InfraRed Emitters with Nano-Antennas – IRENA

Near infrared (NIR) sources are used for short range communication applications such as remote control or free-space optical links. Current infrared technology uses diodes operating in the near infrared because of the quality of the available detectors and sources. However, optical links operating at these wavelenghts are vulnerable to degradation because of Mie scattering from micron-sized particles such as dust or pollutants. Luckily the atmosphere has two transparency regions at longer wavelengths, in the mid Infrared (MIR) at 3-5 µm and 8-12 µm, that are much less affected by this problem. Developing new sources and detectors operating in this part of the spectrum could therefore impact the industry. Furthermore, MIR sources are needed for many applications such as gas detection, sensing, drying, heating.

Currently available sources in this part of the spectum are gas lasers and optical parametric oscillators, that are bulky, and quantum cascade lasers (QCL) that are quite expensive. The only available cheap and compact sources are incandescent ones such as globars or hot membranes.

In this project, we will explore new paradigms for Mid-IR emission in order to achieve i) cheap and compact Mid-IR sources in the 3-12 µm wavelength range, and ii) high frequency modulation of these sources.

We will study Mid-IR electrically excited emitters based on semiconductor quantum wells, and incandescent sources. So far, intersubband transitions in quantum wells are used for quantum cascade lasers. They cannot be used in the spontaneous emission regime (namely the light emitting diode, LED) because the non radiative decay rate (~1ps) is much shorter than the radiative decay rate (~1ns). Hence, the efficiency is very low. This can be improved using nanoantennas to accelerate the radiative decay time by more than 100. Hence, nanoantennas will be the key to the design of MIR LED which could be modulated faster than lasers.
On the other hand, the modulation rate of incandescent sources is limited by the cooling time due to thermal diffusion. Yet, an object with size 100 nm cools down in only 10 ns. Being so small, it hardly emits radiation unless it is coupled to a nanoantenna that can be used to increase the emitted power. Our preliminary calculations show that a periodic array of antennas behaves as a metasurface with an emissivity approaching the ideal value of 1.

In summary, we will design and fabricate nanoantennas that will enable cheap and compact mid IR emitters, either LEDs or incandescent emitters, with record modulation rates.