Demonstration of passively Q-switched multiple quantum wells two-section InGaAs/AlGaInAs diode laser

We present the first demonstration, to our knowledge, of passive Q-switching in InGaAs/AlGaInAs laser diodes. The Q-switched laser devices were based on a ridge waveguide structure fabricated by dry etching using a CH₄/H₂ process to a depth of 1.6 μm. After subsequent SiO₂ isolation and contact window etching, p- and n-contacts were deposited and annealed at 360 °C. In Multiple Quantum Well (MQW) material, a reverse bias section can be used as a saturable absorber which can then either passively Q-switch or mode-lock the laser depending on the relative length of the gain and absorber section. In the devices presented here, the p-contact is split into two sections, one of which is forward biased, the other reverse biased, forming a gain section and saturable absorber both monolithically integrated in a single laser chip. The device dimensions were 450 μm long gain section with 50 μm long absorber