Designing strategy to enhance mode selectivity of higher-output oxide-confined vertical-cavity surface-emitting lasers

摘要

Performance of modern oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSELs) is more sensitive to the construction details than in the case of other VCSELs. In particular, a stable single-fundamental-mode operation is difficult to be achieved in these VCSELs especially in higher-output large-size continuous-wave (cw) operating devices at higher temperatures. In the present paper, an operation of OC VCSELs has been investigated with the aid of the comprehensive fully self-consistent model using the (GaIn)(NAs)/GaAs quantum-well VCSEL with two oxide apertures as a typical example. A new approach is proposed to enhance cw RT single-fundamental-mode low-threshold operation in higher-output OC VCSELs. One of their oxide apertures should be shifted to the node position of the resonator standing wave where it is working as the electrical aperture only. Then diameters of both apertures may be changed independently giving an additional degree of freedom for VCSEL designing, which enables their optimisation. While the larger-diameter optical aperture placed in the anti-node position creates an efficient radial waveguiding effect, the smaller-diameter electrical aperture enhances a more uniform current injection into the VCSEL active region. Due to combining influence of both the apertures, the single-fundamental-mode operation is predicted in a large device with the 10-μm-diameter active region even for 80 K active-region temperature increase over RT of the ambient. An impact of intentional detuning at room-temperature (RT) of VCSEL active-region gain spectrum towards shorter wavelengths with respect to the resonator mode improves mode selectivity is also analysed.