Theoretical considerations of time delays in semiconductor lasers

Calculations have been made of time delays in semiconductor lasers, using a rate-equation approach to describe the transient behavior of photon and electron populations. Three possible models were considered in order to try to explain the delays: a) saturable absorption via conduction-band tail states in equilibrium with the band, with the lasing emission occurring via transitions from the band states; b) saturable absorption via conduction-band tail states not in equilibrium with the band; and c) absorption due to loss of waveguiding as a result of hole injection into the n-type regions of diode lasers. It was found that only the model b) was capable of satisfactorily accounting for the known properties of time delays.