###### Abstract  
Quantum key distribution (QKD) has great potential in ensuring data security. Deploying QKD-related devices in existing optical fiber networks is a cost-effective way to practically implement QKD. However, QKD optical networks (QKDON) have a low quantum key generation rate and limited wavelength channels for data transmission. The simultaneous arrival of multiple QKD services may also lead to wavelength conflicts in QKDON. Therefore, we propose a resource-adaptive routing scheme (RAWC) with wavelength conflicts to achieve load balancing and efficient utilization of network resources. Focusing on the impact of link load and resource competition, this scheme dynamically adjusts the link weights and introduces the wavelength conflict degree. Simulation results indicate that the RAWC algorithm is an effective approach to solving the wavelength conflict problem. Compared with the benchmark algorithms, the RAWC algorithm can improve service request success rate (SR) by up to 30%. quantum key distribution; QKDON; RAWC; load balancing; wavelength conflicts +
Footnote †: _Entropy_
necessary to construct multi-point interconnected QKD networks. Because deploying dedicated optical fibers for QKD alone is too costly, we use wavelength division multiplexing (WDM) technology to multiplex quantum signals and classical signals into the same optical fiber for transmission [25]. It has been proven to be feasible to integrate QKD into optical networks by WDM technology [26; 27; 28; 29]. In addition, to further improve the utilization of wavelength resources as well as the transmission capacity of the fiber, time division multiplexing (TDM) [30] and space division multiplexing (SDM) [31] can also be adopted in QKD optical networks (QKDON). Software-defined networking (SDN) is a new type of network virtualization technique, whose core lies in the ability to define and control the networks programmatically [32]. The introduction of the SDN technique in optical networks can improve the programmability and flexibility of the networks. Recently, some researchers have proposed the architecture of QKD over software-defined optical networks [33]. In this network architecture, quantum key pools (QKPs) between two QKD nodes are constructed to store and manage quantum keys. The SDN controller is deployed to determine the configuration and employment of QKPs through the OpenFlow protocol. QKDON supporting SDN technique can efficiently manage the network-wide key resources in QKPs through centralized control. Although the QKD technique is continuously being improved and the key generation rate is getting higher, it cannot fully meet the encryption needs of the explosive development of data services. Many different solutions are proposed to achieve resource allocation, including routing, wavelength, and quantum key methods. Table 1 compares focus points and performance metrics of the related works [33; 34; 35; 36; 37] with our scheme, where '-' means that this issue is not involved in the corresponding paper. Ref. [33] proposed the KoD scheme to allocate resources and update keys for different services, considering key-updating cases based on time complexity and data complexity. The RWTA algorithm in ref. [34] assigned quantum key channels based on the key-updating periods to enhance security. The dynamic DSKP scheme was proposed in ref. [35] to generate and assign quantum keys for users' different demands. Ref. [36] took the quantum key allocation process and the QKP key supplement process into account from the perspective of system efficiency and security, designing the DDKA scheme to satisfy the efficiency and lightweight requirements of IoT applications. To minimize the wastage of keys and maximize the utilization efficiency of resources, ref. [37] dynamically adjusted the link evaluation indicators by considering key volume, the key generation rate, and the number of path hops comprehensively, and selected the optimal path.