The use of ion-beam-assisted etching to form ~ 1.5-µm diameter waveguiding "posts", or microresonators, in a GaAs/AlAs Fabry-Perot structure grown entirely by molecular beam epitaxy has reduced the device cross-sectional areas, energy requirements and recovery times all by more than an order of magnitude1. Prior to etching the minimum controlling energy required for an optical logic etalon operation2 was 20 pJ. The device diameter, defined as the illuminated region, was about 10 µm and recovery time was estimated to be several ns, both inferred from measurements on comparable devices. For 1.5-µm microresonators the energy is 0.6 pJ and recovery time, ~ 200 ps (Fig. 1). Thus, at least over this size range, the energy and time requirements scale directly with cross-sectional area. It is likely that this scaling will continue down to λ/n diameters, i.e. to 1/4 µm for GaAs, or another factor 36 in area. This would reduce controlling energies to ~ 17 fJ and recovery times to ~ 6 ps for the same Fabry-Perot design. The energies (but not recovery times) should be much further reduced by use of thinner, higher-finesse etalons, and much further still by use of excitonic nonlinearities which are not cancelled out by bandgap renormalization. The latter might be obtained from sufficiently-high-quality quantum confining semiconductors or operation at reduced temperatures. With all these improvements, controlling energies should approach the statistical limit of a few hundred photons3,4.