High-diffraction-efficiency Fresnel lens based on annealed blue-phase liquid crystal–polymer composite

ABSTRACT

We demonstrated a relatively simple and effective method to fabricate a periodically isolated polymer wall of blue-phase liquid crystal Fresnel lens (BPLCFL) by employing a single-masking process of the ultraviolet (UV) irradiation, leading to excellent photopolymerisation-induced phase separation between blue -phase liquid crystal (BPLC) molecules and UV-curable monomers. Nevertheless, some uncured monomers would inherently reside in the BPLC-rich area and slightly inhibit the BPLC molecules realigned under the external electric field. To enhance the optical properties of the polymer-wall BPLCFL considerably, a novel technique for fabricating a pure BPLC zone is proposed that successfully expels the residual monomers from the BPLC volume using a thermal annealing process. Experimental results show that the maximum diffraction efficiency reaches ~36%, which approaches the theoretical limit of ~41%. Consequently, the annealing technique to purify phase-separated composite films has a strong potential to construct the BPLCFL in light of polarisation-free applications.

Graphical Abstract

KEYWORDS:

• Blue-phase liquid crystal
• Fresnel lens
• photopolymerisation-induced phase separation
• thermal annealing
• diffractive optics

Acknowledgements

This research was supported by grants from the Ministry of Science and Technology of Taiwan (MOST 106-2221-E-239-021). The authors also sincerely acknowledge Prof. Shin-Tson Wu of the University of Central Florida for technical assistance.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ministry of Science and Technology of Taiwan [MOST 106-2221-E-239-021].