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.
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.
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.
| 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. | 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. |
| Cost-effective Solution Fewer components & less engineering time. The high-channel capacity feature will save the expenses substantially. | 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. |
| Active DWDM Advantages | Active DWDM Disadvantages |
| Increased in Capacity With 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. | Expensive in Costs The overall active DWDM setup fees are much more expensive compared to passive DWDM solutions. |
| 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. | 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. |
| Easier for Scalability Normally, active DWDM can be easier to scale as the network grows. |
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.
