Electrooptic polymers for high speed modulator

1
Electro-optic polymers for high speed modulator
M. Balakrishnan, M. B. J. Diemeer, A. Driessen,
Integrated Optical Microsystems, MESAInstitute
for Nanotechnology, P.O. Box 217, 7500 AE
Enschede, The Netherlands. M. Faccini, W.
Verboom, D. N. Reinhoudt Laboratory of
Supramolecular Chemistry and Technology,
MESAInstitute forNanotechnology, P.O. Box 217,
7500 AE Enschede, The Netherlands. A.
Leinse LioniX BV, P.O. Box 456, 7500 AH Enschede,
The Netherlands.
Over the past decade the demand for the
telecommunication services and bandwidth has
boomed. To handle this ever increasing demand
high speed electro-optic (EO) modulators
operating over 100 GHz are required. Nonlinear
optical (NLO) polymers have been proposed to be
useful candidates for this application already
two decades ago. The main requirements of EO
polymers are high nonlinearity (r33),
photochemical stability, thermal stability and
ease of processing. Different electro-optic
polymer systems are analyzed with respect to
their electro-optic activity, glass transition
temperature (Tg) and photodefinable properties.
The polymers tested are polysulfone (PS),
polycarbonate (PC) and SU8. The electro-optic
chromophore, tricyanovinylidenediphenylaminobenzen
e (TCVDPA), which was reported to have a highest
photochemical stability has been employed in the
current work. Modified TCVDPA with bulky side
groups has been synthesized and the effect of
intermolecular interaction has been analysed.
EO-Modulator requirements
SU8-TCVDPA crosslinked polymer

• Direct photodefinition of the core layer
• Poling of the defined structures
• Attaching the chromophore to SU8 via epoxy groups
• SU8-15wtTCVDPA r33 5 pm/V , Tg 50C
• SU8-15wt TCVDPA-epoxy r33 9pm/V, Tg 70C
• Tg of SU8 -TCVDPA -Epoxy system can be further
  improved by optimizing the crosslinking process.

Microring
Mach zehnder

• High r33 Low V
• High Tg stability of the poling order
• Good film forming properties- Adhesion and smooth
  surface
• Low losses High Q rings
• High Refractive index Small ring radius

Ring design in PC-TCVDPA main chain polymer

• Tg215C,Refractive index (n)1.62 at 1550 nm
• Photodefinition of inverted ridges in the buffer
  layer VSC n 1.5 at 1550 nm
• Filling of the inverted ridges with SU8 and
  photodefinition of the active region in SU8
• Filling of the active region with PC-TCVDPA

PS-TCVDPA guest host system with TCVDPA
modifications
SU8 passive waveguide losses 5dB/cm
TCVDPA
TCVDPA-tert butyl
TCVDPA-TBDMS
PC-TCVDPA active region
SU8 passive waveguides
TCVDPA-TBDPS
TCVDPA-F
TCVDPA-Dentritic
Phase matching between the ring and the ridge
Conclusions TCVDPA and its modification were
incorporated in PS, PC and SU8. TCVDPA with
tert-butyl as side groups was found to be
effective in reducing the intermolecular
interactions and thereby yielding the highest
measured r33 of 25 pm/V. The reduction of Tg by
chromophore addition was completely prevented by
attaching it to the polymer backbone in PC.
Microring resonators were designed with PC-TCVDPA
as active material. Ridge waveguides were
fabricated by photodefinition and the losses were
measured to be 5 dB/cm in the SU8 passive
waveguides.
r33 25 pm/V at 830 nm 37 wt TCVDPA-tert butyl
Mw TCVDPA lt TCVDPA-tert butly lt TCVDPA dentritic

• The Tg decreases with chromophore addition
• Molecules with lower molecular mass have higher
  plasticizing effect
• TCVDPA-tert butyl was found to yeild the highest
  r33