Experimental and theoretical study of the formation process of photopolymer based self-written waveguides.

Monali Suar,Oliver Melchert,Bernhard Roth,Maik Rahlves

doi:10.1364/oe.27.038326

Abstract

The realization of optical interconnects between multimode (MM) optical fibers and waveguides based on a self-writing process in photopolymer media represents an efficient approach for fast and easy-to-implement connection of light-guiding elements. When light propagates through photopolymer media, it modulates the material properties of the media and confines the spreading of the light beam to create a waveguide along the beam propagation direction. This self-writing process can be realized with a single photopolymer medium and is also suited to connect optical fibers or waveguides with active elements such as light sources and detectors. Numerical simulations of the underlying light-induced polymerization process is carried out by using a diffusion based material model which takes account both monomer diffusion and its conversion to polymer chains in regions exposed to light fields. In this work experimental results obtained from a one-polymer approach are validated with theoretical predictions from the diffusion model. The study involved the demonstration of temporal dynamics and transmittance from self-written waveguide (SWW) couplers during the self-writing process. The measured attenuation coefficient from experiment αexperiment = (8.43 ± 0.3) × 10-5 dB/µm showed good agreement with the theoretically predicted attenuation coefficient αsimulation = 7.93 × 10-5 dB/µm, thus demonstrating a successful application of the diffusion model to epoxy based acrylate SWWs. For comparison, attenuation measurements between optical fibers with SWWs as interconnects and one without SWW, i.e. with an air gap in between, were performed. The obtained results reveal that the theoretical approach correctly describes the waveguide formation process so that in the next step the studies can be extended towards including further relevant parameters such as temperature.

Highlights

Polymer-based optical interconnects attracted much attention in recent years as they can be used in integrated photonic circuits of telecommunication networks
A laser source at 638 nm with 15 mW power is used for writing of the self-written waveguide (SWW) as it provided about 90% transmission efficiency minimizing the absorption for the photopolymer sample at this writing wavelength, see [21]
It was decreased at a later time at 17 s due to increase in refractive index along the direction of the beam propagation axis, see Fig. 5(b)

Summary

Introduction

Polymer-based optical interconnects attracted much attention in recent years as they can be used in integrated photonic circuits of telecommunication networks. The SWWs are created by the self-action of light where the excitation beam is focused and trapped within the material medium due to self-induced change in the refractive index along the direction of beam propagation This photopolymerization mechanism is local in space but non-local in time, i.e., the refractive index modulation is higher in large intensity areas and depends on the history of the electromagnetic fields at earlier times, very much similar to the Kerr effect. The SWWs are called self-induced waveguides as they are fabricated by propagating a light beam through photopolymer media and they can guide beams of different polarization or wavelength This process provides a very relaxed alignment technique between the light source and the propagating media employed for the SWWs. This process provides a very relaxed alignment technique between the light source and the propagating media employed for the SWWs They can be used as interconnects between different optical components (fiber-to-fiber, laser-to-fiber, laser-to-laser and optical sensors) in integrated photonic circuits or in polymer back-planes. Many theoretical and experimental studies were already carried out to understand the underlying self-writing phenomenon of the light within photo-monomer as well as in other photosensitive materials [9,10,11,12,13,14,15,16,17]

Methods

Results

Conclusion