Fabry-Pérot resonators find many applications in different systems, including optics, astronomy and atomic spectroscopy. Beyond their application framework, the basic fundamental concepts of Fabry-Perot resonators could be used to explain many other phenomena, such as those in quantum physics and metrology. Typically, optical resonators use two reflective mirrors separated by a transparent layer to create a peculiar symmetry for the waves traveling within the cavity. This makes it easy to derive the laws governing their operations and their characteristic parameters like free-spectral range and quality factor.
The mirrors are mainly made of either metallic or dielectric materials. When metals are used, the resulting resonators are known as metal-dielectric-metal (MDM) systems, and is widely used in nanotechnology. MDM resonators have proved to be suitable for investigating atomic-cavity interactions in light-matter quantum-electrodynamics experiments due to their high-quality factor, robust fabrication process and small modal volume. However, optimizing the quality factor of Fabry-Pérot -based MDM resonators require a significantly larger mirror thickness that prevents pump radiation from reaching the atoms within the cavity. This makes it difficult to use MDM resonators in applications that require photo-sensible elements like photovoltaic cells.
Several alternatives have been proposed to solve the trade-off between the high-quality factor and the pump radiation coupling efficiency. Where replacing the reflective mirrors is almost impossible, systems with structural resonant behaviors emanating from their lattices, such as photonic crystals, can be used. Although these structures exhibit excellent quality factors, their fabrication process is costly and time-consuming. Therefore, alternative strategies, preferably based on simple multilayers, are desirable. Although it is speculated that metal/dielectric open cavity (MDOC) structures could solve the trade-off effects, there is still lack of experimental evidence to prove the assertions.
Herein, Italian researchers: Dr. Vincenzo Caligiuri, and Professor Antonio De Luca from Universitá della Calabria together with PhD candidate Aniket Patra and Professor Roman Krahne from Istituto Italiano di Tecnologia engineered pseudo-cavity modes (PCMs) in an MDOC system to overcome the trade-off effects. In addition to theoretical explanations, numerical experiments were conducted to explore the ability of the MDOC system to produce lighter-matter interactions and various circumstances. This was proved using an exciton/PCM coupling regime with 160 meV rabi splitting, polarized and angle-dependent spontaneous emissions and by examining the photoluminescence enhancement. The work is currently published in the journal, Advanced Optical Materials.
Similar to cavity modes, the researchers demonstrated that the MDOC system manifests a resonance that can be accessed without using momentum matching devices like gratings. Strong light-matter interaction is achieved between the PCMs and the two-excitons system (R6G), making it an ideal platform for conducting cavity quantum electrodynamics experiments. Consequently, the authors showed that the photoluminescence of a gain material embedded in the MDOC was enhanced by more than 7 times due to its interaction with the PCMs. As such, the emitted radiation was endowed with peculiar directional and polarization properties. The advantages of the proposed system include feasible and cost-effective fabrication, high versatility and, most importantly, its ability to make the photo-responsive layer always directly accessible by external radiation
In summary, the authors explored the strong light-matter interaction of R6G excitons with Fabry-Pèrot -like PCM modes occurring in a MDOC. The Goos-Hänchen shift that commonly occurs at the ITO/Ag interface was found to play a vital role in determining the resonant wavelength. The PCMs not only enhanced the photoluminescence, but also exhibited the ability to simultaneously direct equal-wavelength emitted photons in two directions with different angles, based on their polarizations and MDOC profiles. In a statement to Advances in Engineering, Professor Antonio De Luca and their co-workers said the new system holds potential applications in LEDs and cavity-enhanced solar cells, among other photonic systems.
Patra, A., Caligiuri, V., Krahne, R., & De Luca, A. (2021). Strong Light–Matter Interaction and Spontaneous Emission Reshaping via Pseudo‐Cavity Modes. Advanced Optical Materials, 9(24), 2101076.