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The Top 10 Topics of 40G transceivers You Should be Reading

40G is gradually taking over the 10G network market as the latter is becoming obsolete due to slow speed and other constraints. So, it is worthwhile to study the 40G transceivers in detail. Cozlink, for you avid learners out there, has investigated and collected the top 10 main topics about 40G transceivers. Here is a brief overview of all 10 of them.

Topic 1 - The Definition, Package and Type of 40G transceivers.

(1) Definition

A 40G optical module is a derivative product capable of delivering high density ports and appreciable data transmission speed. It is a high performance, hot-pluggable interconnect solution finding its rampant use in data centers. An integrated model of four independent transmit and receive signals work in consonance to deliver the high density but power-efficient 40G Ethernet connectivity. The 40G applications, apart from in data centers, are also being used widely in high performance computing networks, enterprise core and distribution layers, and telecom operators. 

(2) Package

40G optical modules are popularly categorized into – CFP, QSFP and QSFP+ types.

40G CFP Optical Transceiver 

The 40G CFP optical transceiver is designed to complement single-mode fiber on a 40G Ethernet link. It is equipped with digital diagnostics provided via the MDIO interface as mentioned in CFIO MSA. In addition to it, the 40G optical transceiver is made RoHS-6 compliant to ensure its environment-friendliness.

40G QSFP (Quad Small Form-factor Pluggable) optical module 

The 40G QSFP optical module is basically composed of four independent full-duplex transceiver channels, thus, it can rightly be called as a four-channel small pluggable optical module. The data transfer rate achieved by this four-channel interface is up to 40Gbps. It is four times denser than a typical XFP optical module and similarly, three times denser than an SFP+ optical module. This fiber connectivity solution is quite helpful in achieving high density and high speed transmission.

40G QSFP + optical module 

A typical 40G QSFP+ optical module basically borrows its design from QSFP, thus, it is a better alternative to SFP+ optical module and has higher port density and lower system cost as compared to the latter. 40G QSFP + optical module is made as per the guidelines mentioned in SCSI, 40G Ethernet, 20G / 40G Infiniband and other standards. It has four data transmission channels each of which transmits data at the rate of 10Gbps, thereby, delivering the 40Gbps speed while working in a coordinated fashion. This optical module has two main interfaces: LC and MTP / MPO (below), used in single-mode applications and multi-mode applications.


Since CFP module was not being liked due to the bigger size, the small sized QSFP and QSFP+, therefore, have become very popular and are being widely used in the market.

(3) Main Type and price from Cozlink

Part No.




40GBase-SR4 QSFP+ 850nm 150m MPO MM Duplex Transceiver



40G QSFP+ IR4 1270~1330nm 2km Transceiver LC SM Duplex Optical Module



40GBase-LR4 QSFP+ Transceiver 10km 1310nm LC SM Duplex Optical Module



40G QSFP+ ER4 40km Transceiver 1270~1330nm LC SM Duplex Optical Module



40G QSFP+ CSR4 Transceiver 850nm 300m over OM3 Fiber MM Duplex for 12-fiber MPO/MTP Connector



40G CFP LR4 1310nm 10km Transceiver SC SM Duplex DDM Optical Module


Topic 2 - Characteristics and Applications of 40G optical transceivers

(1) Characteristics

The main characteristics of 40G optical are:

1. These promote rational and effective use of the transmission band. Their spectrum efficiency is relatively high;

2. These effectively reduce the cost and offer more economical networking solution than any other Metropolitan area network;

3. 40G optical transceivers simplify the network architecture by reducing the number of parts. It is worth mentioning that in the metro backbone network applications, the scheduling and integration promised by 40G optical module is far better than the four 10G system. Such integration of four channels can save room area, reduce equipment stack and improve single-node equipment as well as other functionalities, such as, bandwidth management capabilities and scheduling capabilities 

4. In a 40G optical module, usually, a single wavelength can handle multiple data connections. The core network function will be greatly enhanced making it possible for the businesses to undergo expansion effortlessly.


(2) Applications

40G SR4 QSFP + optical module are mainly used to enable the data center network equipment between the connections. It is mainly suitable for short-distance transmission and is used in the data center with OM3 / OM4 ribbon cable connected with Ethernet switches. The  40G LR4 QSFP + optical module and 40G LR4 PSM optical module are suitable for long-distance transmission where the former requires only two single-mode fibers and thus, is cost-effective, while the latter requires eight single-mode fibers, with a higher port density, and can be arranged in a minimal cost.

Topic 3 - The difference between MTP/MPO interface and LC interface 40G QSFP+ transceivers

Currently, there are various types of 40G transceivers options available in the market. All these can be broadly categorized as MTP/MPO and LC 40G transceivers on the basis of connecting interfaces.

Generally, the 40G QSFP+ transceivers with LC interface are used for long-distance transmission over single-mode fiber (SMF), and those with MTP/MPO interface are utilized for short distance transmission over multimode fiber (MMF).

Besides, in the 40G QSFP+ transceivers with LC interface you can find that at the transmit side, 4-channel 10G serial data streams are passed to laser drivers. The laser drivers control directly modulated lasers (DML) with wavelengths. Then the output of the four DMLs is optically multiplexed to a SMF through an industry-standard LC connector, while combining these together as a 40G optical signal. At the receiving end, the 40G optical signal is split into 4 unique channels delivering 10G connectivity. The light of each wavelength is first collected by a discrete photodiode and then amplified by a TIA as an electronic data output. During this process, a pair of single-mode fibers is required for a 4-wavelength CWDM multiplexer and de-multiplexer.


40G QSFP+ transceivers with MTP/MPO interface—At the transmitting end, by using a laser array, the transmitter converts the parallel electronic input signal into a parallel optical signal. Then, the parallel optical signal is transmitted in parallel through the multimode fiber band. At the receiving end, the parallel optical input signal is converted into a parallel electrical output signal through the photodetector array.


Topic 4 - How to choose the right fiber optic cable for the 40G QSFP + transceiver?

The 40G transceivers have usually two kinds of interfaces: MPO and LC. 40G QSFP+ transceivers support short distance connections and are armed with MPO interface. The other 40G transceivers of QSFP+ type delivering long distance transmission up to 10 km usually employ LC interface. So, MPO patch cords and LC patch cords with OM3, OM4 multimode fiber or single-mode fiber are the correct cabling options for 40G QSFP+ transceivers.

40G QSFP+ to 40G QSFP+ cabling options:

a. For distance up to 100m, the 40GBASE-SR4 QSFP+ transceiver can be used with OM3 fiber patch cable attached with an MPO on each end. 

b. For the distance of 150m, the 40GBASE-SR4 QSFP+ module can use OM4 patch cords with an MPO on both ends.

c. For distance up to 10km, the 40GBASE-LR4 QSFP+ transceiver can be used with single-mode fiber with LC connectors.

40G QSFP + to 10G SFP + cabling

To connect 40G QSFP+ to 10G SFP+ transceiver, the ideal arrangement is a fan out patch cable that has an MTP connector at one end and 4 LC duplex connectors at the other end.

Topic 5 -The introduction of three kinds of optical devices under 40G applications

An application using 40G network equipment comprises mainly of three kinds of optical devices - 40G QSFP + optical module, 40G high-speed cable and 40G active cable.

1. 40G QSFP + optical module

The 40G QSFP+ optical modules are mainly of two types - 40GBASE-LR4 QSFP + optical module and 40GBASE-SR4 QSFP+. Of these, the LR4 model can be inducted into the network with the help of LC fiber connectors. The 40GBASE-LR4 optical module is used mainly between the data centers and the internet exchange point. When connected with a single mode fiber, this transceiver can deliver data connectivity up to a distance of 10km.

The 40GBASE-SR4 QSFP + optical module is provided with MPO / MTP fiber connector interfaces. This optical module can be used with multimode OM3 / OM4 fiber to achieve 100m (OM3) and 150m (OM4) transmission links. These can also be used to achieve the interconnection between the two Ethernet switches.

2. 40G high-speed cable

A copper cable and two 40GQSFP + optical transceiver are connected to form a 40G high-speed cable. This high speed cable is suitable for short distance wiring in the data center. The maximum transmission distance provided by it is 5m.

3. 40G active fiber optic cable

40G active fiber optic cable basically comprises of a fiber and two 40GQSFP + optical modules. Transmission link delivered by an active 40G fiber optic cable is 15m.

Topic 6 - What are the differences between 40GQSFP+ transceivers and 40G AOC cable? 

In 40G transmission, for distance less than 100 m, the 40G QSFP+ AOC and 40G SR4 QSFP+ transceiver deliver nearly the same performances. But for the distance more than 100m, the 40G QSFP+ - SR4 proves to be the better option as the AOC option does not show the desired performance output.

The 40G QSFP+ AOC comes with factory pre-terminated connectors, while 40G QSFP+ SR4 transceivers can accept additional MPO connectors and fiber optic cable. As a result, 40G QSFP + AOC performs better in instances of repeated plugging common in daily use as compared to 40G QSFP + SR4 transceivers. Additionally, with no insertion loss and return loss, it can ensure better reliability. Moreover, the price of 40G QSFP + SR4 transceiver is usually higher than that of 40G QSFP+ AOC. To accomplish the connection, additional cost for patch cables is also to be considered for interconnection utilizing 40G QSFP+ SR4 transceivers.

Topic 7 - Which 40G QSFP+ Transceivers Can Be Used for 4x10G?

40GBase-SR4 and 40Gbase-CSR4 are the types of transceivers that come with MTP/MPO interface. Thus, these transceivers can be used in a 4 x 10G arrangement. Understanding the working of QSFP 40GBase – SR4 transceiver can help you know why it is so. In a QSFP 40GBase-SR4 transceiver, four electronic input signals that convert 10G into parallel optical signals are sent to the transmitters of four parallel fibers. Then, the parallel optical signals are converted into parallel electrical signals by the use of a photo detector array and transmitted to the receiver over another 4 parallel fiber strands.

This way the QSFP-40G-SR4 and QSFP-40G-CSR4 transceivers can be easily broken down to 4x10G connections. Each 10G signal lane of QSFP-40G-SR4 is compliant with IEEE 10GBASE-SR specifications. By using MTP - LC cable or MTP cable and MTP - LC breakout patch panel that can be connected with QSFP-40G-SR4 and four 10Gbase - SR modules, the 10G / 40G connection is achieved.

Topic 8 - How to Install a 40G Transceiver?

In general, there are 8 steps to install a 40G transceiver. I will take QSFP+ for example:

Step 1: Wear an ESD wrist strap that is connected to a properly grounded point on the chassis or the rack.

Step 2: Remove the QSFP+ transceiver module out of its protective packaging.

Step 3: Check the label of the QSFP+ transceiver to verify its compatibility with the intended network.

Step 4: Remove the optical bore dust plug of QSFP+ transceivers and keep it safe.

Step 5: For transceivers equipped with a bail-clasp latch

a. Keep the bail-clasp aligned in a vertical position.

b. Align the QSFP+ transceiver in front of the module’s transceiver socket opening and carefully slip the QSFP+ transceiver into the socket until good connection is set. This is how it is done:


Step 6: For QSFP+ transceivers equipped with a pull-tab:

a. Hold the transceiver while keeping the label on the top.

b. Align the QSFP+ transceiver and the port in one line and then carefully slip the QSFP+ transceiver into the port until it connects with the socket electrical connector correctly.

Step 7: Use your thumb to press firmly the front of the QSFP+ transceiver to fit it in the module’s transceiver socket. Like this:


Step 8: Please note that you must reinstall the dust plug on the QSFP + transceiver ribbon before you are ready to connect the network interface cable and do not take out unless the connection is required.

Topic 9 - How Does QSFP-40G-UNIV Transceiver Work?

QSFP-40G-UNIV transceiver is capable of carrying 40G signals over a duplex fiber cable. Speaking about traditional QSFP 40G-SR4, this can work with eight fiber cable arrangement where each cable does the job of transmitting or receiving the 10G signals to enable 40G link. Refer the picture below:


In this image, we can see that QSFP-40G-SR4 transceiver requires fibers four times more to achieve 40G connection than what an SFP-10G-SR transceiver requires for delivering 10G connection. However, one can use a QSFP-40G-univ transceiver for 40G connectivity on the same duplex fiber as the sfp-10g-sr transceiver. In the process, the four transmitters convert four 10G electrical signals into four distinct 10G optical signals. This is followed by four 10G optical signals multiplexing into a 40G signal which is transmitted over a dual fiber cable, and further de-multiplexed into four separate 10G optical signals. Finally, the resultant four light signals will pass through receiver signals and are converted into electrical signals.

Topic 10 - Why 3rd party 40G QSFP Optical Transceivers Are Preferred Over OEM?

The demand for 40G QSFP transceiver is resulting with the rapid developments happening in optical communications industry. Due to low cost and easy interchangeability, third-party 40G QSFPs with good compatibility and stability are preferred by some customers. Some of the advantages of third-party 40gbps transceivers are as below:

(1) Low price

Branded optical products you buy are very expensive because these include the cost of testing and verification, and are priced at high profit margin. Third party QSFP optical transceivers do not have same quality testing procedures; still, their compatibility is proved to be unquestionable. It is because of better compatibility and comparable quality, the 3rd party 40G QSFP optical transceivers are in high demand.

(2) Quality and Reliability

If the transceiver is from a reliable third party vendor, its quality is as good as the original. Additionally, third party vendors also provide warranty and support on the products they sell. Since the third party vendors specialize in optical transceivers and other products, they score high on customer satisfaction.

(3) More for 40G QSFP transceiver

Third-party optical transceivers can be used interchangeably with any other brand of transceivers, thus, a network manager can have more options for populating the data center and enterprise networks.

If you are looking for 40G transceivers compatible with brands preferred by you, Cozlink is the perfect place to buy these. The transceivers produced by it are compatible with a wide variety of brands such as, Cisco, Genetic, Juniper Networks, Arista Networks, Brocade, HPE, Dell, Intel, IBM, etc. 

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