Extended linear polarimeter to measure retardance and flicker: application to liquid crystal on silicon devices in two working geometries

Abstract

Abstract. We focus on the evaluation of the applicability of the classical and well-established linear polarimeter to the measurement of linear retardance in the presence of phase flicker. This analysis shows that there are large errors in the results provided by the linear polarimeter when measuring the linear retardance of a device. These errors depend on the specific retardance value under measurement. We show that there are some points where this limitation can be used to measure the fluctuation amplitude consistently. An elegant method is further proposed, enabling the measurement of the average retardance value, thus extending the applicability of the classical linear polarimeter. Experimental characterization results are provided for various electrical sequences addressed onto a parallel aligned liquid crystal on silicon (LCoS) display. Good agreement is obtained with experiment, thus validating the linear polarimeter methodology proposed. Furthermore, results are provided for the LCoS in two reflection geometries, perpendicular incidence with and without nonpolarizing beam splitter, demonstrating robustness of the method. As a result, the evaluation of both phase modulation range and flicker magnitude for any electrical sequence addressed can be easily obtained, which is very important for optimal use of LCoS displays in applications.

Averaged Stokes polarimetry applied to evaluate retardance and flicker in PA-LCoS devices

“…We observe that the retardance range is about 360° for both sequences with a very good linearity. Recently we have also proposed another technique to obtain both retardance and flicker values [18] based on an adapted version of the classical linear polarimeter, which we have called the extended linear polarimeter. A more detailed characterization can be obtained by the average Stokes polarimetry, however the extended linear polarimeter can be more widely applied by any lab since only two linear polarizers are needed.…”

“…This is generally true in digital backplane devices due to the pulsed digital signal addressed [10,11,15,16]. Typical methods used to characterize linear variable retarders may provide erroneous results [17,18] since they typically assume that the birefringence in the waveplate has a constant value, no fluctuations, during the measurement process. Furthermore, the amplitude of the retardance fluctuation becomes a magnitude of interest for a more accurate characterization and modeling of the device under test.…”

“…Furthermore, the amplitude of the retardance fluctuation becomes a magnitude of interest for a more accurate characterization and modeling of the device under test. Recently appropriate techniques to obtain both retardance and flicker values have been demonstrated by our group [18] and by Ramirez et al [19], based respectively on the classical linear polarimeter and in a combination of linear and circular polarimeters. These are easier techniques to implement, specially the extended linear polarimeter in [18].…”

“…Recently appropriate techniques to obtain both retardance and flicker values have been demonstrated by our group [18] and by Ramirez et al [19], based respectively on the classical linear polarimeter and in a combination of linear and circular polarimeters. These are easier techniques to implement, specially the extended linear polarimeter in [18]. However, a more detailed characterization can be obtained by the average Stokes polarimetry method we recently proposed in [20].…”

LCoS SLM Study and Its Application in Wavelength Selective Switch

“…This effect could be detrimental for images as the gray level is drifting around the desired value; thus such uncertainty could reduce the diffraction efficiency of gratings [50]. By using a higher frequency for the driving sequence, the flicker amplitude can be reasonably reduced, which is also demonstrated by Martínez et al for visible bandwidth [51]. Figure 2 shows the experimental setup for flicker measurement, in which linearly polarized light vibrating at 45 • with respect to the LC director (the LC director is parallel to the long axis of the display for GAEA device) impinges perpendicularly onto the entrance window of the device.…”