Coherence effect on the measurement of optical fiber nonlinear coefficient in continuous-wave dual frequency method

We examined the source coherence effect on the optical fiber nonlinear coefficient measurement in a direct continuous-wave dual frequency method. Highly coherent dual frequency source was constructed with an external cavity laser diode and an acousto-optic frequency shifter. In a highly coherent case, we obtained nonlinear coefficients of -3 % higher than those of an incoherent case.