Abstract
Optical waveguides are becoming increasingly important in the developing area of broadband communications. The field of electronics is advancing rapidly, leading to further demands for larger data storage, smaller components and a better design of integrated optical circuits. The integration of optical interconnects on printed circuit boards (PCBs) requires precise technologies to make this emerging field possible. A promising new microfabrication technique, two-photon photopolymerisation (2PP) can be used to produce three dimensional structures in the sub-micron region. Near-infrared lasers can be used to create 3D optical waveguides by initiating the photopolymerisation of high refractive index monomers in polymeric matrix materials. Terminal silanol groups are intermediates for room temperature vulcaniseable (RTV) silicones and can be cross linked with functional silanes to produce flexible, transparent polymeric materials with high thermal stabilities. A silanol terminated polysiloxane; cross linked with a methyl substituted acryloxy silane has been developed as a suitable material for the fabrication of optical waveguides by two-photon absorption (TPA). A higher refractive index is achieved upon polymerisation of the acrylate functional groups. The material has been shown to be suitable in the fabrication of 3D optical waveguides with a high refractive index contrast. The cured material is fully flexible and exhibits high thermal stability and optical transparency. The material was characterised by Fourier transform infrared spectroscopy (FT-IR), simultaneous thermal analysis coupled with mass spectrometry (STA-MS) and near-infrared spectroscopy (NIRS). Waveguides were observed by phase contrast microscopy, cut back measurements and were additionally directly integrated onto specially designed PCBs by correctly positioning waveguide bundles between optoelectronic components using TPA.
Highlights
Polymer optical waveguides have attracted attention in recent years for applications in active and passive components for optical communication systems
To determine the suitability of the matrix material for two-photon absorption (TPA) applications, one photon experiments were performed to establish how efficiently the acrylate functional groups attached to the polymer backbone polymerise
Samples of silanol terminated dimethyl diphenyl polysiloxane, cross linked with acryloxymethyl trimethoxy silane, containing 1 wt. % dioctyl tin dilaurylate and 1 wt. % Irgacure 379 as photoinitiator were illuminated using a UV spot cure lamp (1.4 W / cm2) and the double bond conversion of the acrylate functional group was monitored using time-based FT-IR spectroscopy
Summary
Polymer optical waveguides have attracted attention in recent years for applications in active and passive components for optical communication systems. The production of sub-micron structures using this technique has demonstrated the potential of this application in optical devices and optical storage [15,16] Another method used to laser structure polymers has been successfully achieved recently via induced avalanche ionization, which achieves high resolutions and avoids the use of photoinitiators [17]. Materials being developed for the use in optical polymer waveguide fabrication by TPA include flexible polydimethyl diphenyl siloxane matrices [20,21]. A silanol terminated dimethyl diphenyl siloxane was chosen, due to its optical properties and speed of curing at room temperature with acryloxymethyl trimethoxy silane Using this tri functional cross linker it was possible to produce an optically transparent, flexible material, which contained high refractive index functional groups attached to the polymer back bone. On-line measurements were carried out on the connected components during the inscription of the waveguides, which enabled the photocurrent to be detected
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