Simply-integrated dual-comb spectrometer via tunable repetition rates and avoiding self-referencing

Dual-comb system with simplified integration acts a crucial role in the next stage of field-deployable application. Here we demonstrate a home-made dual-comb spectrometer that meets this requirement based on optically stabilized erbium-fiber frequency combs. The simplified integration and operability are highlighted by the embedded large motion-span automatic optical delay line that resulted in 1.7 MHz of continuous repetition rate tuning range and avoid multiple fiber cutbacks. This relaxes the second similar frequency comb duplication, therefore simplifies dual-comb system integration. The mutual coherence was enhanced by optical phase lock to a common narrow-linewidth reference laser via pump current modulation. We acquired the absorption feature of acetylene ¹²C₂H₂ molecule in 1.5 μm region with an apodized instrument linewidth of 0.076 cm^-1. The mean signal-to-noise ratio within a spectral bandwidth of 90 cm^-1 achieved 280, and the corresponding noise equivalent absorption coefficient was 3.7 × 10^-6 cm^-1·Hz^-1/2 for an absorption path of 7.5 cm and a pressure of 100 Torr. The accuracy of the retrieved spectrum was further confirmed by comparing with HITRAN database.