Linear Optical Modulator for DAC-Based Coherent Fiber Communications Systems

This paper reviews our recent study on a linear optical modulator (LOM). The LOM has a highly linear field response, which is suitable for digital coherent optical communications systems where advanced multilevel transmission signals are generated in the electrical domain using high-speed digital-to-analog converters (DACs). A twostage lattice optical configuration enables us to compensate for the nonlinearity (sinusoidal nature) of the response of a conventional Mach-Zehnder modulator (MZM), which is an obstacle to achieving low-loss and low-distortion electro-optic conversion of the multilevel signals. We experimentally proved that the LOM has an advantage over the MZM in terms of the trade-off between the linearity and intrinsic optical-power loss.