In recent years, commercial applications of vertical-cavity surface-emitting laser(VCSEL)s are beginning to show up owing to rapid improvement of major characteristics. However, the requirement of fundamental mode operation in VCSEL for high speed modulation has been highly restricted, because of restriction to the mode size enhancement.
So, in this paper we demonstrated curved surface VCSELs for enlarged fundamental mode size. Stable single transverse mode operation is achieved from curved-mirror vertical-emitting lasers at 850 nm using epoxy microlens frame. By including gain-producing layers inside the bottom DBR, we remove unnecessary multi-cavity effect. With continuous wave optical pumping at 663 nm, single mode power up to 7 mW is observed at room temperature. When pumped near the center of the curved mirror made of optical epoxy, the device operates in a single transverse mode reliably. The diameter of the fundamental mode is generally larger than 10μm. As the pump position moves away from the center, lasing from higher-order modes is observed.
And also, we investigated transverse mode characteristics of 980-nm VCSEL including curved-mirror surface. Microlens structure is inscribed by bromium etchant. The optimized condition for operating fundamental mode easily at the current injection range is 244 ~ 300 μm of radius of curvature and 15~18 μm of current guiding oxide aperture. We obtained single fundamental mode laser at full current range, and the cavity mode spectrum in this device has an similarity of previous 850-nm curved mirror VCSEL.
