Research-Page of Dominik G. Rabus

Research

Photonic Integrated Circuits in Polymers

Polymer optical waveguide devices will play a key role in several rapidly developing areas such as optical networks, biophotonic and fluidic applications. Together with my colleagues at the Forschungszentrum Karlsruhe, Institute for Microstructure Technology, I have developed a technology which enables the increase of the refractive index of methylmethacrylate based polymers by deep ultra violet (DUV) radiation. The modification of the dielectric properties of polymers by DUV is a useful technique for the realization of photonic integrated optical circuits. The technique presented here has several advantages with respect to common methods because only a single polymer layer is used, which serves as the substrate and waveguide as well and no further etching or development step is required. The waveguide fabrication is sketched in the figure below.

This method can not only be applied to planar polymer substrates but also to preembossed substrates. This enables the fabrication of ridge waveguide based devices by hot embossing. Work is currently being conducted to realize ridge waveguide based devices.

The UV-irradiation results in a local and controllable increase of the refractive index in the exposed areas of the polymer surface generating the integrated-optical waveguiding structures in a planar polymer plate. Only a thin surface layer of a few micrometers is modified by the DUV-light.

A photograph of a polymer plate (10 × 10 cm) with waveguide based devices is shown in the figure below.

Photographs of a directional coupler, a Y-splitter and the input region of a multimode interference coupler are shown in the figure below.

The figures of merit for the fabricated devices are shown in the table below. Note that the waveguide loss is mainly due to material loss at the measured wavelengths.

Waveguide Loss @ 1550 nm: 0.7 dB/cm

Waveguide Loss @ 650 nm: 0.1 dB/cm

Polarization Dependent Loss: < 0.15 dB

Fiber-Chip Coupling Loss: 0.5 dB / Facet

Excess Loss – Y-Splitter: 0.5 dB

Excess Loss – Directional Coupler: 0.5 dB

Excess Loss – MMI: 1 dB

UV modification of methylmethacrylate polymers additionally leads to a new surface chemistry affecting the selective absorption of proteins and the adhesion of living cells in vitro. The bi-functionality of the modified polymer chips supporting waveguides and cell anchorage capabilities at the same time provides the opportunity to monitor protein adsorption, cell attachment and spreading processes by evanescent-field techniques (see my research on Bio-Photonics).