A new generation of optoelectronic components—such as single-photon sources—makes use of nanometric emitters called "quantum dots," integrated in a photonic structure. Produced by self-assembly, these dots are randomly distributed along a plane within the structure. In practice, it is important to know the position of emitters in order to understand and optimize the performances of components.

With this in mind, physicists have imagined an original localization technique. The photonic structure is strained in such a way as to generate a very heterogeneous mechanical stress inside this same structure. This stress causes a spectral shift in the emission of each quantum dot—toward the blue for compression and toward the red for extension. Since the amplitude of the shift is proportional to the stress intensity, measuring this shift by optical spectroscopy makes it possible to determine the position of a quantum dot on the order of nanometers.

This technique was implemented in a photonic wire containing a plane of quantum dots located at its base. The strain in the wire is obtained through the selective excitation of mechanical vibration modes, using a piezoelectric actuator. Combining the results for two orthogonal flexion modes, the scientists were able to produce a precise map of the dot positions.

This approach will possibly be extended to other photonic structures, such as micropillars or other emitters that are sensitive to mechanical stress.