Internal Structure of the Second-Level Optical Splitter

A second-level optical splitter typically uses a cascaded PLC or Y-branch waveguide structure to divide an optical signal into multiple outputs with uniform or controlled power distribution.

Overview of Second-Level Splitters

In PON networks, a second-level optical splitter is part of a cascaded splitting architecture, where the first-level splitter divides the signal into a few branches, and the second-level splitter further divides each branch to reach the final number of subscribers, such as 1:32 or 1:64 total splits . This approach reduces fiber usage and allows flexible network design.

Internal Components

1. Planar Lightwave Circuit (PLC) Chip: Most second-level splitters in modern FTTH networks use PLC technology, which consists of a silica-on-silicon waveguide array etched onto a planar substrate . The optical signal enters the PLC chip and is guided through a network of waveguides that split the light into multiple paths. The splitting occurs entirely within the waveguide structure, ensuring wavelength-independent and polarization-insensitive performance across the 1260–1650 nm range . 2. Y-Branch Waveguides: Some splitters use Y-branch structures, where the input waveguide bifurcates repeatedly to achieve the desired number of outputs . Each Y-branch divides the optical power approximately equally, with a theoretical loss of −3 dB per 1:2 split. Cascading multiple Y-branches allows higher split ratios while maintaining low insertion loss. 3. Housing and Mechanical Protection: The PLC chip or Y-branch assembly is enclosed in a mini module or cassette housing, which provides mechanical protection but does not affect optical performance . The housing ensures durability in field deployments, including wall-mounted, aerial, or underground enclosures . 4. Input and Output Fibers: The optical fibers are precisely aligned to the waveguide ports using fiber pigtails. Connectors or splices at the outputs may introduce minor additional loss, but the internal splitter structure itself is designed to minimize intrinsic loss .

Optical Behavior

• Power Distribution: The second-level splitter divides the incoming optical power according to the split ratio. In a uniform splitter, each output receives equal power, while non-uniform designs can allocate different power levels to specific outputs .
• Insertion Loss: Each split introduces inherent loss due to power division. For example, a 1:2 split reduces power by ~3 dB, and cascading splits compounds this effect .
• Spectral Response: PLC-based splitters maintain a flat spectral response across the operating wavelength range, ensuring stable performance for all PON services .

Summary

The internal structure of a second-level optical splitter combines a PLC or Y-branch waveguide network with precise fiber alignment and protective housing. It enables efficient, passive division of optical signals in cascaded architectures, supporting high split ratios while maintaining low loss, wavelength independence, and mechanical reliability for FTTH deployments .