Ultimate Guide of QSFP-40G-SR4 and QSFP-40G-LR4

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This post was most recently updated on January 24th, 2022

The 40GBASE QSFP (Quad Small Form-Factor Pluggable) optical transceivers offers a wide variety of cost-effective, high-density, and low-power 40 Gigabit Ethernet connectivity options for high-speed data centers. This article will introduce two of the most popular types of 40GBASE QSFP transceivers, including how they work, their technical specification.

Why Is Demand for 40g QSFP+ Transceivers Increasing? 

Communication technology is developing faster and faster today. However, the development of new technology needs a high-speed information courier carrier. Due to the low loss and strong anti-interference ability of optical fiber communication, it has rapidly replaced coaxial cable in the past few decades, comprehensively improved the overall level of the communication network system and become the backbone network of communication all over the world.

As the backbone network of the whole telecommunication network, the transmission rate of optical fiber communication systems is developing continuously. The technical development of optical devices and optical fiber communication networks complement each other. Various optical communication devices also develop rapidly with the optical communication network technology. However, the 10Gbit/s communication system will gradually not meet the needs of optical communication. A new generation of optical fiber communication systems and higher rate optical modules have become the focus of attention. 100G and 40G modules have become the most popular products in the market. With the increase of data center speed, the 40G QSFP module accounts for most of the growth share of the enterprise network and data center application market.

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With the rapid growth of the 40G QSFP optical module market and 40G optical transceiver replacing the 10G optical transceiver as the mainstream, it is of great significance to study 40G QSFP optical modules. Next, this article will introduce the two most popular types of 40GBASE QSFP portfolio in detail.

What is QSFP-40G-SR4 Transceiver and How It Works

QSFP-40G-SR4 is recognized as the most widely-used and most popular 40G transceiver for short distance transmission. It supports transmission distance of 100m and 150m on OM3 and OM4 multimode fibers. QSFP 40G SR4 is a parallel optical transceiver module, terminating with MTP/MPO connectors and enabling 40G high-bandwidth over 12-fiber parallel fiber. 

How does the 40G SR4 work? 40G QSFP SR4 has four parallel transmission channels to drive four 10G rate VCSEL lasers respectively. A single channel generates the 10G differential electrical signal, which is input into the laser driving chip through a pair of differential data input pins. After a series of processing of the internal circuit of the driving chip, it generates the bias current and modulation current signal required by the laser, so as to generate the 10G optical signal output matching the input signal.

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Figure 1- QSFPTEK Cisco Compatible QSFP-40G-SR4 Transceiver

The QSFP 40G SR4 enables interoperability with four 10GBASE-SR transceivers in a breakout cabling connectivity. The 4x10G connectivity is achieved using an external 12-fiber parallel to 2-fiber duplex breakout cable, which connects the 40GBASE-SR4 module to four 10GBASE-SR optical modules. QSFPTEK QSFP-40G-SR4 is optimized to guarantee interoperability with any IEEE 40GBASE-SR4 and in 4x10G breakout cabling connectivity with the 10GBASE-SR transceivers.

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QSFP-40G-SR4 Tech Specification

High Channel Capacity: 40 Gbps per module.  

Up to 11.1Gbps Data rate per channel.  

Maximum link length of 300m links on OM3 multimode fiber or 400m links on OM4 multimode fiber.  

High Reliability 850nm VCSEL technology.  

Electrically hot-pluggable.  

Digital diagnostic SFF-8436 compliant.  

Case operating temperature range:0°C to 70°C.  

Power dissipation < 0.7 W.  

Compliant to IEEE 802.3ba.  

RoHS Compliant.

What is QSFP-40G-LR4 Transceiver and How It Works

While the QSFP 40G SR4 is designed for short distance transmission, the QSFP-40G-LR4, on the other hand, is for long-haul transmission. It supports transmission distance up to 10km over single-mode fiber. Though they use the same multi-lane technology, the LR4 differs in that instead of using a single fiber strand for each lane, it multiplexes all four wavelengths sending signals into one fiber strand and all four wavelengths receiving signals into another single fiber strand. 

Figure 2- QSFPTEK Cisco Compatible QSFP-40G-LR4 Transceiver

QSFP-40G-LR4 Tech Specification

4 CWDM lanes Mux/Demux design.

Up to 11.1Gbps Data rate per wavelength.  

Up to 10km transmission on SMF.  

Electrically hot-pluggable. 

Digital Diagnostics Monitoring Interface.  

Compliant with QSFP+ MSA with LC connector.  

Case operating temperature range:0°C to 70°C. 

Power dissipation < 2.5 W.  

Compliant to IEEE 802.3ba.  

RoHS Compliant.


Under today’s high-performance data network rapid developments, 40G QSFP+ transceivers guarantee high-density, cost-effective and low-power 40G data transmission links. Full Understanding of the various types of 40G QSFP+ optical transceivers is of great importance when building or upgrading your data center. QSFPTEK company can supply not only a wide variety of high-performance and tested-assured 40G QSFP+ transceivers, but also provide customized technical solutions and help you build a reliable and easy to manage network system.