Optical networks-on-chips (ONoCs) have become a potential solution for on-chip communication of multi- and manycore systems to provide superior communication bandwidth, efficiency in power consumption, and low latency compared with electronic NoCs. Prior studies on this topic have focused on developing efficient architectures of optical routers based on micro-ring resonators (MRRs). However, potential transmission faults of MRRs after manufacturing have still not been considered in architecture design of ONoCs. To enhance the reliability of ONoCs, we propose a framework to construct backup optical paths with wavelength reflection. To minimize power consumption and resource usage, the proposed framework takes advantage of the multi-wavelength resonance property of MRRs, an important feature of MRRs but rarely considered in previous studies. With these concepts, the architectures of ONoCs are enhanced by a modified random search algorithm to achieve fault tolerance. Experimental results demonstrate that all single faults in ONoCs can be dealt with effectively, while the number of backup MRRs can be reduced effectively.