  This article describes experimental research studies conducted towards
understanding the implementation aspects of high-capacity quantum-secured
optical channels in mission-critical metro-scale operational environments using
Quantum Key Distribution (QKD) technology. To the best of our knowledge, this
is the first time that an 800 Gbps quantum-secured optical channel -- along
with several other Dense Wavelength Division Multiplexed (DWDM) channels on the
C-band and multiplexed with the QKD channel on the O-band -- was established at
distances up to 100 km, with secret key-rates relevant for practical industry
use cases. In addition, during the course of these trials, transporting a
blockchain application over this established channel was utilized as a
demonstration of securing a financial transaction in transit over a
quantum-secured optical channel. The findings of this research pave the way
towards the deployment of QKD-secured optical channels in high-capacity,
metro-scale, mission-critical operational environments, such as Inter-Data
Center Interconnects.
