Quantum Dot Laser Diode With Low Threshold And Low Internal Loss

Data are presented demonstrating that a low-threshold quantum dot laser diode can achieve very low internal optical loss. The broad-area laser diode operates at the wavelength 1.22m and delivers 2W of power from a 1.6cm-long cavity with uncoated facets, with a lasing threshold current density of 10.4A/cm2. The laser diode\u27s internal waveguide loss is extracted from cavity length measurements to be ∼0.25cm-1. The interdependence of threshold current density and internal optical loss is discussed. © 2009 The Institution of Engineering and Technology

Very low threshold current density continuous-wave quantum dot laser diode

An important advantage of the quantum dot (QD) laser diode is its ability to reach lasing threshold at very low current density under continuous-wave room temperature operation. This can reduce or eliminate the need for heat sinking in large area laser diodes, and is one of the requirements to reach very high efficiency. Early work on quantum dot laser diodes demonstrated continuous-wave lasing at 19 A/cm2 [1], which was reduced to 17 A/cm2 in subsequent work [2]. In this presentation we report continuous-wave room temperature lasing at a threshold current density of 11.7 A/cm2. To our knowledge this is the lowest threshold current density ever reported for continuous-wave room temperature operation of a laser diode. The broad area laser diodes operate at 1.22 μm have a stripe width of 120 μm and cavity lengths of either 1 cm or 2 cm. The laser facets are left uncoated. As shown in Fig. 1, the 1 cm long laser diode mounted p-side down on a heat sink operates with a room temperature continuous-wave lasing threshold of ∼13 A/cm 2 and delivers up to 1 W of CW power from both facets. Figure 2 shows the CW lasing characteristics of a 2 cm long laser diode operated p-side up on a probe station. No bonding material is used between the substrate and laser diode, so that heat is dissipated mainly through current spreading into the substrate and contact cooling to the metal plate of the probe station. Despite the lack of heat sinking the laser diode operates with a record low room temperature CW threshold of 11.7 A/cm2 and delivers over 0.4 W of power from both facets. Figure 3 shows the spectral measurements and spectral narrowing for a range of room temperature CW current densities. We believe the initial reduction in the spectral width from 2 to 5 A/cm2 is due to preferential emission coming from the peak of the QD ensemble emission. However for current densities greater than ∼ 6 A/cm2 the spectral narrowing is due to stimulated emission. For current density greater than 10 A/cm2 this spectral narrowing due to stimulated emission has a rapid onset to lasing threshold with a total spectral width of a few meV. Therefore the transparency current density in these QD laser diodes under CW room temperature operation is \u3c 6 A/cm2. We believe that reaching very low threshold current density laser operation may have important implications for future technology based on large area or broad area monolithic laser diodes because of importance of threshold current density in heat sinking. ©2008 IEEE