Optical sources operating in the atmospheric window of 3–5 μm are of particular interest for the development of free-space optical communication link. It is more advantageous to operate the free-space optical communication link in 3–5-μm atmospheric transmission window than at the telecom wavelength of 1.5 μm due to lower optical scattering, scintillation, and background radiation. However, the realization of optical communications at the longer wavelength has encountered significant difficulties due to lack of adequate optical sources and detectors operating in the desirable wavelength regions.
Interband Cascade (IC) lasers are novel semiconductor lasers that have a great potential for the realization of high-power, room-temperature optical sources in the 3–5-μm wavelength region, yet no experimental work, until this one, was done on high-speed direct modulation of IC lasers. Here, high-speed interband cascade laser, operating at wavelength 3.0 μm, has been developed and the first direct measurement of the laser modulation bandwidth has been performed using a unique, high-speed quantum well infrared photodetector (QWIP). The developed laser has modulation band-width exceeding 3 GHz. This constitutes a significant increase of the IC laser modulation bandwidth over currently existing devices. This result has demonstrated suitability of IC lasers as a mid-IR light source for multi-GHz free-space optical communications links.