Effects of High-$β$ on Phase-locking Stability and Tunability in Laterally Coupled Lasers

Abstract: Phase-locked laser arrays have been extensively investigated in terms of their stability and nonlinear dynamics. Specifically, enhancing the phase-locking stability allows laser arrays to generate high-power and steerable coherent optical beams for a plethora of applications, including remote sensing and optical communications. Compared to other coupling architectures, laterally coupled lasers are especially desirable since they allow for denser integration and simpler fabrication process. Here, we present the theoretical effects of varying the spontaneous emission factor $\beta$, an important parameter for micro- and nanoscale lasers, on the stability conditions of phase-locking for two laterally coupled semiconductor lasers. Through bifurcation analyses, we observe that increasing $\beta$ contributes to the expanding of the in-phase stability region under all scenarios considered, including complex coupling coefficients, varying pump rates, and frequency detuning. Moreover, the effect is more pronounced for $\beta$ approaching 1, thus underlining the significant advantages of implementing nanolasers with intrinsically high $\beta$ in phase-locked laser arrays for high-power generation. We also show that the steady-state phase differences can be widely tuned - up to $\pi$ radians - by asymmetrically pumping high-$\beta$ coupled lasers. This demonstrates the potential of high-$\beta$ nanolasers in building next-generation optical phased arrays requiring wide scanning angles with ultra-high resolution.