Hybrid Silicon Photonic-Lithium Niobate Electro-Optic Mach-Zehnder Modulator Beyond 100 GHz Bandwidth

Abstract

Electro-optic modulation, the imprinting of a radio-frequency (RF) waveform on an optical carrier, is one of the most important photonics functions, being crucial for high-bandwidth signal generation, optical switching, waveform shaping, data communications, ultrafast measurements, sampling, timing and ranging, and RF photonics. Although silicon (Si) photonic electro-optic modulators (EOMs) can be fabricated using wafer-scale technology compatible with the semiconductor industry, such devices do not exceed an electrical 3-dB bandwidth of about 50 GHz, whereas many applications require higher RF frequencies. Bulk Lithium Niobate (LN) and etched LN modulators can scale to higher bandwidths, but are not integrated with the Si photonics fabrication process adopted widely over the last decade. As an alternative, an ultra-high-bandwidth Mach-Zehnder EOM based on Si photonics is shown, made using conventional lithography and wafer-scale fabrication, bonded to an unpatterned LN thin film. This hybrid LN-Si MZM achieves beyond 100 GHz 3-dB electrical bandwidth. Our design integrates silicon photonics light input/output and optical components, including directional couplers, low-radius bends, and path-length difference segments, realized in a foundry Si photonics process. The use of a simple low-temperature (200C) back-end integration process to bond a postage-stamp-sized piece of LN where desired, and achieving light routing into and out of LN to harness its electro-optic property without any etching or patterning of the LN film, may be broadly-useful strategies for advanced integrated opto-electronic microchips.