Abstract

We have analyzed the physical origins of the temperature gradient of the ordinary refractive index (dno / dT ) of liquid crystals. To achieve a large dno / dT , high birefringence and low clearing temperature play crucial roles. Based on these simple guidelines, we formulated two exemplary liquid crystal mixtures, designated as UCF-1 and UCF-2, and compared their physical properties with a commonly used commercial liquid crystal compound 5CB. The dno / dT of UCF-1 is ~4X higher than that of 5CB at room temperature.

© 2004 Optical Society of America

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References

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Appl. Opt. (1)

Appl. Phys. Lett. (1)

M. Peccianti, A. De Rossi, G. Assanto, A. De Luca, C. Umeton, and I.C. Khoo, �??Electrically assisted self-confinement and waveguiding in planar nematic liquid crystal cells,�?? Appl. Phys. Lett. 77, 7-9 (2000).
[CrossRef]

J. Appl. Phys. (2)

J. Li and S. T. Wu , �??Extended Cauchy equations for the refractive indices of liquid crystals,�?? J. Appl. Phys. 95, 896-901 (2004).
[CrossRef]

J. Li, S. Gauza, S. T. Wu, �??Temperature effect on liquid crystal refractive indices,�?? J. Appl. Phys. (July 1, 2004).

Jpn. J. Appl. Phys. Part 1 (1)

S. Gauza, H. Wang, C. H Wen, S. T. Wu, A. J. Seed and R. Dabrowski, �??High birefringence isothiocyanato tolane liquid crystals,�?? Jpn. J. Appl. Phys. Part 1, 42, 3463-3466 (2003).
[CrossRef]

Liq. Cryst. (1)

A. Spad�?o, R. Dabrowski, M. Filipowicz, Z. Stolarz, J. Przedmojski, S. Gauza, Y. H. Fan, S. T. Wu, �??Synthesis, mesomorphic and optical properties of isothiocyanatotolanes,�?? Liq. Cryst. 30, 191-198 (2003).
[CrossRef]

Mol. Cryst. Liq. Cryst. (1)

M. Warenghem, J. F. Henninot, F. Derrin, and G. Abbate, �??Thermal and orientational spatial optical solitons in dye-doped liquid crystals,�?? Mol. Cryst. Liq. Cryst. 373, 213-225 (2002).
[CrossRef]

Opt. Express (1)

Opt. Lett. (1)

Opt. Spektrosk. (1)

M. F. Vuks, �??Determination of the optical anisotropy of aromatic molecules from the double refraction of crystals,�?? Opt. Spektrosk. 20, 644-647 (1966).

Phys. Rev. A (1)

S. T. Wu, �??Birefringence dispersions of liquid crystals,�?? Phys. Rev. A 33, 1270-1274 (1986).
[CrossRef] [PubMed]

Prog. Solid State Chem. (1)

I. Haller, �??Thermodynamic and static properties of liquid crystals�?? Prog. Solid State Chem. 10, 103-110 (1975).
[CrossRef]

Other (5)

E. H. Stupp and M. S. Brennesholtz, Projection Displays (Wiley, New York, 1998).

S. T. Wu and D. K. Yang, Reflective Liquid Crystal Displays (Wiley, New York, 2001).

I. C. Khoo and S. T. Wu, Optics and Nonlinear Optics of Liquid Crystals (World Scientific, Singapore, 1993).
[CrossRef]

J. D. Jackson, Classical Electrodynamics (Wiley, New York, 1962).

L. Pohl and U. Finkenzeller, Liquid Crystals: Applications and Uses (World Scientific, Singapore, 1990), Chap. 4.

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Figures (5)

Fig. 1.
Fig. 1.

Temperature-dependent refractive indices of UCF-1 and 6CB at λ=589 nm. Red circles and black triangles are refractive indices of UCF-1 and 6CB, respectively. Solid lines are fittings using Eqs. (9a) and (9b). The fitting parameters are listed in Table 3.

Fig. 2.
Fig. 2.

Temperature-dependent refractive indices of UCF-2 and 5CB at λ=589 nm. Magenta circles and blue triangles are refractive indices of UCF-2 and 5CB, respectively, and solid lines are fitting results using Eq. (9). The fitting parameters are listed in Table 3.

Fig. 3.
Fig. 3.

Temperature-dependent average refractive index of UCF-1, UCF-2, 6CB and 5CB at λ=589 nm. Circles represent experimental data and solid lines are fitting results using Eq. (6). The fitting parameters A and B for these four materials are listed in Table 3.

Fig. 4.
Fig. 4.

Temperature-dependent birefringence of UCF-1, UCF-2, 6CB and 5CB at λ=589 nm. Red, Magenta, black and blue circles represent experimental data while solid lines are fitting results using Eq. (8). The fitting parameters (∆n)o and β are listed in Table 3.

Fig. 5.
Fig. 5.

Temperature-dependent dno /dT of UCF-1, UCF-2, 6CB, 5CB, and 5PCH at λ=589 nm. Red, magenta, black, blue and green solid lines represent the calculated dno /dT curves for UCF-1, UCF-2, 6CB, 5CB, and 5PCH, respectively, while the dashed lines represent the calculated -dno /dT curves. The parameters B, (∆n) e and β used in the calculations are listed in Table 3.

Tables (3)

Tables Icon

Table 1. Molecular structures and phase transition temperatures (PTT) of the compounds used for formulating mixtures. Here, Cr, N, S and I stand for crystalline, nematic, smectic, and isotropic phase, respectively.

Tables Icon

Table 2. Physical properties of UCF-1 and UCF-2. ∆n was measured at λ=589 nm and T=23 °C.

Tables Icon

Table 3. Fitting parameters for the average refractive index <n> and birefringence (∆n) of the five LCs studied: UCF-1, 6CB, UCF-2, 5CB and 5PCH at λ=589 nm.

Equations (14)

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ε 1 ε + 2 = 4 π 3 .
n 2 1 n 2 + 2 = 4 π 3 .
n e , o 2 1 < n 2 > + 2 = 4 π 3 N α e , o .
n e = < n > + 2 3 Δ n ,
n o = < n > 1 3 Δ n .
d n e dT = d < n > dT + 2 3 d Δ n dT ,
d n o dT = d < n > dT - 1 3 d Δ n dT .
n = A BT ,
S = ( 1 T / T c ) β ,
Δ n ( T ) = ( Δ n ) o ( 1 T / T c ) β ,
n e ( T ) A BT + 2 ( Δ n ) o 3 ( 1 T T c ) β ,
n o ( T ) A BT ( Δ n ) o 3 ( 1 T T c ) β .
d n e dT = B 2 β ( Δ n ) o 3 T c ( 1 T T c ) 1 β
d n o dT = B + β ( Δ n ) o 3 T c ( 1 T T c ) 1 β

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