Near thresholdless laser operation at room temperature

Abstract

Laser emission using photonic crystal microcavities (PCM) [1] has opened new ways towards very low threshold and highly efficient solid state lasers with also very small size [2,3]. Recently, the term "thresholdless" has been used in the literature [4] to identify lasers presenting two main features: a spontaneous emission coupling factor (β ) close to 1 and low non radiative losses. Non radiative losses are reduced by several orders of magnitude at cryogenic temperatures, although they can never be completely suppressed. When the spontaneous emission factor β is equal to 1 every photon emitted by the device is emitted in the lasing mode. Such "thresholdless" lasers were proposed by Noda [4] to be realized by combining QDs as light emitters and PCMs as high quality resonators. Using that recipe, ultra-low threshold lasing has been achieved at cryogenic temperatures using an ever-decreasing number of QDs within PCMs. [2,[5][6][7] That strategy was adopted by Strauf et al. to demonstrate near thresholdless lasing at low temperature (4.5 K) by using few QDs (between 2 to 4) as active emitters and a high β =0.85 with power theshold values of 124 nW.[5] Khajavikhan et al. recently demonstrated thresholdless operation at low temperature (4 K) using metallic microcavities instead PCMs. [8] In this work we report a RT continuous wave (c.w.) laser with emission characteristics close to those of an deal thresholdless laser. [6]

Self-consistent Maxwell-Bloch model of quantum-dot photonic-crystal-cavity lasers

“…1. Using the simple rate equations, e.g., of Prieto et al [28] for the carrier and photon densities of a QD PC cavity laser system (neglecting nonradiative decay in the carrier density equation), then…”

“…To numerically model a gain medium within the cavity, various techniques have been implemented ranging from the simple inclusion of a negative imaginary component in the refractive index [24] to including rate equations embedded in the FDTD algorithm [3,25,26], or with the finite element method [27]. It is also common to adopt simple rate equations for the population density of carriers and photon flux [28,29], which can quickly connect to experimental data. It is, however, still a major challenge to model arbitrarily shaped gain materials coupled to arbitrarily shaped cavity structures, which is desired for many quantumdot (QD) microcavity structures, especially as the modal properties of the laser cavity change drastically as a function of position and size (which results in spatially dependent radiative coupling and gain dynamics).…”

“…With the current trend of miniaturized semiconductor laser systems, there is now a need for more sophisticated models of PC lasers beyond the simple rate-equation picture [28,64], where the emitters' coherence is assumed to be in steady state or adiabatically eliminated, leading to coupled equations between the available energy levels without any information regarding the system coherence. In many cases, this may fail to describe emerging experiments.…”

“…The usercontrolled plug-in tool returns MB dynamics by solving the OBEs (for each QD), and includes radiative decay, local gain, and inter-QD coupling that is fully captured self-consistently by the FDTD method, as well as pure dephasing included as a phenomenological decay rate, and an incoherent pump term which effectively models a three-level gain system for each QD. The OBE plug-in has the distinct advantage of being completely general, solving lasing dynamics and gain coupling with zero a priori knowledge (other than inherent properties of the QDs), when compared to traditional rate equations [28,29], and they easily capture the statistical behavior of a QD ensemble as well.…”

Rate equation description of quantum noise in nanolasers with few emitters

“…4 Recent experiments have demonstrated high-b lasers using ultra-small photonic crystal cavities, [5][6][7][8] micropillar structures, 9,10 and metal-clad cavities, 11 prompting the question of the noise properties of these lasers.…”