On-chip infrared sensors: redefining the benefits of scaling

Abstract

Infrared (IR) spectroscopy is widely recognized as a gold standard technique for chemical and biological analysis.Traditional IR spectroscopy relies on fragile bench-top instruments located in dedicated laboratory settings, and is thus not suitable for emerging field-deployed applications such as in-line industrial process control, environmental monitoring, and point-of-care diagnosis. Recent strides in photonic integration technologies provide a promising route towards enabling miniaturized, rugged platforms for IR spectroscopic analysis. It is therefore attempting to simply replace the bulky discrete optical elements used in conventional IR spectroscopy with their on-chip counterparts. This size down-scaling approach, however, cripples the system performance as both the sensitivity of spectroscopic sensors and spectral resolution of spectrometers scale with optical path length. In light of this challenge, we will discuss two novel photonic device designs uniquely capable of reaping performance benefits from microphotonic scaling. We leverage strong optical and thermal confinement in judiciously designed micro-cavities to circumvent the thermal diffusion and optical diffraction limits in conventional photothermal sensors and achieve a record 104 photothermal sensitivity enhancement. In the second example, an on-chip spectrometer design with the Fellgett's advantage is analyzed. The design enables sub-nm spectral resolution on a millimeter-sized, fully packaged chip without moving parts.

On-chip spectrometer : design, fabrication and experiment

“…Conventional Fourier-transform (FT) spectrometer using Michelson interferometer is known for high resolution, broadband and high SNR, which is suitable for infrared (IR) applications [32]. On-chip FT spectrometers are also demonstrated such as FT spectrometer based on micro-electromechanical systems (MEMS) technology [33][34][35][36], stationary-wave integrated FT spectrometer (SWIFT) [37,38], spatial heterodyne spectrometers (SHS) [16,[39][40][41][42][43][44], thermally tunable MZI [45,46], co-propagative FT (CPFT) spectrometer [47] and digital Fourier-transform (DFT) spectrometer [48,49]. The similar trade-off between channel count and SNR is encountered in most FT methods.…”