CN104111565B - Micro-nano optical switch based on surface plasmon Fano resonance and cascade optical switch using same - Google Patents

Abstract

The invention discloses a micro-nano optical switch based on surface plasmon Fano resonance, which includes a transparent substrate, and is characterized in that a metal thin film layer, a nematic liquid crystal orientation conversion layer and a photoelectric switching layer are sequentially stacked on the transparent substrate. A polarizer, wherein: the polarizer gives an initial polarization direction to the transmitted light; the nematic liquid crystal alignment conversion layer is used to receive the above-mentioned transmitted light with the initial polarization direction, and control the direction of the transmitted light through it. Polarization direction; the metal thin film layer is etched with a separate metal hole tetramer unit configuration or an array topology formed by the unit through a tetragonal arrangement or a hexagonal arrangement, and the metal hole tetramer unit configuration The four holes are D _2h group symmetric, with orthogonal short axis and long axis; when the polarization direction of the light transmitted through the nematic liquid crystal alignment conversion layer is parallel to the short axis, the optical path is opened, otherwise, the surface plasmon is excited The polariton Fano resonance closes the optical path. The invention not only has all the advantages of the liquid crystal light switch, but also has the wavelength selection function that the traditional liquid crystal light switch does not have.

Description

A micro-nano optical switch based on surface plasmon Fano resonance and its level Optical switch

technical field

The invention relates to a micro-nano optical switch based on surface plasmon Fano resonance and a cascaded optical switch using it.

Background technique

Information technology is closely related to human life and production. Its development has gone through the stages of artificial means, electromagnetic technology and electronic technology, and is now developing towards the stage of photon technology. Photon technology is a modern technology that realizes the transmission, processing and storage of information with photon as the carrier. Because the frequency of photons is more than 1000 times higher than that of electronics, it supports multi-dimensional information processing in space, and is resistant to electromagnetic interference, so photons have incomparable advantages compared with electrons in information communication: larger information carrying capacity and faster information processing Faster, better confidentiality of information transmission. In the growing optical communication network, optical links and optical nodes are the main components; and the basic units of all routing, switching and processing systems in optical nodes are optical switches. Therefore, the optical switch is the core technology and key device of the optical communication network. From the perspective of research trends, optical switches are facing challenges in performance optimization, scalable scale, and functional diversification, and have become a bottleneck in the construction of next-generation optical networks.

An optical switch is strictly defined as: under a certain driving mode, a certain parameter (intensity, wavelength, direction or polarization, etc.) of an optical signal is rapidly, reversibly, and discontinuously changed from one state to another. process. Existing optical switches mainly include mechanical optical switches, magneto-optical switches, acousto-optic switches, liquid crystal switches, MEMS switches, and the like. Among them, compared with other optical switches, liquid crystal optical switches have the advantages of low energy consumption, high isolation, long service life, good stability and reliability, etc., so they have been vigorously developed in recent years. However, traditional optical switches including liquid crystal optical switches are a kind of light intensity switches, which do not have wavelength selectivity, that is, switches are simultaneously realized for all wavelengths. However, the development of optical communication requires not only the switching state of the space domain and the time domain, but also the switching selection function of the frequency domain. On the other hand, the optical communication network is developing towards the direction of integrated optical path. The integration of optical communication is the only way for the development of the information industry, and it is also a major strategic demand of the country. The development of integrated optical circuits inevitably requires that the size of optical components (including optical switches) be gradually reduced to micro-nano optical switches. Therefore, the development of new micro-nano optical switches is an urgent development goal of integrated optical communication technology.

Fano resonance is a characteristic resonance phenomenon produced by the mutual interference between the continuous background field and the discrete resonance field, and it appears as an asymmetric resonance line shape in the spectrum. This phenomenon was discovered by Ugo Fano when he was studying the inelastic scattering of electrons in atomic systems. It was initially considered to be limited to the quantum field, and then expanded to many scientific and engineering fields. In recent years, it has been discovered that metal particles can simulate molecular configurations and generate surface plasmons in different modes under the drive of light. These different modes interfere with each other and oscillate, thereby realizing the Fano resonance. The Fano resonance involved in the present invention is manifested in the asymmetrical line shape of the scattering spectrum, the extremely narrow line width, and the scattering trough corresponding to the dark mode (Dark mode) produced by the surface plasmon phase coherence cancellation.

Contents of the invention

The object of the present invention is: to provide a micro-nano optical switch based on surface plasmon Fano resonance, the working principle of the device is completely different from that of traditional liquid crystal optical switches, and utilizes the birefringence characteristics of liquid crystals, not only has all the advantages of liquid crystal optical switches Advantages, and at the same time, it has the wavelength selection function that traditional liquid crystal optical switches do not have.

The technical solution of the present invention is: a micro-nano optical switch based on surface plasmon Fano resonance, comprising a transparent substrate, characterized in that a metal thin film layer, a nematic liquid crystal layer, and a nematic liquid crystal are sequentially stacked on the transparent substrate. an orientation conversion layer and a polarizer, wherein:

Polarizer, which gives the transmitted light an initial polarization direction;

The nematic liquid crystal alignment conversion layer is used to receive the above-mentioned transmitted light with the initial polarization direction, and control the polarization direction of the light transmitted through it;

The metal thin film layer is etched with a single metal hole tetramer unit configuration or an array topology configuration formed by the unit through a tetragonal arrangement or a hexagonal arrangement, and the four holes in the metal hole tetramer unit configuration It is D _2h group symmetric, with orthogonal short axis and long axis; when the polarization direction of the light transmitted through the nematic liquid crystal alignment conversion layer is parallel to the short axis, the optical path is opened; when the nematic liquid crystal is aligned When the polarization direction of the light transmitted by the conversion layer changes relative to the initial polarization direction and is parallel to the long axis, the surface plasmon Fano resonance is excited and the optical path is closed.

Further, the thickness of the metal thin film layer in the present invention is 20-100 nm, the pore diameters Φ of the four holes in the metal hole tetramer unit configuration are all 90-1000 nm, and the pore spacing s is 3-100 nm.

Further, the nematic liquid crystal orientation conversion layer described in the present invention includes a lower liquid crystal orientation control transparent layer, a nematic liquid crystal layer, and an upper liquid crystal orientation control transparent layer stacked on the metal film layer in sequence; wherein the lower liquid crystal orientation The upper surface of the control transparent layer is provided with a number of grooves distributed in parallel at intervals, and the lower surface of the upper liquid crystal orientation control transparent layer is provided with interdigitated electrodes and lead out electrode lines. The grooves are parallel or vertical. Correspondingly, when the interdigitated electrodes are energized, the direction of the electric field generated by them is vertical or parallel to the grooves below.

Furthermore, the lower transparent layer for controlling liquid crystal orientation in the present invention is a polyimide film layer, ITO or FTO, and the upper transparent layer for controlling liquid crystal orientation is a cover glass layer.

Further, the nematic liquid crystal orientation conversion layer described in the present invention includes a lower liquid crystal orientation control transparent layer, a nematic liquid crystal layer, and an upper liquid crystal orientation control transparent layer stacked on the metal film layer in sequence; wherein the lower liquid crystal orientation The upper surface of the control transparent layer is provided with several grooves distributed in parallel at intervals, and the lower surface of the upper liquid crystal orientation control transparent layer is also provided with several grooves distributed in parallel at intervals, and these grooves are connected with the grooves on the lower liquid crystal orientation control transparent layer. The groove is vertical; it also includes electrode lines respectively connected to the upper and lower liquid crystal orientation control transparent layers for applying a vertical electric field to the nematic liquid crystal layer.

Further, in the present invention, the lower transparent layer for controlling liquid crystal orientation is a polyimide film layer, ITO or FTO, and the upper transparent layer for controlling liquid crystal orientation is an ITO conductive film layer.

Furthermore, in the present invention, the lower surface of the upper liquid crystal orientation control transparent layer is spin-coated with a layer of glass balls with a diameter of 1-10 microns as a pad, and the nematic liquid crystal is filled in the gap of the glass balls to form the Nematic liquid crystal layer. In fact, the glass ball substrate is sandwiched between the upper and lower liquid crystal orientation control transparent layers, and the diameter of the glass ball is equal to the thickness of the nematic liquid crystal layer.

Furthermore, the metal material of the metal thin film layer in the present invention is Au, Ag or Al.

The nematic liquid crystal described in the present invention is conventional technology, for example, n-pentyl biphenylcyanide is selected.

Further, the present invention also includes an analyzer arranged under the transparent substrate.

Both the polarizer and the analyzer in the present invention use polarizers. Like the conventional technology, the polarizer can change the incident compound polarized natural light into a single linearly polarized light, and the analyzer is used for inspection and analysis of light. the polarization state.

The core element involved in the present invention is the metal hole tetramer unit configuration that simulates the molecular configuration: it is composed of four holes and is D _2h group symmetric, when the electric field polarization direction of the light wave is consistent with the metal hole tetramer unit configuration When the short axis of the metal hole tetramer unit configuration is parallel, the transmission spectrum has only one scattering peak; when the electric field polarization direction of the light wave is parallel to the long axis of the metal hole tetramer unit configuration, a narrow trough appears in the transmission peak, corresponding to the surface plasmon dark mode. The orientation of the nematic liquid crystal can be controlled by switching the voltage on and off, and then the polarization direction of the light wave incident through the polarizer can be adjusted, and finally the effective control of the light transmission intensity and wavelength can be realized.

The interaction between light and the micro-nano structure (metal hole tetramer unit configuration) involved in the system of the present invention can be accurately described by solving Maxwell's equations, and the solving methods include numerical methods such as finite time domain, finite element and boundary element. Typical spectral response curves can be obtained through numerical simulations in the time domain and frequency domain. The intrinsic physical mechanism of the spectral response is the coherent oscillation of the surface plasmon modes: when the phases of each mode are consistent, the surface plasmon waves are coherent and constructive, and a scattering peak appears; When the bright mode interacts, due to its opposite phase, the surface plasmon waves are coherent and destructive, and scattering valleys appear. The surface plasmon bright mode is often a dipole mode (dipolemodes), due to the large radiation attenuation rate, the scattering spectrum line is relatively broad; on the contrary, the dark mode cannot directly couple with the incident light, the radiation attenuation rate is very small, and the scattering spectrum The lines are narrower. It is this narrow dark mode that makes the Fano resonance have a resonance linewidth of only tens of nanometers, so the resonance is very sensitive to wavelength and can be applied to wavelength selective devices.

Through the finite element numerical solution of the tetramer electromagnetic properties in the system, the influence of typical geometric parameters on the transmission spectrum of the system is obtained. The increase of the metal pore diameter of the metal pore tetramer unit configuration can red-shift the Fano resonance peak and increase the number of Fano resonances; the increase of the thickness of the metal film layer and the hole spacing can make the resonance wavelength blue-shift. The adjustment of the wavelength by the geometric parameters makes the Fano trough red-shift or blue-shift, which reflects the good resonant wavelength selection ability of the metal hole tetramer.

The metal pore tetramer unit configuration as the core in the present invention can be an independent four-pore unit, or can evolve into a tetragonal or hexagonal array topology based on the unit. The size of the topological structure can be determined according to the required size of the device. For the tetragonal arrangement, there are two periods a and b in the vertical direction; for the hexagonal arrangement, there is a non-90-degree angle between the translation vectors.

Another object of the present invention is to provide a cascaded optical switch formed by connecting at least two micro-nano optical switches based on surface plasmon Fano resonance in series.

That is, the micro-nano optical switch provided by the present invention can not only work alone, but also can be connected in series to form a cascaded optical switch to realize selective filtering of a series of wavelengths. For example, the operating wavelengths of the three micro-nano optical switches correspond to λ3, λ2 and λ1. When they are incident on the first micro-nano optical switch at the same time, λ3 falls on the operating wavelength of the first micro-nano optical switch, that is, the transmission valley cannot pass through , at this time, only λ1 and λ2 pass through; similarly, only λ1 passes through the second micro-nano optical switch, and so on.

The advantages of the present invention are:

1. The micro-nano optical switch based on the surface plasmon Fano resonance provided by the present invention is completely different from the traditional liquid crystal optical switch in its working principle. Advantages, and at the same time, it has the wavelength selection function that traditional liquid crystal optical switches do not have.

2. The metal hole tetramer unit configuration involved in the present invention is a unique structure for simulating molecular configuration proposed for the first time, which is obviously different in structure and in the excitation and coherence of surface plasmon modes The same kind of metal particle structure proposed in the world recently. Studies have shown that the metal hole tetramer unit configuration in the present invention supports high-order surface plasmon modes, such as quadrupoles, hexapoles, and octopoles, while the corresponding metal particle structure only supports dipoles Mode; compared with metal particles, the preparation of the metal hole tetramer unit configuration in the present invention is simpler, the geometric parameters are more sensitive to the regulation of spectral lines, and the Fano resonance spectral lines are narrower.

For example, in a specific example of the present invention, the pore diameter Φ (diameter) of the metal hole tetramer unit configuration is 100 nm, the hole spacing s (hole equidistant gap) is 6 nm, the metal material is Au, and the thickness of the metal film layer is 30 nm. When the above conditions are met, for the polarization directions parallel to the major axis and the minor axis, the light response difference between light and dark is much greater than 5 times in the band around 700nm, which has excellent contrast.

3. The metal hole tetramer unit configuration and its derivative structure involved in the present invention can interact with light to excite surface plasmons; dark mode and bright mode of surface plasmons Coherent oscillations form the Fano resonance, which exhibits strong polarization sensitivity and extremely narrow scattering peaks and valleys, so it can be used to effectively control the on-off of the mode and accurately identify the incident band.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Fig. 1 is one of the micro-nano optical switch device structures based on the surface plasmon Fano resonance of the present invention;

Fig. 2 is the second structure of the micro-nano optical switch device based on the surface plasmon Fano resonance of the present invention;

Figure 3 is a schematic diagram of the configuration of an independent metal hole tetramer unit with "D _2h tetramer molecular configuration";

Fig. 4 is a typical backscattering spectrum (or transmission spectrum) of the metal hole tetramer unit configuration under the voltage on-off situation;

Figure 5 is a tetragonal periodic array topology derived from the metal hole tetramer unit configuration;

Figure 6 is a hexagonal periodic array topology derived from the metal hole tetramer unit configuration;

Fig. 7 is a working principle diagram based on the device structure in Fig. 1;

Fig. 8 is a working principle diagram based on the device structure in Fig. 2;

Figure 9 is a side-by-side schematic diagram of the influence of three geometric parameters of the metal hole tetramer unit configuration on the transmission spectrum;

Fig. 10 is a schematic diagram of a cascaded optical switch proposed according to the wavelength tunability of the metal hole tetramer unit configuration of the present invention.

Among them: 1. Transparent substrate; 2. Metal film layer; 3. Polyimide film layer; 4. Nematic liquid crystal layer; 5. Cover glass layer; 6. Electrode line; 7. Polarizer; 8 , Interdigitated electrodes; 9, grooves; 10, ITO conductive film layer; 11, analyzer.

detailed description

Embodiment 1: As shown in FIG. 1, it is a specific embodiment of a micro-nano optical switch based on surface plasmon Fano resonance provided by the present invention, which uses a glass transparent substrate, and the glass transparent substrate 1 is sequentially A metal thin film layer 2, a nematic liquid crystal orientation switching layer and a polarizer 7 are stacked, and the nematic liquid crystal orientation switching layer in the present invention consists of a polyimide film layer 3 stacked on the metal thin film layer 2 successively. , a nematic liquid crystal layer 4 and a cover glass layer 5. The upper surface of the polyimide film layer 3 is provided with several grooves 9 distributed in parallel at intervals, and the lower surface of the cover glass layer 5 is provided with interdigitated electrodes 8 and lead electrode lines 6, the interdigitated electrodes The interdigitation direction of 8 is parallel to the groove 9 below. In the present invention, an analyzer 11 is provided below the transparent substrate. Both the polarizer 7 and the analyzer 11 in this embodiment are polarizers.

As shown in Figure 3, the metal thin film layer 2 in the present invention is etched with a separate metal hole tetramer unit configuration, the four holes in the unit configuration are D _2h group symmetry, with orthogonal minor axes and long axis. In this embodiment, the aperture Φ (diameter) of the metal holes is 100 nm, the hole spacing s (equal distance gap) is 6 nm, the metal material is Au, and the thickness of the metal thin film layer is 30 nm.

As shown in Figure 4, when the electric field polarization direction of the light wave is parallel to the short axis of the metal hole tetramer unit configuration, the transmission spectrum has only one scattering peak; when the electric field polarization direction of the light wave is parallel to the metal hole tetramer unit configuration When the long axes of the two types are parallel, there is a narrow trough in the transmission peak, corresponding to the surface plasmon dark mode. The orientation of the nematic liquid crystal can be controlled by switching the voltage on and off, and then the polarization direction of the light wave incident through the polarizer can be adjusted, and finally the effective control of the light transmission intensity and wavelength can be realized.

The interaction between light and the micro-nano structure (metal hole tetramer unit configuration) involved in the system of the present invention can be accurately described by solving Maxwell's equations, and the solving methods include numerical methods such as finite time domain, finite element and boundary element. Typical spectral response curves can be obtained through numerical simulations in the time domain and frequency domain. The intrinsic physical mechanism of the spectral response is the coherent oscillation of the surface plasmon modes: when the phases of each mode are consistent, the surface plasmon waves are coherent and constructive, and a scattering peak appears; When the bright mode interacts, due to its opposite phase, the surface plasmon waves are coherent and destructive, and scattering valleys appear. The surface plasmon bright mode is often a dipole mode (dipolemodes), due to the large radiation attenuation rate, the scattering spectrum line is relatively broad; on the contrary, the dark mode cannot directly couple with the incident light, the radiation attenuation rate is very small, and the scattering spectrum The lines are narrower. It is this narrow dark mode that makes the Fano resonance have a resonance linewidth of only tens of nanometers, so the resonance is very sensitive to wavelength and can be applied to wavelength selective devices. Specifically, it can be concluded from the analysis of Figure 4 that: for the polarization directions parallel to the major axis and the minor axis, the light response difference between light and dark is much greater than 5 times in the band around 700nm, which has excellent contrast.

The specific preparation method of the above-mentioned micro-nano optical switch in this embodiment is as follows:

1) On a glass transparent substrate 1 , prepare an Au thin film with a thickness of 30 nm.

2) On the metal thin film layer 2, the metal pore tetramer unit configuration is prepared by using electron beam etc. etching technology, the pore diameter Φ is 100nm, and the pore spacing s is 6nm.

3) Use a spin coater to spin-coat the polyimide film layer 3, keep the temperature at 200 degrees Celsius for 1 hour, and then cool naturally to complete the annealing heat treatment; mechanically polish the polyimide film layer 3 along the same direction to form parallel parallel micro-grooves in the same direction Slot 9.

4) Prepare Au interdigitated electrodes on the cover glass layer 5 by photolithography. The width of the fingers is 50 nanometers, the height is 70 nanometers, the distance between the fingers is 8 microns, and the electrodes are connected and drawn out by solder Line 6.

5) A layer of glass spheres with a size of 5 microns is spin-coated on the side of the cover glass layer 5 where the interdigitated electrodes are arranged, as a gasket material (not shown in the figure).

6) Under an optical microscope, the cover glass layer 5 prepared in step 5) is placed on the polyimide film layer 3 prepared in step 3), ensuring that the interdigitated electrode 8 is aligned with the direction of the polyimide film The sanding directions on layer 3 were consistent (ie, parallel to each other).

7) Fill the gap between the glass balls with nematic liquid crystal n-pentyl biphenylcyanide, so that the liquid crystal enters the gap through capillary force, and heat the liquid crystal until the liquid crystal becomes a uniform phase, that is, the nematic liquid crystal layer 4 is formed, and then naturally cooled to room temperature.

8) A polarizer 7 is pasted on the top of the device (a polarizer 11 is pasted on the bottom for detection), and the device is packaged with epoxy resin tape.

With reference to Fig. 3 and Fig. 7, the specific working principle of the above-mentioned micro-nano optical switch in this embodiment is briefly described as follows:

The initial electric field polarization direction of the polarizer 7 in this embodiment is shown in Figure 1 (the polarization direction is the P direction, and the horizontal arrow on it represents the horizontal direction) and Figure 7, perpendicular to the paper and parallel to the metal hole tetramerization The minor axis of the body element configuration. The incident light is 700nm natural light.

1) The case where the voltage is disconnected (that is, the interdigitated electrodes 8 are not energized). Since the orientation of the groove on the lower surface contacted by the liquid crystal is consistent with that of the interdigitated electrode on the upper surface, the orientation of the liquid crystal is in a consistent nematic state under the action of Van der Waals force; therefore, the polarization filtered by the polarizer 7 Light can directly pass through the liquid crystal and maintain the original polarization direction; combined with the description of Figure 4 and the configuration principle of the metal hole tetramer unit, it can be seen that when the electric field polarization direction perpendicular to the paper is parallel to the metal hole tetramer For the short axis of the unit configuration, Fano resonance cannot occur, and there are no Fano transmission valleys and transmission peaks, so the optical path is turned on, and the analyzer 11 (the polarization direction is the A direction) obtains a high-brightness light signal.

2) Voltage closure (ie interdigitated electrodes 8 energized). 3V voltage is loaded on the interdigitated electrodes, and an electric field perpendicular to the interdigitated direction is formed between the fingers. Under the action of the electric field force, the nearby liquid crystals are twisted to be parallel to the electric field; On the surface, it gradually transitions from vertical orientation to parallel orientation, that is, the twisted nematic phase; under the action of the waveguide of the twisted nematic phase, the polarization direction of the incident light after passing through the liquid crystal is reversed, and the original parallel to the metal hole tetramer unit The polarization direction of the short axis of the configuration is reversed to be parallel to the long axis, so the Fano resonance is excited, the Fano transmission valley corresponding to the dark mode appears, and the optical path is closed. It can be seen from the above that the switching of the voltage leads to the inversion of the liquid crystal orientation, which in turn leads to the Fano resonance from scratch, and finally realizes the opening and closing of the optical path.

In the brief description of the above principles, since the optical switch is in an on state when the voltage is disconnected, it is called a normally white mode. In fact, by changing the orientation of the polarizer, the initial orientation of the liquid crystal, and the orientation of the major and minor axes of the metal hole tetramer unit configuration, the optical switch can be turned from the normally white mode to the normally black mode, that is, the voltage is turned off. Timeway is closed.

Embodiment 2: As shown in FIG. 2, it is a specific embodiment of a micro-nano optical switch based on surface plasmon Fano resonance provided by the present invention, which uses a glass transparent substrate, and the glass transparent substrate 1 is sequentially A metal thin film layer 2, a nematic liquid crystal orientation switching layer and a polarizer 7 are stacked, and the nematic liquid crystal orientation switching layer in the present invention consists of a polyimide film layer 3 stacked on the metal thin film layer 2 successively. , a nematic liquid crystal layer 4 and an ITO conductive film layer 10. Wherein the upper surface of polyimide thin film layer 3 is provided with some grooves 9 that are distributed in parallel at intervals, and the lower surface of ITO conductive film layer 10 is also provided with some grooves 9 that are distributed in parallel at intervals, these grooves 9 and polyimide The grooves 9 on the imide film layer 3 are vertical; in this embodiment, electrode lines are arranged on the upper and lower ends of the nematic liquid crystal layer 4 for applying a vertical electric field.

Shown in conjunction with Fig. 5, Fig. 6, metal thin film layer 2 among the present invention, etch on it by the independent metal hole tetramer unit configuration as shown in Fig. 3 through tetragonal arrangement (Fig. 5), or hexagonal arrangement ( Figure 6) formed the array topology configuration. The four holes in the single unit configuration are D _2h group symmetric, with orthogonal short axis and long axis, the aperture Φ (diameter) of the metal hole is 90nm, the hole spacing s (equidistant gap) is 3nm, and the metal material is selected Au, the thickness of the metal thin film layer is 50nm. The size of the array topology can be determined according to the actual required size of the entire micro-nano optical switch device. For the tetragonal arrangement, there are two periods a=500nm and b=500nm in the vertical direction; for the hexagonal arrangement, the period between the translation vectors There is a non-90-degree angle between them, as shown in Figure 5 and Figure 6 for details.

The specific preparation method of the above-mentioned micro-nano optical switch in this embodiment is as follows:

1) On a glass transparent substrate 1 , prepare an Au thin film with a thickness of 30 nm.

2) On the metal thin film layer 2, the metal pore tetramer unit configuration is prepared by using electron beam etc. etching technology, the pore diameter Φ is 100nm, and the pore spacing s is 6nm.

3) Use a spin coater to spin-coat the polyimide film layer 3, keep the temperature at 200 degrees Celsius for 1 hour, and then cool naturally to complete the annealing heat treatment; mechanically polish the polyimide film layer 3 along the same direction to form parallel parallel micro-grooves in the same direction Slot 9.

4) On the ITO conductive film layer 10, use mechanical method to polish and process so that there are parallel and uniform grooves; then spin-coat a layer of glass balls with a size of 10 microns on one side of the grooves as a pad material ( not shown in the figure).

5) under an optical microscope, the ITO conductive film layer 10 prepared in step 4) is placed on the polyimide film layer 3 prepared in step 3), ensuring that the direction of the groove 9 on the ITO conductive film is consistent with that of the polyimide film. The grinding direction on the film layer 3 is vertical.

6) Fill the gap between the glass balls with nematic liquid crystal n-pentyl biphenylcyanide, so that the liquid crystal enters the gap through capillary force, and heat the liquid crystal at the same time until the liquid crystal becomes a uniform phase, that is, the nematic liquid crystal layer 4 is formed, and then naturally cooled to room temperature.

7) A polarizer 7 is pasted on the top of the device (a polarizer 11 is pasted on the bottom for detection), and the device is packaged with epoxy tape.

With reference to Figure 3 and Figure 8, the specific working principle of the above-mentioned micro-nano optical switch in this embodiment is briefly described as follows:

Based on the fact that the principle of the embodiment shown in FIG. 2 is substantially the same as that of Embodiment 1 shown in FIG. 1 , for the sake of clarity, the normally black mode of the device of the embodiment is briefly described. Compared with embodiment 1, embodiment 2 lacks the interdigitated electrodes 8, and the voltage is not applied on the interdigitated electrodes, but on the upper and lower surfaces of the nematic liquid crystal. Therefore, the initial phase of the liquid crystal of the device is generally a twisted nematic phase, which is mainly realized by making the upper and lower surfaces of the liquid crystal perpendicular to each other or using an opposite alignment agent.

The initial electric field polarization direction of polarizer 7 in the present embodiment is as shown in Fig. 2 (polarization direction is P direction, and the horizontal arrow on it represents horizontal direction) and Fig. 8, is the same as the situation of embodiment 1, also is perpendicular to On paper and parallel to the minor axis of the metal pore tetramer unit configuration. The incident light is 700nm natural light.

1) When the voltage is disconnected (the liquid crystal is not powered up and down), the natural light is filtered by the polarizer 7, and only the polarized light perpendicular to the paper surface enters the liquid crystal, guided by the twisted nematic phase, and the polarization direction is reversed to parallel tetramerization The long axis direction of the body, according to the characteristics of the tetramer unit configuration of the metal hole, excites the Fano resonance and closes the optical path;

2) When the voltage is applied (the liquid crystal is powered up and down), the orientation of the liquid crystal is parallel to the direction of the electric field, and the twisted phase transforms into a consistent phase. The polarization direction perpendicular to the paper remains unchanged after passing through the liquid crystal, and at this time it is parallel to the metal hole tetramer According to the characteristics of the metal hole tetramer unit configuration, the light path is opened in the minor axis direction of the unit configuration. In this device, the normally black mode can be adjusted to the normally white mode by changing the orientation of the polarizer 7 or rotating the axial direction of the metal hole tetramer by 90 degrees.

Through the finite element numerical solution of the tetramer electromagnetic properties in the system, the influence of typical geometric parameters on the transmission spectrum of the system is obtained. As shown in Figure 9, increasing the diameter of the metal hole can red-shift the Fano resonance peak and increase the number of Fano resonances; increasing the thickness of the metal film and the hole spacing can make the resonance wavelength blue-shift. The adjustment of the wavelength by the geometric parameters makes the Fano trough red-shift or blue-shift, which reflects the good resonant wavelength selection ability of the metal hole tetramer. According to this principle, the corresponding metal hole tetramer unit configuration can be designed for different wavelengths, and then a series of micro-nano optical switches can be formed. These micro-nano optical switches can not only work alone, but also can be connected in series to form a cascaded optical switch to achieve selective filtering of a series of wavelengths. Its structure and principle are shown in Figure 10. For example, the operating wavelengths of the three optical switches 1, 2, and 3 correspond to λ3, λ2, and λ1. When they are incident on the optical switch 1 at the same time, λ3 falls on the operating wavelength of the switch 1, that is, it cannot pass through the transmission valley. At this time, only λ1 and λ2 pass through; similarly, only λ1 passes through the optical switch 2, and so on.

The above examples are only to illustrate the technical conception and characteristics of the present invention, and its purpose is to allow people familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (10)

1. A micro-nano optical switch based on surface plasmon Fano resonance, comprising a transparent substrate, characterized in that the transparent substrate (1) is successively stacked with a metal thin film layer (2), a nematic phase Liquid crystal alignment conversion layer and polarizer (7), wherein: A polarizer (7), which gives the transmitted light an initial polarization direction; The nematic liquid crystal alignment conversion layer is used to receive the above-mentioned transmitted light with the initial polarization direction, and control the polarization direction of the light transmitted through it; The metal thin film layer (2) is etched with a single metal hole tetramer unit configuration or an array topological configuration formed by the unit through a tetragonal arrangement or a hexagonal arrangement, and the metal hole tetramer unit configuration is The four holes are D _2h group symmetric, with orthogonal short axis and long axis; when the polarization direction of the light transmitted through the nematic liquid crystal alignment conversion layer is parallel to the short axis, the light path is opened; When the polarization direction of the light transmitted by the liquid crystal alignment conversion layer changes relative to the initial polarization direction and is parallel to the long axis, the surface plasmon Fano resonance is excited and the optical path is closed. 2. A micro-nano optical switch based on surface plasmon Fano resonance according to claim 1, characterized in that the thickness of the metal thin film layer (2) is 20-100 nm, and the metal hole tetramer unit The pore diameters of the four holes in the configuration are all 90-1000 nm, and the hole spacing s is all 3-100 nm. 3. A kind of micro-nano optical switch based on surface plasmon Fano resonance according to claim 1, characterized in that said nematic liquid crystal orientation switching layer includes successively stacked metal thin film layers (2) The upper and lower liquid crystal orientation control transparent layer, the nematic liquid crystal layer (4), and the upper liquid crystal orientation control transparent layer; wherein the upper surface of the lower liquid crystal orientation control transparent layer is provided with a number of grooves (9) distributed in parallel intervals, and the upper The lower surface of the liquid crystal orientation control transparent layer is provided with interdigitated electrodes (8) and lead out electrode lines (6), and the interdigitated direction of the interdigitated electrodes (8) is parallel or perpendicular to the groove (9) below, Correspondingly, when the interdigitated electrodes (8) are energized, the direction of the electric field generated by them is vertical or parallel to the groove (9) below. 4. A kind of micro-nano optical switch based on surface plasmon Fano resonance according to claim 3, characterized in that the lower liquid crystal orientation control transparent layer is a polyimide film layer (3), ITO or FTO, and the upper liquid crystal orientation control transparent layer is the glass cover layer (5). 5. A micro-nano optical switch based on surface plasmon Fano resonance according to claim 1, characterized in that the nematic liquid crystal orientation conversion layer includes a lower layer stacked on the metal thin film layer in turn. A liquid crystal orientation control transparent layer, a nematic liquid crystal layer (4), and an upper liquid crystal orientation control transparent layer; wherein the upper surface of the lower liquid crystal orientation control transparent layer is provided with a plurality of grooves (9) distributed in parallel intervals, and the upper liquid crystal orientation control The lower surface of the transparent layer is also provided with several grooves (9) distributed in parallel at intervals, and these grooves (9) are perpendicular to the grooves (9) on the lower liquid crystal orientation control transparent layer; The electrode lines on the transparent layer are controlled to apply a vertical electric field to the nematic liquid crystal layer (4). 6. A kind of micro-nano optical switch based on surface plasmon Fano resonance according to claim 5, characterized in that the lower liquid crystal orientation control transparent layer is a polyimide film layer (3), ITO or FTO, and the upper liquid crystal orientation control transparent layer is an ITO conductive film layer (10). 7. A micro-nano optical switch based on surface plasmon Fano resonance according to claim 3 or 5, characterized in that the lower surface of the upper liquid crystal orientation control transparent layer is spin-coated with a diameter of 1～ 10-micron glass balls are used as pads, and nematic liquid crystals are filled in the gaps of the glass balls to form the nematic liquid crystal layer (4). 8. A micro-nano optical switch based on surface plasmon Fano resonance according to claim 1, characterized in that the metal material of the metal thin film layer is Au, Ag or Al. 9. A micro-nano optical switch based on surface plasmon Fano resonance according to claim 1, characterized in that an analyzer (11) is arranged below the transparent substrate. 10. A cascaded optical switch formed by connecting at least two micro-nano optical switches according to any one of claims 1-9 in series.