Antenna integrated quantum cascade laser switchable via telecommunications wavelength probe beam

Here we present an antenna-integrated QCL which can be actively and optically modulated using light in the near infrared, creating an optical nanocircuit - coupling two different frequency antennas with a nonlinear active switching element. For our design, we chose two cross-polarized bow-tie antennas with an aligned central spot. We have used detailed FDTD simulations to choose the length of each bow-tie. The larger bow-tie antenna is resonant with the QCL at 6.1 μm wavelength and is aligned perpendicular to the active region of the device because QCL emits TM polarized light. The smaller bow-tie is resonant with the incoming modulating light at 1550 nm and is aligned perpendicularly to the first bow-tie. There is a rectangular region of amorphous germanium below the smaller bow-tie which acts as an absorber at 1550 nm. When light at 1550 nm is incident upon the device, it is focused and enhanced by the smaller bowtie, creating a region of large absorption in the germanium rectangle below. Free carriers are generated, shorting the larger bow-tie which is already focusing and enhancing light from the QCL mode. When the bow-tie arms of the larger bow-tie are shorted by these free carriers, the focusing and enhancement of the light by the larger bow-tie of the QCL mode is severely diminished, affecting the entire laser output, even the far field. Simulation results, fabrication details, and finally experimental results are discussed. Such an all-optical switch could be useful for telecommunications, free space communications, or rangefinding applications.