Femtosecond laser writing of Bragg grating waveguide bundles in bulk glass.

Waveguide bundles in bulk glass materials, consisting of several parallel scans of refractive index modifications, have been generated with a low-repetition femtosecond laser. Additionally, Bragg grating (BG) structures for 840 and 1550 nm have been introduced by segmentation of the central scan. A spectral loss in the transmission signal of >36 dB was achieved at 1550 nm with a second-order Bragg grating waveguide (BGW) in fused silica, which corresponds to an intrinsic grating efficiency of >16 dB/cm. This is to our knowledge the strongest BG structure realized in glass with a femtosecond laser. The BGW were proven to be stable up to a temperature of 250 degrees C in fused silica. The diameter of the waveguide bundles can be adapted very easily for a broad range of wavelengths and have been demonstrated for diameters between 1 and 50 mu m. The transmission properties of the waveguide bundles are affected minorly by the insertion of BG structures, which opens the ability for adjusting the BGW for a broad range of wavelength in single-mode or multimode optical circuits. BGW have been realized successfully in fused silica, borosilicate glass (BOROFLOAT 33), and AF 32 eco Thin Glass from Schott. (C) 2015 Optical Society of America