Silicon photonics rectangular universal interferometer

[EN] Universal multiport photonic interferometers that can implement any arbitrary unitary transformation between input and output optical modes are essential to support advanced optical functions. Integrated versions of these components can be implemented by means of either a fixed triangular or a fixed rectangular arrangement of the same components. We propose the implementation of a fixed rectangular universal interferometer using a reconfigurable hexagonal waveguide mesh circuit. A suitable adaptation synthesis algorithm tailored to this mesh configuration is provided and the experimental demonstration of a rectangular multiport interferometer by means of a fabricated silicon photonics chip is reported. The 7¿hexagonal cell chip can implement 2 × 2, 3 × 3 and 4 × 4 arbitrary unitary transformations. The proposed hexagonal waveguide mesh operates in a similar way as a Field Programmable Gate Array (FPGA) in electronics. We believe that this work represents an important step¿forward towards fully programmable and integrable multiport interferometers.
The authors acknowledge financial support by the ERC ADG-2016 741415 UMWP-Chip, the Generalitat Valenciana PROMETEO 2013/012 research excellency award, I. G. acknowledges the funding through the Spanish MINECO Ramon y Cajal program. D.P. acknowledges financial support from the UPV through the FPI predoctoral funding scheme. D.J.T. acknowledges funding from the Royal Society for his University Research Fellowship. The chips were fabricated in the frame of the CORNERSTONE project funded by the EPSRC in the UK (EP/L021129/1)