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Liquid crystal and composite liquid crystal device manufacturing capabilities

Contact person: L. Dupont

The optics department has a world recognized expertise and know how in the field of liquid crystal engineering[1] and their uses in non-display applications.

Pure liquid crystal technology:

We initiated our studies on liquid crystal with the smectic phases (in particular the FLC) at the end of eighties, investigating this material due to their fast switching time. The department is capable nowadays of engineering any type of smectic materials: smectic C and smectic C*, electroclinic materials such as Sm A, used in either planar or homeotropic configuration, surface stabilized ferroelectric (FLC) and anti-ferroelectric (AFLC) liquid crystals. At the end of nineties we broaden our scope to nematic materials (N, TN or STN), due to their use in composite liquid crystals. Recently we started working on cholesteric liquid crystal (CL) and composite CLC for their interesting polarization and wavelength dependent properties.

Know how:

It concerns not only material studies (phase transitions, surface alignments, driving voltages etc.) as well as their embodiments into various optical devices or structures such as: spatial light modulator, silicon backplane, optical light valve, fibre confinement, wave-guides etc. Among noticeable applications we can mention :

• Fast smectic liquid crystal optical light valve[2].
• Optical correlator for road sign recognition[3].
• Anti-blooing device[4].
• Mach-Zehnder switchable fibre coupler[5].
• Optical waveguide[6].
• Optical space switch[7] (nematic and smectic).

Composite liquid crystal technology:

Polymer materials can be used advantageously to endow liquid crystals with interesting optical properties (e.g. scattering, isotropic phase modulation etc.). Different polymer liquid crystal composite materials have been investigated as well as their related know how (UV curing, monomer to LC compatibility, polymer concentration etc.), to design and realize new functions in particular for telecommunication and security applications. We started our investigation with PDLC, Holo-PDLC and nano-PDLC, for telecom applications and more recently with polymer stabilized LC, for security applications.

PDLC (polymer dispersed liquid crystal), Holo-PDLC and nano-PDLC:

This work has been carried out in collaboration with the company, Optogone, in particular, the material engineering required for telecom qualification tests (e.g. large temperature range, low PDL etc). We have exploited either the scattering (variable attenuation) of PDLC or the isotropic phase modulation of nano-PDLC, used for Polarization controllers or combined with holographic fixed gratings. We developed a in-house expertise on UV curing process and a fine understanding of the material micro-structuring (e.g. droplet size and morphology, phase separation). Among noticeable applications we can mention :

• Dynamic gain and channel equalizer[8].   
• Polarization controller[9].
• Tuneable VCSEL[10].
• Holo-PDLC multiplex[11].

PSLC (polymer stabilized liquid crystal):

In order to combine a larger number of liquid crystal to polymer and then open our field to broader LC polymer combinatory we studied lower polymer concentration, for which the polymer only stabilized the LC material (polymer gels). We are able now to engineer and manufacture any type of LC with low concentration polymer: PSAFLC, PSFLC, PSCLC, PSLC. Among noticeable applications we can mention :

• PSAFLC optical shutter for welding mask[12].
• Photonic PSCLC.

Clean room and technical facilities:

In the way to work in the best conditions, liquid crystal activities are made in a "class 100" clean room. A joining room is endowed with characteristization instrumentation and glass cut machine.

The clean room has been organized following the cells manufacturing. The material description can be presented as the five steps of the liquid crystal cells manufacturing process :

• Cleaning and treatment of the glass plate
  
  Making the electrode pattern (photolithography process: mask, photoresist and ITO electrode etching), chemical treatment, polyimid and Polyvinyl alcohol deposit by spin coating, crystal liquid alignment process: rubbing and photo-alignment.

• Plates assembling:
  
  Spacers pulverization, sealing resin deposit, pressing.

• Cells filling.
  
  Polymer/ liquid crystal mixture filling, cell thickness measurement and assembling quality Control.

• Photo-polymerization process.
  
  Micro and nano structured composite liquid crystal/Polymer: PSLC, PDLC nano-PDLC with PIPS method (Polymerization-induced phase separation) using photocurable material.

• Environmental tests
  
  Temperature and humidity

Contact person: B. Bellini

References:

[1] J.L. de Bougrenet de la Tocnaye, “Engineering liquid crystal for optimal uses in optical communication environments”, Liquid Crystal Journal, pp. 1-29, 2004.

[2] L. Dupont, Z. Y. Wu, P. Cambon and J.L. de Bougrenet de la Tocnaye, "Smectic A and C liquid crystal lightvalves", Revue de Physique III, Vol. 3, pp. 1381-1399, 1993.

[3] L. Guibert, G. Keryer, A. Servel, M. Attia, H. MacKenzie, P. Pellat-Finet, and J.L. de Bougrenet " On-boardable optical joint transform correlator for real-time road sign recognition", Optical Engineering. Vol. 34, N°1, pp. 135-143, 1995.

[4] M. Guéna, Z.Y. Wu, J.L. de Bougrenet de la Tocnaye, "A 120x120 pixel anti-blooming array using optically addressed FLC cells", Optics Letters, Vol. 19, N°13, pp. 1001-1003, 1994.

[5] M. Le Gall, L. Dupont and J.L. de Bougrenet de la Tocnaye, "Liquid crystal confined single mode fibre based devices: technology and potential applications", Ferroelectrics, Vol.246, pp 1133-1140, 2000.

[6] E. Gros and L. Dupont "Ferroelectric liquid crystal optical waveguide switches using double refraction effect", IEEE Photonics Technology Letters, Vol. 13, N°2, pp. 115-117 ,2002.

[7] B. Fracasso, J.L. de Bougrenet de la Tocnaye, M. Razzak and C. Uche, "Design and performance of a versatile holographic liquid crystal wavelength selective switch", IEEE JLT, pp. 2405-2411, Vol. 21, pp. 2405-2414, 2003.

[8] M. Barge, D. Battarel, and J.L. de Bougrenet de la Tocnaye, “A polymer dispersed liquid crystal-based dynamic gain equalizer” IEEE JLT, Vol.23 , pp. 2531-2542, 2005.

[9] Y. Defosse, P. Gautier, J.L. de Bougrenet de la Tocnaye, A. Guenot, « Stabilized liquid crystal rotatable fractional wave-plates stack for fast polarisation analysis and control », Proc. OFC’04, Los Angeles, 2004.

[10] C. Levallois, B. Caillaud, J-L. de Bougrenet de la Tocnaye, L. Dupont, A. Lecorre, H. Folliot, and S. Loualiche, “Nano-PDLC as phase modulator for tunable VCSEL @ 1.55µm”, to appear Applied Optics, 2006.

[11] S. Massenot, J.-L. Kaiser, M. Camacho Perez, R. Chevallier and J.-L. de Bougrenet de la Tocnaye, ‘Multiplexed holographic transmission gratings recorded in holographic polymer dispersed liquid crystals: static and dynamic studies”, Applied Optics, Vol. 44, N°25, pp. 5489-5497, 2005.

[12] B. Caillaud, L. Dupont, J.L. de Bougrenet de la Tocnaye, P. Gautier, « Polymer stabilized FLC shutter exhibiting stabilized safe blocking state for welding filter applications », to appear in Ferroelectrics, 2006.