On single-mode injection laser structures for reduced output fluctuations

This paper explores the possibilities of two principles for reducing the fluctuations in power output of the main mode of an injection laser: 1) including within the laser cavity a section of larger bandgap than the energy of the photons generated; and 2) use of very small wavelength-selective loss differences between the main mode and the side modes. Transient response and steady-state fluctuations are calculated from a rate-equation model. New approximate analytical expressions are given to make possible the calculation of 1) the critical gain-loss term and 2) the consequent laser characteristics. It is shown that a very small side-mode loss difference increases the coupling between the carrier density and the main-mode photons. This produces very fast transient response. It is also shown that the larger bandgap region smoothens the output power and enhances the main-mode power at constant driving current. These results give promise of a low-power-level laser capable of multigigabit direct modulation