This work proposes a refractive index sensing concept of a Tamm plasmon (TP) device by using spectroscopic ellipsometry and phase detection. A TP device is generally composed of a 1-D photonic crystal (PC) with a metallic film on top of it. We found that the sensing performance can be improved by adjusting the parameters of the incident angle of polarized light, the top layer thickness, and the central wavelength of the PC. By designing proper parameters, it was found that the change of the phase difference of p-polarized and s-polarized lights, δ∆, can reach 34° when the ambient environment is changed from air (n = 1.00028) to carbon dioxide (n = 1.00045). A sensitivity of δ∆/δn ~2 × 10⁵ °/RIU can then be obtained for the proposed TP device.

The pretilt angles of liquid crystal molecules can be controlled by using conventional polyimide (PI) alignment material doped with different concentrations of Polyhedral Oligomeric Silsequioxanes (POSS) nanoparticles, which have been observed to spontaneously induce vertical alignment. The addition of POSS in the homogenous PI changes the surface energy of the alignment layer and generates a variable pretilt angle. Experimental results demonstrate that the pretilt angle θ_p is a function of the POSS concentration, and can be tuned continuously over the range of 0°<θ_p<90°. The polar anchoring energy of POSS/PI alignment layer is almost constant regardless of the POSS concentration. This technique is very simple and is compatible with methods familiar in the current LCD industry.

We demonstrate a liquid-crystal (LC)-tuned Tamm-plasmon (TP) resonance device. The term TP polariton refers to plasmonic resonance at the interface between a photonic crystal (PC) and a metallic film. We formulate a precise optical analysis of the proposed device using the transfer-matrix method. A single resonance dip in the photonic band-gap region guarantees that the thickness of the LC layer between the PC and the metallic film can be as small as about 180 nm. Tuning phase retardation in the LC layer is shown to shift the resonance wavelength tens of nanometers, depending on the birefringence and width of the LC layer. Simulation results are in good agreement with the experimental data.

The zinc oxide (ZnO) nanowire arrays on the indium tin oxide (ITO) glass substrates were fabricated by using the two-step hydrothermal method. A high transmittance ~92% of ZnO nanowire arrays on ITO substrate in the visible region was obtained. It was observed that the liquid crystal (LC) directors were aligned vertically to the (ZnO) nanowire arrays. The properties of ZnO nanowire arrays as vertical liquid crystal (LC) alignment layers and their applications for hybrid-aligned nematic LC modes were investigated in this work.

The Tamm-plasmon-polariton (TPP) occurs at the interface between a metallic film and the photonic-crystal (PC) substrate. Unlike conventional surface-plasmon-polariton (SPP), TPP can be directly excited by both the transverse electric (TE) and transverse magnetic (TM) electromagnetic waves without using additional coupling optics. The fact that the optical functionality of most plasmonics devices is determined after fabrication limits their applications. Tunable SPP devices by applying liquid crystals (LCs) have been widely demonstrated due to their large birefringence and easy controllability via external stimuli. However, actively tuning TPP is difficult because the localised electric field is between the metallic film and PC substrate, the change of refractive index above the metallic film has only small influences on TPP. This article is intended to briefly review recent progress towards using LCs for actively tuning TPP devices. Not only TPP devices can gain benefits from LCs, we will also discuss the applications of TPP for measuring the anisotropy of the alignment films of LC devices. The sensitivity of the proposed scheme will be discussed. GRAPHICAL ABSTRACT