| Ultrafast laser processing offers new prospects to miniaturize and integrate highly functional photonic devices directly inside transparent materials. Nonlinear optical interactions induce strong refractive-index changes in sub-micron volumes that permit the generation of two and three-dimensional structures with simple motorized translation stages.; Optical waveguides, the basic elements of all integrated circuits, were formed in fused silica in the focal volume of 50-fs Ti:Sapphire laser that delivers 3-μJ pulse at repetition rate of 100 kHz. Both single-mode and multi-mode propagation were observable, depending on laser exposure conditions and the probing light wavelength. Transmission losses as low as 1.5 dB/cm were noted at telecommunication wavelengths by comparing insertion losses of 1-cm and 2-cm waveguides exposed under identical conditions. Values for the laser-induced refractive index change were estimated by matching calculated waveguide profiles with the observed near-field intensity profile. Refractive index changes in the attractive range of 10−4 to 10 −2 were generated. These values were used to design and fabricate more complex structures Y-splitters, directional couplers and grating-based devices. We demonstrate for the first time that ultrafast lasers can fabricate low-loss three-dimensional photonic devices in bulk glass for operation in the telecom spectral band of ∼1550 nm. |
