Wavelength stabilized BRW RW laser for photon pair generation
Fig. 1. Schematic of the DBR-BRW-RW laser.
Fig. 2. CW power-current characteristic of a 4 mm long DBR-BRW-RW laser (blue) with a 1 mm long grating and a 4 mm long FP-BRW-RW laser (orange) without grating.
Fig. 3. Mapping of the optical spectra measured for varying injected currents. Top: DBR-BRW-RW laser; bottom: FP-BRW-RW laser.
Photon pair sources are crucial for applications utilizing quantum phenomena (e.g., quantum-encrypted communication) and benefit from operating at standard telecom wavelengths to leverage established infrastructure. We’ve therefore developed an electrically driven, wavelength-stabilized Bragg reflection waveguide ridge waveguide (BRW-RW) laser source that simultaneously generates photon pairs. This device is capable of converting lasing light of a high-order vertical waveguide mode into photon pairs of two fundamental modes at twice the wavelength through parametric fluorescence.
As parametric fluorescence is a highly frequency-sensitive process, conventional Fabry-Pérot (FP) lasers are unsuitable due to their lack of wavelength stabilization. To remedy this, we have incorporated a distributed Bragg reflector (DBR) surface grating into a segment of the laser (see Fig. 1). This grating stabilizes the lasing wavelength by providing high modal reflectivity for technologically feasible etch depths. Furthermore, as the wavelength is determined by the Bragg condition, it can be tuned by varying the grating period, shifting it towards the operating point of parametric fluorescence.
Fig. 2 compares the CW power-current characteristics of an Fabry-Pérot FP-BRW-RW and our DBR-BRW-RW laser. As shown in Fig. 3, the optical spectra of both types of lasers reveal that the wavelength of the DBR-BRW-RW laser is stabilized, while the free-running FP-BRW-RW laser exhibits multi-mode operation and mode-hopping. Thus, for the first time, we have demonstrated that the introduction of DBR surface grating yields wavelength stabilized laser emission in Bragg reflection waveguides. This enables tuning of the laser wavelength for optimized photon pair generation.
This work is supported by the Federal Ministry of Research, Technology and Space (BMFTR) under the grant 16KIS1768 (project VOMBAT).
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).