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Multiplexers are also known as MUX or “Passive Mux”.  The MUX is a filter designed to combine multiple communication channels over one physical medium.  On one end of the fiber line the communication channels are “Muxed” together, then they are transmitted over the dark fiber and “De-muxed” at the other end.

This technology is used by both service providers and end users wanting to increase the capacity of leased dark fiber lines at significantly lower costs than using traditional “active” equipment installations.

Solid-Optics offers world class solutions for the design and implementation of dark fiber applications with passive multiplexing and optical transceiver technology.

What do Solid Optics’ multiplexers deliver?

  • Increased capacity through leased dark fiber by up to 800%
    • Typical 60% savings over active equipment installations
    • Increased revenue from existing leased lines
    • Reduced risk of costly service downtime
    • Low cost of redundancy implementation & maintainence
    • Zero software, zero configuration, zero updates


There are two different techniques used for multiplexing which have different grids or channel spacing. The first technique is CWDM, where the C stands for Coarse.  CWDM ranges from 1270nm to 1610nm with 20nm steps, with a max of 18 channels.  Solid Optics offers an 8 channel model and an 18 channel model.  The second technique is DWDM where the D stands for Dense.  The DWDM grid has a typical spacing of 0.8nm and is centered around 1550nm, with a max of 96 channels.  Solid Optics offers DWDM MUXs ranging from 8, 16, 40 and 96 channels.

Both the CWDM & DWDM techniques have distinct advantages and disadvantages.  The Solid Optics team are experts in designing dark fiber networks and can advise you on which technique will best fit your project.


The multiplexer does not use any power and has no software or firmware;  it’s a passive device which only “filters” the specific light emitted by the pluggable optic.  So in the case of CWDM, there are 18 different wavelengths of optics which have a specific color.  In the case of DWDM, there are about 48 channels which are commonly used in the industry.   We also offer DWDM ‘tunable’ optics, which can be programmed/tuned to send a specific light color as needed and are useful to have for spares.

For CWDM the nanometer or “color” of the light is commonly used in the naming.  There are two naming conventions – the official naming is 1611nm/1591nm/1571nm/1551nm, etc.  Many of the Switch/Router manufacturers such as Cisco use 1610nm/1590nm/1570nm/1550nm.  Technically there is no difference and you can easily use a 1610 optic in the 1611 port on a mux as each CWDM band is 15nm wide with the 1611nm as the center. For DWDM, different naming conventions are used – the most common being the Channels of the C-Band 100Ghz Grid.  Some vendors use Ghz and some prefer using nanometers.  For example, 1550.12nm is the equivalent to ‘Channel 34.’

The communication signals can have speeds ranging from 1G, 10G, 40G and 100G.  Since the introduction of this technology, 1G and 10G have been the most commonly used speeds and 40G and 100G are the newest speeds.  Since a multiplexer is simply filtering light, you can mix different speeds on the same multiplexer.

It is important to note that every multiplexer blocks a small percentage of the signal which comes through it.  This is know as the’ insertion loss’ (IL), which is calculated in dBs per channel and increases with the number of channels.  A MUX of good quality will cause less attenuation than a MUX of poor quality.  As an example, the typical loss of an 8 port mux is around 2dB.  For projects using the maximum power budget, Solid Optics offers ultra-low loss muxes.

Another important quality aspect of a mux is the ‘Channel Isolation’ which is the blocking of light between the channels, which should be at least 30dB.  At any lower value, light from neighboring channels can interfere with one another. Solid Optics has over a decade of experience in CWDM & DWDM dark fiber project design.  Please contact us with your details so we can help guide you to the best solution for your needs.

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