We investigate the function of a circularly arranged submicron-scale optical cavity having a GaInNAs gain medium introduced into a two-dimensional photonic crystal slab. GaInNAs gain shows negligible optical degradations due to process damage, probably because of the small surface recombination velocity of the material. The preserved optical property realizes the observation of spectral peaks related to the cavity mode at wavelengths close to 1.3 µm. Moreover, the cavity shows fine tunability of its characteristics via the deliberate adjustment of its structure.