Hybrid polymer-silica waveguides provide tunability
Paula Noaker Powell
Air-silica microstructure fibers allow a diverse range of guided-mode properties to be created. The results can produce unique spectral characteristics when long and short-period gratings are written into photosensitive regions. In addition, it is possible to introduce polymers into the air regions to produce hybrid polymer-silica waveguides that allow enhanced tunability of propagation properties. One example recently investigated by Lucent Technologies Bell Labs (Murray Hill, NJ) and the Laboratory for Physical Sciences (College Park, MD) is a hybrid polymer-silica microstructure fiber with a UV-induced Bragg grating in the fiber core. A key feature-the large air regions of the fiber-reduces fiber fabrication constraints and simplifies the process of polymer infusion into the air regions.
Despite the lack of circular symmetry resulting from the microstructure, the polymer tuning observed is similar to that seen in standard fiber surrounded by polymers or oils. The polymer is contained only inside the air regions, so the outer air-silica interface is intact, allowing, for example, fabrication of on-fiber thin-film heaters for temperature tuning. According to the researchers involved in the project, the Bragg grating transmission spectrum clearly shows different design regimes in which cladding resonances can be wavelength-tuned, suppressed, or amplitude-tuned. This tunability is possible because of the strong temperature dependence of the polymer refractive index. For more information, contact Paul S. Westbrook at firstname.lastname@example.org.