A Comprehensive Guide to Optical Module Form Factors

As the demand for high-performance computing grows, optical modules are evolving to meet these needs. But why choose different optical modules, and how do they function in various situations? This article will delve into the different form factors to help you understand optical modules and explore their close correlation with the number of SerDes channels.

Progression from Fundamental SFP to Advanced OSFP

Optical module consists of optoelectronic devices, functional circuits and optical interfaces, etc. The optoelectronic devices include the transmitter and receiver parts, whose role is to convert the electrical signals into optical signals at the transmitter side, and then convert the optical signals into electrical signals at the receiver side after being transmitted through optical fibers. The form factor of an optical module determines its size and is the primary way to differentiate between optical modules. According to their evolution, optical modules can be mainly divided into nine types, which we will introduce in the following paragraphs.

The Foundation: Small Form-factor Pluggable (SFP)

SFP, or Small Form-factor Pluggable, is a compact, lightweight version of the GBIC module, designed to support gigabit rates. As the successor to GBIC, SFP has become the foundational form factor for modern optical modules.One of the most significant advantages of SFP over GBIC is its reduced size. The SFP module is half the size of a GBIC module, allowing for more than double the number of ports to be configured on the same panel. This space efficiency is crucial for high-density networking environments.SFP modules support a maximum bandwidth of up to 4Gbps and are typically equipped with a single gigabit SerDes (Serializer/Deserializer) channel. This capability makes SFP a versatile and widely used option for various networking applications.

Transition to Higher Speeds: SFP+ and SFP28

SFP+, as we can infer from its abbreviation, is a plus version of the SFP module. Its official name is Enhanced Small Form-factor Pluggable. SFP+ is specifically designed for 10Gbps Ethernet, featuring several technical advancements and compatibility with higher speed standards.

Unlike SFP, which typically supports up to 4Gbps, SFP+ can handle data rates up to 10Gbps, making it a crucial component in modern high-speed networking environments. In addition to the significant increase in data transmission rates, SFP+ retains the compact size and hot-swappable functionality of SFP, allowing for seamless upgrades and maintenance without network downtime. SFP+ modules typically support a single 10Gbps SerDes channel, further enhancing their suitability for high-performance computing and data center applications.

SFP28, short for Small Form-factor Pluggable 28, is an advanced version of the SFP+ module. Although it shares the same size as SFP+, SFP28 supports optical modules with a data rate of 25Gbps. Specifically designed for 25Gbps Ethernet, SFP28 is equipped with a single 28G SerDes channel. SFP28 is essential in modern high-speed networks due to its ability to handle higher data rates while maintaining the compact size and form factor of its predecessors. This compatibility with existing SFP+ slots allows for easy upgrades and integration into current network infrastructures without the need for significant hardware changes.

The introduction of SFP28 addresses the increasing demand for higher bandwidth in data centers, enterprise networks, and other HPC environments. By providing a cost-effective and scalable solution for 25Gbps Ethernet, SFP28 plays a crucial role in the evolution of network technology, ensuring that networks can meet the growing data transmission requirements of today and tomorrow.

Quad Channel Modules: QSFP+ and QSFP28

QSFP+ and QSFP28 are both quad-channel SFP interfaces. Compared to SFP+ optical modules, they are larger in size. The difference between them is that QSFP+ supports 40G, while QSFP28 supports 100G. Specifically, QSFP+ introduces four independent SerDes channels, each supporting 10Gbps, resulting in a total rate of 40Gbps. On the other hand, QSFP28 continues the quad-channel design but increases the rate of each channel to 25Gbps, thereby boosting the total rate to 100Gbps.

Further Enhancements: QSFP56 and QSFP112

QSFP56 and QSFP112 represent advancements in technology with each channel supporting 50Gbps and 100Gbps respectively. QSFP56 offers a total data rate of 200Gbps, while QSFP112 reaches 400Gbps. Both of these modules rely on the same four-channel SerDes technology. However, the significant difference lies in the increased per-channel data rates, allowing for higher overall bandwidth without changing the number of channels. This evolution highlights the ongoing enhancements in optical modules to meet the growing demands for higher data transmission rates in modern high-speed networks.

Exploring Future with QSFP-DD and OSFP

QSFP-DD, or Quad Small Form Factor Pluggable-Double Density, indicates its “Double Density” nature right from its name. This advanced module supports data rates of 200G, 400G, and even up to 800G. With double density achieved through eight channels, QSFP-DD is designed for 400Gbps and beyond. These improvements make it a versatile choice for high-speed networking needs, offering design enhancements that cater to increased bandwidth requirements and various use cases.

On the other hand, OSFP, which stands for Octal Small Form-factor Pluggable, features an octal design, representing eight channels. Slightly larger than QSFP-DD, OSFP modules support 400G, 800G, and up to 1600G data rates. This design not only accommodates higher speeds but also includes considerations for effective thermal management and signal integrity, making OSFP a forward-looking solution for the next generation of high-performance networks.

FS provides newly module catagory of 800G QSFP-DD/OSFP, which paves the way for advancements in optical module technology, addressing the ever-growing demand for higher data rates and efficient performance in modern data centers and network infrastructures.

The Role of SerDes Technology

SerDes, short for Serializer Deserializer, is an electronic circuit commonly used in high-speed communication applications. It converts parallel data into serial data for transmission and then back into parallel data at the receiving end. From the above introduction, it is evident that the speed and number of SerDes channels are directly related to the speed of optical modules. Simply put, increasing the number of channels or enhancing the speed of individual channels are the two main strategies to boost the total transmission rate of optical modules.

As technology advances, optical modules have evolved from single-channel to multi-channel designs, and SerDes speeds have progressed from 10Gbps to 112Gbps and beyond. Consequently, optical module speeds have upgraded from 1G, 10G, 25G, 40G, 100G, 200G, 400G, to 800G.The development of SerDes technology not only determines the data transmission rate of networks but also affects the size, power consumption, and cost of optical modules.


In summary, the evolution of optical module form factors shows trends toward smaller sizes, higher speeds, lower costs, reduced power consumption, long-distance transmission, and hot-swappable capabilities. Increasing the number of channels or the speed of individual channels are the main strategies for boosting optical module speeds. In today’s rapidly advancing information age, the future of optical modules is promising, with ongoing innovations expected to empower high-performance computing and drive further technological progress.