October 18, 2005

Polarization holographic device using photoreactive polymer liquid crystals

For many years, researchers have looked to develop organic materials as a reliable and cost effective replacement for inorganic materials in optical devices. The development of highly functionalized optical devices using photonics instead of optoelectronics has highlighted the need for greater control over the manipulation of optical signals.

Photo-control of molecular orientation of polymer materials is of great interest for the development of highly functionalized holographic optical devices.

In this study published in AZojomo*, by Hiroshi Ono and Nobuhiro Kawatsuki from Nagaoka University of Technology and University of Hyogo, optical phase gratings were fabricated from photo-crosslinkable polymer liquid crystals with mesogenic 4-(4-methoxycinnamoyloxy)biphenyl side groups by irradiating with 325 nm interference lights and subsequent annealing at elevated temperatures. Recorded phase gratings were verified after the annealing process, although no gratings were observed immediately after the exposure. The characteristics of the phase gratings were strongly dependent on the polarization states of the two recording beams, and the resultant gratings involve not only linear birefringence caused by the reorientation of the mesogenic groups but also surface relief modulation generated by the molecular migration.

Diffraction measurement and AFM observation revealed that the intensity holographic gratings involve both linear birefringence and surface relief, while the pure polarization gratings without surface topological relief were formed for the polarization holographic recordings.

It is anticipated that these unique phenomena of the material and phase grating can be applicable to various kinds of optical devices.

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