CN114465014A - Light adjustable broadband terahertz absorber based on intrinsic silicon metamaterial and regulation and control method - Google Patents
Light adjustable broadband terahertz absorber based on intrinsic silicon metamaterial and regulation and control method Download PDFInfo
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- CN114465014A CN114465014A CN202210231884.6A CN202210231884A CN114465014A CN 114465014 A CN114465014 A CN 114465014A CN 202210231884 A CN202210231884 A CN 202210231884A CN 114465014 A CN114465014 A CN 114465014A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0086—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices having materials with a synthesized negative refractive index, e.g. metamaterials or left-handed materials
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Abstract
The invention provides a light adjustable broadband terahertz absorber based on an intrinsic silicon metamaterial and a regulation and control method, which are used for solving the technical problems of complex preparation, low light tuning efficiency and strong reflection effect of a doped silicon absorber and comprise an antireflection layer and a substrate layer, wherein the antireflection layer is a resonance unit array, the resonance unit array is formed by periodically arranged cross columnar resonance units, and the cross columnar resonance units are formed by vertically intersecting the midpoints of a horizontal column and a vertical column; the antireflection layer and the substrate layer are both intrinsic silicon. According to the invention, through a brand-new terahertz absorption scheme and a metamaterial antireflection structure design, the optically adjustable broadband terahertz absorber based on the intrinsic silicon metamaterial is obtained, and under 1064nm continuous laser irradiation, the ultra-large range peak absorption rate adjustment of 0-99% and the broadband absorption of more than 1.3THz are realized; the device only needs a single silicon etching process for preparation, and has the advantages of simple structure, low manufacturing cost, good stability and the like.
Description
Technical Field
The invention belongs to the technical field of novel artificial electromagnetic materials and terahertz science, relates to a terahertz wave absorber, and particularly relates to an intrinsic silicon metamaterial-based optically-tunable broadband terahertz absorber and a regulation and control method.
Background
The electromagnetic wave-absorbing material has low reflectivity and transmittance, and is mainly realized by ohmic loss, dielectric loss, hysteresis loss and the like of electromagnetic waves in the material. The wave-absorbing material is widely applied in the aspects of electromagnetic shielding, RCS reduction and the like. The traditional wave-absorbing material mainly comprises metal micro powder, graphite, ferrite and the like, and most of the materials are difficult to meet the application requirements of light weight, easy large-area preparation, wide band, high-efficiency absorption and the like. The metamaterial absorber mainly enhances ohmic loss or dielectric loss through electromagnetic resonance, and has the advantages of thin thickness and flexible design of absorption frequency bands, so that broadband absorption can be realized, and narrow-band or multi-band absorption can be designed. More importantly, the metamaterial absorber can achieve richer absorption functions such as tunability and polarization selection.
Terahertz absorbers based on all-silicon metamaterials have also attracted interest in recent years. By properly doping the crystalline silicon, a large number of defect carriers are introduced, and free carrier absorption occurs to incident terahertz waves. The doped silicon based absorber can utilize optical pumping to change the carrier concentration near the surface of the structure, and the adjustment of the absorption efficiency is realized by increasing reflection. However, the doped silicon absorber needs to be subjected to steps of doping intrinsic silicon, etching a metamaterial unit and the like, further efficient tuning is difficult to achieve after the doped intrinsic silicon absorber is subjected to laser irradiation, and particularly, the absorption function can hardly be turned off, so that the doped silicon absorber has many limitations in production and application. For example, patent CN105609963B discloses an ultra-wideband terahertz wave absorber prepared by using doped silicon, in which the average absorption rate is over 90% in the range of 1.5THz-10THz, but the absorption rate is lower below 1.5THz, and meanwhile, the prepared terahertz wave absorber lacks adjustability of absorption efficiency. In addition, in order to improve the absorption bandwidth, researchers also develop various absorbers with complex structures and a multilayer structure or a plurality of resonators, and the absorption efficiency of terahertz waves can be obviously improved through the surface structure design; for example, patent CN207752171U discloses an absorber composed of a substrate layer, a silica layer and a pattern having a cross structure, and patent CN107942418B discloses an absorber composed of a metal reflective layer, a dielectric layer and a cross-shaped graphene pattern layer, but the pattern layer prepared in this way is thin, which is only convenient for adjusting and controlling the position of the absorption peak, and it is difficult to improve the absorption efficiency in a wide frequency band.
1064nm continuous laser has good penetrability on intrinsic silicon, generates photon-generated carriers in the thickness range of the whole absorber, realizes the efficient absorption of terahertz waves, and provides a new idea for preparing the broadband adjustable terahertz absorber. However, the terahertz wave has a strong reflection effect on the silicon interface, so that the absorption efficiency is limited, and the application of intrinsic silicon in the terahertz wave absorption field can be increased by reducing the reflection effect of the terahertz wave on the silicon interface.
Disclosure of Invention
Aiming at the technical problems of complex preparation, low light tuning efficiency and strong reflection effect of the existing doped silicon absorber, the invention provides a light-adjustable broadband terahertz absorber based on an intrinsic silicon metamaterial, and the purposes of simple preparation, high light tuning performance and high absorption efficiency of the absorber are achieved.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a light adjustable broadband terahertz absorber based on an intrinsic silicon metamaterial comprises an antireflection layer and a substrate layer, wherein the antireflection layer is a resonance unit array, the resonance unit array is composed of periodically arranged cross columnar resonance units, and each cross columnar resonance unit is composed of a horizontal column and a vertical column which are vertically intersected at the midpoint; the antireflection layer and the substrate layer are both intrinsic silicon.
And designing the metamaterial with the cross-shaped columnar periodic structure as an antireflection layer. According to Snell's law in optical theory, when an electromagnetic wave is perpendicularly incident to an interface of different media, the relative refractive index is defined as n = n2/n1, and the reflectivity is
Obviously, when the terahertz wave is incident to a smooth silicon interface from air, the relative refractive index is 3.45, and the reflectivity reaches about 0.3 at the moment, so that the performance requirement of the absorber is not met. When a silicon surface is etched to form metamaterial units with proper size, the effective refractive index of the equivalent interface of the metamaterial units is reduced, which means that n in the above formula is closer to 1, namely, the reflectivity is reduced. And (3) simulating and optimizing the antireflection performance of the cross metamaterial array by adopting electromagnetic simulation software, and determining the structural parameters of the optical adjustable broadband terahertz absorber.
The horizontal column and the vertical column are the same in length and width, and the conductivity in the light adjustable broadband terahertz absorber reaches 80S/m.
The length of the horizontal column and the vertical column is 90-110 μm, and the width is 20-30 μm.
Preferably, the horizontal and vertical pillars are each 100 μm in length and 25 μm in width.
The height of the antireflection layer is 50-70 μm, and the thickness of the substrate layer is 430-450 μm.
Preferably, the height of the antireflection layer is 60 μm and the thickness of the substrate layer is 440 μm.
The period length of the cross-shaped columnar resonance unit is 110-130 mu m.
Preferably, the period length of the cross-shaped columnar resonance unit is 120 μm.
The method for regulating the light adjustable broadband terahertz absorber based on the intrinsic silicon metamaterial utilizes 1064nm continuous laser to irradiate the light adjustable broadband terahertz absorber, and the irradiation power is 0-1.1W.
And (4) irradiating the device obtained in the step one by using continuous laser with the wavelength of 1064nm, and starting the tunable terahertz absorption function. In the case of laser irradiation of intrinsic silicon, when photon energy is greater than 1.12 eV of the band gap of silicon, the dielectric constant of silicon in the terahertz band can be described by Drude model:
wherein
=11.9，
For the plasma frequency, N is the actual carrier concentration in the silicon, mopt is the optical effective mass of the carriers, and τ d is the relaxation time. It can be seen that the dielectric properties of silicon are mainly determined by the concentration of photo-excited carriers, i.e. by the laser power. The photon energy of the 1064nm laser is 1.16eV, which is only slightly larger than the intrinsic silicon band gap, and the 1064nm laser has weak absorption and good penetrability.
Preferably, the radiation power is 1.1W.
The invention has the beneficial effects that: the intrinsic silicon absorber does not need to dope silicon, and a photo-generated carrier is excited in the intrinsic silicon by continuous laser with the wavelength of 1064nm to serve as an absorption mechanism, so that the device is switched between a completely closed state and a high-efficiency absorption state, and the intrinsic silicon absorber is easier to prepare, flexible and controllable; and the cross-shaped silicon columns which are arranged periodically are designed to be used as an antireflection layer, the adjustment of 0% -99% of peak absorption rate is realized by changing the laser irradiation power, and the effective absorption bandwidth is more than 1.3 THz. The device only needs a single silicon etching process for preparation, and has the advantages of simple structure, low manufacturing cost, good stability and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a partial scanning electron micrograph of a sample prepared according to example 1, in which 1 is an antireflection layer, 2 is a substrate layer;
FIG. 2 is an optical photograph and a partial scanning electron micrograph of a sample prepared in example 1;
FIG. 3(a) is the comparison of time domain transmission signals of samples prepared in example 1 and common intrinsic silicon wafers, and FIG. 3(b) is the comparison of first-order pulse transmission frequency domain signals of the samples;
fig. 4 shows the absorbance change of the device under the same laser power (equivalent to the conductivity in the device) as the sample prepared in example 1, where fig. 4(a) is a simulation value and fig. 4(b) is a measured value.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
An intrinsic silicon metamaterial-based optical tunable broadband terahertz absorber comprises an antireflection layer 1 and a substrate layer 2, wherein the antireflection layer 1 is a resonance unit array, the resonance unit array is composed of periodically arranged cross columnar resonance units, and the cross columnar resonance units are composed of horizontal columns and vertical columns which are vertically intersected at the middle point; the antireflection layer 1 and the substrate layer 2 are both made of intrinsic silicon, the cross column array made of the intrinsic silicon is used as the antireflection layer of the absorber, the intrinsic silicon terahertz dielectric constant is 11.9, and broadband and efficient antireflection performance is achieved.
The horizontal column and the vertical column have the same length and width, the length of the horizontal column and the vertical column is 90-110 μm, and the width of the horizontal column and the vertical column is 20-30 μm.
Preferably, the length is 100 μm and the width is 25 μm.
The height of the antireflection layer 1 is 50-70 μm, and the thickness of the substrate layer 2 is 430-450 μm.
Preferably, the height of the antireflection layer 1 is 60 μm and the thickness of the substrate layer 2 is 440 μm.
The period length of the cross-shaped columnar resonance unit is 110-130 mu m.
Preferably, the period length of the cross-shaped columnar resonance unit is 120 μm.
The 1064nm continuous laser is used for irradiating the adjustable broadband terahertz absorber, and the irradiation power is 0-1.1W.
The irradiation power is preferably 1.1W, and the conductivity in the optical tunable broadband terahertz absorber is 80S/m. Continuous laser excites photon-generated carriers in intrinsic silicon to serve as an absorption mechanism, switching of the device between a complete closing state and a high-efficiency absorption state is achieved, and meanwhile the absorption peak value of the absorber can be controlled.
Example 1
A tunable broadband terahertz absorber based on intrinsic silicon metamaterial is disclosed, as shown in figure 1-2, the thickness of a substrate layer 2 part is 440 μm, the height of an antireflection layer 1 composed of a cross column part is 60 μm, the period length of a cross column-shaped resonance unit is 120 μm, the lengths of a horizontal column and a vertical column are 100 μm, the width is 25 μm, and the size of an actual sample is 1.4cm multiplied by 1.4 cm; and irradiating the absorber by 1.1W 1064nm continuous laser to prepare the optical tunable broadband terahertz absorber, wherein the electrical conductivity of the optical tunable broadband terahertz absorber is 80S/m.
The reflection condition of the prepared optical tunable broadband terahertz absorber in the range of 0.5-2 THz is tested, and as shown in fig. 3(a) and 3(b), the reflection signal in the range of 0.6-1.9 THz is reduced to be below 10% by the antireflection layer through the first-order pulse of the time domain signal and the frequency domain signal.
Example 2
The main difference between the intrinsic silicon metamaterial-based optical tunable broadband terahertz absorber and the embodiment 1 is that a 1064nm continuous laser with the wavelength of 0.83W is adopted to irradiate the absorber to prepare the optical tunable broadband terahertz absorber, and the electric conductivity of the optical tunable broadband terahertz absorber is 50S/m.
Example 3
The main difference between the intrinsic silicon metamaterial-based optical tunable broadband terahertz absorber and the embodiment 1 is that a 1064nm continuous laser with the power of 0.61W is adopted to irradiate the absorber to prepare the optical tunable broadband terahertz absorber, and the electric conductivity of the optical tunable broadband terahertz absorber is 30S/m.
Example 4
The main difference between the intrinsic silicon metamaterial-based optical tunable broadband terahertz absorber and the embodiment 1 is that a 1064nm continuous laser with the power of 0.28W is adopted to irradiate the absorber to prepare the optical tunable broadband terahertz absorber, and the electric conductivity of the optical tunable broadband terahertz absorber is 10S/m.
Examples of the effects of the experiments
The change of the absorption rate of the tunable broadband terahertz absorbers prepared in examples 1 to 4 was tested, and as shown in fig. 4(a) and 4(b), when 1064nm continuous lasers with different powers were used to irradiate the absorbers, the absorption efficiency was gradually improved, and the absorption peak was as high as 99% or more. The absorption bandwidth is gradually widened, and the frequency range with the absorptivity of more than 90 percent is gradually increased to be more than 1.3 THz. According to theoretical calculation of a Drude model and comparison of simulation and test absorption performance in a figure, when the laser power is 1.1W, the electric conductivity in silicon is increased to about 80S/m, and the wave absorbing performance of the absorber is the best.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. The light adjustable broadband terahertz absorber based on the intrinsic silicon metamaterial is characterized in that: the anti-reflection layer (1) is a resonance unit array, the resonance unit array is composed of periodically arranged cross columnar resonance units, and the cross columnar resonance units are composed of horizontal columns and vertical columns which are vertically intersected at the middle point; the antireflection layer (1) and the substrate layer (2) are both intrinsic silicon.
2. The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1, wherein: the length and the width of the horizontal column are the same as those of the vertical column, and the electric conductivity in the light adjustable broadband terahertz absorber is 0-80S/m.
3. The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 2, wherein: the length of the horizontal column and the vertical column is 90-110 μm, and the width is 20-30 μm.
4. The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 3, wherein: the horizontal column and the vertical column both have a length of 100 μm and a width of 25 μm.
5. The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1, wherein: the height of the antireflection layer (1) is 50-70 μm, and the thickness of the substrate layer (2) is 430-450 μm.
6. The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1, wherein: the height of the antireflection layer (1) is 60 mu m, and the thickness of the substrate layer (2) is 440 mu m.
7. The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1, wherein: the period length of the cross-shaped columnar resonance unit is 110-130 mu m.
8. The optically tunable broadband terahertz absorber of intrinsic silicon metamaterial according to claim 1, wherein: the period length of the cross-shaped columnar resonance unit is 120 mu m.
9. The method for regulating the optically tunable broadband terahertz absorber based on the intrinsic silicon metamaterial according to any one of claims 1 to 8, wherein: the 1064nm continuous laser is used for irradiating the adjustable broadband terahertz absorber, and the irradiation power is 0-1.1W.
10. The method for regulating the optically tunable broadband terahertz absorber based on the intrinsic silicon metamaterial according to claim 9, wherein the method comprises the following steps: the irradiation power was 1.1W.
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