Measurement of the phase shift between intensity and frequency modulations within DFB-LD and its influences on PGC demodulation in a fiber-optic sensor system

The parameters of the semiconductor laser source are vital for the performances of optical coherent systems. In this paper, a novel method to measure the phase-shift φm between laser central optical-frequency modulation (COFM) and the accompanied optical-intensity modulation (AOIM) is proposed, which is easy to realize and requires no further fiber etalons or high-speed demodulators. An orthogonal test is utilized to measure φm. Experimental results show that the value of φm approaches 1.09π under different COFM conditions. Then the interference model of phase-generated carrier (PGC) demodulation is modified by taking into account the effect of φm, and the influences of φm on the demodulation results using two methods (look-up table and AOIM-factor division) are further analyzed in detail.