deep ultraviolet photoresist film layer, preferably a positive photoresist.

[0047] Step 404: A Nikon S204B deep ultraviolet lithography machine with a linewidth ≤200nm can be used to pattern the photoresist film layer through a mask. That is, the exposed photoresist area is removed after the development process, and the unexposed photoresist area is retained as an etching protection layer. The core base layer is then subjected to plasma etching. Since the exposed area is not protected by the photoresist film layer, it is etched down to the first cladding layer to form an air layer. The unexposed area is retained to form capillary walls and outer walls. The air layer, capillary walls, and outer walls together constitute the core layer.

[0048] In this embodiment, the photoresist film layer under the photomask can be exposed using a photolithography machine. Then, the photoresist film layer is patterned using a development technique. Finally, the developed photoresist film layer is used to perform plasma etching on the core layer base layer until the etching penetrates to the first cladding layer, forming the core layer.

[0049] In this embodiment, the core layer includes an air core and a plurality of capillary walls distributed symmetrically to both sides of the air core. The thickness of the capillary walls is determined based on the anti-resonance condition, which is determined by the wavelength of the transmitted light, the effective refractive index of air, and the effective refractive index of the capillary wall material. This document has been combined with Figure 1 Figure 3 illustrates the air core and capillary wall in this embodiment, and will not be repeated here.

[0050] Step 405: Form a second cladding layer on the core layer.

[0051] In this embodiment, the second cladding layer can be prepared separately, and the preparation method is the same as that of the first cladding layer. That is, a cladding material of a first thickness is first deposited on the upper surface of another substrate using PECVD, and then a second thickness cladding material is deposited on the upper surface of the first thickness cladding material using LPCVD. Finally, the upper surface of the second thickness cladding material is bonded to the upper surface of the core layer, and the substrate is removed using CMP.

[0052] Figure 5 A schematic flowchart illustrating a method for fabricating a hollow waveguide structure based on the anti-resonance effect according to another embodiment of the present invention is shown. Figure 5 As shown, substrate 1 is made by dissolving high-purity polycrystalline silicon, then pulling single crystals, slicing, and grinding. The thickness can be adjusted by CMP process according to application requirements.

[0053] The thickness of the first cladding layer 2 is 5 micrometers. To ensure the uniformity and density of the film layer, a 4-micrometer silicon oxide is first deposited on the upper surface of the substrate 1 using plasma enhanced chemical vapor deposition (PECVD) process, and then a 1-micrometer silicon oxide is deposited on the upper surface of the 4-micrometer silicon oxide using low pressure chemical vapor deposition (LPCVD) process.

[0054] The core layer 3 has a thickness of 15-20 micrometers. First, a 15-20 micrometer silicon nitride base layer is deposited on the upper surface of the first cladding layer 2 using a PECVD process. Then, a uniform deep ultraviolet photoresist film layer with a thickness of about 3 micrometers is prepared on its upper surface using a photoresist coater. The photoresist film layer under the mask is exposed by a deep ultraviolet lithography machine (DUV). Finally, after developing the photoresist film layer to form a pattern, the silicon nitride base layer is subjected to plasma etching with an etching depth of 15-20 micrometers, which needs to penetrate to the first cladding layer 2.

[0055] The second cladding layer 4 needs to be prepared separately. The preparation method is the same as that of the first cladding layer 2. First, 4-micron silicon oxide is deposited on the surface of another substrate using PECVD process. Then, 1-micron silicon oxide is deposited on the surface of the 4-micron silicon oxide using LPCVD process. Finally, the second cladding layer 4 is bonded to the core layer 3, and the substrate is removed using CMP process to complete the preparation.

[0056] Compared with the prior art, the embodiments of the present invention can achieve at least one of the following beneficial effects: 1. The present invention proposes a hollow waveguide structure based on the anti-resonance principle. By integrating optical technology, a hollow waveguide structure based on the anti-resonance effect is constructed on a photonic integrated chip, breaking the large size effect of traditional HC-ARF. The size of the hollow waveguide structure of the present invention can be 15~20 micrometers, realizing on-chip integration and significantly reducing bending loss.

[0057] 2. The hollow waveguide structure proposed in this invention confines the energy of light to the air for transmission through the anti-resonance principle, eliminating the intrinsic losses caused by the dielectric material in traditional on-chip waveguides, including intrinsic material absorption and surface / interface scattering, thus significantly improving transmission efficiency.

[0058] 3. The hollow waveguide structure in this invention is fabricated using a semiconductor process compatible with CMOS (Complementary Metal Oxide Semiconductor), which can significantly improve production efficiency and reduce manufacturing costs.

[0059] 4. The hollow waveguide structure proposed in this invention adopts the standard process of traditional waveguides, which can be realized through three steps: film deposition, plasma etching, and bonding. There are no special process steps, the fabrication is easy, and it can support large-scale mass production.

[0060] It should be understood that although various elements may be described herein using terms such as first, second, etc., these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element, without departing from the teachings of this disclosure.

[0061] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A hollow waveguide structure based on anti-resonance effect, characterized in that, include: The first cladding layer, the core layer, and the second cladding layer are stacked sequentially. The core layer includes an air core and a plurality of capillary walls that are centrally symmetrically distributed on both sides of the air core. The thickness of the capillary walls is determined based on an anti-resonance condition, which is determined by the wavelength of the transmitted light, the effective refractive index of air, and the effective refractive index of the material of the capillary walls.

2. The hollow waveguide structure of claim 1, wherein The air core is set to a square shape, and the thickness of the air layer between the capillary walls is a fixed value.

3. The hollow waveguide structure according to claim 1, characterized in that, The thickness of the core layer is 10 to 30 micrometers, and the thickness of the hollow waveguide structure is less than 125 micrometers.

4. The hollow waveguide structure according to claim 1, characterized in that, The first cladding layer and the second cladding layer are made of silicon oxide, and the core layer and the capillary wall are made of silicon nitride.

5. The hollow waveguide structure according to claim 1, characterized in that, The thickness t of the capillary wall is given by the following formula: in, Let n be the wavelength of light transmitted in the waveguide, n0 be the effective refractive index of air, n1 be the effective refractive index of the capillary wall material, and m be the resonance order of the anti-resonance condition.

6. A method for fabricating a hollow waveguide structure based on the anti-resonance effect, characterized in that, Includes the following steps: A first cladding layer is formed on the substrate; A core base layer is formed on the first cladding layer; A photoresist film layer is formed on the core base layer; The photoresist film layer is patterned, and the patterned photoresist film layer is used to perform plasma etching on the core layer base layer to form a core layer. The core layer includes an air core and multiple capillary walls distributed symmetrically to both sides of the air core. The thickness of the capillary walls is determined based on an anti-resonance condition, which is determined by the wavelength of the transmitted light, the effective refractive index of air, and the effective refractive index of the capillary wall material. A second cladding layer is formed on the core layer.

7. The preparation method according to claim 6, characterized in that, Forming the first cladding layer on the substrate includes: A cladding material of a first thickness is deposited on a substrate using plasma-enhanced chemical vapor deposition (PECVD); and A second cladding material of a thickness less than the first thickness is deposited on a cladding material of a first thickness using a low-pressure chemical vapor deposition process.

8. The preparation method according to claim 6, characterized in that, Forming a core base layer on the first cladding layer includes: A core layer material of a third thickness is deposited on the first cladding layer using a plasma-enhanced chemical vapor deposition process to form the core layer base layer.

9. The preparation method according to claim 6, characterized in that, Forming a second cladding layer on the core layer includes: A cladding material of the first thickness is deposited on another substrate using a plasma-enhanced chemical vapor deposition process; A low-pressure chemical vapor deposition process is used to deposit a second-thickness cladding material on a first-thickness cladding material, wherein the second thickness is less than the first thickness; The core layer is bonded to the upper surface of the cladding material of the second thickness; and The other substrate was removed using a chemical mechanical polishing process.

10. The preparation method according to claim 8, characterized in that, The third thickness is 10 to 30 micrometers, and the total thickness of the first cladding, the core layer, and the second cladding is less than 125 micrometers.

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