Bi-functional optoelectronic devices have significant potential for commercial applications in short haul links where, due to their ability to operate either as source or receiver, they can be used in "ping-pong" communication systems. Such systems are causing increasing interest due to the potential simplification of network design and the cost reductions that can result. In this paper, a new dual-purpose vertical-cavity optoelectronic component (VCOC) is reported, which is shown to allow successful bi-directional link operation, and has the potential of being used in highly parallel systems. The VCOC device developed within our work is based on a standard vertical cavity surface emitting laser diode (VCSEL) in which mirror reflectivities are adjusted to allow both good lasing action and efficient resonant cavity enhanced (RCE) avalanche photodetection. When the VCOC is operated under reverse bias as a detector, the low absorption of the quantum well active region is enhanced by the RCE, as light inside the laser cavity is recycled, thus increasing the probability of carriers being photogenerated [l]. Under forward bias the cavity maintains efficient lasing action. To allow a flexible study, the VCOCs are formed by modifying standard VCSELs using focussed ion beam etching to determine suitable structures for dual purpose operation. Here etches are made to reduce the reflectivity of the top mirror to enhance detection, the etches being formed either across the whole device aperture, or in rings or spots so that separation of the detection and emitting regions can be achieved. This technique is extremely flexible, allowing arbitrary etches to be made on a chip by chip basis.