Infrared (IR) spectroscopy is routinely used for material identification and characterization. Numerous chemical functional groups have characteristic absorption bands and absorption patterns (called “fingerprints”) in the IR spectrum that allow determining, or at least narrowing the possibilities for, the types of molecules present in a sample. A common laboratory instrument used for IR spectroscopy is a Fourier transform infrared (FTIR) spectrometer. F spectrometers are benchtop-size apparatus that generally test one sample at a time; are not easily portable; and, as a result, cannot be easily used in the field. In recent years, therefore, efforts have been made to develop chip-scale photonics-based IR spectrometers and chemical/biochemical sensors, e.g., using standard rigid photonic material platforms, such as silicon (Si) on silicon oxide (SiO2).
In parallel with the development of photonic chemical sensors, flexible photonics has attracted a lot of attention due to its key role in emerging applications such as portable and wearable imaging and display arrays, sensors, and optical interconnects. Both passive and active photonic devices have been successfully integrated on flexible polymer substrates. These polymer substrates, however, are opaque in the mid-IR wavelength range (corresponding to wavelengths greater than 2.5 μm), into which the characteristic absorptions of many chemicals fall. Furthermore, the polymeric substrates decompose and deform under high temperature and degrade when exposed to organic solvents, limiting they applications in harsh environmental conditions. Accordingly, current flexible photonics platforms are unsuited for many chemical sensing applications.