Microscale generation and control of nanosecond light by light in a liquid crystal.

The softness of liquid crystals, their anisotropic material properties, their strong response to external fields and their ability to align on patterned surfaces makes them unsurpassable for a number of photonic applications, such as flat-panel displays, light modulators, tunable filters, entangled photon light sources, lasers and many others. However, the microscale integration of liquid crystals into microphotonic devices that not only perform like silicon photonic chips but also use less energy, operate exclusively on light, are biocompatible and can self-assemble has not been explored. Here we demonstrate a soft-matter photonic chip that integrates tunable liquid-crystal microlasers and laser microprinted polymer waveguides. We demonstrate the control of the liquid crystal's microlaser emission by nanosecond optical pulses and introduce the concept of resonant stimulated-emission depletion to switch the light by light. This opens a way to design an entirely new class of photonic integrated devices that can be made both biodegradable and biocompatible with a rich variety of applications in medicine, wearable photonics and logic circuits. We anticipate that soft-matter photonic circuits will not only outperform solid-state photonics in terms of a huge reduction in the number of production steps, the use of non-toxic chemicals and a better energy efficiency, but also could open an avenue to the paradigm of soft-matter photonics.