Tunable optical router based on graphene-silicon waveguide

Abstract

The invention discloses a tunable optical router based on a graphene-silicon waveguide. The tunable optical router comprises a straight waveguide, a micro-ring silicon waveguide, a cross coupling waveguide and a graphene modulation area. A graphene modulation area is integrated in a partial area of the micro-ring silicon waveguide, a graphene layer of the graphene modulation area is stacked into double-layer graphene through a mechanical stripping method and extends to the position below a metal electrode, the Fermi level of the graphene is changed by applying voltage to the electrode, the effective refractive index of the graphene-silicon waveguide can be dynamically adjusted, and the refractive index of the graphene-silicon waveguide can be dynamically adjusted. Therefore, the resonance state of the micro-ring is changed, and finally the wavelength selective optical routing function is realized. According to the device, through a mode of embedding graphene and an insulating material, on the basis of maintaining good compatibility with a traditional CMOS (Complementary Metal-Oxide-Semiconductor Transistor) manufacturing process, innovative expansion of device functions is realized, and meanwhile, the dynamic regulation and control requirements of a complex wavelength division multiplexing system can also be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated optics, and particularly relates to a tunable optical router based on graphene-silicon waveguide, which can be used to implement optical wavelength division multiplexing and optical routing functions. Background Art

[0002] The rapid development of on-chip optical network (ONoC) technology provides a new breakthrough for the future of multi-core processors. Compared with the limitations of traditional electronic interconnections in meeting the high-frequency communication requirements of multi-core processors, optical interconnections are expected to significantly improve the communication efficiency between cores inside the chip due to their higher data transmission bandwidth, lower signal latency, and smaller signal attenuation. Currently, chips integrating photonic devices and transistors have been realized, enabling high-speed optical communication between chips through the photonic devices on the chip.

[0003] In the architecture of on-chip optical networks, optical routers, as core components, are responsible for selecting paths between a set of input and output ports. Traditional optical routers generally suffer from the problems of large volume and difficulty in integration, which limit their applications in miniaturized or portable devices. In addition, the performance of some optical routers may depend on specific wavelengths, restricting their applications in wavelength division multiplexing (WDM) systems. Therefore, the research on optical routers is developing towards smaller size, higher efficiency, and lower power consumption. With the progress of integrated optoelectronics, integrated optical routers can achieve complex optical signal processing functions on a single chip, which is of great significance for improving data transmission speed and reducing energy consumption.

[0004] Graphene is a single-atom layer material composed of carbon atoms arranged in a hexagonal honeycomb structure, which exhibits many unique and excellent physical properties in the field of optoelectronics. Among them, electro-tunability is one of its important advantages, that is, its Fermi level can be flexibly adjusted by applying an external voltage. This property makes graphene have broad application prospects in electro-optical modulation. Integrating graphene with silicon waveguides can not only achieve dynamic regulation of optical signals, but also provide new design ideas and technical paths for the structural optimization and performance improvement of optical routers. Summary of the Invention

[0005] The present invention proposes a tunable optical router based on graphene-silicon waveguide, which can change the effective refractive index of the graphene-silicon waveguide by applying different voltages to the electrodes, and then change the resonance state of the micro-ring, so as to flexibly select and separate optical signals with specific wavelength values.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A tunable optical router based on graphene-silicon waveguide, characterized in that: it includes straight waveguides (1, 4, 5), a micro-ring silicon waveguide (2), a cross-coupling waveguide (3), a graphene modulation region (6), and a SiO2 substrate (7). The straight waveguide is composed of an input section (1), a direct-through output section (4), and a cross output section (5). The input section (1) and the direct-through output section (4) extend to the right along the upper side of the micro-ring silicon waveguide, and the cross output section (5) extends downward along the right side of the micro-ring silicon waveguide. The cross-coupling waveguide (3) is arranged at the intersection of the input section (1), the direct-through output section (4), and the cross output section (5). The whole or part of the micro-ring silicon waveguide is integrated with a graphene modulation region (6). The graphene modulation region (6) includes, from bottom to top, a micro-ring silicon waveguide layer (8), a lower insulating layer (9), a graphene layer (10), an upper insulating layer (9), a micro-ring silicon waveguide layer (8), and a cladding (SiO2).

[0008] In the above solution, the straight waveguides (1, 4, 5), the micro-ring silicon waveguide (2), the cross-coupling waveguide (3), and the graphene modulation region (6) are integrally integrated above the SiO2 substrate (7) in the SOI structure.

[0009] In the above solution, the input section (1) and the cross output section (5) are connected to two of the ports of the cross-coupling waveguide (3) for introducing optical signals.

[0010] In the above solution, the inner diameter and outer diameter of the graphene modulation region (6) are the same as those of the micro-ring silicon waveguide (2). This region includes a graphene material (10) and an insulating material (9). The insulating material (9) is embedded in the micro-ring silicon waveguide (2), and then the graphene (10) is embedded in the insulating material (9). Both extend below the metal electrode (12). The graphene-terminal metal electrode is connected to the positive electrode, and the Si waveguide-terminal metal electrode is connected to the negative electrode to form a capacitive structure.

[0011] In the above solution, at the graphene layer of the graphene modulation region (6), a bilayer graphene structure is stacked by mechanical exfoliation method.

[0012] In the above solution, the heights and widths of the straight waveguides (1, 4, 5) and the micro-ring silicon waveguide (2) are the same; the width is different from that of the cross-coupling waveguide (3).

[0013] In the above solution, the straight waveguides (1, 4, 5), the micro-ring silicon waveguide (2), the cross-coupling waveguide (3), and the graphene modulation region (6) are all coated with SiO2 to form a protection structure.

[0014] In the above solution, when the number of graphene-silicon waveguide optical routers reaches two or more, each micro-ring optical router can be connected in series to construct a composite optical router structure with multiple ports.

[0015] Compared with the prior art, the present invention has the following characteristics:

[0016] 1. The present invention independently designs a novel structure for the graphene modulation region, selects a material with a higher dielectric constant to construct the insulating layer, and stacks a double-layer graphene structure to enhance the interaction between the optical field and the material, which can significantly increase the refractive index dynamic tuning range. This structure enables a breakthrough improvement in the equivalent refractive index tuning sensitivity and the dimensionality of functional realization of the device.

[0017] 2. The present invention applies different voltages to graphene through electrodes to regulate its chemical potential, thereby changing the effective refractive index of the silicon-graphene waveguide, and further changing the resonance state of the micro-ring, so as to realize the selection of optical signals with different wavelengths to achieve the optical routing function. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a three-dimensional structure schematic diagram of the present invention.

[0019] Figure 2 It is a top-plan view schematic diagram of the present invention.

[0020] Figure 3 It is a cross-sectional structure diagram of the micro-ring including the graphene modulation region of the present invention.

[0021] Figure 4 It is a relationship curve diagram of the graphene chemical potential of the present invention with respect to the applied voltage.

[0022] Figure 5 It is a relationship curve diagram of the graphene complex refractive index of the present invention with respect to the change of its chemical potential.

[0023] Figure 6 It is a relationship curve diagram of the effective mode refractive index (real part and imaginary part) of the graphene-silicon waveguide of the present invention at a wavelength of 1550 nm and in the TE mode with respect to the change of the graphene chemical potential.

[0024] Figure 7 It is a relationship curve diagram of the transmittance at the straight waveguide (4) of the present invention with respect to the working wavelength when the graphene chemical potential is 0.55 eV and 1 eV respectively.

[0025] Figure 8 It is an electric field distribution diagram of the optical signal resonating at 0.55 eV in the micro-ring of the present invention.

[0026] Figure 9 It is an electric field distribution diagram of the optical signal not resonating at 1 eV in the micro-ring of the present invention. Detailed implementation mode

[0027] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific examples.

[0028] As Figure 1 shown, a tunable optical router based on a graphene-silicon waveguide is composed of straight waveguides (1, 4, 5), a microring silicon waveguide (2), a cross-coupled waveguide (3) and a graphene modulation region (6). In this example, the straight waveguides (1, 4, 5) and the microring silicon waveguide (2) both adopt strip waveguide structures, with the height set to 220 nm and the width set to 450 nm; the height of the cross-coupled waveguide (3) is set to 220 nm and the total length is set to 200 nm; the coupling distance between the microring silicon waveguide (2) and the straight waveguides (1, 5) is set to 0.1; the radius of the microring silicon waveguide (2) is set to 6.2 μm, and the thickness of the SiO2 substrate (7) is set to 3 μm.

[0029] The straight waveguides (1, 4, 5), the microring silicon waveguide (2), the cross-coupled waveguide (3) and the graphene modulation region (6) are integrally integrated above the SiO2 substrate (7) in the SOI structure. The straight waveguides (1, 4, 5) and the cross-coupled waveguide (3) are processed from the topmost silicon layer by etching and other methods, and the refractive index of silicon is set to 3.47; the cladding of the present invention is set to the SiO2 layer, and its refractive index is set to 1.44.

[0030] As Figure 2 shown, the coverage range of the graphene modulation region (6) is defined by the arc length corresponding to the microring circle (the arc length formula is ). In this example, the graphene modulation region is set to an arc length of 6.2π corresponding to a central angle of 180° of the microring, and the inner diameter and outer diameter of the modulation region are the same as those of the microring silicon waveguide, and its position is set near the maximum value of the electromagnetic field intensity of the microring cross-section.

[0031] As Figure 3As shown in the figure, from bottom to top at the graphene modulation region (6), there are successively arranged: a SiO2 substrate layer (7), a silicon waveguide layer (8), an upper insulating layer (9), a graphene layer (10), a lower insulating layer (9), a silicon waveguide layer (8), and a SiO2 cladding layer; the graphene layer is stacked into a bilayer graphene structure by the mechanical exfoliation method. The insulating layer (9) is made of HfO2, with a thickness of 5 nm and a refractive index of 1.98. The HfO2 is disposed at half of the height of the microring silicon waveguide, and then the graphene is disposed at half of the thickness of the HfO2; the metal electrode material is set as Au, and a metal electrode Pd material (12) is disposed below the metal electrode Au at the graphene end. This material can ensure ohmic contact. The metal electrode at the graphene end is connected to the positive electrode, and the metal electrode at the Si waveguide end is connected to the negative electrode to form a capacitive structure.

[0032] As Figure 4 shown in the figure, this figure is the curve of the graphene chemical potential changing with the applied voltage; using the formula to calculate the relationship between the graphene chemical potential (μ c ) and the applied voltage (V). The height of the insulating layer (HfO2) is set as 5 nm, and the relative permittivity ε r of the insulating layer (HfO2) is set as 20; V0 is the offset voltage generated by natural doping, set as 0 V; the Fermi velocity ν F is set as 1.1×10 6 m / s. It can be seen from the figure that as the applied voltage increases, the graphene chemical potential increases accordingly. Therefore, the graphene chemical potential can be controlled by adjusting the voltage.

[0033] As Figure 5 shown in the figure, this figure is the curve of the graphene complex refractive index changing with the graphene chemical potential; as the graphene chemical potential changes, it will cause the change of the graphene conductivity (σ), which will in turn affect the change of the graphene permittivity (ε), and finally the graphene complex refractive index (n G ) will change. In this example, the scattering rate is set as 0.015 meV, the incident light wavelength is 1550 nm, and the temperature T is 300 K; it can be seen from the figure that when the chemical potential μ c is 0.4 eV, the material properties of graphene will change significantly, that is, graphene switches between the dielectric state and the metal state. Based on this characteristic, the light modulation ability of graphene under different chemical potentials has changed, providing an important support for the design and implementation of silicon-based photonic devices.

[0034] As Figure 6As shown in the figure, this is the curve of the effective refractive index (real part and imaginary part) of the graphene-silicon waveguide varying with the chemical potential of graphene. It can be seen from the figure that after the chemical potential of graphene reaches 0.5 eV, the imaginary part of the effective refractive index tends to 0, which means less light absorption and thus less loss. At the same time, the real part of the effective refractive index gradually decreases, which means a change in phase. Therefore, the resonant wavelength of the micro-ring can be modulated by changing the chemical potential of graphene. In this example, the chemical potentials of graphene are set to 0.55 eV and 1 eV respectively as the two states of the device.

[0035] As Figure 7 shown, this figure is the curve of the transmittance of the output section (4) varying with the wavelength at a wavelength of 1550 nm and in the TE mode under different chemical potentials. In this example, when the chemical potential of graphene is set to 0.55 eV, the micro-ring resonates at 1552.03 nm; when the chemical potential of graphene is set to 1 eV, the micro-ring resonates at 1548 nm; as the chemical potential of graphene increases, the resonant curve shows a blue shift. Therefore, when multiple wavelength-division multiplexed optical signals with different central wavelengths are input from the input section (1), by applying different voltages to the graphene modulation region through the electrodes (i.e., adjusting the chemical potential of graphene), the resonant wavelength of the micro-ring can be shifted, so that the signal with the resonant wavelength is output from the cross output section (5), and the remaining optical signals are output from the through output section (4), thus realizing the function of a tunable optical router.

[0036] As Figure 8 and Figure 9 shown, Figure 8 is the electric field distribution diagram when the chemical potential of graphene is 0.55 eV and the optical wavelength is set at 1552.03 nm. At this time, the optical signal resonates and is output from the cross output section (5); Figure 9 is the electric field distribution diagram when the chemical potential of graphene is 1 eV and the optical wavelength is set at 1552.03 nm. At this time, the optical signal does not resonate and is output from the through output section (4).

[0037] When the number of graphene-silicon waveguide optical routers reaches two or more, each micro-ring optical router can be connected in series to construct a composite optical router structure with multiple ports. By applying different voltages to the metal electrodes of each optical router respectively, independent control of optical signals with different wavelengths can be realized, thus having the wavelength-division multiplexing (WDM) function.

[0038] In summary, by applying different voltages to the graphene modulation region in the present invention, the chemical potential can be effectively regulated, and then the resonant conditions of the micro-ring resonator can be changed to achieve the selective transmission of optical signals with specific wavelengths, and finally the function of a tunable optical router is realized.

[0039] It should be noted that although the embodiments described above of the present invention are illustrative, they are not a limitation of the present invention. Therefore, the present invention is not limited to the above specific embodiments. Without departing from the principle of the present invention, any other embodiments obtained by those skilled in the art under the inspiration of the present invention are deemed to be within the protection scope of the present invention.

Claims

1. A tunable optical router based on graphene-silicon waveguide, characterized in that: It includes straight waveguides (1, 4, 5), a microring silicon waveguide (2), a cross-coupled waveguide (3), a graphene modulation region (6), and a SiO2 substrate (7). The straight waveguides are composed of an input section (1), a direct-through output section (4), and a cross output section (5). The input section (1) and the direct-through output section (4) extend to the right along the upper side of the microring silicon waveguide, and the cross output section (5) extends downward along the right side of the microring silicon waveguide. The cross-coupled waveguide (3) is arranged at the intersection of the input section (1), the direct-through output section (4), and the cross output section (5). The whole or part of the microring silicon waveguide region is integrated with a graphene modulation region (6). The graphene modulation region (6) includes, from bottom to top, a microring silicon waveguide layer (8), a lower insulating layer (9), a graphene layer (10), an upper insulating layer (9), a microring silicon waveguide layer (8), and a cladding (SiO2).

2. The tunable optical router based on graphene-silicon waveguide according to claim 1, wherein: The straight waveguides (1, 4, 5), the microring silicon waveguide (2), the cross-coupled waveguide (3), and the graphene modulation region (6) are uniformly integrated above the SiO2 substrate (7) in the SOI structure.

3. The tunable optical router based on graphene-silicon waveguide according to claim 1, wherein: The input section (1) and the cross output section (5) are connected to two of the ports of the cross-coupled waveguide (3) for introducing optical signals.

4. The tunable optical router based on graphene-silicon waveguide according to claim 1, wherein: The inner diameter and outer diameter of the graphene modulation region (6) are the same as those of the microring silicon waveguide (2). This region includes a graphene material (10) and an insulating material (9). The insulating material (9) is embedded in the microring silicon waveguide (2), and then the graphene (10) is embedded in the insulating material (9). Both extend below the metal electrode (12). The metal electrode at the graphene end is connected to the positive electrode, and the metal electrode at the Si waveguide end is connected to the negative electrode to form a capacitive structure.

5. The tunable optical router based on graphene-silicon waveguide according to claim 1, characterized in that: At the graphene layer of the graphene modulation region (6), a bilayer graphene structure is stacked by the mechanical exfoliation method.

6. The tunable optical router based on graphene-silicon waveguide according to claim 1, characterized in that: The heights and widths of the straight waveguides (1, 4, 5) and the microring silicon waveguide (2) are the same, and are inconsistent with the width of the cross-coupled waveguide (3).

7. The tunable optical router based on graphene-silicon waveguide according to claim 1, characterized in that: The straight waveguides (1, 4, 5), the microring silicon waveguide (2), the cross-coupled waveguide (3), and the graphene modulation region (6) are all coated with SiO2 to form a protection structure.

8. The tunable optical router based on graphene-silicon waveguide according to claim 1, wherein: When the number of graphene-silicon waveguide optical routers reaches two or more, each microring optical router can be connected in series to construct a composite optical router structure with multiple ports. By applying different voltages to the metal electrodes of each optical router respectively, independent control of optical signals with different wavelengths can be achieved, thus having the wavelength division multiplexing (WDM) function.

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