Mid infrared polarization independent tapered waveguide based multianalyte sensor- a theoretical study

Group-IV photonics has gained a lot of interest in recent years due to its CMOS compatibility. Silicon on Insulator (SOI) has dominated the optical and optoelectronics field for past decades. On the other hand Germanium based platform, GeOI is another promising candidate for the above mentioned field.1 It has wide application in Mid Infrared Sensing due to it’s abundance, transparency and high index contrast (Δn = 2.6 at 3 μm) with reference to silicon on insulator. In order to take the advantage of wide transparency of Germanium in the Mid Infrared applications like chemical sensing, where most hazardous chemical molecules have their fingerprints, we have designed a compact adiabatic tapered waveguide2-4 sensor based on evanescent wave coupling which will be able to sense more than six analytes (Carbon dioxide (CO2), Nitrous oxide (N2O), Nitrogen dioxide (NO2), Nitric oxide (NO), Ammonia (NH3), Ethylene (C2H4), Acetylene (C2H2), Hydrogen Cyanide (HCN) and Methane (CH4)) having absorption peaks in between 2.5 to 3.5 μm. The proposed device provide a suitable method for label-free detection of target molecules and can be integrated on-chip for industrial and environmental monitoring , health analysis and food processing which can be leveraged over hefty conventional spectrometer like Fourier Transform Infrared Spectroscopy (FTIR). We have also studied and found an optimum tapered length of 40 μm for the proposed geometry, having more than 80 % transmission for both fundamental Transverse Electric (TE) and Transverse Magnetic (TM) mode making it polarisation insensitive.