Interband cascade technology for energy-efficient mid-infrared free-space communication

Space-to-ground high-speed transmission is of utmost importance for the development of a worldwide broadband network.Mid-infrared wavelengths offer numerous advantages for building such a system,spanning from low atmospheric attenuation to eye-safe operation and resistance to inclement weather conditions.We demonstrate a full interband cascade system for high-speed transmission around a wavelength of 4.18μm.The low-power consumption of both the laser and the detector in combination with a large modulation bandwidth and sufficient output power makes this technology ideal for a free-space optical communication application.Our proof-of-concept experiment employs a radio-frequency optimized Fabry–Perot interband cascade laser and an interband cascade infrared photodetector based on a type-II InAs/GaSb superlattice.The bandwidth of the system is evaluated to be around 1.5 GHz.It allows us to achieve data rates of 12 Gbit/s with an on–off keying scheme and 14 Gbit/s with a 4-level pulse amplitude modulation scheme.The quality of the transmission is enhanced by conventional pre-and post-processing in order to be compatible with standard error-code correction.

High-capacity free-space optical link in the midinfrared thermal atmospheric windows using unipolar quantum devices

Free-space optical communication is a very promising alternative to fiber communication systems,in terms of ease of deployment and costs.Midinfrared light has several features of utter relevance for free-space applications:low absorption when propagating in the atmosphere even under adverse conditions,robustness of the wavefront during long-distance propagation,and absence of regulations and restrictions for this range of wavelengths.A proof-of-concept of high-speed transmission taking advantage of intersubband devices has recently been demonstrated,but this effort was limited by the short-distance optical path(up to 1 m).In this work,we study the possibility of building a long-range link using unipolar quantum optoelectronics.Two different detectors are used:an uncooled quantum cascade detector and a nitrogen-cooled quantum well-infrared photodetector.We evaluate the maximum data rate of our link in a back-to-back configuration before adding a Herriott cell to increase the length of the light path up to 31 m.By using pulse shaping,pre-and post-processing,we reach a record bitrate of 30 Gbit s−1 for both two-level(OOK)and four-level(PAM-4)modulation schemes for a 31-m propagation link and a bit error rate compatible with error-correction codes.