In fiber optic sensing a Fiber Bragg Grating (FBG) is a common measurement device to measure temperature or strain. The great advantage of such a sensor device is the wavelength encoded measurement. This means amplitude deviations do not disturb the signal and as long as there can be obtained a spectrum a measurement is possible. Typical commercial devices for FBG interrogation are available at wavelength ranges in the IR at telecom wavelengths (~1550 nm). But there are also fiber lasers working in different ranges due to different dopants of the fiber. This is why for Yb based lasers the range from 1000 nm -to 1200 nm is of great interest. Wavelength converting lasers do expand the range of addressable FBG wavelengths even further. Therefore, one also need a setup to measure the FBG characteristics over a very broad wavelength range which can be done using a super luminescent LED (SLED) and an optical spectrum analyzer (OSA). The task of your thesis would be to build a setup and software which can measure the FBG reflection and transmission spectrum over a wide range and in dependence of the polarization.

• Basic knowledge on LEDs and Semiconductor lasers
• Basic knowledge on optical spectrum analyzers
• Basic knowledge on optical fibers
• LabVIEW
• Python or MATLAB
• Skill of self-organized and independent working

• Begin: immediately
• Topics: FBGs, optical fibers, OSA, hands on lab experiments
• Scientific work in a good lab environment
• Supervision by Prof. Johannes Roths and Alexander Röhrl
• Support from young and skilled colleagues
• Opportunities for discussions within a scientific framework
• Insights into topics beyond the lectures
• Eventual contributions for scientific publications in peer-reviewed journals

In the Photonics Laboratory of FK06, we're actively engaged in applied research in the realm of fiber Bragg grating (FBG)-based sensing. Through a DFG-funded project, we're developing high-resolution optical H2 sensors designed to accurately measure very low hydrogen concentrations (‹ 400 ppm) nd simultaneously temperature within a multi-parameter sensor platform.
Within this project, advanced optical fibers with reduced cladding diameters will be utilized. Therefore, the fibers must be characterized precisely with respect to their effective refractive indices as well as their temperature- and strain-dependence. These observations can be performed using laser-inscribed fiber Bragg gratings that are fabricated throughout this thesis with i) a nanosecond UV-Excimer-laser source and ii) an ultrashort pulse laser. The processing of the optical fibers with the lasers will be monitored and analyzed carefully. Using these results, the effective refractive indices will be measured. In consecutive experiments, you will use these fiber Bragg gratings as sensors to measure their, and hence, the optical fiber’s temperature and strain sensitivity. -

• Begin: immediately
• Investigated topics: Properties of advanced optical fibers, fiber Bragg gratings, handling of optical and mechanical components and equipment, model-data-comparisons, advanced data processing
• Scientific activity in a well-equipped lab
• Supervision by a doctoral student and Prof. Dr. Roths
• A young, motivated team is always by your side
• Opportunity to participate in and contribute to technical discussions
• Option to combine the thesis with a working student position (SHK) up to 8 hr/week
• Insight into topics beyond the scope of lectures
• Potential involvement in scientific publications

Fiber optical sensing is an effective opportunity when it comes to sensing applications needing rugged sensors due to a harsh environment. Fused silica fibers withstand temperatures up to 1200°C which is approximately the glass transition temperature. However, sensing at comparable temperatures is not applicable because of sensor drifts and strong signal degradation. Therefore, crystalline sapphire fiber is a promising material for the sensor itself while the main light guidance can still take place in the silica fiber. We recently demonstrated a sapphire Fabry-Pérot Interferometer based sensor utilizing a sapphire optical fiber.
Within this thesis the senor should be further improved. The task consists of a simulation of the sensor, and the manufacturing of further improved sensors based on the data of the simulation. Together with a PhD candidate a waveguiding structure should be designed and employed for further sensor optimization.

• Knowledge of light propagation in different media and interferometry
• Some hands-on experience when it comes to optical fibers
• LabVIEW
• Python or MATLAB
• Skill of self-organized and independent working
• Fun at exploring the limits of fiber sensing

• Begin: immediately
• Topics: Fabry-Pérot Interferometers; optical fiber sensing with silica and sapphire fiber; Waveguiding
• Scientific work in a good lab environment
• Supervision by Prof. Johannes Roths and Alexander Röhrl
• Support from young and skilled colleagues
• Opportunities for discussions within a scientific framework
• Insights into topics beyond the lectures
• Eventual contributions for scientific publications in peer-reviewed journals

In the Photonics Laboratory of FK06, we're actively engaged in applied research in the realm of fiber Bragg grating (FBG)-based sensing. Through a DFG-funded project, we're developing high-resolution optical H2 sensors designed to accurately measure very low hydrogen concentrations (‹ 400 ppm) and simultaneously temperature within a multi-parameter sensor platform.
Special focus is placed on investigating temperature cross-sensitivities, minimum detectable concentrations, and response times. As part of your work, you will characterize various generations of sensors based on the mentioned properties. Additionally, you will further develop the calibration setup, evaluate the coating systems using a microscope, and contribute to enhancing the sensor elements. You will plan experiments, carry them out, and perform data analyzation. Your results will be discussed in the research group and – if successful and sufficiently novel – your results may contribute to publications.

• Begin: immediately
• Investigated topics: Properties of optical fibers, pi-shifted fiber Bragg gratings, handling of optical and mechanical components, model-data-comparisons, advanced data processing
• LabVIEW
• Scientific activity in a well-equipped lab
• Supervision by a doctoral student and Prof. Dr. Roths
• A young, motivated team is always by your side
• Opportunity to participate in and contribute to technical discussions
• Option to combine the thesis with a working student position (SHK) up to 8 hr/week
• Insight into topics beyond the scope of lectures
• Potential involvement in scientific publications