Silicon–Lithium Niobate Hybrid Intensity and Coherent Modulators Using a Periodic Capacitively Loaded Traveling-Wave Electrode

Abstract

High-performance silicon and thin-film lithium niobate hybrid electro-optic modulators are demonstrated. In order to break the voltage–bandwidth limit in a normal traveling-wave modulator, a periodic capacitively loaded traveling-wave electrode is employed in this hybrid platform. The silicon substrate is undercut-etched to achieve index matching of the optical wave and microwave. A hybrid waveguide with a lithium niobate thin film bonded on a silicon wire is employed. Lithium niobate etching is not required for making the hybrid optical waveguides. We realize an intensity modulator of 12.5 mm long modulation section, which exhibits a low half-wave voltage of 1.7 V and a large 3 dB modulation bandwidth of >70 GHz. Data transmissions with various modulation formats beyond 100 Gbit/s are successfully achieved with dynamic extinction ratios of >8 dB. Combining the advantages of the silicon and thin-film lithium niobate platforms, a compact dual polarization coherent modulator is also experimentally demonstrated, on which 96 Gbaud 16-level quadrature amplitude modulation signals in both polarizations are successfully transmitted.

Thin‐Film Lithium Niobate Optical Modulators with an Extrapolated Bandwidth of 170 GHz

“…Certain efforts have been made to minimize the RF loss by increasing the spacing between the electrodes at the cost of larger V π , [11] or by designing segmented electrodes, which makes the velocity matching more challenging. [17,23] Here, instead of positioning the optical waveguides at the center of the gap between the signal and ground electrodes, they are shifted closer to the signal electrode, whose vicinity has a stronger electric field profile. The parameter D (see Figure 1a) denotes the distance between the center of the optical waveguide and the center of the gap between the electrodes.…”

“…Certain efforts have been made to minimize the RF loss by increasing the spacing between the electrodes at the cost of larger V π , [ 11 ] or by designing segmented electrodes, which makes the velocity matching more challenging. [ 17,23 ]…”

“…[21] Various TFLN modulators on silicon substrate have been reported to expand the 3 dB bandwidth of a single modulator up to 100 GHz and higher. [11,12,22,23] One method is to use a large gap between the electrodes, which leads to a bandwidth of more than 100 GHz, but with a V π > 13 V, [11] due to the weak overlap between the electric and optical fields inside the gap. Another approach is to utilize asymmetric arms in a Mach-Zehnder modulator (MZM) and to operate at a null point of the transfer function.…”

110 GHz, 110 mW hybrid silicon-lithium niobate Mach-Zehnder modulator

“…These periodic features increase the effective index of the microwave mode and slow the RF traveling wave to match the optical wave [41][42][43][44][45] . Capacitively-loaded (T-rail based) SWE structures have been demonstrated in other reports 45,46 to achieve RF-optical velocity matching when using lower index substrates such as quartz or selectivelyremoved Si. In this case, the hybrid Si/LN group index is simulated to be 2.32 and the slow-wave RF index is 2.34 at 110 GHz, resulting in ∆n < 1% between the optical and RF waves before the nonlinear change of the index is taken into account.…”

High-Speed Optical Fiber Communication in China

“…The electro-optical modulator is the core device of a DCI system. Chinese scientists have conducted research in this area for many years, especially in thin-film LiNbO3, which has made great progress. − We will summarize the progress on this topic. Cost is a core consideration in a DCI system.…”