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Recently, there have been notable advances in nanophotonic structural color generation which enabled various applications in display, anti-counterfeiting, sensors and detectors. However, most advances in this domain have been achieved through the use of high-index materials which require expensive and complex fabrication. In this work, we enable low-index polymer nanostructures to generate structural colors using the multipolar decomposition technique which allows a better understanding and design of the scattering process by identifying the dominant multipole modes from the scattered fields. We set a polymeric (n~1.56) cuboid as the structural color generation platform, examined the contributions of various multipoles from the wave scattered by it, and synthesized the desired color spectrum by adjusting only the height of the cuboid. To validate our findings, we fabricated the designed structural color pixels via light-controlled, low-pressure nanoimprinting and measured the color and spectrum from them. Our experimental results agreed well with the simulation results, providing insights for bringing further advances to structural coloring. 

Understanding the dynamic behavior of photopolymers in nanoscale environment is essential to improving MEMS/NEMS device fabrication technologies. Here, we unveil the highly nonlinear behaviors of photopolymers exhibited during the process of light-controlled, low-pressure nanoimprinting. Such peculiarities can complicate the relation between the UV-dose and the height of the nanoimprinted feature, degrading the accuracy of the height control. To address the issue, we establish a theoretical process model and used the control of the nanoimprinting height for structural coloring applications. Our findings will broadly benefit nanotechnology and nanoscience. 

Recently, two-photon polymerization has been successfully employed to fabricate high-contrast one-dimensional photonic crystals. Using this approach, photonic bandgap reflectivities over 90% have been demonstrated in the infrared spectral range. As a result of this success, modifications to the design are being explored which allow additional tunability of the photonic bandgap. In this paper, a one-dimensional photonic crystal fabricated by two-photon polymerization which has been modified to include mechanical flexures is evaluated. Experimental findings suggest these structures allow mechanically induced spectral shifting of the entire photonic bandgap. These results support the use of one-dimensional photonic crystals fabricated by two-photon polymerization for opto-mechanical applications. 

Diffraction gratings are ubiquitous in many optical applications such as sensors, filters, and optical security devices. Capillary force lithography, which utilizes the capillary rise of photopolymer into nanoscale cavities, is a simple and rapid method to construct diffraction gratings without necessitating expensive instruments or complex steps. With the help of spatial light modulators, such as the digital micromirror device, the height of the grating can also be spatially modulated, printing spatially height-modulated gratings. When white light normally impinges on the grating, the light propagates into the grating interferes with light that propagates into air. By varying the height of the grating, the optical path lengths of two lights can be varied, leading to different interference effects and structural coloring. Judicious design of the grating’s parameters and patterning process will even allow encoding of multiple images. In this work, by tuning the height of the grating through the light-controlled capillary force lithography, we demonstrate grating-based structural color printing. This technique is promising for producing the custom patterns for anti-counterfeiting, authentication, and cryptography.