High-power And Microlens-integrated Vertical Cavity Surface Emitting Lasers

Vertical cavity surface emitting lasers (VCSELs) as a compact structure, excellent performance of novel light sources are widely applied for optical interconnection communication, optical communication, optical storage and other fields. Compared to the conventional edge-emitting lasers (EELs), VCSELs have the following advantages: lower threshold current; circular output beam, small divergence angle, efficiently fiber coupling and easy beam shaping; not prone to catastrophic optical damage due to large emitting windows; operating on dynamic single longitudinal mode; highly integrated two-dimensional area array with high power; easy welding and package; easy mass production. Particularly for single-mode VCSELs have important applications in many fields, such as free space optical interconnection, laser written, medical diagnostics, airborne light detection and laser ranging system, and so high power single-mode VCSELs with excellent beam quality and low divergence far-field angle are necessary. However, because vertical-cavity surface-emitting laser’s active region has a transverse width, so there will be some high order transverse modes are emitted. Thus, vertical cavity surface emitting lasers with large emitting windows usually operated on multi-transverse-mode and single longitudinal mode.In this paper, the main parts include directly fabricating microlens on the emitting windows of vertical cavity surface emitting laser in order to improve the beam quality of the device and compress far-field divergence angle. Firstly, the basic principle of the microlens coupling vertical-cavity surface-emitting lasers is theoretically analysised and calculated. The important parameters such as the effective reflectivety, threshold current, differential quantum efficiency, electro-optical conversion efficiency and spectral characteristics are demonstrated. We also optimize the structure of the device wafer and the key to the device manufacturing process technology. And then GaAs microlens and microlens array with different diameter are directly fabricated by using limited-diffusion wet etching technique on the substrate. The maximum continuous output power of microlens-integrated single device with an emitting windows of 400μm at room temperature is more than 200mW at a current of 4A, and the far field divergence angles of that are 8.4°and 8.7°, respectively. However, the far-field divergence angle of the same structure without microlens devices is 18.9°and 19.8°. For the 6×6 microlens-integrated vertical-cavity surface-emitting laser array, the maximum continuous output power at room temperature is more than 1W, and the far field divergence angle is less than 6.6°. Yet, the far-field divergence angle of the same structure without microlens devices is more than 15°. The results of experiment are basically consistent with the results of theoretical simulation.