Aim and Scope of the project

PICSONDE focuses on designing and fabricating an embedded sensing system based on optical feedback interferometry (OFI) in a laser diode, thus integrating the light source, the interferometer, and the photodetector within the same package. This proposed OFI-based sensor combines a photonic integrated circuit (PIC) that allows to retrieve the frequency modulated (FM) channel of the OFI signal, with a system-on-chip (SoC) for both data acquisition and signal processing. The sensor resolution targets the OFI quantum limited performance of 0.1 pm/√Hz noise power spectrum density over a large bandwidth (up to 100 kHz) for real-time experimental modal analysis applied to predictive maintenance applications in particular.

This performance is three orders of magnitude better than existing OFI systems that process the optical output power modulated by OFI, also referred to as the amplitude modulated (AM) channel. For this purpose, four main technological barriers should be resolved: (1) acquire RIO signals with both the highest dynamic range and signal to noise ratio, (2) retrieve the information embedded within highly non-linear RIO signals, (3) assess in real-time the optical feedback factor between the laser and the target, and (4) detect the interferometric fringes in the presence of speckle. To achieve the target resolution, it is required to exploit the FM channel of OFI signals instead of the AM channel to benefit from greatly enhanced noise performances since the OFI signal is no longer limited by the laser shot noise but by its linewidth. The inherent compactness of the PIC will also enhance the system robustness for operation in an industrial environment. In addition, we propose to assimilate the OFI signals to an inherent non-uniform sampling system to be directly processed by an SoC. The laser thus becomes both the sensor and the non-uniform optical data acquisition system.

By combining the laser with the PIC and the signal processing SoC, a sensor prototype will be fabricated, and in situ tests will be carried out in collaboration with an industrial end user for predictive maintenance. Nevertheless, this compact high-resolution interferometric sensor can also be used to measure refractive index variations that correspond to optical path changes. Additionally, the sensor can, via the PIC, potentially be exploited to optically probe MEMS structures. This opens a pathway to develop high-resolution (bio)chemical refractometric sensors and optically integrated MEMs sensors.