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Passive DWDM vs. Active DWDM

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Posted on February 22, 2017
September 22, 2020
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DWDM, short for dense wavelength division multiplexing, refers to an optical multiplexing technology used to increase bandwidth over existing fiber networks. DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. It has revolutionized the transmission of information over long distances. Generally speaking, DWDM can be divided into passive DWDM and active DWDM. The differences and selections between passive DWDM vs. active DWDM will be explained in this article.

Passive DWDM vs. Active DWDM, What's the Difference?

Passive DWDM

First and foremost, passive DWDM systems have no active components. The line functions only due to the optical budget of transceivers used. No optical signal amplifiers and dispersion compensation modules (DCM) are used in a passive DWDM system. The sweet spot for the passive DWDM system is that it has a high channel capacity and potential for expansion, but the transmission distance is limited to the optical budget of transceivers used. The passive DWDM system is typically used in metro networks and high-speed communication lines with a high channel capacity.

Passive DWDM Working Principle

Active DWDM

Active DWDM systems commonly can be regarded as a transponder-based system, which helps to transport large amounts of data between sites in a data center interconnect setting. The transponder takes the outputs of the SAN or IP switch format, usually in a short wave 850nm or long wave 1310nm format, and converts them through an optical-electrical-optical (OEO) DWDM conversion. When creating long-haul DWDM networks, several EDFA amplifiers are installed sequentially in the line. The number of amplifiers in one section is limited and depends on the optical cable type, channel count, data transmission rate of each channel, and permissible OSNR value.

Active DWDM Working Principle

The possible length of lines when using an active DWDM system is determined not only with the installed optical amplifiers and the OSNR value but also with the influence of chromatic dispersion—the distortion of transmitted signal impulses, on transmitted signals. At the design stage of the DWDM network project, permissible values of chromatic dispersion for the transceivers should be taken into account, and, if necessary, chromatic dispersion compensation modules are included in the line. DCM introduces additional attenuation into the line, which leads to a reduction of the amplified section length.

Passive DWDM vs. Active DWDM, How to Choose?

The benefits and limitations of passive DWDM and active DWDM are obvious to tell based on the abovementioned inherent natures, which has influences on the selection between passive DWDM and active DWDM.

Pros and Cons of Passive DWDM

Passive DWDM Advantages Passive DWDM Disadvantages
  • Easier Setup
    Not complex at all, just plug and play. Since there is no need to tune wavelengths for all the connections.

  • Cost-effective Solution
    Fewer components & less engineering time. The high-channel capacity feature will save the expenses substantially.

  • Limited Scalability
    The DWDM network is restricted to colored optics and fewer wavelengths on the transport fiber. Thus, more passive components will be adopted when expanding as the network grows. However, the more passive devices, the more difficult to manage.

  • Inconvenient Control
    If you need to change a wavelength or connection, you'll have to take it out of service and disconnect the physical cabling as the wavelength is tied to the optic.

Pros and Cons of Active DWDM

Active DWDM Advantages Active DWDM Disadvantages
  • Increased in CapacityWith Reduced Fibers
    Fitting more wavelengths onto one single fiber pair. The single fiber pair can carry more bandwidth. Fewer physical fibers will be used between two sites accordingly.

  • Flexible in Setups
    The users can dynamically re-tune wavelengths without dropping connections for the transparency nature, which may grant you more control over your optical network.

  • Easier for Scalability
    Normally, active DWDM can be easier to scale as the network grows.

  • Expensive in Costs
    The overall active DWDM setup fees are much more expensive compared to passive DWDM solutions.

  • Complex in Configuration
    There are many more components involved in active builds. Thus, the configuration will be a serious undertaking and require a solid understanding of optical networks.

Passive DWDM vs active DWDM, the selection is normally dependent on several factors: distance requirements; network scalability; initial installation & future management; the expense. If there are no particular requirements for the distances and future network upgrades, passive DWDM that provides user-friendly and cost-effective solutions is suitable for those with a tight budget. If it is required for long-haul applications and convenience when changing and updating in the predictable future, the active DWDM solution may fit for those with high bandwidth demands. Note that IT knowledge for configuration is needed in this kind of situation.

Brief Summary

No matter passive DWDM or active DWDM, choose the one that suits your network best. Knowing their own features can help you better judge which one you need. DWDM mux/demux is a must in both passive DWDM and active DWDM. However, a DWDM networking deployment covers more than just DWDM muxes/demuxes. Common Solutions for A Secured DWDM Network will introduce the typical DWDM transport network solutions for you.