Design and fabrication of a four-arm integrated photonic interferometer for quantum enhanced multiphase estimation

In this thesis work, we present the fabrication and the full characterization of the components required for the realization of an integrated photonic multimode interferometer. In particular, two distinct 4-modes coherent optical splitters (quarters) are fabricated in two glass substrates by means of femtosecond laser waveguide writing. Interestingly, this fabrication techniques allows for a three-dimensional prototyping of the devices, that can therefore be fabricated in a simple and cost-effective fashion. The optical characterization of the quarters testified their correct functioning, with an average power division of 25% +- 0.16% among all possible input-output channels. Each of the two optical chips incorporate six thermo-optics phase shifters, for both ensuring a balanced phase-operation of the quarters, and for the active manipulation of all the internal phases of the interferometer. Each phase shifter allows to provide a full 2pi modulation on its optical mode with a maximum power dissipation of 500 mW, and with reduced cross talks to the other modes. As it will be discussed thorough the thesis, the realization of these low-loss and reliable quarters required to improve beyond the state of the art both the optical circuit inscription and the micro-heaters deposition processes. The devices presented can be considered ready for being combined by butt coupling and glued, in order to complete the realization of a four-modes reconfigurable interferometer. We expect that this device will have a strong impact in the field of quantum metrology, as it enables the robust benchmarking of several protocols of quantum multi-parameters estimation, with a precision beyond the Standard Quantum Limit.

Lo scopo di questa tesi è quello di disegnare, fabbricare e caratterizzare un interferometro fotonico integrato a quattro braccia. Questo disposivito, composto dalla cascata di due diversi splitter a quattro porte chiamati quarter, è scritto in un substrato di vetro tramite la tecnica della Femtosecond Laser Micromachining (FLM). Questa ci permette di ottenere una grande flessibilità nel design e un'ottima stabilità del circuito. In entrambi i circuiti, 6 parametri interni possono essere attivamente controllati attivando degli sfasatori termo-ottici. Questa alta riconfigurabilità permette al dispositivo di essere usato sia per misure super risolute a singolo parametro che per implementare algoritmi di stima multi-fase, con una precisione che supera lo Standard Quantum Limit.