CN115016149A - Plasmon ultrafast polarization selective optical modulator based on vanadium dioxide phase change - Google Patents
Plasmon ultrafast polarization selective optical modulator based on vanadium dioxide phase change Download PDFInfo
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/008—Surface plasmon devices
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/0009—Materials therefor
- G02F1/009—Thermal properties
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Abstract
A plasmon ultrafast polarization selective optical modulator based on vanadium dioxide phase change belongs to the technical field of modulators. The grating structure comprises an upper layer of orthogonal grating and a lower layer of orthogonal grating, wherein the lower layer of the orthogonal grating is of a gold grating structure, a vanadium dioxide grating is arranged on the gold grating, and grid lines of the gold grating and the vanadium dioxide grating are mutually vertical. Two kinds of linearly polarized light which are respectively parallel to the two grid lines have different local field enhancement, and the generated LSPR is in different wave bands, thereby being more beneficial to improving the signal-to-noise ratio. The phase change of the vanadium dioxide is caused by adopting a light regulation and control mode, and the ultrafast regulation and control within the subpicosecond time is realized.
Description
Technical Field
The invention relates to a vanadium dioxide phase change-based plasmon ultrafast polarization selective optical modulator, and belongs to the technical field of modulators.
Background
The optical field regulation is usually the regulation of the intensity, phase, polarization, frequency and other parameters of the optical field. Polarization is an important physical quantity describing light, embodies the oscillation characteristic of light as transverse waves, is one of the inherent characteristics of electromagnetic waves, and plays an important role in optical communication, calculation, imaging, encryption and display. Different polarization states can be loaded with different information, and polarization multiplexing can be realized. Conventional methods of controlling the polarization state typically involve bulky optical elements such as mirrors, crystals and prisms, which are not feasible for miniaturization and integration of optical systems. The realization of large-scale integration and dynamic regulation and control of ultra-small-size and low-energy-consumption photonic devices becomes a research hotspot in the field of micro-nano photonics at home and abroad at present, and therefore various artificial structures with different performances are designed. In recent years, with the progress of micro-nano processing technology and method, the construction of a micro-optical modulator with novel polarization characteristics becomes a key breakthrough for solving the technical problem of complicated on-chip polarization.
Recently, surface plasmons in metal structures have been used for optical field regulation, and the localization of electromagnetic fields in sub-wavelength scale nanostructures is enhanced, thereby enhancing light-material interactions. The plasmon super surface is formed by micro-nano structures distributed in a plane, and plasmon resonance is formed between metal and dielectric medium, so that characteristics such as polarization, phase and amplitude of electromagnetic waves can be further regulated and controlled. The metal nano structure can modulate the resonance mode of the metal nano structure by adjusting the geometric parameters of the structure or the incident light angle, and the structure can also present anisotropy so as to realize the polarization characteristic. The surface plasmon optical modulator has the advantages of large working bandwidth, high speed, small volume and the like, and more researches are proposed.
Vanadium dioxide (VO) as phase change material 2 ) The contrast of optical constants is large when undergoing a semiconductor to metal phase transition. VO when the temperature exceeds 68 DEG C 2 A first order phase transition of insulator-metal occurs. At low temperature, VO 2 In the insulating phase, with a Monoclinic crystal structure (Monoclinic, M1); at high temperature, VO 2 In the metallic phase, has a Rutile crystal structure (Rutile, R). VO accompanying the change of lattice structure 2 Physical properties such as electrical conductivity, complex refractive index, dielectric constant, work function, etc. all change dramatically. VO (vacuum vapor volume) 2 The phase change can be controlled by temperature, and the light speed response can be obtained by adopting a light pumping method, and the phase change is suitable for the micro-processing technology due to the mature growth technology and stable material performance. When optically triggered, this transition occurs in sub-picoseconds, which makes the device suitable for ultrafast applicationsA pulsed laser.
The optical modulator is an indispensable core device in photonics and optoelectronics, and is widely applied to the fields of optical interconnection, medical treatment, biology, environmental monitoring and the like, and due to the fact that the demand for high-speed and compact optical modulators is higher and higher, the design of the optical modulator is researched towards the direction of small-size and rapid modulation. The phase-change material vanadium dioxide is combined with the plasmon super surface to realize ultra-small-size ultra-fast modulation of polarized light, so that the method has guiding significance for realizing a low-power-consumption and integrated optical modulator, and is beneficial to realizing an integrated photon loop and all-optical interconnection. The optical modulator can be divided into mechanical regulation, thermal regulation, acoustic regulation, electrical regulation, optical regulation and the like according to the modulation principle, wherein the phase-change material VO is subjected to 2 Most of the regulation and control of (2) are realized by utilizing direct heating to regulate and control or applying current to generate resistance heat, and the regulation and control time of the regulation and control mode is usually in millisecond order and cannot meet the requirement of rapid modulation.
Disclosure of Invention
The invention designs that the femtosecond laser is used as the control light to irradiate the surface plasmon generated on the sample to generate the hot electron to inject into VO 2 To reduce VO 2 The phase transition threshold in turn reduces the light intensity requirements. The double-layer orthogonal grating is arranged to generate different local field enhancement for linearly polarized light with mutually orthogonal polarization states, and further realize polarization selective light regulation and control on signal light. The micro-size plasmon super surface is designed to realize the regulation and control of linearly polarized light, the response time of the regulation and control is in the sub-picosecond order, and the ultrafast modulation is realized.
And (3) preparing a micron-sized plasmon super surface light modulator to realize ultrafast polarization selective light regulation.
A plasmon ultrafast polarization selective optical modulator based on vanadium dioxide phase change is composed of unit structures which are periodically arranged, wherein the top view of the unit structures is shown in figure 1, each unit structure comprises an upper layer of orthogonal grating and a lower layer of orthogonal grating, the lower layer of the orthogonal grating is a gold grating structure, a vanadium dioxide grating is arranged on the gold grating, and grid lines of the gold grating and the vanadium dioxide grating are perpendicular to each other.
Further light modulationThe structure of the device is as follows from bottom to top: SiO 2 2 A substrate, a gold grating layer, a vanadium dioxide grating layer, as shown in FIG. 2, on SiO 2 The substrate is provided with a gold grating layer, the gold grating layer is provided with a vanadium dioxide grating layer, and the gold grating in the gold grating layer is vertical to the grid line of the vanadium dioxide grating in the vanadium dioxide grating layer. The further concrete parameters are as follows: thickness of gold grating is t 1 200nm with period P 1 400nm, the width of the grid line is a 1 120 nm; the thickness of the vanadium dioxide grating is t 2 100nm with period P 2 600nm, gate line width a 2 ＝200nm。
Linearly polarized light is used as incident light, Ey is defined when the polarization direction of the light is parallel to the grid line (y direction) of the gold grating, and Ex is defined when the polarization direction of the light is parallel to the grid line (x direction) of the vanadium dioxide grating; incident light is normally incident on the super-surface area at 0 degree, sequentially passes through the vanadium dioxide grating and the gold grating, and finally passes through the SiO 2 And (4) ejecting the substrate.
5. Advantages and positive effects
1) The designed optical modulator utilizes hot electrons generated by LSPR, the phase change threshold of vanadium dioxide is reduced by injecting the hot electrons, and the requirement on the light intensity of control light is reduced.
2) The optical modulator consists of two layers of orthogonal gratings, two linearly polarized light beams parallel to the two grid lines respectively have different local field enhancement, and the generated LSPR is in different wave bands, so that the signal-to-noise ratio is improved.
3) The optical modulator adopts a light regulation mode to cause the phase change of the vanadium dioxide, and the ultrafast regulation within the subpicosecond time is realized.
4) The light modulator is designed to be on the micron scale.
The invention has the advantages that the mutually orthogonal double-layer grating is designed, different local field enhancements are generated for the two linearly polarized light with mutually vertical polarization directions, the polarization selectivity is realized, the polarization states of the control light and the signal light are mutually vertical and the light wavelengths are different, and the signal light is more beneficial to screening the signal light and improving the signal-to-noise ratio. Hot electron injection into VO using LSPR 2 Internally reduce VO 2 The phase transition threshold value of (1) is to induce VO in a light regulation mode 2 The phase change not only reduces the requirement on light intensity, but also realizes ultrafast regulation and control of sub picosecond magnitude in time, and is more favorable for quick response of the optical modulator and miniaturization of devices.
Drawings
FIG. 1 is a top view of a light modulator cell structure
FIG. 2 is a schematic diagram of an optical modulator
FIG. 3-1 absorption of Ey light at normal incidence to a light modulator
Transmissivity and transmissivity difference for Ey light normally incident light modulator of FIGS. 3-2
FIG. 4-1 absorption of Ex light at normal incidence to the light modulator
Transmittance and transmittance difference for Ex light normally incident light modulator of FIGS. 4-2
Detailed Description
The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.
Example 1
The structure is shown in figures 1-2.
1) And processing the gold grating mask plate by using an electron beam exposure process. Firstly, a layer of photoresist is spin-coated on a quartz substrate, then an electron beam photoresist grating with the period of 400nm and the grid line width of 280nm is etched by electron beam exposure, and a structural pattern is obtained by development and fixation.
2) Vapor plating of Au with a thickness of 180-200nm on the surface of the photoresist grating structure by using a vacuum thermal vapor plating process, wherein the current is adjusted during vapor plating to keep the vapor plating speed at
Prevent the thickness of the film from being uneven and ensure the hardness of the Au film. And putting the sample into a degumming agent to strip the photoresist, thereby obtaining the Au grating with the period of 400nm and the grid line width of 120 nm.
3) Depositing VO with the thickness of 90-100 nm on a quartz plate by utilizing a magnetron sputtering coating technology 2 Thin film, then annealing treatment, and finally testing to ensure VO 2 The phase change is enabled.
4) Deposit VO 2 Soaking the quartz plate in BOE corrosive liquid to obtain VO 2 The film will be formed from SiO 2 Stripping on a substrate and then stripping the VO 2 The film was transferred to a prepared Au grating.
5) For VO by using focused ion beam etching technique 2 The film is etched to obtain a period of 600
VO with nm and grid line width of 200nm 2 Grating, etched VO 2 The grid lines of the grating are perpendicular to those of the lower Au grating.
In the step of Au plating, a vacuum thermal evaporation coating technology can be used, and a magnetron sputtering coating technology can also be used; the Au grating structure can be prepared by firstly plating gold on a quartz plate and then etching a gold film on the quartz plate in a small area by using a focused ion beam etching technology.
Finite element analysis software (COMSOL) is used for simulating the structure, and the mutual orthogonal double-layer gratings have different local field enhancements on Ex light and Ey light, so that feasibility is provided for realizing polarization selectivity. The absorption rate of Ey light in a normal incidence structure is shown in figure 3-1, localized plasmons (LSPR) are generated near the 1190nm wavelength (the position of a dotted line in figure 3-1), the LSPR is localized at the contact position of the gold grating and the vanadium dioxide grating, and the LSPR can provide hot electron injection to the vanadium dioxide and reduce the phase change threshold of the vanadium dioxide, so that the vanadium dioxide can be excited to change phase by using light with lower intensity. The transmittance and transmittance change difference of Ey light before and after vanadium dioxide phase change are shown in fig. 3-2, most of the Ey light is absorbed to form LSPR, the transmittance is lower in a near infrared band, and the transmittance change of the optical modulator before and after vanadium dioxide phase change is small. The formula for calculating the transmittance difference is as follows:
ΔT＝T (after phase transition) -T (before phase transition)
Where Δ T represents the transmittance difference, T (before phase transition) Denotes the transmittance, T, of the vanadium dioxide phase-change front light modulator to Ex light or Ey light (after phase transition) Indicating the transmittance of the light modulator to Ex light or Ey light after vanadium dioxide phase transition.
When Ex light is normally incident on the optical modulator, the absorptance before and after the phase transition of vanadium dioxide is shown in fig. 4-1. When Ey light is not incident, vanadium dioxide in the optical modulator does not change phase, and LSPR when Ex light is incident appears near 900 nm. When Ey light is incident, vanadium dioxide is subjected to phase change, and LSPR incident to Ex light is near 735 nm. The phase change of vanadium dioxide causes the LSPR generated when Ex light is incident to undergo blue shift, the transmittance of the optical modulator to Ex light is changed, and the transmittance difference before and after the phase change of vanadium dioxide when Ex light is incident are shown in fig. 4-2. The transmission rate of Ex is increased after the vanadium dioxide phase change, the transmission rate at the wavelength of 945nm is obviously changed before and after the vanadium dioxide phase change, and the modulation depth can reach 39.3%.
The LSPR generated on the optical modulator by Ey light with the wavelength of 1190nm at normal incidence provides hot electron injection to reduce the phase change threshold of vanadium dioxide and cause the vanadium dioxide to have phase change, and whether the vanadium dioxide has the phase change has little influence on the transmissivity of the Ey light, so the Ey light is more suitable to be used as control light. When Ex light is normally incident, the position of LSPR on a spectrum is changed by the phase change of vanadium dioxide, and what is important is that the transmissivity of the optical modulator before and after the phase change is greatly changed, so that the optical modulator is more suitable for being used as signal light. Therefore, Ey light with the wavelength of 1190nm is selected as control light for regulating and controlling the phase change of the vanadium dioxide, Ex light with the wavelength of 945nm is selected as signal light to be regulated and controlled, and the designed optical modulator can realize the function of selective regulation and control of the ultrafast polarization state.
Claims (6)
1. A plasmon ultrafast polarization selective optical modulator based on vanadium dioxide phase change is characterized in that the optical modulator is formed by periodically arranging unit structures, each unit structure comprises an upper layer of orthogonal grating and a lower layer of orthogonal grating, the lower layer of the orthogonal grating is a gold grating structure, a vanadium dioxide grating is arranged on the gold grating, and grid lines of the gold grating and the vanadium dioxide grating are perpendicular to each other.
2. The plasmon ultrafast polarization selective optical modulator based on vanadium dioxide phase change according to claim 1, characterized in that the structure of the optical modulator is, from bottom to top: SiO 2 2 A substrate, a gold grating layer, a vanadium dioxide grating layer on SiO 2 A gold grating layer on the substrate, and vanadium dioxide on the gold grating layerAnd the grid lines of the gold grating in the gold grating layer and the vanadium dioxide grating in the vanadium dioxide grating layer are mutually vertical.
3. The plasmon ultrafast polarization selective optical modulator based on vanadium dioxide phase change according to claim 1, characterized in that the specific parameters are as follows: thickness of gold grating is t 1 200nm with period P 1 400nm, the width of the grid line is a 1 120 nm; the thickness of the vanadium dioxide grating is t 2 100nm with period P 2 600nm, gate line width a 2 ＝200nm。
4. The plasmonic super-surface ultrafast polarization selective optical modulator based on vanadium dioxide phase change according to claim 1, wherein linearly polarized light is used as incident light, and is defined as Ey when the polarization direction of the light is parallel to the grid line (y direction) of the gold grating, and is defined as Ex when the polarization direction of the light is parallel to the grid line (x direction) of the vanadium dioxide grating; incident light is normally incident on the super-surface area at 0 degree, sequentially passes through the vanadium dioxide grating and the gold grating, and finally passes through the SiO 2 And (4) ejecting the substrate.
5. The plasmon ultrafast polarization selective optical modulator based on vanadium dioxide phase change according to claim 1, wherein Ey light with a wavelength of 1190nm is selected as control light for adjusting and controlling vanadium dioxide phase change, and Ex with a wavelength of 945nm is selected as signal light to be adjusted and controlled, so that the function of ultrafast polarization state selective adjustment is realized.
6. The plasmonic super surface ultrafast polarization selective optical modulator based on vanadium dioxide phase transition as claimed in claim 1, wherein the modulator size is in micron dimension.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116626920A (en) * | 2023-07-21 | 2023-08-22 | 南京大学 | Super surface polarization modulator integrated with light emitting diode |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116626920A (en) * | 2023-07-21 | 2023-08-22 | 南京大学 | Super surface polarization modulator integrated with light emitting diode |
| CN116626920B (en) * | 2023-07-21 | 2023-11-03 | 南京大学 | Super surface polarization modulator integrated with light emitting diode |
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