The visible and near-infrared (NIR) spectral ranges have for a long time dominated
developments in photonics research including establishing and implementation of photonic
integrated circuits (PICs) for sensing and telecom applications. However, nowadays, the
mid-infrared (MIR) range and in particular MIR PICs move into focus, making their first
footsteps as fully monolithic integrated and functional devices. They demonstrate the ability
to uniquely address applications such as by probing fundamental molecule absorptions in
bio-chemical liquid sensing experiments or in free-space telecommunication in the MIR
transparency windows of the atmosphere.
This presentation will start with a brief introduction to the field of PICs, followed by focusing
on recent developments in the very mature material platform of InP for optoelectronic devices
and NIR and MIR PICs. In the NIR InP has reached a level of commercial availability of PICs
which as will be shown can be designed to realize novel on-chip quantum transmitter PICs
for QKD around 1550 nm. In the MIR, typical quantum cascade (QC) devices do also benefit
from the maturity of the InP material system itself, but especially complex, multi-element and
functional PICs have not yet been demonstrated. This mainly originates from the complicated
quantum structure and hence difficult epitaxial growth and following PIC fabrication process,
together with the lack of suitable and readily implemented MIR waveguide materials that
support on-chip beam-guiding. It will be demonstrated how this can be conceptually and
technology overcome by integrating active QC devices with passive elements using
plasmonic waveguiding schemes and on-chip integrated micro-optics. The presented fully
monolithic MIR PICs will cover simpler linear lab-on-chip geometries that are used in in-situ
reaction monitoring experiments of protein unfolding and a fully operational complex on-chip
MIR beam combiner.