Opt. Express 22, A1650–A1658 (2014)

In the past few years several researchers have reported greater than unity efficiency for converting electric power into optical power in LEDs. This >100% wall-plug efficiency is explained by a contribution to the pumping by lattice heat that additionally enables net cooling of the diode's semiconductor lattice. Duanni Huang and colleagues from the Massachusetts Institute of Technology in the USA have experimentally created a free-space optical communication channel using such a thermo-electrically pumped infrared LED. This means that the electrical energy required for optical communication can be very low — less than the energy of the photon created. For example, the authors report that they need to input as little as 4.3 meV of electrical energy to create a 520 meV photon (with the deficit coming from thermal energy). Using this device, data has been transmitted at a rate of 3 kbps, which equates to a power consumption of only 120 pW of electrical power and an energy per binary digit of only 40 femtojoules. The bit error rate of the transmission was 3 × 10−3.