CN103293572B - TE polarization spectrum selective absorber - Google Patents

Abstract

A TE polarization spectrally selective absorber for the visible light band (400-800nm), the period, duty cycle and thickness of the top grating of the absorber are 310-314 nm, 0.35-0.37, 216-220 nm, respectively, The film thickness of the intermediate dielectric isolation layer is 103-107 nanometers. When the TE polarized light is incident in the range of -15 degrees to 15 degrees, the incident light in a narrow band near the center wavelength of 561 nanometers will be absorbed, and the absorption spectrum will change with the change of structural parameters and incident angles. With a small frequency shift, the peak absorption wavelength will shift slightly, but the absorption can always maintain nearly 100% at each peak wavelength, and the full width at half maximum of the absorption line is always less than 20 nanometers. The TE polarization spectrum selective absorber of the present invention is processed by an electron beam direct writing device combined with a microelectronic deep etching process, which is convenient for material acquisition, low in cost, capable of mass production, and has important practical prospects.

Description

TE Polarization Spectral Selective Absorber

technical field

The invention relates to a spectrally selective absorber, in particular to a TE polarization (the vibration direction of the electric field vector is perpendicular to the incident surface) spectrally selective absorber used in the visible light band.

Background technique

In order to achieve ideal spectrally selective absorption, many methods have been proposed, such as metal nanoparticles, metamaterials, and so on. Among these proposed nanostructures, the one-dimensional grating structure serves as an important and structurally simple device that can be used to enhance absorption. The main advantage of grating-based devices is that they are easier to design and fabricate than other metamaterials with complex structures. With optimization, nearly 100% perfect absorption can be achieved at the resonant wavelength. The spectrally selective absorber based on the grating structure is compact in structure and has good optical performance in a wide range of incident angles. Therefore, it has broad application prospects as a new type of absorbing device.

C.Wu et al. proposed a simple grating-based device that can be used to achieve ultra-thin, wide-angle perfect absorption in the near-infrared band. The grating-based device can achieve nearly 100% absorption at the resonant wavelength, and in In the range of incident angles from 0 to 45°, the absorption of P polarization is higher than 95%, and the absorption of S polarization is higher than 90% [see prior art 1: C. Wu et al., Proc. SPIE 7029, Metamaterials: Fundamentals and Applications, 70290W (2008)]. Later, C. Wu et al. theoretically designed and experimentally verified a simple grating-based metamaterial wide-angle plasmonic absorber, which has narrow-band spectral selective absorption/radiation characteristics, and can be used as a sub-diffraction-sized infrared pixel [ See prior art 2: C.Wu et al., Physical Review B 84, 075102 (2011)]. J.A.Mason et al. designed a grating-based metamaterial absorber for the mid-infrared band, which has extremely high selectivity and large angle independence (can be used for incident angles of 0-45°) [see prior art 3: J.A.Mason et al., Applied Physics Letters 98, 241105-241103 (2011)]. M.Diem et al designed a perfect absorbing/heat emitting device with a peak absorption of 99.99% at the resonant wavelength and can maintain extremely high absorption over a large range of incident angles, except for a small center frequency shift [See prior art 4: M.Diemetal., Physical Review B 79, 033101 (2009)]. Nevertheless, so far, selective absorbers based on grating structures are mainly for TM polarization and work in the infrared band. This is because for TM polarization, perfect selective absorption can be obtained by an ultra-thin grating structure, and the advantage of an ultra-thin grating structure is that it has greater angle independence, especially in the infrared region (due to the larger wavelength-to-structure size ratio).

The rectangular grating is a grating with a rectangular groove shape processed on a substrate by using a micro-nano machining process. Diffraction problems of subwavelength rectangular gratings cannot be handled by simple scalar grating diffraction, but must be solved precisely by coded computer programs using Maxwell's equations in vector form combined with boundary conditions. Moharam et al. have given the algorithm of strict coupled wave theory [see prior art 5: M.G.Moharam et al., J.Opt.Soc.Am.A.12, 1077(1995)], which can solve this kind of subwavelength Diffraction of gratings. But as far as we know, so far, no one has given a TE polarization spectrally selective absorber based on a grating structure fabricated on a fused silica substrate for the visible light band.

CN101344604A discloses a reflective quartz polarization beam splitting grating for 1550 nanometer wave band, which is the closest prior art of this application.

Contents of the invention

The technical problem to be solved by the present invention is to provide a TE polarization spectrum selective absorber for the visible light band. When the TE polarized light is incident in the range of -15 degrees to 15 degrees, the selective absorber will absorb the incident light in a narrow band near the center wavelength of 561 nanometers. With the change of structural parameters and incident angles, The absorption spectrum will undergo a small frequency shift, and the peak absorption wavelength will also undergo a small frequency shift, but the absorption can always maintain nearly 100% at each peak wavelength, and the full width at half maximum of the absorption line is always less than 20 nanometers. Therefore, the spectrally selective absorber has important practical value.

Technical solution of the present invention is as follows:

A TE polarized spectrum selective absorber for the visible light band is characterized in that it is composed of a silver film, a fused silica isolation layer and a silver layer that are sequentially evaporated on a fused silica sheet. The silver layer is engraved with a grating, and the period of the grating is , duty cycle and thickness are 310-314 nanometers, 0.35-0.37, 216-220 nanometers respectively, the film thickness of the fused silica isolation layer is 103-107 nanometers, and the thickness of the silver film is greater than 100 nanometers.

The period, duty ratio and thickness of the grating are 312 nanometers, 0.36 nanometers and 218 nanometers respectively, and the film thickness of the intermediate dielectric isolation layer is 105 nanometers.

Technical effect of the present invention is as follows:

Especially when the top grating period, duty cycle and thickness of the absorber are 312nm, 0.36nm and 218nm respectively, and the film thickness of the intermediate dielectric isolation layer is 105nm, when the TE polarized light in the 400-800nm band is at -15° When it is incident on the grating in the range of ~15 degrees, the incident light in a narrow band near the central wavelength of 561 nanometers will be absorbed, and the absorption rate at the central wavelength is approximately 100%, and the full width at half maximum of the absorption line is 18nm.

The invention has the advantages of flexible and convenient use, high peak absorption efficiency, and small full width at half maximum of the absorption spectrum. It is produced at low cost, and the performance of the etched absorber is stable and reliable, and has important practical prospects.

Description of drawings

Fig. 1 is a geometric structure diagram of the TE polarization spectrum selective absorber used in the visible light band according to the present invention.

In the figure, 1 represents air in area 1 (refractive index n ₁ ), 2 represents fused silica in area 2 (refractive index n ₂ ), 3 represents the grating, and the material of the grating layer is silver (Ag), 4 represents the dielectric isolation layer, the material is fused silica, 5 is the bottom metal layer, the material is Ag, and 6 represents incident TE polarized light. d is the grating period, f is the grating duty cycle, h ₁ and h ₂ are the thicknesses of the grating layer and the dielectric isolation layer, respectively.

Fig. 2 is a curve of absorption efficiency of TE polarized light as a function of wavelength according to an embodiment of the present invention.

FIG. 3 is a two-dimensional plot of the absorption efficiency of the embodiment of FIG. 2 as a function of incident angle and wavelength.

Detailed ways

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

Please refer to FIG. 1 first. FIG. 1 is a geometric structure diagram of the TE polarization spectrum selective absorber used in the visible light band according to the present invention. In the figure, regions 1 and 2 are uniform, respectively air (refractive index n ₁ =1) and fused silica (refractive index n ₂ =1.46), TE polarized light (corresponding to the vibration direction of the electric field vector perpendicular to the incident surface ) is incident on the device at an angle θ. As can be seen from the figure, the TE polarized spectrum selective absorber of the present invention is composed of a silver film 5, a fused silica spacer 4 and a silver layer that are successively evaporated on the fused silica plate 2, and the silver layer is engraved with a grating 3, and the grating The period, duty cycle and thickness of 3 are 310-314 nanometers, 0.35-0.37, 216-220 nanometers respectively, the film thickness of the fused silica isolation layer 4 is 103-107 nanometers, and the thickness of the silver film 5 is greater than 100 nm.

Table 1 provides a series of embodiments of the TE polarization spectrum selective absorber of the present invention. In the table, d is the grating period, f is the grating duty ratio, h ₁ and h ₂ are the thicknesses of the grating layer and the dielectric isolation layer respectively, A is the absorption efficiency at the central wavelength of 561 nanometers, λ _max represents the peak wavelength of each absorption spectrum, and A _max represents the absorption efficiency at the peak wavelength of the absorption spectrum. In the structure of Fig. 1, the silver mold at the bottom is generally selected thicker (usually as long as it is greater than the skin depth of silver in the visible light band, and the skin depth of silver in the visible light band is generally tens of nanometers, in this embodiment we choose The thickness of the bottom silver mold is 200nm, deviation from this thickness has no effect on the absorption efficiency of the device), so as to avoid light transmission. Since it can block the transmission of light (T=0), the absorption efficiency of the device can be calculated from the reflection efficiency R:

A≡1-R (1)

When making the TE polarization spectrum selective absorber used in the visible light band of the present invention, the period, duty ratio, thickness and the thickness of the dielectric isolation layer of the grating can be properly selected according to Table 1. High absorption can be obtained within a certain range of incident angles. efficient TE polarization-selective absorbers.

Fig. 2 is a curve of absorption efficiency of TE polarized light as a function of wavelength according to an embodiment of the present invention.

FIG. 3 is a two-dimensional plot of the absorption efficiency of the embodiment of FIG. 2 as a function of incident angle and wavelength.

The TE polarization spectrum selective absorber of the present invention has the advantages of flexible and convenient use, high peak absorption efficiency, small peak wavelength shift of the absorption spectrum, and small full width at half maximum of the absorption spectrum line, and is a very ideal absorption device. Using the electron beam direct writing device combined with the microelectronic etching process, it can be produced in large quantities and at low cost. The performance of the etched absorber is stable and reliable, and has important practical prospects.

Table 1 Parameters of a series of embodiment gratings of TE polarization spectrally selective absorber

Claims (2)

1. the TE polarization spectrum selective absorbing device for visible light wave range, it is formed is the silverskin (5) of evaporation successively on vitreous silica sheet (2), vitreous silica separation layer (4) and silver layer, this silver layer carves grating (3), it is characterized in that, cycle of this grating (3), dutycycle and thickness be respectively 310 ~ 314 nanometers, 0.35 ~ 0.37,216 ~ 220 nanometers, the thickness of described vitreous silica separation layer (4) is 103 ~ 107 nanometers, and the thickness of described silverskin (5) is greater than 100 nanometers.

2. TE polarization spectrum selective absorbing device according to claim 1, it is characterized in that described grating (3) cycle, dutycycle and thickness are respectively 312 nanometers, 0.36 and 218 nanometers, the thickness of described vitreous silica separation layer (4) is 105 nanometers.