Efficient, low crosstalk and compact programmable photonic circuits by 3D femtosecond laser micromachining

Photonic Integrated Circuits (PICs) are today both pervading our life and enabling several novel experiments in research applications by tackling the issues of complex bulk optical setups. Their development is closely following what already witnessed for the microelectronics industry, with two main design approaches: on the one hand, application-specific PICs guarantee optimal performance by purposely tailoring the design for a given application, while, on the other hand, programmable PICs based on a mesh of reconfigurable Mach-Zehnder Interferometers (MZIs) provide a flexible solution to implement an arbitrary unitary transformation that can be modified at run-time. Such devices are usually referred to as programmable photonic processors [1] . To date, the most common technique to reconfigure large MZI meshes is thermo-optic phase shifting.