Investigation of partially coherent interaction in fiber Bragg grating stabilized 980-nm pump modules

Partially coherent interaction of feedback light with the field in the laser cavity is affirmed with fiber Bragg grating (FBG) stabilized 980-nm pump lasers, in contrast to the normally accepted totally incoherent state of interaction. A coherence parameter γ was defined to identify the fraction of feedback light interacting coherently. γ was determined by fitting the measured power-difference versus pumping-rate curve to the simulation results. From the fits, it is found that coherence parameter γ decreases when the distance between the FBG and the laser facet increases and vice versa. The relationship between γ and the spectral bandwidth of the reflectivity of the feedback element was also investigated. This work is important to understand and improve the characteristics of FBG stabilized 980-nm pump modules.