Reduced Complexity, Low-Power Linear Modulator for DAC-Based Multilevel Coherent Transmitters

We present a simpler, power efficient, and cost-effective linear optical field modulator (LOFM) for digita-lto-analog-based multilevel coherent transmitter. The new design has four advantages compared with the existing LOFM. First, it only uses one Mach-Zehnder modulator (with very short and broadband non-traveling waveguide phase modulators), which is configured for double-pass modulation to linearize the optical field response. Second, it has excellent linearity performance with a superior normalized deviation value of 0.8% when the power split ratio r of the asymmetric coupler is set to 0.113. Third, it has inherent compensation functionality that mitigates the increased distortion when parameter r is not optimized due to fabrication error. Finally, it reduces the radio frequency power consumption by one-half. Operational restrictions of the new device compared with current LOFM are also briefly noted.