Beam steering mechanism in phased vertical cavity laser arrays

Beam steering with optical phased arrays is accomplished by introducing a relative phase shift between array elements (McManamon et al., 2009). This is typically achieved by altering the refractive index difference between elements, which alters the optical path length of incident radiation traveling through the elements. Beam steering with VCSEL arrays has also been shown to rely on such a refractive index variation (Johnson et al.) which is implemented by adjusting the current injection to the elements. However, if we view the VCSEL array as a waveguide from the active region through the distributed Bragg Reflectors, it can be shown that the index-induced phase shift between elements would only account for less than 1/100^th of the observed phase shift. It is thus evident that phased VCSEL arrays rely on a fundamentally different phase-shifting mechanism. To investigate this, we turn to coupled mode theory, which has previously been applied to the dynamics of coupled edge emitting laser arrays and phase tuning in injection-locked VCSELs.