Heterogeneous integration of LN and Si3N4 waveguides using an optical interlayer coupler

Abstract

Abstract Integrated optical gyros (IOG) draw attention due to the remarkable promise of miniaturization, mass-manufacturability and high reliability. However, the wafer-scale integration of these devices is not available. A heterogeneous platform of lithium niobate (LN) and silicon nitride (Si3N4) waveguide is proposed in this study to enable the integration of phase modulator and resonator firstly, with large polarization intensity extinction ratio and low loss. The optical interlayer coupling between LN and Si3N4 waveguide is realized using Si3N4 bilevel taper above the lithium niobate on insulator (LNOI) substrate. The relationship between polarization intensity extinction ratio and lithium niobate thin film (LNTF) thickness of LN waveguide is developed based on polarization model. The optimal polarization intensity extinction ratio is achieved when the thickness of LNTF is 0. 2 μ m . At the start of the interlayer coupler, the Si3N4 strip with width=0. 9 μ m and thickness=0. 1 μ m is designed to maximize the fraction of optical power in the LNTF layer. The polarization intensity extinction ratio of the LN waveguide is 85.6 dB/mm. At the end of the coupler, the optical power in the Si3N4 strip with width of 0. 9 μ m and thickness of 0. 9 μ m reaches its maximum. Along the direction of light propagation from LN to Si3N4 waveguide, the optical interlayer coupler with length= 110 μ m is designed to achieve optical coupling between LN and Si3N4 waveguide while maintaining its state of polarization all the way from the feeder waveguides. The coupling efficiency of the optimized interlayer coupler has been improved to about 99 %.