Achromatic Linear Polarization Switch for Visible and Near Infrared Radiation Based on Dual-Frequency Twisted Nematic Cell

The switchable polarization rotators are of prime importance in many modern optical applications, such as displays, spatial light modulators, and beam deflectors. Such a rotator can be designed with a half-wave electrically controlled nematic cell with antiparallel alignment at the two boundary plates. However, this rotator can operate only in a narrow spectral band where the half-wave condition is satisfied. A rotator comprised of multiple liquid crystal (LC) cells can provide a broader operational spectral region [1, 2]. A twisted nematic (TN) cell alone can provide the achromatic polarization rotation controlled by an applied electric field [3]. An ‘ideal’ achromatic rotation for a broad optical range with a high contrast (a small induced ellipticity) might be achieved when the cell thickness d, light wavelength λ and the nematic birefringence n ∆ satisfy the Mauguin condition / 2 d n λ >> ∆ [4, 5]. Unfortunately, a large d needed to satisfy this condition causes a long switching time of the nematic device, t∂d, see, for example Ref. [6]. Several approaches have been suggested to use rather thin TN cells for polarization rotation [7-11], however their dynamics have not been explored. Recently we have shown that by using dual-frequency nematics one can significantly speed up a switching of rather thick nematic cells with antiparallel alignment and large “pretilt” angle [12-14]. In this work, we present the first results on the dynamics of dual-frequency TN cells and evaluate their performance as polarization rotators. We demonstrated the operation of electrically switchable thick TN cells as achromatic linear polarization rotators for the wavelength range between 0.4 μ m and 2.7 μ m with fast switching within 10 ms.