Tuning of liquid-crystal birefringence using a square ac variable frequency voltage

Abstract

We demonstrate that the birefringence of the liquid-crystal cell (LCC) can be varied by applying different frequency values of a single applied ac square voltage. For the experimental evaluation of the birefringence, associated with a certain wavelength λ, as a function of the frequency FLCC of the electrical signal applied to the LCC, we use, for the first time to our knowledge, what we call here a frequency-dependent transmission technique. It consists in measuring the transmission responses between crossed and parallel polarizers as a function of the frequency FLCC. Experimental tests were carried out using a 7 μm-thick E63 nematic LCC and a laser source emitting at λ = 1.55 μm with a launch power of −3 dBm. The tuning voltage VLCC applied to the LCC is an alternative square wave electrical signal whose frequency ranges from 0.5 to 15 kHz. The peak to peak amplitude of the electrical signal is 5 V. The curve of the measured variations of the optical path difference of the LCC versus the frequency FLCC has a positive slope. Application to the tuning of the center wavelength of the transmission response of a one stage hybrid birefringent filter is shown as a proof-of-principle test.

Suppression of Speckle Noise in Digital Holography With Spatial and Temporal Domain Depolarization

“…Liquid crystal is a kind of positive and single axis photoelectric material, which has the characteristics of changing the potential energy of molecules to the lowest state, and the characteristics of forced orientation arrangement of external electric field [27]. When the potential energy of the liquid crystal molecule is the lowest, it means that the direction of the liquid crystal molecule is the same as that of the field line of the external electric field.…”