Hybrid plasmonic optical waveguide

Abstract

The application discloses a hybrid plasmonic optical waveguide, which comprises an oxidation protection layer and an alkali metal layer, wherein the oxidation protection layer and the alkali metal layer do not react under normal temperature conditions, and the alkali metal layer is sodium or potassium. The application can further improve the mode field confinement capability of the hybrid plasmonic waveguide, realize low-loss plasmonic mode transmission, and has important application value in the field of subwavelength photonic integration in a communication waveband.

Description

Technical Field

[0001] This invention relates to the technical field of optical communication and photonic integration, specifically to a hybrid plasmonic optical waveguide, and particularly to a subwavelength optical waveguide device in the optical communication band. Background Technology

[0002] Photonic integrated chips are gaining increasing popularity in optical interconnects and optical communications due to their advantages such as small size, low power consumption, and high bandwidth. Photonic integrated chips can be made from various materials, including silicon, indium phosphide, silicon nitride, polymers, silicon dioxide, and lithium niobate. They aim to bring the advantages of the semiconductor industry, particularly wafer-level manufacturing, to photonics. Compared to traditional optical devices, photonic integrated chips offer numerous advantages, including smaller size, higher speed, lower power consumption, and better reliability. Currently, photonic integrated chips are primarily used in high-speed transceiver modules operating in coherent or incoherent modes.

[0003] Silicon photonic chips are a current mainstream trend in the industry, leveraging existing semiconductor manufacturing capabilities to integrate photonic modules with different functions onto a single chip. In the future, silicon photonic chips will continue to expand their integration advantages and will be combined with other types of materials. For example, laser components may use indium phosphide (IPS), detectors may use germanium, modulators may use lithium niobate, and optical interconnects may use silicon dioxide. The unique compatibility of silicon photonic chips with complementary metal-oxide-semiconductor (CMOS) processes makes the hybrid integration of photonic and electronic devices possible.

[0004] Similar to electronic chips, photonic chips are seeing increasingly smaller unit sizes. However, due to the diffraction limit, when the waveguide structure size is smaller than the incident wavelength, the energy of the optical waveguide modes diffuses out of the waveguide, significantly weakening the localized performance of the mode field. This hinders the development of integrated optics and the miniaturization of devices. Therefore, traditional silicon photonic devices are generally limited to the micrometer scale, making it impossible to integrate them with nanoscale electronic devices. Realizing subwavelength photonic devices for chip-level high-speed, high-capacity optical interconnects has become a current research hotspot.

[0005] Surface plasmon-based optical waveguides can overcome the diffraction limit to achieve subwavelength optical signal transmission, making them one of the main pathways for high-density photonic integration. Hybrid plasmon optical waveguides, as an important branch of surface plasmon photonic devices, have attracted much attention due to their numerous advantages, including lower transmission loss, nanoscale optical field confinement capabilities, smaller inter-waveguide crosstalk, and wideband operating characteristics. Summary of the Invention

[0006] This invention provides a hybrid plasmonic waveguide that enhances the mode field confinement capability of hybrid waveguides while achieving low-loss plasmonic mode transmission. It features ultra-low loss and strong localization, making it suitable for high-speed, high-capacity subwavelength photonic integrated systems. Traditional hybrid plasmonic waveguides are mostly based on metal (gold / silver / copper) waveguide structures. These include metal-silicon dioxide-silicon type, metal-silicon dioxide-silicon dioxide-metal type, and metal-air-silicon type. However, to meet propagation distance requirements, the traditional hybrid waveguides support relatively weak confinement of the optical field by the supported plasmonic modes.

[0007] This invention relates to a hybrid plasmonic waveguide, comprising an anti-oxidation protective layer, an alkali metal layer, a low-refractive-index material layer, a high-refractive-index material waveguide, another low-refractive-index material layer, and a substrate layer. The anti-oxidation protective layer is made of a material that does not react with the alkali metal at room temperature, such as silicon dioxide; the alkali metal layer is made of alkali metals such as sodium or potassium; the low-refractive-index material layer is made of materials such as silicon dioxide, spin-coated glass, or organic photoresist; and the high-refractive-index material waveguide and substrate layer are made of materials such as silicon, silicon nitride, gallium arsenide, polymers, or lithium niobate.

[0008] The combination of an anti-oxidation protective layer and an alkali metal layer differs from common metallic hybrid plasmonic waveguide structures, as the metal material used is an alkali metal. However, because alkali metals are relatively reactive, an additional protective layer is needed to prevent oxidation and loss of their metallic properties. This material selection has two advantages: ① stronger waveguide mode field confinement; ② lower waveguide mode transmission loss.

[0009] Stacking alkali metal layers, low-refractive-index material layers, and high-refractive-index material waveguides in sequence constitutes an alkali metal hybrid plasmonic waveguide structure, further reducing the size of photonic devices. The eigenmodes of the alkali metal-based hybrid plasmonic waveguide are formed by the hybridization of surface plasmonic modes in the alkali metal layer and waveguide modes in the high-refractive-index material waveguide. The energy of the hybridized modes is mainly concentrated in the low-refractive-index material layer. Because surface plasmonic modes have high localization and high loss characteristics, while waveguide modes have low loss and low localization characteristics, the hybrid mode combines the characteristics of both. When the distance between the high-refractive-index waveguide and the alkali metal layer increases, or when the width of the high-refractive-index waveguide increases, the waveguide mode characteristics become more prominent, with the hybrid mode exhibiting superior waveguide characteristics, characterized by low loss and low localization. Conversely, when the distance between the high-refractive-index waveguide and the alkali metal layer decreases, the surface plasmon mode characteristics become more prominent, with the hybrid mode exhibiting superior plasmon characteristics, characterized by high loss and high localization. Overall, however, the hybrid mode exhibits lower loss than the plasmon mode and better localization characteristics than the waveguide mode.

[0010] The choice of metallic materials. Unlike traditional metal hybrid plasmon waveguides made of gold, silver, copper, etc., it is made of alkali metals. This waveguide structure has the characteristics of long propagation distance and small effective mode area. Compared with the traditional metal (gold / silver / copper) hybrid plasmon waveguide structure, it can further reduce the size of optical waveguide devices and be applied to the field of subwavelength photonic integration.

[0011] The presence of an anti-oxidation protective layer is used for waveguide encapsulation.

[0012] The optical waveguide operates at wavelengths of 1200 nm to 1700 nm.

[0013] A hybrid plasmonic waveguide, the hybrid plasmonic waveguide comprising:

[0014] Anti-oxidation protective layer, alkali metal layer;

[0015] Among them, the anti-oxidation protective layer does not react with alkali metals under normal temperature conditions;

[0016] The alkali metal layer consists of sodium and potassium.

[0017] The preferred anti-oxidation protective layer is made of a material that does not react with the alkali metal layer.

[0018] The preferred anti-oxidation protective layer is silicon dioxide, spin-coated glass, organic photoresist, or aluminum oxide.

[0019] Preferably, the hybrid plasmonic waveguide further includes a low-refractive-index material layer, a high-refractive-index material waveguide, a low-refractive-index material layer, and a substrate layer.

[0020] Preferably, the thickness of the low-refractive-index material layer is in the range of 170~700 nm, the thickness of the high-refractive-index material waveguide is in the range of 150~300 nm, the thickness of the low-refractive-index material layer is in the range of 2~3 μm, and the thickness of the substrate layer is about 700 μm.

[0021] Its preferred structure, from bottom to top, includes:

[0022] substrate

[0023] A low-refractive-index material layer and / or an anti-oxidation protective layer on top of the substrate.

[0024] Alkali metal layer above a low refractive index material layer and / or an anti-oxidation protective layer

[0025] A high-refractive-index material layer and / or a low-refractive-index material layer on top of an alkali metal layer.

[0026] Its preferred structure, from bottom to top, includes:

[0027] substrate

[0028] A low-refractive-index material layer above the substrate.

[0029] A high-refractive-index material layer on top of a low-refractive-index material layer

[0030] A low-refractive-index material layer on top of a high-refractive-index material layer

[0031] Alkali metal layer above a low-refractive-index material layer

[0032] An anti-oxidation layer is applied to the alkali metal layer.

[0033] Preferably, the low refractive index material layer is a material that does not react with alkali metals, such as silicon dioxide, spin-on glass (SOG), organic photoresist, or alumina.

[0034] The high refractive index material waveguide is silicon, silicon nitride, gallium arsenide, polymer, or lithium niobate; wherein the polymer is polymethyl methacrylate (PMMA) and its fluorides and deuterides, epoxy resin, polystyrene, polyorganosilooxane, cross-linked benzocy-clobutane (BCB), cross-linked acrylate polymers, fluorinated polyarylene sulfides and fluorinated polyarylene ethers, epoxy resin, polyimide and fluorinated polyimide, etc.

[0035] The substrate is typically made of silicon dioxide, silicon, silicon nitride, gallium arsenide, lithium niobate, or the aforementioned polymer materials.

[0036] Preferably, the operating wavelength of the optical waveguide is 1200 nm to 1700 nm.

[0037] Beneficial effects: The purpose of this invention is to propose a hybrid plasmonic waveguide structure based on alkali metals, which can realize subwavelength photon transmission in the communication band. This waveguide has the characteristics of high locality and low loss, thus constituting an integrated alkali metal hybrid plasmonic subwavelength photon system. Attached Figure Description

[0038] Figure 1 This invention relates to a hybrid plasmon optical waveguide based on alkali metals. Figure 1 The structure includes: an anti-oxidation protective layer (1), an alkali metal layer (2), a low refractive index material layer (3), a high refractive index material waveguide (4), a low refractive index material layer (5), and a substrate layer (6).

[0039] Figure 2 The fabrication process of alkali metal hybrid plasmon optical waveguides.

[0040] Figure 3 .a is Figure 1 The intrinsic mode field distribution at 1200 nm wavelength when the width of the structural waveguide is 50 nm;

[0041] Figure 3 .b is Figure 1 The intrinsic mode field distribution at 1200 nm wavelength when the width of the structural waveguide is 200 nm;

[0042] Figure 3 .c is Figure 1 The intrinsic mode field distribution at 1700 nm wavelength when the width of the structural waveguide is 50 nm;

[0043] Figure 3 .d is Figure 1 The intrinsic mode field distribution at 1700 nm wavelength when the width of the structural waveguide is 200 nm.

[0044] Figure 4 for Figure 1 Comparison of transmission losses between sodium / potassium hybrid plasmon optical waveguides and those hybridized with precious metal silver.

[0045] Figure 5 for Figure 1 The first variation of the structure shown.

[0046] Figure 6 for Figure 1 The second variation of the structure shown.

[0047] Figure 7 .a is Figure 5 The intrinsic mode field distribution at 1200 nm wavelength when the width of the structural waveguide is 50 nm;

[0048] Figure 7 .b is Figure 5 The intrinsic mode field distribution at 1200 nm wavelength when the width of the structural waveguide is 200 nm;

[0049] Figure 7 .c is Figure 5 The intrinsic mode field distribution at 1700 nm wavelength when the width of the structural waveguide is 50 nm;

[0050] Figure 7 .d is Figure 5 The intrinsic mode field distribution at 1700 nm wavelength when the width of the structural waveguide is 200 nm.

[0051] Figure 8 for Figure 5 Comparison of transmission losses between sodium / potassium hybrid plasmon optical waveguides and those hybridized with precious metal silver.

[0052] Figure 9 .a is Figure 6The intrinsic mode field distribution at 1200 nm wavelength when the width of the structural waveguide is 50 nm;

[0053] Figure 9 .b is Figure 6 The intrinsic mode field distribution at 1200 nm wavelength when the width of the structural waveguide is 200 nm;

[0054] Figure 9 .c is Figure 6 The intrinsic mode field distribution at 1700 nm wavelength when the width of the structural waveguide is 50 nm;

[0055] Figure 9 .d is Figure 6 The intrinsic mode field distribution at 1700 nm wavelength when the width of the structural waveguide is 200 nm.

[0056] Figure 10 for Figure 6 Comparison of transmission losses between sodium / potassium hybrid plasmon optical waveguides and those hybridized with precious metal silver. Detailed Implementation

[0057] The alkali metal-based hybrid plasmon waveguide comprises an anti-oxidation protective layer (1), an alkali metal layer (2), a low-refractive-index material layer (3), a high-refractive-index material waveguide (4), a low-refractive-index material layer (5), and a substrate layer (6). The alkali metal-based hybrid plasmon waveguide proposed in this invention can transmit optical waves in the communication band.

[0058] This invention proposes an alkali metal-based hybrid plasmon waveguide capable of transmitting optical waves in the communication band. Its fabrication process is as follows: Figure 2 As shown, the process can be roughly divided into six steps: a. preparing the SOI wafer; b. placing the mask; c. photolithography; d. removing the mask; e. growing or spin-coating a low-refractive-index material layer; f. spin-coating or evaporating an alkali metal and then encapsulating it.

[0059] Example 1: As Figure 1As shown, the anti-oxidation protective layer (1) and the low refractive index material layers (3) and (5) are silicon dioxide with a refractive index of 1.44; the alkali metal layer (2) is sodium metal with a refractive index of 0.105+7.09i (@1550nm); the high refractive index material waveguide (4) and the substrate layer (6) are silicon with a refractive index of 3.4. The wavelength corresponding to the above refractive indices is 1550 nm. The thickness of the anti-oxidation protective layer (1) and the alkali metal layer (2) is not strictly required. The distance between the lower end face of the alkali metal layer (2) and the upper end face of the high refractive index waveguide (4) is 20 nm to 400 nm. The width of the high refractive index waveguide (4) is greater than 20 nm. As the waveguide width increases, the number of modes supported by the hybrid waveguide also increases, gradually changing from a single-mode waveguide to a multi-mode waveguide. The height of the high refractive index waveguide is in the range of 150 nm to 350 nm, which is usually the thickness of the silicon layer of the SOI wafer (220 nm). The low refractive index material layer (5) has a thickness of about 2~3 μm and the substrate layer (6) has a thickness of about 700 μm.

[0060] Figure 3 Figures 3.a and 3.b show the intrinsic mode field distribution at a wavelength of 1200 nm when the waveguide widths are 50 nm and 200 nm, respectively. Figure 3 .c and Figure 3 .d shows the intrinsic mode field distribution at a wavelength of 1700 nm when the waveguide width is 50 nm and 200 nm.

[0061] Figure 4 The figure shows a comparison of the transmission losses of alkali metal sodium / potassium and noble metal silver hybrid plasmonic waveguides, which can be calculated by solving the imaginary part of the refractive index of the waveguide eigenmodes. In this structure, the distance between the lower end face of the alkali metal layer (2) and the upper end face of the high refractive index waveguide (4) is 50 nm. As shown in the figure, when the waveguide width is fixed, the transmission loss of the silver-based hybrid plasmonic waveguide is greater than that of the sodium-based hybrid waveguide, especially when the waveguide width is 200 nm, the difference in transmission loss between the two reaches its maximum value. Therefore, the sodium-based hybrid plasmonic waveguide has a relatively smaller transmission loss; while when the transmission loss is fixed, the width of the silver-based hybrid plasmonic waveguide is also greater than that of the sodium-based hybrid waveguide, so it can be considered that the sodium-based hybrid plasmonic waveguide has a stronger mode field confinement capability.

[0062] Figures 5 to 7 for Figure 1 The diagram shows three variant structures of alkali metal-based hybrid plasmon waveguides. Among them, Figure 5 and Figure 6 The low-refractive-index material layer can act as an anti-oxidation protective layer.

[0063] Example 2: The alkali metal layer (2) is potassium metal with a refractive index of 0.05+4.90i (@1550nm). All other structural parameters are the same as in Example 1.

[0064] Example 3: The alkali metal layer is sodium or potassium; the low refractive index material layer is a non-reactive material such as spin-on glass (SOG), organic photoresist, or alumina; the high refractive index material layer is silicon nitride, gallium arsenide, polymer, or lithium niobate. All other structural parameters are the same as in Example 1.

[0065] Example 4: Figure 5 As shown, the low-refractive-index material layer is silicon dioxide with a refractive index of 1.44; the alkali metal layer is sodium metal with a refractive index of 0.105+7.09i (@1550nm); and the high-refractive-index material waveguide and substrate layer are silicon with a refractive index of 3.4. The wavelength corresponding to these refractive indices is 1550 nm. The distance between the upper surface of the alkali metal layer and the lower surface of the high-refractive-index waveguide ranges from 20 nm to 400 nm. The width of the high-refractive-index waveguide is greater than 20 nm. The height of the high-refractive-index waveguide ranges from 150 nm to 350 nm.

[0066] Figure 7 Figures 7.a and 7.b show the intrinsic mode field distribution at a wavelength of 1200 nm when the waveguide widths are 50 nm and 200 nm, respectively. Figure 7 .c and Figure 7 .d shows the intrinsic mode field distribution at a wavelength of 1700 nm when the waveguide width is 50 nm and 200 nm. Figure 8 This image shows a comparison of transmission losses between alkali metal sodium / potassium hybrid plasmon waveguides and noble metal silver hybrid waveguides. In this structure, the distance between the alkali metal layer and the high-refractive-index waveguide is 50 nm.

[0067] Example 5: The alkali metal layer is potassium metal with a refractive index of 0.05 + 4.90i (@1550 nm). All other structural parameters are the same as in Example 4.

[0068] Example 6: The alkali metal layer is sodium or potassium; the low refractive index material layer is a non-reactive material such as spin-on glass (SOG), organic photoresist, or alumina; the high refractive index material layer is silicon nitride, gallium arsenide, polymer, or lithium niobate. All other structural parameters are the same as in Example 4.

[0069] Example 7: As Figure 6As shown, the low-refractive-index material layer is silicon dioxide with a refractive index of 1.44; the alkali metal layer is sodium metal with a refractive index of 0.105+7.09i (@1550nm); the high-refractive-index waveguide and substrate layer are silicon with a refractive index of 3.4. The wavelength corresponding to the above refractive indices is 1550 nm. The distance between the upper surface of the alkali metal layer and the lower surface of the high-refractive-index waveguide is 20 nm to 400 nm. The width of the high-refractive-index waveguide is greater than 20 nm. The height of the high-refractive-index waveguide is between 150 nm and 350 nm. The difference from Example 4 is that this waveguide structure is a buried type; while the structure shown in Example 4 is a ridge-like waveguide type.

[0070] Figure 9 Figures 9.a and 9.b show the intrinsic mode field distribution at a wavelength of 1200 nm when the waveguide widths are 50 nm and 200 nm, respectively. Figure 9 .c and Figure 9 .d shows the intrinsic mode field distribution at a wavelength of 1700 nm when the waveguide width is 50 nm and 200 nm. Figure 10 This image shows a comparison of transmission losses between alkali metal sodium / potassium hybrid plasmon waveguides and noble metal silver hybrid waveguides. In this structure, the distance between the alkali metal layer and the high-refractive-index waveguide is 50 nm.

[0071] Example 8: The alkali metal layer is potassium metal with a refractive index of 0.05 + 4.90i (@1550 nm). All other structural parameters are the same as in Example 7.

[0072] Example 9: The alkali metal layer is sodium or potassium; the low refractive index material layer is a non-reactive material such as spin-on glass (SOG), organic photoresist, or alumina; the high refractive index material layer is silicon nitride, gallium arsenide, polymer, or lithium niobate. All other structural parameters are the same as in Example 7.

Claims

1. A method of fabricating a hybrid plasmonic optical waveguide, the method comprising: The hybrid plasmonic optical waveguide comprises: ​ An anti-oxidation protective layer (1) and an alkali metal layer (2); The anti-oxidation protective layer (1) and the alkali metal layer (2) do not react at room temperature; The alkali metal layer (2) is sodium or potassium; The alkali metal layer (2) and the anti-oxidation protective layer (1) are located above the high-refractive-index material waveguide (4), and a first low-refractive-index material layer (3) is arranged between the high-refractive-index material waveguide (4) and the alkali metal layer (2). The preparation method of the hybrid plasmonic optical waveguide comprises the following steps: a. preparing an SOI wafer; b. placing a mask; c. photoetching; d. removing the mask; e. growing or spin-coating a low-refractive-index material layer; f. spin-coating or evaporating an alkali metal and performing packaging.

2. The method of claim 1, wherein: The anti-oxidation protective layer (1) is a material that does not react with the alkali metal layer.

3. The method of claim 1 or 2, wherein: The anti-oxidation protective layer (1) is silicon dioxide, spin-on glass, organic photoresist or aluminum oxide.

4. The method of claim 1, wherein: The hybrid plasmonic optical waveguide further comprises a second low-refractive-index material layer (5) and a substrate layer (6).

5. The method of claim 4, wherein: The thickness of the first low-refractive-index material layer (3) ranges from 170 nm to 700 nm, the thickness of the high-refractive-index material waveguide (4) ranges from 150 nm to 300 nm, the thickness of the second low-refractive-index material layer (5) ranges from 2 μm to 3 μm, and the thickness of the substrate layer (6) is 700 μm.

6. The method of claim 4, wherein: The structure comprises, from bottom to top, in sequence: a substrate layer a second low-refractive-index material layer above the substrate layer a high-refractive-index material layer above the second low-refractive-index material layer a first low-refractive-index material layer above the high-refractive-index material layer an alkali metal layer above the first low-refractive-index material layer an anti-oxidation layer above the alkali metal layer.

7. The method of claim 4, 5, or 6, wherein: The first low-refractive-index material layer (3) is silicon dioxide, spin-on glass, organic photoresist or aluminum oxide. The high-refractive-index material waveguide (4) is silicon, silicon nitride, gallium arsenide, a polymer, lithium niobate, wherein the polymer is polymethyl methacrylate, polymethyl methacrylate fluoride, polymethyl methacrylate deuteride, epoxy resin, polystyrene, polysiloxane, cross-linked benzocyclobutane, cross-linked acrylic acid salt polymer, fluorine-containing polyarylsulfide, fluorine-containing polyarylether or polyimide. The substrate layer (6) is one or more of silicon dioxide, silicon, silicon nitride, gallium arsenide and lithium niobate.

8. The method of claim 1, wherein: The working wavelength of the optical waveguide is 1200 nm to 1700 nm.

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