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Asynchronous optical sampling THz spectroscopy system based on monolithically modelocked laser diodes

Subject Area Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Term from 2014 to 2025
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 236759088
 
Final Report Year 2025

Final Report Abstract

The project goal was to develop a compact, powerful THz-TDS-System (Terahertz-Time domain spectroscopy) with new sampling concepts on the basis of monolithic hybrid modelocked laser diodes. For that purpose, partner FBH developed multi-section laser diodes with variable geometries (e.g. variable absorber lengths). The integration of a tapered gain section within a for power boosting has been comprehensively experimentally and theoretically investigated. The tapered laser can generate optical pulses with a duration of 3 ps and a peak power of approximately 40 W. The pulses are chirped, making them suitable for subsequent compression. By integrating an S-bend waveguide, a detuning of the repetition rate by about 10 MHz is achieved. Partner EST developed successfully the driving electronics for the hybrid modelocking. It enables stable hybrid modelocking with low temporal jitter and tunability of the repetition rate by up to 30 MHz, the latter being crucial for the envisioned asynchronous sampling concepts. Partner PTT was responsible for the laser characterization and the system development. The laser diodes with short (100 µm) absorber segment delivered too low bandwidths for THz applications. The later available laser diodes with 200 µm long absorbers in contrast delivered broad spectral bandwidth with strongly chirped pulses. These laser diodes thus delivered sufficient specifications for reaching the project goals. However, the system development proved to be challenging. In this respect, the project partners only jointly defined the final design of the system at a late stage of the project. The lasers required for this were realized, but could no longer be made available within the regular project duration. A continuation of the work has been agreed between the partners.

Link to the final report

https://doi.org/10.34657/27647

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