Electrically reconfigurable optical color filters using heterogeneous chiral liquid crystals

Abstract Optical signals necessitate using optical filters that selectively transmit light with the desired wavelength information. In visual imaging-related optical devices, a color filter acts as an optical wavelength selector to extract the certain color information from the incident light. To overcome the optical limitations of the conventionally commercialized pigmented color filters, such as low efficiency and low color purity, biomimetic structural color filters have recently attracted significant interest. Chiral liquid crystals form a self-organized periodic helical nanostructure and the implemented structural color can be tunable. However, most of chiral liquid crystal color and control of filtered color wavelength have been limited to the reflection rather than optically transmissive color filters. This study proposes an electrically tunable color filter using a heterogeneous chiral liquid crystal structure whose transmissive light can be tuned among different colors (red, green, and blue) with extremely small voltages not exceeding 1.2 V for the first time to the best of our knowledge. To obtain electrical controllability of transmissive colors, electrothermal tuning of chiral liquid crystals is approached. Moreover, analog pixel binning with a heterogeneous chiral liquid crystal color filter in a tetra-layout is investigated. Dynamic and direct binning of the color filter could relieve the quality degradation of the captured images under low-light illumination in image sensors and higher image resolutions. Considering the highly desired requirement of low driving voltage in practical devices, the tunable heterogeneous CLC color filter proposed in this study is expected to facilitate the advancement of future electro-optical color filter applications.