Relaxation oscillation in Er^3+-doped and Yb^3+/Er^3+co-doped fiber grating lasers

Relaxation oscillations in Er(3+)-doped and Yb(3+)/Er(3+) co-doped fiber grating lasers were investigated. Intensity noise models were established for both cases in which the fluctuations of pump power and cavity loss were analyzed. Simulation indicates that the relaxation oscillation is induced by the pump power fluctuation, and fluctuation of the cavity loss can broaden the relaxation oscillation peak and enhance the amplitude. The relaxation oscillation of a laser with Er(3+)-doped fiber exhibits a lower frequency and larger amplitude than that of an Yb(3+)/Er(3+) co-doped fiber grating laser. Distributed Bragg reflector fiber grating lasers with Er(3+)-doped fiber and Yb(3+)/Er(3+) co-doped fiber were fabricated, and the relaxation oscillations were measured. For the former, the relaxation oscillation frequency is at the magnitude of several hundreds of kilohertz and linearly shifts toward the higher frequency with the pump power. For the latter, no obvious relaxation oscillation was measured.