Fundamental aspects of closed optical mode formation in Fabry–Perot semiconductor lasers based on AlGaAs/GaAs (905 nm) asymmetric heterostructures

Abstract

Experimental static and dynamic electro-optical characteristics of 905 nm high power mesa-stripe semiconductor laser diodes based on an AlGaAs/GaAs asymmetric heterostructure operating under Fabry–Perot cavity mode quenching have been investigated. We have shown that Fabry–Perot cavity mode reversible turn-off is due to the fulfillment of a high-Q closed mode threshold condition. The mode is propagating along both gain and passive areas of the laser diode and characterized by nearly zero output optical losses. We have demonstrated that fundamental reasons of closed mode threshold condition fulfillment are (i) gain spectra shift in the long wavelength region due to band gap shrinkage and thermal heating effects and (ii) the band gap absorption decrease in the passive area. It has been shown that the process of closed mode turn-on consists of two stages. In the first stage, Fabry–Perot cavity modes and closed modes are lasing simultaneously under high residual band gap absorption in the passive area. In the second stage, closed mode optical losses become lower than Fabry–Perot cavity mode optical losses due to a positive feedback between the residual absorption and closed mode photon stimulated generation rate. This results in an accumulation of photogenerated carriers in the quantum well active region of the laser diode passive area. As a result, the threshold concentration in the gain area decreases providing lasing emission switching from the Fabry–Perot cavity mode to the closed mode.