Light emission spectra of columnar-shaped self-assembled InGaAs/GaAs quantum-dot lasers: Effect of homogeneous broadening of the optical gain on lasing characteristics

Abstract

We examined the current–output power characteristics and light emission spectra for columnar-shaped self-assembled InGaAs quantum-dot lasers with a room temperature lasing threshold of 6 mA. Lasing threshold currents became obscure as temperature decreased below 180 K. While lasing occurred with one line including a series of longitudinal modes at room temperature, spectra at 80 K showed broad lasing emission over a range of 50–60 meV. We conclude that dots with different energies start lasing independently at low temperatures due to their spatial localization, while at room temperature the dots contribute to one-line lasing collectively via homogeneous broadening of optical gain.

Dephasing in InAs/GaAs quantum dots

“…However, it also implies that the laser behavior can be dominated by the homogeneous broadening, resulting in single mode lasing very useful for cw applications, as also recently reported. 22 In conclusion, we have presented the first measurements on the room temperature dephasing in InAs/In x Ga 1Ϫx As/GaAs self-assembled quantum dots. A T 2 only weakly dependent on the excitation density, with a low density value of 290Ϯ80 fs from spectal-hole burning and of 260Ϯ20 fs from four-wave mixing, is found.…”

Time-resolved four-wave mixing in InAs/InGaAs quantum-dot amplifiers under electrical injection

“…This implies a dominant homogeneous broadening behavior in QD lasers, as also recently reported. 9 Moreover, the FWM response around transparency shows clear features of the discrete values of the occupation number in QDs, different from what is observed in bulk and QWs.…”

Femtosecond pulse generation in passively mode locked InAs quantum dot lasers

“…Laser action first occurs at the peak of this spectrum, and additional current above threshold not only supplies a higher stimulated emission rate at the lasing dots but also increases the occupation of non-lasing dots so the lasing spectrum broadens. 10,11 This suggests the pulse duration of mode-locked lasers could be reduced by operating in the random population regime, where the gain spectrum is wider, and the dots act as independent oscillators enabling this width to be accessed above threshold. The purpose of this paper is to explore this prospect: first the underlying physics, then reporting our modelocking results.…”

“…10,11 The threshold current as a function of increasing temperature has a distinctive minimum at around 200 K as the dots go from random to quasi-equilibrium distributions. 11,13 Since the random occupation probability is independent of energy, all dots become inverted at the same current, and the gain spectrum extends over the inhomogeneous width and follows the dot size distribution.…”

“…8 At room temperature, the carriers on the dot states are in quasi-equilibrium with the wetting layer; 9 their fractional occupation varies with their energy and this limits the width of the gain spectrum. Laser action occurs over a narrow line 10,11 at the peak of the gain spectrum and additional current above threshold supplies this lasing process rather than increasing the population of dots of different sizes which further restricts the width of the available gain spectrum above threshold.…”