Multiple-wavelength laser arrays at 1.55 μm are key components of wavelength division multiplexing (WDM) systems
for increased bandwidth. Vertical cavity surface-emitting lasers (VCSELs) grown on GaAs substrates outperform their
InP counterparts in several points. We summarize the current challenges to realize continuous-wave (CW) GaInNAsSb
VCSELs on GaAs with 1.55 μm emission wavelength and explain the work in progress to realize CW GaInNAsSb
VCSELs. Finally, we detail two techniques to realize GaInNAsSb multiple-wavelength VCSEL arrays at 1.55 μm. The
first technique involves the incorporation of a photonic crystal into the upper mirror. Simulation results for GaAs-based
VCSEL arrays at 1.55 μm are shown. The second technique uses non-uniform molecular beam epitaxy (MBE). We have
successfully demonstrated 1x6 resonant cavity light-emitting diode arrays at 850 nm using this technique, with
wavelength spacing of 0.4 nm between devices and present these results.
Quantum cascade lasers based on planar quantum wells have emerged as a leading candidate for infrared laser sources. However, these lasers are ultimately limited by phonon emission, and exhibit useful optical gain only for the tranverse magnetic polarization. Quantum dot (QD) gain material to replace the planar gain regions is very attractive because the unipolar approach can then lead to both a phonon bottleneck, and surface emission. However, tunneling phenomenon is quite different for unipolar QD injection, and designs that follow the now standard approaches based on planar quantum wells are known to have unfavorable tunneling characteristics. In this paper we present a new device design based on QDs that can lead to important advantages for realizing high performance unipolar injection infrared lasers. The new quantum dot cascade laser design is based on controlling electron tunneling in the different quantum dimensional systems, from zero-dimensional to two-dimensional, to both block as well as enhance tunneling in a gain stage so as to obtain the population inversion necessary for infrared gain. This new device, the quantum dot cascade laser (QDCL), can operate with a phonon bottleneck, and therefore can exhibit improved high temperature performance in contrast to planar heterostructure unipolar devices. In addition, the zero-dimensional confinement can also provide transverse electric polarization in the radiation field, and therefore surface emission. Epitaxial growth experiments based on self-organized quantum dots to realize the new QDCL approach are presented and discussed.
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