We demonstrate the relationship between inter-core crosstalk and Q-factor in a multicore transmission line including a multicore fiber and a multicore amplifier by using an in-service inter-core crosstalk monitoring method we propose. The method estimates inter-core crosstalk by using tones with different wavelengths for each core. We measured Q-factors at the center wavelength of the WDM channel. The measured crosstalk was -20.2 dB and the Q-factor was 5.8 dB after 411.2-km transmission. The Q-factor estimated from the monitored crosstalk was found to closely match the measured value.
