Wavelength tuning limitations in optically pumped type-II antimonide lasers

In this paper, we examine the wavelength tuning limitations of type-II antimonide lasers containing InAs/InGaSb/InAs quantum wells. Wavelength tuning is accomplished by varying the thickness of the InAs electron wells while keeping all else fixed. In principle, these wells can be tuned from lambda approximate to 2.5 mu m out to far IR wavelengths by increasing the thickness of the InAs layers. However, a practical upper limit of lambda approximate to 9.5 mu m is set due to the high waveguide losses a(wg) and the diminishing modal overlap with the gain at longer wavelengths. The waveguide losses grow as a(wg)alpha lambda(3.44) and are attributable to free carrier absorbance. In order for the long-IR laser devices to achieve threshold, they must continually band fill, spectrally tuning to shorter wavelengths, until the laser gain exceeds the losses, which occurs near 9.5 mu m. (C) 2008 American Institute of Physics.