Semiconductor lasers beyond the fiber optics telecommunication wavelength

Abstract

Semiconductor lasers emitting at 1.55 microns are the cornerstone of the high bandwidth optical communications industry. Semiconductor lasers operating at this and other wavelengths are also used in the engineering, biology, chemistry and medical fields. The light emission in most semiconductor lasers is due to the optical transition between the valence and conduction bands of the semiconductor active material. This means that the intrinsic properties of the semiconductor active material i.e., the bandgap energy dictates the emission wavelength. This limits the efficient operation of these lasers at wavelengths above 3 microns. In the mid 1990s this limitation was overcome with the emergence of new laser architectures, such as the intersubband and interband Quantum Cascade (QC) lasers. The emission wavelength in these QC lasers is set by engineering the bandgap to extend the accessible spectral range well beyond 3 microns. Optical radiation from intersubband QC lasers is emitted by electrons undergoing an optical transition between the quantized energy levels in the conduction band rather than by direct transition from the conduction to the valence bands as in conventional semiconductor lasers. Quantum engineering of the electronic energy levels has enabled demonstration of intersubband QC lasers covering a very wide spectral range from 3.5 to 150 microns (except for a window for the Reststrahlen gap). Despite rapid and tremendous progress in the research and development of these QC laser sources, the technology is far from being sufficiently mature to be deployed for use in space instruments. We will discuss our efforts at the Jet Propulsion Laboratory to advance QC laser technology sufficiently to enable their use in new instruments for future NASA Earth and Solar System Exploration missions.