Photonic digital-to-analog conversion using a blue frequency chirp in a semiconductor optical amplifier

In this Letter, we present a photonic digital-to-analog conversion (DAC) technique based on blue-chirp spectral slicing using a semiconductor optical amplifier (SOA). Because the gain change in an SOA leads to a refractive-index change based on the change in intensity of the input data signal, the probe signals experience a dynamic frequency shift to a shorter-wavelength side called a blue-chirp. After passing through the SOA, the probe signals corresponding to the logic level of the input digital signal are extracted by filtering only the blue-chirp component of the probe signals using rectangular-shape filters. In this study, we experimentally demonstrate a 10-Gb/s, 2-bit photonic DAC from a 10-Gb/s digital signal with various data patterns to a four-level amplitude signal assuming an analog signal. In addition, we evaluate the resolution performance of the photonic DAC in terms of differential and integral nonlinearities and an effective number of bits.