High-efficiency and economical solar-energy-pumped laser with Fresnel lens and chromium codoped laser medium

A tunable-focus spherical lens using two flat substrates and inhomogeneous electric field over a homogeneous liquid crystal ͑LC͒ layer is demonstrated. The top flat substrate has an imbedded spherical indium-tin-oxide ͑ITO͒ electrode and the bottom has a planar ITO electrode on its inner surface. The inhomogeneous electric field generates a centrosymmetric gradient refractive index profile within the LC layer which causes the focusing behavior. The focal length of the LC lens can be tuned continuously from infinity to 0.6 m by the applied voltage.

Polarization-independent phase-only modulation of a polymer-dispersed liquid crystal ͑PDLC͒ is demonstrated. In the low voltage region, PDLC is translucent because of light scattering. Once the voltage exceeds a saturation level, PDLC is highly transparent and exhibits phase-only modulation capability. Although the remaining phase is not too large, it is still sufficient for making adaptive microdevices, such as microlens. A tunable-focus microlens for arrays using PDLC is demonstrated. This kind of microlens is scattering free, polarization independent, and has fast response time.

A fast-response and scattering-free homogeneously aligned polymer network liquid crystal (PNLC) light modulator is demonstrated at λ=1.55 μm wavelength. Light scattering in the near-infrared region is suppressed by optimizing the polymer concentration such that the network domain sizes are smaller than the wavelength. The strong polymer network anchoring assists LC to relax back quickly as the electric field is removed. As a result, the PNLC response time is ∼250× faster than that of the E44 LC mixture except that the threshold voltage is increased by ∼25×.