Nanoscopic Imaging of Photonic Modes Excited in Square-Shaped Perylene Microcrystals

Organic microcrystals have attracted much attention because of their light confinement and transport capability on the micrometer scale. The capability is closely related to the photonic modes resonantly excited in the organic microcrystal, and therefore, visualization of photonic modes is important not only for a deeper understanding of organic microcrystals but also for their practical application. Here, we directly visualized the photonic modes excited in square-shaped perylene microcrystals by using a scanning nearfield optical microscope. From the near-field optical images and the electromagnetic simulations, we demonstrate that the Fabry-Perot modes are predominantly excited compared with the whispering gallery modes in two-dimensional organic microcrystals. The findings provide a deeper understanding of the photonic modes and should be beneficial for the design of microscale waveguides and photonic integrated circuits.