Soft Matter Macro and Micro-Photonics workshop

All-optical programmable liquid-crystal photonic circuits
and smectic bubble lasers

Matjaž Humar
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

I will present two directions in liquid crystal photonics. In the first part, I will describe a fully programmable planar photonic platform based on optically induced nematic-to-isotropic phase transitions. By locally heating a nematic cell with a focused infrared beam, we reversibly create isotropic domains that act as programmable optical potentials with refractive-index contrasts two orders of magnitude larger than in solid-state platforms. We demonstrate reconfigurable waveguides, lenses, beam splitters, diffraction gratings, and all-optical logic gates — all combinable into functional circuits and re-drawable on demand within a single unmodified cell. The integration of topology optimization and inverse design enables high-performance functionality, establishing the system as a fabrication-free photonic breadboard. In the second part, I will present optofluidic lasers based on smectic liquid crystal bubbles. Dye-doped smectic bubbles with molecularly uniform thickness support whispering gallery mode lasing with frequency-comb-like spectra. The extreme softness of these cavities enables their use as highly sensitive electric-field and pressure sensors with a wide dynamic range, placing them among the best microsensors of their kind.