The most commonly used optical couplers include fused biconic taper (FBT) couplers, planar lightwave circuit (PLC) couplers, Y/T splitters, combiners, and wavelength division multiplexing (WDM) couplers.

Fused Biconic Taper (FBT) Couplers

FBT couplers are made by fusing two or more optical fibers together and tapering the fused region to create a coupling area. They allow light to transfer between fibers using evanescent field coupling. FBT couplers are widely used in Passive Optical Networks (PONs) and Wavelength Division Multiplexing (WDM) systems due to their simplicity and cost-effectiveness .

Planar Lightwave Circuit (PLC) Couplers

PLC couplers are fabricated on a flat substrate using lithography and etching techniques. They provide high stability and can handle multiple wavelengths, making them suitable for large-scale optical networks, optical amplifiers, and switches. PLC couplers are ideal for applications requiring precise splitting or combining of signals with minimal loss .

Y and T Couplers

These are basic splitter types where a single input is divided into two outputs. Y-couplers distribute power equally, while T-couplers provide uneven power distribution. They are commonly used in simple fiber optic networks and monitoring applications .

Combiners and X-Couplers

Combiners merge two or more optical signals into a single output, often handling multiple wavelengths simultaneously. X-couplers and other multi-port configurations, such as N×M couplers, allow flexible network designs and are used in complex optical systems .

Wavelength Division Multiplexing (WDM) Couplers

WDM couplers combine or split optical signals of different wavelengths, enabling multiple channels to share the same fiber. They are essential in high-capacity telecommunication networks and optical transport systems .

Additional Types

• Tapered couplers: Use a tapered structure to couple signals between fibers or devices.
• Micro-optic couplers: Employ lenses or mirrors for precise signal coupling.
• Star and tree couplers: Multi-port devices used for distributing signals in cable-TV or large optical networks .

Key Considerations

When selecting an optical coupler, factors such as insertion loss, return loss, polarization-dependent loss (PDL), number of ports, and wavelength compatibility are critical. Couplers can be designed for single-mode or multimode fibers and for single, dual, or wideband wavelength windows, depending on the application .