Monolithic silicon nitride electro-optic modulator enabled by optically-assisted poling

Electro-optic (EO) modulation is a key functionality to have on-chip. However, achieving a notable linear EO effect in stoichiometric silicon nitride has been a persistent challenge due to the material's intrinsic properties. Recent advancements revealed that the displacement of thermally excited charge carriers under a high electric field induces a second-order nonlinearity in silicon nitride, thus enabling the linear EO effect in this platform regardless of the material's inversion symmetry. In this work, we introduce optically-assisted poling of a silicon nitride microring resonator, removing the need for high-temperature processing of the device. The optical stimulation of charges avoids the technical constraints due to elevated temperature. By optimizing the poling process, we experimentally obtain a long-term effective second-order nonlinearity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mi>χ</mml:mi></mml:mrow> <mml:mrow><mml:mi>eff</mml:mi></mml:mrow> <mml:mrow><mml:mrow><mml:mo>(</mml:mo> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> <mml:mo>)</mml:mo></mml:mrow> </mml:mrow> </mml:msubsup> </mml:math> of 1.218 pm/V. Additionally, we measure the high-speed EO response of the modulator, showing a bandwidth of 4 GHz, only limited by the quality factor of the microring resonator. This work goes towards the implementation of monolithic, compact silicon nitride EO modulators, a necessary component for high-density integrated optical signal processing.