Figure 4

Schemes of the fabrication processes used for realizing the required optical waveguides. (a) An hot embossing process was employed to create multi-mode waveguides. Hereby (1) a PMMA foil (Plexiglas XT 99524, ThyssenKrupp, Germany) was placed between a stamp containing the master structure and a planar holder. (2) Applying a temperature slightly above the glass temperature of PMMA (\(T_g\approx 120\) \(^\circ \)C) and a pressure of \(\approx 35\) bar transferred the structure from the master stamp to the PMMA foil. (3) After the sample cooled down close to room temperature, the pressure was reduced and the sample containing the negative of the master structure was removed. In a final step, the fabricated channel in the PMMA was filled (4) with an epoxy resin (NOA68) mixed with the molecular switches or (5) filled with an epoxy on top of which the molecular switches were applied after the curing process, respectively. (b) To investigate single mode structures, SWWs were used. (1) Therefore, an epoxy was applied in between two aligned single mode fibers with a small gap. (2) Subsequently, light with an UV-near wavelength (\(\lambda =406\) nm) was illuminated through one fiber starting the curing process of the epoxy locally at the end of the fiber. This, again, increases the refractive index locally, which traps the light and creates a straight waveguide. (3) Finally, the surrounding resin can be cured with UV-flood exposure if the epoxy was already mixed with molecular switches to achieve a distribution of the particle inside the core. (4) Alternatively, the residual resin can be removed using isopropanol enabling free access to the core.