Planar lightwave circuits for PON applications

Many components used in passive optical networks (PONs) can be fabricated on a planar lightwave circuit (PLC). These include 1×N splitters, 2×N splitters and video overlay filters. A broadband 2×2 splitter is a critical component for PON. A directional coupler and even a single stage Mach-Zehnder is unsuitable for this application because each provides a splitting ratio that has excessive wavelength dependence. We demonstrate a PLC-based, broadband 2×2 splitter constructed from a two-stage lattice filter that has low loss and high uniformity from 1260 nm to 1625 nm. Y-branch splitters can be cascaded to make 1×N splitters or integrated with a 2×2 splitter to make 2×N splitters. We compare insertion loss and uniformity for splitters that are fabricated with silica on silicon technology versus silica on quartz technology. By using silica on quartz technology, we demonstrate low-loss 1×32 splitters. The 2×32 splitter has increased functionality with negligible loss penalty. We demonstrate that PLC-based splitters satisfy all reliability requirements. A video overlay filter can be used for video overlay onto a bidirectional, digital, fiber optic communication system. The video overlay uses 1550 nm light, while the digital communication system either uses 1310 nm light in both directions or uses 1310 nm light for one direction and 1490 nm light in the other direction. With PLC technology, the filter is based on integrated Mach-Zehnders. We also demonstrate a video overlay filter designed for digital channels using both 1310 nm light and 1490 nm light.