We report on a method to create multiple waveguides simultaneously in 3D in fused silica. A combination of adaptive beam shaping with femtosecond laser writing is used to write two waveguides with changing separation and depth. The method is based on a programmable phase modulator and a dynamic variation of the phase-pattern during the writing process. The depth difference can be dynamically varied by changing a chirp parameter of the applied phase grating pattern. It can be employed in various photonic devices such as couplers, splitters and interferometers. Here we demonstrate splitters with both outputs ending in different depth.

We report a novel method to create waveguide devices such as couplers in fused silica. A combination of adaptive beam shaping with femtosecond laser writing is used to simultaneously write two waveguides with changing separation. IntroductionFemtosecond laser irradiation in transparent materials is a powerful and straightforward method for the fabrication of high-quality optical waveguides. When a femtosecond laser pulse is tightly focused inside the bulk, the intensity in the focal volume becomes high enough to cause absorption through nonlinear processes, leading to a permanent refractive index modification after relaxation of the plasma. Under suitable irradiation conditions the refractive index change is positive, allowing for direct fabrication of guiding structures. At present, optical devices such as couplers, splitters, and interferometers are fabricated in a serial way, which means that each waveguide is written after the other. However, these photonic devices require a precise control over the relative positions of the parallel or overlapping structures.In this paper we introduce a novel technique, based on adaptive beam shaping of the femtosecond laser with a Spatial Light Modulator (SLM), which allows for the implementation of multiple foci with controlled power distribution and dynamically variable distance [1,2]. We use this technique for the fabrication of optical devices in a single sweep.

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