Tunable bandpass filter for mid-infrared wavelengths using liquid crystal elastomer actuators

Mid-Infrared (MIR) spectroscopy is a powerful method to identify different molecular species due to the fact that molecular vibrations exhibit strong responses in this spectral range. In order to control and optimize the chemistry process, as well as enhance the chemical output, an in-situ measurement is necessary. However traditional MIR spectrometers are usually bulky and expensive, and are difficult to use for a spatially distributed, real-time detection, especially in a micro-reactor. We present here a highly-miniaturized continuously tunable optical bandpass filter in the MIR range for chemical detection in microreactors. Similar to a Fabry-Perot interferometer, the micro filter consists of two parallel multi-thin-film Bragg mirrors and an air gap, spaced by Liquid Crystal Elastomers (LCEs). The LCE is a novel actuator material composed of crosslinked polymer chains exhibiting strong macroscopic contraction as temperature is raised. We will show that the LCE can provide an extremely precise yet large mechanical movement of the two parallel mirrors leading to large freedom in the wavelength tuning range. Design, fabrication and measurements will be shown, demonstrating the functionality of the filter.