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Although both modules provide 100Gbps-class connectivity, their optical technologies are fundamentally different. SR4 uses 850nm parallel optics over multimode fiber for short-distance connections, while LR4 uses four wavelength channels over duplex single-mode fiber for links up to 10km. Fiber type, connector, optical architecture, and transmission distance are the primary factors when selecting between them.
1. What Is a 100G SR4 Optical Transceiver?
A 100G SR4 optical transceiver is a short-reach QSFP28 module designed for high-speed connections over multimode fiber. It typically uses 850nm VCSEL technology and four optical transmit lanes combined with four receive lanes.
Each optical lane carries approximately 25Gbps-class data, providing an aggregate transmission rate of approximately 100Gbps. The four transmit and four receive channels operate over separate fiber cores within a parallel-fiber connection.
Typical 100GBASE-SR4 characteristics:
Form factor: QSFP28
Aggregate data rate: 100Gbps
Optical wavelength: 850nm
Optical technology: VCSEL
Fiber type: Multimode fiber (MMF)
Fiber interface: MPO/MTP, typically MPO-12 with eight optical positions used
Standard reach: Up to 70m over OM3 and 100m over OM4, subject to channel specifications
Typical applications: Data center racks, switch-to-switch links, and high-performance computing networks
SR4 is suitable for short-distance optical connections where multimode fiber infrastructure is already installed. Its parallel optical architecture provides high bandwidth without requiring four different wavelength channels.
2. What Is a 100G LR4 Optical Transceiver?
A 100G LR4 optical transceiver is a long-reach QSFP28 module designed for 100Gbps-class Ethernet transmission over single-mode fiber. Unlike SR4, which uses parallel optical paths, LR4 combines four wavelength channels using wavelength-division multiplexing (WDM).
The four optical channels operate around the 1310nm region. They are multiplexed into one transmitting fiber and separated at the receiving end. A second fiber carries signals in the opposite direction, enabling full-duplex communication over a duplex single-mode fiber connection.
Typical 100GBASE-LR4 characteristics:
Form factor: QSFP28
Aggregate data rate: 100Gbps-class
Optical technology: Four-channel WDM
Nominal wavelength region: 1310nm
Fiber type: Single-mode fiber (SMF)
Fiber interface: Duplex LC
Standard reach: Up to 10km
Typical applications: Campus networks, data center interconnects, and enterprise backbone links
LR4 is designed for longer connections than SR4 and is commonly deployed where single-mode fiber infrastructure is available. Its WDM architecture allows four optical channels to share each directional fiber path.
3. 100G SR4 vs 100G LR4: Technical Comparison
The main difference between these two modules is not the aggregate data rate, but the optical transmission architecture and fiber infrastructure required by each solution.
| Parameter | 100G SR4 | 100G LR4 |
|---|---|---|
| Form factor | QSFP28 | QSFP28 |
| Aggregate data rate | 100Gbps | 100Gbps-class |
| Optical architecture | Parallel optical transmission | Four-channel WDM |
| Optical wavelength | 850nm | Four wavelengths around 1310nm |
| Laser technology | VCSEL | Typically LAN-WDM laser technology |
| Fiber type | Multimode fiber | Single-mode fiber |
| Fiber cores | 4 Tx + 4 Rx | 1 Tx + 1 Rx |
| Typical connector | MPO/MTP | Duplex LC |
| Standard reach | 70m on OM3; 100m on OM4 | Up to 10km |
| Typical application | Short-distance data center links | Campus and longer data center links |
| Fiber infrastructure | Parallel multimode fiber cabling | Duplex single-mode fiber cabling |
4. Fiber Type: Multimode Fiber vs Single-Mode Fiber
Fiber type is one of the most important considerations when selecting a 100G SR4 or LR4 transceiver. The two modules are designed for different optical fiber systems and should not be treated as interchangeable.
100G SR4 Uses Multimode Fiber
SR4 operates at 850nm and is designed for multimode fiber such as OM3 and OM4. Multiple fiber cores carry the individual transmit and receive channels. This parallel arrangement is well suited to short-distance connections inside data centers.
OM4 fiber generally supports a longer SR4 reach than OM3. For standard 100GBASE-SR4 links, the commonly specified distances are up to 70m on OM3 and 100m on OM4. Actual performance depends on channel insertion loss, fiber characteristics, connector quality, and the applicable specification.
100G LR4 Uses Single-Mode Fiber
LR4 operates in the 1310nm wavelength region and uses single-mode fiber. The four wavelength channels are multiplexed together, allowing the module to transmit 100G-class data over a duplex fiber pair.
Single-mode fiber is suitable for longer distances and is commonly used in enterprise backbone networks, campus connections, and data center interconnects. A standard 100GBASE-LR4 link supports distances up to 10km when the complete optical channel meets the required specifications.
Important: An SR4 module should be connected to a suitable multimode fiber channel, while an LR4 module requires a suitable single-mode fiber channel. Using the wrong fiber type or an incompatible connector arrangement can prevent the link from establishing correctly.
5. Connector Differences: MPO/MTP vs Duplex LC
The physical connector is another clear difference between 100G SR4 and LR4. Their optical architectures require different fiber arrangements.
SR4: MPO/MTP Connector
A typical 100G SR4 module uses an MPO-12 connector. Eight optical positions are used for four transmit lanes and four receive lanes, while the remaining positions are generally unused in the standard SR4 arrangement.
MPO/MTP connectivity is common in high-density data center cabling. MPO trunk cables, patch panels, and breakout assemblies can help organize multiple parallel optical connections.
LR4: Duplex LC Connector
A typical 100G LR4 module uses a duplex LC connector. One LC fiber carries the transmitted optical signal, and the other carries the received signal.
Duplex LC connectivity is widely used in single-mode fiber infrastructure. It can be integrated into existing patch panels and fiber distribution systems without requiring an MPO parallel-fiber connection.
| Connector Detail | 100G SR4 | 100G LR4 |
|---|---|---|
| Connector type | MPO/MTP | Duplex LC |
| Optical paths | Four transmit and four receive lanes | One transmit fiber and one receive fiber |
| Fiber arrangement | Parallel fiber array | Duplex fiber pair |
| Typical cabling | MPO trunk or compatible breakout cabling | Duplex LC single-mode patch cord |
6. Transmission Distance and Application Scenarios
SR4 and LR4 are designed for different link distances. Choosing the correct module helps avoid unnecessary optical costs and reduces the risk of using an unsuitable fiber infrastructure.
| Application Scenario | 100G SR4 | 100G LR4 |
|---|---|---|
| Server-to-switch connection within a rack | Suitable for short multimode links | Usually unnecessary unless the design requires single-mode optics |
| Switch-to-switch connection within a data hall | Suitable when the distance and OM3/OM4 channel limits are met | Suitable when single-mode fiber is deployed |
| Data center interconnect | Limited by short multimode reach | Suitable for links up to 10km |
| Enterprise campus network | Generally limited to short-distance connections | Suitable for longer single-mode fiber links |
| Long-distance backbone connection | Not designed for this application | Suitable within its 10km reach and optical budget |
7. Cost and Deployment Considerations
The cost difference between SR4 and LR4 depends on the existing cabling infrastructure, required distance, transceiver pricing, and installation requirements. It is not accurate to assume that one option is always cheaper in every network environment.
SR4 deployment: A suitable OM3 or OM4 multimode fiber system is required. It is commonly used for short-distance connections inside data centers.
LR4 deployment: A duplex single-mode fiber pair is required. It is more suitable for longer connections and existing single-mode infrastructure.
Connector infrastructure: SR4 requires MPO/MTP-compatible cabling, while LR4 uses duplex LC connections.
Distance planning: The module reach must cover the actual link distance, including patch cords, connectors, and intermediate distribution points.
Equipment compatibility: Both transceivers must be supported by the host equipment, including the QSFP28 port, module coding, and required operating mode.
For a short link with suitable multimode fiber already installed, SR4 may be a practical choice. For a longer connection over single-mode fiber, LR4 is generally the more appropriate option.
8. C-LIGHT 100G SR4 and LR4 Optical Transceiver Solutions
C-LIGHT provides 100G QSFP28 optical transceiver solutions for both short-reach multimode and longer-reach single-mode applications.
100G QSFP28 SR4 100m Optical Transceiver
The C-LIGHT QSFP28 100G SR4 100m optical transceiver is designed for short-distance 100G connections over multimode fiber. It uses 850nm VCSEL technology and an MPO optical interface.
Published product features include:
QSFP28 form factor
850nm VCSEL optical technology
Four-channel parallel optical architecture
MPO connector
100G Ethernet and OTU4 dual-rate options
Data center and high-performance computing applications
Refer to the specific product datasheet for the supported fiber grade, reach, temperature range, and host compatibility.
100G QSFP28 LR4 10km Optical Transceiver
The C-LIGHT 100G QSFP28 LR4 optical transceiver is designed for 100G-class transmission over single-mode fiber with a duplex LC interface.
Published product features include:
QSFP28 form factor
100G-class aggregate data rate
Four optical channels
Up to 10km transmission distance
Duplex LC interface
Single-mode fiber connectivity
For exact wavelength values and operating parameters, confirm the datasheet for the selected part number before deployment.
For additional 100G optical transceiver options, visit the C-LIGHT optical transceiver portfolio. Product selection can be based on transmission distance, fiber type, connector, switch model, and required network protocol.
9. How to Choose Between 100G SR4 and LR4
The correct choice depends primarily on the fiber infrastructure and the required transmission distance.
Choose 100G SR4 When:
The link is within the supported short-reach distance.
OM3 or OM4 multimode fiber is available.
The network uses MPO/MTP parallel-fiber cabling.
The application involves rack-level or data-hall connectivity.
The host equipment supports the selected QSFP28 SR4 module.
Choose 100G LR4 When:
The link distance is beyond the practical SR4 multimode range.
Duplex single-mode fiber is available.
The network uses duplex LC connections.
The application involves campus links or data center interconnects up to 10km.
The host equipment supports the selected QSFP28 LR4 module.
Before purchasing a 100G optical transceiver, verify the following:
Switch or router model and port type.
Required Ethernet operating rate.
Actual fiber type: OM3, OM4, or single-mode fiber.
Link distance and total optical insertion loss.
Connector type: MPO/MTP or duplex LC.
Module wavelength, coding, and compatibility.
Operating temperature and power requirements.
10. Conclusion
100G SR4 and 100G LR4 provide 100Gbps-class connectivity through different optical transmission architectures. SR4 uses 850nm parallel optics over multimode fiber and is designed for short-distance connections, while LR4 uses four wavelength channels over duplex single-mode fiber to support links up to 10km.
SR4 is a suitable option for short data center connections using OM3 or OM4 fiber and MPO/MTP cabling. LR4 is more appropriate for longer links that require single-mode fiber and duplex LC connectivity.
The final selection should be based on fiber type, transmission distance, connector infrastructure, optical budget, and host equipment compatibility. For 100G SR4 and LR4 product selection or technical support, Contact C-LIGHT.
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