Download LCD panel characterization by measuring full

LCD panel characterization by measuring full
Jones matrix of individual pixels using
polarization-sensitive digital holographic
microscopy
Jongchan Park,1 Hyeonseung Yu,1 Jung-Hoon Park,1,2 and YongKeun Park1,*
1
Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, South Korea
2
Current affiliation: Howard Hughes Medical Institute, Janelia Farm Research Campus, 19700 Helix Drive,
Ashburn, Virginia 20147, USA
*
[email protected]
Abstract: We present measurements of the full Jones matrix of individual
pixels in a liquid-crystal display (LCD) panel. Employing a polarizationsensitive digital holographic microscopy based on Mach-Zehnder
interferometry, the complex amplitudes of the light passing through
individual LCD pixels are precisely measured with respect to orthogonal
bases of polarization states, from which the full Jones matrix components of
individual pixels are obtained. We also measure the changes in the Jones
matrix of individual LCD pixels with respect to an applied bias. In addition,
the complex optical responses of a LCD panel with respect to arbitrary
polarization states of incident light were characterized from the measured
Jones matrix.
©2014 Optical Society of America
OCIS codes: (110.0180) Microscopy; (160.3710) Liquid crystals; (180.3170) Interference
microscopy.
References and links
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
P.-G. De Gennes and J. Prost, The Physics of Liquid Crystals (Clarendon, 1993), Vol. 23.
H. Kawamoto, “The History of Liquid-Crystal Displays,” Proc. IEEE 90(4), 460–500 (2002).
R. H. Chen, Liquid Crystal Displays: Fundamental Physics and Technology (John Wiley & Sons, 2011).
G. H. Heilmeier, “Electro-Optical Device,” U.S. Patent 3,499,122 (1970).
G. H. Heilmeier and L. Zanoni, “guest‐host interactions in nematic liquid crystals. a new electro‐optic effect,”
Appl. Phys. Lett. 13(3), 91–92 (1968).
J.-h. Kim and J.-k. Song, “Vertically aligned liquid crystal display,” U.S. Patent 6,424,396 (2002).
M. Schadt and W. Helfrich, “Voltage-dependent optical activity of a twisted nematic liquid crytstal,” Appl. Phys.
Lett. 18(4), 127–128 (1971).
E. S. Kim and Y. K. Lee, “Fringe field switching liquid crystal display,” U.S. Patent 6,580,487 (2003).
A. Takeda, S. Kataoka, T. Sasaki, H. Chida, H. Tsuda, K. Ohmuro, T. Sasabayashi, Y. Koike, and K. Okamoto,
“41.1: A Super‐High Image Quality Multi‐Domain Vertical Alignment LCD by New Rubbing‐Less
Technology,” in SID Symposium Digest of Technical Papers, (Wiley Online Library, 1998), 1077–1080.
Y. J. Lim, C. W. Woo, S. H. Oh, A. Mukherjee, S. H. Lee, J. H. Baek, K. J. Kim, and M. S. Yang, “Enhanced
contrast ratio of homogeneously aligned liquid crystal displays by controlling the surface-anchoring strength,” J.
Phys. D Appl. Phys. 44(32), 325403 (2011).
M. Oh‐e and K. Kondo, “Electro‐optical characteristics and switching behavior of the in‐plane switching mode,”
Appl. Phys. Lett. 67(26), 3895–3897 (1995).
D. H. Brainard, D. G. Pelli, and T. Robson, “Display characterization,” Encyclopedia of imaging science and
technology (2002).
A. Márquez, I. Moreno, C. Iemmi, A. Lizana, J. Campos, and M. J. Yzuel, “Mueller-Stokes characterization and
optimization of a liquid crystal on silicon display showing depolarization,” Opt. Express 16(3), 1669–1685
(2008).
P. Boher, T. Leroux, and D. Glinel, “0.0: Polarization Imaging for characterization of LCDs and their
components,” (2009).
J. E. Bigelow and R. A. Kashnow, “Poincaré sphere analysis of liquid crystal optics,” Appl. Opt. 16(8), 2090–
2096 (1977).
S. Pancharatnam, “Generalized theory of interference, and its applications. Part I. Coherent pencils,” in
Proceedings of the Indian Academy of Sciences, Section A, (Indian Academy of Sciences, 1956), 247–262.
#220357 - $15.00 USD
Received 4 Aug 2014; revised 1 Sep 2014; accepted 8 Sep 2014; published 26 Sep 2014
(C) 2014 OSA
6 October 2014 | Vol. 22, No. 20 | DOI:10.1364/OE.22.024304 | OPTICS EXPRESS 24304
17. T. H. Chyba, L. J. Wang, L. Mandel, and R. Simon, “Measurement of the Pancharatnam phase for a light beam,”
Opt. Lett. 13(7), 562–564 (1988).
18. R. C. Jones, “A new calculus for the treatment of optical systems,” J. Opt. Soc. Am. A 31(7), 488–493 (1941).
19. Y. Kim, J. Jeong, J. Jang, M. W. Kim, and Y. Park, “Polarization holographic microscopy for extracting spatiotemporally resolved Jones matrix,” Opt. Express 20(9), 9948–9955 (2012).
20. Z. Wang, L. J. Millet, M. U. Gillette, and G. Popescu, “Jones phase microscopy of transparent and anisotropic
samples,” Opt. Lett. 33(11), 1270–1272 (2008).
21. T. Sarkadi and P. Koppa, “Measurement of the Jones matrix of liquid crystal displays using a common path
interferometer,” J. Opt. 13(3), 035404 (2011).
22. T. Colomb, F. Dürr, E. Cuche, P. Marquet, H. G. Limberger, R.-P. Salathé, and C. Depeursinge, “Polarization
microscopy by use of digital holography: application to optical-fiber birefringence measurements,” Appl. Opt.
44(21), 4461–4469 (2005).
23. U. Schnars and W. Jueptner, Digital holography (Springer, 2005).
24. R. K. Singh, D. N. Naik, H. Itou, Y. Miyamoto, and M. Takeda, “Stokes holography,” Opt. Lett. 37(5), 966–968
(2012).
25. M. Yamauchi, A. Marquez, J. A. Davis, and D. J. Franich, “Interferometric phase measurements for polarization
eigenvectors in twisted nematic liquid crystal spatial light modulators,” Opt. Commun. 181(1-3), 1–6 (2000).
26. C. Lingel, T. Haist, and W. Osten, “Optimizing the diffraction efficiency of SLM-based holography with respect
to the fringing field effect,” Appl. Opt. 52(28), 6877–6883 (2013).
27. V. Nercissian, F. Geier, A. Berger, S. Dmitriev, Z. Ghadyani, I. Harder, K. Mantel, and N. Lindlein, “Phase
measurement of a spatially varying polarization distribution,” in Proceedings of 113th Annual Meeting of the
DGaO, 2012)
28. G. Lazarev and A. Sedashev, “Laser microinterferometer for estimation of red blood cell volume,” in Saratov
Fall Meeting 2006: Optical Technologies in Biophysics and Medicine VIII, (International Society for Optics and
Photonics, 2007), 653516–653516–653517.
29. V. Andreev, K. Indukaev, O. Ioselev, A. Legkii, G. Lazarev, and D. Orlov, “Phase modulation microscope
MIM-2.1 for measurements of surface microrelief. Results of measurements,” J. Russ. Laser Res. 26(5), 394–
401 (2005).
30. S. K. Debnath and Y. Park, “Real-time quantitative phase imaging with a spatial phase-shifting algorithm,” Opt.
Lett. 36(23), 4677–4679 (2011).
31. M. K. Kim, “Principles and techniques of digital holographic microscopy,” SPIE Reviews 1, 018005 (2010).
32. K. Lee, K. Kim, J. Jung, J. H. Heo, S. Cho, S. Lee, G. Chang, Y. J. Jo, H. Park, and Y. K. Park, “Quantitative
phase imaging techniques for the study of cell pathophysiology: from principles to applications,” Sensors (Basel)
13(4), 4170–4191 (2013).
33. E. Hecht, “Optics, “Pearson Education,” Inc. 360, 366–367 (2002).
34. Y. Park, T. Yamauchi, W. Choi, R. Dasari, and M. S. Feld, “Spectroscopic phase microscopy for quantifying
hemoglobin concentrations in intact red blood cells,” Opt. Lett. 34(23), 3668–3670 (2009).
35. Y. Jang, J. Jang, and Y. Park, “Dynamic spectroscopic phase microscopy for quantifying hemoglobin
concentration and dynamic membrane fluctuation in red blood cells,” Opt. Express 20(9), 9673–9681 (2012).
36. J. H. Jung, J. Jang, and Y. Park, “Spectro-refractometry of individual microscopic objects using swept-source
quantitative phase imaging,” Anal. Chem. 85(21), 10519–10525 (2013).
37. D. K. Yoon, M. C. Choi, Y. H. Kim, M. W. Kim, O. D. Lavrentovich, and H.-T. Jung, “Internal structure
visualization and lithographic use of periodic toroidal holes in liquid crystals,” Nat. Mater. 6(11), 866–870
(2007).
38. T. Kato, “Self-assembly of phase-segregated liquid crystal structures,” Science 295(5564), 2414–2418 (2002).
39. C. Tschierske, “Liquid crystal engineering--new complex mesophase structures and their relations to polymer
morphologies, nanoscale patterning and crystal engineering,” Chem. Soc. Rev. 36(12), 1930–1970 (2007).
40. S. J. Woltman, G. D. Jay, and G. P. Crawford, “Liquid-crystal materials find a new order in biomedical
applications,” Nat. Mater. 6(12), 929–938 (2007).
41. P. Phelps, A. D. Steele, and D. J. McCarty, Jr., “Compensated polarized light microscopy. Identification of
crystals in synovial fluids from gout and pseudogout,” JAMA 203(7), 508–512 (1968).
42. W. Mickols, M. F. Maestre, I. Tinoco, Jr., and S. H. Embury, “Visualization of oriented hemoglobin S in
individual erythrocytes by differential extinction of polarized light,” Proc. Natl. Acad. Sci. U.S.A. 82(19), 6527–
6531 (1985).
1. Introduction
Liquid crystals are one of the most fascinating optical materials that exhibit both liquid and
solid crystals phase [1, 2]. Liquid crystal molecules are arranged to their own orientations
during solid crystal phase; however they undergo fluidization and rearrange molecular
orientations above specific temperature. Liquid crystals have been extensively used in
numerous optical devices due to their extraordinary optical properties; liquid crystal
molecules exhibit birefringence, and their orientations can be controlled by externally
applying electric field.
One of the most popular applications of liquid crystals is liquid-crystal display (LCD)
technology which utilizes birefringence of rod-like liquid crystal molecules [2–4]. In LCDs,
#220357 - $15.00 USD
Received 4 Aug 2014; revised 1 Sep 2014; accepted 8 Sep 2014; published 26 Sep 2014
(C) 2014 OSA
6 October 2014 | Vol. 22, No. 20 | DOI:10.1364/OE.22.024304 | OPTICS EXPRESS 24305
the polarization states of light are spatially modulated by rotating the orientations of liquid
crystal molecules, thus allowing the control of the transmittance of light through the LCD
panel. Since the first demonstration in 1968 by Heilmeier and colleagues [4, 5], various types
of LCD panels have been developed and utilized. Conventionally, LCD techniques are
classified by the types of arrangements of liquid crystal molecules: twisted nematic, vertically
aligned, homogeneous aligned LCDs, fringe field switching and so on [3, 6–10]. Recently
developed in-plane switching liquid-crystal displays (IPS-LCD) has been widely used in
commercial LCD products, because it provides larger viewing angle and higher transmission
efficiency compared to conventional LCD techniques [11].
The optical characterization of LCD panels is crucial for the developing and testing of
LCDs. Conventional techniques for LCD characterizations were mostly based on intensity
measurements since the transmittance of light after propagating through a polarizer and
analyzer is the figure of merit for LCD performance characterization [12]. However, the
optical responses of LCDs can only be fully described in the manner of polarization states,
which is the working principle of LCDs. Polarization-sensitive LCD characterizations using
the Stokes parameters have been reported in which the polarization ellipse of the observed
electric field is measured to characterize LCDs [13, 14]. In these cases, the Poincaré sphere
has been used to visualize the relationship between the Stokes parameters and orthogonal
vectors in the lab-axis [15–17]. However, although the Stokes parameters can define the
polarization ellipse of light, it does not directly describe the complex nature of electric field.
Jones matrix measurement can be used for the full characterization of the complex optical
responses of materials to incident polarized light [18]. When polarized light propagates
through optical elements, the progressive alterations in the polarization state can be found by
multiplying the Jones matrix describing the optical elements to the Jones vector describing
the initial polarization state. Components of the Jones matrix represent the complex optical
transformation between the orthogonal axes. Although degree of polarization is not accounted
in Jones matrix formalism, Jones matrix directly describes the complex optical responses of
optical materials. To access this information, measurement of both amplitude and phase of the
complex field in terms of orthogonal polarization states must be achieved. Digital holography
has been utilized to determine the polarization states of various samples ranging from
polarization-sensitive optical fibers, to liquid crystal droplets, and to biological cells and
tissues [19–24]. Recently, there has also been attempts to measure polarization states of light
in LCDs [21, 25]. Polarization eigenvectors [25] and Jones matrix [21, 26, 27] of LCDs have
been measured using interferometry. However, spatially resolved full Jones matrix
characterization of LCD display at the individual pixel scales has yet to be demonstrated.
Here, we employ polarization-sensitive digital holographic microscopy (DHM) for
characterizing the full-Jones matrix of individual pixels in an IPS-LCD panel. Using MachZehnder interferometry and off-axis holographic recording [28, 29], 2-D complex optical
amplitude containing both the amplitude and phase of light are quantitatively measured. A set
of a polarizer and an analyzer are controlled in order to selectively record electrical fields of
light passing a LCD pixel in terms of the orthogonal polarization components. The optical
responses of the LCD panel with respect to the incident light of arbitrary polarization are
systematically measured as a function of the applied bias (grayscale value) to the LCD panel,
allowing the complete optical characterization of individual pixels in a LCD panel.
2. Method
2.1 Experimental setup
The polarization-sensitive DHM setup for measuring the full Jones matrix is shown in Fig.
1(a). Mach-Zehnder interferometry with off-axis holographic recording is employed in order
to record the 2-D full-field complex amplitude of the beam passing through LCD panels. An
unpolarized He-Ne laser (λ = 633 nm, 5.0 mW, Thorlabs, USA) is used for an illumination
source. The beam from the laser is first spatially filtered, then the polarization state and
intensity of the laser beam is modulated by placing a polarizer (LPVISE100-A, ∅1″ linear
#220357 - $15.00 USD
Received 4 Aug 2014; revised 1 Sep 2014; accepted 8 Sep 2014; published 26 Sep 2014
(C) 2014 OSA
6 October 2014 | Vol. 22, No. 20 | DOI:10.1364/OE.22.024304 | OPTICS EXPRESS 24306
polarizer with N-BK7 protective windows, 400-700 nm) and rotating a half-wave plate
(WPH10M-633, ∅1″ zero-order half-wave plate, 633 nm, Thorlabs, USA). The beam is then
divided by a beam splitter (BS1) into two arms: a sample and a reference arm. One beam
passes through an IPS-LCD (FLATRON 20EA34TQ, LG electronics, Korea) panel and
serves as a sample arm. In order to characterize LCD pixels only, polarization sheets attached
to the LCD panel were removed before measurements. The beam transmitted through the IPSLCD is collected by an objective lens (LMPLFLN, × 20, NA = 0.4 Olympus, USA) and
projected onto the image plane, where a CMOS camera (C11440-22C, 2048 × 2048 pixels
with a 6.5-μm pixel size, Hamamatsu, Japan) is placed, via a 4-f telescopic imaging system.
The total lateral magnification from the sample to the image plane is × 8.33. The reference
arm is recombined with the sample arm by a beam splitter with a slightly tilted angle, and
both the sample and reference arms interfere at the image plane. A neutral density filter is
placed in the path of the reference arm to enhance the fringe contrast of the interferograms by
equalizing the intensity of the sample and reference arms. The field of view of IPS-LCD
panel is set to an area covering 800 μm × 800 μm. An analyzer (LPVISE100-A, ∅1″ linear
polarizer with N-BK7 protective windows, 400-700 nm) was placed in front of the camera in
order to selectively record a specific component of the polarization states of the electric field.
In order to reconstruct one spatially resolved Jones matrix map from a sample,
interferograms with two different polarization states should be measured for two incident
beams with different polarization states; a total of four independent interferograms need to be
measured. To achieve this, the polarization state of illumination was controlled by the rotation
of the half wave plate before BS1 (BS004, 50:50 non-polarizing beamsplitter, 400-700 nm,
1/2″, Thorlabs, USA), the polarization state of interferograms was selected by the orientation
of the analyzer placed after BS2 (BS013, 50:50 non-polarizing beamsplitter, 400-700 nm, 1″,
Thorlabs, USA). The representative four different interferograms of LCD pixels obtained
with different polarization states are shown in Fig. 1(b), in which 9 LCD pixels are shown
while each pixel contains two sub pixels − the characteristic feature of IPS-LCD. The inset of
Fig. 1(b) shows the magnified view of an interferogram which shows spatial fringe patterns
due to off-axis modulation. From the measured interferograms, complex amplitude maps
containing both the amplitude and phase information can be retrieved via appropriate field
retrieval algorithm [30]. Figures 1(c) and 1(d) show corresponding amplitude and phase
images obtained from the interferograms shown in Fig. 1(b). The details of DHM,
quantitative phase imaging, and field retrieval can be found elsewhere [31, 32].
Polarizer
Analyzer
Y11
CCD camera
f =150 mm
Obj. lens
×20, NA 0.4
BS1
f = 100 mm
polarizer
BS2
ND filter
f = 200 mm
mirror
(c)
(d)
Half
waveplate
polarizer
ND filter
Y22
Amplitude (a.u.)
IPS-LCD
Y21
He-Ne laser
π
φ (rad)
mirror
Y12
Interferogram
(b)
(a)
-π
Fig. 1. (a) Polarization-sensitive DHM based on Mach-Zehnder interferometry. (b) A set of
measured interferograms with different polarizer and analyzer compositions. Inset: Single
pixels of the IPs-LCD is constituted by two subpixels. (c) Amplitude and (d) phase maps of
corresponding interferograms. Scale bar, 300 μm.
#220357 - $15.00 USD
Received 4 Aug 2014; revised 1 Sep 2014; accepted 8 Sep 2014; published 26 Sep 2014
(C) 2014 OSA
6 October 2014 | Vol. 22, No. 20 | DOI:10.1364/OE.22.024304 | OPTICS EXPRESS 24307
2.2 Extracting Jones matrix components
The polarization state of light can be described by a Jones vector. Conventionally, two
components of the Jones vector describe x- and y-components of the complex electric field
traveling along the z-direction optical axis. The linear optical response of a system to
polarized light can be described by a Jones matrix:
J
J =  11
 J 21
J12 
J 22 
(1)
where Jij (i, j = 1, 2) connects the jth axis component of the output electric field to the ith axis
component of an input beam. Here, the 1st and 2nd axis corresponds to the x- and y-axis,
respectively. A spatially resolved Jones matrix of an LCD panel can be extracted from four
interferograms measured with different combinations of polarizer and analyzer orientations.
Yij (i, j = 1, 2) indicates the complex electric field response with respect to the ith axis of the
polarizer orientation and the jth axis of the analyzer orientation. To decide the normalized
amplitude of Jones matrix components, the amplitudes of the electric fields of the reference
and the sample arms without the LCD were calibrated before measuring LCD panels.
By rotating the half-wave plate by the angle of + 22.5° and −22.5°, the polarization state
of the incident beam can be rotated by the angle of + 45° and −45° with respect to the y-axis,
then the Jones vector components of the incident wave can be expressed as below,
respectively:
1
1
E+45 = c1   , E−45 = c2   ,
1

 −1
(2)
where c1, c2 are constants with real values which can be determined from measurements
without a sample. In Eq. (2), the first row indicates the x-axis and the second row indicates
the y-axis components of Jones vector. The linear relationship between Jones matrix
components and the measured complex electric field response can then be described as:
 Y11   c1
Y   c
 12  =  2
Y21   0
  
Y22   0
c1
0
−c2
0
0
c1
0
c2
0   J11 
0   J12 
,
c1   J 21 
 
−c2   J 22 
(3)
where Yij (i,j = 1,2) represents the complex-valued optical field of a sample with the ith
polarization state of the incident beam and the jth polarization state of the analyzer orientation.
For example, Y11 represents the sample field information that was measured with a linearly
polarized incident beam where the polarization direction is tilted by an angle of + 45 degree,
and the horizontally aligned analyzer. In order to determine the real-value constants c1 and c2,
the optical fields of the sample are divided by optical fields measured without the sample.
Then spatially resolved Jones matrix maps with complex values can be retrieved from the
measurement of a set of four holograms with independent polarization states Yij (i,j = 1,2)
using Eq. (3).
2.3 Visualization of polarization states
For an intuitive representation, polarization states of light are usually described by
polarization ellipses. The x- and y-axis in the observing plane are commonly chosen for
describing the polarization ellipses [33]. The polarization ellipse can be reconstructed from
the complex field information of both axes of the orthogonal polarization states, as follow:
E1 = A1eiφ1 , E2 = A2 eiφ2
(4)
#220357 - $15.00 USD
Received 4 Aug 2014; revised 1 Sep 2014; accepted 8 Sep 2014; published 26 Sep 2014
(C) 2014 OSA
6 October 2014 | Vol. 22, No. 20 | DOI:10.1364/OE.22.024304 | OPTICS EXPRESS 24308
where the Ai and φi (i = 1, 2) indicates the amplitude and phase delay of the polarization state
along the 1st and 2nd axis which corresponds to the x- and y-axis, respectively. The
polarization ellipse can then be described by a parametric equation of a curve as:
x = A1 cos (φ1 + t )
(5)
y = A2 cos (φ2 + t )
where t varies between 0 and 2π. When the ellipticity of the polarization ellipse is zero or
infinity, it represents a linearly polarized state. The ellipticity of one corresponds to a
circularly polarized state. An oscillating orientation of the polarization state can be effectively
described by the dynamic modulation of the azimuthal angle of the polarization ellipse.
3. Results and discussions
In order to systematically characterize the optical response of individual pixels in a LCD
panel, we quantitatively measured the Jones matrix components of individual pixels as a
function of an applied bias β. The bias was controlled by using the IPS-LCD via a RGB
output cable and displaying gray-scale images to all three color channels within a range from
β = 0 (min) to β = 255 (max). As we have used the illumination laser with a wavelength of
633 nm, only the red channel in the LCD display among the three color channels were used to
measure the Jones matrix components. Figure 2 shows the amplitude and phase maps of each
Jones matrix components (J11, J12, J21 and J22) for 9 LCD pixels, in which the applied bias
was half of the full dynamic range, i.e. β = 128. As can be seen in Fig. 2, a single pixel unit in
an IPS-LCD panel is composed of two subpixels and each subpixel displays a different
optical response, which is a characteristic feature of an IPS-LCD. The 3 × 3 rectangular
patterns in Fig. 2(a) correspond to the controlled pixels in the red channels where dim
rectangular patterns adjacent to the controlled pixels are green and blue channels [indicated
by the block dotted box in Fig. 2(b)]. Due to the embedded color filters in the LCD panel,
light can only passes through the red channels although the optical field itself can also be
modulated in the other channels. The phase modulation characteristics of the green and blue
channels as indicated as the dotted square in Fig. 2(b) were also resolved even under low
transmittance, demonstrating the sensitivity of the present polarization-sensitive DHM in
recovering the phase information even from a hologram with low light intensity.
|J11|
|J12|
|J21|
|J22|
(b)
1
∠J11
∠J12
∠J21
∠J22
0
π
(rad)
(a)
-π
Fig. 2. Measurements of the full Jones matrix of individual pixels in a IPS-LCD. (a) Amplitude
and (b) phase of spatially resolved Jones matrix components of the individual pixels. Half of
the maximum bias was applied to the pixel in the center. Scale bar, 300 μm.
To address the optical modulation capability of LCD pixels, we measured the Jones
matrix components of individual pixels as a function of applied bias. The amplitude and
phase maps of each Jones matrix components (J11, J12, J21 and J22) for a specific pixel
positioned in the center were measured as a function of bias. For other adjacent pixels, a fixed
bias was applied, keeping the amplitude and phase values remain constant. These adjacent
#220357 - $15.00 USD
Received 4 Aug 2014; revised 1 Sep 2014; accepted 8 Sep 2014; published 26 Sep 2014
(C) 2014 OSA
6 October 2014 | Vol. 22, No. 20 | DOI:10.1364/OE.22.024304 | OPTICS EXPRESS 24309
pixels were used as a set of reference pixels for determining the relative change in phases of
Jones matrix components. Figures 3(a) and (b) show the amplitude and phase modulation
characteristics of the Jones matrix components of individual pixels as a function of applied
bias, respectively. The J21 component of the Jones matrix corresponds to the polarizer and
analyzer orientations utilized in the IPS-LCD. When the applied bias is smaller than
approximately an eighth of the maximum value (β = 32), the amplitude of the J21 component
remain same with small offset from zero. The amplitude of the J21 component linearly
increases as a function of the applied bias after this threshold value. The phase modulation on
the other hand steeply increases as the bias become higher during the first quarter and then
saturates after the bias reaches the half-maximum.
Normalized amplitude (a.u.)
(a)
|J11|
0.6
|J21|
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0.2
0
0
128
β
256
0
∠J11
-π
0
128
β
256
0
0
128
β
256
0
0
128
β
256
0
0
π
π
π
0
0
0
∠J12
-π
0
128
β
256
∠J21
-π
0
128
β
256
|J22|
0.6
0.4
(b) π
Phase delay (rad)
|J12|
0.6
128
β
256
∠J22
-π
0
128
β
256
Fig. 3. (a) Amplitude and (b) phase modulation characteristics of the Jones matrix components
of individual pixels in an IPS-LCD panel as a function of applied bias. Five measurements
were performed for different pixels in the IPS-LCD. Blue lines, averaged value. Shade areas,
standard error.
To address the capability of the measurements of the Jones matrix components of LCD
pixels, we demonstrate the retrieval of polarization ellipses of the pixels from the measured
Jones matrix. The measured Jones matrix information of individual pixels can be used to
construct the polarization response of the IPS-LCD panel using Eqs. (4)-(5). Figure 4 shows
the polarization ellipses of light transmitted through individual pixels with respect to the
incident polarization states. The solid- and dotted lines denote for the response of the lowerand the upper subpixel of individual pixels. These polarization ellipses were calculated as a
function of applied bias.
Initially, when the applied bias is zero, the polarization state of the transmitted wave is
unchanged and identical to that of the incident wave. When a non-zero bias is applied, the
polarization direction of light passing each subpixel rotates in an opposite direction with
respect to the each other; the direction of polarization rotates clockwise and counterclockwise for lower- and upper subpixels, respectively. The polarization ellipses rotate up to a
maximum azimuthal angle of 45° when the maximum bias was applied. The orientation of a
polarizer for incident waves in the used IPS-LCD was set to x-direction. When the incident
wave is y-polarized [Fig. 4(b)], an ellipticity of the polarization ellipse exhibits a higher
degree in comparison with the case when the incident wave is x-polarized [Fig. 4(a)]. This
result shows the asymmetry in the system response for the different orthogonal polarization
states which is crucial for functional characterization.
#220357 - $15.00 USD
Received 4 Aug 2014; revised 1 Sep 2014; accepted 8 Sep 2014; published 26 Sep 2014
(C) 2014 OSA
6 October 2014 | Vol. 22, No. 20 | DOI:10.1364/OE.22.024304 | OPTICS EXPRESS 24310
(a)
0.6
(b)
x-polarized
incident wave
β = 240
β = 240
β = 60 β = 0
y-polarized
incident wave β = 120
β = 180
β = 180
0.3 β = 180
0.3
β = 60
β = 60
β= 0
0
β= 0
-0.3
-0.3
-0.3
0
0.3
β = 240
β = 180
β = 120
Lower subpixel
Upper subpixel
-0.6
-0.6
β = 240
β = 120
β = 120
0
0.6
0.6
-0.6
-0.6
-0.3
β = 60 β = 0
0
0.3
0.6
Fig. 4. Polarization ellipses of light transmitting individual pixels in IPS-LCD with respect to
the (a) x-polarized and (b) y-polarized incident light.
4. Conclusion
We present a method to characterize the individual pixels in a LCD panel by measuring the
spatially resolved Jones matrix components of the light passing through the pixels.
Employing polarization-sensitive DHM based on off-axis Mach-Zehnder interferometry, the
four spatially modulated holograms of the light field passing through LCD panel were
sequentially measured as a set of orthogonal combinations of incident and transmitted
polarizations; from which, the full-field amplitude and phase images of Jones matrix
components were quantitative and precisely obtained. The responses of each Jones matrix
components were systematically measured as a function of applied bias to the LCD panel. In
addition, we demonstrated that the measured Jones matrix components can also be used for
constructing the polarization ellipses. To date, this is the first reported experimental
measurement of spatially resolved full Jones matrix components of individual LCD pixels.
Even though we focused on the measurements of an IPS-LCD for this work, the present
approach can be directly employed to characterize and test individual pixels in other types of
LCDs. The Jones matrix of full RGB channels of LCD pixels can also be characterized by
employing the illumination with multiple lasers or spectroscopic modality in DHM [34–36].
Furthermore, fast dynamic responses of LCD pixels upon applied bias change can also be
measured using an instrument which alternate the polarization states of probing laser beam in
high speed [19]. Although this work characterized the polarization-sensitive response of
individual pixels in an IPS-LCD using the Jones matrix formalism, the approach presented in
this study is general so that it can be applied to various applications including formation of
complex liquid crystal structures [37–39] and biophysical aspects of birefringent materials
[40–42].
Acknowledgments
This work was supported by KAIST, the Korean Ministry of Education, Science and
Technology (MEST), the National Research Foundation (2012R1A1A1009082,
2013M3C1A3063046,
2012-M3C1A1-048860,
2013K1A3A1A09076135,
2014M3C1A3052537), APCTP.
#220357 - $15.00 USD
Received 4 Aug 2014; revised 1 Sep 2014; accepted 8 Sep 2014; published 26 Sep 2014
(C) 2014 OSA
6 October 2014 | Vol. 22, No. 20 | DOI:10.1364/OE.22.024304 | OPTICS EXPRESS 24311