Epsilon-near-zero (ENZ) metamaterials have been studied in various research areas such as wavefront engineering, supercoupling effect, strong coupling, nonlinear optics, and perfect absorption. An ideal ENZ material of ε=0 is highly omnireflective at any angle of incidence. For a real ENZ material of Re(ε)≈0 the imaginary part Im(ε) is not zero from the causality principle. At an ENZ wavelength at Re(ε)≈0, the normal electric field (E_z ) in an ENZ thin film with a very small Im(ε) becomes very strong and the group velocity slows down; E_z is inversely proportional to the thickness of the film and the imaginary part of ε, resulting in a large light absorption in a low optical loss ENZ thin film. We investigate the tunable ENZ wavelength of indium tin oxide (ITO) thin films in the NIR wavelength regime which are controlled by the film growth conditions and demonstrate the broadband perfect absorption (PA) using the ITO multilayers of different ENZ wavelengths.
Coherent perfect absorption (CPA) is an optical phenomenon occurring in an absorbing thin film by the interaction of two counter-propagating coherent waves. We propose a new broadband CPA scheme based on ENZ multilayer films and investigate the multi-wavelength optical switching, indicating that the on- and off-states can be controlled by the phase shift and wavelength of the two incident waves.
In this lecture we provide design principles and fabrication guidelines for thin film ENZ devices for PA and CPA, which can find various applications in optical switches, modulators, filters, sensors, and energy harvesting devices.
A bilayer wire grid polarizer composed of UV-replicated nanograting and deposited aluminum layer was designed,
fabricated and evaluated for a simpler and less costly reflective polarizer. An electroformed nickel stamp was fabricated
using a lithographed photo resist master pattern having a nanograting with a pitch of 80 nm, a line width of 50 nm, and a
height of grating of 100 nm. A polymer grating was fabricated by the UV replication process and an aluminum layer
with a thickness of 50 nm was deposited by electron-beam evaporation. To examine the performance of the fabricated
bilayer wire-grid polarizer, the transmission spectra of TM- and TE-polarized light, and the extinction ratio spectra were
measured and compared with the simulated values obtained from the rigorous coupled wave analysis. The measured TMtransmittance
and extinction ratio of the fabricated bilayer wire grid polarizer were ~ 40 % and ~ 103 in whole visible
We present a polarization analysis system to measure the birefringence of scanning lens. This technique is based on
rotating-analyzer ellipsometer. The liquid immersion method is applied to measure the birefringence distribution
regardless of the shape of the test lens. In this report, the principle of the two dimensional measurement system and the
result of 2-D birefringence distribution in scanning lens are presented.
The Shack-Hartmann or Hartmann-Shack wavefront sensors are particular forms of the Hartmann sensor and are the most commonly used in adaptive optics. The traditional Hartmann screen in the pupil is replaced by an array of small lenslets at a conjugate to an image of the pupil or deformable mirror. Each lenslet forms an independent image of the incoming wavefront. Shifts in the positions of these images can be shown by simple geometric optics to be proportional to the mean wavefront gradient over each lenslet. The measurement range or dynamic range of a conventional Shack-Hartmann sensor is normally limited by the sub-aperture size of the detector plane, in which each spot should remain. In order to overcome this restriction, several methods, such as modified unwrapped algorithm or a spatial-light modulator as a shutter, have been proposed. We first simulated the image forming of a conventional Shack-Hartmann wavefront sensor for highly aberrated spherical aberrations through computer simulation, which confirmed that the well-known effect that high aberration shifts the spots outside its conventionally detectable area. We first develop a computer program that simulates Shack-Hartmann’s image forming and we show that simple defocusing the CCD plane can allocate the out-boundary spots to initial or reference positions, which results in the increase of the dynamic range of the Shack-Hartmann sensor.
Optical, electrical, and microstructural properties of thermally evaporated Cr thin films assisted by the low-energy Ar ion beam were investigated. The result shows that the optical and electrical properties are close to those of the corresponding bulk Cr: both refractive index and extinction coefficient increase, reflectance increases, and electrical resistivity decreases. The tensile stress decreases while the grain size changes slightly. From this experimental study, it is found that the low-energy Ar ion beam bombardment on growing Cr films modifies the microstructure of Cr films to improve the optical and electrical properties.