An optical numerical comparator based on graphene-silicon-based MRRs

Abstract

This invention discloses an optical numerical comparator based on graphene-silicon MRR, comprising: a substrate layer and a microring resonator structure embedded on the upper surface of the substrate layer. The substrate layer is a silicon dioxide substrate. The microring resonator structure includes a Y-shaped branch waveguide, two sets of straight waveguides connected to the two symmetrical bifurcated ends of the Y-shaped branch waveguide and arranged in parallel intervals, and four sets of microring waveguides symmetrically distributed in pairs outside the two sets of straight waveguides in a rectangular arrangement. The two sets of microring waveguides located on the same side of the straight waveguides are spaced apart with a center-to-center distance of 4.5 μm. The coupling distance between each set of microring waveguides and the adjacent straight waveguide is 0.05 μm. The microring resonator structure is made of silicon-based material, and a hexagonal boron nitride layer, a graphene layer, and a silicon dioxide layer are sequentially and completely covered on the microring waveguides. Metal electrodes are provided on both the graphene layer and the microring waveguides. The optical numerical comparator of this invention has the advantages of high extinction ratio, high contrast, compact structure, and high stability.

Description

Technical Field

[0001] This invention relates to the field of silicon-based optical device technology, and more specifically to an optical numerical comparator based on graphene-silicon MRR. Background Technology

[0002] In recent years, many silicon-based MRR-based optical devices have been reported, such as various commonly used logic gates and half-adders / half-subtractors. However, the micro-ring radii in these devices are relatively large, typically 3–10 μm, which affects the improvement of integration density in practical applications of silicon-based optoelectronic integrated devices. Furthermore, due to the weak light interaction originating from silicon itself, a large power consumption is required to achieve the resonant wavelength shift, thus posing a challenge to achieving low power consumption and small size.

[0003] In view of this, it is necessary to improve the existing optical numerical comparators to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to disclose an optical numerical comparator based on graphene-silicon MRR. Based on the principle of light absorption by graphene, the effective refractive index n of the silicon-based microring waveguide is changed by applying a bias voltage to control and alter its chemical potential. eff The imaginary part of the light and the loss of the optical signal in the silicon-based microring cause the coupling state in the all-pass silicon-based microring resonator structure to switch between critical coupling and overcoupling, thereby changing the transmission path of the optical signal in the silicon-based microring waveguide and ultimately realizing the function of an optical numerical comparator. It has the advantages of high extinction ratio, high contrast, compact structure and high stability.

[0005] To achieve the above objectives, the present invention provides an optical numerical comparator based on graphene-silicon MRR, comprising:

[0006] The substrate layer and the microring resonator structure embedded on the upper surface of the substrate layer, wherein the substrate layer is a silicon dioxide substrate, and the microring resonator structure includes a Y-type branch waveguide, two sets of straight waveguides connected to the two symmetrical bifurcated ends of the Y-type branch waveguide and arranged in parallel intervals, and four sets of microring waveguides symmetrically distributed in pairs outside the two sets of straight waveguides and arranged in a rectangular pattern.

[0007] The two sets of microring waveguides located on the same side of the straight waveguide are spaced apart with a center-to-center distance of 4.5 μm. The coupling distance between each set of microring waveguides and the adjacent straight waveguide is 0.05 μm.

[0008] The microring resonator structure is made of silicon-based material, and a hexagonal boron nitride layer, a graphene layer, and a silicon dioxide layer with a coverage angle of θ are sequentially laid on the microring waveguide.

[0009] Both the graphene layer and the micro-ring waveguide are provided with metal electrodes for applying an external bias voltage to the graphene layer.

[0010] As a further improvement of the present invention, the coverage laying angle θ is 360°.

[0011] As a further improvement of the present invention, the comparator area is 120 μm. 2 The micro-ring waveguide has a radius of 1.8 μm, and the hexagonal boron nitride layer has a thickness of 5 nm and the silicon dioxide layer has a thickness of 50 nm.

[0012] As a further improvement of the present invention, the Y-shaped branch waveguide, the straight waveguide, and the micro-ring waveguide are all silicon-based waveguides, and the width of the silicon-based waveguide is 0.4 μm and the height is 0.22 μm.

[0013] As a further improvement of the present invention, the graphene layer is a single layer of graphene.

[0014] This invention also discloses an application method for an optical numerical comparator, comprising the following steps:

[0015] S1, a bias voltage is applied to the graphene layer through a metal electrode to change the effective refractive index n of the microring waveguide. eff The imaginary part and the transmission loss of optical signals in the micro-ring waveguide.

[0016] S2, adjust the bias voltage applied in step S1 to switch the coupling state in the microring resonator structure between critical coupling and overcoupling, and finally change the transmission path of the optical signal in the microring waveguide.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] (1) An optical numerical comparator based on graphene-silicon MRR, consisting of four silicon-based micro-ring waveguides covered with monolayer graphene, two silicon-based straight waveguides, one silicon-based Y-type branch waveguide, and a silicon dioxide substrate. The structure of the entire device is symmetrical about the X-axis. Compared with existing optical numerical comparators, this invention has the advantages of high extinction ratio, high contrast, compact structure, and high stability. It is easy to integrate with other optical systems, which is beneficial to the development of silicon-based photonic integrated devices and is of great significance to improving the performance of optical computing circuits.

[0019] (2) A 5nm thick dielectric hexagonal boron nitride layer is separated between the graphene and the silicon-based micro-ring waveguide. This not only prevents the charge carriers loaded in the graphene from being injected into the silicon-based micro-ring waveguide and affecting the modulation effect, but also enhances the interaction between the graphene and light, thereby enhancing the effect on the effective refractive index of the silicon-based micro-ring waveguide. In addition, a 50nm thick SiO2 layer is covered on top of the graphene to prevent the graphene from being exposed to the air and thus affecting its performance. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the three-dimensional structure of an optical numerical comparator based on graphene-silicon MRR according to the present invention;

[0021] Figure 2 This is a schematic cross-sectional view of a microring waveguide for an optical numerical comparator based on graphene-silicon MRR according to the present invention.

[0022] Figure 3 This is a top view schematic diagram of an optical numerical comparator based on graphene-silicon MRR according to the present invention.

[0023] Figures 4(a)-4(d) This is a normalized power curve of each output port of an optical numerical comparator based on graphene-silicon MRR according to the present invention, under each combination.

[0024] In the figure: 1. Substrate layer; 2. Micro-ring waveguide; 3. Hexagonal boron nitride layer; 4. Graphene layer; 5. Silicon dioxide layer; 6. Metal electrode; 7. Y-branch waveguide; 8. Straight waveguide. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. All equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are within the scope of protection of the present invention.

[0026] Please refer to Figures 1 to 4(d) The present invention illustrates a specific embodiment of an optical numerical comparator based on graphene-silicon MRR.

[0027] An optical numerical comparator based on graphene-silicon MRR includes: a substrate layer 1 and a microring resonator structure embedded on the upper surface of the substrate layer 1. The substrate layer 1 is a silicon dioxide substrate. The microring resonator structure includes a Y-shaped branch waveguide 7, two sets of straight waveguides 8 connected to the two symmetrical bifurcated ends of the Y-shaped branch waveguide 7 and arranged in parallel and spaced apart, and four sets of microring waveguides 2 symmetrically distributed in pairs outside the two sets of straight waveguides 8 and arranged in a rectangular pattern. The two sets of microring waveguides 2 located on the same side of the straight waveguide 8 are spaced apart with a center-to-center distance of 4.5 μm. The coupling distance between each set of microring waveguides 2 and the adjacent straight waveguide 8 is 0.05 μm. The microring resonator structure is made of silicon-based material, and a hexagonal boron nitride layer 3, a graphene layer 4, and a silicon dioxide layer 5 with a coverage angle of θ are sequentially laid on the microring waveguide 2. Metal electrodes 6 are provided on the graphene layer 4 and the microring waveguide 2 for applying an external bias voltage to the graphene layer 4.

[0028] In this embodiment, the monolayer graphene covers the silicon-based microring waveguide 2 at a 360° angle, meaning the monolayer graphene completely covers the top of the silicon-based microring waveguide 2, resulting in optimal performance. The comparator area is 120 μm. 2 The micro-ring waveguide 2 has a radius of 1.8 μm, the hexagonal boron nitride layer 3 has a thickness of 5 nm, and the silicon dioxide layer 5 has a thickness of 50 nm. The Y-shaped branch waveguide 7, the straight waveguide 8, and the micro-ring waveguide 2 are all silicon-based waveguides.

[0029] The graphene layer 4 is a single layer of graphene. A chemical potential of 0.7 eV is selected as the "on" state of the graphene-silicon-based MRR modulator, while a chemical potential of 0.05 eV is selected as the "off" state.

[0030] The working process of the proposed optical numerical comparator is described in detail below, referring to... Figure 3 The model was built and simulated using Lumerical's INTERCONNECT software. The results are shown in Figures 4(a) to (d), which describe the simulation output results for the combinations of AB=00, AB=01, AB=10 and AB=11, respectively.

[0031] Referring to Figure 4(a), when AB = 0, the corresponding -AB- = 11. At this time, the graphene-microring waveguide structures in MRR1 and MRR4 are in a high-loss state, while the graphene-microring waveguide structures in MRR2 and MRR3 are in a low-loss state. The operating wavelength is λ. CW The continuous optical signal is input from the Input port, and transmitted through the Y-branch waveguide 7 at a 50%:50% split. Critical coupling occurs when the optical signal passes through the coupling region of MRR1, so there is no optical signal input at the input of MRR2. Therefore, at F... A>BThere is no optical signal output from the port. However, when the optical signal passes through the coupling region of MRR3, over-coupling occurs, so there is an optical signal input at the input end of MRR4. Then, critical coupling occurs when the optical signal passes through the coupling region of MRR4, so F A<B There is also no optical signal output from the port.

[0032] Refer to Fig. 4(b). When AB = 01, the corresponding —AB— = 10. At this time, the graphene-micro-ring waveguide structures in MRR1 and MRR2 are in a high-loss state, while the graphene-micro-ring waveguide structures in MRR3 and MRR4 are in a low-loss state. A continuous optical signal with a working wavelength of λ CW is input from the Input port and is split and transmitted by the Y-branch waveguide 7 in a 50%:50% ratio. Critical coupling occurs when the optical signal passes through the coupling regions of MRR1 and MRR2, so F A>B There is no optical signal output from the port. However, over-coupling occurs when the optical signal passes through the coupling regions of MRR3 and MRR4, so the optical signal is output from F A<B port.

[0033] Refer to Fig. 4(c) and Fig. 4(d). Similarly, the situations when AB = 10 and AB = 11 are similar to the situations when AB = 01 and AB = 00 respectively above, and finally the output changes of F A>B port and F A<B port are achieved. And when a continuous optical signal with a working wavelength of λ CW only outputs from the F A>B port or the F A<B port, it is defined as the situation of A > B or A < B, while when there is no optical signal output from both the F A>B port and the F A<B port simultaneously, it is defined as the situation of A = B.

[0034] Comparison of the logical values and simulation results of the optical numerical comparator proposed in Table 1-1 below

[0035]

[0036] The present invention also discloses an application method of an optical numerical comparator, including the following steps: S1, applying a bias voltage to the graphene layer 4 through the metal electrode 6 to change the imaginary part of the effective refractive index n eff of the micro-ring waveguide 2 and the transmission loss of the optical signal in the micro-ring waveguide 2; S2, adjusting the bias voltage applied in the step S1 to make the coupling state in the micro-ring resonator structure switch between critical coupling and over-coupling, and finally change the transmission path of the optical signal in the micro-ring waveguide 2.

[0037] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An optical numerical comparator based on graphene-silicon MRR, characterized in that, include: The substrate layer and the microring resonator structure embedded on the upper surface of the substrate layer, wherein the substrate layer is a silicon dioxide substrate, and the microring resonator structure includes a Y-type branch waveguide, two sets of straight waveguides connected to the two symmetrical bifurcated ends of the Y-type branch waveguide and arranged in parallel intervals, and four sets of microring waveguides symmetrically distributed in pairs outside the two sets of straight waveguides and arranged in a rectangular pattern. The two sets of microring waveguides located on the same side of the straight waveguide are spaced apart with a center-to-center distance of 4.5 μm. The coupling distance between each set of microring waveguides and the adjacent straight waveguide is 0.05 μm. The microring resonator structure is made of silicon-based material, and a hexagonal boron nitride layer, a graphene layer, and a silicon dioxide layer with a coverage angle of θ are sequentially laid on the microring waveguide. Both the graphene layer and the micro-ring waveguide are provided with metal electrodes for applying an external bias voltage to the graphene layer.

2. The optical numerical comparator based on graphene-silicon MRR according to claim 1, characterized in that, The coverage angle θ is 360°.

3. The optical numerical comparator based on graphene-silicon MRR according to claim 1, characterized in that, The micro-ring waveguide has a radius of 1.8 μm, the hexagonal boron nitride layer has a thickness of 5 nm, and the silicon dioxide layer has a thickness of 50 nm.

4. The optical numerical comparator based on graphene-silicon MRR according to claim 1, characterized in that, The Y-shaped branch waveguide, straight waveguide, and micro-ring waveguide are all silicon-based waveguides, with a width of 0.4 μm and a height of 0.22 μm.

5. An optical numerical comparator based on graphene-silicon MRR according to claim 1, characterized in that, The graphene layer is a single layer of graphene.

6. A method for applying an optical numerical comparator, based on the graphene-silicon-based MRR optical numerical comparator described in claim 1, characterized in that, Includes the following steps: S1, a bias voltage is applied to the graphene layer through a metal electrode to change the effective refractive index n of the microring waveguide. eff The imaginary part and the transmission loss of optical signals in the micro-ring waveguide. S2, adjust the bias voltage applied in step S1 to switch the coupling state in the microring resonator structure between critical coupling and overcoupling, and finally change the transmission path of the optical signal in the microring waveguide.

Images