Efficient power extraction in surface-emittingsemiconductor lasers using graded photonicheterostructures

摘要

Symmetric and antisymmetric band-edge modes exist in distributed feedback surface-emittingsemiconductor lasers, with the dominant difference being the radiation loss. Devices generallyoperate on the low-loss antisymmetric modes, although the power extraction efficiency is low.Here we develop graded photonic heterostructures, which localize the symmetric mode inthe device centre and confine the antisymmetric modes close to the laser facet. This modalspatial separation is combined with absorbing boundaries to increase the antisymmetric modeloss, and force device operation on the symmetric mode, with elevated radiation efficiency.Application of this concept to terahertz quantum cascade lasers leads to record-high peakpower surface emission (>100mW) and differential efficiencies (230mWA-1), together with low-divergence, single-lobed emission patterns, and is also applicable to continuous-waveoperation. such flexible tuning of the radiation loss using graded photonic heterostructures,with only a minimal influence on threshold current, is highly desirable for optimizing secondorder distributed feedback lasers.