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The fundamental vibrational-rotational absorption signature of almost all the chemical compounds lies in the Mid- IR spectrum (λ=3-15μm) thus offering superior light-analyte interaction in this regime. In particular, the successful inscription of infrared-spectroscopy in a multi-pass cell has significantly boosted its use mainly in the gas-sensing application at the sub-ppm/ppb level. However, the requirement of bulky, alignment sensitive, and need of expertise-hands makes it inappropriate for many fields especially in portable applications like stand-alone environment monitoring, detection of chemical-warfare-agent in the battlefield, Astro-biological applications, etc. An external disruption-free handheld device (i.e., unaffected from any external vibration, physical stress, and thermal variations) with high specificity and selectivity are still prerequisites for such in-situ applications. The advancements in photonics have shown enormous possibilities to miniaturize all spectroscopic components to a single chip. In this context, the slow light-assisted engineered photonic structure on a QCL/QCD (quantum confined laser and detector) is most promising to replace bulky multi-pass cell optics. In principle, it slows down the light with several folds to enhance the light-analyte interaction and thus open an avenue for an on-chip sensing platform. Most efficient QCLs demonstration explored in the InP platform, also a selection of InP-InGaAs eliminates the requirement of the costly wafer-bonding process. In this paper, we consider slow-light assisted and wavelength-tunable periodic photonic structures. The device is designed such that it supports transverse magnetically polarized mode directly emitted from QCLs. It eliminates the use of any additional polarization-rotator (conversion from TM to TE mode) which reduces fabrication complexity and additional space on the chip.
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