Miniaturization of image sensors and increase of their resolution creates a demand for new miniature optical
components providing classical functions in optics, like auto-focus (AF) and optical image stabilization (OIS).
Several routes have been explored in order to realize AF and OIS functions in miniaturized components, for
example electro-wetting liquid lenses, MEMS components and liquid crystal (LC) lenses. Our recent attempt to
provide OIS with LC lenses showed the possibility to shift an image but limitations appeared. The sectorization
of the electrodes generates aberrations due to the discontinuities of the electric field at the junction between two
sectors. To overcome these limitations, we propose a new structure featuring a resistive electrode. This structure
consists in substrates with thin electrodes joined with a ring-shaped resistive electrode (10kΩ/sq.) made of
PEDOT-PSS and etched by oxygen plasma. A high resistivity layer (10MΩ/sq.) is then coated on the optical
aperture and the cell is assembled like a classical LC modal lens. With this electrode structure, we succeeded
to linearize the electric potential between the electrodes and reduce aberrations of the resulting wavefronts.
First we simulated the lens by finite elements method to study the impact of the ring-shaped resistive electrode
and to calibrate the physical parameters of each components (metallic electrodes, ring-shaped electrode, high
resistivity layer, LC...). Then, we realized lenses and we characterized them in terms of focus, deviation angle
and aberrations.
Miniaturization and reduction of production cost of optical components in consumer electronics leads to wafer
level optics. This miniaturization, associated with the increase of CMOS sensors resolution, generates new needs
such as auto-focus (AF) and optical image stabilization (OIS) in order to reduce the blurring caused by hand
jitter.
In this paper, we propose a wafer scale technology to perform AF and introduce OIS functionality. We
managed to create a tunable focal lens by filling with nematic liquid crystal (LC) an assembly of two glass
substrates coated with circular hole patterned chromium electrodes and resistive transparent layers of Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS). When a voltage with tunable magnitude and
frequency is applied to the electrodes, the resistive layer creates a non-uniform voltage distribution from the
edge to the center of the aperture which depends on electrical parameters of PEDOT-PSS and LC. The resultant
electric field generates a gradient orientation of the nematic director which allows to focus light polarized along
the director. It is also possible to shift the optical axis of the lens by dividing the hole patterned electrodes
in several sectors and to apply different voltages on each sectors. The principle of the shifting effect has been
demonstrated but its magnitude has to be increased by using more adapted electrode structure to ensure the
OIS function. Finally, we characterised the dynamical behaviour of the lens in both focus and shifting modes.
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