Femtosecond-laser written structures in crystalline laser media for integrated optical applications

• Applicant: Dr. Thomas Calmano
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 261102386

The goal of this project is the research on active integrated optical devices. The field of integrated optics addresses the development of optical systems with different functions and the combination of these systems on a single substrate. This makes a miniaturization and a cost reduction of the complete system possible. Similar to electrical integrated circuits (IC), which enable modern data processing and computer technology, integrated optical circuits (IOC) are the essential elements for data communication with light. Basic components for integrated optics are waveguides, which guide light into a certain direction. For instance, by a certain arrangement of theses waveguides the light-wave and thus the signal can be split. In this case the optical element is called a beam-splitter. Furthermore the light can also be guided around curves and be transferred to other waveguides with so called couplers. By the fabrication of structures, which exhibit a size of several hundreds of nanometers, which is in the order of the wavelength of the light, the spectral properties of the light and thus of the signal can be modified. This is also possible with waveguides, which guide the light in a circle. If one fabricates the waveguiding structures in active optical materials, for example in crystals which are utilized for lasers, the light signal can even be generated or amplified within the integrated circuit itself. In this case the system is called waveguide laser or amplifier.We will fabricate the waveguiding structures by the femtosecond laser writing technique. With this method structures on a micrometer scale are inscribed directly into dielectric materials with laser pulses. We will utilize laser crystals and thus optically active materials as substrates, which exhibit better thermomechanical and optical properties in comparison to glasses. Due to the structuring within the volume, thus in three dimensions, fs-laser writing is a very flexible method. We will perform basic investigations on straight and curved waveguides in three different crystalline materials within the project. Beside these basic investigations we want to demonstrate the usability of the femtosecond laser writing technique for the fabrication of active integrated optical elements. For this purpose, we will realize beam-splitters, couplers and ring-resonators for the first time in laser crystals. One part of the project will include the fabrication of waveguide lasers, which will emit a continuous laser beam or laser pulses. For the pulsed waveguide lasers we will integrate special optical elements, so called saturable absorbers, directly onto the substrate.

• DFG Programme: Research Grants