Next-Generation Organic Photonics: The Emergence of Flexible Crystal Optical Waveguides

Organic crystals possessing both flexibility and light-guiding properties are attractive candidates for spatial control of the light output for next-generation technological applications, namely photonic devices and circuits, optoelectronic devices, optical sensors, and so on. Most of the organic crystals are inclined to break or crack under external stress limiting their usage in many device applications. However, some molecular crystals are bizarrely flexible due to the presence of unusual molecular packing and weak intermolecular interactions. This comprehensive review summarizes these remarkably flexible organic crystal waveguides reported to date. The summary also includes i) naturally bent active/passive crystal waveguides, ii) various external factors (mechanical, chemical, light) which trigger bending of macrocrystals, iii) a comparison between the crystal structure of both linear and bent waveguides, and the use of crystal engineering strategies in designing flexible waveguides, iv) advent of micromechanical manipulation technique based on atomic force microscopy to effectively modify the geometry and position crystals as small as<2 mu m, v) some promising next-generation devices made from flexible crystals such as organic field-effective waveguides, wavelength division multiplexing, polarization rotors, and optical directional couplers, and vi) future outlook and opportunities of this growing research field.