Polarization exchange of optical eigenmode pair in twisted-nematic Fabry-Pérot resonator

The polarization exchange effect in a twisted-nematic Fabry-Pérot resonator is experimentally confirmed in the regimes of both uniform and electric-field-deformed twisted structures. The polarization of output light in the transmission peaks is shown to be linear rather than elliptical. The polarization deflection from the nematic director grows from $0^{\circ }$ to ${90}^{\circ }$ angle and exchanges the longitudinal and transverse directions. Untwisting of a nematic by a voltage leads to the rotation of the polarization plane of light passing through the resonator. The polarization exchange effect allows using the investigated resonator as a spectral-selective linear polarizer with the voltage-controlled rotation of the polarization plane.

Figure 1

Schematic of the experimental setup for studying the polarization exchange effect in TN-FPR. ${\mathrm{ZrO}}_2\text{−}{\mathrm{SiO}}_2$ multilayer mirrors are formed on the substrates with transparent ITO electrodes. The resonator is filled with the twisted nematic 5CB (see inset on the top). The analyzer $A$ is a Glan prism.

Figure 2

Spectra of the TN-FPR modes under unpolarized incident light: (a) measured and (b) simulated using the $4\times 4$ transfer matrix method with extinction ($Im{n}_{\mathrm{LC}}=7.8\times {10}^{-4}$). The arrow shows the wavelength ${\lambda }_{max}=560\mathrm{nm}$ corresponding to the Gooch-Tarry maximum condition. For convenience, the $ro$- and $re$-modes are right-to-left numbered by odd (even) numbers.

Figure 3

Polarization deflection angles $\theta$ for 26 TN-FPR transmission peaks presented in Fig. 2. Closed circles show experimental values, open circles show calculated values obtained by the direct numerical simulation. Dashed and solid lines are plotted functions of the angle $\theta$ obtained from Eq. (2); the dashed line corresponds to the resonator extraordinary $re$-modes and the solid line corresponds to the resonator ordinary $ro$-modes.

Figure 4

Experimental dependence of TN-FPR transmission on the applied voltage. The maximal and minimal transmissions are shown with black and white, respectively. The polarization exchange effect voltages at which the modes are polarized at the angles of $\pm {45}^{\circ }$ are shown for nine peak pairs. Closed circles show experimental values obtained by the intensity equalization technique and open circles show the calculated values.

Figure 5

Equalization of the transmission peak intensities by voltage: avoided crossing phenomenon in the vicinity of the $ro$-mode (484.5 nm) induced by a voltage of $U=1.0$ V without polarizer $P$ at the analyzer $A$ orientations of (a) $0^{\circ }$, (b) $+{45}^{\circ }$, and (c) $-{45}^{\circ }$. Both vertical and horizontal axes in (a)–(c) are at the same exact scale.