JRA2: Tuneable planar photonic crystal devices

1
JRA2 Tuneable planar photonic crystal devices
R. Ferrini (1) , J. Martz (1), B. Wild (2), L.A.
Dunbar (2), F. Robin (3), S. Anand (4), R. Houdré
(2), and L. Zuppiroli (1)

• Lab. dOptoélectronique des Matériaux
  Moléculaires

(3) Communication Photonics Group - Electronics
Lab. ETHZ, CH-8092 Zürich, Switzerland
(2) Institut de Photonique et dÉlectronique
Quantique
EPFL, CH-1015 Lausanne, Switzerland
(4) Dept. of Microelectronics and Information
Technology KTH, S-16440 Kista, Sweden
rolando.ferrini_at_epfl.ch
Infiltration technology
The major difficulty is given by the small size
of the holes
BUT
The physical infiltration of the holes is
assisted by the capillary forces
High-vacuum chamber for infiltration experiments

• PhC surface cleaning by low-power plasma

• Working under vacuum allows one
• to empty the gaseous content of the holes
• to minimize the effects of gas trapping in the
  LC mixture

• Control of temperature and gas flows
• during the infiltration procedure

If necessary Chemical surface modification
by grafting of self- assembled monolayers
(SAMs) may be used to improve LC wettability
Syringe
Without SAMs
With SAMs
Liquid crystals
PhC sample
J. Martz et al., Langmuir 20 (2004), 11428.
Infiltration procedure

• Evacuation
• The chamber is heated and pumped ? 110C and 10-6
  mbar
• The air is evacuated from the holes
• The LC mixture is degassed

Fundamental parameters
Pressure Temperature

• Optical characterization
• Optimization
• Reliability
• Repeatability

Contact The LC mixture is deposed on the sample
surface or The sample is dropped in the reservoir

• Purification of the LC mixture
• Reduction of the LC viscosity
• Reduction of wall contamination
• by humidity residuals

• Infiltration
• The chamber is released at atmospheric pressure
• The pressure differential helps the infiltration

Conclusions

• Trimming and (temperature) tuning of the optical
  properties of planar PhCs
• by liquid crystal infiltration have been
  clearly demonstrated

• The developed infiltration procedure is
  reproducible and reliable

• Transmission measurements as a function of both
  temperature and polarisation
• are necessary to study the LC molecule
  orientation inside the holes

• A phenomenological model is being developed to
  confirm
• the molecule orientation ? to the hole axis.
  The comparison with
• 2D and/or 3D FDTD calculations where nhole is
  a tensor is envisaged

• The molecule orientation ? to the hole axis
  opens the way
• to the electrical and optical tuning