Smart Mini-Cameras

Focusing unpolarized light with a single-nematic liquid crystal layer

“…Its clear aperture was ∅ ≈ 2.5 mm, the optical birefringence of the NLC used (homemade mixture) was Δn ¼ 0.2, and the thickness L of the planar oriented [thanks to polyimide (PI) layers] NLC was 50 μm. The lens used a well-known "modal control" scheme, 1,8 where the bottom and top substrates of the cell are coated, respectively, by uniform and hole-patterned (HP) indium tin oxide (ITO) electrodes (Fig. 2).…”

“…1 One of the highly desired features of such cameras is the autofocus function required for bar code or text scanning. Today, the widely accepted approach, enabling the autofocus, is based on the use of the axial mechanical movement of the camera's base lens with the help of voice coil motors (VCMs).…”

“…Such a reorientation may generate, for example, a spherical phase delay to create a lens, similar to a gradient index (GRIN) lens, the refractive index profile of which may be expressed as (see, e.g., Ref. 1) n GRIN ðrÞ ¼ n c − r 2 ∕ð2fLÞ;…”

“…18). Such a lens may provide an electrically variable optical power (OP) 1 that may be approximately expressed as…”

“…6 Many approaches have been demonstrated to also build nematic LC (NLC) components for optical imaging. 1,[7][8][9][10][11][12][13][14][15][16][17] However, those materials have a fundamental limitation: they are polarization sensitive since the refractive index modulation here is achieved by the electrical field-induced reorientation of their local anisotropy axis (commonly called "director," representing the local average direction of the long molecular axes of the NLC 4 ). Figure 1(a) schematically demonstrates an electrically variable NLC lens using a single-layer of NLC that is in the Y; Z plane (with its ground state director being parallel with the Y-axis).…”