Improved linewidth enhancement factor of 1.3-µm InAs/GaAs quantum dot lasers by direct Si doping

Abstract

We report on the significantly improved linewidth enhancement factor (αH-factor) of 1.3-µm InAs/GaAs quantum dot (QD) lasers by direct Si doping, compared with ones having identical structures but without the Si doping. It is found that the αH-factors for the ground-state and first excited-state at their gain peak positions of the Si-doped QD lasers are 1.48 and 0.63 while those of the undoped QD lasers are 2.07 and 1.07, greatly decreasing by about 28.5% and 41.1%, respectively. Furthermore, theoretical calculation and analysis suggest that direct Si doping would increase the electron quasi-Fermi level in conduction, leading to the increase in population inversion. Meanwhile, the appearance of a built-in electric field caused by the Si doping would accelerate the capture of electrons into QDs and strengthen the confinement effect of electrons, resulting in an increased differential gain.

Design of Quantum-dot Semiconductor Optical Amplifiers With Near-zero Linewidth Enhancement Factor

“…These fluctuations are particularly pronounced near the transition frequency [3,4]. Consequently, when an input optical beam is amplified through the active region, the occurrence of refractive index fluctuations induces phase distortion and compromises the spatial and temporal coherence of the amplified beam [5,6]. Since maintaining the coherence of an amplified laser beam holds great importance in almost all applications, it becomes crucial to minimize refractive index fluctuations.…”

“…Since maintaining the coherence of an amplified laser beam holds great importance in almost all applications, it becomes crucial to minimize refractive index fluctuations. The parameter indicative of such fluctuations within the SOA active region is the linewidth enhancement factor (LWEF, also denoted by α) [3][4][5][6][7][8][9][10]. Numerous studies have underscored the adverse effects of a high LWEF on the performance of optoelectronic devices, particularly in terms of stability and coherence [3][4][5][6][7][8][9][10][11].…”

“…The parameter indicative of such fluctuations within the SOA active region is the linewidth enhancement factor (LWEF, also denoted by α) [3][4][5][6][7][8][9][10]. Numerous studies have underscored the adverse effects of a high LWEF on the performance of optoelectronic devices, particularly in terms of stability and coherence [3][4][5][6][7][8][9][10][11]. Consequently, previous research endeavors have concentrated on devising SOAs with low LWEFs that are compatible with practical optoelectronic devices [12][13][14].…”

“…Moreover, computational modeling is challenging due to the strong interdependence of each SOA parameter [3,11,12,20]. Therefore, the development of a simple and effective algorithm for accurately evaluating the LWEF of an SOA holds significant importance, necessitating the systematic formulation of a corresponding design strategy [3][4][5][6]11,20]. Previous experimental investigations on the LWEF have revealed LWEF values ranging from 1 to 9 for the majority of SOAs [3][4][5][6][7][8][13][14][15][16][17][18][19][20][21][22], with only a few studies delving into design strategies aimed at achieving minimal LWEF [6,20,21].…”

“…Previous experimental investigations on the LWEF have revealed LWEF values ranging from 1 to 9 for the majority of SOAs [3][4][5][6][7][8][13][14][15][16][17][18][19][20][21][22], with only a few studies delving into design strategies aimed at achieving minimal LWEF [6,20,21]. Certain recent studies propose that quantum confinement could potentially reduce LWEF to near-zero levels [5,6,20,21]. However, conflicting findings from other studies cast doubt on such assertions [8,17,25].…”