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Soft Photonic Devices

Next-Generation Photonic Devices

Photonic Crystal (PC) is a periodic structure of dielectric slabs that can control certain wavelengths of visible light. It is a kind of nanostructured system whose refractive index changes in a periodic fashion. In nature, many animals such as birds, fish, insets, & mammals display strong & distinct colors through interference, diffraction, and absorption of incident light through regular structures on their wings & body. In practice, PCs allow us to control the flow of light in 3 dimensions without much loss. However, conventional PCs are based on semiconductor materials. These are not tunable. In order to tune the photonic band gaps, we either need to control the periodicity or refractive index of the structure, which are very difficult to achieve for conventional PCs. In addition, conventional PCs are targeted for longer wavelengths, such as IR and microwaves, due to the complexity of fabrications. And generally, conventional PCs are fabricated by lithography-related techniques, a top-down approach that requires high technology & high-cost & sophisticated instruments.

The LC is a self-assembly of anisotropic rod-like molecules characterized by a degree of orientation. These self-assembled molecules do not require high-technology and sophisticated instruments. Instead, it is fabricated by a bottom-up approach which is very easy & low-cost. And the interesting property of LC is that they exhibit selective reflection of visible light due to the anisotropic permittivity at optical frequencies.

Our group tried to combine these LCs with photonic structures. Therefore, we can have a PC with the advantages of LC, such as nanoscale structures, self-assembly properties, and easy tunability. Therefore, it can overcome the difficulties of conventional PCs. In addition, the direction of orientation of LC can be easily controlled by a temperature gradient, pressure, and electric fields. Adopting this concept, we proposed several tunable PCs with potential 3D display and AR/VR applications.  

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