Resumen de Novel semiconductor laser-based architectures for dual-comb spectroscopy in the near-infrared, mid-infrared and thz ranges
The potential of Optical Frequency Combs as multimode sources featuring unprecedented high levels of accuracy, high resolution and broad bandwidth has rendered these instruments into one of the preferred tools across an ever-increasing range of disciplines. To fully capitalize on these astonishing virtues, one of the most successful approaches in recent years is the so-called dual-comb technique, or in a more general sense, dual-comb spectroscopy. The rationale of this method for comb detection lies in the employment of a second Optical Frequency Comb with different line spacing to simultaneously access to the whole spectral content of its counterpart, thus allowing for ultra-fast measurements (usually below one second) without sacrificing any of the outstanding capabilities of the Optical Frequency Combs. Nevertheless, in spite of the astounding development that dual-comb architectures have undergone in the past decade, advancements in terms of simplicity, robustness, associated cost, reduced footprint and adaptability to the target application are still underway.
In order to address this set of limitations, this Ph.D dissertation explores new possibilities for dual-comb spectroscopy and demonstrates their potential by means of a number of contributions across the most spectroscopically relevant regions of the electromagnetic spectrum (i.e., Near-Infrared, Mid-Infrared and the THz range). In particular, special emphasis has been laid on two aspects: the reduction in the design complexity regardless of the spectral region, and the external customization of the main set of parameters that dictate the performance of the sources so that they can easily fit the application of interest. For that purpose, different commercial off-the-shelf components, laser devices and well-established interdisciplinary techniques have been employed to establish synergies that have helped to increase the proficiency of these systems.
The present work has unveiled the first demonstrations of Near-Infrared (1.5 μm) dual-comb spectrometers whose operating principle stems from Gain-Switching in semiconductor lasers together with Optical Injection Locking and has further harnessed the use of the latter technique for the implementation of a novel multiheterodyne setup that relies on electro-optic modulation for remote comb detection. In a different original contribution, Near-Infrared dual-combs based on electro-optic modulation have been successfully shifted to the Mid-Infrared region via nonlinear mixing in a single periodically-poled lithium niobate crystal for ultra-fast absorption spectroscopy in the 3.5 μm region. Moreover, the use of large-signal modulation has been applied to a single-mode Distributed Feedback Quantum Cascade Laser emitting at 7.5 μm to demonstrate the generation of coherent multiharmonic signals with adaptable line spacing for the first time in this kind of device. Finally, an innovative architecture based on electro-optic modulation and Optical Injection Locking has been devised for the photonic synthesis of THz dual-combs featuring a series of unprecedented characteristics in this spectral domain. This collection of schemes and methods have been successfully validated with a number of spectroscopic samples that exhibit different properties, from low-pressure gases (hydrogen cyanide or methane) and fibre-Bragg grating sensors to electronic microwave filters, thus demonstrating the versatility of the proposed systems.
In summary, most of the efforts in this thesis have been devoted to the development of dual-comb architectures in the main spectral windows of interest for the scientific community, with special emphasis on flexible designs aimed to cater towards the requirements of a wide range of applications that may enable their eventual adoption beyond metrology laboratory environments.
