Fiber optic splitters divide a single optical signal into multiple outputs, while couplers can both split and combine optical signals, with various types and customizable splitting ratios.

Overview

Fiber optic splitters are passive devices that divide an optical signal into multiple parts, commonly used in FTTx/PON networks, cable TV, ATM circuits, and local/metropolitan area networks. They typically have at least 2 ports and can scale up to 128 ports, with fixed splitting ratios such as 1x2, 1x4, 1x8, 1x16, or higher . Fiber optic couplers, on the other hand, can split one input into multiple outputs or combine multiple inputs into a single output. They are widely used in bidirectional links, LANs, WDM systems, and optical amplifiers for signal routing, monitoring, and injection . Couplers are characterized by an N x M configuration, where N is the number of input fibers and M is the number of output fibers, often in multiples of two (e.g., 1x2, 2x2, 1x4) .

Types and Fabrication Methods

1. Fused Biconical Taper (FBT) Splitters/Couplers: Made by twisting and fusing fibers together, offering low cost and competitive performance. They are suitable for small port counts and standard splitting ratios .
2. Planar Lightwave Circuit (PLC) Splitters: Fabricated using photolithography and etching, ideal for high-density applications with many outputs. PLC splitters provide compact size, broad bandwidth, and fixed or custom splitting ratios, though they have slightly higher insertion loss .
3. Fusion Couplers: Created by melting twisted fibers, offering very low insertion loss (~0.3 dB) and high power handling, but with limited wavelength bandwidth and polarization extinction ratio .
4. Micro-Optic Couplers: Use lensed fiber collimators and optical elements to achieve ultra-broad bandwidth, high polarization extinction, and excellent thermal stability, suitable for advanced optical systems .

Splitting Ratios and Customization

Splitters and couplers can have fixed or variable splitting ratios, such as 50/50, 40/60, 30/70, 10/90, or even highly asymmetric ratios like 1/99. Custom ratios are achievable depending on the fabrication method and application requirements .

Applications

• Splitters: Primarily for distributing signals evenly to multiple users or lines, e.g., in FTTx/PON networks, cable TV, and antenna systems .
• Couplers: Used for signal monitoring, injection, extraction, and combining in optical communication systems, test setups, and WDM networks .

Operating Principles

Most fiber couplers operate via evanescent wave coupling, where two fiber cores are brought close together so that light transfers between them over a short coupling region. This principle allows precise control of splitting ratios and minimal insertion loss . In summary, splitters are optimized for signal distribution with fixed ratios, while couplers offer more flexibility, including combining signals, and both are essential components in modern optical networks and laboratory setups.