Gas cell– and Fabry-Pérot interferometer–based self-calibration filtering system for a tunable laser to enhance the optical signal-to-noise ratio

This study presents a self-calibrating synchronous filtering system that improves the optical signal-to-noise ratio (OSNR) of external-cavity tunable lasers. It integrates a hydrogen cyanide gas cell with a Fabry-Pérot interferometer featuring a 1.5-GHz free spectral range for real-time wavelength calibration over a 1535-1555-nm sweep band. Leveraging this calibration process, a field-programmable gate array processes spectral fingerprints and dynamically controls a microelectromechanical system-based tunable optical filter, allowing the passband of the filter to synchronously track the instantaneous center wavelength of the laser. Experimental validation demonstrated an OSNR improvement exceeding 20 dB, increasing from >60 dB to >80 dB.