The overall objective of the project has been to develop low-cost remote gas sensing systems, based on dual-comb spectroscopy, for atmospheric pollutants. The optical frequency combs are generated by gain switching of semiconductor lasers with optical injection. It was proposed to develop these systems first with discrete components and then with InP-based Photonic Integrated Circuits (PICs).
The main achievements of the project have been:
A new technique has been developed for the generation of low repetition frequency OFCs by densification using phase modulation with binary pseudorandom sequences. In addition, the use of an alternative technique to gain switching for the generation of OFCs was proposed, based on Q switching through the inclusion of an intracavity electroabsorption modulator. This technique was demonstrated in simulations, and additional work is in progress to demonstrate it experimentally.
Several novel systems for dual comb spectroscopy of atmospheric pollutants have been demonstrated: i) a low-cost system using low-cost sources such as pulse generators and a Software Defined Radio equipment as a digitizer. ii) a system capable of measuring four different gases (NH3, HCN, CO and CO2) using optically injected Fabry-Perot lasers; (iii) a system based on the densification technique with the advantage of improving spectral resolution; (iv) a system in which for the first time a single gain-switched slave laser is used by time multiplexing.
Different InP-based PICs were designed for the development of OFCs and for gas spectroscopy using dual combs. OFCs with good characteristics were obtained in both DFB lasers and ring lasers injected at different wavelengths for sensing different gases. A PIC with dual comb generation system was designed and characterized based on the integration of a tunable laser injecting light into two integrated ring lasers operating in gain switching. It was possible to demonstrate for the first time in a PIC the generation of dual combs by gain switching using OFCs with differentfrecuencias de repetición.