Low-threshold, single-transverse-mode, 940-nm vertical-cavity surface-emitting laser with a mode filter and half-wavelength cavity

We demonstrate a structure for a vertical-cavity surfaceemitting laser (VCSEL) with a mode filter and half-wavelength (λ/2) cavity. The effects of λ/2- and λ-cavities on the threshold current are studied. The thickness and etched diameter of the mode filter are optimised to achieve single-transverse-mode output. The results show that when changing from λ-cavity to λ/2-cavity, the threshold current of the VCSEL decreases by 30.8% (from 0.85 mA to 0.65 mA). In addition, for the mode-filter thickness of 80 nm, and the etched diameter of 2.5 μm, the side mode suppression ratio reaches 90 dB, which meets the requirement of single-transversemode output. The VCSELs with the optimised design can overcome many difficulties and have great potential in 3D face recognition.