In-situ monitoring of slow light structures in dye-doped polymer waveguide materials

In this work, we describe a technique for positioning the passband and monitoring the slowing factor of Moire grating written into PMMA-DR1 waveguides during fabrication. Slow light structures made with material platforms such as silicon must fabricated before their actual slowing properties can be measured. In our dye doped polymer waveguides, the slowing can be decided beforehand and the fabrication controlled to achieve the desired performance figure. The resulting group velocity slowing in the composite waveguide can be controlled by varying the index contrast of the grating. In dye-doped polymer materials we use, the index contrast can be changed using the process of irreversible photobleaching. Our technique uses a broadband source to monitor the reflectance spectrum of the grating and the delay of the structure is determined from this measurement. The theory behind the technique is reviewed and results are presented for a Moire grating written into waveguides fabricated in the dye-doped polymer material system, PMMA-DR1.