Modified astigmatic beam technique for laser writing

Abstract

The ultrafast laser writing of optical waveguides and devices is increasingly ubiquitous among the photonics community, mostly for its flexibility and three-dimensional fabrication capability. The well-known astigmatic beam technique is the simplest method to inscribe near-circular cross-section waveguides. In this paper, we report on a significant enhancement to the widely used astigmatic beam technique that makes it more flexible and yields a more circular waveguide cross section. By simply superposing a long-focus lens before the laser inscription objective lens, we demonstrate that the normalized squared radial deviation from a perfectly circular waveguide cross section can be reduced to &lt;<!-- 4 × 1 0 − 4 , which is a significant improvement compared to &gt; 0.1 typically obtained using the standard astigmatic beam technique, or &gt; 0.7 with a Gaussian beam. The modified technique also makes it easy to use the full power delivered by the laser, which is not usually the case with the standard technique. A technique to optimize the waveguide shape prior to the inscription by in situ laser-induced plasma emission imaging is also discussed.

Precise mode control of laser-written waveguides for broadband, low-dispersion 3D integrated optics

“…Remarkably, the OCMS method enables not only positive but also negative RI control, such as in the alkali-rich glass K9 (see Supplementary text S3 for details); or further, the OCMS approach allows for arbitrarily customizing the degree of laser-induced thermal modifications with exceptionally high resolution, providing an efficient route to produce submicron or nanoscale structural modifications in glasses beyond current thermal FLDW techniques 17 – 19 . Additionally, the proposed OCMS processing strategy is not limited to the objective lens used, but can be easily extended to any objective lens according to practical applications, by carefully tailoring the RI structure of a single scanline through laser beam shaping methods, including astigmatic beam shaping 20 , 21 , aberration correction 22 and manually added spherical aberration 9 .…”

“…Additionally, the proposed OCMS processing strategy is not limited to the objective lens used, but can be easily extended to any objective lens according to practical applications, by carefully tailoring the RI structure of a single scanline through laser beam shaping methods, including astigmatic beam shaping 20,21 , aberration correction 22 and manually added spherical aberration 9 .…”

Enhancing Evanescent Wave Coupling of Near-Surface Waveguides with Plasmonic Nanoparticles

“…The photo-inscription of near-surface waveguides was achieved according to a previously reported procedure [17] and using a modified astigmatic beam technique [30] to improve the waveguide cross section. Briefly, a femtosecond laser (Ti:sapphire, Coherent RegA) operating at a wavelength of 790 nm and a repetition rate of 250 kHz was used to modify the refractive index.…”

“…The samples were then translated at a speed of 10 mm/s, across the focal point, perpendicular to the laser beam, using motorized mechanical stages (Newport XML210 and GTS30V). A cylindrical lens telescope and a long focal lens were used to produce an astigmatic beam and shape the focal volume in such way as to form waveguides with near-circular cross sections [30].…”

Ultrafast laser writing of arbitrary long low-loss waveguides in optical fibers

“…By moving the sample, various advanced photonic components such as directional couplers, wavelength division multiplexers, interferometers, gratings, or resonators can be directly integrated in the bulk. Nowadays, advanced beam shaping techniques are commonly used to optimize the energy deposition during the laser-matter interaction allowing the improvement of device performances [13,14]. Beyond its 3D capabilities, the DLW technique also offers a great versatility in terms of materials that can be processed.…”