Power partition fluctuations in two-mode-degenerate distributed-feedback lasers

Measurements are presented along with a theoretical analysis of power partition fluctuations in a distributed feedback (DFB) laser operating in continuous wave with the two DFB degenerate modes as the only significant longitudinal modes. The power ratio of the two modes was varied from 1.1 to 2500:1 by electrical control using a two-electrode DFB laser. The laser was observed to exhibit (1) transient power dropouts and (2) two-mode relaxation oscillation. The dropout depths were less than 30% of the main-mode power in all cases, except when the laser was subjected to external optical feedback. The relaxation oscillations of the two-mode power are anticorrelated, which is different from the relaxation oscillation of the total power due to photon-carrier interaction. The calculated result based on a Fokker-Planck analysis agrees with the experiment, except for the two-mode relaxation oscillation, which was not considered in the theory.<>