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

1D polymer-based photonic crystals in the 1.55 μm wavelength range can be easily created using a two-photon direct laser writing system. To achieve shorter period structures, the use of thermal shrinkage of two-photon polymerized structures is reported at elevated temperatures, to eliminate unpolymerized material, leading to the uniform shrinkage of the distributed Bragg reflector (DBR) structures by a ratio of ≈2.5 to 5. The finite-difference time-domain simulation and the angle-resolved light scattering characterization technique using the Fourier image spectroscopy measurements show that the low-order photonic bandgaps of DBRs blueshift across the NIR–visible region (850 to 400 nm) as the shrinkage increases.