Compact electric field sensors based on indirect bonding of lithium niobate to silicon microrings

An electric field sensor based on the indirect bonding of submicrometer thin films of lithium niobate to silicon microring resonators is presented using benzocyclobutene as an intermediate bonding layer. The hybrid material system combines the electro-optic functionality of lithium niobate with the high-index contrast of silicon waveguides, enabling compact and metal-free electric field sensors. A sensor is designed and fabricated using ion-sliced z-cut lithium niobate as the top cladding of a 20 μm radius silicon microring resonator. The optical quasi transverse magnetic mode is used to access the largest electro-optic coefficient in the lithium niobate. Optical characterization of the hybrid device results in a measured loaded quality factor of 13,000 in the infrared. Operation of the device as an electric field sensor is demonstrated by detecting the fringing fields from a microstrip electrical circuit operating at 1.86 GHz. The demonstrated sensitivity to electric fields is 4.5 V m-1 Hz-1/2.