Synthesis of Photosensitive Organic-Inorganic Hybrid Polymers via Anhydrous Sol-Gel Process for Integrated Optics
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Synthesis of Photosensitive Organic-Inorganic Hybrid Polymers via Anhydrous Sol-Gel Process for Integrated Optics Xinshi Luo, Congji Zha, Barry Luther-Davies Laser Physics Centre, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200, Australia
ABSTRACT Photosensitive organic-inorganic hybrid polymers were synthesised for integrated optical and optoelectronic devices by a non-hydrous sol-gel process of hydrolysis/condensation of 3-methacryloxypropyltrimethoxysilane (MPS), diphenyldimethoxysilane (DPhDMS), and zirconium isopropoxide (TPZ) with boric acid under anhydrous conditions. The methacryl groups of MPS are UVpolymerizable, which are suitable for low cost fabrication of waveguides with a “UV write/develop” process. The incorporation of DPhDMS and TPZ was found useful in reducing the optical loss and in enhancing the thermostability of the polymer. The refractive index of the hybrid polymer is tuneable from 1.4950 to 1.5360 by variation of the ratio among MPS, DPhDMS and TPZ. Optical characterisation showed that the material has low optical losses at the telecommunications windows (0.16 dB/cm at 1310 nm and 0.4 dB/cm at 1550nm). The hybrid polymer also showed a low birefringence (1.2×10-4), a large thermo-optic (TO) coefficient (-2.77 ×10-4), and an outstanding linearity of dn/dT in a wide range of temperature (from 25 oC to 200 oC). Waveguides forming ability for the hybrid polymer with UV imprinting was also demonstrated.
INTRODUCTION Silica-on-silicon has become a materials technology in fabrication of planar light circuits because of its low loss and high temperature stability [1]. The limitations for this technology however are obvious. Silica must be processed at high temperature, which leads to problems with built-in stress. It has been known that birefringence produced by this thermal stress is a cause of unwanted polarization dependence in any resulting devices. Silica also has a very low thermo-optic coefficient, which is not desired for the devices such as digital thermo-optic switch and thermally tuneable grating. In seeking solutions for these limitations, research on polymeric optical waveguides has attracted considerable attention [2,3]. Compared with silica-on-silicon technology, planar polymer waveguides for application as optical components in optical interconnects and optical devices have some distinguished advantages. Polymeric thin films can easily be fabricated at low temperature by various methods such as spin-coating, dipping, thermo-curing, and photo-curing. These films are generally flexible and tough, and they can be conveniently patterned to fine structure by photolithography, etching, or stamping. Polymer materials also provide advantages in tuning refractive index and in maintaining low polarization sensitivity. Polymeric materials for planar optical waveguides are considered to be low cost and volume producible.
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