With the successful completion of his doctoral dissertation at TU Berlin, “Monolithically Integrated InP Polarization Diversity Coherent Receivers,” Hendrik Boerma, a research associate at Fraunhofer Heinrich-Hertz-Institut (HHI), has made a major contribution to photonics-based communications. His work advances coherent optical transmission technology, a key foundation of global digital connectivity.
Advances in Coherent Optical Transmission and Integrated Lasers
Coherent receivers are critical components in high-speed data transmission networks particularly for advanced modulation formats such as DP-16-QAM (dual-polarization 16-quadrature amplitude modulation). The research goal of Hendrik Boerma’s work was to develop indium phosphide-based coherent receivers that integrate polarization diversity with high bandwidth and responsivity. The work utilized a novel adiabatic mode evolution approach for efficient polarization conversion and mode splitting, which represents a major technological breakthrough.
Using this integration concept, Hendrik Boerma and the Fraunhofer HHI team developed a fully monolithically integrated receiver chip with outstanding performance, achieving a polarization extinction ratio of more than 17 dB, a bandwidth of 95 GHz, and a responsivity of 0.08 A/W.
Another major highlight of the dissertation is the realization of a tunable laser with a record linewidth of just 8.2 kHz — the narrowest linewidth reported so far for a monolithically integrated indium phosphide laser. This laser is especially important for demodulating higher-order modulation formats such as 64-QAM and helps optimize coherent receiver systems by enabling extremely precise and stable demodulation.
New Opportunities for Research and Industry
Beyond significantly improving and diversifying photonic integrated circuits in InP, this research also opens the door to pioneering applications in areas such as quantum communications and microwave photonics. The ability to fabricate complete photonic integrated chips — including waveguide structures, photodiodes, and lasers — in a single semiconductor material offers major benefits in terms of efficiency, scalability, and system integration.
Hendrik Boerma developed a deeper interest in photonics while studying electrical engineering at TU Berlin. He joined Fraunhofer HHI in 2017 as a student assistant and has since built an impressive scientific profile. With a total of 26 publications associated with this work, his dissertation highlights both the depth of his expertise and the significance of his contributions to photonic integration.
Academic Classification and Collaboration
The dissertation was supervised by a distinguished team of photonics experts: doctoral advisor Prof. Martin Schell (formerly Fraunhofer HHI), committee chair Prof. Michael Lehmann (TU Berlin), reviewer Prof. Kevin Williams (TU Eindhoven), reviewer Prof. Anna Lena Schall-Giesecke (University of Duisburg-Essen), and supervisor Dr. Patrick Runge (Fraunhofer HHI).
This research is a strong example of Fraunhofer HHI’s role as a leading institute in photonics. It demonstrates how excellent scientific work can not only push the boundaries of technology but also deliver tangible benefits for industrial applications.