High performance thin-film lithium niobate modulator on silicon substrate with a thick silica buffer layer

The integration of thin-film lithium niobate (TFLN) modulators into optical communication systems has garnered significant attention due to their potential for enabling high-speed and energy-efficient optical modulation. As the demand for higher data transmission rates continues to grow, there is an urgent need to enhance the bandwidth and performance of TFLN modulators to meet the requirements of next-generation communication networks. Recent advancements have demonstrated that capacitively loaded traveling wave electrodes (CL-TWEs) on quartz and silicon-removed substrates can significantly improve the bandwidth of TFLN modulators. However, these approaches are hindered by fabrication complexities and immaturity compared to well-established silicon-based TFLN wafers, limiting their practical adoption in commercial systems. In this work, we propose a solution to these challenges by developing a high-performance in-phase/quadrature (IQ) modulator fabricated on a TFLN wafer with a 15-µm-thick silica buried layer. The thick buffer layer plays a critical role in achieving velocity matching between the CL-TWEs and the optical wave on a silicon substrate, thereby optimizing the TFLN modulator's performance. Experimental results demonstrate that the proposed modulator achieves an electro-optic (EO) bandwidth exceeding 67 GHz, a remarkably low fiber-to-fiber loss of only 4 dB, and an extinction ratio greater than 30 dB. These performance metrics highlight the modulator's capability to support high-speed and high-order modulation formats, which are essential for modern optical communication systems.