Precise Fiber Optic Alignment on Multi-Layer Ceramic Modules for radio-frequency over fiber (RFoF) Integration

Abstract

Low-temperature co-fired ceramics (LTCC) technology is recognized as a robust and space-approved method that facilitates three-dimensional microwave designs. Currently, we are advancing further by integrating this technology with optical fiber technology to develop multifunctional, multipurpose hybrid assemblies. In these systems, achieving precise fiber alignment is critical. The inclusion of additional components for fiber alignment, however, complicates and increases the bulkiness of the system. Given the compactness benefits of ceramic multi-layer technology, it is beneficial to employ this technology for the passive alignment of optical fibers directly above the optical source. In this research paper, we discuss the use of passive fiber alignment techniques, specifically the flip-chip mounting of a vertical cavity surface emitting laser (VCSEL) onto a ceramic substrate. We evaluate the performance of the created optical link, focusing on metrics crucial for radio-over-fiber (RFoF) applications, such as link gain, noise figure, and spurious-free dynamic range. The performance outcomes are then compared with those of a configuration where the VCSEL was wire-bonded to the circuit. This comparison helps to highlight the advantages and potential limitations of employing LTCC technology for integrating optical components in RFoF systems.