Innovative Device Concepts for Infrared Applications
Interband Cascade Lasers (ICLs)
ICLs are a novel class of coherent light sources in the near-to-mid-IR spectral range. They combine the concept of diode lasers with the cascading structure of QCLs. Distributed feedback gratings provides mode-selection for various types of high-performance single-mode light sources.
The light field, which is obtained by combining the light emitted by two uncorrelated single-mode lasers operating at slightly different frequencies, contains terms, which oscillate at the sum and the difference frequency. The linewidth broadening originates from intrinsic phase noise of both uncorrelated lasers and phase noise. For high resolution spectroscopic applications narrow linewidths are crucial. An optical phase locked loop can thus be used to establish a fixed phase relation between the two laser sources.
Quantum cascade detectors (QCD) are photovoltaic mid-infrared detectors based on intersubband transitions. Owing to the sub-picosecond carrier transport between subbands and the absence of a bias voltage, QCDs are ideally suited for high-speed and room temperature operation. QCDs make use of a series of subbands spaced by the LO phonon energy. This LO phonon ladder can be seen as a built-in field to extract the photoexcited electronsfrom the upper state of the optical transition and inject them into the ground state of the next period.