Active dielectric nanoantennas for directional lasing

IntroductionDielectric nanoantennas offer an attractive alternative platform to plasmonics to control light in the nanoscale. Apart from their lower absorption losses, due to the absence of free electrons, the wealth of... [ view full abstract ]

Introduction

Dielectric nanoantennas offer an attractive alternative platform to plasmonics to control light in the nanoscale. Apart from their lower absorption losses, due to the absence of free electrons, the wealth of optical modes supported in this kind of structures enables interference effects that may be used to obtain high directionality. At the same time, some of the materials suitable for this platform, such as III-V semiconductors, have interesting electronic properties that may be used to design advanced opto-electronic and active devices. Among those, photoluminescence can be used to generate LEDs and, potentially, lasers in the nanoscale. However, the low quality factor (Q) of the optical resonances supported by this class of nanoantennas has prevented, so far, the realization of the latter. In this work we demonstrate, for the first time, that it is possible to obtain lasing in active dielectric nanoantenna arrays through a combination of individual resonances and collective generation of so called bound-states-in-the-continuum (BIC).

Methods and Results

We demonstrate, theoretically and experimentally, directional lasing action in arrays of dielectric nanoantennas made of GaAs. By theoretical analysis we show that the studied arrays support a symmetry-protected BIC associated to the resonant excitation of an electric dipole resonance in the individual antennas. A quasi-BIC with high-Q is observed experimentally for finite sized arrays, which serves as the feedback mechanism for the laser. Lasing is obtained in a range of temperatures from 77K to 200K, with lasing thresholds as low as 10 μJ/cm2. The laser shows a strong directionality that can be controlled by tuning the array geometry and temperature, without significantly sacrificing the high-Q of the quasi-BIC, via radiation out-coupling through designed diffraction orders. Experimentally, we show tuning of the laser emission from 3° up to 20° with respect to the normal.

Discussion

The results presented in this work represent a significant step towards new functionalities in which the interesting properties of dielectric nanoantennas are combined with gain dielectric materials to obtain active devices. Next steps towards further miniaturization and prospects for electrical addressing will be also discussed.