The coexistence of quantum information and classical signals within the same fiber link is essential for realizing future quantum networks that utilize the well-established optical fiber infrastructure. In this work, we demonstrate the coexistence of $C$-band energy-time entanglement and $L$-band classical data. By employing wavelength-division multiplexing techniques and polarization management, we achieve quantum entanglement distribution over a 40-km-long fiber carrying $4\mu \mathrm{W}$ of bidirectional received power. Under the highest noise conditions, we obtain a visibility of $84.59\pm 0.68\%$ from Franson interference and calculate a secret key rate of 1.89 kbps using the Bennett-Brassard-Mermin 1992 (BBM92) protocol, showing improved performance compared to an all-$C$-band setup. These results pave the way for large-scale quantum-classical coexistence within existing optical fiber infrastructure.

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• Quantum channels
• Quantum communication
• Quantum communication, protocols & technology
• Quantum correlations, foundations & formalism
• Quantum entanglement
• Quantum networks