We demonstrate a new technique to all-optically identify the precise temporal locations and durations of the payloads of optical packets consisting of a variable length 40-Gb/s return-to-zero payload and 10-Gb/s nonreturn-to-zero label. The all-optically generated payload envelope signal can be used to erase the original optical label and rewrite a new label. The recovered payload envelope has 300-ps rise time and edge root-mean-square average jitter of 30 ps over a 10-dB dynamic range of input optical packet power. These numbers indicate that this technique enables the use of very short guard bands between payloads. The technique is demonstrated using optical semiconductor devices that are straightforward to monolithically integrate on a single chip