Dispersionless time-lens with an integrated silicon nitride ring resonator

Abstract

The observation of ultrafast signals by expanding them to a time scale that enables the measurement with conventional high-speed systems is of considerable interest in many applications. Usually, a time-lens can be used for this purpose. Like a lens in optics, a time lens expands the signal in time. This can be accomplished by a strong first order dispersion. However, higher order dispersion leads to a distortion of the signal and an integration of elements with a strong first order dispersion is challenging. Here we present a dispersion-less time-lens with an integrated ring resonator. Several replicas of a single input signal are generated by a microring resonator having a free spectral range (FSR) much less than the bandwidth of the input signal. These copies are then subjected to a coupled Mach-Zehnder intensity modulator (MZM) system driven by a single sinusoidal radio frequency (RF) signal to generate copies of the input spectrum. In the time-domain this can be seen as a multiplication of the input signal with a sinc-pulse sequence. The sinc-pulse sequence is tunable by the single sinusoidal radio frequency. By choosing a suitable radio frequency, the signal waveform can be sampled at a different position for each copy, so that an expanded waveform with a configurable stretching factor determined by the input RF can be achieved. This time lens system can be fully integrated into a photonic integrated circuit and requires neither an optical source nor a dispersive medium. In first preliminary experiments we present a sampling rate of around 110 GSa/s.