Frequency chirp is a unique phenomenon in semiconductor optical amplifiers (SOAs), and provides intensity-to-frequency conversion based on dynamic refractive index change in the devices. Until now, we have investigated the chirp properties in SOAs, and shown that red (shift to longer wavelength) and blue (shift to shorter wavelength) frequency chirps have different and unique behaviors. A photonic analog-to-digital conversion (PADC) using red chirp, and a photonic digital-to-analog conversion (PDAC) using blue chirp are proposed. We experimentally demonstrate a PADC and PDAC using a SOA and evaluate its performance.