Characterization by IR spectroscopy of an hybrid sol–gel material used for photonic devices fabrication

Abstract

In the last few years, ORganically MOdified Silicates [RxSi(OR)4−x] prepared by sol–gel process were particularly attractive for integrated optics fabrication. A composition based on MAPTMS (3-(trimethoxysilyl)propylmethacrylate) has already allowed the industrial fabrication of optical integrated devices. For this kind of materials, the polymerization of the organic network is typical of free radical curing. This material is the more advanced and industrialized material but the composition has some disadvantages which can complicate or prohibit specific IOC fabrication. In this work, we try to obtain waveguides with another hybrid precursor [2-(3,4-epoxycyclohexylethyltrimethoxysilane)] using cationic polymerization. The main advantage of cationic polymerization is its ability to allow spontaneous cure reaction in presence of oxygen, in contrast with radical polymerization. We choose cycloaliphatic compounds because of their well known high polymerization rates. The polymerization of the organic network of this hybrid material requires a cationic photoinitiator. High losses of light propagation at 1550nm are mainly due to the presence of OH groups originating from the sol–gel process at low temperature. Thus, improvement of the final properties of this material is correlated with the inhibition of OH group concentration. In this work, near and middle IR spectroscopy experiments show the presence of a still too high proportion of OH species in the structure. Polymerization is studied through the absorption band of the epoxy ring-opening before and after irradiation. In order to reduce the OH content, we study the effect of a post bake treatment.