Non-iridescent Transmissive Structural Color Filter Featuring Highly Efficient Transmission and High Excitation Purity

Abstract

Nanostructure based color filtering has been considered an attractive replacement for current colorant pigmentation in the display technologies, in view of its increased efficiencies, ease of fabrication and eco-friendliness. For such structural filtering, iridescence relevant to its angular dependency, which poses a detrimental barrier to the practical development of high performance display and sensing devices, should be mitigated. We report on a non-iridescent transmissive structural color filter, fabricated in a large area of 76.2 × 25.4 mm2, taking advantage of a stack of three etalon resonators in dielectric films based on a high-index cavity in amorphous silicon. The proposed filter features a high transmission above 80%, a high excitation purity of 0.93 and non-iridescence over a range of 160°, exhibiting no significant change in the center wavelength, dominant wavelength and excitation purity, which implies no change in hue and saturation of the output color. The proposed structure may find its potential applications to large-scale display and imaging sensor systems.

Uniformly thick tri-color filters capitalizing on an etalon with a nanostructured cavity

“…In order to further improve the performance of the proposed filters, a thick metallic film may be possibly applied in conjunction with an antireflection coating, so as to simultaneously reduce the spectral bandwidth and enhance the reduced peak transmission caused by the increased metal thickness [20]. We may cautiously attempt a configuration of cascaded etalons, thereby diminishing the bandwidth [19]. …”

“…2(d), both the transmission and the bandwidth tend to decrease when the thickness of the metallic film increases from 15 to 50 nm. Due to a narrower bandwidth leading to better color purity [19], the fact that the color purity is only improved by sacrificing the transmission efficiency suggests a trade-off between the transmission efficiency and the bandwidth. As a result, we selected a metal thickness of 15 nm, resulting in a high transmission and an appropriate spectral bandwidth of ∼43 nm.…”

“…In particular, an etalon having a metal-dielectric-metal configuration is regarded as a prime candidate for color filters on account of its conspicuous characteristics where the spectral passband can be tailored by simply varying the thickness of the dielectric cavity. However, in order to build a suite of filters exhibiting different passbands on the same platform, we evidently need to adopt different cavity thicknesses via additional fabrication steps [17][18][19][20][21]. It is imperative in terms of practical applications that tri-color filters, encompassing red, green, and blue (RGB), are produced such that they have a uniform thickness.…”

“…[1][2][3][4][5][6][7][8][9][10]. Inspired by color filtering in nature, several schemes of nanostructures, such as subwavelength grating structures exhibiting plasmonic and/or guided-mode resonances and Fabry-Perot (FP) etalons, have been extensively studied [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In particular, an etalon having a metal-dielectric-metal configuration is regarded as a prime candidate for color filters on account of its conspicuous characteristics where the spectral passband can be tailored by simply varying the thickness of the dielectric cavity.…”

Optimization of sharp and viewing-angle-independent structural color

“…Previous work on synthetic structural color has explored a wide range of designs, but none simultaneously achieves the narrow bandwidth and broad viewing angle that are required for the transparent display application. Multilayer films [20][21][22], periodically-modulated surfaces [23][24][25][26], and three-dimensional photonic crystals [27] reflect light only at a discrete set of angles rather than omnidirectionally. Structural randomness can decrease the angular dependence and is generally understood to be the reason for the non-iridescence of Morpho butterfly's blue color [28][29][30][31][32][33], but the randomization also broadens the bandwidth to about 100 nm or larger.…”