Dynamic bend mode in pi-cells

After a bend structure has been obtained through application of an appropriate voltage, a pi-cell exhibits one of two stable structures: a bend structure if the applied bias is above a certain threshold (~ 2V), and a twist structure at a lower voltage. For use in an optical device, the pi-cell must be operated with the bend structure. It was found, however, that when the bias is switched quickly to a level lower than the threshold, a metastable structure exists for a few hundreds of milliseconds before relaxing to a twist structure. From dynamic optical transmittance analysis, this structure is considered to have a bend configuration. The temporary bend structure persists at lower voltages because it takes a while to initiate an energy redistribution from the bend structure to the twist. This is considered as a novel physical state, and is called a "dynamic bend structure." It enables the pi-cell to be operated even if the bias is below the threshold voltage, provided that the device is biased at higher voltages for a fraction of each cycle to retain the bend structure.