Femtosecond laser processing of miniaturized optical systems and sensors in glass substrates

Ultrashort laser pulses (< 100 fs) are very well suited for tailored processing of optical transparent materials on a micrometer scale. Due to the very short time of interaction no thermal processes arise and a structural change of materials is restricted to the laser focus volume. By adjusting carefully the laser parameters in glasses an increased refractive index change can be induced by femtosecond pulses. Based on this we developed a technique for direct writing of optical waveguide structures in nearly all glass materials. In figure 1 waveguides with different diameters for single or multi mode applications are shown. A further advantage of our technique is the ability of an easy adaption of the diameter of the waveguides, tailored for the mode field and wavelength of the guided light for a broad wavelength range from the visible to NIR. Additionally Bragg grating structures can be introduced inside the waveguides. This Bragg grating waveguides (BGW) can be used as high reflection mirrors or spectral filter elements for wavelengths from visible to NIR in optical circuits (figure 2). All optical structures are not visible by eyes. 3D-Optical elements like splitter or coupler waveguide elements, spectral filters or mirrors can be introduced in nearly all glass materials, enabling miniaturized applications in measurement engineering (figure 3).

We have successfully introduced BGW in ultra thin glasses from Schott (figure 4). This opens new applications for sensing of local deformation of surfaces (displays) or can be used as optical microphones. Ultra thin glasses often are used as packaging materials for MEMS. With our technique now this can be combined for integration of optical elements enabling new architectures in design of photonics and MEMS.

Glass chips with BGW structures are also suited very well for sensitive chemical analytics or for monitoring industrial chemical production processes. For this the waveguides with the Bragg grating structures are guided close to the surface of the glass substrate. Due to evanescent interactions with the chemical medium, surrounding the glass chip, a shift of the reflection wavelength is introduced. The sensitivity for specific chemical targets can be increased by deposition of associated receptors.

In summary, our technique is best suited for rapid prototyping of miniaturized optics for wavelength from visible to near infrared in glass substrates. In comparison to lithographic techniques for fabrication of waveguides no time consuming development for masking and etching is necessary, but rather new technological developments are made accessible.