System and methods for gas spectroscopic sensing with photon counting and tunable integrated photonic filters

A method for single-photon spectroscopy, comprising the steps of:

• collecting photons using a beam expander into a collimated single-mode fiber;
• letting said photons pass through a long-pass filter to create long-pass filtered photons and to eliminate photons from other bands;
• filtering said long-pass filtered photons with a band-pass filter to define a spectral window adapted to pick a single gas absorption line-shape and obtain filtered light;
• utilizing a fiber polarizer to select said filtered light along a certain polarization, thereby producing filtered and polarized light;
• splitting said filtered and polarized light into a first portion of light and a second portion of light;
• routing said first portion of light through a signal photon counting channel comprising a calibrated micro-ring resonator filter and a field-programmable-gate-array;
• tuning the resonance of said micro-ring resonator filter to sweep through said spectral window;
• using said field-programmable-gate-array to tune a center wavelength of said micro-ring resonator filter;
• acquiring first photon counting data from said signal photon counting channel following the performance of said tuning and using steps;
• directly after the performance of said splitting step, coupling said second portion of light into a bypass photon counting channel;
• detecting photons at a close-by wavelength in said bypass photon counting channel, said close-by wavelength having a center spectrum 1 nm or less away from said center wavelength of said single gas absorption line-shape, thereby obtaining second photon counting data;
• and
• producing synchronized photon counting data from said first photon counting data and said second photon counting data.