Polarization-Dependent Microlens Array Using Reactive Mesogen Aligned by Top-Down Nanogrooves for Switchable Three-Dimensional Applications

Abstract

We propose a reactive mesogen (RM) lens array to obtain good focusing behavior along with a short focal plane, where the focusing behavior is switchable according to the polarization state of incident light. Polarization-dependent focusing behavior is obtained using a planoconvex RM microlens array on a planoconcave isotropic lens template. Even though the sagitta of our RM lens is high, to obtain the short focal length, the RM layer can be aligned well by introducing a top-down alignment effect, using a nanogrooved template. The optical noise due to the moiré effect generated by the nanogrooves on the surface of the planoconvex RM layer can be removed simply by overcoating a thin RM layer, which is self-aligned by the geometric surface effect, without an additional alignment process. We demonstrate a hexagonal-packed RM lens array that has a very high fill factor and symmetric phase profile, for an ideal lens.

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“…To sufficiently reduce the thickness of the PMLA to one which promises to be viable for a compact module, the RM-based MLA was prepared as the PMLA. One of the other merits of the RM-based lens is that the focusing and defocusing optical properties determined by the incident polarization can be precisely designed to produce ideal phase profiles by using the refractive index and the surface curvature conditions [33]. These polarization-dependent controls of the focusing and defocusing phase profiles can also be preserved well after converting the RM layer to a solidified film with UV-induced polarization.…”

“…Although the fabricated RM-based PMLA has almost 100% fill-factor MLA condition, each elemental lens exhibits ideally symmetric concentric fringe patterns, showing that there is no RM layer alignment defect. This was achieved due to the top-down and bottom-up alignment effects during the thermal annealing process performed for the RM alignment stabilization [33]. To obtain the PMLA with the f-number condition of f/16, a very thin RM layer (maximum thickness of 4 μm on the interfacial curvature of the planarconcave isotropic polymer layer) was required.…”

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“…2(a). On the contrary, when the polarization direction of the incident light is parallel to the slow axis of the RM layer (field-on state of the TN LC layer), the incident light is focused because the refractive index of the plano-convex RM layer is larger than the refractive index of the plano-concave isotropic polymer layer [5].…”

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“…Therefore, when the polarization direction of incident ray is parallel to the alignment axis of the RM layer, the incident ray is periodically refracted in the surface of an MLA structure because the refractive index n e of the RM layer is larger than the refractive index n p of the isotropic polymer layer. On the contrary, when the polarization direction of the incident ray is orthogonal to the alignment axis of the RM layer, the incident ray is not refracted, because the refractive index n e of the RM layer is the same with refractive index n p of the isotropic polymer layer [6]. In case of our virtual-moving MLA, the RM molecules are aligned to the x-axis direction in the top PDMLA.…”