Classical control for a compact squeezed vacuum source

Advanced gravitational-wave interferometric detectors, such as Advanced LIGO and AdvancedVirgo, are quantum-noise limited over a significant portion of their detection band. To overcome this limitation, special states of light, known as squeezed states, are employed to minimize the quantum noise in the signal quadrature at the expense of the orthogonal one. With this application in mind, several squeezed-light sources have been developed over the past few decades, achieving up to 15dB of noise suppression in the signal quadrature compared to of the ``conventional'' light. These devices are highly complex and delicate, typically requiring densely populated optical benches. In this thesis, we investigate a novel approach, referred to as a hybrid squeezer, in which the light sources used for the generation and control of the squeezed state are implemented in a fiber-optic circuit, while the actual squeezing process takes place in a free-space Optical Parametric Oscillator (OPO). This approach is expected to simplify the optical setup required for the generation of squeezed light, making it more accessible to a broader range of users and easier to replicate. The work presented in this thesis primarily focuses on the characterization of the fiber-optic sources, with the aim of assessing their compliance with the requirements for achieving 15dB of squeezing at 1550nm. In particular, the work focuses on the generation of the second-harmonic signal used to pump the OPO, the generation of the Quantum Control Field (QCF) required for the stabilization of the squeezed angle through an Acousto Optic Modulators (AOM), and the characterization of the phase noise of the laser employed in the setup conducted using an unbalanced Mach-Zehnder interferometer. These preliminary characterizations provide crucial bounds on residual classical seed contamination in the QCF, the available pump power and its stability, the level of phase noise introduced by the laser which ultimately determine the performance of squeezed-state generation.