08 Aug. Photon pairs straight out of the laser
Photon pair sources are crucial for applications that utilize quantum phenomena (e.g., quantum-encrypted communication). In order to use the established infrastructure, they must operate at standard telecommunications wavelengths. Researchers at the Ferdinand Braun Institute, Leibniz Institute for High Frequency Technology (FBH) in Berlin have developed an electrically driven laser source that generates photon pairs. The laser is based on a wavelength-stabilized Bragg reflection waveguide-rib waveguide structure (BRW-RW). According to the researchers, the laser is capable of converting laser light from a high-order vertical waveguide mode into photon pairs of two fundamental modes with double the wavelength through parametric fluorescence.
Since parametric fluorescence is a highly frequency-sensitive process, conventional Fabry-Pérot lasers (FP lasers) are unsuitable due to their lack of wavelength stabilization. To remedy this, the team integrated a distributed Bragg reflector surface grating (DBR) into part of the laser. This grating stabilizes the laser wavelength by providing high mode reflectivity for technologically feasible etching depths. Since the wavelength is determined by the Bragg condition, it can be tuned toward the operating point of parametric fluorescence by varying the grating period.
CW power-current behavior of an FP-BRW-RW laser without a Bragg reflector surface grating (orange) and the DBR-BRW-RW laser (blue). The lasers are 4 mm long. Image: FBH
The research team was able to show that the wavelength of the DBR-BRW-RW laser is stabilized, while a free-running FP-BRW-RW laser exhibited multimode operation and mode hopping. This demonstrated that the introduction of a DBR surface grating leads to wavelength-stabilized laser emission in Bragg reflection waveguides. This enables the laser wavelength to be tuned for optimized photon pair generation.
The optical spectra of both laser types. Image: FBH
This work is supported by the German Federal Ministry of Education and Research (BMFTR) under grant number 16KIS1768 (project VOMBAT).
Original publication
[T. Tenzler, J. Koester, H. Wenzel; Theoretical study of Bragg reflection waveguide laser structures with surface gratings for spontaneous parametric down conversion. Physica Scripta 100(5), 055105 (2025)]
Source and image: www.fbh-berlin.de