Polarization independent ultra-narrow band high-transmission optical filter based on guided-mode resonance principle

Abstract

The application discloses a polarization-independent ultra-narrow-band high-transmission filter based on a guided-mode resonance principle, which comprises, from bottom to top, a substrate, a first dielectric layer, a waveguide layer, a buffer layer, a metal grating, a second dielectric layer and a third dielectric layer. The metal grating has structural symmetry and is a periodic nanowire array, and the cross section of the nanowire is square or circular. In the visible light range, different central wavelengths can be selected by changing the period of the metal grating. The second and third dielectric layers can effectively suppress sidebands and improve the color purity of filtered light. The buffer layer and the first dielectric layer can adjust the full width at half maximum of the transmission peak, and the first dielectric layer can also improve the transmittance of the filter. The filter has the advantages of high transmission peak, extremely narrow full width at half maximum, polarization independence, high optical quality, high light energy utilization rate and the like, and has wide application in the fields of spectral imaging, biological molecule detection and interaction, medical diagnosis and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical devices, and relates to the structural design of optical filters, in particular to a polarization-independent ultra-narrow-band high-transmission filter based on the principle of guided-mode resonance. BACKGROUND

[0002] Traditional visible light filters are mainly made of organic dye molecules, which are prone to degradation or aging under high temperature and ultraviolet light, and have great limitations in filtering performance, scalability and durability. With the development of nanofabrication technology, structural filters based on guided-mode resonance effect have been widely used, becoming one of the main directions to replace dye-type filters.

[0003] As a new type of optical filter, the guided-mode resonance filter is superior to the traditional dye-type filter in terms of size adjustability, integration and stability, and can produce extremely narrow reflection or transmission peaks in a wide wavelength range. In particular, after adding a metal grating, the waveguide layer and buffer layer medium in the guided-mode resonance filter interact with the grating, which can exhibit better performance, and is usually applied in the fields of optical communication, microscopic imaging, laser, holographic imaging, solar cells, etc.

[0004] However, most of the guided-mode resonance filters made by the prior art are reflective or infrared range adjustable, and there are few studies on transmission-type guided-mode resonance filters in the visible light range. Moreover, due to the inherent ohmic loss and material dispersion of metals, transmission-type guided-mode resonance filters in the visible light range usually have problems such as low peak transmittance and large bandwidth. It cannot meet the demand of producing high-purity and high-intensity transmitted light of specific wavelength in the visible light band. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a polarization-independent ultra-narrow-band high-transmission filter based on the principle of guided-mode resonance, which improves the problems of low peak transmittance, large bandwidth and low color purity of the filtered light of the existing subwavelength metal grating filter by adding a dielectric layer.

[0006] The polarization-independent ultra-narrow-band high-transmission filter based on the principle of guided-mode resonance comprises, from bottom to top, a substrate, a first dielectric layer, a waveguide layer, a buffer layer, a metal grating, a second dielectric layer and a third dielectric layer. The refractive index of the first dielectric layer is not less than the refractive index of the buffer layer. The metal grating is a periodic nanowire array, and the cross section of the nanowire is circular or square. The refractive index of the second dielectric layer is 1, and the thickness is 65-120 nm. The material of the third dielectric layer is silicon dioxide, and the thickness is 70-100 nm.

[0007] Preferably, the material of the first dielectric layer is aluminum oxide, and the thickness is 20-50 nm.

[0008] Preferably, the material of the metal grating is silver or aluminum, the thickness is 45nm, the period is 270nm-500nm, and the duty cycle is 0.8-0.85.

[0009] Preferably, the material of the substrate is quartz.

[0010] Preferably, the material of the waveguide layer is silicon nitride, the thickness is 100nm-135nm, and the material of the buffer layer is magnesium fluoride, the thickness is 130nm-250nm.

[0011] The present application has the following advantages:

[0012] The present application adds three dielectric layers to the existing guided mode resonance filter. The first dielectric layer is an antireflection layer, which can improve the transmittance and reduce the full width at half maximum to a certain extent. The second and third dielectric layers are used to effectively suppress the sideband and improve the color purity of the filtered light. In addition, the two-dimensional grating used has structural symmetry, and the transmittance peak wavelength is independent of the polarization direction of the incident light, thereby improving the utilization efficiency of the incident light. By adjusting the grating period, the central wavelength in the visible light range can be moved, realizing the selection of different wavelengths in the visible light range and breaking the limitation of the adjustment range of the existing filter. Compared with other subwavelength metal grating filters, the present application has the advantages of low sideband, narrow full width at half maximum, high transmittance, and high utilization efficiency of incident light. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 FIG. 1 is a structural schematic diagram of the filter in Example 1;

[0014] Figure 2 FIG. 3 is an energy distribution diagram of the filter in Example 1 when working;

[0015] Figure 3 FIG. 6 is a schematic diagram of the cross section of the metal grating in Example 2;

[0016] Figure 4 FIG. 8 is the transmittance spectrum under TE and TM polarized light incidence in Example 2;

[0017] Figure 5 FIG. 10 is the visible light transmittance spectrum of different wavelengths in Example 3. DETAILED DESCRIPTION

[0018] The present application will be further explained and described below with reference to the accompanying drawings;

[0019] Example 1

[0020] As Figure 1As shown, the polarization-independent ultra-narrowband high-transmission filter based on the guided-mode resonance principle comprises, from bottom to top, a substrate 1, a first dielectric layer 2, a waveguide layer 3, a buffer layer 4, a metal grating 5, a second dielectric layer 6, and a third dielectric layer 7. The refractive index of the waveguide layer 3 is higher than that of the first dielectric layer 2 and the buffer layer 4, and the refractive index of the first dielectric layer 2 is not lower than that of the buffer layer 4. The metal grating is composed of a periodically distributed array of nanowires with a duty cycle of 0.8–0.85. The nanowires are made of silver or aluminum, have a square or circular cross-section, and a height of 45 nm.

[0021] When incident light strikes the upper surface of the filter perpendicularly, the light passes sequentially through the third dielectric layer 7 and the second dielectric layer 6 to reach the metal grating 5. The third dielectric layer 7 and the second dielectric layer 6 effectively suppress sidebands and improve the color purity of the filtered light. The incident light excites plasmons on the surface of the metal grating 5, and then the incident light diffracted by the metal grating 5 resonates with the guided mode of the planar waveguide, thereby achieving light transmission at a specific frequency. Due to the structural symmetry of the metal grating 5, the transmission peak wavelength is independent of the polarization direction of the incident light, which improves the utilization efficiency of the incident light. By adjusting the period of the metal grating 5, the center wavelength can be shifted within the visible light range to achieve selection of different wavelengths within the visible light range. The buffer layer 4 is used to improve the light loss caused by the metal grating 5; the full width at half maximum (FWHM) of the transmission peak can be adjusted by changing the thickness of the buffer layer 4. The first dielectric layer 2, as an antireflection layer, has a refractive index between that of the waveguide layer and the substrate, which can improve the transmittance of the filter and reduce the FWHM to some extent. Figure 2 As shown in the figure, the elliptical coil represents the energy distribution loop in the filter. Most of the energy is concentrated within the range of this coil. As can be seen from the figure, in the filter described in this embodiment, the surface plasmon resonance energy excited by the metal grating is completely coupled into the waveguide layer, which can generate guided mode resonance.

[0022] Example 2

[0023] In this embodiment, the first dielectric layer 2 is selected as aluminum oxide with a thickness of 40 nm, the waveguide layer 3 is selected as silicon nitride with a thickness of 135 nm, the buffer layer 4 is selected as magnesium fluoride with a thickness of 165 nm, the second dielectric layer 6 is selected as a material with a refractive index of 1 and a thickness of 300 nm, and the third dielectric layer 7 is selected as silicon dioxide with a thickness of 100 nm. Figure 3 As shown, the metal grating 5 is made of silver, has a square cross-section, and has a period and duty cycle of 400 nm and 0.85, respectively.

[0024] Figure 4 The figure shows the transmission spectra of TE and TM polarized light incident at 660 nm. As can be seen from the figure, the transmission spectrum characteristic curve does not change when the polarization state of the incident light is changed, indicating that the structure of this filter is polarization independent.

[0025] Example 3

[0026] The period of metal grating 5 was adjusted within the range of 270 nm to 500 nm, and the results are as follows: Figure 5 As shown, when the period of the metal grating 5 increases, the center wavelength shifts to the right. Adjusting the duty cycle of the metal grating 5 within the range of 0.8 to 0.85 can further reduce the full width at half maximum (FWHM) of the transmission spectrum. By changing the period and duty cycle of the metal grating 5 to meet the matching condition with the incident light wave vector, different wavelengths can be selected.

[0027] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polarization independent ultra-narrow band high transmission optical filter based on the principle of guided-mode resonance, comprising from bottom to top a substrate, a waveguide layer, a buffer layer, and a metal grating, characterized in that: A first dielectric layer is arranged between the substrate and the waveguide layer, and a second dielectric layer and a third dielectric layer are arranged in sequence above the metal grating; wherein the refractive index of the first dielectric layer is between the refractive index of the waveguide layer and the refractive index of the substrate; the refractive index of the second dielectric layer is 1, and the thickness is 65nm-120nm; the material of the third dielectric layer is silicon dioxide, and the thickness is 70nm-100nm. The metal grating is a periodic nanowire array, and the cross section of the nanowire is circular or square.

2. The polarization independent ultra-narrow band high-transmission optical filter based on the principle of guided-mode resonances according to claim 1, characterized in that: The material of the first dielectric layer is aluminum oxide, and the thickness is 20nm-50nm.

3. The polarization independent ultra-narrow band high-transmission optical filter based on the principle of guided-mode resonances according to claim 1, characterized in that: The material of the metal grating is silver or aluminum, the thickness is 45nm, the period is 270nm-500nm, and the duty cycle is 0.8-0.

85.

4. The polarization independent ultra-narrow band high-transmission filter based on the principle of resonant guided-mode according to claim 1 or 3, characterized in that: The period of the metal grating is increased, so that the central wavelength of the optical filter is increased.

5. The polarization independent ultra-narrow band high-transmission optical filter based on the principle of guided-mode resonances according to claim 1, characterized in that: The material of the substrate is quartz.

6. The polarization independent ultra-narrow band high-transmission optical filter based on the principle of guided-mode resonances according to claim 1, characterized in that: The refractive index of the waveguide layer is higher than the refractive index of the first dielectric layer and the buffer layer.

7. The polarization independent ultra-narrow band high-transmission filter based on the principle of resonant guided modes according to claim 1 or 6, characterized in that: The material of the waveguide layer is silicon nitride, and the thickness is 100nm-135nm.

8. The polarization independent ultra-narrow band high-transmission filter based on the principle of resonant guided-mode according to claim 1 or 6, characterized in that: The material of the buffer layer is magnesium fluoride, and the thickness is 130nm-250nm.

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