Mid-Infrared Fiber Coupler for Multiband Infrared Countermeasure (IRCM) Lasers

Compact high power (>100 W) mid-infrared (2-5 microns) lasers are highly desired for military applications, such as infrared counter measures (IRCM). Semiconductor lasers, such as quantum cascade lasers (QCLs), are efficient compact sources that operate in the desired wavelength range. However, these lasers are currently limited in output power (~5 W). To achieve high powers, the output of several lasers must be merged. Free-space optics can be used to combine the lasers. Such combining system can suffer from vibrational induced misalignment in military vehicles or aircrafts. Couplers that are fiber-based would be ideal devices, since they are compact, environmentally stable and lightweight. Unfortunately, available fiber couplers are made from silica glass, which absorbs light below 2 microns. Mid-infrared transmitting fibers, conversely, have been demonstrated to transmit light in wavelengths beyond 10 microns. These fibers have been used in IRCM systems with great success and can be used to develop power couplers in the desired wavelength band. The proposed work will demonstrate feasibility of developing innovative mid-infrared fused-fiber devices designed for concatenating laser wavelength between 2-5 microns. Such technology can be the platform for developing broadband couplers for mid-infrared lasers, such as quantum cascade lasers, to achieve high power outputs.