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Optical communication networks – long-haul and short-reach as well as classical and quantum-based networks of the future – require modulators that actively alter the phase, amplitude, wavelength, and polarization of light. For decades, lithium niobate electro-optic (EO) modulators have met the requirements for EO modulation in long-haul networks. However, as optical links continue to present ever-greater advantages at shorter length scales, other more compact and integrable material platforms have been investigated, including silicon, indium phosphide, and, most recently, two-dimensional materials. Although much progress has been made on Si and InP and there is much promise for 2D materials, no technology to date has been shown with the concomitant properties of high EO bandwidth, wide optical range, low voltage, and compact size. To address this need, we have taken the approach of developing thin film BaTiO3 as an optoelectronic platform for high frequency, low voltage, and compact modulators. Epitaxial BaTiO3 films are a silicon-compatible optoelectronic material with among the highest known EO coefficient, more than 10 times larger than that of LiNbO3. Using BaTiO3 thin films with 1 mm long interaction length, we have previously demonstrated intensity modulators with voltage-length products nearly an order of magnitude smaller than that of silicon. We have also shown the potential for high frequency operation by demonstrating modulation out to 50 GHz and 28 GHz 3 dB EO bandwidth. Here we demonstrate the high-frequency and low-voltage phase modulation of light using epitaxial thin film BaTiO3. Clear EO phase modulation of 1550 nm light is measured out to 50 GHz using an optical spectral analysis method. We also show that, by incorporating low dimensional, photonic crystal (PC) waveguides to enhance the EO coefficient, the operating voltage can be significantly reduced.
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