Slow-Light Enhanced CO$_{2}$ Sensing Using 3-D Photonic Crystals Fabricated Using Two-Photon Polymerization

Photonic crystals (PhCs) have periodically structured alternating dielectric layers, creating an energy band structure that prevents certain wavelengths of light from transmitting through the PhC. This range of wavelengths is called the photonic band gap (PBG). An engineered defect in the dielectric layers creates a defect mode in PBG that allows a few wavelengths of light to transmit at a slower group velocity, known as slow light. The ability to slow down the group velocity of light can be used for enhanced sensing of gases due to enhanced light–matter interaction. In this letter, we present direct-laser-written 3-D PhC fabricated using two-photon polymerization for enhanced mid-infrared spectroscopy sensing of carbon dioxide (CO
$_{2}$
), a potent greenhouse gas. Finite element analysis was performed to study defect mode in a perfect 2-D PhC, later extended to 3-D PhCs. A group velocity study of the defect mode is also shown. Two-photon polymerization was used to fabricate 3-D PhCs to realize the defect mode experimentally. The PhC sensors targeting CO
$_{2}$
detection were fabricated and tested for 1% CO
$_{2}$
at a room temperature of 295 K. An enhancement factor of 12 with 95% 2
$\sigma$
confidence is achieved by the addition of PhCs resulting in enhanced sensing of CO
$_{2}$
.