Understanding Fiber Optics - Part 3

Understanding Fiber Optics – Your Quick Guide to SFP Transceivers

What is an SFP Transceiver?

SFP (small form-factor pluggable) is a compact, hot-pluggable optical module transceiver used for both telecommunication and data communications applications. These applications -usually on networking hardware- feature an SFP interface which is a modular (plug-and-play) slot for a variable, media-specific transceiver in order to connect a fiber optic cable or sometimes a copper cable.

The form factor and electrical interface are specified by a multi-source agreement (MSA) under the Small Form Factor Committee umbrella; a popular industry format jointly developed and supported by many network component vendors.

Types of SFP transceivers

There are a number of types of SFP Transceivers based on the different classification standards. To help you pick the best SFP Transceiver for your application, it is important to understand these different classifications and characteristics and more importantly, to tell them apart.

They may seem like a lot to digest, but not to worry. We have taken time to outline a summary of the most common classifications and differences, to serve as a quick guide to selecting the right SFP Transceiver.

Let’s explore them in detail…

Single Mode vs. Multimode SFP Transceivers

Based on the types of optical fibers SFP transceivers work with, SFP transceivers are divided into single mode SFP that works with single-mode fiber and multimode SFP that works with multimode fiber. Explore the major differences between them. Single-mode SFP transceivers are designed to transmit signals over long distances, while Multimode SFP transceivers are specially designed for short distance data transmission. Explore some more differences below…

  Single Mode SFP Multimode SFP
Wavelength 1310nm and 1550nm 850nm
Colour Coding Blue color-coded bale clasp for 1310nm SFP. Yellow color-coded bale clasp for 1550nm SFP. Black color-coded bale clasp.
Fiber Jacket Colour Yellow jacket for Single Mode fiber. Orange jacket for OM1 & OM2 Multimode fiber
Transmission Distance Long distance transmission such as 2 km, 10 km, 20 km, 40 km, 80 km, 100 km and 120 km. Short distance transmission such as 100 m and 500 m.
Single Mode SFP vs Multimode SFP

SFP Fiber Module vs SFP Copper Module

Copper SFP modules allow communication over twisted pair networking cables while fiber modules allow communication over fiber optic cables. Explore more differences below;

  Transceiver Type Connector Distance Data Rate
SFP Fiber Module CWDM/DWDM SFP LC Duplex 10km-120km over Single Mode Fiber 100Mbps/ 1000Mbps
SFP Copper Module 1000BASE-T 10/100BASE-T 10/100/1000BASE-T RJ45 100m over copper twist pair cable 100Mbps/ 1000Mbps

Copper SFP vs Fiber SFP

Simplex SFP vs Duplex SFP

Simplex SFP transceivers use only a single fiber for transmission while Duplex SFP transceivers use dual fibers. Simplex SFPs, are also known as bidirectional (BiDi) SFPs. It is very easy to distinguish simplex SFP and duplex SFP from the receptacle as shown in the diagram below;

Simplex SFP vs Duplex SFP

Note: All SFP transceivers should be used in pairs. For duplex SFPs at the two sides, we should connect two SFPs of the same wavelengths. For example, two 850nm SFPs or two 1310nm SFPs. However, for simplex/BiDi SFPs, we should use two SFPs that have opposite wavelengths for transmitter and receiver.

Bandwidth; SFP vs SFP+

The trend towards higher speed and higher bandwidth is always unstoppable, from Fast Ethernet to Gigabit Ethernet. At the same time, new devices for transmitting data are published; SFP+ for 10 Gigabit and SFP28 for 25 Gigabit Ethernet. While they all use the same form-factor packaging, the most obvious difference between them is the data rate. Explore the differences below;

  SFP SFP+ SFP28
Data Rate 1.25G 2.5G/3G/4.25G 6G/8.5G/10G 25G
Types Single-mode/Multimode Simplex/Duplex CWDM/DWDM Single-mode/Multimode Simplex/Duplex CWDM/DWDM Single-mode/Multimode
Distance 100 m up to 150km 220m up to 80km 100m up to 10km

Dense Wavelength-Division Multiplexing (DWDM) vs Coarse Wavelength-Division Multiplexing (CWDM)

Simply put, Wavelength-Division Multiplexing (WDM) is a technology that enables transmission of multiple signals simultaneously on a single fiber. WDM is utilized by telecom systems in long distance transmission. In these systems, the lasers of SFP transceivers are chosen with precise wavelengths closely spaced but not so close they interfere with each other.

Wavelength-division multiplexing for SFP transceivers is either DWDM (dense WDM) or CWDM (coarse WDM). Discover more below;

DWDM SFPCDWDM SFP
Wavelength SpacingUp to 45 wavelengths (Channel 17 to Channel 61 according to ITU) of C Band (1525 nm to 1565 nm) or L Band (1570 nm to 1610 nm) with a 0.8nm spacing Up to 18 wavelengths from 1270 nm to 1610 nm with a 20nm spacing, i.e. 1270 nm, 1290 nm, 1310 nm, 1330 nm…
Transmission DistanceUp to 80 or 200 kmUp to 100 km, typically 80 km
ApplicationLong distance DWDM SONET/SDH transmission, Gigabit Ethernet, Fibre Channel, Metro Network Gigabit Ethernet, Fibre Channel (FC), Metro Access Network, Point-to-Point Network, Synchronous Optical Network (SONET), SDH (Synchronous Digital Hierarchy).
BenefitsUp to 32 channels can be done passively. Up to 160 channels with an active solution. Active solutions involve optical amplifiers to achieve longer distances. Passive equipment that uses no electrical power. Much lower cost per channel than DWDM. Scalability to grow the fiber capacity as needed with little or no increased cost. Protocol transparent. Ease of use.

 

Quick guide to selecting SFP

When selecting the correct SFP transceiver, the main factor to consider is the application scenario based on the classifications outlined above. In summary,

-Which type of Fiber Optic Cable are you connecting to the SFP transceiver?

-At what data rate do you want to transmit?

-What is the distance of your link?

-What type of signal are you transmitting?  

There’s one more important consideration technicians are careful to look into…

With quite a number of third party SFP optical transceivers in the market, compatibility is often the most parameter users care about. Before place your order, you can check the vendors’ optics testing center to confirm whether the SFP module you choose is compatible with your devices.

Or just talk to us for details about the SFP transceiver compatibility.

Source:

Small form-factor pluggable transceiver | Fiber Optic Cabling Solutions | SFP Module: What’s It and How to Choose It?

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