Abstract

The gap of a planar-aligned liquid crystal (LC) cell is measured by a novel method: Monitoring the change in output wavelength of an external-cavity diode laser by varying the voltage driving the LC cell placed in the laser cavity. This method is particularly suitable for measurement of LC cells of small phase retardation. Measurement errors of ±0.5 % and ±0.6 % for 9.6-μm and 4.25-μm cells with phase retardations of 1.63 μm and 0.20 μm respectively are demonstrated.

© 2005 Optical Society of America

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References

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    [CrossRef]
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  3. Shyu-Mou Chen, Ru-Pin Pan, and Ci-Ling Pan, �??Interferometric measurements of the thickness of nematic liquid crystal films with a free surface,�?? Appl. Opt. 28, 4969 �?? 4971 (1989).
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    [CrossRef]
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    [CrossRef]
  6. Seo Hern Lee, Won Sang Park, Gi-Dong Lee, Kwan-Young Han, Tae-Hoon Yoon, and Jae Chang Kim, �??Low-cell-gap measurement by rotation of a wave retarder,�?? Jpn. J. Appl. Phys. 41, 379-383 (2002).
    [CrossRef]
  7. Marenori Kawamura, Yoshiaki Goto, and Susumu Sato, �??Two-dimensional measurements of cell parameter distributions in reflective liquid crystal displays by using multiple wavelengths Stokes parameters,�?? J. Appl. Phys. 95, 4371-4375 (2004).
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  8. Zhan He, Ying Zhou, and Susumu, �??A two-dimensional Stokes parameter method for determination of cell thickness and twist angle distributions in twisted nematic liquid crystal devices,�?? Jpn. J. Appl. Phys. 37, 1982-1988 (1998).
    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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  13. Gi-Dong Lee, Tae-Hoon Yoon, and Jae Chang Kim, �??Cell gap measurement method for single-polarizer reflective liquid crystal cells,�?? Jpn. J. Appl. Phys. 40, 3330-3331 (2001).
    [CrossRef]
  14. Yu-Ping Lan, Chao-Yuan Chen, Ru-Pin Pan, and Ci-Ling Pan, �??Fine-tuning of a diode laser wavelength with a intracavity liquid crystal element,�?? Opt. Eng. 43, 234-238 (2004).
    [CrossRef]
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  17. Ru-Pin Pan, Shyang-Rong Liou, and Chao-Ken Lin, �??Voltage-controlled optical fiber coupler using a layer of low-refractive-index liquid crystal with positive dielectric anisotropy,�?? Jpn. J. Appl. Phys. 34, 6410-6415 (1995).
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Appl. Opt. (1)

IEEE Trans. Electron Dev. (1)

Xinyu Zhu, Wing-Kit Choi, and Shin-Tson Wu, �??A simple method for measuring the cell gap of a reflective twisted nematic LCD,�?? IEEE Trans. Electron Dev. 49, 1863-1867 (2002).
[CrossRef]

J. Appl. Phys. (7)

Jong Seok Chae and Soo Gil Moon, �??Cell parameter measurement of a twisted-nematic liquid crystal cell by the spectroscopic method,�?? J. Appl. Phys. 95, 3250-3254 (2004).
[CrossRef]

S. T. Tang and H. S. Kwok, �??Transmissive liquid crystal cell parameters measurement by spectroscopic ellipsometry,�?? J. Appl. Phys. 89, 80-85 (2001)
[CrossRef]

A. Lien and H. Takano, �??Cell gap measurement of filled twisted nematic liquid crystal displays by a phase compensation method,�?? J. Appl. Phys. 69, 1304-1309 (1991).
[CrossRef]

Hiap Liew Ong, �??Cell thickness and surface pretilt angle measurements of a planar liquid-crystal cell with obliquely incident light,�?? J. Appl. Phys. 71, 140-144 (1992).
[CrossRef]

K. H. Yang, �??Measurements of empty cell gap for liquid-crystal displays using interferometry methods,�?? J. Appl. Phys. 64, 4780-4781 (1988).
[CrossRef]

K. Y. Yang and H. Takano, �??Measurements of twisted nematic cell gap by spectral and split-beam interferometric methods,�?? J. Appl. Phys. 67, 5-9 (1990).
[CrossRef]

Marenori Kawamura, Yoshiaki Goto, and Susumu Sato, �??Two-dimensional measurements of cell parameter distributions in reflective liquid crystal displays by using multiple wavelengths Stokes parameters,�?? J. Appl. Phys. 95, 4371-4375 (2004).
[CrossRef]

Jpn. J. Appl. Phys. (5)

Zhan He, Ying Zhou, and Susumu, �??A two-dimensional Stokes parameter method for determination of cell thickness and twist angle distributions in twisted nematic liquid crystal devices,�?? Jpn. J. Appl. Phys. 37, 1982-1988 (1998).
[CrossRef]

Jin Seog Gwag, Kyoung-Ho Park, Gi-Dong Lee, Tae-Hoon Yoon, and Jae Chang Kim, �??Simple cell gap measurement method for twisted-nematic liquid crystal cells,�?? Jpn. J. Appl. Phys. 43, L30-L32 (2004).
[CrossRef]

Seo Hern Lee, Won Sang Park, Gi-Dong Lee, Kwan-Young Han, Tae-Hoon Yoon, and Jae Chang Kim, �??Low-cell-gap measurement by rotation of a wave retarder,�?? Jpn. J. Appl. Phys. 41, 379-383 (2002).
[CrossRef]

Gi-Dong Lee, Tae-Hoon Yoon, and Jae Chang Kim, �??Cell gap measurement method for single-polarizer reflective liquid crystal cells,�?? Jpn. J. Appl. Phys. 40, 3330-3331 (2001).
[CrossRef]

Ru-Pin Pan, Shyang-Rong Liou, and Chao-Ken Lin, �??Voltage-controlled optical fiber coupler using a layer of low-refractive-index liquid crystal with positive dielectric anisotropy,�?? Jpn. J. Appl. Phys. 34, 6410-6415 (1995).
[CrossRef]

Opt. Eng. (2)

Shin-Tson Wu, Chiung-Sheng Wu, Marc Warenghem, and Mimoun Ismaili, �??Refractive index disperasions of liquid crystals,�?? Opt. Eng. 32, 1775-1780 (1993).
[CrossRef]

Yu-Ping Lan, Chao-Yuan Chen, Ru-Pin Pan, and Ci-Ling Pan, �??Fine-tuning of a diode laser wavelength with a intracavity liquid crystal element,�?? Opt. Eng. 43, 234-238 (2004).
[CrossRef]

Opt. Lett. (1)

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Figures (3)

Fig. 1.
Fig. 1.

The schematic diagram for LC cell gap measurement. LD: laser diode; Obj: Objective, LC: liquid crystal, λ-meter: wavelength meter.

Fig. 2.
Fig. 2.

(a) Output wavelength of the laser and (b) transmittance of the LC cell (9.6 μm) through crossed polarizers as a function of the driving root-mean square (rms) voltage of the LC cell.

Fig. 3.
Fig. 3.

(a) Output wavelength of the laser and (b) transmittance of the LC cell (4.25 μm) through crossed polarizers as a function of the driving root-mean-square (rms) voltage of the LC cell.

Tables (2)

Tables Icon

Table 1. Results of LC layer thickness measurement

Tables Icon

Table 2. Error sources for LC layer thickness measurement by the present method

Equations (9)

Equations on this page are rendered with MathJax. Learn more.

n eff ( θ ) = [ sin 2 ( θ ) n e + cos 2 ( θ ) n o ] 1 2 ,
ΔΦ = k 0 d [ n eff ( z ) n 0 ] dz ,
Δ Φ max = 2 π λ ( n e n o ) d .
Δ l l = Δ λ λ ,
δd δ ( Δ λ ) Δ λ d .
δd = 1 Δ n δf f .
δd = δl d l .
δd = Δ λ λ δ ( Δ n ) ( Δ n ) 2 = d Δ n δ ( Δ n )
δd = d tan θ · δθ .

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