Single‐Step Generation of Flexible, Free‐Standing Arrays of Multimode Cylindrical Waveguides

Polymer matrices patterned with 3‐D waveguide circuitry are critical components of flexible photonics but cannot be fabricated through conventional, linear lithographic techniques. By exploiting the spontaneous filamentation and modulation instability (MI) of a uniform optical field in a range of silicone‐acrylate‐based photopolymerizable fluids, the authors report the generation of free‐standing arrays of cylindrical, multimode waveguides with tunable flexibility in a single, room‐temperature step. A broad, incandescent beam becomes unstable and spontaneously divides into a large population (≈10 000 cm⁻²) of microscopic filaments; each filament becomes entrapped within a self‐induced cylindrical waveguide and propagates through the medium without diverging. By spatially modulating the beam, it is possible to generate cylindrical waveguide arrays with square symmetry. By controlling the extent of cross‐linking and the relative amount of silicone surfactant in the polymerized matrix, it is possible to tune the hardness of the arrays over an order of magnitude (Shore‐OO 9 ± 5 to 94 ± 2). The authors show that flexible waveguide arrays that possess relatively low values of hardness can be reversibly compressed to up to 70% of their original lattice parameter while retaining waveguiding capacity; the arrays exhibit 100% recovery after multiple cycles of compression and decompression.