Enabling Enhanced Emission and Low Threshold Lasing of Organic Molecules Using Special Fano Resonances of Macroscopic Photonic Crystals

Abstract

The nature of light interaction with matter can be dramatically altered in optical cavities, often inducing nonclassical behavior. In solid-state systems, excitons need to be spatially incorporated within nanostructured cavities to achieve such behavior. Although fascinating phenomena have been observed with inorganic nanostructures, the incorporation of organic molecules into the typically inorganic cavity is more challenging. Here, we present a unique optofluidic platform comprising organic molecules in solution suspended on a photonic crystal surface, which supports macroscopic Fano resonances and allows strong and tunable interactions with the molecules anywhere along the surface. We develop a theoretical framework of this system and present a rigorous comparison with experimental measurements, showing dramatic spectral and angular enhancement of emission. We then demonstrate that these enhancement mechanisms enable lasing of only a 100-nm thin layer of diluted solution of organic molecules with substantially reduced threshold intensity, which has important implications for organic light-emitting devices and molecular sensing.fluorescence enhancement | enhanced light-matter interaction O rganic molecules are pervasive in daily life: from natural proteins, to human synthesized fluorescing labels, to organic semiconductors. The interaction of light with such molecules is at the heart of important technological advances in biomolecular detection (1-4), fluorescent microscopy (5), and organic light-emitting devices (6-9), as well as more fundamental studies of cavity quantum electrodynamics (10-12) and various types of enhanced spectroscopy (13) and sensing (14). In all, it is frequently sought to alter (15-18) and often to enhance this interaction by allowing it to occur in a typically nanostructured cavity, where both the lifetime of the resonances and the optical density of states (DOS) (19) can be tailored. However, there are inherent challenges in incorporating organic molecules in such cavities: first, their dissimilar compositional structure makes it difficult to incorporate them within the highdielectric regions of the cavity, where long-lifetime resonances concentrate their electromagnetic energy. Second, micro-and nanostructured cavities typically only have a small portion of their mode volumes extending outside their high-dielectric regions, making it challenging to bring external entities precisely to within that volume. Third, patterning of organic materials at the nanoscale is extremely challenging and incompatible with inorganic processes. As a result, experimental realizations of systems of excitons of organic molecules and optical resonances are limited compared with systems of inorganic quantum nanostructures.Here, we present and study a unique dielectric surface that enables simple incorporation of organic molecules onto a macroscopic nanostructured resonant cavity. This system demonstrates strongly enhanced interaction of light with organic molecules that are brought to within 100 nm of its m...

Bound states in the continuum

“…This makes them useful for many optical and photonic applications. In particular, the macroscopic size (on the centimeter scale or larger) and ease of fabrication make BICs in PhC slabs unique for large-area high-power applications such as lasers [214][215][216][217][218][219] , sensors 220,221 , and filters 222 .…”

“…Researchers first observed this effect via a suppression of radiation into the normal direction in a surface-emitting distributed feedback laser with onedimensional periodicity 58,59 . This led to PhC surface emitting lasers (PCSELs) that lase through BICs with two-dimensional periodicity 214,215 , followed by the realizations of various lasing patterns 216,217 , lasing at the blue-violet wavelengths 218 , and lasing with organic molecules 221 . The suppressed radiation at the normal direction means that a PCSEL can have a low lasing threshold but also with a limited output power.…”

“…Another type of sensing relies on measuring fluorescence signals. It was shown that the spontaneous emission from organic molecules can be strongly enhanced and the angular distribution can be strongly modulated near BICs in a PhC slab, leading to a total enhancement of angular fluorescence intensity by 6300 times 221 . BICs also enabled large-area narrow-band filters in the infrared regime 222 due to their high and tunable Q factors.…”

Spectrally selective chiral silicon metasurfaces based on infrared Fano resonances

“…28) of such photonic resonances are often caused by the so-called guided resonance modes (GRMs) 22,23,29 . The spectrally narrow linewidth of these modes originates from the suppression of their radiative losses through the long-range destructive interference between multiple unit cells of a photonic crystal and, therefore, is extremely sensitive to the light's incidence angle 22,24,25,28,30,31 . Such angular sensitivity prevents miniaturization of photonic crystal devices 22,26,32 and imposes severe restrictions on the angular divergence of the incident light beams.…”

“…One promising approach to decreasing radiative losses while maintaining finite coupling to free-space radiation is to utilize the phenomenon of Fano interference 35 originally introduced in atomic physics to describe asymmetrically shaped ionization spectral lines of atoms. More recently, the concept of Fano resonances was introduced to the field of photonics and metamaterials 23,28,[36][37][38][39] in which a photonic structure possesses two resonances generally classified as 'bright' (that is, spectrally broad and strongly coupled to incident light) and 'dark' (spectrally sharp, with negligible radiative loss). The weak nearfield coupling between the bright and dark resonances leads to coupling of the incident light to the dark resonance that maintains its low radiative loss, thereby remaining high-Q.…”