AU2020101434A4

AU2020101434A4 - A refractive index manipulation method for realize multiple logic operations

Info

Publication number: AU2020101434A4
Application number: AU2020101434A
Authority: AU
Inventors: Yiyuan Xie; Yunchao Zhu
Original assignee: Southwest University
Current assignee: Southwest University
Priority date: 2020-07-21
Filing date: 2020-07-21
Publication date: 2020-08-27
Anticipated expiration: 2028-07-21

Abstract

Optical logic device is the core component of ultrahigh speed computing system, artificial intelligence and communication system. In this patent, a plasmonic logic device with the refractive index manipulation method is invented. It mainly consists of two coupled semi-circle resonators and a waveguide as shown in Fig. 1. The different refractive indexes of the semi-circle resonators represents the different input states of the logic gate. Different refractive indexes of the semi-circle resonators cause the shift of transmission spectrum, which is the main idea in achieving logic operation. Eventually, six logic operations (AND, OR, NAND, NOR, XOR, and XNOR) can be achieved at the same time in the structure by monitoring the different wavelengths. This invention pave a way to achieve highly nano-integrated optical chip circuits. Fig. 1 SPPsFg Fig. 2

Description

Fig. 1

SPPsFg

Fig. 2

Editorial Note 2020101434 There is only five pages of the description

A REFRACTIVE INDEX MANIPULATION METHOD FOR REALIZE MULTIPLE LOGIC OPERATIONS

1. Technical Field

The present invention relates to the field of plasma photonics and nanoscale optical logic device.

2. Background and Purpose

With the progress of technology, Al (artificial intelligence), cloud computing, big data, and other science and technology industries are developing rapidly, This leads to an increasing demand for computing power of chip, and the integration of chip determines its computing power. The size of traditional silicon-based optical devices is limited by the diffraction limit, which can not meet the requirements of continuous improvement of integration. The optical devices based on SPPs (surface plasmon polaritons) have been studied by many scholars because of its characteristic of the break of the classical diffraction limit and the manipulate of light in the sub-wavelength range. Among these optical devices, optical logic device that the core component of computing system, artificial intelligence and communication system, has attracted tremendous attention of many researchers. Recently, a variety of optical logic devices based on SPPs have been designed. Many optical logic device proposed use the interference between the mutiple signals or the change of structure parameters to realize logic operation. However, it is diffcult to change the structure parameters of the device when the manufacturing is finished, and the phase difference between the input signals is hard to accurately control, which may cause instable of out signal. Besides, the proposed structures in other papers only can implement about two logic operations, and they are not necessarily able to realize logic operations at the same time. Definitely, a structure that implement multiple logic operations simultaneously can improve computing speed and integration of chip. For these demand, a novel plasmonic optical logic device that the refractive index of the semi-circle cavity expresses the Boolean value of the input signal is invented in this patent. Different refractive index will affect the effective optical path, and then lead to the change of the transmission spectra. Six logic operations (AND, OR, NAND, NOR, XOR, and XNOR) can be achieved at the same time in the structure by monitoring the different wavelengths. Consequently, it acquires higher computing speed and integration than traditional optical devices. This method can be used for the designing of optical logic device on-chip of the photonic integrated circuits

3. Brief Description of the Drawings

Fig. 1: Three-dimensional structure diagram of logic device. Fig. 2: Two-dimensional structure diagram of logic device. Fig. 3: Transmission spectrum for the proposed structure with the different refractive index in the two semi-circle cavities. Fig. 4: Transmission spectrum of OR logic operation of the device from 690 nm to 715 nm with different input states. Fig. 5: Transmission spectrum of the XOR logic operation of the device from 595 nm to 600 nm with different input states. Fig. 6: Transmission spectrum of XNOR logic operation of the device from 585 nm to 590 nm with different input states. Fig. 7: Transmission spectrum of NOR logic operation of the device from 607 nm to 612 nm with different input states. Fig. 8: Transmission spectrum of AND logic operation of the device from 600 nm to 605 nm with different input states. Fig. 9: Transmission spectrum of NAND logic operation of the device from 723 nm to 728 nm with different input states.

4. Detailed Implementation Description

The two-dimensional schematic diagram of the present invention is clearly demonstrated in Fig. 2. It is composed of two directly coupled semi-circle cavities side coupled with the MIM waveguide. And the radii of two semicircle cavities are the same. The refractive index ofupper semi-circle cavity and lower semicircle-cavity are nu, ni respectively. The parameters of the device are set as follows: radius of semi-circle cavity r = 225 nm, coupling distance between the lower semi-circle cavity and the waveguide h = 10 nm, coupling distance between two semi-circle cavities d = 15 nm, and waveguide width w =50 nm. The dielectric in the waveguide is set as air. The refractive index of upper semi-circle cavity and lower semicircle-cavity are nu, ni respectively. The metal in the proposed structure is assumed as silver, and its complex relative permittivity can be expressed by Drude model:

Em(O) = Ex -- (1)

Here, e, = 3.7 eV is the dielectric constant at the infinite frequency. op = 9.1 eV represents the bulk plasma frequency. o is the angular frequency of the incident wave. y = 0.018 eV stands for the electron collision frequency, which is related to absorption loss. Due to the wavelength of the incident light is much larger than the width of the waveguide, only the fundamental TM waveguide mode can exist in the structure. The dispersion relation of SPPs in the MIM waveguides can be obtained by the following equations:

(Emkd)tanh(wkd) + Edkm 0 (2) kd = 2 -k 2 (3) km = 2 (4mkz) Where kd and km represent the permittivities of the dielectric and metal respectively. kd and km stand for the propagation constants of the dielectric and metal individually. ko = 2rc/A is the wave vector in vacuum. # = koneff denotes the wave vector in thewaveguide The transmission T of the structure can be expressed by the temporal coupled mode theory as: 2 (-2ozke2 s,0U,12 j(&-i)+ki+ke2_ T = = 2(&& 2 )+k 2 +k 2 (5) = S-in j(-1)+ko1+ke1+ke2 I(e 2)+k 2 +k 2

Where ai and a 2 stand for the resonance frequency of different cavities. kei is the delay rate owing to energy escape into the bus waveguide, ke2 is the delay rate due to couping loss between lower cavity and upper cavity. koi and koz are the delay rate result from internal loss of different cavities. The transmission characteristics of the structure is analyzed and demonstrated by finite difference time domain (FDTD) method. The Boolean values of the two input signals of the logic device are expressed by X and Y, which are represented by the different refractive index in the upper and lower semi-circle cavities respectively. When the refractive index of the upper semi-circle cavity is 1.03 or 1, it represents X = 1 or X = 0. Similarly, when the refractive index of the lower semi-circle cavity is 1.03 or 1, it indicates Y = 1 or Y =0. Fig. 3 shows the transmission spectrum of the structure with the different input states (X=, Y=), (X=, Y=1), (X=1, Y=0), and (X=1, Y=1). The variation of the transmission ratio of the specific wavelengths with the different input states are shown in Fig. 4-9. These figures are selected from Fig. 3 with a certain wavelength range, which show the variation of the transmission ratio of the six monitored wavelengths more clearly. The six monitored wavelengths are 703.6 nm, 596.8 nm, 587.1 nm, 609.6 nm, 602.1 nm and 725.6 nm. Table 1 shows the concrete transmission ratio of the corresponding six monitored wavelengths with the different input states. The output logic state can be achieved by comparing the transmission value with the threshold value 0.3. To be specific, when the transmission value is greater than 0.3, it represents the Boolean value of the output signal is 1, or else 0. The function of logic operation is realized as follows: The truth table of the six logic operations are depicted in Table 2. The OR logic operation can be achieved by monitoring the transmission ratio at 703.6 nm. When the input signal is (X=0,Y=1), (X=1,Y=0) or (X=1,Y=1), the transmission ratio at 703.6 nm is 65.46%, 70.18% or 86.86%, respectively. These transmission ratios represent logic 1. However, when the input signal is (X=0,Y=0), the transmission ratio at 703.6 nm obtained the minimum value, and the minimum value is 4.75%, which means logic 0. So the structure we designed can realize OR logic operation at 703.6 nm. Similarly, by monitoring the transmission at 596.8 nm, 587.1 nm, 609.6 nm, 602.1 nm and 725.6 nm, logic operation XOR, XNOR, NOR, AND, and NAND can be implemented. Besides, the contrast ratio of the logic operation above are 11.93dB, 16.1dB, 10.26dB, 5.8dB, 6.44dB and 7.66dB respectively.

Table 1. Transmission of different input states at six wavelengths.

Input Logic State Transmission

X Y 703.6nm 596.8nm 587.1nm 609.6nm 602.1nm 725.6nm

0 0 4.75% 1.25% 55.16% 40.78% 13.94% 68.78%

0 1 65.46% 43.63% 4.56% 18.32% 12.56% 57.1%

1 0 70.18% 46.2% 4.55% 9.62% 6.43% 40.78%

1 1 86.86% 0.96% 41.55% 3.79% 48.33% 9.51%

Table 2. The truth table of OR, XOR, XNOR, NOR, AND, and NAND logic operations.

Input Logic State Out Logic State

X Y OR XOR XNOR NOR AND NAND

0 0 0 0 1 1 0 1

0 1 1 1 0 0 0 1

1 0 1 1 0 0 0 1

1 1 1 0 1 0 1 0

Claims

Editorial Note 2020101434 There is only one page of the claim

The claims defining the invention are follows: 1. A plasmonic multiple logic operations device with the refractive index manipulation method is invented in this patent, and the two semi-circle cavities are coupled to each other. The metal in the proposed structure is assumed as silver. The dielectric in the waveguide is set as air. The refractive index of the material of the semi-circle cavity can be changed. Different refractive index of the semic-circle cavity represents the input states. Distinct transmission ratio of the outport of the device can be achieved by changing the refractive index of the semic-circle cavity. Eventually, six logic operations (AND, OR, NAND, NOR, XOR, and XNOR) can be achieved at the same time in the structure by monitoring the different wavelengths.
2. Different refractive index of the semic-circle cavity represent the different input states of the logic gate (as mentioned in claim 1) are embodied as:

When the refractive index of the upper semi-circle cavity is 1.03, it represents the Boolean value of the input state 0. Conversely, when the refractive index of the upper semi-circle cavity is 1.03, the input state of the device treats as Boolean value 1. Compared with the traditional method that using the change of structural parameters to represent different input states, this method is easier to implement.
3. The influence of the refractive index of the semi-circle cavity on the transmission ratio (as mentioned in claim 1) is as follows:

When the incident light is injected into the bus waveguide, the SPPs (surface plasmon polaritons) forms by the resonance between the free electrons on the metal surface and the incident light. The SPPs wave couple into the lower semicircle cavity, and then the SPPs wave in the lower semicircle cavity couple into the upper semi-circle cavity. Different refractive indices affect the effective optical path that SPPs wave travels through the semi-circle cavity, and then lead to the change of the resonate wavelength. Therfore, the transmission characteristic of the output port also transform. Many traditional methods use the change of structure parameters to realize the variation of the transmission characteristic. However, it is diffcult to change the structure parameters of the device when the manufacturing is finished.
4. A method for realizing six logic operations in the same structure (as mentioned in claim 1) is as follows:

Due to the different refractive indices of the semi-circle cavity, the effective optical path that SPPs wave travels through the semi-circle cavities is different (as mentioned in claim 3). This leads to the variation of resonate wavelength. Thus, the transmission ratio of the output port changes. The Boolean values of the two input signals of the logic device are expressed by the different refractive index in the upper and lower semi-circle cavities respectively. The Boolean value of the output signal is related to the transmission value in output port. By monitoring the transmission ratio of output port at the different wavelengths under different input states, six logic operations can be realized at the same time.

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