Modelling and experimental validation of an x-cut four phase modulators structure

Abstract

A general model to describe the operation of an x-cut LiNbO3 optical modulator comprised of four phase modulators in parallel, originating two inner Mach–Zehnder modulators (MZMs) integrated in one outer MZM is proposed. This model considers the application of arbitrary electrical signals to the electrode inputs, instead of electrical tones as in previous models. Such improvement allows the accurate modelling of a wide range of applications to the optical modulator. Moreover, an experimental method to characterise the steady state of each inner MZM and outer MZM, without the interference of the other MZMs, is proposed. This characterisation provides the three bias voltages required to apply to each MZM according to the desired output modulation. Validation of the proposed model for dynamic operation is done using transmission of non-return to zero signals along a dispersive fibre with chirped and chirp-free signals at the output of the modulator. Excellent agreement between experimental and theoretical results is obtained in both steady-state and dynamic regimes.