Micro- and nanosecond electro-optic liquid crystal modulators

Oleg D. Lavrentovich
Kent State University, Ohio, United States

Keywords: liquid crystal modulators, microsecond and nanosecond switching

The main obstacle on the progress of nematic liquid crystal (NLC) electro-optic devices is a long relaxation time, when the field is switched off. This relaxation time is in the range of milliseconds. To achieve switching time on the order of hundred microseconds, we employ dual frequency NLCs in which the dielectric anisotropy is positive below some critical frequency fc and negative above it. The electric field drives the optic axis in both directions and the switching times below 200 microseconds is achieved. Even more dramatic reduction of the response time, to tens of nanoseconds, is achieved by the approach recently proposed by our group and called Nanosecond Electrically Modified Order Parameter (NEMOP) effect. In this approach, the electric field alters the refractive indices of NLC rather than reorients the optic axis as in standard approaches used so far. We demonstarate that the NEMOP technology can provide ultra-fast (tens nanoseconds) change of optical retardance of the NLC cell up to 800 nm by the driving voltage less than 600 V in the broad working temperature range, 20 degrees that encloses the room temperature. The work was supported by NSF grants DMR-1410378 and IIP-1500204.