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40G SR4 QSFP module is a short-range multimode short wave transceiver based on a 4 x 10G parallel optical architecture, “SR” stands for short reach, and is currently one of the most representative 40G Ethernet solutions. It is transmitted in parallel on an 8 fibers with 4 transmitters and 4 receivers through the MPO-12 UPC interface, with a total bandwidth of 40Gbps.
Technical Specifications
| Model | 40G QSFP+ SR4 |
| Package type | QSFP+ (hot swappable) |
| Transmission rate | 41.25Gbps (4 x 10.3125Gbps NRZ) |
| Interface type | MPO-12 / MTP-12 UPC |
| Fiber optic type | MMF |
| Transmission distance | OM3: 100m / OM4: 150m |
| Working wavelength | 850nm VCSEL array |
| Power consumption | <1.5W |
| Optical channel architecture | 4 send 4 receive parallel (using 8 cores) |
| Operating Temperature | Commercial grade: 0℃ to 70℃;Industrial grade: -40℃ to+85℃ |
| Electrical interface speed | 4 × 10.3125Gbps NRZ |
| Digital diagnosis | Support DOM/DDM functions |
| Protocol standard | IEEE 802.3ba 40GBASE-SR4 |
Key Technical Parameters
| Item | Value | Remark |
| Transmitting optical power (per channel) | -7.1 ~ +1.9 dBm | VCSEL laser output power |
| Receiving sensitivity (per channel) | < -10.3 dBm | PIN detector receiving capability |
| center wavelength | 840-860nm | 850nm band range |
| Power budget | About 3.2-3.5 dB | Maximum allowable loss of the link |
| extinction ratio | >3 dB | Signal quality indicators |
| Maximum input power | 2.4 dBm | Avoid overloading the receiver |
| Bit Error Rate (BER) | 1E-12 | Industry standard requirements |
Difference SR4 vs eSR4 vs LR4 vs PSM4
SR4 short wave transceiver has a clear positioning in the QSFP 40G family, and the following table compares its core parameters with similar solutions:
| Model | 40G QSFP+ SR4 | 40G QSFP+ eSR4 | 40G QSFP+ LR4 | 40G QSFP+ PSM4 |
| Technical Architecture | 4×10G NRZ Parallel | 4×10G NRZ Parallel Enhanced | 4×25G NRZ + WDM | 4×10G NRZ Parallel |
| Transmission medium | MMF | MMF | SMF | SMF |
| transmission distance | 100m (OM3) / 150m (OM4) | 300m / 400m | 10km | 2km |
| Interface and number of cores | MPO-12 (8 fiber) | MPO-12 (8 fiber) | Duplex LC (2 fiber) | MPO-12 (8 fiber) |
| power consumption | <1.5W | <1.5W | <3.5W | <2.5W |
| Standards and Core Applications | IEEE 802.3ba | Fact standard (widely used domestically in China) | IEEE 802.3ba | Fact standard |
40GBE QSFP Application
Short Distance Interconnection Within Data Centers
(40G Switch ↔ 40G Switch Direct Connection）
Scenario description: Using MPO trunk cables, address the high-speed data transmission requirements between devices within the data center, such as Spine Leaf architecture and interconnection between cabinets/racks
Technical advantages:
- Mature and stable: 40GBASE-SR4 is an IEEE standard with good interoperability among multiple vendors
- Cost optimal: Multimode VCSEL technology is mature, with lower module and fiber costs compared to single mode solutions
- Low power consumption: 40G SR4 QSFP module power consumption is less than 1.5W, suitable for high-density deployment
- High density: QSFP+ packaging supports high-density port deployment
40G to 4x10G Breakout Application
(QSFP+ to SFP+)
Scenario description: Using MPO brakout cables, a 40G port is split into four 10G ports to connect multiple 10G devices, achieving flexible network deployment and cost savings.
Notes:
- MPO breakout cables are key accessories used to achieve physical splitting
- The QSFP+ port on the 40G side needs to support “breakout”
- Not all switches support breakout, please refer to the equipment manual in advance for confirmation.
Mixed Networking with 10G Networks
- Scenario description: Within the data center, SR4 QSFP modules are mixed with 10GBASE-SR devices for deployment, achieving a hybrid network of 40G core network and 10G access network.
- Compatibility: The SR4 QSFP module is compatible with the SFP 10GSR 850 module in branch mode – through MPO to LC breakout cable, the 4 x 10G channels separated from the 40G SR4 port can be directly connected to standard 10GBASE-SR SFP module SFP-10G-SR.
Enterprise Core Network
- Scenario description: Deploy 40G backbone links in campus networks or enterprise data centers, connect aggregation layer switches, and enhance overall bandwidth
- Advantage: Building a high bandwidth enterprise core network to meet the growing demand for business traffic
Conclusion
QSFP QSFP+ SR4 is currently the most mature and popular short-range 40G optical module solution. It adopts 4-channel parallel technology and MPO interface, with the advantages of low power consumption and high density, becoming the standard for short-range interconnection within data centers. Its plug and play features and wide compatibility with mainstream switch devices make it the cornerstone of building 40G Ethernet.
| Model | QSFP-40G-SR4 |
| Positioning | The most mainstream 40G short distance transmission solution in the industry |
| Core technology | 4 x 10G NRZ parallel architecture + 850nm VCSEL array + MPO-12 interface |
| Transmission distance | OM3:100m / OM4:150m |
| Power consumption | <1.5W |
| Core advantage | Mature standards, good interoperability among multiple vendors, optimal cost, and support for branching |
| Typical Applications | Data center Leaf Spine interconnection, 40G → 4 x 10G branch connections, enterprise core network |
