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

Abstract

The application discloses an ultra-narrow-band high-transmission filter based on a guided-mode resonance principle. A waveguide film, a buffer layer, a sub-wavelength metal grating, a first dielectric layer and a second dielectric flat film are sequentially laid on a substrate. By fixing the grating duty cycle and changing the period of the metal grating, the range adjustment of the filter output wavelength can be realized; by adjusting the thickness of the first dielectric layer and the second dielectric layer on the grating, the height of the short-wave band sideband can be suppressed, the peak value intensity of the transmission peak can be increased, and the half-wave full width can be reduced. The application combines the multi-layer waveguide structure with the sub-wavelength metal grating, and provides an ultra-narrow-band transmission filter structure which is used for the full-waveband coordination in the visible light range. Compared with the existing re-banding filter, the application has the characteristics of filter center coordination in the whole visible light range, high transmissivity, low sideband and sharp transmission peak, and the filter bandwidth reaches 0.41nm-2.5nm.

Description

Technical Field

[0001] This invention belongs to the field of guided wave optics technology and relates to filters based on guided mode resonance, specifically to an ultra-narrowband high-transmission filter based on the guided mode resonance principle. Background Technology

[0002] Ultra-narrowband transmissive filters in the visible light wavelength range have wide applications, such as spectral imaging, semiconductor (CMOS) image sensors, and biosensors, playing a particularly important role in spectral imaging, biomolecular detection and interaction, and medical identification. However, with the increasing demands for color resolution and accuracy, as well as the growing requirements for filter compatibility, compactness, stability, and multifunctionality, achieving high-performance filters presents many challenges. Furthermore, most filters currently researched in the industry are reflective filters, with very few transmissive filters in the visible light range. Existing transmissive filters suffer from low diffraction efficiency, wide FWHM (field-wide wavelength range), low flatness factor, and high sidebands, leading to reduced structural color saturation and insufficient color resolution saturation and accuracy. Guided-mode resonance (GMR) subwavelength grating filters stand out among many filters due to their excellent characteristics, such as ultra-narrow band, high transmittance, and low sidebands generated by anomalous resonance.

[0003] In guided-mode resonance (GMR) waveguide structures, incident light that satisfies the phase-matching condition between the waveguide's intrinsic modes is coupled into the waveguide layer. Since this energy cannot be maintained indefinitely within the waveguide layer, leakage occurs, forming a leaky film. This leaked energy then interferes with the uncoupled beam, ultimately producing reflection and transmission spectra. GMR subwavelength grating filters combine subwavelength gratings with the GMR effect, utilizing a periodic grating structure to ensure phase matching between the incident light and the waveguide's intrinsic modes. This allows for the formation of a sharp resonance peak with high transmission / reflection and a narrow bandgap through anomalous resonance. Small-size, thin-film GMR subwavelength gratings break the diffraction limit, achieving compatibility of light within a certain range, while also possessing advantages such as high diffraction efficiency and extremely small full-width at half-wave (FWHM).

[0004] Guided-mode resonance (GMR) subwavelength grating filters have attracted widespread attention from researchers due to their sharp resonance peaks. In 2014, Daniel B. Mazulquim et al. [Daniel B. Mazulquim, Kyu Jin Lee, Jae Woong Yoon, Leone V. Efficient band-pass color filters enabled by resonant modes and plasmons near the Rayleigh anomaly[J], Opt. Express 22(25), 30843-30852(2014)] designed a surface plasmon resonance-related narrowband guided-mode resonance structure, which consists of a metal grating and a waveguide flat film. The sharp transmission peak is achieved by utilizing the low contrast of refractive index between the superconducting flat film and the substrate. The narrowband width is about 20 nm and the transmittance is about 80%. In 2019, Wenze Wu et al. [Wenze Wu, Leonard Weber, Nano-structured transmissive spectral filter matrix based on guided-mode resonances[J]. European Optical Society-Rapid Publications, 15(19), 1-10(2019)] proposed a nanostructured transmissive spectral filter matrix based on guided-mode resonance. This guided-mode resonance filter uses a metal grating, a SiO2 buffer layer, and a high-transmittance waveguide layer. The surface plasmon resonance mode of the metal grating is excited and coupled to the guided waveguide mode, achieving a sharp low-sideband transmission peak with anomalous resonance. However, the full width at half maximum (FWHM) of the transmission peak obtained by the above structural design is still relatively wide and has high sidebands, failing to achieve ultra-narrow banding and unable to achieve stable coordination across the entire visible light range. This results in poor filter precision and accuracy, and the filter's performance cannot meet the application requirements. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes an ultra-narrowband high-transmission filter based on the guided mode resonance principle. By changing the structure and materials of the filter, it solves the problems of limited research on visible light transmission filters, low peak-to-peak filtering, high sidebands, difficulty in achieving ultra-narrow bandwidth, and difficulty in achieving coordinated peak-to-peak transmission across the entire visible light range.

[0006] An ultra-narrowband high-transmission filter based on the guided-mode resonance principle comprises, from bottom to top, a substrate, a waveguide layer, a buffer layer, a strip-shaped subwavelength metal grating, a first dielectric layer, and a second dielectric layer. The refractive indices of the first and second dielectric layers are similar to those of the substrate. The thickness of the first dielectric layer is 30 nm to 100 nm, and the thickness of the second dielectric layer is 20 nm to 50 nm. By fixing the duty cycle of the subwavelength metal grating and increasing its period, the resonant wavelength is shifted to a longer wavelength band.

[0007] Preferably, the material of the first dielectric layer is SiO2, and the material of the second dielectric layer is Al2O3.

[0008] Preferably, the substrate is made of glass material N-BK7.

[0009] Preferably, the waveguide layer has a thickness of 90nm to 150nm, and the buffer layer has a thickness of 50nm to 100nm.

[0010] Preferably, the strip-shaped subwavelength metal grating has a period of 150nm to 400nm, a duty cycle of 0.5 to 0.9, and a thickness of 40nm to 80nm.

[0011] Preferably, the waveguide layer is made of TiO2.

[0012] Preferably, the material of the buffer layer is SiO2.

[0013] The present invention has the following beneficial effects:

[0014] This application combines a subwavelength grating with the guided-mode resonance (GMR) effect to form a sharp resonance peak with high transmission / reflection and a narrow bandgap through anomalous resonance. The refractive indices of the two dielectric thin films stacked above the grating are matched with those of the substrate, effectively reducing the sideband height, increasing the peak intensity of the transmission peak, and achieving a full width at half maximum (FWHM) between 0.4 nm and 2.5 nm, significantly lower than existing technologies, resulting in a sharper transmission peak spectrum. Furthermore, by changing the grating period, the resonant center wavelength can be altered, achieving coordinated transmission peaks across the entire visible light range, demonstrating broad application prospects in the field of visible light transmissive device integration. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the planar structure of the filter in the embodiment;

[0016] Figure 2 This is a schematic diagram of a filter without a dielectric layer in the embodiment;

[0017] Figure 3 This is a comparison chart of the resonant peak transmittance of different filters in the embodiments;

[0018] Figure 4 The diagram shows the transmission spectrum as a function of the grating period in the example. Detailed Implementation

[0019] The present invention will be further explained below with reference to the accompanying drawings;

[0020] Example 1

[0021] like Figure 1 As shown, an ultra-narrowband high-transmission filter based on the guided-mode resonance principle includes a single-layer subwavelength metal grating and a multi-layer dielectric planar waveguide structure. From bottom to top, it includes a substrate 1, a waveguide layer 2 with a thickness of 90nm to 150nm, a buffer layer 3 with a thickness of 50nm to 100nm, a strip-shaped subwavelength metal grating 4 with a thickness of 40nm to 80nm, a first dielectric layer 5 with a thickness of 30nm to 100nm, and a second dielectric layer 6 with a thickness of 20nm to 50nm.

[0022] The period of the strip subwavelength metal grating 4 is 150nm to 400nm, and the duty cycle is 0.5 to 0.9. The refractive index of the buffer layer 3 needs to be less than that of the waveguide layer 2. The refractive indices of the first dielectric layer 5 and the second dielectric layer 6 are matched with the refractive index of the substrate 1 and are not higher than that of the waveguide layer 2.

[0023] When visible light 7 is incident directly into the filter, its electric field component is parallel to the incident plane, and the polarization direction of the plane wave is perpendicular (y-direction) to the groove direction of the periodic metal grating. The portion of visible light 7 that matches the guided mode couples into waveguide layer 2, but it is not confined there indefinitely. This energy leaks out, interfering with uncoupled transmitted (reflected) light to achieve guided mode resonance, forming a sharp transmission peak at a certain wavelength in the transmission spectrum. This wavelength is called the guided mode resonance wavelength, while the transmittance at other non-resonant locations is extremely low. Since the strip subwavelength metal grating 4 is made of metal, surface plasmon resonance (SPR) is generated, which affects the guided mode resonance effect. Adding a buffer layer 3 between waveguide layer 2 and strip subwavelength metal grating 4 effectively reduces the influence of SPR on waveguide layer 2 and increases peak transmittance. The refractive indices of the first dielectric layer 5 and the second dielectric layer 6 are matched with the refractive index of the substrate 1, which can effectively reduce the sideband height, increase the peak intensity of the transmission peak, and reduce the full width at half maximum (WWM), thereby obtaining a sharper transmission peak spectrum.

[0024] Example 2

[0025] In this embodiment, substrate 1 is made of N-BK7 glass, and waveguide layer 2 is made of TiO2 with a thickness of 100 nm, which has a higher refractive index than other layers. Buffer layer 3 has a thickness of 55 nm and is made of SiO2. The strip-shaped subwavelength metal grating 4 is made of Ag metal with a thickness of 70 nm, a period of 300 nm, and a duty cycle of 0.7. The first dielectric layer 5 has a thickness of 55 nm and is made of the same material as buffer layer 3, SiO2. The second dielectric layer 6 has a thickness of 35 nm and is made of Al2O3.

[0026] The interaction between the first dielectric layer 5 and the second dielectric layer 6 can suppress short-wavelength sidebands, increase transmission peak intensity, and reduce the full width at half maximum (FWHM). The filter structure without the first dielectric layer 5 and the second dielectric layer 6 is as follows: Figure 2 As shown. Figure 3 As shown, the dashed and solid lines represent the transmission spectra of the filter with and without the first dielectric layer 5 and the second dielectric layer 6, respectively. Without the first dielectric layer 5 and the second dielectric layer 6, the short-wavelength region of the transmission spectrum exhibits strong sidebands, and the transmittance is significantly low at only 63%, with a large full width at half maximum (FWHM) of approximately 2 nm. After adding the first dielectric layer 5 and the second dielectric layer 6, the sidebands in the short-wavelength region of the transmission spectrum are effectively suppressed, the peak transmittance is significantly improved to 80%, and the FWHM is significantly reduced to 1.6 nm, resulting in a sharp transmission spectrum with high transmittance, low sidebands, and an extremely narrow bandwidth.

[0027] Example 3

[0028] This embodiment, based on embodiment 2, adjusts the period of the strip subwavelength metal grating 4 to vary it within the range of 160nm-400nm. The changes in the filter's transmittance and guided-mode resonant wavelength with the period are as follows: Figure 3 As shown, when the period Λ changes from small to large, the guided mode resonance wavelength shifts from short wave to long wave in the visible light region, and the transmittance can reach more than 80%, with a half-wavelength range of 0.41nm to 2.5nm. This achieves modulation of the transmission spectrum with high transmittance, low sideband, and high narrowband in the visible light range.

[0029] The embodiments described above are merely illustrative of several implementation methods of this application. Their detailed descriptions are intended to clearly illustrate the inventor's verification process, but are not intended to limit the scope of protection of this invention. It should be noted that those skilled in the art can make various improvements and optimizations without departing from the principles of this invention, and these improvements all fall within the scope of protection of this application.

Claims

1. An ultra-narrowband high-transmission filter based on the guided-mode resonance principle, characterized in that: From bottom to top, the structure includes a substrate, a waveguide layer, a buffer layer, a strip subwavelength metal grating, a first dielectric layer, and a second dielectric layer. The refractive index of the buffer layer needs to be less than that of the waveguide layer. The refractive indices of the first and second dielectric layers are similar to those of the substrate and not higher than those of the waveguide layer. The thickness of the first dielectric layer is 30 nm to 100 nm, and the thickness of the second dielectric layer is 20 nm to 50 nm.

2. The ultra-narrowband high-transmission filter based on the guided-mode resonance principle as described in claim 1, characterized in that: The material of the first dielectric layer is SiO2.

3. The ultra-narrowband high-transmission filter based on the guided-mode resonance principle as described in claim 1, characterized in that: The material of the second dielectric layer is Al2O3.

4. The ultra-narrowband high-transmission filter based on the guided-mode resonance principle as described in claim 1, characterized in that: The waveguide layer is made of TiO2.

5. The ultra-narrowband high-transmission filter based on the guided-mode resonance principle as described in claim 4, characterized in that: The thickness of the waveguide layer is 90nm~150nm.

6. The ultra-narrowband high-transmission filter based on the guided-mode resonance principle as described in claim 1, characterized in that: The buffer layer is made of SiO2 and has a thickness of 50nm~100nm.

7. The ultra-narrowband high-transmission filter based on the guided-mode resonance principle as described in claim 1, characterized in that: The strip-shaped subwavelength metal grating has a period of 150nm~400nm, a duty cycle of 0.5~0.9, and a thickness of 40nm~80nm.

8. An ultra-narrowband high-transmission filter based on the guided-mode resonance principle as described in claim 1 or 7, characterized in that: By fixing the duty cycle of the subwavelength metal grating and increasing its period, the resonant wavelength of the filter is shifted to the longer wavelength band.

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