Single-step polarization holographic method for programmable microlens arrays

Abstract

Optical microsystems have become important tools for imaging, optofluidics, and sensor applications. Here we show a versatile method to create microlens arrays (MAs) exploiting spatial-light-modulator-assisted polarization holography, which enables an efficiency of diffraction up to 100%. We demonstrate the large flexibility of the proposed approach by codifying mixed MAs, i.e., composed of spherical and cylindrical lenses with different focal lengths, either positive or negative. Reconfigurable MAs with 70% total diffraction efficiency have been recorded on a photosensitive polymer that exhibits linear photoinduced birefringence with long time stability as well as optical and thermal reversibility. The good quality of the MA has been shown by a digital holographic test.

Liquid crystal microlens arrays recorded by polarization holography

“…This method allowed us to design a GRIN on a thin LC cell to create different MAs configurations. By changing the circular polarization handedness of the probe beam, the MAs can be switched between positive and negative focal length over the two 1 diffracted orders, as it was reported in a previous work [18]. A feature with respect to [18] is that the controllable linear birefringence, through an applied voltage, and the transparency of the LC helps to maximize the diffraction efficiency close to 100%, in the whole visible range.…”

“…By changing the circular polarization handedness of the probe beam, the MAs can be switched between positive and negative focal length over the two 1 diffracted orders, as it was reported in a previous work [18]. A feature with respect to [18] is that the controllable linear birefringence, through an applied voltage, and the transparency of the LC helps to maximize the diffraction efficiency close to 100%, in the whole visible range. We have shown two MAs configurations characterized by spherical and cylindrical microlenses with different focal lengths that are in good agreement with the focalization properties of these types of elements.…”

“…Thanks to this important property, LC MAs with planar geometries have been produced through the gradient index refraction (GRIN) modulation [16]. Recent studies have shown that GRIN can be created in birefringent materials through polarization holography [17,18].…”

“…In particular, our MAs have potential applications in biophotonics [20], fiber coupling [21], patterning by flood illumination [22], and solar cells [23]. In addition, unlike the MAs obtained by direct recording on photobirefringent polymer [18], by applying a small voltage to the NLC cell, the MAs diffraction efficiency can be optimized for the spectral range of interest. Here we have demonstrated an efficiency of 90% at 633 nm.…”

Phase Structure Recording in a Nematic Side-Chain Liquid-Crystalline Polymer

“…This method was used to record conventional [18][19][20][21][22] and Fresnel [23][24][25] lenses. Phase structures, including microlens arrays [26], can be recorded in amorphous polymers. In this case, sufficiently high absorption coefficient is usually required.…”