Cavity Q, Mode Volume, and Lasing Threshold in Small Diameter Microdisks with Embedded Quantum Dots

In this chapter, we continue our study of taper-coupled microdisk-QD structures by considering device performance as the disks are scaled down in size. In section 7.1, we use finite element simulations to examine the behavior of Q and Veff as a function of disk diameter. We relate these parameters to those used in cQED, and from this, determine that disks of 1.5-2 μm in diameter are optimal for use in future experiments with InAs QDs. In sections 7.2 and 7.3, we present experimental measurements of fabricated devices. Through passive characterization (section 7.2), cavity Qs as high as 1.2×105 are demonstrated for devices with a predicted Veff ∼ 2.2(λ/n)3. In addition, photoluminescence measurements (section 7.3) show that the devices operate as lasers with room temperature (RT), continuous-wave thresholds of ∼1 μW of absorbed pump power. Finally, the optical fiber taper is used to increase the efficiency of out-coupling by nearly two orders of magnitude, so that an overall fiber-coupled laser differential efficiency of ξ ∼ 16% is achieved. We conclude by presenting some estimates of the number of QDs contributing to lasing and the spontaneous emission coupling factor (β) of the devices. The majority of this chapter is based on ref. [76].