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

本课题的目标是有源集成光器件的研究。集成光学领域涉及具有不同功能的光学系统的开发以及这些系统在单一基板上的组合。这使得整个系统的小型化和成本降低成为可能。集成光学电路（IOC）与使现代数据处理和计算机技术成为可能的集成电路（IC）类似，是与光进行数据通信的基本要素。集成光学的基本部件是波导，它将光引导到一定的方向。例如，通过这些波导的某种排列，光波和信号可以被分离。在这种情况下，光学元件称为分束器。此外，光也可以引导周围的曲线和转移到其他波导所谓的耦合器。通过制造出几百纳米大小的结构，也就是光的波长，光的光谱特性和信号的光谱特性就可以被改变。这对于波导也是可能的，它引导光在一个圆上。如果在有源光学材料中制造波导结构，例如在用于激光器的晶体中，光信号甚至可以在集成电路本身内产生或放大。在这种情况下，该系统被称为波导激光器或放大器。我们将利用飞秒激光刻字技术制作波导结构。该方法利用激光脉冲将微米尺度的结构直接刻入介质材料中。我们将利用激光晶体和光学活性材料作为衬底，与玻璃相比，它们具有更好的热机械和光学性能。由于在体积内的结构，因此是三维的，激光书写是一种非常灵活的方法。我们将在项目中对三种不同晶体材料的直波导和弯波导进行基本研究。除了这些基础研究外，我们还想证明飞秒激光书写技术在制造有源集成光学元件方面的可用性。为此，我们将首次在激光晶体中实现分束器、耦合器和环形谐振器。该项目的一部分将包括制造波导激光器，它将发射连续的激光束或激光脉冲。对于脉冲波导激光器，我们将集成特殊的光学元件，即所谓的可饱和吸收器，直接在衬底上。

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.