Abstract

Mode hopping, or rapid erratic switching between adjacent longitudinal modes, occurs for particular combinations of laser injection current and temperature. A map of mode hopping as a function of injection current and temperature reveals periodicity that can be related to the temperature-induced motion of the gain profile relative to the longitudinal modes of the laser. A Mitsubishi ML 4402 laser was mounted so that the temperature could be controlled to within a few mK. The collimated beam was split, with one part incident on a PIN photodiode, and the other part going to a spectrograph. The spectrum of the laser was detected by a linear photodiode array. The longitudinal modes, separated by ~0.3 nm, were easily observed as was switching between modes. The ac component of the PIN photodiode voltage increases as mode hopping occurs, with the maximum voltage corresponding to the maximum mode hopping activity.

© 1991 Optical Society of America