CN111443549B

CN111443549B - Terahertz multifunctional logic gate device based on pseudo surface plasmon waveguide

Info

Publication number: CN111443549B
Application number: CN202010193179.2A
Authority: CN
Inventors: 廖怡; 袁明瑞; 栗岩锋; 谷建强; 韩家广
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2021-11-16
Anticipated expiration: 2040-03-18
Also published as: CN111443549A

Abstract

The invention discloses a terahertz multifunctional logic gate device based on a pseudo surface plasmon waveguide, which consists of a pseudo surface plasmon waveguide with a Mach-Zehnder interference shape; the silicon substrate is made of high-resistance silicon with the resistivity larger than 3000 omega, a periodically arranged cuboid structure is obtained on the silicon substrate by adopting photoetching and deep etching technologies, and gold with the thickness larger than 200nm is covered on the whole silicon structure by an evaporation technology; the structure of the logic gate device is divided into two parts, wherein the first part provides input signals for the logic gate, and the second part performs logic calculation. Controlling the phase attribute of the pseudo surface plasmon waveguide by changing the shape and the spacing parameters of the metal cuboid structure, thereby adjusting the propagation phase between two or more than two paths of propagated pseudo surface plasmon waveguides; AND 7 logic gate devices for realizing different functions of an AND gate (AND), an OR gate (OR), a NOT gate (NOT), a NAND gate (NAND), a NOR gate (NOR), an exclusive OR gate (XOR) AND an exclusive OR gate (XNOR).

Description

Terahertz multifunctional logic gate device based on pseudo surface plasmon waveguide

Technical Field

The invention belongs to the field of terahertz on-chip integrated systems, and relates to a terahertz multifunctional logic gate device based on pseudo surface plasmon waveguide.

Background

Terahertz (THz) waves generally refer to frequencies between 0.1THz and 10THz (1THz ═ 10¹²Hz) band, is located between infrared and microwave, is a special region of transition from electronics to photonics on the electromagnetic spectrum, and is also a transition region from the macroscopic classical theory to the microscopic quantum theory. The development of infrared and microwave technologies on both sides of the terahertz wave band was relatively mature before the middle of the 80's 20 th century, but people have limited knowledge of the terahertz wave band, and the reason for this is that a so-called "terahertz gap" is formed due to the lack of effective means for generating and detecting terahertz waves. Terahertz has many special properties different from other electromagnetic waves due to its special position in the electromagnetic spectrum, which mainly includes: transient, coherent, low energy, high transmission, water absorption, fingerprint spectrum. As the knowledge of the terahertz wave band is deepened more and more, people begin to realize the huge application value brought by the rich physicochemical characteristics of the terahertz wave band, which causes the worldwide understandingThe trend of terahertz wave research is particularly in the technical fields of spectroscopy, imaging, communication and the like. Therefore, there is an increasing demand for terahertz-band functional devices such as sensors, absorbers, filters, modulators, and the like. However, the existing terahertz functional devices are large in size, have the problems of phase mismatch, large occupied space of free space optical paths and the like, and the existing commercial devices cannot meet all the requirements of the existing terahertz functional devices, so that the rapid development of the practical application of the terahertz technology is seriously limited.

With the increasing demand of people for smaller, more compact and multifunctional integrated terahertz functional devices, a plasmon-based scheme is receiving great attention. When an electromagnetic wave is oscillated collectively by electrons or electron groups at the metal/dielectric interface and propagates in a direction parallel to the metal/dielectric interface, a plasmon is formed. By the interaction of the electromagnetic wave and electrons in the conductor, the plasmon localizes the electromagnetic field at the sub-wavelength level, thereby realizing the possibility of manipulating the electromagnetic wave at the sub-wavelength level. In 1960, the concept of surface plasmons (surface plasma) was first proposed by e.a.stern and r.a.ferrel [1 ]. In 1968, Kretschmann and Reather excited surface plasmons by means of total internal reflection in a prism [2 ]. In the same year, Otto also proposed a similar but non-contacting structure to excite surface plasmons [3 ]. In 1998, T.Ebbesen et al found that light has an abnormal anti-reflection effect after passing through a subwavelength periodic metal pore array [4], and further found that surface plasmons can overcome diffraction limit to realize high-resolution imaging [5 ]. In the 21 st century, work of surface plasmons in the microwave and terahertz bands has been gradually developed, and surface plasmon photonics (Plasmonics) has emerged therefrom [6 ]. Since surface plasmons can propagate in a spatial range limited to a subwavelength and can serve as an information carrier, surface plasmon waveguides are expected to become a basic structure of integrated photonics [7,8 ]. The optical element based on the surface plasmon reduces the size difference between the optical device and the electronic device, and can realize interconnection with the electronic device.

The logic gate device that relates to in this patent is worked in terahertz wave band, because the surface plasmon of constraint mode all is located near the plasma frequency of metal, and the plasma frequency of most metals all is located the ultraviolet band, leads to at terahertz wave band, and most metals are shown as good conductor, and the metal surface does not support the surface plasmon of constraint state. One-dimensional or two-dimensional periodic grooves or three-dimensional microstructures are processed on the metal surface, which can support electromagnetic waves similar to surface plasmons, and the properties of the electromagnetic waves are the same as those of surface plasmons in an optical band, so that the electromagnetic waves are called pseudo surface plasmons or artificial surface plasmons (spoofsurface plasmon polaritons) [9 ]. The plasma frequency of the pseudo surface plasmon can be artificially controlled by changing the size of the metal surface microstructure, so that the propagation control of the terahertz surface wave is realized [10 ].

In order to adapt to the development of modern informatization, meet the requirement of continuously increasing information transmission capacity, get rid of the limitation of 'electronic bottleneck' of the traditional electronic device, realize the ultra-long distance, ultra-large capacity and ultra-high speed transmission of signals, the terahertz on-chip integrated system based on the pseudo surface plasmon polariton is produced. The logic operation device is a basic element of a signal processing system and is a bridge spanning electrical calculation and optical calculation, so that the logic operation device has great potential application in the fields of optical calculation and ultra-high-speed information processing. Transistor-based boolean logic gates are the basic unit of electronic circuits. In photonic circuits, logic functions can be realized by linear interference effects and nonlinear optical processes. The optical logic operation device has a size much larger than that of an electronic integrated circuit due to the limit of diffraction limit. Surface plasmon-based logic operation devices have been proposed and studied because they can confine light within a sub-wavelength scale. For linear surface plasmon optical logic gates, the logical operation depends on the relative optical phase difference of the two input signals. Constructive or destructive interference of input signals can generate corresponding logical operation results, and the operation results have lower field intensity, high integration potential and good stability and expandability.

In recent years, various surface plasmon-based all-optical logic gates have been proposed and studied in the high-frequency band. Weii et al implemented boolean logic gates on silver nanowires and NOR gates [11,12] by cascading OR and NOT gates, a problem with this type of device is that it is less field-binding, resulting in higher losses. Compared with a silver nanowire structure, the metal slot waveguide has better field limiting capability and is easier to integrate into complex structures and networks. Fu et al propose a logic gate structure based on a metal slot waveguide [13 ]. Based on a Y-type branch structure, the XNOR gate, the XOR gate, the NOT gate and the OR gate are realized by utilizing the interference effect of input light. Pan et al further studied metal slot waveguide based logic gate structures, and they proposed the implementation of a variety of logic gates using either single or double Y-shaped structures [14 ]. In addition to logic gates based on nanowire structures and metal slot waveguides, i.s.maksymov also implements boolean logic functions based on surface plasmon-photonic crystal structures [15 ]. Chen et al, for the first time, implemented multiple logic functions in a multimode structure, namely AND, NOT, XOR AND OR gates [16], by adjusting the coupling distance between two MIM waveguides AND the coupling distance of three MMI metal waveguides, using the multimode interference effect in a multilayer mode structure. However, although these studies provide a smart solution for boolean logic operations, most of the studies have focused on plasmonic waveguides in the optical band, and are not applicable in the terahertz band. To date, the research on terahertz-band related devices has been nearly zero due to the lack of an effective and convenient terahertz near-field measurement method. Achieving high performance compact broadband logic gates remains a significant challenge.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a terahertz multifunctional logic gate device based on pseudo surface plasmon waveguide.

The purpose of the invention is realized by the following technical scheme:

a terahertz multifunctional logic gate device based on a pseudo surface plasmon waveguide is composed of a pseudo surface plasmon waveguide with a Mach-Zehnder interference shape; the terahertz wave detector is made of high-resistance silicon with the resistivity larger than 3000 omega (the high resistivity is adopted to reduce the loss of materials to terahertz waves), a periodically-arranged cuboid structure is obtained on a silicon substrate by adopting photoetching and deep etching technologies, and gold with the thickness larger than 200nm (the thickness is larger than the skin depth of terahertz waves) is covered on the whole silicon structure by adopting an evaporation technology; the structure of the logic gate device is divided into two parts, wherein the first part provides input signals for the logic gate, and the second part performs logic calculation.

Further, the height of the cuboid structures is 80 μm, the length is 50 μm, the width is 120 μm, and the distance between the cuboid structures is 100 μm.

Furthermore, the phase attribute of the pseudo surface plasmon waveguide is controlled by changing the shape and the spacing parameter of the metal cuboid structure, so that the propagation phase between two or more than two paths of propagated pseudo surface plasmon waveguides is adjusted; AND 7 logic gate devices for realizing different functions of an AND gate (AND), an OR gate (OR), a NOT gate (NOT), a NAND gate (NAND), a NOR gate (NOR), an exclusive OR gate (XOR) AND an exclusive OR gate (XNOR).

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1. the logic operation device is a basic element of an optical signal processing system and has great potential application in the fields of optical computation and ultra-high-speed information processing. Many current optical logic gate devices are still electro-optically controlled and require high operating voltages. The logic gate device utilizing the nonlinear effect of the material has a single function and needs strong signal light. The invention aims to overcome the defects AND provides a series of passive waveguide-based multifunctional logic gate devices, which can complete logic operations of 4 different functions of an AND gate (AND), an OR gate (OR), a NOT gate (NOT) AND an exclusive OR gate (XOR) through coherent interference of two paths of surface plasmon waves; two paths of coherent interference systems are cascaded, wherein one path is used as a control end to complete 3 logic operations with different functions of a NAND gate (NAND), a NOR gate (NOR) and an XNOR gate (XNOR).

2. The size of the optical logic operation device is far larger than that of an electronic integrated circuit due to the limit of diffraction limit. The plasmons localize the electromagnetic field at the sub-wavelength level through the interaction of the electromagnetic wave and electrons in the conductor, thereby enabling manipulation of the electromagnetic wave at the sub-wavelength level. The terahertz surface plasmon polariton logic operation device can limit light in a sub-wavelength scale, so that compared with the prior art, the terahertz surface plasmon polariton logic operation device can be reduced to 8-12 mm in size, and has the advantages of compactness, small size, multiple functions and the like.

3. The invention can realize single device integration on the same material by using the same micro-processing technology, can also carry out multifunctional integration with other complex devices, such as complex transmission devices, coupling devices, active regulation and control devices and the like, does not need processing and manufacturing technology, is convenient to process, and is a convenient and practical multifunctional logic gate device. The terahertz signal on-chip integrated link can be widely applied to the terahertz signal on-chip integrated link.

Drawings

Fig. 1 is a schematic diagram of a basic unit of a terahertz multifunctional logic gate device related to the invention.

Fig. 2(a) and fig. 2(b) are schematic structural diagrams of a multifunctional logic gate device based on coherent interference of two paths of surface plasmon waves according to embodiment 1 of the present invention.

Fig. 3(a) to a (f) are simulation diagrams of electric field distribution results of the terahertz multifunctional logic gate device according to embodiment 1 of the present invention.

Fig. 4(a) and fig. 4(b) are schematic structural diagrams of a multi-functional logic gate device based on two-way coherent interference system cascade according to embodiment 2 of the present invention.

Fig. 5(a) to 5(f) are simulation diagrams of electric field distribution results of the terahertz multifunctional logic gate device according to embodiment 2 of the present invention.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Fig. 1 is a schematic structural diagram of a terahertz multifunctional logic device pseudo surface plasmon waveguide basic unit provided by the present invention, where the waveguide basic unit 1 specifically includes a metal substrate layer 10 and a metal column layer 11. The cuboid structure layer can comprise N metal cuboid structures 110, wherein N is more than or equal to 1. Only two cuboid structures 110 are shown in fig. 1. The structure and function of which are explained below.

The metal base layer 10 is located below the metal pillar layer 11. The rectangular parallelepiped structure 110 is arranged on the metal base layer 10, the size of the metal structure has a great influence on the dispersion relation of the surface wave, and the bound state at different frequencies can be realized by changing the size of the metal structure. The metal base layer 10 may be used to support the metal pillar layer 11. The metal pillar layer 11 can be used to support highly confined terahertz surface waves.

In the embodiment of the invention, the metal substrate layer 10 and the metal column layer 11 are made of high-resistivity silicon with a resistivity greater than 3000 Ω, the periodically arranged cuboid structures 110 are obtained on the silicon substrate by adopting the traditional photoetching and deep etching technology, and gold with a thickness of 200nm is covered on the silicon structures by adopting the evaporation technology. The base layer length of the metal base layer 10 can be denoted by e, the base layer width of the metal base layer 10 can be denoted by f, and the base layer thickness of the metal base layer 10 can be denoted by h. The rectangular parallelepiped structures 110 in the metal pillar layer 11 are periodically arranged on the metal base layer 10, and the distance between the centers of two adjacent rectangular parallelepiped structures 110 can be represented by p. The length of the rectangular parallelepiped structure 110 can be represented by l, the width of the rectangular parallelepiped structure 110 can be represented by w, and the height of the rectangular parallelepiped structure 110 can be represented by g.

Example 1:

the multifunctional logic gate device related to the embodiment is composed of a pseudo surface plasmon waveguide with a mach-zehnder interference shape, as shown in fig. 2(a) and 2(b), the phase of two paths of light is controlled and separated by changing the size of a cuboid structure, when the phase difference is odd times of pi, two beams of light can be cancelled, and when the phase difference is even times of pi, the light coherence can be realized. In which fig. 2(a) implements AND/OR operations by constructive interference AND fig. 2(b) implements NOT/XOR operations by destructive interference. The structure is divided into two parts, the first part provides input signals for the logic gate, and the second part performs logic calculation. In this device, two signals output from the first section are taken as signal input ports (denoted by I1 and I2) of the second section, and the two signals are transmitted from the input ports to the connection point and then to the output ports (denoted by O).

The logic gate discrimination mechanism adopted in this embodiment is an On-off-keyed (OOK) mechanism, that is, the amplitude of the input signal is used as the discrimination criterion of the input logic signal, and if the light intensity of the input signal is zero, the logic gate is logic "0", otherwise, the logic gate is logic "1". The input signal of the logic gate is encoded according to its intensity, the amplitudes of which are respectively E_I1And E_I2Determined by the phase of the input signal E_I1And E_I2Performs constructive or destructive interference to determine the amplitude E of the output port signal_O. By selecting a suitable output threshold value (I)_O) The structure can simultaneously realize various logic operations.

For a logic device input port, the "presence" and "absence" of a signal represent a "1" and a "0". While for the output port, the Boolean value is determined by the output threshold I_ODetermining if the output signal strength is greater than I_OIs 1, otherwise if the output signal strength is less than I_OAnd is "0". In this structure, the surface plasmon polariton excited by the grating is divided into two equal-energy beams by the Y-shaped beam-splitting waveguide of the first part, thereby making E_I1＝E_I2＝E。

For the constructive interference structure shown in fig. 2(a), the truth table of the AND/OR operation involved is shown in the following table:

when the input is (0,0), the output signal intensity is 0; (| E!) when (0, E) and (E,0)²(ii) a (E, E) output Signal intensity of 4| E². When the output threshold value 0 is selected<I_O<|E|²When the output of (0,0) is "0" and the outputs of (0, E), (E,0) and (E, E) are "1", the OR operation is completed at the O port. When the output threshold | E! is selected²<I_O<4|E|²The outputs of (0,0), (0, E) AND (E,0) are "0" AND the output of (E, E) is "1", at which point the AND operation can be done at the O port.

For the destructive interference structure shown in FIG. 2(b), by increasing the length of part of the metal cuboid structural unit structure, the propagation wave vector of the surface wave in the upper arm of the Mach-Zehnder interferometer at the same frequency becomes k due to the change of the structure, which causes the change of the surface plasmon mode₂While the lower arm is still k₁After propagation over a distance, the difference in wave vectors between the two arms will result in a phase difference, when the accumulated phase difference satisfies: (k)₁-k₂) When L ═ 2n +1) pi (where n is an integer), the two input signals will differ in phase by pi and the two waves will cancel at the convergence. This season E_I1＝-E，E_I2E. The NOT/XOR operation truth table is shown as the following table:

when the inputs are (0,0) and (-E, E), the output signal strength is 0; (| E!) when (0, E) and (-E,0)². When the output threshold value 0 is selected<I_O<|E|²When the outputs of (0,0) and (-E, E) are "0" and the outputs of (0, E) and (-E,0) are "1", the XOR operation can be completed on the O port. When we set input port I₁Is a control port and hold E_I1is-E, port I₂As input port, continue to select output threshold |0<I_O<|E|²When the input signal of the I2 port is "0" and "E" (i.e., -E,0) and (-E, E)), the output result is "1" and "0", respectively, and NOT operation can be completed at the O port.

Fig. 3(a) to 3(c) are graphs showing results of electric field distribution in the case of different input signals for AND/OR operation, AND fig. 3(d) to 3(f) are graphs showing results of electric field distribution in the case of different input signals for NOT/XOR operation.

Example 2:

the NAND, NOR, and XNOR operation devices according to this embodiment are composed of two sets of pseudo surface plasmon waveguides having mach-zehnder interference shapes in cascade, as shown in fig. 4(a) and 4 (b). These complex logical operations are combinations of simple operations AND can therefore be implemented by cascading NOT, OR, AND XOR operations, respectively. The structure is divided into two parts, the first part provides input signals for the logic gate, and the second part performs logic calculation. The logic calculation part comprises two stages of operation, the first stage of operation is the same as embodiment 1, and the input signal I can be realized₁And I₂AND/OR operation AND NOT/XOR operation of which output signal is O₁. In order to realize 2 × 2 cascaded logic gates, a control signal I needs to be added_CAnd performs coherent interference with the output result of the first stage operation, and the two signals reach the output port (denoted by O). By selecting a suitable output threshold value (I)_O) Various logical operations can be obtained.

For the structure shown in FIG. 4(a), the truth table for NOR/NAND operations involved is shown in the following table:

the structure is the cascade of AND/OR operation AND NOT operation, AND controls a port I_CHolding E_IC-2E, when the input is (0,0), the output signal strength is 4| E tint²(ii) a (| E!) when (0, E) and (E,0)²(ii) a And (E, E) the output signal intensity is 0. When the output threshold value 0 is selected<I_O<|E|²When the output of (0,0) is "0", and the outputs of (0, E), (E,0) and (E, E) are "1", the NAND operation can be completed at the O port. When the output threshold | E! is selected²<I_O<4|E|²When the outputs of (E,0), (0, E) and (E, E) are "0" and the output of (0,0) is "1", the NOR operation can be completed at the O port.

For the structure shown in fig. 4(b), the XNOR operation truth table involved is shown in the following table:

order control port I_CHolding E_IC-E, when the inputs are (0,0) and (E, E), the output signal strength is | E tint²(ii) a And (0, E) and (E,0) are 0. When the output threshold value 0 is selected<I_O<|E|²When the outputs of (0, E) and (E,0) are "0" and the outputs of (0,0) and (E, E) are "1", the XNOR operation can be completed at the O port.

Fig. 5(a) to 5(c) are graphs showing results of electric field distribution in the case of different input signals for NOR/NAND operation, and fig. 5(d) to 5(f) are graphs showing results of electric field distribution in the case of different input signals for XNOR operation.

Reference documents:

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the present invention is not limited to the above-described embodiments. The foregoing description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above specific embodiments are merely illustrative and not restrictive. Those skilled in the art can make many changes and modifications to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A terahertz multifunctional logic gate device based on a pseudo surface plasmon waveguide is characterized by comprising a pseudo surface plasmon waveguide with a Mach-Zehnder interference shape; the pseudo surface plasmon waveguide is made of high-resistance silicon with the resistivity larger than 3000 omega, a periodically arranged cuboid structure is obtained on a silicon substrate by adopting photoetching and deep etching technologies, and gold with the thickness larger than 200nm is covered on the whole silicon structure by an evaporation technology; the structure of the logic gate device is divided into two parts, the first part provides input signals for the logic gate, the second part performs logic calculation, the height of the cuboid structure is 80 micrometers, the length of the cuboid structure is 50 micrometers, the width of the cuboid structure is 120 micrometers, the distance between the cuboid structures is 100 micrometers, and the phase attribute of the pseudo surface plasmon waveguide is controlled by changing the shape and the interval parameter of the metal cuboid structure, so that the propagation phase between two or more than two paths of propagated pseudo surface plasmon waveguides is adjusted; AND 7 logic gate devices for realizing different functions of an AND gate (AND), an OR gate (OR), a NOT gate (NOT), a NAND gate (NAND), a NOR gate (NOR), an exclusive OR gate (XOR) AND an exclusive OR gate (XNOR).