Transverse and longitudinal mode control in semiconductor injection lasers

Theoretical analyses of the transverse and longitudinal mode control of injection lasers are combined and discussed. Guided mode and transverse mode control are addressed, and lasing gain calculated by application of the density matrix formalism is reviewed. Electron transition mechanisms in semiconductor crystals are examined, and linear and nonlinear gain coefficients are calculated. Coupled variations of the electron density and light intensity are formulated in improved rate equations by which mode coupling or mode competition can be discussed. Numerical results demonstrating the relationship between the saturated gain profile and the intraband relaxation time are given. The relation between the single longitudinal mode operation and other physical phenomena such as transverse mode control, the spontaneously emitted optical field, impurity concentration in the active region, and direct modulation are discussed.