Abstract

Based on liquid crystal polymers (LCP) a compact micro-optical polarizer with high efficiency has been designed and realized. By using cylindrical microlens arrays made of LCP and index matching layer, a complete separation of both polarization components of the unpolarized input light is achieved. Combined with a patterned twisted nematic (TN) cell, allowing a rotation of only one polarization component, a polarizer with high efficiency (72,5% (measured)) is realized. Simulations and measurements are presented.

©2008 Optical Society of America

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References

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  1. C. Gu and P. Yeh, Optics of Liquid Crystal Displays, (Wiley, New York, 1999).
  2. D. J. Broer, “Reation of supramolecular thin film architectures with liquid-crystalline networks,” Mol. Cryst. Liq. Cryst.,  261, 513–523 (1995).
    [Crossref]
  3. N. Nieuborg, A. Kirk, B. Morlion, H. Thienpont, and I. Veretennicoff, “Polarization selective diffractive optical elements with index matching gap material,” Appl. Opt. 36, 4681–4685 (1997).
    [Crossref] [PubMed]
  4. C. W. McLaughlin, “Progress in projection and large-area displays,” Proc. IEEE,  90, 521–532 (2002).
    [Crossref]
  5. T. Scharf, “Static birefringent microlenses,” Optics and Lasers in Engineering 43, 317–327 (2005).
    [Crossref]
  6. G. Boer and T. Scharf, “Polarization Ray tracing in twisted Liquid Crystal Systems,” Mol. Cryst. Liq. Cryst.,  375, 301–311 (2002).
  7. P. Nussbaum, R. Volkel, H. P. Herzig, M. Eisner, and S. Haselbeck, Design, fabrication and testing of microlens arrays for sensors and microsystems, Pure Appl. Opt.6, 617–636 (1997).
    [Crossref]
  8. Y. Xia and G. M. Whitesides, “Soft lithography,” Annu. Rev. Matter. Sci. 28, 153–184 (1998).
    [Crossref]
  9. T. Scharf, Polarized Light in Liquid Crystals and Polymers, (Wiley and Sons, 2006).
    [Crossref]

2005 (1)

T. Scharf, “Static birefringent microlenses,” Optics and Lasers in Engineering 43, 317–327 (2005).
[Crossref]

2002 (2)

G. Boer and T. Scharf, “Polarization Ray tracing in twisted Liquid Crystal Systems,” Mol. Cryst. Liq. Cryst.,  375, 301–311 (2002).

C. W. McLaughlin, “Progress in projection and large-area displays,” Proc. IEEE,  90, 521–532 (2002).
[Crossref]

1998 (1)

Y. Xia and G. M. Whitesides, “Soft lithography,” Annu. Rev. Matter. Sci. 28, 153–184 (1998).
[Crossref]

1997 (1)

1995 (1)

D. J. Broer, “Reation of supramolecular thin film architectures with liquid-crystalline networks,” Mol. Cryst. Liq. Cryst.,  261, 513–523 (1995).
[Crossref]

Boer, G.

G. Boer and T. Scharf, “Polarization Ray tracing in twisted Liquid Crystal Systems,” Mol. Cryst. Liq. Cryst.,  375, 301–311 (2002).

Broer, D. J.

D. J. Broer, “Reation of supramolecular thin film architectures with liquid-crystalline networks,” Mol. Cryst. Liq. Cryst.,  261, 513–523 (1995).
[Crossref]

Eisner, M.

P. Nussbaum, R. Volkel, H. P. Herzig, M. Eisner, and S. Haselbeck, Design, fabrication and testing of microlens arrays for sensors and microsystems, Pure Appl. Opt.6, 617–636 (1997).
[Crossref]

Gu, C.

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

Haselbeck, S.

P. Nussbaum, R. Volkel, H. P. Herzig, M. Eisner, and S. Haselbeck, Design, fabrication and testing of microlens arrays for sensors and microsystems, Pure Appl. Opt.6, 617–636 (1997).
[Crossref]

Herzig, H. P.

P. Nussbaum, R. Volkel, H. P. Herzig, M. Eisner, and S. Haselbeck, Design, fabrication and testing of microlens arrays for sensors and microsystems, Pure Appl. Opt.6, 617–636 (1997).
[Crossref]

Kirk, A.

McLaughlin, C. W.

C. W. McLaughlin, “Progress in projection and large-area displays,” Proc. IEEE,  90, 521–532 (2002).
[Crossref]

Morlion, B.

Nieuborg, N.

Nussbaum, P.

P. Nussbaum, R. Volkel, H. P. Herzig, M. Eisner, and S. Haselbeck, Design, fabrication and testing of microlens arrays for sensors and microsystems, Pure Appl. Opt.6, 617–636 (1997).
[Crossref]

Scharf, T.

T. Scharf, “Static birefringent microlenses,” Optics and Lasers in Engineering 43, 317–327 (2005).
[Crossref]

G. Boer and T. Scharf, “Polarization Ray tracing in twisted Liquid Crystal Systems,” Mol. Cryst. Liq. Cryst.,  375, 301–311 (2002).

T. Scharf, Polarized Light in Liquid Crystals and Polymers, (Wiley and Sons, 2006).
[Crossref]

Thienpont, H.

Veretennicoff, I.

Volkel, R.

P. Nussbaum, R. Volkel, H. P. Herzig, M. Eisner, and S. Haselbeck, Design, fabrication and testing of microlens arrays for sensors and microsystems, Pure Appl. Opt.6, 617–636 (1997).
[Crossref]

Whitesides, G. M.

Y. Xia and G. M. Whitesides, “Soft lithography,” Annu. Rev. Matter. Sci. 28, 153–184 (1998).
[Crossref]

Xia, Y.

Y. Xia and G. M. Whitesides, “Soft lithography,” Annu. Rev. Matter. Sci. 28, 153–184 (1998).
[Crossref]

Yeh, P.

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

Annu. Rev. Matter. Sci. (1)

Y. Xia and G. M. Whitesides, “Soft lithography,” Annu. Rev. Matter. Sci. 28, 153–184 (1998).
[Crossref]

Appl. Opt. (1)

Mol. Cryst. Liq. Cryst. (2)

D. J. Broer, “Reation of supramolecular thin film architectures with liquid-crystalline networks,” Mol. Cryst. Liq. Cryst.,  261, 513–523 (1995).
[Crossref]

G. Boer and T. Scharf, “Polarization Ray tracing in twisted Liquid Crystal Systems,” Mol. Cryst. Liq. Cryst.,  375, 301–311 (2002).

Optics and Lasers in Engineering (1)

T. Scharf, “Static birefringent microlenses,” Optics and Lasers in Engineering 43, 317–327 (2005).
[Crossref]

Proc. IEEE (1)

C. W. McLaughlin, “Progress in projection and large-area displays,” Proc. IEEE,  90, 521–532 (2002).
[Crossref]

Other (3)

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

P. Nussbaum, R. Volkel, H. P. Herzig, M. Eisner, and S. Haselbeck, Design, fabrication and testing of microlens arrays for sensors and microsystems, Pure Appl. Opt.6, 617–636 (1997).
[Crossref]

T. Scharf, Polarized Light in Liquid Crystals and Polymers, (Wiley and Sons, 2006).
[Crossref]

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Figures (19)

Fig. 1.
Fig. 1. Operation principle, on the top lens of the picture, the incoming light is split by the microlens, TE polarization is focused on the twisted nematic (TN) cell and converted into TM polarization while TM component is not focused and converted into TE polarization. The bottom lens shows the same system but with a switched zone in the TN cell located at the focal point, resulting in a whole TE polarization at the output of the TN cell. Note that if the TN cell is switched the polarization is maintained.
Fig. 2.
Fig. 2. Illustration of the behaviors of a perfect dichroic polarizer (top part) compared to the case of a perfect micro-optical polarizer MP (bottom part) under different illumination conditions. The arrow in the polarizer and the MP gives their optical axis orientation.
Fig. 3.
Fig. 3. Illustration of the complete device. The whole system is less than 2 mm thick.
Fig. 4.
Fig. 4. Illustration of the different losses present in the system and ray tracing interpretation of the polarization state at the output of the micro-optical polarizer.
Fig. 5.
Fig. 5. Resulting intensity distribution for perfectly collimated light at normal incidence.
Fig. 6.
Fig. 6. Resulting intensity distribution for perfectly collimated light at 4° of incidence. The focalized polarization does no more pass through the switched area of the TN cell.
Fig. 7.
Fig. 7. Simulated polarization efficiency Pe as a function of the angle of incidence of collimated input light for a system with microlens diameter Ø = 145 µm, pitch ΛLenses= 150 µm, hlens = 25 µm and a width of the commuted TN area of WTN = 20 µm. Pe is defined as the ratio of the output intensity I2 and input intensity I0.
Fig. 8.
Fig. 8. SEM Pictures of free standing birefringent microlenses, detail of the alignment grating parallel and orthogonal. (Scales, 10 µm and 60 µm)
Fig. 9.
Fig. 9. Pictures of the realized prototype taken at different distances inside the system showing the microlenses, the focal line and the output light. The three pictures have been taken using the same polarizer configuration.
Fig. 10.
Fig. 10. Pictures of the realized device in the three possible states under unpolarized collimated white light. Picture (1) the electrodes are switched off, picture (2) switched on, picture (3) black position and TN electrodes switched on.
Fig. 11.
Fig. 11. Illustration of the configuration used in the measurements of the polarization efficiency Pe of the micro-optical polarizer MP. The intensity I1 is first detected without MP but with a conventional dichroic polarizer (A) and with the addition of the MP, intensity I2 (B). The intensity of the light I0’ at the output of the MP is not directly measured because of its polarization state is not linear.
Fig. 12.
Fig. 12. Measured and simulated polarization efficiency as a function of the angle of incidence for a system with microlens diameter Ø = 145 µm, pitch = 150 µm, hlens = 25 µm and a width of the commuted TN area WTN of 20 µm.
Fig. 13.
Fig. 13. Schematic illustration of the design optimization. (a) Total internal reflection (TIR); (b) Spherical aberration, the focused polarization reaches no more the TN area; (c) Focused ray; (d) Off axis ray still focused; (e) TIR of an off axis ray. ROC and WTN are parameters to optimize. Fresnel reflections are not illustrated.
Fig. 14.
Fig. 14. Simulated polarization efficiency for sources with different F-numbers and various ROC of the microlenses. The microlens array period is ΛLenses = 150 µm, the gap of Wgap = 5 µm and the TN switched area WTN = 20 µm.
Fig. 15.
Fig. 15. Simulated efficiency for three sources with different F-numbers in function of the width of the commuted zones in the TN cell. The ROC of microlenses is 0.09 mm, the microlens period ΛLenses = 150 µm, the gap of Wgap= 5 µm
Fig. 16.
Fig. 16. Illustration of the head to head configuration. The optical axis of the two birefringent microlens arrays are set orthogonal. Both polarizations are focalized. A complete separation of each polarization is performed, with a direct possibility of increasing the width of the TN areas to half the pitch of the microlens arrays.
Fig. 17.
Fig. 17. Simulated and measured polarization efficiency versus the angle of incidence of collimated light for Basic and Head to Head configurations systems with microlens diameter Ø = 145 µm, pitch ΛLenses = 150 µm, hlens = 25 µm and a width of the commuted TN area of WTN = 20 µm.
Fig. 18.
Fig. 18. Pictures of focalization of one polarization component (1), of the orthogonal component (2) and both (3).
Fig. 19.
Fig. 19. Pictures of head to head device illuminated with collimated white light seen through orthogonal polarizer (A) and parallel polarizer (B) and superimposed picture of the whole cell seen between crossed polarizers.

Equations (9)

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f = ROC n e n ,
L 1 = 1 2 · W TN Λ Lenses .
L 2 = 1 2 · W Gap Λ Lenses .
P e = 1 ( L 1 + L 2 ) ,
P e Measured = I 2 I 1 2 · I 1 + 0.5 .
F # = f 2 · r 1 2 · NA
α max = arctan ( 1 2 · F # ) .
P e = 1 ( W gap Λ Lenses ) .
c = I max I min ,

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