Optical Network-on-Chip (ONoC) is a promising communication medium for large-scale Multiprocessor System on Chip (MPSoC) with advantages in terms of throughput and latency. ONoC can support multiple transactions at the same time on different wavelengths by using Wavelength Division Multiplexing. However, sharing the same waveguide for simultaneous communications leads to inter-channel crosstalk noise due to the short wavelength spacing between optical signals and resonance frequency of the Microring Resonator (MR). This problem impacts the Signal to Noise Ratio (SNR) of the optical signal, which leads to an increase in the Bit Error Rate (BER) at the receiver side. To limit crosstalk noise during communication between parallel application tasks, we propose a strategy to allocate the wavelengths by evaluating the loss induced by spatio-temporal communication conflicts. Simulation results show that the proposed algorithm can significantly reduce the crosstalk of optical signal.