In this paper, we focus on the design, simulation, fabrication, and characterization of a high-bandwidth silicon-based electro-optic modulator for integration in next generation high-speed optical interconnects and coherent communication systems. As data-intensive applications such as cloud computing, artificial intelligence, and high-performance computing rapidly evolve, the demand for photonic components that support ultra-high-speed data transmission with low latency and high energy efficiency continues to grow. Among these components, electro-optic modulators play a critical role in optical transmitters, directly influencing overall system performance. However, achieving high bandwidth and low optical loss simultaneously within a complementary metal oxide semiconductor (CMOS)-compatible platform remains a significant challenge.

To address these competing design considerations, we propose a single-ended push-pull Mach-Zehnder modulator (MZM) based on a carrier-depletion modulation mechanism implemented on a silicon-on-insulator (SOI) platform. The design focuses on achieving a balanced trade-off between electro-optic bandwidth and insertion loss, both of which are essential for the performance of coherent optical transmitters.

Through rigorous numerical simulations and parametric optimization, we investigate the influence of key structural parameters, including waveguide geometry, PN junction positioning, electrode configuration, and traveling-wave architecture. The final optimized device exhibits a 3 dB electro-optic bandwidth of 25 GHz with an active modulation length of 2.5 mm (Fig. 7). The insertion loss remains between 6 dB and 7 dB, reflecting a well-considered balance between modulation efficiency and propagation attenuation. The device structure is further optimized to minimize overlap between the optical mode and highly doped regions, thus reducing free-carrier absorption while maintaining efficient phase modulation. To validate the simulated results, the modulator is fabricated on a commercial silicon photonics platform and subjected to detailed post-fabrication characterization. Frequency response measurements confirm a measured electro-optic 3 dB bandwidth exceeding 20 GHz (Fig. 10), supporting data rates of up to 40 Gbit/s per polarization (Fig. 11). The packaged device is then integrated into a coherent transmitter testbed for system-level evaluation. Eye diagram and constellation analysis under quadrature phase-shift keying (QPSK) signaling demonstrate clear and symmetric eye openings, with error-free performance observed across a data rate range of 10?50 Gbit/s during simultaneous in phase (I) and in quadrature (Q) channel transmission (Fig. 13). These results verify the modulator’s strong bandwidth adaptability and its ability to sustain low optical loss under high-speed operation.

The proposed silicon-based single-ended push-pull MZM demonstrates a well-optimized trade-off between electro-optic bandwidth and optical insertion loss, two of the most critical performance metrics for coherent optical communication systems. The device successfully achieves a measured 3 dB bandwidth exceeding 20 GHz while maintaining an insertion loss in the range of 6?7 dB, fulfilling the core requirements for 100 Gbit/s dual-polarization quadrature phase-shift keying (DP-QPSK) coherent transmitters. These performance attributes validate the effectiveness of the design methodology and confirm the suitability of the device for deployment in high-speed, low-loss photonic integrated circuits. Moreover, the compact single-ended push-pull architecture is inherently favorable for integration with CMOS-compatible driver circuits, enabling scalable and cost-effective packaging strategies. The systematic optimization of waveguide structure, doping profile, and electrode configuration described in this paper provides a robust design framework that can be extended to future modulator designs targeting higher-order modulation formats, such as 16 quadrature amplitude modulation (16-QAM) and beyond. Overall, we offer valuable insights and practical guidance for advancing high-performance modulators in next-generation silicon photonics platforms.