Multi-junction distributed-feedback laser diodes - synergy of high optical power and single-mode operation

• Applicant: Professor Dr. Ulrich Theodor Schwarz
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544925332

The aim of the proposed project is to demonstrate a completely new type of optoelectronic device - a multi-junction distributed feedback (DFB) laser diode (LD). We expect this device to offer unprecedently high optical power and single-mode operation from a compact and robust semiconductor chip. The device will be based on GaN and will be operating in the visible spectrum. This ensures many possible applications such as “last mile” telecommunication based on plastic fibers, Li-Fi, Light Detection and Ranging (LIDAR) systems, underwater communication, strontium-based atomic clocks, gas sensing and environmental monitoring. A multi-junction LD consists of have several pn junctions with one active laser region each interconnected with tunnel junctions (TJs). The advantage of this device, compared to single pn junction devices, is that for the same vertical current flow, the recombination occurs in each of the active regions. In principle, one can expect an N-fold increase in output power of the multi-junction LD with N sections. This results in differential efficiency (photons per injected electrons) higher than 100%, which comes at the cost of additional voltage required for each section. Multi-junction LDs have been demonstrated for conventional semiconductor systems such as GaAs and InP. Devices operating at a wavelength range of 800 to 2000 nm are commercially available and find applications in LIDAR and range finding. Multi-junction LDs operating in the visible spectrum were elusive until recently. At the Institute of High Pressure Physics Polish Academy of Sciences (IHPP PAS), which is project partner within the weave program, GaN-based multi-junction LDs consisting of two and three sections operating in the visible spectral region were demonstrated recently. With the proposed project we plan to force the multi-junction LDs to operate in a single mode by coupling of its optical mode to a surface diffraction grating along the full length of the resonator as is done in DFB LDs. The device will operate on high order transversal mode with maxima of the mode in the active regions and minima in the TJs. The multi-section design will enable high optical power while high coupling of the mode to the surface grating will ensure a single-mode operation of the proposed device.

• DFG Programme: Research Grants
• International Connection: Poland
• Cooperation Partner: Dr.-Ing. Grzegorz Muziol