  Digital twin has revolutionized optical communication networks by enabling
their full life-cycle management, including design, troubleshooting,
optimization, upgrade, and prediction. While extensive literature exists on
frameworks, standards, and applications of digital twin, there is a pressing
need in implementing digital twin in field-deployed optical networks operating
in real-world environments, as opposed to controlled laboratory settings. This
paper addresses this challenge by examining the uncertain factors behind the
inaccuracy of digital twin in field-deployed optical networks from three main
challenges and proposing operational guidance for implementing accurate digital
twin in field-deployed optical networks. Through the proposed guidance, we
demonstrate the effective implementation of digital twin in a field-trial
C+L-band optical transmission link, showcasing its capabilities in performance
recovery in a fiber cut scenario.
