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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 3 — Jan. 31, 2011
  • pp: 2294–2300
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Polarization-independent liquid crystal lens based on axially symmetric photoalignment

Andy Y.-G. Fuh, Shih-Wei Ko, Shu-Hao Huang, Yan-Yu Chen, and Tsung-Hsien Lin  »View Author Affiliations


Optics Express, Vol. 19, Issue 3, pp. 2294-2300 (2011)
http://dx.doi.org/10.1364/OE.19.002294


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Abstract

A polarization-independent liquid crystal lens that is based on axially symmetric photoalignment is demonstrated. This liquid crystal lens is fabricated by combining radially and azimuthally aligned liquid crystal films with gradient alignments. The configurations of liquid crystals on the substrates are confirmed both optically and using a scanning electron microscope. The focal length of the polarization-independent liquid crystal lens can be controlled by applying various voltages. The device is simple to fabricate, and very convenient to use. It therefore has great practical potential.

© 2011 OSA

1. Introduction

Optical lenses are extensively utilized in science, industry, and daily life. The development of tunable lenses with variable focal lengths and focal intensities is very important. One of the methods to achieve such variability is based on the reorientation of nematic liquid crystal (NLC) molecules under an externally applied electric field. The advantage of NLCs is that their large optical birefringence. Therefore, the optical path lengths (OPLs) can be controlled over a wide range by the application of a voltage.

The lens effect occurs when a light beam propagating through a medium with spatially varying OPLs. It can therefore be produced by varying the thickness of material (as in glass lenses), by varying the refractive index across the light beam, or by a combination of these two variations. The development of NLC lenses began in the late 1970s [1

1. C. Bricot, M. Hareng, and E. Spitz, “Optical projection device and an optical reader incorporating this device,” U.S. patent 4,037,929 (1977).

,2

2. S. Sato, “Liquid-crystal lens-cells with variable focal length,” Jpn. J. Appl. Phys. 18(9), 1679–1684 (1979). [CrossRef]

]. The initial design of an NLC lens was based on conducting film-coated curved substrates of parabolically or spherically for example varying thicknesses, to control the LC orientation. Since then, various approaches have been developed. They can be seen in NLC lenses of a uniform thickness, but with ring-patterned electrodes to achieve various distributions of LC alignments when suitable voltages are applied across the multiple electrodes [3

3. S. T. Kowel, D. S. Cleverly, and P. G. Kornreich, “Focusing by electrical modulation of refraction in a liquid crystal cell,” Appl. Opt. 23(2), 278–289 (1984). [CrossRef] [PubMed]

,4

4. W. W. Chan and S. T. Kowel, “Imaging performance of the liquid-crystal-adaptive lens with conductive ladder meshing,” Appl. Opt. 36(34), 8958–8969 (1997). [CrossRef]

], Fresnel-type lenses filled with LCs [5

5. S. Sato, A. Sugiyama, and R. Sato, “Variable-focus liquid crystal Fresnel lens,” Jpn. J. Appl. Phys. 24(Part 2, No. 8), L626–L628 (1985). [CrossRef]

,6

6. L.-C. Lin, H.-C. Jau, T.-H. Lin, and A. Y.-G. Fuh, “Highly efficient and polarization-independent Fresnel lens based on dye-doped liquid crystal,” Opt. Express 15(6), 2900–2906 (2007). [CrossRef] [PubMed]

], LC lenses with a polymer network of spatially varying densities [7

7. H. Ren and S.-T. Wu, “Tunable electronic lens using a gradient polymer network liquid crystal,” Appl. Phys. Lett. 82(1), 22–24 (2003). [CrossRef]

,8

8. Y.-H. Fan, H. Ren, and S.-T. Wu, “Switchable Fresnel lens using polymer-stabilized liquid crystals,” Opt. Express 11(23), 3080–3086 (2003). [CrossRef] [PubMed]

], LC lenses produced by patterning electrodes, of either the slit type [9

9. H. Ren, Y.-H. Fan, S. Gauza, and S.-T. Wu, “Tunable-focus cylindrical liquid crystal lens,” Jpn. J. Appl. Phys. 43(2), 652–653 (2004). [CrossRef]

] or the hole type [10

10. M. Ye and S. Sato, “Optical properties of liquid crystal lens of any size,” Jpn. J. Appl. Phys. 41(Part 2, No. 5B), L571–L573 (2002). [CrossRef]

], and other lenses [11

11. A. F. Naumov, M. Yu. Loktev, I. R. Guralnik, and G. Vdovin, “Liquid-crystal adaptive lenses with modal control,” Opt. Lett. 23(13), 992–994 (1998). [CrossRef]

,12

12. I. R. Gural’nik and S. A. Samagin, “Optically controlled spherical liquid-crystal lens: theory and experiment,” Quantum Electron. 33(5), 430–434 (2003). [CrossRef]

].

Many methods for controlling the distribution of LC pretilt angles have been demonstrated for producing a refractive index distribution in an LC cell of uniform thickness [13

13. W.-Y. Wu, C.-C. Wang, and A. Y. Fuh, “Controlling pre-tilt angles of liquid crystal using mixed polyimide alignment layer,” Opt. Express 16(21), 17131–17137 (2008). [CrossRef] [PubMed]

,14

14. J. Y. L. Ho, V. G. Chigrinov, and H. S. Kwok, “Variable liquid crystal pretilt angles generated by photoalignment of a mixed polyimide alignment layer,” Appl. Phys. Lett. 90(24), 243506 (2007). [CrossRef]

]. In this investigation, LC cells with the substrates having an axially symmetric gradient distribution of LC pretilt angles were formed by the effective planar and high pretilt (almost-vertical) alignment forces. The former was associated with the axially symmetrical ripple structure formed by the photo-adsorbed azo dye, while the latter was associated with a mixed polyimide alignment layer. Finally, a polarization-independent LC lens was formed by combining axially symmetrical radial and azimuthal LC cells with gradient pretilt angle distributions (Fig. 2
Fig. 2 Images of axially symmetric (a) radial and (b) azimuthal cells under linearly polarized probing light. The insets in (a) and (b) show the LC director alignments. (c) Top-view, (e) side-view of LC structures in axially symmetric radial cell; (d) top-view, and (f) side-view of LC structures in axially symmetric azimuthal cell. P: polarization of probing light.
below). The focal intensity of the formed LC lens can be controlled by applying a voltage to the sample.

2. Device fabrication

The NLC and azo dye that were used in this experiment were E7 (Merck) and Methyl Red (MR; Aldrich), respectively. The MR:E7 mixing ratio was 1:99 wt%. In the part of the film with the high pretilt alignment, a mixture of vertical- (AL-00010) and planar- (AL-1426B) aligned polyimides (PIs), obtained from Daily Polymer was applied [13

13. W.-Y. Wu, C.-C. Wang, and A. Y. Fuh, “Controlling pre-tilt angles of liquid crystal using mixed polyimide alignment layer,” Opt. Express 16(21), 17131–17137 (2008). [CrossRef] [PubMed]

] to substrates. A mixture of the polyimide AL-00010 (4.76 wt%) and AL-1426B (95.24 wt%), dissolved in dimethyl sulfoxide (DMSO), with a concentration of the polyimide mixture of around 50% by weight relative to the total weight of the solution, was prepared. The polyimide mixture was spin-coated onto indium-tin-oxide (ITO)-coated glass slides at 2000 rpm for 30 s. The slides were prebaked at 80°C for 30 min, and then fully baked at temperatures from 200°C to 220 °C for 60 min. Two ITO-coated glasses with a mixed PI alignment layer, separated by 12 μm ball spacers, were used to fabricate an empty cell. Then, the homogeneously mixed MR/E7 compound was injected into an empty cell in the isotropic state to form a dye-doped liquid crystal (DDLC) sample.

The photo-alignment of both sides of a DDLC cell was performed following our earlier investigation [15

15. S.-W. Ko, Y.-Y. Tzeng, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric liquid crystal devices based on double-side photo-alignment,” Opt. Express 16(24), 19643–19648 (2008). [CrossRef] [PubMed]

] using a linearly polarized DPSS (diode-pump solid state) laser (λ = 532 nm), whose wavelength was close to that of the peak in the MR absorption spectrum as the light source. The Gaussian DPSS pump laser beam, propagating along the z-axis with an intensity of ~0.8 W/cm2, was expanded into a collimated beam with a diameter of ~21 mm. It then passed through a linear mask with a line-width of ~200 um, and was focused using a cylindrical lens onto the cell. Notably, the axially symmetric LC devices can also be achieved using a cylindrical lens without a linear mask. The sample was attached to a rotating motor, and maintained at a temperature of ~65°C (which exceeds the clear temperature of E7, ~61°C) with pumping to ensure double-sided photoalignment [15

15. S.-W. Ko, Y.-Y. Tzeng, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric liquid crystal devices based on double-side photo-alignment,” Opt. Express 16(24), 19643–19648 (2008). [CrossRef] [PubMed]

]. The MR dyes underwent trans–cis isomerization after they were pumped using green light. They then exhibited continuous molecular reorientation. Finally, the excited MR dyes diffused and were adsorbed on the two ITO surfaces that were coated with the mixed PI alignment layer to form an axially symmetric ripple structure which is the so-called light-induced ripple structure (LIRS) [16

16. C.-R. Lee, T.-L. Fu, K.-T. Cheng, T.-S. Mo, and A. Y.-G. Fuh, “Surface-assisted photoalignment in dye-doped liquid-crystal films,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 69(3), 031704 (2004). [CrossRef] [PubMed]

]. The angle, θ, made between the polarization of the pump beam and the x-axis (Fig. 1
Fig. 1 Sample fabrication setup.
) can be changed using a wave-plate in front of the beam expander. The period of illumination was ~60 minutes and the rate of rotation was ~90 rpm. Since the pump laser was a Gaussian beam, the amplitude of the formed ripple structure peaked in the center of the beam, and decreased toward its edge. Therefore, consistent with the Berreman theory [17

17. D. W. Berreman, “Solid Surface Shape and the Alignment of an Adjacent Nematic Liquid Crystal,” Phys. Rev. Lett. 28(26), 1683–1686 (1972). [CrossRef]

], the formed ripple structure herein the investigation exerts the planar alignment force which peaks in the center and declines toward the perimeter of the beam. The combination of the formed ripple structure with the mixed PI alignment layer (that produced an almost vertical alignment) gives rise to the gradient LC pretilt angles in a DDLC cell (Fig. 2).

3. Results and discussion

Figure 2 schematically presents the conformation and the optical images of axially symmetric LC cells obtained under linearly polarized light. Notably, the shaded areas represent the dark areas in Figs. 2(a) and 2(b). Since the dichroic MR dyes absorb light strongly when the polarization of the probing light is parallel to the long axes of the MR dyes, the images in Figs. 2(a) and 2(b) are reasonable. Based on these images, Figs. 2(c), 2(e), and 2(d), 2(f) illustrate the structures of the axially symmetric radial and azimuthal DDLC cells, respectively.

As described above, the formation of LIRP structures is one of the key processes in causing an LC cell to have an axially symmetric, gradient distribution of LC pretilt angles. To verify the formation of the LIRSs of the dyes that are adsorbed on the substrates, a scanning electron microscope (SEM) was used to study the dye-adsorption morphology on the substrates in the radial and azimuthal DDLC cells. Figure 3
Fig. 3 Images of axially symmetric azimuthal cell under scanning electron microscope (SEM). Magnifications are (a) x 2500, (b) x 10000 (c) x 30000. Red dotted rectangles in insets are the observed areas on the azimuthal cell.
presents the LIRS that is formed by the adsorption of dye in an azimuthal cell (Fig. 2(b)) under various SEM magnifications. The spacing (ΛExp.) of the formed LIRS is around 345 nm, which is close to the theoretical value Λ = 349 nm, calculated using Λ~λ/n, where λ and n are the wavelength in a vacuum and the refractive index of the material, respectively [16

16. C.-R. Lee, T.-L. Fu, K.-T. Cheng, T.-S. Mo, and A. Y.-G. Fuh, “Surface-assisted photoalignment in dye-doped liquid-crystal films,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 69(3), 031704 (2004). [CrossRef] [PubMed]

]. The amplitude of LIRSs in the center clearly exceeds that at the periphery because the beam is more intense there. Similar observation (result not shown) was made of an axially symmetric radial sample. We elucidated the mechanism of formation of LIRSs in a DDLC cell elsewhere [16

16. C.-R. Lee, T.-L. Fu, K.-T. Cheng, T.-S. Mo, and A. Y.-G. Fuh, “Surface-assisted photoalignment in dye-doped liquid-crystal films,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 69(3), 031704 (2004). [CrossRef] [PubMed]

,18

18. A. Y.-G. Fuh, C.-K. Liu, K.-T. Cheng, C.-L. Ting, C.-C. Chen, P. C.-P. Chao, and H.-K. Hsu, “Variable liquid crystal pretilt angles generated by photoalignment in homeotropically aligned azo dye-doped liquid crystals,” Appl. Phys. Lett. 95(16), 161104 (2009). [CrossRef]

]. Briefly, it is believed that the LIRS formation is associated with the interference between the incoming polarized laser beam and the wave that is scatted by the adsorbed dyes on the surface. In this investigation, the excited azo dyes undergo trans–cis isomerization and molecular reorientation, and are then adsorbed onto the two substrate surfaces (double-side photo-alignment) forming LIRSs that exert the aligning force on LC molecules [6

6. L.-C. Lin, H.-C. Jau, T.-H. Lin, and A. Y.-G. Fuh, “Highly efficient and polarization-independent Fresnel lens based on dye-doped liquid crystal,” Opt. Express 15(6), 2900–2906 (2007). [CrossRef] [PubMed]

,15

15. S.-W. Ko, Y.-Y. Tzeng, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric liquid crystal devices based on double-side photo-alignment,” Opt. Express 16(24), 19643–19648 (2008). [CrossRef] [PubMed]

].

Throughout the photo-isomerization, the pump laser irradiates the sample as the sample is rotated about the z-axis. The illumination is stronger in the center of the beam than at the periphery. The axially symmetric photoalignment exerts a gradient aligning force on the LCs along the surface on the substrates, resulting in the gradient pretilt angle distributions that are shown in Figs. 2(e) and 2(f).

To fabricate an axially symmetric radial (azimuthal) LC cell with an LIRS, the polarization angle of the pumping beam was set to θ = 90° (θ = 0°) with polarization along the y-axis, as shown in Fig. 1. As described above, since the sample was rotated and thermally controlled at a fixed temperature, the excited dyes underwent trans–cis isomerization, molecular reorientation, diffusion and, then adsorption onto the two ITO surfaces, finally forming the LIRSs. The double-side photoalignment forms LIRSs, and causes the formation of axially-symmetric radial and azimuthal LC cells, shown in Figs. 2(a) and 2(b), respectively. The optical properties of the central areas of these axially symmetric LC samples were the same as those observed elsewhere [15

15. S.-W. Ko, Y.-Y. Tzeng, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric liquid crystal devices based on double-side photo-alignment,” Opt. Express 16(24), 19643–19648 (2008). [CrossRef] [PubMed]

,19

19. Y.-Y. Tzeng, S.-W. Ke, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric polarization converters based on photo-aligned liquid crystal films,” Opt. Express 16(6), 3768–3775 (2008). [CrossRef] [PubMed]

]. The main difference between the present axially symmetric LC samples with those described elsewhere studies [15

15. S.-W. Ko, Y.-Y. Tzeng, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric liquid crystal devices based on double-side photo-alignment,” Opt. Express 16(24), 19643–19648 (2008). [CrossRef] [PubMed]

,19

19. Y.-Y. Tzeng, S.-W. Ke, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric polarization converters based on photo-aligned liquid crystal films,” Opt. Express 16(6), 3768–3775 (2008). [CrossRef] [PubMed]

] is that the formed LIRSs align the LC molecules parallel to the direction of polarization of pumping light, because the aligning force of LC molecules is provided by the microgrooves of LIRSs, which are parallel to the polarization direction of pumping light [16

16. C.-R. Lee, T.-L. Fu, K.-T. Cheng, T.-S. Mo, and A. Y.-G. Fuh, “Surface-assisted photoalignment in dye-doped liquid-crystal films,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 69(3), 031704 (2004). [CrossRef] [PubMed]

,18

18. A. Y.-G. Fuh, C.-K. Liu, K.-T. Cheng, C.-L. Ting, C.-C. Chen, P. C.-P. Chao, and H.-K. Hsu, “Variable liquid crystal pretilt angles generated by photoalignment in homeotropically aligned azo dye-doped liquid crystals,” Appl. Phys. Lett. 95(16), 161104 (2009). [CrossRef]

], while the studies in Refs. [15

15. S.-W. Ko, Y.-Y. Tzeng, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric liquid crystal devices based on double-side photo-alignment,” Opt. Express 16(24), 19643–19648 (2008). [CrossRef] [PubMed]

,19

19. Y.-Y. Tzeng, S.-W. Ke, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric polarization converters based on photo-aligned liquid crystal films,” Opt. Express 16(6), 3768–3775 (2008). [CrossRef] [PubMed]

]. are associated with less illumination dosage of pumping laser on the sample resulting in the dye adsorption without forming a ripple structure on the substrates. The LC molecules are aligned parallel to the adsorbed dye direction, which is perpendicular to the pump-beam polarization.

The transmittances of the axially symmetric DDLC films were measured at various positions under various applied voltages, to determine the relationship between the phase retardation, ψ, of the device at various points with the applied voltage. Here, position x is the distance of a point from the center of the irradiated DDLC area. The measurements were made using an He-Ne laser (λ = 634 nm) with the cell placed between two crossed polarizers. The angle made by the polarizer axis and the projection of the LC director onto the substrate surface was 45°. Figure 4
Fig. 4 Measured phase retardations of an (a) radial and (b) azimuthal axially symmetric DDLC cell with a gradient pretilt angle.
plots the ψ-x curves obtained under various applied voltages. Figure 4 clearly reveals that the phase retardation of an axially symmetric cell peaks at the center of the beam, and decreases towards the perimeter of the beam indicating a gradient pretilt-angle distribution across the beam [18

18. A. Y.-G. Fuh, C.-K. Liu, K.-T. Cheng, C.-L. Ting, C.-C. Chen, P. C.-P. Chao, and H.-K. Hsu, “Variable liquid crystal pretilt angles generated by photoalignment in homeotropically aligned azo dye-doped liquid crystals,” Appl. Phys. Lett. 95(16), 161104 (2009). [CrossRef]

]. The phase retardation decreases as the voltage increases because LCs (Δε>0) align with their long axes parallel to the electrical field when a voltage is applied.

The gradient phase retardation has a focusing effect. Two orthogonally oriented LC layers with gradient distribution alignment have been shown to produce a polarization-independent lens if the phase modulations of the two films are identical [20

20. Y. H. Lin, H. Ren, Y. H. Wu, Y. Zhao, J. Fang, Z. Ge, and S.-T. Wu, “Polarization-independent liquid crystal phase modulator using a thin polymer-separated double-layered structure,” Opt. Express 13(22), 8746–8752 (2005). [CrossRef] [PubMed]

,21

21. H. Ren, Y. H. Lin, and S. T. Wu, “Polarization-independent and fast-response phase modulators using double-layered liquid crystal gels,” Appl. Phys. Lett. 88(6), 061123–061125 (2006). [CrossRef]

]. To demonstrate a polarization-independent LC lens, radial and azimuthal symmetric cells with orthogonal directors were stacked together, as shown in Fig. 5
Fig. 5 Unpolarized light incident onto a LC lens based on stacked radial axially symmetric DDLC cells.
.

The properties of the formed polarization-independent liquid crystal lens were measured using the setup that is shown in Fig. 6
Fig. 6 Setup for measuring properties of polarization-independent liquid crystal lens device. (Cells A and B are radial and azimuthal, respectively.)
. A rotatable analyzer was placed behind a polarizer and a λ/4 plate to produce circularly polarized light and change the polarization of the probing beam that is incident onto the lens. AC voltages Va and Vb (square waveform; 1 KHz) were applied to the radially (sample A) and azimuthally (sample B) symmetric cells, respectively to equalize the phase retardations that they caused. Figure 7
Fig. 7 Focal intensities of transmitted light are measured at under various operating conditions using a rotating analyzer.
presents the measurements of the relationship between the analyzer-axis angle (ωo) and the focal intensity under various measuring conditions. Triangular data points represent the intensity of a probing beam that does not propagate through the lens. Rhombus and square points represent the focal intensities when voltages Va = 1.3 V, Vb = 0 V, and Va = 10 V, Vb = 10 V, respectively, are applied. The results are quite consistent with the phase-retardation distribution curves in Fig. 4. When Va = 1.3 V and Vb = 0 V, the phase retardations in the radial (A cell) and azimuthal cells (B cell) equal each other, and so the lens focuses the probing beam effectively, as revealed by rhombuses in Fig. 7. The focal intensities are independent of the analyzer angle, indicating that the lens is a polarization-independent liquid crystal lens. In this experiment, the focal length of the LC lens device is around 0.5 m. However, the effective focal length can be increased by increasing the applying voltage. Notably, the focal length of the lens without the application of a voltage can be varied by changing the pump-beam intensity distribution, since the distribution of the pump-beam intensity determines the LIRSs on the substrates, which affect the gradient LC pretilt distribution, and the intrinsic focal length of the lens. Notably, it is found that the MRs adsorbed on the ITO-coated glass substrates are stable. No change of the lens performance is observed, when the lens is further exposed to the green laser used in the present study. Yet, the performance may be slightly changed with the lens being probed in the green-blue spectrum range due to light absorption. In this case, we can resolve it simply by using a MR dye with no absorption in the visible.

4. Conclusion

In conclusion, a polarization-independent LC lens that is based on stacking radially and azimuthally symmetric cells with mutually orthogonal directors is demonstrated. These axially symmetric liquid crystal cells are fabricated from dye-doped liquid crystal cells by double-side photoalignment with LCs oriented with a gradient pretilt angle. The focal length of the polarization-independent liquid crystal lens can be controlled by applying various voltages. The numerical aperture (NA) of the present lens is ~0.035. To increase the NA value of the lens, we can simply use a laser having a large enough power. Additionally, the lens is simple to fabricate, and convenient to use. It therefore has great potential for practical applications.

Acknowledgments

This work is supported by the Advanced Optoelectronic Technology Center, National Cheng Kung University and the National Science Council of China (Taiwan) under contract NSC 98-2112-M-006-001-MY3.

References and links

1.

C. Bricot, M. Hareng, and E. Spitz, “Optical projection device and an optical reader incorporating this device,” U.S. patent 4,037,929 (1977).

2.

S. Sato, “Liquid-crystal lens-cells with variable focal length,” Jpn. J. Appl. Phys. 18(9), 1679–1684 (1979). [CrossRef]

3.

S. T. Kowel, D. S. Cleverly, and P. G. Kornreich, “Focusing by electrical modulation of refraction in a liquid crystal cell,” Appl. Opt. 23(2), 278–289 (1984). [CrossRef] [PubMed]

4.

W. W. Chan and S. T. Kowel, “Imaging performance of the liquid-crystal-adaptive lens with conductive ladder meshing,” Appl. Opt. 36(34), 8958–8969 (1997). [CrossRef]

5.

S. Sato, A. Sugiyama, and R. Sato, “Variable-focus liquid crystal Fresnel lens,” Jpn. J. Appl. Phys. 24(Part 2, No. 8), L626–L628 (1985). [CrossRef]

6.

L.-C. Lin, H.-C. Jau, T.-H. Lin, and A. Y.-G. Fuh, “Highly efficient and polarization-independent Fresnel lens based on dye-doped liquid crystal,” Opt. Express 15(6), 2900–2906 (2007). [CrossRef] [PubMed]

7.

H. Ren and S.-T. Wu, “Tunable electronic lens using a gradient polymer network liquid crystal,” Appl. Phys. Lett. 82(1), 22–24 (2003). [CrossRef]

8.

Y.-H. Fan, H. Ren, and S.-T. Wu, “Switchable Fresnel lens using polymer-stabilized liquid crystals,” Opt. Express 11(23), 3080–3086 (2003). [CrossRef] [PubMed]

9.

H. Ren, Y.-H. Fan, S. Gauza, and S.-T. Wu, “Tunable-focus cylindrical liquid crystal lens,” Jpn. J. Appl. Phys. 43(2), 652–653 (2004). [CrossRef]

10.

M. Ye and S. Sato, “Optical properties of liquid crystal lens of any size,” Jpn. J. Appl. Phys. 41(Part 2, No. 5B), L571–L573 (2002). [CrossRef]

11.

A. F. Naumov, M. Yu. Loktev, I. R. Guralnik, and G. Vdovin, “Liquid-crystal adaptive lenses with modal control,” Opt. Lett. 23(13), 992–994 (1998). [CrossRef]

12.

I. R. Gural’nik and S. A. Samagin, “Optically controlled spherical liquid-crystal lens: theory and experiment,” Quantum Electron. 33(5), 430–434 (2003). [CrossRef]

13.

W.-Y. Wu, C.-C. Wang, and A. Y. Fuh, “Controlling pre-tilt angles of liquid crystal using mixed polyimide alignment layer,” Opt. Express 16(21), 17131–17137 (2008). [CrossRef] [PubMed]

14.

J. Y. L. Ho, V. G. Chigrinov, and H. S. Kwok, “Variable liquid crystal pretilt angles generated by photoalignment of a mixed polyimide alignment layer,” Appl. Phys. Lett. 90(24), 243506 (2007). [CrossRef]

15.

S.-W. Ko, Y.-Y. Tzeng, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric liquid crystal devices based on double-side photo-alignment,” Opt. Express 16(24), 19643–19648 (2008). [CrossRef] [PubMed]

16.

C.-R. Lee, T.-L. Fu, K.-T. Cheng, T.-S. Mo, and A. Y.-G. Fuh, “Surface-assisted photoalignment in dye-doped liquid-crystal films,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 69(3), 031704 (2004). [CrossRef] [PubMed]

17.

D. W. Berreman, “Solid Surface Shape and the Alignment of an Adjacent Nematic Liquid Crystal,” Phys. Rev. Lett. 28(26), 1683–1686 (1972). [CrossRef]

18.

A. Y.-G. Fuh, C.-K. Liu, K.-T. Cheng, C.-L. Ting, C.-C. Chen, P. C.-P. Chao, and H.-K. Hsu, “Variable liquid crystal pretilt angles generated by photoalignment in homeotropically aligned azo dye-doped liquid crystals,” Appl. Phys. Lett. 95(16), 161104 (2009). [CrossRef]

19.

Y.-Y. Tzeng, S.-W. Ke, C.-L. Ting, A. Y.-G. Fuh, and T.-H. Lin, “Axially symmetric polarization converters based on photo-aligned liquid crystal films,” Opt. Express 16(6), 3768–3775 (2008). [CrossRef] [PubMed]

20.

Y. H. Lin, H. Ren, Y. H. Wu, Y. Zhao, J. Fang, Z. Ge, and S.-T. Wu, “Polarization-independent liquid crystal phase modulator using a thin polymer-separated double-layered structure,” Opt. Express 13(22), 8746–8752 (2005). [CrossRef] [PubMed]

21.

H. Ren, Y. H. Lin, and S. T. Wu, “Polarization-independent and fast-response phase modulators using double-layered liquid crystal gels,” Appl. Phys. Lett. 88(6), 061123–061125 (2006). [CrossRef]

OCIS Codes
(160.3710) Materials : Liquid crystals
(220.1140) Optical design and fabrication : Alignment
(220.3630) Optical design and fabrication : Lenses

ToC Category:
Optical Design and Fabrication

History
Original Manuscript: November 15, 2010
Revised Manuscript: December 25, 2010
Manuscript Accepted: January 16, 2011
Published: January 24, 2011

Virtual Issues
Vol. 6, Iss. 2 Virtual Journal for Biomedical Optics

Citation
Andy Y.-G. Fuh, Shih-Wei Ko, Shu-Hao Huang, Yan-Yu Chen, and Tsung-Hsien Lin, "Polarization-independent liquid crystal lens based on axially symmetric photoalignment," Opt. Express 19, 2294-2300 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-3-2294


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References

  1. C. Bricot, M. Hareng, and E. Spitz, “Optical projection device and an optical reader incorporating this device,” U.S. patent 4,037,929 (1977).
  2. S. Sato, “Liquid-crystal lens-cells with variable focal length,” Jpn. J. Appl. Phys. 18(9), 1679–1684 (1979). [CrossRef]
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