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Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film
Optics Communications xxx (xxxx) xxx
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Optics Communications journal homepage: www.elsevier.com/locate/optcom
Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film Wenqiang Wan a , Minghui Luo b , Zhimin Liu a , Yanfeng Su c ,∗ a
School of Science, East China Jiaotong University, Nanchang 330013, China SVG Optronics, Co., Ltd, Suzhou 215026, China c College of Optical and Electronic Technology, China Jiliang University, Hangzhou 310018, China b
ARTICLE
INFO
Keywords: Color filters Cavity resonator Broad color gamut High efficiency
ABSTRACT In this paper, we design and numerically investigate ultrathin high-efficiency, variable-color filters. The color filters, based on a cavity resonator covered with a compensated dielectric film, promise an adjustable spectral bandwidth while preserving the same resonant wavelength. A broad color gamut and widely tuned color saturation can be obtained by gradually varying the cavity depth and the top mirror thickness, respectively. The numerical results show that the transmitted peak wavelength remains unchanged with the angle of incident range from 0 to 60◦ for TM polarization and the transmission efficiency is above 65% at the resonant peak wavelength. Moreover, the physical mechanism of the device is investigated. The light field is mainly concentrated in the cavity, leading to the strong resonant effect. The proposed designs can be fabricated more easily by the deposition methods for the practical applications.
1. Introduction Color filters, regarded as an essential element of photoelectric devices, have received substantial attentions for various applications, such as display, imaging sensor, anti-counterfeiting, and colorful decoration. Conventional color filters are highly vulnerable to longstanding ultraviolet irradiation and heat exposure using chemical colorant pigments, which results in significant performance degradation [1]. Color filters based functional nanostructures, employing an interaction between light and structures, realize adjustable colors output exhibiting high efficiency, high spatial resolution, and high stability. In recent years, diverse designs of structural colors have been reported utilizing surface plasmon resonances (SPR), Fano resonances (FR), Mie resonances (MR), and guided-mode resonances (GMR) [2–22]. Wide colors covering the entire visible band can be achieved by tuning the geometry of optical structures that results in selectively transmitting or reflecting a specific wavelength. However, the angle sensitive behavior, off-resonant wavelength components and complicated fabricating methods limit the practical applications in large scale. Fabry–Perot (FP) cavity resonators, based on metal–dielectric–metal (MDM) system, have been demonstrated to address the above drawbacks of functional nanostructures for color filters applications [23– 27]. Colors with controllable wavelength and brightness were obtained by varying the dielectric thickness and the filling factor [24]. Nevertheless, it is disappointed that the color saturation of their output cannot
be efficiently controlled while maintaining the resonant wavelength, which means a shift of center spectrum for different bandwidth. In this paper, we propose ultrathin high-efficiency, variable-color filters. The proposed filters, consisting of a FP cavity resonator stacked with a compensated dielectric film (CDF), present an adjustable bandwidth at a fixed resonant wavelength. A broad color gamut and widely tuned color saturation can be obtained by gradually varying the cavity depth and the top mirror thickness, respectively. The CDF covering as a compensated layer is utilized to improve the angular tolerance by adopting the material of phase compensation instead of common oxides. The numerical results show that the transmitted peak wavelength remains unchanged with the angle of incident varying from 0 to 60◦ for TM polarization and the transmission efficiency is above 65% for the peak wavelength. Compared with those elaborate structural colors, the proposed filter system can be large-scale fabrications under the deposition methods. 2. Structural design and results Fig. 1 shows the schematic view of our ultrathin color filters, where an MDM system composing of a silicon nitride (Si3 N4 ) cavity sandwiched between two metallic film of Silver (Ag) that is vertically stacked with a CDF of Si3 N4 . Ag is selected as a metallic mirror since its lowest absorption and highest reflectivity in the visible regime. The top Si3 N4 layer as a compensated material is employed to improve
∗ Corresponding author. E-mail address: [email protected] (Y. Su).
https://doi.org/10.1016/j.optcom.2019.124884 Received 23 August 2019; Received in revised form 9 October 2019; Accepted 1 November 2019 Available online xxxx 0030-4018/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
W. Wan, M. Luo, Z. Liu et al.
Optics Communications xxx (xxxx) xxx
as 2 for the visible wavelength range from 400 nm to 700 nm. A plane beam is incident from the top side of the device. The parameters of the proposed color filters should be optimized so that the resonant spectra render not only red (R), green (G), and blue (B) in relation to the transmission peaks but also cyan (C), magenta (M), and yellow (Y) pertaining to the reflection dips. In our simulations, the top and bottom Ag layers are set as 20 and 22 nm, respectively. Fig. 2 shows the trans-reflective characteristics of the proposed color filters at normal incidence. The thickness of the Si3 N4 cavity is determined to be 110, 86, and 63 nm, corresponding to the R, G, and B spectra at the resonant wavelengths of 𝜆0 = 650, 550, and 457 nm, respectively. The CDF is correspondingly optimized to be h0 = 86, 69, and 64 nm. The simulated spectral bands for the three filters are shown in Fig. 2(a)–(c). Fig. 2(a) presents a resonant wavelength of 650 nm with a peak transmission of 68% and reflection efficiency of 0.3%. Similarly, Fig. 2(b) and (c) permit homologous trans-reflective characteristics in the wavelength of 550 and 457 nm, respectively. For the G and B filters, the peak transmissions reach above 70% and the reflection efficiency drop to be almost 0. In order to appraise the color purity, the color coordinates calculated from both the simulated transmission and reflection spectra are represented in the standard International Commission on Illumination (CIE) 1931 chromaticity diagram, as plotted in Fig. 2(d). From the chromaticity diagram, it is obvious that our proposed color filters can achieve vivid colors output with rendering RGB colors in transmission and CMY colors in reflection. To demonstrate a broad palette for our color filters, we investigate the transmission and reflection spectra for different thickness of Si3 N4 cavity at normal incidence. As shown in Fig. 3(a)–(b), the transmission peak and reflection dip could be fine-tuned by gradually varying the Si3 N4 cavity thickness. Obviously, the entire visible range from 400 nm to 700 nm with a high efficiency (above 60%) can be achieved in transmission. Fig. 3(c)–(d) show the color coordinates (dotted lines) from the transmission and reflection spectra for various Si3 N4 cavity thickness in the CIE 1931 chromaticity diagram. From Fig. 3(c), we can observe that a broad color gamut is obtained in the transmission spectra, where R, G, and B colors with high purity are achieved. However, the color gamut in the reflection spectra is relatively narrow, as mapped in Fig. 3(d). The different geometries (solid and hollow) marked in Fig. 3(c)–(d)
Fig. 1. Schematic view of the proposed ultrathin high-efficiency, variable-color filters.
the angular sensitivity. Here, the calculated optical characteristics of the proposed color filter were completed by the finite difference time domain (FDTD) arithmetic [28]. In simulations, the index of the Ag film is derived from the Palik [29] and the index of the Si3 N4 layer is set
Fig. 2. Calculated transmission and reflection spectra for (a) R (C), (b) G (M), and (c) B (Y) colors, respectively. (d) The corresponding colors output are represented in the CIE 1931 diagram.
2
Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
W. Wan, M. Luo, Z. Liu et al.
Optics Communications xxx (xxxx) xxx
Fig. 3. The calculated (a) transmission and (b) reflection spectra for different Si3 N4 cavity thickness. The color coordinates (dotted lines) from the (c) transmission and (d) reflection spectra for various Si3 N4 cavity thickness in the CIE 1931 chromaticity diagram.
Fig. 4. For TM polarization, transmission spectra as a function of wavelength and angle of incidence for (a) R, (b) G, and (c) B colors, respectively. For TE polarization, transmission spectra as a function of wavelength and angle of incidence for (d) R, (e) G, and (f) B colors, respectively.
represent the rendering RGB colors in transmission and CMY colors in reflection in Fig. 2, respectively.
transmission is almost unchanged with the incident angle increases
Next, we explore transmission spectra dependence on the incident angle of beam for both TE and TM polarizations. As shown in Fig. 4(a)– (c), the transmission peaks remain at the same resonant wavelength over the incident angle range from 0◦ to 60◦ for TM polarized light, and the R, G, and B colors with high efficiency (above 65%) for different incident angle can be observed. For TE polarized light, the high
RGB colors when the incident angle varies from 0◦ to 60◦ , as drawn
from 0◦ to 60◦ , but the resonant peak wavelengths blue shifted for the in Fig. 4(d)–(f). Those results indicate that the proposed color filters can present a wide angular tolerance while remain high transmitted efficiency for TM polarization, which are essential for the practical applications. 3
Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
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Optics Communications xxx (xxxx) xxx
Fig. 5. The (a) transmission and (b) reflection spectra in response to the thickness of the top Ag for R color, respectively. (c) The color coordinates (dotted lines) from the transmission and reflection spectra for various top Ag thickness in the CIE 1931 chromaticity diagram.
Fig. 6. (a) Electric field distributions at the peak of 550 nm. (b) The transmission spectra for the device without Si3 N4 overlay. The (c) transmission and (d) reflection intensity with various Ag mirror thickness at the resonant wavelength of 550 nm, respectively.
Color filters with a manipulated color saturation are critical to the display applications. For our designs, the color saturation is directly relevant to the spectral bandwidth at a constant resonant wavelength [30]. Here, we explore the transmission/reflection spectra with various thickness of the top Ag mirror. Fig. 5 shows that an adjustable spectral bandwidth can be achieved by gradually tuning the top Ag mirror thickness while preserving the same resonant wavelength. As presented in Fig. 5(a)–(b), as the thickness of the top Ag increases from 10 nm to 50 nm, the bandwidth of transmission spectrum gets narrower for the resonant wavelength of 650 nm, which is a consequence of the phase shift of light in the top Ag layer. That means the proposed devices permit a flexibly tailored bandwidth at a fixed resonant wavelength, which gives rise to improve the color saturation. For the top Ag thick up to be above 50 nm, the reflective intensity of the top Ag film becomes higher, leading to a weakly transmission. Fig. 5(c) shows the color
coordinates (dotted lines) from the transmission and reflection spectra for various top Ag thickness in the CIE 1931 chromaticity diagram. From Fig. 5(c), we can observe that a widely tuned color saturation is obtained in the transmission spectra. Considering that a reflection dip is concurrent with the corresponding transmission peak over the visible range, the color saturation for the reflected optical output is also easily modulated. Consequently, it is confirmed that the color saturation of our color filters could be widely tuned, performing no obviously shift at the resonant wavelength for the transmission and reflection spectra. 3. Analysis and conclusions To order to reveal the physical mechanism of the proposed ultrathin variable-color filters, we investigate the resonance effect in the devices based the asymmetric cavity resonator stacked with a CDF overlay. 4
Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
W. Wan, M. Luo, Z. Liu et al.
Optics Communications xxx (xxxx) xxx
Here, we simulate the electric field distributions at peak of 550 nm as illustrated in Fig. 6(a). It is found that the light field is mainly trapped at the Si3 N4 cavity, exhibiting a strong resonant effect in the ultrathin dielectric layer. The cavity mode resonance is excited by the interference effects of standing waves formed between the two metallic Ag mirrors. The outstanding resonance are responsible for the weak reflection and high transmission at the peak wavelength. In addition, the Si3 N4 overlay as a phase compensated material can be used to improve the angular tolerance for TM polarization. Fig. 6(b) shows the transmission spectra with various incident angle for the device without Si3 N4 overlay at the resonant wavelength of 550 nm. It is worth noting that the device without Si3 N4 overlay distinctly blue shifted when the incident angle increases from 0◦ to 60◦ comparing to the device with Si3 N4 overlay as shown in Fig. 4(b). Therefore, the CDF overlay reduces the sensibility of the incident angle for TM polarization. Finally, we explore the transmission and reflection spectra dependence on the both Ag mirror thickness at the resonant wavelength of 550 nm, as shown in Fig. 6(c)–(d). To reduce the reflection efficiency while preserving high transmission, the thickness of top and bottom Ag layers is optimized as 20 and 22 nm, respectively. In conclusion, ultrathin high-efficiency, variable-color filters have been numerically investigated. By adopting an Ag-Si3 N4 -Ag resonator covered with a Si3 N4 layer as a CDF, an adjustable bandwidth at a fixed resonant wavelength can be achieved. The proposed color filters can provide vivid colors output with a broad color gamut and widely tuned color saturation, which can render RGB colors with high efficiency (above 65%) in transmission and CMY colors in reflection. Moreover, the numerical results show that the transmitted peak wavelength remains unchanged for the angle of incident varying from 0 to 60◦ for TM polarization. Our devices have great potential for applications in displays and colorful decoration under a large-area fabricating process.
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Acknowledgments The present study was supported by the Natural Science Foundation of China (NSFC) (61905077), Jiangxi Provincial Natural Science Foundation of China (No. 20192BAB217014), Foundation of Jiangxi educational committee (No. GJJ180355), the Zhejiang Lab’s International Talent Fund for Young Professionals. We thank the School of Optoelectronics Science and Engineering, Soochow University and the SVG Optronics Corporation for the numerically simulated support. References [1] R.W. Sabnis, Color filter technology for liquid crystal displays, Displays 20 (3) (1999) 119–129. [2] Y.T. Yoon, C.H. Park, S.S. Lee, Highly efficient color filter incorporating a thin metal–dielectric resonant structure, Appl. Phys. Express 5 (2) (2012) 022501. [3] T. Xu, Y.K. Wu, X. Luo, L.J. Guo, Plasmonic nanoresonators for high-resolution colour filtering and spectral imaging, Nature Commun. 1 (2010) 59. [4] Y. Ma, N. Sun, R. Zhang, L. Guo, Y. She, J. Zheng, Z. Ye, Integrated color filter and polarizer based on two-dimensional superimposed nanowire arrays, J. Appl. Phys. 116 (4) (2014) 044314. [5] J. Cui, X.C. Cui, H. Xu, Y. Liu, J. Zheng, Z.C. Ye, Polarized structure color from thin dielectric gratings on a metal film, Appl. Opt. 54 (13) (2015) 3868–3872. [6] V.R. Shrestha, S.S. Lee, E.S. Kim, D.Y. Choi, Polarization-tuned dynamic color filters incorporating a dielectric-loaded aluminum nanowire array, Sci. Rep. 5 (2015) 12450.
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Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film Wenqiang Wan a , Minghui Luo b , Zhimin Liu a , Yanfeng Su c ,∗ a
School of Science, East China Jiaotong University, Nanchang 330013, China SVG Optronics, Co., Ltd, Suzhou 215026, China c College of Optical and Electronic Technology, China Jiliang University, Hangzhou 310018, China b
ARTICLE
INFO
Keywords: Color filters Cavity resonator Broad color gamut High efficiency
ABSTRACT In this paper, we design and numerically investigate ultrathin high-efficiency, variable-color filters. The color filters, based on a cavity resonator covered with a compensated dielectric film, promise an adjustable spectral bandwidth while preserving the same resonant wavelength. A broad color gamut and widely tuned color saturation can be obtained by gradually varying the cavity depth and the top mirror thickness, respectively. The numerical results show that the transmitted peak wavelength remains unchanged with the angle of incident range from 0 to 60◦ for TM polarization and the transmission efficiency is above 65% at the resonant peak wavelength. Moreover, the physical mechanism of the device is investigated. The light field is mainly concentrated in the cavity, leading to the strong resonant effect. The proposed designs can be fabricated more easily by the deposition methods for the practical applications.
1. Introduction Color filters, regarded as an essential element of photoelectric devices, have received substantial attentions for various applications, such as display, imaging sensor, anti-counterfeiting, and colorful decoration. Conventional color filters are highly vulnerable to longstanding ultraviolet irradiation and heat exposure using chemical colorant pigments, which results in significant performance degradation [1]. Color filters based functional nanostructures, employing an interaction between light and structures, realize adjustable colors output exhibiting high efficiency, high spatial resolution, and high stability. In recent years, diverse designs of structural colors have been reported utilizing surface plasmon resonances (SPR), Fano resonances (FR), Mie resonances (MR), and guided-mode resonances (GMR) [2–22]. Wide colors covering the entire visible band can be achieved by tuning the geometry of optical structures that results in selectively transmitting or reflecting a specific wavelength. However, the angle sensitive behavior, off-resonant wavelength components and complicated fabricating methods limit the practical applications in large scale. Fabry–Perot (FP) cavity resonators, based on metal–dielectric–metal (MDM) system, have been demonstrated to address the above drawbacks of functional nanostructures for color filters applications [23– 27]. Colors with controllable wavelength and brightness were obtained by varying the dielectric thickness and the filling factor [24]. Nevertheless, it is disappointed that the color saturation of their output cannot
be efficiently controlled while maintaining the resonant wavelength, which means a shift of center spectrum for different bandwidth. In this paper, we propose ultrathin high-efficiency, variable-color filters. The proposed filters, consisting of a FP cavity resonator stacked with a compensated dielectric film (CDF), present an adjustable bandwidth at a fixed resonant wavelength. A broad color gamut and widely tuned color saturation can be obtained by gradually varying the cavity depth and the top mirror thickness, respectively. The CDF covering as a compensated layer is utilized to improve the angular tolerance by adopting the material of phase compensation instead of common oxides. The numerical results show that the transmitted peak wavelength remains unchanged with the angle of incident varying from 0 to 60◦ for TM polarization and the transmission efficiency is above 65% for the peak wavelength. Compared with those elaborate structural colors, the proposed filter system can be large-scale fabrications under the deposition methods. 2. Structural design and results Fig. 1 shows the schematic view of our ultrathin color filters, where an MDM system composing of a silicon nitride (Si3 N4 ) cavity sandwiched between two metallic film of Silver (Ag) that is vertically stacked with a CDF of Si3 N4 . Ag is selected as a metallic mirror since its lowest absorption and highest reflectivity in the visible regime. The top Si3 N4 layer as a compensated material is employed to improve
∗ Corresponding author. E-mail address: [email protected] (Y. Su).
https://doi.org/10.1016/j.optcom.2019.124884 Received 23 August 2019; Received in revised form 9 October 2019; Accepted 1 November 2019 Available online xxxx 0030-4018/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
W. Wan, M. Luo, Z. Liu et al.
Optics Communications xxx (xxxx) xxx
as 2 for the visible wavelength range from 400 nm to 700 nm. A plane beam is incident from the top side of the device. The parameters of the proposed color filters should be optimized so that the resonant spectra render not only red (R), green (G), and blue (B) in relation to the transmission peaks but also cyan (C), magenta (M), and yellow (Y) pertaining to the reflection dips. In our simulations, the top and bottom Ag layers are set as 20 and 22 nm, respectively. Fig. 2 shows the trans-reflective characteristics of the proposed color filters at normal incidence. The thickness of the Si3 N4 cavity is determined to be 110, 86, and 63 nm, corresponding to the R, G, and B spectra at the resonant wavelengths of 𝜆0 = 650, 550, and 457 nm, respectively. The CDF is correspondingly optimized to be h0 = 86, 69, and 64 nm. The simulated spectral bands for the three filters are shown in Fig. 2(a)–(c). Fig. 2(a) presents a resonant wavelength of 650 nm with a peak transmission of 68% and reflection efficiency of 0.3%. Similarly, Fig. 2(b) and (c) permit homologous trans-reflective characteristics in the wavelength of 550 and 457 nm, respectively. For the G and B filters, the peak transmissions reach above 70% and the reflection efficiency drop to be almost 0. In order to appraise the color purity, the color coordinates calculated from both the simulated transmission and reflection spectra are represented in the standard International Commission on Illumination (CIE) 1931 chromaticity diagram, as plotted in Fig. 2(d). From the chromaticity diagram, it is obvious that our proposed color filters can achieve vivid colors output with rendering RGB colors in transmission and CMY colors in reflection. To demonstrate a broad palette for our color filters, we investigate the transmission and reflection spectra for different thickness of Si3 N4 cavity at normal incidence. As shown in Fig. 3(a)–(b), the transmission peak and reflection dip could be fine-tuned by gradually varying the Si3 N4 cavity thickness. Obviously, the entire visible range from 400 nm to 700 nm with a high efficiency (above 60%) can be achieved in transmission. Fig. 3(c)–(d) show the color coordinates (dotted lines) from the transmission and reflection spectra for various Si3 N4 cavity thickness in the CIE 1931 chromaticity diagram. From Fig. 3(c), we can observe that a broad color gamut is obtained in the transmission spectra, where R, G, and B colors with high purity are achieved. However, the color gamut in the reflection spectra is relatively narrow, as mapped in Fig. 3(d). The different geometries (solid and hollow) marked in Fig. 3(c)–(d)
Fig. 1. Schematic view of the proposed ultrathin high-efficiency, variable-color filters.
the angular sensitivity. Here, the calculated optical characteristics of the proposed color filter were completed by the finite difference time domain (FDTD) arithmetic [28]. In simulations, the index of the Ag film is derived from the Palik [29] and the index of the Si3 N4 layer is set
Fig. 2. Calculated transmission and reflection spectra for (a) R (C), (b) G (M), and (c) B (Y) colors, respectively. (d) The corresponding colors output are represented in the CIE 1931 diagram.
2
Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
W. Wan, M. Luo, Z. Liu et al.
Optics Communications xxx (xxxx) xxx
Fig. 3. The calculated (a) transmission and (b) reflection spectra for different Si3 N4 cavity thickness. The color coordinates (dotted lines) from the (c) transmission and (d) reflection spectra for various Si3 N4 cavity thickness in the CIE 1931 chromaticity diagram.
Fig. 4. For TM polarization, transmission spectra as a function of wavelength and angle of incidence for (a) R, (b) G, and (c) B colors, respectively. For TE polarization, transmission spectra as a function of wavelength and angle of incidence for (d) R, (e) G, and (f) B colors, respectively.
represent the rendering RGB colors in transmission and CMY colors in reflection in Fig. 2, respectively.
transmission is almost unchanged with the incident angle increases
Next, we explore transmission spectra dependence on the incident angle of beam for both TE and TM polarizations. As shown in Fig. 4(a)– (c), the transmission peaks remain at the same resonant wavelength over the incident angle range from 0◦ to 60◦ for TM polarized light, and the R, G, and B colors with high efficiency (above 65%) for different incident angle can be observed. For TE polarized light, the high
RGB colors when the incident angle varies from 0◦ to 60◦ , as drawn
from 0◦ to 60◦ , but the resonant peak wavelengths blue shifted for the in Fig. 4(d)–(f). Those results indicate that the proposed color filters can present a wide angular tolerance while remain high transmitted efficiency for TM polarization, which are essential for the practical applications. 3
Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
W. Wan, M. Luo, Z. Liu et al.
Optics Communications xxx (xxxx) xxx
Fig. 5. The (a) transmission and (b) reflection spectra in response to the thickness of the top Ag for R color, respectively. (c) The color coordinates (dotted lines) from the transmission and reflection spectra for various top Ag thickness in the CIE 1931 chromaticity diagram.
Fig. 6. (a) Electric field distributions at the peak of 550 nm. (b) The transmission spectra for the device without Si3 N4 overlay. The (c) transmission and (d) reflection intensity with various Ag mirror thickness at the resonant wavelength of 550 nm, respectively.
Color filters with a manipulated color saturation are critical to the display applications. For our designs, the color saturation is directly relevant to the spectral bandwidth at a constant resonant wavelength [30]. Here, we explore the transmission/reflection spectra with various thickness of the top Ag mirror. Fig. 5 shows that an adjustable spectral bandwidth can be achieved by gradually tuning the top Ag mirror thickness while preserving the same resonant wavelength. As presented in Fig. 5(a)–(b), as the thickness of the top Ag increases from 10 nm to 50 nm, the bandwidth of transmission spectrum gets narrower for the resonant wavelength of 650 nm, which is a consequence of the phase shift of light in the top Ag layer. That means the proposed devices permit a flexibly tailored bandwidth at a fixed resonant wavelength, which gives rise to improve the color saturation. For the top Ag thick up to be above 50 nm, the reflective intensity of the top Ag film becomes higher, leading to a weakly transmission. Fig. 5(c) shows the color
coordinates (dotted lines) from the transmission and reflection spectra for various top Ag thickness in the CIE 1931 chromaticity diagram. From Fig. 5(c), we can observe that a widely tuned color saturation is obtained in the transmission spectra. Considering that a reflection dip is concurrent with the corresponding transmission peak over the visible range, the color saturation for the reflected optical output is also easily modulated. Consequently, it is confirmed that the color saturation of our color filters could be widely tuned, performing no obviously shift at the resonant wavelength for the transmission and reflection spectra. 3. Analysis and conclusions To order to reveal the physical mechanism of the proposed ultrathin variable-color filters, we investigate the resonance effect in the devices based the asymmetric cavity resonator stacked with a CDF overlay. 4
Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.
W. Wan, M. Luo, Z. Liu et al.
Optics Communications xxx (xxxx) xxx
Here, we simulate the electric field distributions at peak of 550 nm as illustrated in Fig. 6(a). It is found that the light field is mainly trapped at the Si3 N4 cavity, exhibiting a strong resonant effect in the ultrathin dielectric layer. The cavity mode resonance is excited by the interference effects of standing waves formed between the two metallic Ag mirrors. The outstanding resonance are responsible for the weak reflection and high transmission at the peak wavelength. In addition, the Si3 N4 overlay as a phase compensated material can be used to improve the angular tolerance for TM polarization. Fig. 6(b) shows the transmission spectra with various incident angle for the device without Si3 N4 overlay at the resonant wavelength of 550 nm. It is worth noting that the device without Si3 N4 overlay distinctly blue shifted when the incident angle increases from 0◦ to 60◦ comparing to the device with Si3 N4 overlay as shown in Fig. 4(b). Therefore, the CDF overlay reduces the sensibility of the incident angle for TM polarization. Finally, we explore the transmission and reflection spectra dependence on the both Ag mirror thickness at the resonant wavelength of 550 nm, as shown in Fig. 6(c)–(d). To reduce the reflection efficiency while preserving high transmission, the thickness of top and bottom Ag layers is optimized as 20 and 22 nm, respectively. In conclusion, ultrathin high-efficiency, variable-color filters have been numerically investigated. By adopting an Ag-Si3 N4 -Ag resonator covered with a Si3 N4 layer as a CDF, an adjustable bandwidth at a fixed resonant wavelength can be achieved. The proposed color filters can provide vivid colors output with a broad color gamut and widely tuned color saturation, which can render RGB colors with high efficiency (above 65%) in transmission and CMY colors in reflection. Moreover, the numerical results show that the transmitted peak wavelength remains unchanged for the angle of incident varying from 0 to 60◦ for TM polarization. Our devices have great potential for applications in displays and colorful decoration under a large-area fabricating process.
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Please cite this article as: W. Wan, M. Luo, Z. Liu et al., Ultrathin high-efficiency, variable-color filters with an adjustable bandwidth by combining a cavity resonator and a dielectric film, Optics Communications (2019) 124884, https://doi.org/10.1016/j.optcom.2019.124884.