  Universal photonic processors (UPPs) are fully programmable photonic
integrated circuits that are key components in quantum photonics. With this
work, we present a novel platform for the realization of low-loss, low-power
and high-fidelity UPPs based on femtosecond laser writing (FLW) and compatible
with a large wavelength spectrum. In fact, we demonstrate different UPPs,
tailored for operation at 785 nm and 1550 nm, providing similar high-level
performances. Moreover, we show that standard calibration techniques applied to
FLW-UPPs result in Haar random polarization independent photonic
transformations implemented with average amplitude fidelity as high as 0.9979
at 785 nm (0.9970 at 1550 nm), with the possibility of increasing the fidelity
over 0.9990 thanks to novel optimization algorithms. Besides being the first
demonstrations of polarization-transparent UPPs, these devices show the highest
level of control and reconfigurability ever reported for a FLW circuit. These
qualities will be greatly beneficial to applications in quantum information
processing.
