Mid-IR QC laser switches with near-IR telecom wavelength

Researchers at Northwestern University’s Bio-Inspired Sensors and Optoelectronics Laboratory (BISOL) led by Professor Hooman Mohseni have used a novel gap-loaded nanoantenna that shows resonance at dual wavelengths when integrated onto the facet of a quantum-cascade laser (QCL). The antenna design shows resonance at the QCL wavelength of 6.1 μm and the switch-beam wavelength of 1.55 μm. Coupled by a nonlinear nanoswitch, the two antennas differ from other gap-loaded nanoantennas in that the cross-polarized switch beam antenna allows for enhanced absorption in the gap-loaded germanium region, which increases the switching efficiency. With switching power on the order of picojoules, the dual-wavelength operation of the device suggests applications in telecommunications, free-space optical communications, and laser rangefinding.

The optical nanocircuit is extremely small (less than half a cubic micron) and integrated directly at the laser facet. When light at 1550 nm is coupled to the antenna, its intensity is enhanced by the smaller bowtie. This changes the refractive index of the germanium, and therefore modulates the larger antenna and thus the overall QCL power. Experimental data for the device shows excellent agreement with simulation data. The device shows a modulation depth of approximately 15% at the switch-beam power of 70 μW, resulting in a switching energy of 8.4 pJ—comparable to other all-optical switch designs, but with a much smaller device size. Contact John Kohoutek at [email protected].