Determining the linewidth enhancement factor via optical feedback in quantum dot micropillar lasers

Abstract

The linewidth enhancement factor α is a key parameter determining the spectral and dynamical behavior of semiconductor lasers. Here, we propose and demonstrate a method for determining this parameter based on a direct measurement of variations in the laser gain and emission spectrum when subject to delayed optical feedback. We then use our approach to determine the pump current dependent linewidth enhancement factor of a high-β quantum dot micropillar laser. The validity of our approach is confirmed comparing it to two conventional methods, one based on the comparison of the linewidths above and below threshold and the other based on injection locking properties. Furthermore, the pump power dependence of α is quantitatively described by simulations based on a quantum-optical model.

Dynamics of a Micro-VCSEL Operated in the Threshold Region Under Low-Level Optical Feedback

“…However, their extremely small photon numbers render an in-depth characterization quite challenging. Thus, aside from a couple of older investigations [28], [29] (even at the single-photon level [30]), only recently have concerted efforts surfaced, covering optoelectronic feedback [31] or external light feedback both in microcavities [32], [33], [34] and in photonic-crystal-based Fano-lasers [35], [36].…”

Minimizing the linewidth enhancement factor in multiple-quantum-well semiconductor optical amplifiers

“…Because the carrier collision rate for each partitioned active region is expected to become greater due to quantum confinement, which would yield a lower LWEF for the overall active region across which the beam propagation takes place, as will be shown later. It has indeed been shown by previous experimental studies that quantum confinement based SOAs display a smaller LWEF [18][19][20][21]. In the upcoming section we will investigate and explain why this decrease in the LWEF occurs in the case of quantum confinement, and the mechanism through which the partitioning of the active area using QWs influences the LWEF variation in relation to reduced intraband collision time.…”

“…Appreciable research has been done to enhance the gain-bandwidth product of SOAs [4][5][6][7][8][9][10][11]. The gain of SOAs is known to be intertwined with linewidth enhancement (LWE) due to refractive index fluctuations within the gain bandwidth, which is quantified by a parameter called the linewidth enhancement factor (LWEF) [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Therefore, in the context of enhancing the gain-bandwidth product of SOAs, taking the LWEF of SOAs into consideration is a must to account for the enhanced phase noise that distorts the output signal [18][19][20][21][22][23][24][25].…”

“…The gain of SOAs is known to be intertwined with linewidth enhancement (LWE) due to refractive index fluctuations within the gain bandwidth, which is quantified by a parameter called the linewidth enhancement factor (LWEF) [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Therefore, in the context of enhancing the gain-bandwidth product of SOAs, taking the LWEF of SOAs into consideration is a must to account for the enhanced phase noise that distorts the output signal [18][19][20][21][22][23][24][25]. One example is the case of Fourier domain mode locked lasers where SOA partakes as the most critical element, and the sharp variation of the LWEF introduces significant phase noise in the output intensity pattern [3,26,27].…”

Photon statistics and dynamics of nanolasers subject to intensity feedback

“…The interest in such a configuration, often related to numerous applications, arises from the rich phenomenology observed, ranging from increased noise, mode hopping, linewidth narrowing and broadening, and transition to developed chaos (coherence collapse) [17]. Recent work in small-scale devices ("high-β" lasers) subject to optical feedback reveals interesting physics, including chaos [18], modeswitching [19], linewidth enhancement [20] and various nonlinear dynamical phenomena [21,22]. However, a complete understanding of the physical mechanisms as the basis of this behaviour at the nanoscale still needs further investigation, given the simultaneous role played by deterministic rules -which determine the dynamicsand stochastic effects -originating from the spontaneous processes -in the behaviour of nanodevices [23].…”