Efficient Alignment of Optical Fibers and Edge Couplers based on FP Cavity

【Objective】Silicon photonic chips can achieve low-loss coupling with optical fibers through the on-chip silicon-based edge couplers (here in after referred to as edge couplers) integrated on the chips. In the packaging process of commercial silicon photonic chips, the demand for large-scale alignment of optical fibers and silicon photonic chips has raised higher requirements for the alignment efficiency of optical fibers and edge couplers. The research purpose of this paper is to optimize the alignment process between optical fibers and edge couplers based on the Fabry-Perot (FP) cavity formed between the optical fiber facet and the edge coupler facet. After measuring the distance between the optical fiber and the edge coupler in the axial direction of the fiber (represented as the x- axis in this article), high-precision alignment of the optical fiber and the edge coupler can be achieved by a single adjustment of the fiber position in this direction.【Methods】This paper studied the FP cavity structure formed between the optical fiber facet and the edge coupler facet. It also established the physical model between the reflection / transmission spectrum of the FP cavity and the distance between the facets. The optical fiber alignment platform is constructed to experimentally measure the distance between the facets through the FP cavity. Based on the distance measurement results, a single position adjustment of the optical fiber is realized along the axial direction of the optical fiber to achieve the alignment with the edge coupler.【Results】The deviation between the FP cavity length obtained in the experiment and the FP cavity length simulated by the ideal FP cavity model is less than 1 μm. The measured displacement of the optical fiber is within the error range (± 1 μm) of the actual displacement. After adjusting the position of the optical fiber based on the distance measurement results, the optical coupling loss is 3.52 dB between the optical fiber and the edge coupler at the output port, and the error with the reference value (3.30 dB) is only 0.22 dB.【Conclusion】The work verifies the feasibility of achieving efficient alignment between optical fibers and edge couplers based on FP cavity. Through the FP cavity, the measurement accuracy of the distance between the optical fiber and the edge coupler is at the sub-micrometer level and the measurement accuracy of the optical fiber displacement is also at the sub-micrometer level. The experiments demonstrate that the high-precision alignment between the optical fiber and the edge coupler could be realized with only a single adjustment of fiber position according the measurement results obtained by the FP cavity.