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What are the types of QSFP28 fiber optical transceivers and how to test them?

Date: 2019-10-16 10:45:00 From: C-light Onclick:

The continuous and rapid development of the Internet, people's desire for higher-speed optical networks, promote the vigorous development of the entire optical communications industry, while vigorously promoting independent research and development and innovation breakthroughs of many core technologies including optoelectronic device technology. The 100G optical transceivers are the product of this era of big data.

According to different packaging methods, 100G optical transceivers mainly include CFP/CFP2/CFP4, CXP and QSFP28. Among them, CFP/CFP2/CFP4 and CXP are the packaging methods of early 100G modules.The QSFP28 module is smaller than other 100G modules, so it is receiving more and more attention. Therefore, QSFP28 is the mainstream package of 100G optical transceivers.The principle of the 100G QSFP28 module is similar to that of the 40G QSFP+ module, which transmits 100G optical signals in 4×25 Gbps.

What are the types of QSFP28 fiber optical transceivers?
1.100G QSFP28 LR4 module

For 100G long-distance transmission, IEEE also developed the 100GBASE-LR4 standard for 100G QSFP28 modules. The 100G QSFP28 LR4 module uses four fiber channels. The difference is that it introduces WDM technology, which can multiplex the different wavelengths of four fiber channels onto one fiber for transmission.Therefore, the 100G QSFP28 LR4 module uses the duplex LC interface, which can be used up to 10km when used with single mode fiber.

2.100G QSFP28 SR4 Module

Since most of the data centers use multimode fiber, IEEE has developed 100GBASE-SR4 for 100G QSFP28 modules, which supports multimode fiber short-distance transmission applications.100G QSFP28 SR4 module uses MTP interface (8-core), the transmission distance when used with OM3 multimode fiber is 70m, and the transmission distance when used with OM4 multimode fiber is 100m.

3.100G QSFP28 PSM4 module
The 100G-PSM4 is a multi-source protocol (MSA) developed primarily for 100G QSFP28 modules,which mainly used for medium and long-distance transmission applications. 100G QSFP28 modules uses an MTP interface (8-core) and can transmit up to 500m when used with single-mode multi-core fiber.

4.100G QSFP28 CWDM4 module
100G-CWDM4 is also a multi-source protocol (MSA). The 100G QSFP28 CWDM4 module also introduces WDM technology,which  adopts duplex LC interface. When used together with single-mode fiber, the transmission distance can reach 2km. 


What are the advantages of the QSFP28 module?
1.Power consumption
The power consumption usually does not exceed 3.5W during operation, while the power consumption of other 100G modules is usually between 6W and 24W. So the QSFP28 optical module consumes much less power than others.

2. Cost    
The current data center is mainly 10G network architecture. Its interconnection solutions are mainly 10GBASE-SR optical modules and duplex LC multimode optical fiber jumpers. If you upgrade directly to the 40/100G network based on the existing 10G network architecture, It will save a lot of time and cost. Therefore, one of the main interconnect trends in the data center is to upgrade from a 10G network to a 40/100G network without changing the existing duplex multimode infrastructure network architecture. In this case, the MPO/MTP branch cable is undoubtedly the ideal solution for 10G to 40/100G upgrades.

100G transmission technology is used to provide the data center with the connection between the rack switch and the core network, which increases the panel bandwidth density by 150% compared to the 40G QSFP solution.


 How to test QSFP28 optical transceivers?
Test performance is an essential step when using QSFP28 modules that is composed of a transmitter and a receiver. The QSFP28 is tested and is mainly divided into tests for transmitters and receivers.

1.The transmitter part
The quality of the input signal used to test the transmitter must be good enough. In addition, the quality of the electrical measurements must be confirmed by jitter measurements and eye diagram measurements. Eye diagram measurements are a common method of checking the transmitter output waveform because the eye diagram contains a wealth of information that reflects the overall performance of the transmitter.
The output optical signal of the transmitter must be measured by eye diagram test, optical quality indicators such as optical modulation amplitude and extinction ratio.

2.The receiver part
Unlike test transmitters, the quality of the optical signal must be sufficiently poor when testing the receiver to create a light stress eye diagram of the worst signal. This worst optical signal must be calibrated by jitter measurement and optical power testing.There are three main types of tests.

(1)Eye diagram test is usually achieved by the depth of the bit error rate.
(2)Jitter test to test different types. 
(3)Jitter tracking and tolerance, test the tracking of jitter by the internal clock recovery circuit.

All in all, testing fiber optical transceivers is a complex task, which is also an indispensable step to ensure good performance. As a widely used measurement method, eye diagram measurement can effectively test the transmitting end. The receiver test is more complicated and requires more test methods.

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