Mechanophotonics: Pseudo-Plastic Organic Crystal as a Fermat Spiral Optical Waveguide

An unprecedented organic Fermat spiral optical waveguide (FSOW) self-transducing green fluorescence is fabricated using a pseudo-plastic (E)−1-(((5-bromopyridin-2-yl)imino)methyl)naphthalene-2-ol (BPyIN) crystal. A 1.618-millimeter-long crystal is initially bent into a hairpin-like bent waveguide. Later, a meticulous mechanophotonic strategy is employed to sculpt the hairpin-like bent waveguide into the Fermat spiral geometry, covering a compact area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$330\times 238~\mu $ </tex-math></inline-formula>m2. The optical signal in FSOW survives two sharp 180° turns to produce optical output. The remarkably low bending-induced optical loss in FSOW can be ascribed to the smooth-defect-free surface morphology of the crystal. The development of such versatile optical components capable of transducing light through sharp bends is pivotal for realizing large-scale all-organic photonic circuits.