We report mechanical frequency and amplitude modulation of a quantum cascade laser (QCL) integrated with a plasmonic antenna operating at ~6.1 μm. We have observed a shift in the lasing frequency by over 30 GHz and an intensity modulation of ~74% when an atomic force microscope (AFM) tip approaches the hot spot of a metal-dielectricmetal (MDM) bow-tie antenna integrated onto the facet of the laser. The tip diameter is ~λ/60 and in non-contact mode its amplitude of motion is ~λ/120. We have presented a theoretical model based on the rate equations for a QCL which affirms our experimental observations. Our experiment demonstrates the strong influence of the hot spot on the laser cavity modes, despite the fact that the former is many orders of magnitude smaller than the latter. We have compared our device to a previous mechanically frequency modulated QCL and calculated a figure of merit, change in frequency divided by change in distance of the mechanical component (Δf/Δd), which is an order of magnitude higher, while our design uses a volumetric change per λ3 that is five orders of magnitude smaller. Our device differs from optical gradient force actuated devices in that our device is externally mechanically actuated while those devices are self actuated through the optical force. This sensitivity of the laser cavity mode to the position of a nanometer-scale metallic absorber opens up the opportunity for modulating large amount of optical power by changing the optical properties of a miniscule volume in an integrated, chip-scale device.

Date Published: 15 October 2012
PDF: 7 pages
Proc. SPIE 8456, Nanophotonic Materials IX, 84560K (15 October 2012); doi: 10.1117/12.2006932

Published in SPIE Proceedings Vol. 8456:
Nanophotonic Materials IX
Stefano Cabrini; Taleb Mokari, Editor(s)