A hybrid surface plasmonic directional coupler for optical on-chip networks

Abstract

The application discloses a hybrid surface plasmonic directional coupler for optical chip network, comprising a silicon dioxide substrate and two parallel adjacent hybrid surface plasmonic waveguides. The waveguide structure model is stacked from top to bottom by a rectangular organic polymer nanowire, a silicon dioxide layer and a silver layer, wherein the rectangular organic polymer nanowire material is a host-guest doped electro-optic polymer (25% IPC-E+Polysulfone) prepared from IPC-E and Polysulfone (refractive index is 1.67). The application has small size, excellent transmission characteristics and coupling characteristics. To some extent, the problems of the traditional surface plasmonic directional coupler, such as large transmission loss, weak coupling condition, difficulty in actual production and processing, difficulty in simultaneously realizing strong field localization and good transmission characteristics, are solved. The application has reference significance for the research of related micro-nano photonic devices and has good application prospect in the field of optical chip network in the future.

Description

Technical Field

[0001] This invention relates to the field of optical network-on-a-chip (ONA) technology, and more specifically to a hybrid surface plasmon directional coupler for ONA. Background Technology

[0002] Surface plasmon directional couplers (SPCs) are fundamental and indispensable components in optical systems, widely used in phase modulators, beam splitters, mode converters, and lasers. While many reported SPCs achieve efficient transmission and directional coupling, to meet the requirements of nanophotonic integration, the coupling length should be kept as short as possible to avoid an overly large overall structure that would render it meaningless in practical optical interconnect applications. Furthermore, SPC waveguide modes exhibit significant ohmic losses, leading to relatively high overall transmission losses in traditional SPCs. The overall design of SPCs, in pursuit of structural compactness, often overlooks the limitations of weak coupling conditions and the difficulties in actual fabrication. Traditional SPCs also struggle to simultaneously achieve strong field localization and good transmission characteristics. Building upon traditional SPC waveguide structures, the proposed hybrid SPC waveguide offers a new approach to constructing optical waveguides with both superior optical field confinement and low loss. Hybrid SPC waveguides typically consist of a high-refractive-index dielectric region, a metallic region, and a nanoscale low-refractive-index dielectric region between them. Due to the superposition of surface plasmon modes based on metals and dielectric waveguide modes based on high-refractive-index materials, the optical field energy is further enhanced and confined to the low-refractive-index material region. Furthermore, by utilizing a hybrid transmission mode, the optical field energy is confined to the low-loss low-refractive-index material region, effectively increasing the waveguide's transmission distance. Therefore, based on existing research on surface plasmon directional couplers and considering current challenges, this study investigates and designs a novel hybrid surface plasmon directional coupler with excellent overall performance that meets the requirements of on-chip network interconnection applications. Summary of the Invention

[0003] The present invention addresses the problems of existing surface plasmon directional couplers in optical networks on-chip based on optical interconnects, such as high transmission loss, weak coupling conditions and difficulty in actual fabrication, and difficulty in simultaneously achieving strong field localization and good transmission characteristics. The invention provides a hybrid surface plasmon directional coupler for optical networks on-chip.

[0004] To solve the above problems, the present invention is achieved through the following technical solution: a hybrid surface plasmon directional coupler for optical on-chip networks, comprising a silicon dioxide substrate (1-3) and two parallel adjacent hybrid surface plasmon waveguides (1-1, 1-2), wherein the waveguide structure model is composed of rectangular organic polymer nanowires (2-1), a silicon dioxide layer (2-2), and a silver layer (2-3) stacked from top to bottom, wherein the rectangular organic polymer nanowires are host-guest doped electro-optic polymers (25% IPC-E + Polysulfone) prepared by IPC-E and Polysulfone (refractive index 1.67). The combination sequence of the directional coupler structure model is as follows: a silver (Ag) layer (2-3) with a thickness of h3 is disposed on the silicon dioxide (SiO2) buffer substrate (1-3); a SiO2 capping layer (2-2) with a thickness of h2 and parallel to each other is deposited on the silver layer; and two parallel rectangular organic polymer nanowires (2-1) are placed on the SiO2 capping layer. The three main materials, Ag, SiO2, and electro-optic polymer, are arranged in an orderly manner and combined to form two adjacent hybrid surface plasmon waveguides, thereby forming the proposed directional coupler.

[0005] In the above scheme, the two adjacent hybrid surface plasma waveguide structure models are completely identical, that is, the materials, lengths, widths and heights are the same.

[0006] In the above scheme, the separation distance between the two adjacent hybrid surface plasma waveguides is adjustable.

[0007] In the above scheme, all components of the device are exposed to the air.

[0008] In the above scheme, subtle changes in the rectangular organic polymer nanowire structure can, to a certain extent, cause a conversion between the coupling and transmission characteristics of the device. Appropriately adjusting the rectangular organic polymer nanowire structure can achieve a combination of various optimized characteristics.

[0009] Compared with the prior art, the present invention has the following characteristics:

[0010] 1. A hybrid surface plasmon directional coupler for optical on-chip networks was designed entirely independently. The hybrid surface plasmon waveguide structure was designed by combining surface plasmon polaritons and high refractive index materials—organic polymers—and used as a component of the directional coupler.

[0011] 2. Directional couplers based on hybrid surface plasmon waveguide structures can achieve micro-nano scale dimensions, giving them a significant competitive advantage in realizing ultra-compact, low-transmission-loss directional couplers.

[0012] 3. The fabrication process of the directional coupler based on the rectangular organic polymer nanowire hybrid surface plasmon waveguide is more compatible and the structure is simpler.

[0013] 4. The directional coupler designed based on the hybrid surface plasmon waveguide structure has excellent transmission and coupling characteristics, which can be used as a reference for the research of related micro and nano photonic devices and has a good application prospect in the future field of optical networks on a chip. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a three-dimensional structure of a hybrid surface plasmonic directional coupler for optical-on-a-chip networks.

[0015] Figure 2 This is a top view of a hybrid surface plasmon directional coupler for optical-on-a-chip networks.

[0016] Figure 3 This is a schematic cross-sectional view of a hybrid surface plasmonic directional coupler for optical-on-a-chip networks.

[0017] Figure 4 This is a schematic diagram of the three-dimensional structure of a rectangular organic polymer nanowire hybrid surface plasmon waveguide.

[0018] Figure 5 This is a schematic diagram of a two-dimensional structure of a hybrid surface plasmon directional coupler for optical-on-a-chip networks.

[0019] Figure labels: 1-1: Rectangular organic polymer nanowire hybrid surface plasmon waveguide; 1-2: Rectangular organic polymer nanowire hybrid surface plasmon waveguide; 1-3: Silica substrate; 2-1: Rectangular organic polymer nanowire; 2-2: Silica layer; 2-3: Silver layer; w1: Waveguide width; w2: Silica substrate width; w3: Waveguide separation spacing; h1: Rectangular organic polymer nanowire thickness; h2: Silica layer thickness; h3: Silver layer thickness; h4: Silica substrate thickness; port1: Input port 1; port2: Input port 2; port3: Input port 3; port4: Output port 4; Interaction Length: Coupling length. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific examples.

[0021] A hybrid surface plasmon directional coupler for optical-on-a-chip networks, such as Figure 1 , Figure 2 and Figure 3As shown. It includes a silicon dioxide substrate and two parallel, adjacent hybrid surface plasmon waveguides, where the waveguide structure model is as follows. Figure 4 As shown, the waveguide is composed of rectangular organic polymer nanowires (2-1), a silicon dioxide layer (2-2), and a silver layer (2-3), stacked from top to bottom. The rectangular organic polymer nanowires are a host-guest doped electro-optic polymer (25% IPC-E + Polysulfone) with a refractive index of 1.67, prepared from IPC-E and polysulfone. In this embodiment, the waveguide gain dielectric layer is made of an organic polymer, which has excellent optical and electrical properties, can improve coupling efficiency, reduce loss, and can be fabricated on any semiconductor material.

[0022] The assembly sequence of the device structure model is as follows: a silver (Ag) layer (2-3) with a thickness of h3 is placed on a silicon dioxide (SiO2) buffer substrate (1-3); a SiO2 capping layer (2-2) with a thickness of h2 and parallel to each other is deposited on the silver layer; and two parallel rectangular organic polymer nanowires (2-1) are placed on the SiO2 capping layer. The three main materials, Ag, SiO2, and electro-optic polymer, are arranged in an orderly manner and combined to form two adjacent hybrid surface plasmon waveguides (1-1, 1-2), thereby forming the proposed directional coupler.

[0023] In this embodiment, combining the mode coupling theory and perturbation theory model of optical waveguides, the coupled system composed of independent waveguides (1-1) and (1-2) can achieve its maximum energy coupling efficiency only when the coupled system is in a weak coupling state and the phase matching condition of mode coupling is satisfied. When the coupled system is composed of two identical optical waveguides arranged in parallel and symmetrical combination, the phase matching condition of mode coupling is automatically satisfied, and it can be used for the directional coupler device design in this example.

[0024] In this example, all components are exposed to air, and a plane wave with an incident wavelength of λ = 1550 nm is used to excite surface plasmons. The refractive index of air is set to 1, while the refractive indices of silica, silver, and the organic polymer are 1.445, 0.1453 + 11.3587i, and 1.67, respectively, at this incident wavelength. Studies have shown that the skin depth of the surface plasmons in the silver layer remains approximately 20 nm in the near-infrared wavelength range. Therefore, to avoid the surface plasmon mode in the hybrid waveguide being affected by the silver layer thickness, the silver film thickness h3 is set to 90 nm. Considering the feasibility of this hybrid waveguide (1-1, 1-2) in directional couplers, the geometric dimensions of the structural model are chosen as w1 = 225 nm; h1 = 180 nm; h2 = 27 nm; h3 = 450 nm; w2 = 720 nm; w3 = 90 nm.

[0025] In this example, a two-dimensional structural schematic diagram of the hybrid surface plasmon directional coupler is shown below. Figure 5 As shown, the hybrid surface plasmon waveguide is assumed to be uniform along the z-axis, and the energy within the directional coupler waveguide is transmitted along the z-axis at a communication wavelength of 1550 nm. The electric field energy component of the directional coupler exhibits good optical field localization in the y-axis direction. The optical field energy is distributed within the waveguide, primarily confined to the silica layer and above it, with most of the energy coupled to corresponding positions in adjacent waveguides. The energy is highly concentrated at the lower edge of the organic polymer nanowires, which helps to increase the evanescent field of the surface plasmon wave between the silica layer and the surrounding dielectric, thereby improving the coupling efficiency. In the symmetric mode, the optical waves in the two waveguides are in phase, while in the antisymmetric mode, the optical waves in the two waveguides are in phase. Regardless of whether it is the symmetric or antisymmetric mode, the energy peak exists only within the waveguide, with only a small portion of the energy spilling out in the coupling region between the two waveguides. Generally, when the separation distance between two parallel waveguides is less than a certain threshold, the coupling between the waveguides becomes more complex, and the weak coupling condition of the optical waveguide perturbation theory no longer applies. When the separation distance between the two waveguides is w3 = 90 nm, the overlap of electric field energy in the coupling region of the directional coupler is very small and can be almost ignored. Therefore, this situation can be considered as a weak coupling case.

[0026] Based on the independent variable of the separation distance w3 between the two waveguides, the real part Re(Neff) of the effective mode refractive index and the propagation length L are analyzed. m Functional relationships in symmetric and antisymmetric modes. Through perturbation theory analysis of optical waveguide coupling, it is shown that Re(Neff) in both symmetric and antisymmetric modes is closely related to the coupling length, and the propagation length has a significant impact on the maximum size of photonic devices and optical paths. The distance a surface plasmon wave travels along a waveguide until its mode power or intensity drops to 1 / e of its initial value is called the propagation length L. m ,Right now:

[0027] L m =λ0 / [4πL m (N eff )]

[0028] Based on the above formula, the propagation length of the directional coupler can be calculated, where L m (N eff () represents the effective mode refractive index N eff The imaginary part.

[0029] In this example, to analyze the coupling characteristics of optical waveguides in depth, mode interference theory is used to study a coupled system consisting of two optical waveguides (1-1, 1-2). Based on the relationship between the propagation constant and the effective mode refractive index, the expression for the coupling length when the effective mode refractive index is in complex form is obtained as follows:

[0030] L c =λ / [2Re(n) sym -n asym )]

[0031] Where, n sym and n asym Let represent the effective mode refractive indices of the symmetric and antisymmetric modes, respectively. Therefore, the effective mode refractive indices of the coupled system in both symmetric and antisymmetric modes can be obtained through numerical simulation. Combining this with the above formula, the coupling length can be obtained, and finally, the coupling coefficient k = π / 2L can be calculated based on the coupling length. c .

[0032] In summary, this example achieves the maximum energy coupling efficiency of the coupled system only under the condition of phase matching for mode coupling. When the coupled system is composed of two identical optical waveguides (1-1, 1-2) arranged in parallel and symmetrical combination, the phase matching condition for mode coupling is automatically satisfied. Although a closer distance between the two optical waveguides can improve the coupling efficiency, there are certain limitations. This example comprehensively considers the application conditions of coupling theory and the current level of manufacturing technology to ensure that the coupled system is as weakly coupled as possible, while conforming to the existing manufacturing standards for optical waveguide devices. The coupled system is optimized and analyzed as a whole using simulation software. By calculating the basic parameters in symmetrical and antisymmetric modes, other parameters such as coupling length and coupling efficiency are obtained.

[0033] In summary, this example demonstrates excellent transmission and coupling characteristics, providing valuable insights for the research of related photonic devices and showing promising application prospects in the future field of optical interconnects.

[0034] It should be noted that although the embodiments described above are illustrative, they are not intended to limit the invention. Therefore, the invention is not limited to the specific embodiments described above. Any other embodiments obtained by those skilled in the art under the guidance of this invention without departing from its principles are considered to be within the protection scope of this invention.

Claims

1. A hybrid surface plasmon directional coupler for optical-on-a-chip networks, characterized in that, The proposed directional coupler consists of a silica substrate (1-3) and two parallel adjacent hybrid surface plasmon waveguides (1-1) and (1-2). The waveguide structure model is composed of rectangular organic polymer nanowires, a silica layer, and a silver layer stacked from top to bottom. The rectangular organic polymer nanowires are host-guest doped electro-optic polymers (25% IPC-E + Polysulfone) with a refractive index of 1.67, prepared from IPC-E and Polysulfone. The combination sequence of the directional coupler structure model is as follows: a silver (Ag) layer with a thickness of h3 is placed on a silica (SiO2) buffer substrate (thickness h4); a SiO2 capping layer with a thickness of h2 and parallel separation is deposited on the silver layer; and two parallel rectangular organic polymer nanowires (thickness h1) are placed on the SiO2 capping layer. The three main materials, Ag, SiO2, and electro-optic polymer, are ordered and combined to form two adjacent hybrid surface plasmon waveguides, thereby forming the proposed directional coupler.

2. The hybrid surface plasmon directional coupler for optical on-chip networks according to claim 1, characterized in that, The two parallel adjacent waveguides (1-1) and (1-2) have the same structure and size.

3. A hybrid surface plasmon directional coupler for optical-on-a-chip networks according to claim 1, characterized in that, The separation distance between two parallel adjacent waveguides (1-1) and (1-2) is adjustable.

4. A hybrid surface plasmon directional coupler for optical-on-a-chip networks according to claim 1, characterized in that, The gain dielectric layer of the two parallel adjacent waveguides (1-1) and (1-2) is a rectangular organic polymer nanowire, which is a host-guest doped electro-optic polymer (25% IPC-E + Polysulfone) (refractive index 1.67) prepared by IPC-E and polysulfone.

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