Compact electro-optical modulators are demonstrated on thin films of lithium niobate on silicon operating up to 50 GHz. The half-wave voltage length product of the high-performance devices is 3.1 V.cm at DC and less than 6.5 V.cm up to 50 GHz. The 3 dB electrical bandwidth is 33 GHz, with an 18 dB extinction ratio. The third-order intermodulation distortion spurious free dynamic range is 97.3 dBHz2/3 at 1 GHz and 92.6 dBHz2/3 at 10 GHz. The performance demonstrated by the thin-film modulators is on par with conventional lithium niobate modulators but with lower drive voltages, smaller device footprints, and potential compatibility for integration with large-scale silicon photonics.
Second-order optical nonlinear effects (second-harmonic and sum-frequency generation) are demonstrated in the telecommunication band by periodic poling of thin films of lithium niobate wafer-bonded on silicon substrates and rib-loaded with silicon nitride channels to attain ridge waveguide with cross-sections of ~ 2 µm 2 . The compactness of the waveguides results in efficient second-order nonlinear devices. A nonlinear conversion of 8% is obtained with a pulsed input in 4 mm long waveguides. The choice of silicon substrate makes the platform potentially compatible with silicon photonics, and therefore may pave the path towards on-chip nonlinear and quantum-optic applications.
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The excellent optical and unique material properties of lithium niobate have long established it as a prevailing photonic material, especially for the long‐haul telecom modulator and wavelength‐converter applications. However, conventional lithium niobate optical waveguides are bulky, hence large‐scale photonic circuit implementations are impeded and high power requirements are imposed. To address these shortcomings, thin‐film lithium niobate technology has been a topic of intense research in the last few years and a plethora of ultracompact devices with significantly superior performances than the conventional counterparts have been demonstrated. These efforts have rejuvenated lithium niobate for novel electro‐, nonlinear‐, and quantum‐optic applications. Herein, the most recent advancements of this booming field are summarized and a perspective for future directions is given.
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