Characterization of C-Band Coherent Receiver Front-Ends for Transmission Systems beyond S-C-L-Band

The reuse of already deployed single mode fiber is seen as one of the key enablers for cost-efficient capacity upgrades of optical transmission systems. Unlocking the benefits of other transmission bands, to further increase the capacity, can enable optical networks to adapt to highly dynamic traffic patterns. In the here and now, C-band based optical coherent receiver frontends would be a cost-effective solution to support bandwidth division multiplexing without the need for bespoke and expensive per band receiver designs. To investigate a potential use of already existing C-band receivers for multi-band applications, we present a simple and rapid measurement method to characterize the quadrature phase error and the electrical output swing. We experimentally characterize four different commercially available C-band receivers from the upper E- to lower U-band covering 25.4 THz (i.e. 200 nm) of total bandwidth. The obtained results reveal that micro-optics based discrete 90° hybrids and discrete indium phosphide (InP) balanced photodetectors are promising candidates for multi-band systems. While at the same time, the investigated receivers based on photonic integrated circuits in InP suffer from a strong quadrature phase error and a reduced common mode rejection ratio in the wavelength regime below the C-band.