Abstract

Various attempts have been tried to increase single mode yield or output power of the oxide-confined VCSEL, as seen in the examples of long monolithic cavity, ¹ and surface relief.² Yet as another approach, we propose to integrate a partial concave mirror on top of an otherwise ordinary VCSEL device. In this scheme, a part of VCSEL laser output emitted from the VCSEL microcavity is reflected from the mirror and subsequently fed back into the microcavity. Upon re-entering, the light travels inside the cavity, with its path folded back and forth whenever encountering the high-reflection planar mirrors composing the microcavity. This allows multiple overlaps of the feedback light with quantum well (QW) active layer. Along this pa age of light, the spot size of the reflected laser beam gradually shrinks due to the focusing effect of the concave mirror until it reaches the minimum at the mirror focal length. Therefore the total field strength that the QW active layer effectively feels is to be much concentrated spatially toward the aperture center. This in turn results in locking laser oscillation to the fundamental transverse mode since it matches best with the accumulated reflected beam profile among the possible VCSEL modes. This process is schematically illustrated in Fig. 1.

© 2002 Optical Society of America