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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 6 — Mar. 14, 2011
  • pp: 5500–5510
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Time-domain analysis of optically controllable biphotonic gratings in azo-dye-doped cholesteric liquid crystals

Hui-Chen Yeh  »View Author Affiliations


Optics Express, Vol. 19, Issue 6, pp. 5500-5510 (2011)
http://dx.doi.org/10.1364/OE.19.005500


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Abstract

This study investigated optically controllable biphotonic gratings (BGs) in azo-dye-doped cholesteric liquid crystals. The BGs were formed under the illumination of one green beam with the simultaneous irradiation of an interference field generated by two coherent red beams. This study ascribes the formation of the BGs to the green-beam-induced dye reorientation and elongation of the helical pitch through trans-cis isomerization and red-beam-induced suppression of dye reorientation and elongation of the helical pitch by cis-trans back isomerization. The diffraction characteristics strongly depended on the helical pitch of the cholesteric structure, the polarization state of the probe beam, and the relative intensity of the green and red beams. Application of the finite-difference time-domain method demonstrated that the model of photoinduced distortion of the cholesteric liquid crystal structure satisfactorily explains this dependence.

© 2011 OSA

1. Introduction

Photochromic materials have been attracting considerable attention for their potential application in all optical devices associated with the control of molecular alignment in liquid crystal (LC) phases [1

1. K. Ichimura, “Photoalignment of liquid-crystal systems,” Chem. Rev. 100(5), 1847–1874 (2000). [CrossRef]

,2

2. T. Ikeda, “Photomodulation of liquid crystal orientations for photonic applications,” J. Mater. Chem. 13(9), 2037–2057 (2003). [CrossRef]

]. Azobenzene is a representative photochromic molecule using light-induced molecular reorientation through photoactivated isomerization [3

3. W. M. Gibbons, P. J. Shannon, S. T. Sun, and B. J. Swetlin, “Surface-mediated alignment of nematic liquid crystals with polarized laser light,” Nature 351(6321), 49–50 (1991). [CrossRef]

,4

4. T. V. Galstyan, B. Saad, and M. M. Denariez-Roberge, “Excitation transfer from azo dye to nematic host during photoisomerization,” J. Chem. Phys. 107(22), 9319–9325 (1997). [CrossRef]

]. Photoexcited azobenzene undergoes a reversible conformational transformation between trans-longitudinal and unstable cis-excited isomers [5

5. Y. Yu and T. Ikeda, “Alignment modulation of azobenzene-containing liquid crystal systems by photochemical reactions,” J. Photochem. Photobiol. C 5(3), 247–265 (2004). [CrossRef]

,6

6. Y. J. Wang and G. O. Carlisle, “Optical properties of disperse-red-1-doped nematic liquid crystal,” J. Mater. Sci. Mater. Electron. 13(3), 173–178 (2002). [CrossRef]

]. Repetition of the trans-cis-trans isomerization cycles may lead to changes in the chemical and physical properties of azo-dye-doped liquid crystals, such as the order of orientation, molecular orientation, and LC-isotropic phase transition temperature.

2. Experiments

2.1. Sample preparation and experimental setup

The experimental setup is schematically illustrated in Fig. 1
Fig. 1 Schematic illustration of the biphotonic gratings in azo-dye-doped cholesteric liquid crystal films. (a) The photoinduced variations in the CLC structure created by one s-polarized green beam and two coherent s-polarized red beams. (b) The intensity distribution of the interference field along the x axis.
. Two s-polarized coherent red beams from a He-Ne laser with an operating wavelength of 633 nm were used as a pump laser to create a spatially intensity-modulated interference field. The two pump beams with equal intensity intersected on the cell at an angle of 2.84° in air, resulting in a grating period Λ of approximately 12.8 μm. The normalized intensity distribution of the interference field along the x axis is:
I(x)=cos2(πxΛ).
(1)
One s-polarized green beam derived from an Ar+ laser with an operating wavelength of 514 nm impinged simultaneously on the interference region. The bright region of the red interference field was called “region R”, and the dark region “region G”. The diffraction properties of the induced BGs were probed using a He-Ne laser with a wavelength of 633 nm and an intensity of 1mW/cm2 at normal incidence. To characterize the BGs, the polarization state of the probe beam was varied using a quarter- or half-wave plate.

2.2. Results

The present study revealed that the diffraction performance of the BGs depended heavily on the polarization state of the probe beam and relative intensity of the green and red beams. Figure 2
Fig. 2 Dependence of the first order diffraction efficiency on the intensity of the green beam for sample 1 probed using left-handed circularly (LHC)-, s-, p- and right-handed circularly (RHC)-polarized beams. The intensity of each red pump beam is 909 mW/cm2.
illustrates the variations in the first order diffraction efficiency of BGs with the intensity of the green beam for sample 1 using four polarization states of the probe beam.

In the Bragg condition, the left-handed circularly (LHC) polarized beam transmitted through the right-handed CLC. The reflection band of sample 1 was in the infrared region; therefore, the transmittance under different handedness of the probe beam was nearly equal before illumination with the green beam. However, diffraction performance clearly differed following the formation of the BGs. To investigate the polarization dependent properties, BGs were created based on sample 2 and variations in the texture of the CLC on photoirradiation were inferred according to the spectral characteristics measured using a spectrometer for the visible region (Ocean Optics USB4000). The wavelength of the probe beam was out of the reflection band of sample 2. As with sample 1, the transmittance for different handedness of the probe beam was nearly equal before illumination with the green beam. Figure 3
Fig. 3 Dependences of the first order diffraction efficiency on the intensity of the green beam for sample 2, probed using LHC-, s-, p- and RHC-polarized beams. The intensity of each red pump beam is (a) 909 mW/cm2 and (b) 340 mW/cm2.
illustrates the diffraction properties of sample 2 versus the intensity of the green beam for four polarization states of the probe beam under varying intensities of red pump beams.

BGs were formed by green-beam-induced dye reorientation through trans-cis isomerization in the dark regions (region G) of the red interference field and by red-beam-induced suppression of dye reorientation via cis-trans back isomerization in the bright regions (region R) [16

16. H. C. Yeh, G. H. Chen, C. R. Lee, and T. S. Mo, “Optically switchable biphotonic gratings based on dye-doped cholesteric liquid crystal films,” Appl. Phys. Lett. 90(26), 261103 (2007). [CrossRef]

,21

21. M. R. Lee, J. R. Wang, C. R. Lee, and A. Y. G. Fuh, “Optically switchable biphotonic photorefractive effect in dye-doped liquid crystal films,” Appl. Phys. Lett. 85(24), 5822–5824 (2004). [CrossRef]

,22

22. C. R. Lee, T. S. Mo, K. T. Cheng, T. L. Fu, and A. Y. G. Fuh, “Electrically switchable and thermally erasable biphotonic holographic gratings in dye-doped liquid crystal films,” Appl. Phys. Lett. 83(21), 4285–4287 (2003). [CrossRef]

]. An increase in the intensity of the green beam resulted in an increase in distortion and thus a greater difference between textures in the two regions, thereby increasing the first order diffraction efficiency [Fig. 3 (a)]. However, the first order diffraction efficiency declined when the red beams were too weak to suppress the strong green-beam-induced reorientation of the dyes and LCs in region R [Fig. 3(b)]. The Stokes parameters S 0, S 1, S 2, and S 3 were measured using the circular method [23

23. E. Collett, Polarized Light: Fundamentals and Applications (Dekker, 1993).

] to determine the polarization state of the first order diffracted beam. Figure 4
Fig. 4 Dependence of the normalized Stokes parameters of the first order diffracted beam versus the intensity of the green beam for (i) LHC-, (ii) s-, (iii) p-, and (iv) RHC-polarized probe beams. The filled and open symbols represent the experimental and simulation results, respectively. The intensity of each red pump beam is (a) 909 mW/cm2 and (b) 340 mW/cm2.
illustrates the measured normalized Stokes parameters S 1,2,3’ = S 1,2,3/S 0 of the first order diffracted beam of the BGs versus the intensity of the green beam.

3. FDTD analysis

3.1. FDTD algorithm for periodic anisotropic structures

The FDTD method is a powerful approach to solve Maxwell’s time-dependent curl equations, used to govern the propagation of light waves. For sourceless nonmagnetic anisotropic media, discrete expressions of electric and magnetic fields in Maxwell’s equations can be approximated using the central difference scheme based on the Yee grid [24

24. K. S. Yee, “Numerical solutions of initial boundary value problems involving Maxwell’s equations in isotropic media,” IEEE Trans. Antenn. Propag. AP-14, 302–307 (1966).

] as follows:
En=En1+Δtε0ε˜1×Hn1/2
(2)
and
Hn+1/2=Hn1/2Δtμ0×En
(3)
where n represents the time points, Δt is the time step, and ε˜1 is the inverse of the spatially varying relative permittivity tensor. For a uniaxial LC medium, the relative permittivity tensor ε˜is written in the xyz coordinate system as:
ε˜=[εxxεxyεxzεyxεyyεyzεzxεzyεzz]
(4)
with [25

25. A. Lien, “Extended Jones matrix representation for the twisted nematic liquid crystal display at oblique incidence,” Appl. Phys. Lett. 57(26), 2767–2769 (1990). [CrossRef]

]
εxx=no2+(ne2no2)cos2θcos2φεxy=εyx=(ne2no2)cos2θsinφcosφεxz=εzx=(ne2no2)cosθsinθcosφεyy=no2+(ne2no2)cos2θsin2φεyz=εzy=(ne2no2)cosθsinθsinφεzz=no2+(ne2no2)sin2θ
where no and ne are the ordinary and extraordinary refractive indices, θ is the tilt angle between the LC director and the surface of the substrate (xy-plane), and ϕ is the twist angle between the projection of the LC director on the xy-plane and the x axis. In the CLC structure, the twist angle ϕ = 2πz/P, where P is the helical pitch. Once ε˜ is defined at every grid point within the computational space, the sequence of light propagation in the structure can proceed, ruled by the time updating algorithm from Maxwell’s equations.

The present study implemented the FDTD method in a two-dimensional (2D) computational space. Even though the problem was reduced to a 2D structure, all components of electric and magnetic fields should be considered due to the coupling between all field components induced by the anisotropy of the media. To suppress artificial reflections, the computational space was terminated using two Berenger’s perfectly matched layers (PMLs) normal to the z-axis. Transverse direction boundaries were truncated by imposing Bloch periodic boundary conditions, in consideration of the periodic structure. The incident plane wave was launched into the computational space based on the total-field/scattered-field technique. Dual-time excitation was utilized to define the polarization of the input continuous wave. Transforming the calculated near-field results at the exit face of the device to far-field provided far-field information. The far-field diffraction of gratings yielded discrete diffracted orders, corresponding to the Fourier series of the field distribution across an infinitely periodic structure [26

26. E. Hecht, Optics (Addison Wesley, 2002). [PubMed]

]. With normal incidence, the diffraction angle θm of the m th-order maximum was determined using the diffraction equation
Λsinθm=mλ
(5)
where λ is the wavelength of incident light and Λ is the grating period. Far-field optical disturbance was obtained using the vectorial Fourier transform of the near-fields Ex,y,z along the near-field collection line, spanning the extent of the grating period immediately following the structure, as follows [27

27. C. Oh and M. J. Escuti, “Time-domain analysis of periodic anisotropic media at oblique incidence: an efficient FDTD implementation,” Opt. Express 14(24), 11870–11884 (2006). [CrossRef] [PubMed]

]:
E//m(t)=1Λ0Λ[Ex(t,x)cosθmEz(t,x)sinθm]exp(j2πmΛx)dx
(6)
Em(t)=1Λ0ΛEy(t,x)exp(j2πmΛx)dx
(7)
where E//m and Em denote the far-field components of the m th-order diffraction beam parallel and perpendicular to the 2D computational space, respectively. The intensity of the m th-order diffracted beam was proportional to the time-averaged value of the square of the instantaneous electric field over an interval T equal to one period [26

26. E. Hecht, Optics (Addison Wesley, 2002). [PubMed]

]:
Im=1TtT/2t+T/2c2ε0(|E//m(t)|2+|Em(t)|2)dt.
(8)
Diffraction efficiency was calculated as the ratio of the intensity of the m th-order diffracted beam to the total intensity of the transmitted light.

3.2. Simulation results and discussion

The FDTD method was adopted for optical wave calculations due to the transverse variation in the structure of BGs, for which the stratified medium approach was inadequate. To clarify the LC director configuration under photoirradiation and define the permittivity tensor for the FDTD implementation, the spectral characterization was measured. Figure 5
Fig. 5 Transmission spectra of sample 2 with varying intensities of the green beam (a) at the initiation of excitation and (b) in photostationary equilibrium (approximately 3 min of irradiation).
illustrates the transmission spectra of sample 2 under irradiation using various intensities of the green beam. Following the initiation of excitation, variations in the reflection band at the long-wavelength edge were clearer than those of the reflection band at the short-wavelength edge [Fig. 5(a)], due to the photoinduced tilt of the director in the CLC medium toward the z axis, confirmed by implementing FDTD calculations. Similar to an electric field [28

28. W. Greubel, “Bistability behavior of texture in cholesteric liquid crystals in an electric field,” Appl. Phys. Lett. 25(1), 5–7 (1974). [CrossRef]

], the tilt angle of the LC director in the photoinduced distorted structure was zero at the inner surfaces of the two glass plates due to the boundary conditions, reaching its maximum θm, the midlayer tilt angle, at the center of the cell. The photoinduced θm depended on the intensity of the green beam and the electric-field-induced θm depended on the strength of the applied field. With an increase in irradiation time, the reflection band redshifted and the bandwidth shortened [Fig. 5(b)], indicating an elongation in the pitch of the CLC and a decrease in the birefringence of LC caused by photoisomerization and the concomitant thermal effect [15

15. H. C. Yeh, G. H. Chen, C. R. Lee, and T. S. Mo, “Photoinduced two-dimensional gratings based on dye-doped cholesteric liquid crystal films,” J. Chem. Phys. 127(14), 141105 (2007). [CrossRef] [PubMed]

]. Figure 6
Fig. 6 The effects of photoirradiation on (a) the midlayer tilt angle θm, (b) the helical pitch P, and the birefringence Δn in the inset for sample 2. The green diamonds correspond to the results fitting the transmission spectra in Fig. 5 under irradiation with the green beam. The blue and red diamonds correspond to the results fitting the first order diffraction efficiencies in Figs. 3(a) and 3(b), respectively.
demonstrates the effects of photoirradiation on the midlayer tilt angle θm, the helical pitch P, and the birefringence Δn for sample 2.

Midlayer tilt angles were first calculated by fitting the transmission spectra in Fig. 5(a), assuming no variation in the helical pitch and the refractive indices at the beginning of excitation. These results were used to determine the helical pitches and refractive indices by fitting the transmission spectra in Fig. 5(b), assuming that the midlayer tilt angles in the photostationary equilibrium were the same as the midlayer tilt angles at the beginning of excitation. The calculated midlayer tilt angle, the helical pitch, and the birefringence under irradiation with the green beam were used to calculate the relative permittivity tensor ε˜ in the center of region G of the BGs. To obtain the configuration of the LC director in region R of the BGs, the midlayer tilt angle and the helical pitch in the center of region R were calculated by fitting the experimental diffraction efficiencies in Fig. 3. The refractive indices ne and no in region R were assumed to be the same as the indices in region G due to heat diffusion. The geometry of the FDTD simulation is schematically illustrated in Fig. 7
Fig. 7 (a) Schematic layout of the two-dimensional FDTD simulation space. (b) The tilt angle θ of the LC director along the z axis. (c) The midlayer tilt angle θm along the x axis in one spatial period. θmR and θmG correspond to the midlayer tilt angle in the centers of regions R and G, respectively.
. For simplicity, the ITO contacts were assumed to possess the optical behavior of the glass substrate. Table 1

Table 1. Overview of FDTD Simulation Parameters

table-icon
View This Table
summarizes the numerical parameters used for the simulation.

The tilt angle distribution along the z axis was set as a sinusoidal function under irradiation subject to boundary conditions and electrostatic energy density. The midlayer tilt angle θm and the helical pitch P, modulated by the intensity distribution of the red interference field along the x axis, were approximated as:
θm(x)=θmR+(θmGθmR)sin(πxΛ)
(9)
P(x)=PR+(PGPR)sin2(πxΛ)
(10)
where θmR and θmG correspond to the midlayer tilt angles in the centers of regions R and G, respectively. PR and PG correspond to the pitches. Differences in the structure between regions R and G increased with an increase in the intensity of the green beam. Differences in the structure between regions R and G diminished under a red pump beam of low intensity when the red beams were unable to suppress the effects of the strong green beam on the structure of the CLC (Fig. 6). The results support the proposed model for the formation of the BGs [16

16. H. C. Yeh, G. H. Chen, C. R. Lee, and T. S. Mo, “Optically switchable biphotonic gratings based on dye-doped cholesteric liquid crystal films,” Appl. Phys. Lett. 90(26), 261103 (2007). [CrossRef]

]. To examine the configuration of the simulated LC director, the Stokes parameters of the first order diffracted beam were calculated and plotted in Fig. 4. The calculated results are in good agreement with the experimental data.

Figure 8
Fig. 8 Calculated development of (i) the x component, (ii) the y component, and (iii) the z component of the electric field at the near-field collection line in one temporal period for (a) LHC-, (b) s-, (c) p-, and (d) RHC-polarized probe beams with the same intensity. The intensities of the red and green beams forming BGs are 909 mW/cm2 and 306 mW/cm2, respectively. Axes x and t are scaled in the grid spacing Δx and the time step Δt, respectively.
illustrates the calculated development of the electric field at the near-field collection line in one temporal period for four types of polarization of the probe beam. The instantaneous electric fields Ex and Ey along the x axis were modulated most deeply for the LHC polarized probe beam, resulting in the highest first order diffraction efficiency for the LHC polarized probe beam among the four types of polarization under the same excitation conditions. To better understand the physical mechanisms involved, Fig. 9
Fig. 9 Polarization of the transmitted light at the centers of regions R (red lines) and G (green lines) for (a) LHC-, (b) s-, (c) p-, and (d) RHC-polarized probe beams. The asterisks indicate the electric fields at the beginning of the temporal period.
depicts the polarization of the transmitted light at the centers of regions R and G for four types of polarization of the incident beam. The electric fields of the incident beams are represented as:
s:Ey=cosωt
(11)
p:Ex=sinωt
(12)
LHC:Ex=sinωt,Ey=cosωt
(13)
RHC:Ex=sinωt,Ey=cosωt
(14)
where ω is the angular temporal frequency. Due to optical activity [29

29. P. G. de Gennes and J. Prost, The Physics of Liquid Crystals (Oxford Science, 1993).

], the polarization of a linearly polarized beam passing through the CLC rotates through an angle [Figs. 9(b) and 9(c)]. The incident circularly polarized beams are regarded as the superposition of p- and s-polarized beams. According to the principle of superposition, the corresponding outgoing light [Figs. 9(a) and 9(d)] of LHC- and RHC-polarized beams are the subtraction and addition of the corresponding outgoing light [Figs. 9(c) and 9(b)] of p- and s-polarized beams, respectively. These results indicate that the LHC-polarized beam exhibited a greater difference in amplitude between the centers of regions R and G than the RHC-polarized beam did. Because the optical rotatory power is pitch dependent [29

29. P. G. de Gennes and J. Prost, The Physics of Liquid Crystals (Oxford Science, 1993).

], CLC samples with different helical pitches resulted in different rotation angles of linearly polarized beams through the CLCs, which in turn lead to differences in the diffraction performance for different polarization states of probe beam (Figs. 2 and 3).

4. Conclusion

The present study demonstrated optically controllable BGs based on ADDCLC cells, and analyzed the diffraction characteristics using the FDTD method. The BGs were formed under the illumination of one green beam with the simultaneous irradiation of an interference field generated by two coherent red beams. The green beam induced elongation of the helical pitch and dye reorientation in the direction of the wave vector via trans-cis isomerization and the red beams suppressed the elongation of the helical pitch and dye reorientation via cis-trans back isomerization in the dark and bright regions of the red interference field. The first order diffraction efficiency increased with an increase in the intensity of the green beam, but decreased when the red beams were unable to suppress dye reorientation induced by the strong green beam. Application of the FDTD algorithm demonstrated that the model of photoinduced distortion of the CLC structure explained the diffraction performance of the BGs well. The electric fields of LHC polarized probe beams in one spatial period were modulated most deeply with four polarized probe beams passing through the gratings. Therefore, the first order diffraction efficiency under the LHC polarized probe beam was the largest among the four polarized probe beams under the same excitation conditions.

Acknowledgments

The author would like to thank two anonymous reviewers and the editor for their comments.

References and links

1.

K. Ichimura, “Photoalignment of liquid-crystal systems,” Chem. Rev. 100(5), 1847–1874 (2000). [CrossRef]

2.

T. Ikeda, “Photomodulation of liquid crystal orientations for photonic applications,” J. Mater. Chem. 13(9), 2037–2057 (2003). [CrossRef]

3.

W. M. Gibbons, P. J. Shannon, S. T. Sun, and B. J. Swetlin, “Surface-mediated alignment of nematic liquid crystals with polarized laser light,” Nature 351(6321), 49–50 (1991). [CrossRef]

4.

T. V. Galstyan, B. Saad, and M. M. Denariez-Roberge, “Excitation transfer from azo dye to nematic host during photoisomerization,” J. Chem. Phys. 107(22), 9319–9325 (1997). [CrossRef]

5.

Y. Yu and T. Ikeda, “Alignment modulation of azobenzene-containing liquid crystal systems by photochemical reactions,” J. Photochem. Photobiol. C 5(3), 247–265 (2004). [CrossRef]

6.

Y. J. Wang and G. O. Carlisle, “Optical properties of disperse-red-1-doped nematic liquid crystal,” J. Mater. Sci. Mater. Electron. 13(3), 173–178 (2002). [CrossRef]

7.

H. Choi, J. W. Wu, H. J. Chang, and B. Park, “Holographically generated twisted nematic liquid crystal gratings,” Appl. Phys. Lett. 88(2), 021905 (2006). [CrossRef]

8.

S. P. Gorkhali, S. G. Cloutier, G. P. Crawford, and R. A. Pelcovits, “Stable polarization gratings recorded in azo-dye-doped liquid crystals,” Appl. Phys. Lett. 88(25), 251113 (2006). [CrossRef]

9.

T. Sasaki, H. Ono, and N. Kawatsuki, “Three-dimensional vector holograms in anisotropic photoreactive liquid-crystal composites,” Appl. Opt. 47(13), 2192–2200 (2008). [CrossRef] [PubMed]

10.

C. Y. Huang, H. Y. Tsai, Y. H. Wang, C. M. Huang, K. Y. Lo, and C. R. Lee, “Linear polarization rotators based on dye-doped liquid crystal cells,” Appl. Phys. Lett. 96(19), 191103 (2010). [CrossRef]

11.

F. Simoni and O. Francescangeli, “Effect of light on molecular orientation of liquid crystals,” J. Phys. Condens. Matter 11(41), R439–R487 (1999). [CrossRef]

12.

Y. J. Wang, M. Pei, and G. O. Carlisle, “Polarization-independent photochromic diffraction in a dye-doped liquid crystal,” Opt. Lett. 28(10), 840–842 (2003). [CrossRef] [PubMed]

13.

P. Yeh and C. Gu, Optics of Liquid Crystal Displays (Wiley, 1999).

14.

H. K. Lee, K. Doi, H. Harada, O. Tsutsumi, A. Kanazawa, T. Shiono, and T. Ikeda, “Photochemical modulation of color and transmittance in chiral nematic liquid crystal containing an azobenzene as a photosensitive chromophore,” J. Phys. Chem. B 104(30), 7023–7028 (2000). [CrossRef]

15.

H. C. Yeh, G. H. Chen, C. R. Lee, and T. S. Mo, “Photoinduced two-dimensional gratings based on dye-doped cholesteric liquid crystal films,” J. Chem. Phys. 127(14), 141105 (2007). [CrossRef] [PubMed]

16.

H. C. Yeh, G. H. Chen, C. R. Lee, and T. S. Mo, “Optically switchable biphotonic gratings based on dye-doped cholesteric liquid crystal films,” Appl. Phys. Lett. 90(26), 261103 (2007). [CrossRef]

17.

H. C. Yeh, J. D. Wang, K. C. Lo, C. R. Lee, T. S. Mo, and S. Y. Huang, “Optically controllable transflective spatial filter with high- and low-pass or notch- and band-pass functions based on a dye-doped cholesteric liquid crystal film,” Appl. Phys. Lett. 92(1), 011121 (2008). [CrossRef]

18.

T. Sasaki, A. Emoto, T. Shioda, and H. Ono, “Transmission and reflection phase gratings formed in azo-dye-doped chiral nematic liquid crystals,” Appl. Phys. Lett. 94(2), 023303 (2009). [CrossRef]

19.

S.-Y. Huang, Y.-S. Chen, H.-C. Jau, M.-S. Li, J.-H. Liu, P.-C. Yang, and A. Y.-G. Fuh, “Biphotonic effect-induced phase transition in dye-doped cholesteric liquid crystals and their applications,” Opt. Commun. 283(9), 1726–1731 (2010). [CrossRef]

20.

A. Taflove and S. C. Gedne, Computational Electrodynamics: The Finite-Difference Time-Domain Method (Artech House Inc., 2005).

21.

M. R. Lee, J. R. Wang, C. R. Lee, and A. Y. G. Fuh, “Optically switchable biphotonic photorefractive effect in dye-doped liquid crystal films,” Appl. Phys. Lett. 85(24), 5822–5824 (2004). [CrossRef]

22.

C. R. Lee, T. S. Mo, K. T. Cheng, T. L. Fu, and A. Y. G. Fuh, “Electrically switchable and thermally erasable biphotonic holographic gratings in dye-doped liquid crystal films,” Appl. Phys. Lett. 83(21), 4285–4287 (2003). [CrossRef]

23.

E. Collett, Polarized Light: Fundamentals and Applications (Dekker, 1993).

24.

K. S. Yee, “Numerical solutions of initial boundary value problems involving Maxwell’s equations in isotropic media,” IEEE Trans. Antenn. Propag. AP-14, 302–307 (1966).

25.

A. Lien, “Extended Jones matrix representation for the twisted nematic liquid crystal display at oblique incidence,” Appl. Phys. Lett. 57(26), 2767–2769 (1990). [CrossRef]

26.

E. Hecht, Optics (Addison Wesley, 2002). [PubMed]

27.

C. Oh and M. J. Escuti, “Time-domain analysis of periodic anisotropic media at oblique incidence: an efficient FDTD implementation,” Opt. Express 14(24), 11870–11884 (2006). [CrossRef] [PubMed]

28.

W. Greubel, “Bistability behavior of texture in cholesteric liquid crystals in an electric field,” Appl. Phys. Lett. 25(1), 5–7 (1974). [CrossRef]

29.

P. G. de Gennes and J. Prost, The Physics of Liquid Crystals (Oxford Science, 1993).

OCIS Codes
(000.4430) General : Numerical approximation and analysis
(050.1950) Diffraction and gratings : Diffraction gratings
(160.3710) Materials : Liquid crystals
(230.1150) Optical devices : All-optical devices

ToC Category:
Imaging Systems

History
Original Manuscript: January 19, 2011
Revised Manuscript: February 24, 2011
Manuscript Accepted: February 25, 2011
Published: March 9, 2011

Citation
Hui-Chen Yeh, "Time-domain analysis of optically controllable biphotonic gratings in azo-dye-doped cholesteric liquid crystals," Opt. Express 19, 5500-5510 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-6-5500


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References

  1. K. Ichimura, “Photoalignment of liquid-crystal systems,” Chem. Rev. 100(5), 1847–1874 (2000). [CrossRef]
  2. T. Ikeda, “Photomodulation of liquid crystal orientations for photonic applications,” J. Mater. Chem. 13(9), 2037–2057 (2003). [CrossRef]
  3. W. M. Gibbons, P. J. Shannon, S. T. Sun, and B. J. Swetlin, “Surface-mediated alignment of nematic liquid crystals with polarized laser light,” Nature 351(6321), 49–50 (1991). [CrossRef]
  4. T. V. Galstyan, B. Saad, and M. M. Denariez-Roberge, “Excitation transfer from azo dye to nematic host during photoisomerization,” J. Chem. Phys. 107(22), 9319–9325 (1997). [CrossRef]
  5. Y. Yu and T. Ikeda, “Alignment modulation of azobenzene-containing liquid crystal systems by photochemical reactions,” J. Photochem. Photobiol. C 5(3), 247–265 (2004). [CrossRef]
  6. Y. J. Wang and G. O. Carlisle, “Optical properties of disperse-red-1-doped nematic liquid crystal,” J. Mater. Sci. Mater. Electron. 13(3), 173–178 (2002). [CrossRef]
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