Adaptive slit beam shaping for direct laser written waveguides

Abstract

We demonstrate an improved method for fabricating optical waveguides in bulk materials by means of femtosecond laser writing. We use an LC spatial light modulator (SLM) to shape the beam focus by generating adaptive slit illumination in the pupil of the objective lens. A diffraction grating is applied in a strip across the SLM to simulate a slit, with the first diffracted order mapped onto the pupil plane of the objective lens while the zeroth order is blocked. This technique enables real-time control of the beam-shaping parameters during writing, facilitating the fabrication of more complicated structures than is possible using nonadaptive methods. Waveguides are demonstrated in fused silica with a coupling loss to single-mode fibers in the range of 0.2 to 0.5 dB and propagation loss <0.4 dB/cm.

Ultrafast-laser-inscribed 3D integrated photonics: challenges and emerging applications

“…In either case, if a 90 ∘ bent waveguide is required, the cylindrical telescope, slit or the sample itself has to be mechanically rotated in order to preserve the circular waveguide cross section along the bend. Mechanical rotation of optics or the sample can be avoided by imprinting a virtual slit onto a software programmable spatial light modulator (SLM) [71,72]. The virtual slit also enables dynamic tapering of the waveguides [71].…”

“…Mechanical rotation of optics or the sample can be avoided by imprinting a virtual slit onto a software programmable spatial light modulator (SLM) [71,72]. The virtual slit also enables dynamic tapering of the waveguides [71]. Also a deformable mirror (DM) can be used instead of an SLM in order to astigmatically shape the laser focal spot [73].…”

Optical Analysis of Direct Laser Written Structures

“…This three dimensional resolution is similar to that of our recently demonstrated third harmonic generation (THG) microscope, but achieved by a simpler optical system [9]. A deformable mirror is incorporated to correct aberrations encountered in imaging [10,11]. Figure 1 (a) shows a confocal microscope characterisation of the defects fabricated in fused silica, while Figure 1 (b) and (c) show waveguide cross-sections from a THG microscope.…”

Fabrication of Micro-optical Components in Glass

“…Thus, a disk-shaped focal spot is produced. A similar effect can also be achieved using deformable mirrors and adaptive slits [14][15][16]. Figure 6.1c shows a Fig.…”