A Complete Guide to Optical Transceiver Nomenclature

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When entering the world of optical transceivers, one quickly runs into an intimidating selection of alphanumeric soups that are confusing to the uninitiated. For example, take a look at this optical transceiver product page from FiberMall.

In this post, we will go through what each of these terms mean in a step-by-step fashion. At the end of this article, you’ll be reading optical transceiver product pages like a seasoned industry professional.

The naming standards you see in this product page originates from the IEEE Ethernet Working Group that defines the electrical and optical specifications at the PHY layer via the IEEE 802.3 standard. The 802.3 is not a single standard, but a whole family with various amendments along the way. At the PHY level, their main purpose is to define the electrical and optical characteristics used in signal transmission - things like optical power, link budgets, acceptable bit error rates, and signal encoding. For instance, the upcoming 802.3dj scheduled for release in spring 2026 defines 200 Gbps, 400 Gbps, 800 Gbps and 1.6 Tbps aggregate bandwidths using 200 Gbps lanes, and is also popularly known as Ultra Ethernet.

The way an optical interconnect is defined most often follows the format below (give or take, because there is no rigid way this is defined in the industry):

[Connector-Form-factor]-[Baseband-Speed]-[Reach][Number of Lanes]-[Modulation]-[Multiplexing]-[FiberMode]-[Other Info]

Let’s break down the product name in the example above: QSFP-DD-400G-FR4 PAM4 CWDM4 2km LC SMF FEC, according to the template shown above and dive into every aspect of it.

1) Small Form-Factor Pluggable (SFP)

The first part of the product name corresponds to the form factor of the pluggable connector that houses the optical transceiver. In the example above, QSFP stands for Quad Small Form-Factor Pluggable connector and it looks like the picture below.

The “quad” comes from the