Electro-optic properties of aligned and non-aligned polymer dispersed liquid crystals driven by an amplitude-modulated electric signal

We present an experimental study of the effect of field strength and modulating frequency of the applied amplitude modulated (AM) electric signal on the electro-optic (EO) properties of aligned and non-aligned polymer dispersed liquid crystals (PDLCs). A low modulating frequency is used to control the pulse duration of the driving AM electric signal. Two PDLC films of thickness 5 μm were prepared from a standard mixture of UV curable polymer/liquid crystal (NOA65/E7) with and without alignment layers. The EO properties are significantly enhanced in aligned PDLC thin film compared to non-aligned. A small increase of the modulating frequency decreases considerably the total response time at relatively low applied electric field strength. However, the increase of the applied field strength from 0.63 V/ μm to 2.05 V/μm reduces significantly the total response time by a factor of two. When proper combination of the applied field strength and modulating frequency is achieved the EO properties of PDLC is enhanced and tuned effectively at relatively low applied voltage. This study shows how relatively fast response and large dynamic range optical tuning of PDLC material can be achieved at low frequency. This is important findings to be implied in PDLC-based economic photonic devices.