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Bidirectional or BiDi Transcievers Explained

Fiber optics are great for achieving extremely fast networks. They’re also essential for very long networking connections that extend multiple kilometers in total distance. If the latter is important for your operation, then SFP is likely the fiber optic connection that you will need.

Traditionally, SFP is a single-mode fiber, meaning that signals can only travel in one direction at a time. While the systems can still efficiently communicate, the ability to send signals in both directions would speed up communications and improve efficiency.

Well, there is a technology that allows SFP hardware to send and receive data along the same fiber. It’s called BiDi, and it’s worth considering as a means to improve your fiber infrastructure.

What Is BiDi?

Bidirectional (BiDi) transceivers are SFP transceivers that are able to send and receive data on the same fiber. Without BiDi, data can only travel in one direction on a single fiber, meaning each transceiver is only uploading or downloading. BiDi allows for more efficient networking and cabling by allowing a diplex signal over single fibers.

In order to make this work, bidirectional transceivers have to work on two different wavelengths. Communication in each direction will be on a separate wavelength, allowing the transceivers to easily decode which signals are meant for which communication streams.

As an example, a BiDi transceiver could send information in one direction on a 1310 nm signal and receive information from the other direction on a 1490 nm signal.

In order for a single transceiver to accomplish this, it will need a diplexer (to analyze and disentangle the signals) and two modules (one for each wavelength).

What Does It Mean for Network Design?

If you want to take advantage of Bidi SFP networking, there are a few things to note.

First, the technology is formally known as wavelength division multiplexing (WDM), and it is standardized according to the SFP multi-source agreement (MSA). This standardization allows you to source equipment with certainty of compatibility and functionality. Just look for MSA compliance, and you know your hardware is up for the job.

The second thing to note is that bidirectional SFP shares the same pros and cons as unidirectional SFP. That is, the fiber is great for long distances and medium speeds, but it is not ideal for the very fastest of speeds.

To put that in context, a BiDi network can support up to 10G speeds at distances of 80 km. Or, it can support 25G speeds at distances up to 10 km. QSFP+ setups can get speeds up to 40G, but only at distances of around 150 meters.

Considering these pros and cons, BiDi is ideal for saving cabling and making communications more efficient when you need very long cable runs at medium speeds. This includes applications like closed circuit TV, metropolitan area networks, and 5G deployment.

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