Calibrated Monolithically Integrated 90 $^{\circ} $ Downconverter for Colorless Operation in the C+L Band

We propose a 90° hybrid-based monolithically integrated coherent receiver suitable for colorless operation in the complete C- and L-band (1530-1625 nm). In-phase and quadrature (IQ) signal components are obtained from a calibrated analog IQ recovery circuit, which adequately combines all the four photocurrents at the output of the 90° hybrid nearly cancelling the baseband interference from the self-beating of adjacent wavelength division multiplexing channels. We numerically demonstrate that the proposed downconverter supports colorless reception of 128 channels with 16-quadrature amplitude modulation at 112 Gbps in the C+L band. Aside from this, this receiver exhibits a noticeable dynamic range, thereby not requiring a variable optical attenuator on the signal path, and it is pretty robust under realistic fabrication errors of the optoelectronic chip.