CN106094093A - A kind of sub-wavelength ultra broadband transmission-type two-dimensional metallic wave plate - Google Patents

Abstract

The invention discloses a sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate, which is composed of several periodic wave plate units, and the wave plate unit includes a _SiO2 substrate and an orthogonal cross silver nanorod structure located on the substrate , the substrate is a square substrate, its side length P is 800~1000nm, the height H of the orthogonal crossed silver nanorod structure is 100~150nm, and the first width W of the orthogonal crossed silver nanorod structure is 200~300nm , the second length Lx of the orthogonal cross silver nanorod structure is 550-650 nm, and the second width Ly of the orthogonal cross silver nano-rod structure is 150-170 nm. The invention greatly widens the working bandwidth, and has a higher tolerance for parameter changes. Due to the limitation of the manufacturing precision of the current micro-nano structure, the structure is reasonable and easy to manufacture. It can be used in optical sensing systems, advanced nano-photonic devices and integrated optical systems. , has great application value.

Description

A Subwavelength Ultra-Broadband Transmissive Two-Dimensional Metallic Waveplate

technical field

The invention relates to a sub-wavelength ultra-broadband transmission type two-dimensional metal wave plate, and relates to the field of optical elements.

Background technique

In the prior art, the polarization state is a very important optical characteristic of light waves. Birefringent crystal materials have the characteristic of having different optical refractive indices along the orthogonal directions parallel to and perpendicular to the optical axis, and are widely used in conventional devices for controlling the polarization state. When the light passes through the birefringent crystal, the transmitted light will produce a phase difference in the orthogonal direction to realize the conversion of the polarization state. At present, the miniaturization development of new industries requires highly integrated optoelectronic components, while the traditional crystal wave plate is limited by the physical size, which promotes the rapid development of sub-wavelength structural optical devices. Among them, the sub-wavelength metal structure based on surface plasmon resonance The metasurface wave plate has been widely valued and studied.

Optical metasurfaces, or subwavelength metasurfaces, refer to an artificial layered material with a thickness smaller than the wavelength, which can realize flexible and effective control of electromagnetic wave phase, polarization mode, propagation mode and other characteristics. Compared with traditional waveplates, waveplates based on metasurfaces can enhance the properties of electromagnetic fields to regulate light waves on an ultrathin platform. Waveplates based on metasurfaces generally use anisotropic resonant element arrays, such as nanoslits, L-antennas, H-antennas, V-antennas, etc... and waveplates based on these structures are often limited by narrow bands.

In view of this, it is obviously necessary to provide a new two-dimensional metal wave plate to solve the problem of narrow application range in the prior art due to narrow bandwidth.

Contents of the invention

The purpose of the present invention is to provide a sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate, which solves the problem of narrow bandwidth in the prior art.

In order to achieve the above-mentioned purpose of the invention, the technical solution adopted in the present invention is: a sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate, which is composed of several periodic wave plate units, and the wave plate units include SiO2 substrates and located at the Orthogonal cross silver nanorod structure on the substrate,

The substrate is a square substrate, and its side length P is 700 ~ 900nm,

The height H of the orthogonal cross silver nanorod structure is 50-150nm,

The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate,

The first width W of the orthogonal cross silver nanorod structure is 100~200nm,

The second length Lx of the orthogonal cross silver nanorod structure is 600~750nm,

The second width Ly of the orthogonal cross silver nanorod structure is 100-200 nm.

Preferably, the substrate is a square substrate, its side length P=950nm, the height H=125nm of the orthogonal cross silver nanorod structure,

The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate,

The first width W=300nm of the orthogonal cross silver nanorod structure,

The second length Lx=600nm of the orthogonal cross silver nanorod structure,

The second width Ly=160nm of the orthogonal cross silver nanorod structure.

Preferably, the substrate is a square substrate, its side length P=950nm, the height H=125nm of the orthogonal cross silver nanorod structure,

The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate,

The first width W=300nm of the orthogonal cross silver nanorod structure,

The second length Lx=600nm of the orthogonal cross silver nanorod structure,

The second width Ly=160nm of the orthogonal cross silver nanorod structure.

Preferably, the substrate is a square substrate, its side length P=880nm, the height H=100nm of the orthogonal cross silver nanorod structure,

The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate,

The first width W=300nm of the orthogonal cross silver nanorod structure,

The second length Lx=560nm of the orthogonal cross silver nanorod structure,

The second width Ly=160nm of the orthogonal cross silver nanorod structure.

Preferably, the shape of the substrate is square, its side length P=850nm, and the height H=140nm of the orthogonal cross silver nanorod structure,

The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate,

The first width W=210nm of the orthogonal cross silver nanorod structure,

The second length Lx=630nm of the orthogonal cross silver nanorod structure,

The second width Ly=165nm of the orthogonal cross silver nanorod structure.

Preferably, when linearly polarized light is incident, its polarization angle changes with wavelength, so that the amplitude component Ex = Ey, while the phase distribution of the metal wave plate remains unchanged.

The design principle of the present invention is as follows: after a beam of linearly polarized light passes through the quarter-wave plate along the direction of 45° with the fast axis of the quarter-wave plate, the phase difference of the transmitted field along the two orthogonal directions is π/2 Odd multiples, and the amplitudes Ex and Ey are equal, that is, the quarter-wave plate has the function of converting linearly polarized light into circularly polarized light.

In the design process of the wave plate, the influence of various structural parameters on the transmission field distribution of the metasurface is analyzed respectively by controlling variables. As an anisotropic optical resonator, the height H of the metal rod and the width W of the vertical silver nanorod play a major role in the regulation of the phase difference, and the thickness of the metal also affects the transmission efficiency of the wave plate, while the vertical width of the horizontal nanorod Ly is sensitive to where resonance occurs at short wavelengths. Therefore, after determining the metal thickness and selecting an appropriate structural period, the phase distribution in the orthogonal direction is adjusted by fine-tuning Lx and W to obtain the performance of a quarter-wave plate.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

The present invention designs a new type of sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate, which realizes the function of a transmissive quarter-wave plate in the near-mid-infrared ultra-wide band range, compared with the existing wave plate , the two orthogonal components of the transmitted electric field are in the ultra-wide wavelength range of at least 2500nm, and the phase difference changes below 2% of π/2, instead of just at the intersection of two adjacent resonance peaks, which greatly broadens the working bandwidth, and this The invention has a high tolerance for parameter changes. Due to the limitation of the production accuracy of micro-nano structures, the structure is reasonable and easy to manufacture. It has great application value in optical sensing systems, advanced nanophotonic devices and integrated optical systems. .

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

Fig. 2 is a structural schematic diagram of the wave plate unit of the present invention.

Fig. 3 is a top view of the wave plate unit in Fig. 2 .

Fig. 4 is a comparison diagram of the amplitude and phase distribution of the transmitted light in the orthogonal direction of the wave plate unit with different structural parameters in the first embodiment.

Fig. 5 is a distribution diagram of the phase and phase difference of the transmitted light of the sub-wavelength transmissive two-dimensional metal wave plate in the first embodiment as a function of the incident wavelength.

Fig. 6 is a graph showing the distribution of transmittance versus wavelength when the polarization angle of the incident light is incident along the x- and y-axis directions in the first embodiment.

Fig. 7 is a graph showing the variation of the transmittance of the two-dimensional metal wave plate with wavelength under different incident polarization angles.

Fig. 8 is a diagram showing the distribution of the amplitude and phase of the transmitted light of the two-dimensional metal wave plate as a function of the incident wavelength under different polarization angles of the incident ray polarization.

FIG. 9 is a distribution diagram of the phase and phase difference of the transmitted light of the sub-wavelength transmissive two-dimensional metal wave plate in the second embodiment as a function of the incident wavelength.

FIG. 10 is a diagram showing the distribution of transmittance versus wavelength when the polarization angle of the incident light is incident along the x and y axis directions in the second embodiment.

Fig. 11 is a distribution diagram of the phase and phase difference of the transmitted light of the sub-wavelength transmissive two-dimensional metal wave plate in the third embodiment as a function of the incident wavelength.

FIG. 12 is a graph showing the distribution of transmittance versus wavelength when the polarization angle of the incident light is incident along the x and y axes in the third embodiment.

Among them: 1. Substrate; 2. Orthogonal cross silver nanorod structure.

detailed description

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

Embodiment 1: Referring to Fig. 1, a sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate is composed of several periodic wave plate units. The structural diagram of the wave plate unit is shown in Fig. 2. The unit includes a SiO2 substrate 1 and an orthogonal cross silver nanorod structure 2 on the substrate,

Referring to Fig. 3, it is a top view of the wave plate unit, the shape of the substrate is square, its side length P=950nm, and the height H=125nm of the orthogonal cross silver nanorod structure,

The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate,

The first width W=300nm of the orthogonal cross silver nanorod structure,

The second length Lx=600nm of the orthogonal cross silver nanorod structure,

The second width Ly=160nm of the orthogonal cross silver nanorod structure.

Preferably, the incident light polarization angle θ ranges from 30° to 70°.

The above-mentioned orthogonal cross silver nanorod structure includes a rectangular structure and rectangular protrusions arranged on both sides of the rectangular structure, the rectangular protrusions are formed by extending outward from both sides of the rectangular structure, and the first length above is the length of the rectangular structure, The first width is the width of the rectangular structure, the second length is the distance between the outermost sides of the opposite rectangular protrusions on two sides of the rectangular structure, and the second width is the width of the rectangular protrusions. In this embodiment, the distance between adjacent rectangular protrusions on the same side of the metal wave plate is equal to the period of the wave plate unit.

In this embodiment, the numerical calculation method of finite difference time domain FDTD is used for modeling and simulation. The FDTD method differentiates the time-domain field curl equation differential in Maxwell's equations to obtain the finite difference equation of the field component, and uses the same parameter space grid to simulate electromagnetic scattering.

Referring to FIG. 4 , it is a comparison diagram of the amplitude and phase distribution of the transmitted light in the orthogonal direction of the wave plate unit with different structural parameters as a function of wavelength. As shown in Figure 4(a), due to the similar shape of the orthogonal nanorods, the parameters change little. Generally, the positions of these two resonance peaks are adjacent to each other, and they are represented as two close narrow and high transmission peaks on the transmittance curve. The narrow-band wave plate function can only be realized in a small band between the two peaks. It can be seen from Figure 4(b) that as the length in the vertical direction gradually becomes longer, it can be seen that the orthogonal excitation resonance peaks are pulled apart. A gentle phase distribution appears between the two peaks, and the bandwidth increases. As can be seen from Figure 4(c), the resonance peak of the vertical rods of this embodiment moves to the far-infrared band and the peak height decreases, that is, its resonance effect becomes weaker, eliminating the phase dispersion of the unwanted vertical rods in the near-infrared . At the same time shorten the length of the horizontal rod, introduce phase dispersion in the near-middle infrared and a continuous π/2 phase difference with the vertical direction, by adjusting the thickness of the metal, the phase curve in the orthogonal direction can be far apart The resonant peaks are close to parallel, and this effect directly leads to a gentle phase difference in the ultra-wide range of the near-infrared band, that is, the generation of ultra-broadband. The divergence of the amplitude ratio can be solved by changing the polarization angle of the incident light with the wavelength, thereby changing the resonance point of Ex = Ey.

Referring to Figure 5, it is a distribution diagram of the phase and phase difference of the transmitted light of the sub-wavelength transmissive two-dimensional metal wave plate in this embodiment as a function of the incident wavelength, as shown in Figure 6, which is the polarization angle of the incident light in this embodiment When incident along the x and y axis directions, the transmittance varies with wavelength. From Figure 5 and Figure 6, it can be seen that the phase difference is in the ultra-wide wavelength range between 2000nm and 4500nm, and the two orthogonal components of the transmitted electric field The phase difference change is less than 2% of π/2, which satisfies the necessary phase difference condition for a quarter-wave plate.

Referring to FIG. 7 , the graph showing the transmittance of the two-dimensional structure as a function of wavelength under different incident polarization angles. Because the amplitude ratio diverges with the wavelength, the electric field polarization angle of the transmitted wave diverges when converting circularly polarized light to linearly polarized light. When converting linearly polarized light to circularly polarized light, due to the divergence of the amplitude ratio of the electric field component in the orthogonal direction of the transmitted field, it is necessary to change the polarization angle of the incident light with the wavelength to obtain the broadband effect. That is, when the polarization angle of the incident light changes, the point of Ex = Ey moves, while the phase distribution of the structure remains unchanged. The simulation shows that the incident polarization angle that needs to be rotated is at most 70°.

Referring to FIG. 8 , it is a distribution diagram of the amplitude and phase of the transmitted light of the two-dimensional metal wave plate as a function of the incident wavelength under different polarization angles of the incident ray. In Figure 8(a), the angle between the incident light polarization angle and the x direction is θ=50°, and the electric field component Ex =Ey in the orthogonal direction of the transmission field at 2113nm of the structure, the phase difference is 1.59rad, which is approximately π/2, which can be As a quarter-wave plate, the transmittance is 54%; in Figure 8(b), the angle between the polarization angle of the incident light and the x direction is θ=55°, and the electric field component in the orthogonal direction of the transmission field at 2970nm is Ex =Ey, the phase difference is π/2, it can be regarded as a quarter-wave plate, and the transmittance is 46%. At 3964nm, the electric field component Ex =Ey in the orthogonal direction of the transmission field, the phase difference is 1.54rad, approximately π/2, which can be regarded as a quarter-wave plate with a transmittance of 32%; in Figure 8(d), the incident The angle between the light polarization angle and the x direction is θ=66°, and the electric field component Ex =Ey in the orthogonal direction of the transmission field of this structure at 4164nm, the phase difference is 1.54rad, which is approximately π/2, which can be regarded as a quarter wave plate. The transmittance is 21%.

In summary, this embodiment realizes the function of an ultra-broadband transmission quarter-wave plate in the range of near-mid-infrared 2000nm~4500nm, and its bandwidth is at least 2500nm. The phase difference of the cross component changes less than 2% of π/2, and the polarization angle of the incident light changes with the wavelength, which effectively broadens the bandwidth of the transmissive wave plate, and this structure has a high tolerance for parameter changes, due to Now the fabrication precision of micro-nano structure is limited, the structure is reasonable and easy to fabricate, and has great application value in optical sensing system, advanced nano-photonic device and integrated optical system.

Embodiment 2: A sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate is composed of several periodic wave plate units, and the wave plate unit includes a SiO2 substrate and an orthogonal cross silver nanorod structure located on the substrate.

The shape of the substrate is square, its side length P=880nm, the height of the orthogonal cross silver nanorod structure H=100nm,

The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate,

The first width W=300nm of the orthogonal cross silver nanorod structure,

The second length Lx=560nm of the orthogonal cross silver nanorod structure,

The second width Ly=160nm of the orthogonal cross silver nanorod structure. The angle between the polarization angle of the incident light and the x direction is θ=45°.

Referring to Figure 9, it is a distribution diagram of the phase and phase difference of the transmitted light of the sub-wavelength transmissive two-dimensional metal wave plate in Embodiment 2 as a function of the incident wavelength, as shown in Figure 10, the polarization angle of the incident light is along x and y The distribution diagram of the transmittance versus wavelength when the axis is incident, it can be seen that the phase difference of the two orthogonal components of the transmitted electric field is less than 2% of π/2 in the ultra-wide wavelength range between 2200nm and 4800nm. Satisfying the necessary phase difference condition of a quarter-wave plate realizes ultra-wideband.

Embodiment 3: A sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate is composed of several periodic wave plate units, and the wave plate unit includes a SiO2 substrate and an orthogonal cross silver nanorod structure located on the substrate.

The shape of the substrate is square, its side length P=850nm, the height of the orthogonal cross silver nanorod structure H=140nm,

The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate,

The first width W=210nm of the orthogonal cross silver nanorod structure,

The second length Lx=630nm of the orthogonal cross silver nanorod structure,

The second width Ly=165nm of the orthogonal cross silver nanorod structure. The angle between the polarization angle of the incident light and the x direction is θ=45°.

Referring to Figure 11, it is a distribution diagram of the phase and phase difference of the transmitted light of the sub-wavelength transmissive two-dimensional metal wave plate in Embodiment 3 as a function of the incident wavelength, as shown in Figure 12, the polarization angle of the incident light is along x and y The distribution diagram of the transmittance versus wavelength when the axis is incident, it can be seen that the phase difference of the two orthogonal components of the transmitted electric field is less than 2% of π/2 in the ultra-wide wavelength range between 2500nm and 5000nm. Satisfying the necessary phase difference condition of a quarter-wave plate realizes ultra-wideband.

Claims (5)

1. A sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate is composed of several periodic wave plate units, characterized in that: the wave plate unit includes SiO ₂ substrate and an orthogonal cross positioned on the substrate silver nanorod structure, Described substrate is a square substrate, and its side length P is 800～1000nm, The height H of the orthogonal cross silver nanorod structure is 100-150nm, The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate, The first width W of the orthogonal cross silver nanorod structure is 200~300nm, The second length Lx of the orthogonal cross silver nanorod structure is 550~650nm, The second width Ly of the orthogonal cross silver nanorod structure is 150-170 nm. 2. The sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate according to claim 1, characterized in that: the substrate is a square substrate, its side length P=950nm, and the orthogonal cross silver nanorod structure The height H=125nm, The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate, The first width W=300nm of the orthogonal cross silver nanorod structure, The second length Lx=600nm of the orthogonal cross silver nanorod structure, The second width Ly=160nm of the orthogonal cross silver nanorod structure. 3. The sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate according to claim 1, characterized in that: the substrate is a square substrate, its side length P=880nm, and the orthogonal cross silver nanorod structure The height H=100nm, The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate, The first width W=300nm of the orthogonal cross silver nanorod structure, The second length Lx=560nm of the orthogonal cross silver nanorod structure, The second width Ly=160nm of the orthogonal cross silver nanorod structure. 4. The sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate according to claim 1, characterized in that: the substrate is square in shape, its side length P=850nm, and the cross silver nanorod structure of the orthogonal Height H=140nm, The first length of the orthogonal cross silver nanorod structure is equal to the side length of the substrate, The first width W=210nm of the orthogonal cross silver nanorod structure, The second length Lx=630nm of the orthogonal cross silver nanorod structure, The second width Ly=165nm of the orthogonal cross silver nanorod structure. 5. The sub-wavelength ultra-broadband transmissive two-dimensional metal wave plate according to claim 1, characterized in that: when linearly polarized light is incident, its polarization angle changes with the change of wavelength, so that the amplitude component Ex=Ey, and The phase distribution of the metal wave plate remains unchanged.