Thin-Film Filter-Based SWDM Multiplexer/Demultiplexer via Gouy phase Control

The demand for compact, high-bandwidth optical interconnects in modern military and commercial avionics is rapidly increasing, driven by modular open system architectures (MOSA), sensor fusion, and data-intensive payloads. While wavelength division multiplexing (WDM) is well established in single-mode fiber systems, shortwave WDM (SWDM) for multimode fiber (MMF) remains underdevelopedóparticularly in ruggedized formats suitable for airborne deployment. Existing SWDM solutions are designed for data centers and lack the size, thermal stability, and mechanical robustness required in aircraft environments.ÝThis project proposes the design and feasibility demonstration of a micro-optic 4-channel SWDM multiplexer/demultiplexer (mux/demux) compatible with OM3/OM4/OM5 multimode fiber and VCSEL sources operating in the 850ñ950 nm range. It turns out thin-film filter-based single-mode WDM mux/demux can be configured to form multi-mode SWDM mux/demux, as long as the Gouy phase associated with different spatial modes are equalized when the multi-mode signal traverses the thin-film filters. This can be accomplished by ensuring the Rayleigh range of the input beam is sufficiently large in comparison to the distances between the thin-film filtersÝThe device will target a compact form factor (?1 cm≥), low insertion loss (<1 dB), and high channel isolation (>20 dB for mux, >40 dB for demux), while operating reliably over a -40∞C to +95∞C temperature range. It will support integration with transmitter and receiver optical subassemblies (TOSAs/ROSAs), as well as launch-conditioning interfaces for fiber optic test equipment.ÝIn Phase I, we will develop the optical and mechanical design, simulate thermal and modal performance, and validate feasibility through modeling and experimental demonstrations. This technology will enable dense, high-speed, and rugged optical links across next-generation aircraft systems without replacing existing MMF infrastructureóoffering substantial advantages in bandwidth scalability, packaging, and lifecycle cost.