Future high-speed optical communications networks operating at data rates in excess of 100Gbit/s per channel will require a sensitive and ultrafast technique for precise optical signal monitoring. The standard way of characterising high-speed optical signals to use a fast photodetector in conjunction with a high-speed oscilloscope. However, this method is limited to a maximum data rate of approximately 40Gbit/s. An alternative is to employ all-optical sampling techniques based on ultrafast optical nonlinearities present in optical fibres, optical crystals and semiconductors. One such nonlinearity is the optical-to-electrical process of Two-Photon Absorption (TPA) in a semiconductor. This paper presents an optical sampling technique based on TPA in a specially designed semiconductor microcavity. By incorporating the microcavity design, we are able to enhance the TPA efficiency to a level that can be used for high-speed optical sampling.