Tuning multichannel filters based on FBG in multicore fibers
Multichannel filter elements based on fiber Bragg gratings in multicore fibers (MCF) feature excellent potential for applications in astrophotonics. However, due to slight core-to-core variations of the refractive index (RI), the resonance wavelength of the inscribed FBGs differs. For an optimized functionality, the filter properties, especially the resonance wavelengths, should be equal across all cores. Therefore, we present a post-treatment procedure by ultrashort pulsed laser irradiation in order to tune the resonance wavelength of an individual FBG. To shift the resonance wavelength, a constant RI change in addition to the RI modulation is induced. Precisely tuned wavelength shifts up to 255 pm are demonstrated. Finally, we demonstrate precise tuning of the FBG resonance wavelength in a single core inside an MCF.