What Is SFP

What is SFP

SFP (Small Form-factor Pluggable) is a small, hot-swappable network transceiver module used in switches and routers to connect them to fiber-optic or copper cables. Its main job is to convert electrical signals from the device into optical signals (for fiber) or electrical signals (for copper), and vice versa.

In short, SFP allows a network device to support different types of connections (fiber or copper) and different distances by simply changing the module instead of replacing the whole switch.

Type of SFP

SFP (Small Form-factor Pluggable) modules are classified based on speed, fiber type, transmission distance, and wavelength. Each type is designed for a specific network requirement. Below is a detailed explanation of the main types of SFP modules.

 1. 1G SFP Modules (Gigabit SFP)

These modules support 1 Gbps speed and are commonly used in enterprise and campus networks.

  • SFP SX (Short Wavelength)
    Uses multi-mode fiber (MMF) with 850 nm wavelength and supports distances up to 550 meters. It is mainly used inside buildings or data centers.

  • SFP LX (Long Wavelength)
    Uses single-mode fiber (SMF) with 1310 nm wavelength and supports distances up to 10 km. It is suitable for inter-building or campus connections.

  • SFP ZX
    Uses single-mode fiber with 1550 nm wavelength and supports long distances up to 70–80 km. It is used for long-haul WAN or ISP links.

  • Copper SFP (RJ45 SFP)
    Uses normal Ethernet copper cable and supports distances up to 100 meters. It is useful when a switch has only SFP ports but copper connectivity is required.

2. SFP+ Modules (10G SFP)

These modules support 10 Gbps speed and are used in data centers and backbone networks.

  • SFP+ SR (Short Range)
    Uses multi-mode fiber and supports distances up to 300 meters.

  • SFP+ LR (Long Range)
    Uses single-mode fiber and supports distances up to 10 km.

  • SFP+ ER (Extended Range)
    Uses single-mode fiber and supports distances up to 40 km.

  • SFP+ ZR
    Uses single-mode fiber and supports distances up to 80 km.

3. SFP28 Modules (25G SFP)

These modules support 25 Gbps speed and are used in high-performance enterprise and data-center networks.

  • SFP28 SR – Multi-mode fiber (short distance)
  • SFP28 LR – Single-mode fiber (long distance)

 4. QSFP+ Modules (40G)

These modules support 40 Gbps speed and are used for core and aggregation switches.

  • QSFP+ SR4 – Multi-mode fiber
  • QSFP+ LR4 – Single-mode fiber

 5. QSFP28 Modules (100G)

These modules support 100 Gbps speed and are mainly used in ISP and data-center backbone networks.

  • QSFP28 SR4
  • QSFP28 LR4
  • QSFP28 ER4

6. By Fiber Type

SFP modules can also be grouped by fiber type:

  • Multi-mode fiber (MMF) → SX, SR
  • Single-mode fiber (SMF) → LX, LR, ER, ZR

Summary (Easy)

  • 1G SFP: SX, LX, ZX, RJ45
  • 10G SFP+: SR, LR, ER, ZR
  • 25G SFP28: SR, LR
  • 40G QSFP+: SR4, LR4
  • 100G QSFP28: SR4, LR4, ER4

In short, SFP allows a network device to support different types of connections (fiber or copper) and different distances by simply changing the module instead of replacing the whole switch.

Wavelength

In fiber-optic communication, wavelength (measured in nanometers – nm) refers to the color of light used to transmit data through the fiber cable. Different wavelengths are used because each one behaves differently in terms of distance, signal loss (attenuation), and performance. Fiber optics mainly use three important wavelength ranges: 850 nm, 1310 nm, and 1550 nm, along with some extended and special wavelengths for advanced systems.

1. 850 nm (Short wavelength – Multimode fiber)

The 850 nm wavelength is mainly used with multimode fiber (MMF). It is suitable for short-distance communication such as inside buildings, data centers, and server rooms. This wavelength has higher signal loss compared to others, so it is limited to shorter distances (typically up to 300–550 meters). It is commonly used by SFP/SFP+ SR modules and is cost-effective for local networks.

2. 1310 nm (Long wavelength – Single-mode fiber)

The 1310 nm wavelength is used mostly with single-mode fiber (SMF) and is designed for longer distances such as between buildings or across a campus. It has lower attenuation than 850 nm and can travel up to 10 km or more depending on the transceiver type. It provides stable performance and is widely used in enterprise and ISP networks (LX, LR modules).

3. 1550 nm (Extended / very long distance wavelength)

The 1550 nm wavelength is used for very long-distance fiber communication. It has the lowest signal loss, which allows transmission up to 40 km, 80 km, or even more. This wavelength is commonly used in backbone networks, metro networks, and WAN links (ER, ZR modules). It is also used in DWDM (Dense Wavelength Division Multiplexing) systems where multiple wavelengths travel on the same fiber.

4. CWDM Wavelengths (1270 nm – 1610 nm)

CWDM (Coarse Wavelength Division Multiplexing) uses multiple wavelengths such as 1270, 1290, 1310, 1330 … up to 1610 nm. Each wavelength carries separate data on the same fiber. This is used to increase capacity without installing new fiber cables and is common in telecom and ISP networks.

 5. DWDM Wavelengths (1525 nm – 1565 nm)

DWDM mainly operates in the 1550 nm band (C-band and L-band) and supports many closely spaced wavelengths. It is used for extremely high-capacity long-distance transmission (hundreds of kilometers) in backbone and submarine fiber networks.

How Many Types of SFP Transceivers

How Many Types of SFP Transceivers Do You Know?

There are many 1G SFP types available today like copper RJ45 SFP, fiber optic SFP, and WDM SFP modules, so what makes them different, and how do you know which is best for you? According to different classification standards, 1G modules have different types.
 
By SFP Media Type
1G Ethernet SFP module can work over optical fiber and Ethernet cables, so fiber SFP module and copper SFP are the two main SFP types.
Within the fiber SFP category, there are two distinct types—single-mode SFPs, which are compatible with single-mode fibers, and multimode SFPs, which are suited for multimode fibers. These classifications correspond with the specific fiber patch cables they interface with. Refer to Table 1 for a detailed comparison of the key differences between single-mode and
Specfication
Multimode SFP
Single-mode SFP
Fiber Type
62.5/125µm or 50/125µm core MMF
9/125µm core SMF
Working Wavelength
Mainly in 850 nm and 1300 nm
Mainly in 1310 nm and 1550 nm
Color Coding
 
Black
Blue for 1310nm SFP
Yellow for 1550nm SFP
Transmission Distance
100m / 550m
2km up to 200km
The 1000Base-T RJ45 SFP transceiver module represents a robust interface for copper-based networking, leveraging the ubiquitous twisted-pair cabling standards inclusive of Category 5e (Cat5e), Category 6 (Cat6), and the advanced Category 6a (Cat6a). This module is specially engineered to deliver high-speed gigabit connectivity across these copper mediums with an operational reach of up to 100 meters, ensuring compatibility and optimal performance in both data center architectures and enterprise LAN environments. Its design adheres to industry standards, offering a high degree of reliability and interoperability for network expansions or integrations where existing copper network infrastructure is leveraged.
Specfication
Multimode SFP
Single-mode SFP
Fiber Type
62.5/125µm or 50/125µm core MMF
9/125µm core SMF
Working Wavelength
Mainly in 850 nm and 1300 nm
Mainly in 1310 nm and 1550 nm
Color Coding
 
Black
Blue for 1310nm SFP
Yellow for 1550nm SFP
Transmission Distance
100m / 550m
2km up to 200km
The 1000Base-T RJ45 SFP transceiver module represents a robust interface for copper-based networking, leveraging the ubiquitous twisted-pair cabling standards inclusive of Category 5e (Cat5e), Category 6 (Cat6), and the advanced Category 6a (Cat6a). This module is specially engineered to deliver high-speed gigabit connectivity across these copper mediums with an operational reach of up to 100 meters, ensuring compatibility and optimal performance in both data center architectures and enterprise LAN environments. Its design adheres to industry standards, offering a high degree of reliability and interoperability for network expansions or integrations where existing copper network infrastructure is leveraged.
By SFP Cable Core Diameter
FS has different types of 1G fiber SFP transceivers, including multi-mode, single-mode, BiDi, and WDM. For specific transmission range function details, please refer to Table 2.
 
Product 
Wavelength
Max. Transmit Distance
Connector
Multimode SFP
1000BASE-SX-85
850nm
550m
LC Duplex
1000BASE-SX-31
1310nm
2km
LC Duplex
Single mode SFP
 
1000BASE-LX-31
1310nm
20km
LC Duplex
1000BASE-LH-31
1310nm
40km
LC Duplex
1000BASE-EX-55
1550nm
40km
LC Duplex
1000BASE-ZX-55
1550nm
80km
LC Duplex
1000BASE-EZX-55
1550nm
120km
LC Duplex
1000BASE-ZXC-55
1550nm
160km
LC Duplex
BiDi SFP
1000BASE-BX
1310nm/1550nm, 1310nm/1490nm, 1510nm/1590nm
2km~160km
LC Duplex/Simplex
WDM SFP
1000BASE-CWDM
1270nm~1610nm
20km~160km
LC Duplex
1000BASE-DWDM
C17~C61
80km~100km
LC Duplex
By SFP Operating Temperature
According to the different operating temperatures, SFP modules can usually be divided into three types:
 
Commercial grade (Commercial)
 
Commercial grade SFP modules are suitable for standard work environments, and their operating temperature range is usually between 0 ° C and 70 ° C. This type of SFP module performs well in ordinary office and data center environments.
 
Industrial grade (Industrial) 
 
Industrial grade SFP modules are designed for use in more demanding industrial environments, where the operating temperature range is typically between -40 ° C and 85 ° C. This type of SFP module is suitable for industrial control systems, outdoor equipment, and other applications that require reliable operation in extreme temperature conditions.
 
Military Grade (Military) 
 
Military grade SFP modules are designed for military applications and typically operate over a temperature range of -55 ° C to 100 ° C. This type of SFP module offers greater durability and reliability for long periods of stable operation in extreme environmental conditions.
At present, our company only provides commercial-grade and industrial-grade modules. It is very important to choose the SFP module with the appropriate operating temperature range according to actual needs and environmental conditions to ensure the stability and reliability of network equipment.
 
By SFP Variants
SFP transceivers come in various variants to cater to different networking requirements, including data rate, distance, wavelength, and compatibility with different types of optical fiber. Here is a brief overview of some common SFP variant types:
 
SFP
 
The standard SFP transceivers support speeds up to 1 Gbps and are used for Gigabit Ethernet and Fibre Channel.
 
SFP+
 
An enhanced version of the SFP that supports data rates up to 10 Gbps. SFP+ modules are commonly used in 10 Gigabit Ethernet and can support 8 Gbps Fibre Channel, and some variants offer Direct Attach (DAC) capabilities with copper cables.
 
SFP28
A variant that is designed for 25 Gbps Ethernet connections. This allows for higher speeds and is backwards compatible with SFP+ ports.
 
QSFP
 
Quad Small Form-factor Pluggable modules are not the same size as SFPs; they’re wider and support four channels of data transfer, providing solutions for 40 Gbps (QSFP+) and even 100 Gbps (QSFP28) rates.
The selection of an appropriate SFP variant depends on factors including required throughput, distance the signal needs to travel, type of fiber optic cabling, and environmental conditions. It is important to match the SFP specification to the networking equipment, as well as to the operational requirements, to ensure compatibility and optimal performance. For in-depth insights into the distinctions between these advanced transceiver modules, I invite you to explore 
By SFP Application
Based on different applications, SFP types are usually categorized by the following types.
 
Regular SFP: Most commonly transceivers that deliver data via a duplex fiber. Based on market development and user requests, 2.5G SFP and 100M SFP have emerged successively
 
BIDI SFP: Can transmit and receive signals in simplex fiber.
 
WDM SFPs: Support CWDM/DWDM transmission to maximize the bandwidth while saving the fiber cabling.
 
SONET/SDH SFP: Compatible with the SONET/SDH and ATM standard which covers the standard range of data rates extending from OC-3/STM-1 (155 Mbps) to OC-48/STM-16 (2488 Gbps) for multimode (MM), short-reach (SR), intermediate-reach (IR1), and long-reach (LR1/LR2) applications.
 
PON SFPs: Used in the Optical Line Terminal (OLT) at the Central Office and the Optical Network Terminal/Unit (ONT/ONU) at the subscriber’s premises.
 
3G-SDI video SFPs: Designed to meet the high standard video transmission needs in the High Definition (HD) environment.
 
SONET/SDH SFP: Compatible with the SONET/SDH and ATM standard which covers the standard range of data rates extending from OC-3/STM-1 (155 Mbps) to OC-48/STM-16 (2488 Gbps) for multimode (MM), short-reach (SR), intermediate-reach (IR1), and long-reach (LR1/LR2) applications.
 
Fibre Channel SFP: A high-speed network technology (commonly running at 1, 2, 4, 8, 16, 32, and 128 gigabits per second rates) primarily used to connect computer data storage to servers in the SAN data center environment.
Each category serves a unique role in network architecture, with different performance metrics and standardized compliance to ensure connectivity and communication across a variety of platforms.

SFP, SFP+, SFP28, QSFP+, QSFP28, What Are the Differences?

SFP, SFP+, SFP28, QSFP+, and QSFP28 are different fiber transceiver types on the market. They are all hot-pluggable optical modules that are used to connect network switches or other devices. Then, SFP vs. SFP+, SFP28 vs. SFP+, QSFP vs. QSFP28, what are their differences? Can SFP28 transceiver plug into SFP+ slots? And how to choose between these five form factors transceiver modules? All explanations are here.

What are They?
Before concluding the differences of SFP vs SFP+ vs SFP28 vs QSFP+ vs QSFP28, it’s wise to figure out what those form factors stand for.
SFP: SFP was first introduced in 2001, and built to replace the larger form factor GBIC and support data rates of up to 1G data rate. But with the demands for higher bandwidths like 5G applications or IoT, 1G SFP modules nowadays are estimated to be out of the market in the future, although they still have some market share.
 
SFP+: 2006 saw the introduction of SFP+, an enhanced version of SFP with a higher data rate of up to 10 Gbps. SFP+ module is now still a dominant industry format transceiver module. Data transmission is available at 8Gbps, 10Gbps, and 16Gbps. Transmission distances cover from 30m to 120km and SFP+ transceivers are available with several different connector types such as LC Duplex, LC Simplex, and RJ45.
 
SFP28: With the same physical dimensions as the SFP and SFP+, the SFP28 fiber transceiver type was launched in 2014 and designed for up to 25Gbps transmission rate. Mainly used for 25G Ethernet and 100G (4x25Gbps) Ethernet.
 
QSFP+: Launched in 2012, QSFP+ (Enhanced Quad Small Form-factor Pluggable) is composed of 4 channels of 10Gb/s rate that support LC duplex and MPO-12 fiber connectors.
 
QSFP28: QSFP28 was also introduced in 2014 and shares the same physical dimensions as QSFP+, but uses 4 lanes of 25Gbps. QSFP28 is now the standard interface of choice for 100G applications.
By SFP Cable Core Diameter
FS has different types of 1G fiber SFP transceivers, including multi-mode, single-mode, BiDi, and WDM. For specific transmission range function details, please refer to Table 2.
 
Product 
Wavelength
Max. Transmit Distance
Connector
Multimode SFP
1000BASE-SX-85
850nm
550m
LC Duplex
1000BASE-SX-31
1310nm
2km
LC Duplex
Single mode SFP
 
1000BASE-LX-31
1310nm
20km
LC Duplex
1000BASE-LH-31
1310nm
40km
LC Duplex
1000BASE-EX-55
1550nm
40km
LC Duplex
1000BASE-ZX-55
1550nm
80km
LC Duplex
1000BASE-EZX-55
1550nm
120km
LC Duplex
1000BASE-ZXC-55
1550nm
160km
LC Duplex
BiDi SFP
1000BASE-BX
1310nm/1550nm, 1310nm/1490nm, 1510nm/1590nm
2km~160km
LC Duplex/Simplex
WDM SFP
1000BASE-CWDM
1270nm~1610nm
20km~160km
LC Duplex
1000BASE-DWDM
C17~C61
80km~100km
LC Duplex

How to Tell if My SFP is Single-Mode or Multimode

To determine if your SFP (Small Form-factor Pluggable) module is single mode or multimode, you can look for specific markings or labels on the module itself. Typically, single mode SFP modules are labeled as “SM” or “single mode,” while multimode modules may be labeled as “MM” or “multimode.” Additionally, single mode modules often have yellow-colored connectors, while multimode modules may have orange or aqua-colored connectors. It is important to check the specifications or documentation provided by the manufacturer to confirm the mode of your SFP module, as the labeling and color coding conventions may vary.
 
What is Single-Mode vs. Multimode SFP?
SFP, or Small Form-factor Pluggable, is a type of transceiver used in data communication and telecommunications networks. It allows for the connection of a network device to various types of fiber optic or copper cabling. SFP modules are standardized by the MSA (Multi-Source Agreement), meaning they can be used across different brands of networking equipment. There are two primary types of fiber optic SFP transceivers based on the mode of the fiber: Single-Mode SFP (SMF) and Multimode SFP (MMF).
 
Single-Mode SFP
Fiber Type: Single-mode fiber (SMF) uses one mode of light to propagate through the fiber. This means there is a single light path and it’s usually a laser-based light source.
 
Core Diameter: A single-mode fiber has a small core diameter, typically around 9 micrometers.
 
Distance: Single-mode SFP can transmit data over long distances, generally up to 150 kilometers, depending on the SFP model and its optical budget.
 
Speed and Bandwidth: Single-mode fiber offers higher bandwidth than multimode and can support higher data rates because it has no modal dispersion due to the single light path.
Color Coding: Single-mode SFPs are typically identified by blue-colored bail or coding.
 
Multimode SFP
Fiber Type: Multimode fiber (MMF) allows multiple modes or light paths to propagate through the fiber, resulting in differential mode delay. This is usually an LED-based light source but can be laser-optimized for higher performance on later multimode fiber versions.
 
Core Diameter: Multimode fiber has a larger core size, usually 50 or 62.5 micrometers, which enables multiple light paths.
 
Distance: Multimode SFPs are suitable for shorter distances, generally up to 2 kilometers, but most are used for distances under 600 meters.
 
Speed and Bandwidth: Multimode SFPs offer high bandwidth at short distances, but the bandwidth potential decreases with increased cable length due to modal dispersion.
 
Color Coding: Multimode SFPs often have a black or beige bail, or aqua in the case of the enhanced 10Gbps versions (OM3/OM4).
 
When choosing an SFP for a network application, it’s essential to consider the required distance, data rate, compatibility with the existing network infrastructure, and the cost. Single-mode fiber solutions are generally more suitable for long-haul applications, whereas multimode fiber is often preferred for short-range data communications, such as within a data center or a building.
The most common color of single-mode SFP Bale Clasp is blue, there are also some in yellow, red, etc. Fiber optic jumpers used with single-mode optical modules are generally yellow.

SFP Slide Guide

SFP Short Explain

1. What is an SFP?

SFP stands for Small Form-factor Pluggable.

It is a small, removable module that you plug into network devices like:

  • Switches
  • Routers
  • Media converters

An SFP lets the device send and receive data over:

  • Fiber optic cable (most common)
  • Sometimes copper cable (RJ45 SFPs)

 Instead of having fixed ports, SFPs make the port flexible.

2. What is a Fiber SFP?

A Fiber SFP is an SFP module that uses fiber-optic cables to transmit data as light signals.

  • Electrical signals (from the switch) ➜ Light (into fiber)
  • Light (from fiber) ➜ Electrical signals (into the switch)

3. Why Fiber SFPs are used

Fiber SFPs are used when you need:

  • Long distance communication (hundreds of meters to kilometers)
  • High speed (1G, 10G, 25G, 40G, 100G)
  • No interference (fiber is immune to electrical noise)
  • Reliable backbone connections

4. Main parts of a Fiber SFP

  • Laser transmitter – sends light
  • Photodiode receiver – receives light
  • Optical connector – connects the fiber cable
  • EEPROM – stores module information

Metal housing – reduces interference and heat

  • 5. Types of Fiber SFPs (Very Important)
  • A. By Speed
    SFP TypeSpeed
    SFP1 Gbps
    SFP+10 Gbps
    SFP2825 Gbps
    QSFP+40 Gbps
    QSFP28100 Gbps

B. By Fiber Type

1. Multimode Fiber SFP (Short Distance)

Uses MMF fiber

  • Color: usually aqua
  • Distance: 100m – 550m
  • Laser: 850nm
  • Type name: SX

Example:

  • 1000BASE-SX
  • 10GBASE-SR

2. Single-Mode Fiber SFP (Long Distance)

Uses SMF fiber

  • Color: usually yellow
  • Distance: 10km – 80km+
  • Laser: 1310nm or 1550nm
  • Type name: LX, LR, ER, ZR

Example:

  • 1000BASE-LX
  • 10GBASE-LR

C. By Connector Type

Most common:

  • LC connector (small, modern)
  • SC connector (older, bigger)

6. Common Fiber SFP Names Explained

Let’s break one down:

Example: 1000BASE-LX SFP

  • 1000 = 1 Gbps
  • BASE = baseband signaling
  • LX = Long wavelength (1310nm)
  • Works on single-mode fiber
  • Distance ≈ 10 km

7. Duplex vs Simplex (BiDi)

Duplex Fiber SFP

  • Uses 2 fibers
  • One fiber transmit (TX)
  • One fiber receive (RX)

BiDi (Bidirectional) SFP

  • Uses 1 fiber
  • TX and RX use different wavelengths
  • Must be used in pairs

Example:

  • SFP-A: TX 1310 / RX 1550
  • SFP-B: TX 1550 / RX 1310

8. How Fiber SFPs are installed

  • Insert SFP into switch/router
  • Lock it in place
  • Connect fiber cable

Ensure:

  • Correct fiber type
  • Correct wavelength
  • Same speed on both ends

9. Compatibility Rules (Very Important)

  • Speed must match on both sides
  • Fiber type must match (SMF vs MMF)
  • Wavelength must match
  • Some vendors lock SFPs (Cisco, HP, etc.)

⚠️ A 10G SFP+ will not work in a 1G SFP port.

10. Advantages of Fiber SFP

✅ Long distance
✅ High speed
✅ Low signal loss
✅ No electrical interference
✅ Hot-swappable

PON SFP Details

PON SFP (Passive Optical Network SFP) is a special type of optical transceiver module used in fiber-based broadband networks to connect network devices like OLT (Optical Line Terminal), switches, or routers to a PON fiber network. Unlike normal Ethernet SFP modules (which work point-to-point), a PON SFP works in a point-to-multipoint architecture where one fiber from the OLT is split using passive splitters to serve many ONUs/ONTs (customers). PON SFP modules support standards such as EPON, GPON, XG-PON, and XGS-PON and are designed to handle downstream broadcast traffic and upstream time-shared traffic using TDMA (Time Division Multiple Access).

A PON SFP uses different wavelengths for upstream and downstream communication. For example, GPON SFP typically uses 1490 nm for downstream data, 1310 nm for upstream data, and 1550 nm for video (optional RF overlay). XG-PON and XGS-PON use higher wavelengths such as 1577 nm for downstream and 1270 nm for upstream, allowing higher bandwidth and coexistence with older PON systems on the same fiber. These SFP modules are usually classified into optical power classes like B+, C+, or C++ (GPON) and PR10/PR20/PR30 (XG/XGS-PON), which define how far the signal can travel (20 km, 30 km, or even 40 km).

Functionally, a PON SFP installed in an OLT port manages authentication and communication with multiple ONTs using unique identifiers (ONU IDs) and encryption (AES). Downstream traffic is broadcast to all ONTs, but only the intended ONT can decrypt and read its own data. Upstream traffic is carefully scheduled so that each ONT transmits in its assigned time slot, preventing collisions. This makes PON SFP modules critical components in ISP networks, FTTH (Fiber to the Home) deployments, and enterprise fiber access solutions. In short, a PON SFP is not just a fiber optic transmitter—it is a smart optical interface designed for high-speed, long-distance, multi-user fiber access networks.

PON SFP Power

A PON SFP (Passive Optical Network SFP) is a special optical transceiver module used in OLT equipment to transmit and receive fiber signals in a PON network. The two most important technical characteristics of a PON SFP are its output power (optical power class) and its wavelengths, which determine how far the signal can travel and how many users can be served on one fiber through passive splitters.

In GPON PON SFP modules, different power classes such as B+, C+, and C++ define the optical output power and link budget. A B+ class PON SFP typically transmits downstream at around +1.5 dBm to +5 dBm and supports up to 20 km distance with an optical budget of about 28 dB. A C+ class PON SFP has higher output power, usually around +3 dBm to +7 dBm, allowing distances up to 30 km with an optical budget of about 32 dB. The highest common class, C++, provides even stronger output power of approximately +5 dBm to +9 dBm, enabling transmission up to 40 km and supporting high splitter ratios such as 1:64 or 1:128. Higher power output means the signal can overcome more fiber loss and splitter attenuation, but it also requires proper design to avoid overloading the receiver.

PON SFP modules use different wavelengths for upstream and downstream traffic so both directions can work simultaneously on a single fiber. In GPON, the downstream wavelength from OLT to ONU is 1490 nm, while the upstream wavelength from ONU to OLT is 1310 nm. An optional video overlay service uses 1550 nm. In newer technologies like XG-PON and XGS-PON, higher wavelengths are used: 1577 nm for downstream and 1270 nm for upstream, which allows higher data rates and coexistence with GPON on the same fiber. In summary, a PON SFP’s output power determines how far and how many users it can serve, while its wavelengths determine how upstream and downstream communication are separated and optimized on a single optical fiber.

Quick Comparison (Output Power)

ClassTX Output Power (1490 nm)Optical BudgetDistance
B++1.5 to +5 dBm~28 dB20 km
C++3 to +7 dBm~32 dB30 km
C+++5 to +9 dBm~35 dB40 km

Downstream Upstream EPON GPON How Work OLT ONU

In fiber access networks, EPON (Ethernet Passive Optical Network) and GPON (Gigabit Passive Optical Network) use a point-to-multipoint architecture where one fiber from the OLT is shared by many ONUs through passive splitters. The terms download stream (downstream) and upload stream (upstream) describe the direction in which data flows between the service provider and the customer. Although EPON and GPON are based on different standards, both use separate wavelengths and controlled transmission methods to allow reliable two-way communication on a single optical fiber.

In both EPON and GPON, the downstream (download stream) is the traffic sent from the OLT to all connected ONUs. This stream carries user data such as web pages, video streaming, software downloads, IPTV, and updates from the service provider. Downstream traffic is broadcast in nature, meaning the OLT sends data to every ONU on the same PON line at the same time, but each ONU only reads and decrypts the data meant for it. EPON downstream typically operates at 1.25 Gbps using a wavelength of 1490 nm (or sometimes 1550 nm), while GPON downstream operates at 2.5 Gbps using a wavelength of 1490 nm. Because downstream is shared among many users, the available bandwidth is divided among all connected ONUs based on demand and OLT scheduling policies.

The upstream (upload stream) is the traffic sent from each ONU back to the OLT. This stream includes activities such as uploading files, sending emails, video conferencing, cloud backups, and any data generated by the user toward the internet. Since many ONUs share the same fiber path back to the OLT, upstream communication is carefully controlled using TDMA (Time Division Multiple Access). The OLT assigns specific time slots to each ONU so that only one ONU transmits at a time, preventing signal collision on the fiber. In EPON, upstream speed is typically 1.25 Gbps at a wavelength of 1310 nm, while in GPON the upstream speed is 1.25 Gbps also at 1310 nm. This structured time-slot system ensures fair bandwidth usage and stable performance for all users.

In summary, for both EPON and GPON, the downstream (download stream) flows from OLT to ONU using higher-power broadcast transmission to deliver internet and media services, while the upstream (upload stream) flows from ONU to OLT using time-controlled transmission to avoid collisions. EPON usually provides symmetrical speeds of about 1.25 Gbps in both directions, whereas GPON provides higher downstream speed (2.5 Gbps) and lower upstream speed (1.25 Gbps), making GPON more suitable for services like video streaming and IPTV where download traffic is heavier than upload traffic.

 

In simple terms:
OLT → ONU (Downstream): 1490 nm (GPON/EPON) or 1577 nm (XG/XGS-PON)
ONU → OLT (Upstream): 1310 nm (GPON/EPON) or 1270 nm (XG/XGS-PON)

 

GPON OLT SFP Class C++ 1490nm-TX/1310nm-RX 20km Transceiver

SFP Module Video Guide