Direct observation of lasing mode in a microdisk laser by a near-field-probing technique

Evanescent field profiles of whispering gallery (WG) modes in a 1.6-μm-GaInAsP microdisk injection laser were investigated by scanning a nanoprobe near the periphery of a lasing microdisk. The increase in threshold current due to the light scattering by the probe and the corresponding decrease in laser light were observed experimentally. Two-dimensional images of the evanescent field, which agreed well with theoretical expectations, were obtained by the use of a Pt–Ir probe. The images indicate that the WG mode is strongly locked by the fourfold symmetry in the microdisk with center post claddings. This characteristic is favorable for the microdisk laser itself to be used as an active near-field probe. A lower contrast image obtained by the use of a tapered silica fiber probe suggests that the microdisk probe can be sensitive to both surface profiles and optical properties of the object.