Analysis of 2-D Surface-Emitting ROW-DFB Semiconductor Lasers for High-Power Single-Mode Operation

A detailed analysis of 2D surface-emitting active-photonic-crystal (APC) lasers composed of a resonant-optical-waveguide (ROW) array and Pi-phaseshifted second-order distributed feedback/distributed Bragg reflector (DFB/DBR) gratings, made atop the ROW-array elements, is performed. Coupled-mode theory and the transfer-matrix method are used for analysis in the longitudinal direction, and 2D rigorous array modeling is used for analysis in the lateral direction. The gratings, beside their usual functions (i.e., feedback and outcoupling), act as strong lateral-mode (i.e., array-mode) selectors by exploiting the array-modes' different field-intensity overlap with the element regions, at the in-phase-mode resonance. The in-phase array mode is strongly favored to lase at and around its (lateral) resonance due both to better longitudinal-field overlap with the active-grating (i.e., DFB) region
and
to much lower interelement loss than the other array modes. The loss in the interelement regions that suppresses lasing of the nonresonant modes is due to strong absorption to both the metal contact (i.e., Au) as well as to the semiconductor/metal grating layers (i.e., GaAs-Au) in the element regions. The intermodal discrimination can be further enhanced by introducing strong free-carrier absorption in the interelement regions. For 20-element arrays with 700 mum/600 mum DFB/DBR gratings, emitting at 0.98 mum and of 100-mum-wide lateral dimension, the intermodal discrimination, DeltaJ
_th
, is high (~500 A/cm
²
) at the in-phase-mode resonance, and > 70 A/cm
²
as the regrown interelement-region thickness t is varied (during fabrication) over a 0.02-mum range. The external differential quantum efficiency reaches 58%, and the guided-field intensity profile is virtually uniform in both the lateral and longitudinal directions. For 40-element devices, the projected CW power in a single, diffraction-limited lobe is 2.4 W at 10 x threshold. For 20-element arrays with intentionally introduced free-carrier absorption in the interelement regions, DeltaJ
_th
is very high (~6500 A/cm
²
) at the in-phase-mode resonance, and >70 A/cm
²
as t is varied over a 0.035-mum range. The projected single-mode, diffraction-limited continuous-wave power, from 40-element devices at 10x threshold, is similar: 2.4 W.