An integrated entangled photons source for mid-infrared ghost spectroscopy

In this work, we investigate the application of intermodal spontaneous four wave mixing (SFWM) to ghost spectroscopy in the mid-infrared (MIR) spectral region. This technique is of great interest for MIR sensing, being able to overcome the limitations faced by MIR detectors in terms of background noise and dark counts. Through intermodal SFWM in a Silicon-On-Insulator (SOI) waveguide, two temporally correlated photons are generated: using a standard C-band pump, the idler photon is in the near-infrared (NIR) and the signal photon is in the MIR. The integrated source, with a coincidence to accidental ratio (CAR) of 114 +/- 4, is used to demonstrate that, in situations of environmental noise, ghost spectroscopy yields advantages with respect to the traditional absorption spectroscopy. The time-energy entanglement of the photon pairs is used to enhance the visibility of the measurement against noisy background conditions and to increase the spectral resolution in the MIR by spectral filtering the NIR photons. Modeling and experimental data support these improvements.