| Optically-pumped type-II mid-infrared index-coupled tunable distributed feed-back (DFB) semiconductor lasers have been developed to provide continuous-wave (CW) single longitudinal mode (SLM) operation with features including narrow spectral linewidth, high output power, good beam quality and wide continuous wavelength tunability for applications such as remote sensing or spectroscopy in the 3 to 5 microm midwave-infrared range of atmospheric transmission window.;In the demonstration of this type of laser, a hyperbolically chirped grating was patterned using interferometric lithography (IL) with spherical wavefronts which was then transferred into the top clad of the slab waveguide epi-structure of the laser device. Wavelength tuning is achieved by translationally projecting pump stripe at different positions of this chirped grating on the laser device, thus different grating periods along the pump stripe at different pump positions select different lasing wavelengths. Primary results were acquired on one device of 4 mm in lateral dimension with continuously tuning range of about 80 nm centered at 3100 nm, single facet output power of 830 mW and typical spectral linewidth of 1.2 nm at 2.5xthreshold pumping. Fabry-Perot (F-P) interferometer was used as artificial target gas to demonstrate potential application of gas spectroscopy with this type of laser. |
