Single-lobe, surface-normal beam surface emission from second-order distributed feedback lasers with half-wave grating phase shift

Abstract

Half-wave phase shifts were fabricated in the center of second-order GaAs gratings, for use in surface-emitting, horizontal-cavity, semiconductor diode lasers (λ=0.98 μm). Incorporating such gratings in diode lasers with distributed-feedback (DFB) active regions and distributed Bragg reflectors (DBRs) is found to provide surface-normal, single-lobe beam emission, as predicted by theory. InGaAs/AlGaAs/InGaP, two-quantum-well structures are employed. A 500-μm-long GaAs/Au second-order grating with half-wave phase shift represents the DFB region, which provides feedback and unidirectional light outcoupling. GaAs/SiO2/Au, 500-μm-long, second-order gratings are the DBR regions, on either side of the DFB region, which provide both frequency-selective feedback as well as unidirectional outcoupling. Lateral-mode control is achieved via a 2.5-μm-wide ridge waveguide. Surface emission is obtained through a 80-μm-wide window stripe in the metallization on the substrate n-side. Single-frequency lasing in an orthonormally emitted, single-lobe, diffraction-limited beam is obtained to 3× threshold under pulsed-drive conditions (200 ns wide pulses, 1 kHz repetition rate).