Thermal Shrinkage-Induced Modifications in Photonic Band Gaps of Two-Photon Polymerized Bragg Reflectors

One-dimensional (1D) polymer-based photonic crystals (PhCs) in the $1.55~\mu{}m$ wavelength range can be easily created using a two-photon direct laser writing system. To achieve shorter period structures, we report the use of thermal shrinkage of two-photon polymerized structures, at elevated temperatures, to eliminate unpolymerised material, leading to the uniform shrinkage of the distributed Bragg reflector (DBR) structures by a ratio of $\sim$ 2.5 to 5. Our Finite Difference Time Domain (FDTD) simulation and the angle-resolved light scattering characterization technique using Fourier image spectroscopy (FIS) measurements show that the low order photonic bandgaps of DBRs blue-shift across the NIR-visible region (850 to 400 nm) as the shrinkage increases.