Feasibility of a localized mode analysis method in an SOI platform based on carrier grating

Abstract

In order to measure the intensity of modes that are transmitted inside the devices on the silicon-on-insulator (SOI) platform, researchers usually use pre-processed couplers to make the optical modes diffract out of the chip. However, the output couplers have an influence (e.g., attenuation and wavelength selectivity) on the modes of concern. Besides, as the quantity and variety of devices integrated into the SOI platform continue to escalate, the traditional method also shows limits on detecting devices far from the chip edge. So, is it feasible to directly and locally measure one specific mode’s intensity on some waveguide-based devices like the directional coupler, polarization beam splitter, and so on? Interference of two coherent pump beams has the capability to induce a periodic carrier distribution in the material, thus modulating the refractive index, effectively creating a temporary and erasable diffraction grating. In this study, an off-chip, non-destructive, and localized detection method based on carrier grating is proposed. A theoretical model is developed to calculate carrier dynamics under various pump configurations. Leveraging the finite-difference time-domain (FDTD) method and accounting for free carrier index (FCI) and free carrier absorption (FCA) effects, analysis of the quantitative impact of pump intensity and radius on the diffraction efficiency of the carrier grating in the silicon-on-insulator (SOI) platform and its far-field divergence characteristics is provided. Ultimately, this research contributes to a discussion on several commonly used application scenarios and the feasibility of experimental approaches. A spatial resolution of less than 10 µm and a diffraction efficiency of −15dB while simultaneously maintaining a far-field divergence of 7.8° for the SOI platform are proposed at the end of this article.