Quantum-dot devices get a funding boost
Project leader Johann Reithmaier of the University of Wurzburg in Germany and colleagues across several European research organizations plan to make external cavity lasers that tune over 300 nm, directly modulated chirp-free 1.5 µm DFB lasers, as well as high-speed optical amplifiers for multi-wavelength applications.
QDs are three-dimensional semiconductor structures only nanometers in size. Reithmaier says that if QDs are used as the gain material in lasers, the devices have a gain bandwidth that is three times broader than the bandwidth in a typical QW laser. The lasers also exhibit a faster recovery time for optical amplification, multi-wavelength amplification and a reduced chirp factor.
Reithmaier s team plan to grow the QD structures using GS-MBE with Group V gas sources. "We have had a lot of experience with this type of system and have an excellent control over dot formation," Reithmaier told Compound Semiconductor.
Using GS-MBE, the researchers have already grown quantum-dash lasers based on a separate confinement heterostructure design. To grow the lasers, the researchers first deposited a 200 nm thick Si-doped InAlAs bottom cladding layer onto a S-doped InP wafer.
A 480 nm thick AlGaInAs inner waveguide was grown onto the cladding, and the active layer - which comprises four self-assembled InAs quantum-dash layers - was embedded in the waveguide.
A 25 nm AlGaInAs layer separated each quantum-dash layer, and by altering the size of the dashes in the active region, the researchers adjusted the emission wavelengths from 1.54 to 1.78 µm. The researchers formed the upper cladding with a 100 nm AlInAs layer, a 1700 nm InP layer and a 150 nm GaInAs cap.
With their latest funding, Reithmaier says that his team has already improved the threshold current densities and efficiencies of its lasers. "The first devices will be SOAs and DFB lasers, and we will also develop external cavity lasers during this time," said Reithmaier.
The European Union is funding the project, and other organizations involved are Politecnico di Torino, Italy, the Technical University of Denmark, Thales Research and Technology of France, the Israel Institute of Technology and Nettest Photonics, France.
