Electro-optic polymers for high speed modulator

1. Electro-optic polymers for high speed modulator M. Balakrishnan, M. B. J. Diemeer, A. Driessen, Integrated Optical Microsystems, MESA+Institute for Nanotechnology, P.O. Box 217, 7500 AE Enschede, The Netherlands. M. Faccini, W. Verboom, D. N. Reinhoudt Laboratory of Supramolecular Chemistry and Technology, MESA+Institute 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, tricyanovinylidenediphenylaminobenzene (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 • SU8-15wt%TCVDPA : r33 = 5 pm/V , Tg ~ 50°C • SU8-15wt% TCVDPA-epoxy: r33 = 9pm/V, Tg ~ 70°C • 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: • Tg~215°C,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 < TCVDPA-tert butly < 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