Design of all-fiber, single cavity dual-comb laser

Abstract

Dual-comb spectroscopy (DCS) has proven to be a powerful technique for high-resolution and high sensitivity broadband spectroscopy, but the cost and complexity of the available laser sources has limited its application beyond research laboratories. A recent approach, aiming to simplify the DCS laser sources, reduce their cost and extend this spectroscopy technique for industrial applications, has been to develop dual-comb fiber lasers that emit two combs from a single cavity. In this thesis, an experimental and numerical study of a novel design of a bidirectional dual-comb fiber laser based in an all-normal, all-polarization maintaining (PM) fiber scheme is proposed. The experimental demonstration of this laser was limited to independent mode-locked operation in both directions, but the simultaneous dual-comb operation was not successful. A numerical study gave insights into the problem investigation and identified the key parameters preventing the dual-comb operation. The method followed to simulate the dual-comb was to replicate the experimental cavity by modeling independently each component of the oscillator and transmitting a pulse through for a fixed number of roundtrips. The simulations showed that the insertion losses of the cavity components were determinant to obtain dual-comb solutions. Additionally, it was shown that this dependence was characteristic of the dual-comb design, and not observed in single comb cavities with similar properties. Simulations also suggest that the reason why the experimental dual-comb was not achieved was possibly due to the imbalance of the losses and coupled gain inside the cavity. Another possible reason is that in the experiments, different SESAMs were used in both directions. These results provide insights about some determinant cavity parameters for dual-comb operation, helping to improve the design to successfully achieve dual-comb operation.