Abstract

A mode of operation is introduced for the standard 90° twisted nematic (TN) liquid-crystal cell when placed together with an interference filter and positioned between crossed polarizers such that a small stimulating voltage of between ±2.0 and ±3.0 V is required in order to attain the light state. Further incrementation of the driving electronics reverts the system back to a darker phase. Such cells offer advantages over those of the standard 90° TN device operating in the normally white mode, in that the unit maintains the fast response time from the light to the dark state associated with the employment of TN cells placed between crossed polarizers. In addition, a low transmittance state is achieved when the unit is in the inactivated phase; this is an effect usually correlated with the normally black mode of operation. These cells are therefore ideal candidates for incorporation into fast, automatically darkening, welding filters that are designed to change rapidly from the light to the dark protective state, while offering an improved level of safety by not holding in a potentially hazardous light state should the controlling electronics malfunction. The requirement for this phenomenon to be observed is that the cell displays a low optical transmittance over the green wavelengths of the visible spectrum when in the inactivated phase and placed between crossed polarizers. The presence of an interference filter that possesses a peak transmittance over the central part of the visible spectrum is also necessary. It is shown that there are only two possible cell types that satisfy this criteria, and the optical properties of such cells are analyzed in some detail.

© 1996 Optical Society of America

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References

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  1. Hörnell Innovation AB, Tunavägen 281, 781 73 Borlänge, Sweden.
  2. B. Bahadur, Liquid Crystals: Applications and Uses (World Scientific, Singapore, 1990), Vol. 1, Chap. 12.2.3.
  3. H. A. Macleod, Thin Film Optical Filters, 2nd ed. (Hilger, Bristol, 1986), Chap. 5.
  4. C. H. Gooch, H. A. Tarry, “The optical properties of twisted nematic liquid crystal structures with twist angles less than 90°,” J. Phys. D 8, 1575–1584 (1975).
  5. MathSoft, Inc., 201 Broadway, Cambridge, Mass. 02139.
  6. Colorimetry, The CIE 1931 Standard Colorimetric Observer for daytime viewing, Pub. 15 E-1.3.1 (Commission Internationale de L’Eclairage, Paris, 1971).
  7. Deutsches Institut für Normung Standards Taschenbuch, Optik: Augenoptik und Augenschutz (Oskar Zach GmbH, Berlin, 1991), Chap. 1, p. 107.
  8. Lichtmesstechnik, Helmholtzstraße 9, Berlin 10, Germany.
  9. Deutsches Institut für Normung, Westliche 56, 7530 Pforzheim, Germany.
  10. Merck Postfach 41 19, Frankfurterstrasse 250, 6100 Darmstadt 1, Germany.
  11. Dodwell Hi-Tech KK, Kowa No. 16 Annex, 9-20 Akasaka 1-Chome, Minato-ku, Tokyo 107, Japan.
  12. S. T. Wu, A. M. Lackner, “Mylar-film compensated π and parallel aligned liquid crystal cells for direct-view and projection displays,” Appl. Phys. Lett. 64, 2047 (1994).
  13. S. Gunz, L. Ghisleni, “Blendschutzvorrichtung,” European patentEP 0550384 A1 (7July1993).
  14. L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Liquid crystal display element,” U.S. patent 4,398,803 (16August1983).
  15. L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Low-Δn-twisted nematic cell with improved optical properties,” Appl. Phys. Lett. 38, 497–499 (1981).
  16. Nitto Denko Corporation, 1-1-2 Shimohozumi, Ibaraki, Osaka, Japan.

1994 (1)

S. T. Wu, A. M. Lackner, “Mylar-film compensated π and parallel aligned liquid crystal cells for direct-view and projection displays,” Appl. Phys. Lett. 64, 2047 (1994).

1981 (1)

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Low-Δn-twisted nematic cell with improved optical properties,” Appl. Phys. Lett. 38, 497–499 (1981).

1975 (1)

C. H. Gooch, H. A. Tarry, “The optical properties of twisted nematic liquid crystal structures with twist angles less than 90°,” J. Phys. D 8, 1575–1584 (1975).

Bahadur, B.

B. Bahadur, Liquid Crystals: Applications and Uses (World Scientific, Singapore, 1990), Vol. 1, Chap. 12.2.3.

Baur, G.

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Low-Δn-twisted nematic cell with improved optical properties,” Appl. Phys. Lett. 38, 497–499 (1981).

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Liquid crystal display element,” U.S. patent 4,398,803 (16August1983).

Eidenschink, R.

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Low-Δn-twisted nematic cell with improved optical properties,” Appl. Phys. Lett. 38, 497–499 (1981).

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Liquid crystal display element,” U.S. patent 4,398,803 (16August1983).

Fehrenbach, W.

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Low-Δn-twisted nematic cell with improved optical properties,” Appl. Phys. Lett. 38, 497–499 (1981).

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Liquid crystal display element,” U.S. patent 4,398,803 (16August1983).

Ghisleni, L.

S. Gunz, L. Ghisleni, “Blendschutzvorrichtung,” European patentEP 0550384 A1 (7July1993).

Gooch, C. H.

C. H. Gooch, H. A. Tarry, “The optical properties of twisted nematic liquid crystal structures with twist angles less than 90°,” J. Phys. D 8, 1575–1584 (1975).

Gunz, S.

S. Gunz, L. Ghisleni, “Blendschutzvorrichtung,” European patentEP 0550384 A1 (7July1993).

Lackner, A. M.

S. T. Wu, A. M. Lackner, “Mylar-film compensated π and parallel aligned liquid crystal cells for direct-view and projection displays,” Appl. Phys. Lett. 64, 2047 (1994).

Macleod, H. A.

H. A. Macleod, Thin Film Optical Filters, 2nd ed. (Hilger, Bristol, 1986), Chap. 5.

Pohl, L.

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Low-Δn-twisted nematic cell with improved optical properties,” Appl. Phys. Lett. 38, 497–499 (1981).

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Liquid crystal display element,” U.S. patent 4,398,803 (16August1983).

Postfach, Merck

Merck Postfach 41 19, Frankfurterstrasse 250, 6100 Darmstadt 1, Germany.

Tarry, H. A.

C. H. Gooch, H. A. Tarry, “The optical properties of twisted nematic liquid crystal structures with twist angles less than 90°,” J. Phys. D 8, 1575–1584 (1975).

Weber, G.

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Low-Δn-twisted nematic cell with improved optical properties,” Appl. Phys. Lett. 38, 497–499 (1981).

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Liquid crystal display element,” U.S. patent 4,398,803 (16August1983).

Wu, S. T.

S. T. Wu, A. M. Lackner, “Mylar-film compensated π and parallel aligned liquid crystal cells for direct-view and projection displays,” Appl. Phys. Lett. 64, 2047 (1994).

Appl. Phys. Lett. (2)

S. T. Wu, A. M. Lackner, “Mylar-film compensated π and parallel aligned liquid crystal cells for direct-view and projection displays,” Appl. Phys. Lett. 64, 2047 (1994).

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Low-Δn-twisted nematic cell with improved optical properties,” Appl. Phys. Lett. 38, 497–499 (1981).

J. Phys. D (1)

C. H. Gooch, H. A. Tarry, “The optical properties of twisted nematic liquid crystal structures with twist angles less than 90°,” J. Phys. D 8, 1575–1584 (1975).

Other (13)

MathSoft, Inc., 201 Broadway, Cambridge, Mass. 02139.

Colorimetry, The CIE 1931 Standard Colorimetric Observer for daytime viewing, Pub. 15 E-1.3.1 (Commission Internationale de L’Eclairage, Paris, 1971).

Deutsches Institut für Normung Standards Taschenbuch, Optik: Augenoptik und Augenschutz (Oskar Zach GmbH, Berlin, 1991), Chap. 1, p. 107.

Lichtmesstechnik, Helmholtzstraße 9, Berlin 10, Germany.

Deutsches Institut für Normung, Westliche 56, 7530 Pforzheim, Germany.

Merck Postfach 41 19, Frankfurterstrasse 250, 6100 Darmstadt 1, Germany.

Dodwell Hi-Tech KK, Kowa No. 16 Annex, 9-20 Akasaka 1-Chome, Minato-ku, Tokyo 107, Japan.

Nitto Denko Corporation, 1-1-2 Shimohozumi, Ibaraki, Osaka, Japan.

S. Gunz, L. Ghisleni, “Blendschutzvorrichtung,” European patentEP 0550384 A1 (7July1993).

L. Pohl, G. Weber, R. Eidenschink, G. Baur, W. Fehrenbach, “Liquid crystal display element,” U.S. patent 4,398,803 (16August1983).

Hörnell Innovation AB, Tunavägen 281, 781 73 Borlänge, Sweden.

B. Bahadur, Liquid Crystals: Applications and Uses (World Scientific, Singapore, 1990), Vol. 1, Chap. 12.2.3.

H. A. Macleod, Thin Film Optical Filters, 2nd ed. (Hilger, Bristol, 1986), Chap. 5.

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Figures (9)

Fig. 1
Fig. 1

Optical properties of a five-period interference filter that uses alternate layers of Al2O3 and Ag.

Fig. 2
Fig. 2

Calculated transmittance at 550 nm for liquid-crystal cells placed between crossed polarizers oriented at 45° relative to the molecular alignment vectors, as a function of both the twist angle and the Δnd value.

Fig. 3
Fig. 3

Calculated optical transmittance of a 0° LT cell possessing a Δnd value of 0.52 μm, placed between crossed polarizers oriented at 45° relative to the molecular alignment directors.

Fig. 4
Fig. 4

Electro-optic properties of a 4-μm, 0° LT cell with the Merck 4246 liquid-crystal mixture and crossed LC81 polarizers oriented at 45° relative to the molecular alignment directors. A standard interference filter is present.

Fig. 5
Fig. 5

Calculated optical transmittance of a 90° TN cell with a Δnd value of 0.80 μm placed between crossed polarizers oriented at 45° relative to the molecular alignment directors.

Fig. 6
Fig. 6

Electro-optic properties of an 8-μm, 90° TN cell with the Merck 6096 liquid-crystal mixture and crossed LC81 polarizers oriented at 45° relative to the molecular alignment directors. A standard interference filter is present.

Fig. 7
Fig. 7

Safe-state shade step for an 8-μm, 90° TN cell with the Merck 6096 liquid-crystal mixture as a function of the crossed LC81 polarizer alignment, relative to the entrance molecular director. A standard interference filter is present.

Fig. 8
Fig. 8

Optical angular properties of an 8-μm, 90° TN cell in the (a) light (±2.4 V) and (b) dark (±7.5 V) states with the Merck 6096 liquid-crystal mixture and crossed LC81 polarizers oriented at 45° relative to the entrance molecular director. A standard interference filter is present.

Fig. 9
Fig. 9

Optical angular properties of a double-cell design that uses 8-μm, 90° TN cells with the Merck 6096 liquid-crystal mixture placed between three LC81 polarizers oriented at 45° relative to the molecular alignment directors. The cells are driven together in order to attain a shade number of 12, and a standard interference filter is present.

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