Networks - Wavelength Multiplexing (WDM)

Combine multiple signals for transmission along fibre optics

Multiplexing, or “muxing”, is a technique used to launch multiple wavelengths into a single optical fibre. Multiple wavelengths travelling through a single fibre can also be demultiplexed, or “demuxed”, into individual fibres.

Wavelength division multiplexing (WDM) is a technology that allows multiple wavelengths to propagate along the same length of optical fibre. As independent wavelength channels can be used to transmit data, the network capacity is increased compared to using one fibre per wavelength.

Fused biconical taper (FBT) couplers are joined fibres that allow multiple inputs to be combined into a single output. When operated in a reversed configuration, this technology is typically referred to as a fibre splitter.

There are several technologies for wavelength division multiplexing including

  • Fused Biconical Taper (FBT) couplers
  • Thin Film Filters (TFF)
  • Arrayed Waveguide Gratings (AWG)

Thin film filters (TFFs) are dichroic optics that reflect and transmit specific wavelengths due to thin-film interference inside the filter material. Multiple filters may be combined and coupled with optical fibres in order to perform wavelength division multiplexing.

Coarse Wavelength Division Multiplexing (CWDM)

CWDM typically supports up to 16 wavelengths with 20 nm spacing in the 1270-1610 nm region. CWDM can also refer to less complex systems, such as a 1310/1550 nm mux.

Uncooled laser diodes may be employed for CWDM as the wide channel spacing allows for some wavelength variation due to temperature fluctuations.

An Arrayed Waveguide Grating (AWG) is a complex WDM technology that has the capacity to support more wavelength channels than TFF and FBT technologies.

Dense Wavelength Division Multiplexing (DWDM)

DWDM supports around 160 wavelengths with approximately 0.2 nm spacing between each wavelength. DWDM typically operates in a much smaller portion of the spectrum in the C-band (1525 – 1565 nm) where attenuation in standard optical fibre is at a minimum.

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