Månadsvis arkiv: januari 2018

100G Optical Transceivers: Do You Know?

As we all know, 100G is the future trend of network development. For the 100G optical transceivers market, the demand for 100G CFP optical transceivers in the telecom market in 2017 has increased by several times in the past year, and the follow-up demand for 100G optical transceiver solutions will also continue to increase. Before deciding to design a product or purchasing a 100G optical transceiver, you should understand the type and characteristics of the 100G optical transceivers to be able to make better judgments and choices. Here we will provide a comprehensive introduction about 100G optical transceivers for all of you.

100G Standard Introduction

100G interface standards include: SR4 (Short Reach), SR10, LR4 (Long Reach), ER4, ZR4; Among them, all the standard electrical signals are 1010G, For LR4 and ER4, the external optical signal is 425G. In addition, SR4 and SR10 are mainly used for short-distance transmission. The transmission distance does not exceed 100M. LR4, ER4 and CR4 are mainly used for long-distance transmission. LR4 transmission distance support 10KM, ER4 support 40KM. ZR4 supports 80KM.

100G Optical Transceiver Types

At present, the mainstream 100G optical transceiver models introduced on the market mainly include: CXP optical transceiver, CFP/CFP2/CFP4 optical transceiver and QSFP28 optical transceiver.


C for CXP represents 12 in hexadecimal, because CXP is a 12 full-duplex channel module with 12 * 10G transceivers. CXP is simple to implement, support hot-pluggable and has a smaller form factor than CFP. It supports 100GBASE-SR10 of the short-distance transmission. Under SR10 standard, it can interflow with CFP, CFP2, CFP4, and QSFP28 optical transceivers.

CFP Series (CFP / CFP2 / CFP4):

The C of 100G CFP optical transceiver stands for the number 100 (centum). It is a form factor pluggable optical transceiver, the volume is very large. CFP2 and CFP4 optical transceivers are smaller and smaller, CFP2 size is the half of the CFP half and the size of the CFP4 optical transceiver is one-half of the CFP2, supporting 40G / 100G. CFP4 optical transceiver width and power consumption has been greatly improved. The compact size is more suitable for high-density 100G Ethernet.

Note: CFP4 does not support the SR10 standard.

QSFP28 (Quad Small Form-factor Pluggable)

The 100G QSFP28 is implemented with 4 * 25 Gbps channels. In addition, the QSFP28 optical transceiver has an upgraded electrical interface that supports signals up to 28G and achieves the highest possible rate of 4 × 28 Gbit / s. 100G QSFP28 form factor sizes are smaller than the CFP4 optical transceiver, you can switch with high port density. Currently, there are four kinds of popular QSFP28 optical transceivers in the market based on different form factors: 100G QSFP28 CWDM4, 100G QSFP28 PSM4, 100G QSFP28 SR4 and 100G QSFP28 LR4. As the QSFP28 technology matures, the cost of the QSFP28 optical transceiver decreases, prompting the QSFP28 optical transceiver to become more and more popular.


The 100G form factor interface is introduced by Cisco, currently supporting 100GBASE-SR10, 100GBASE-SR4, and 100GBASE-LR4.

Types of 100G Optical Transceiver Connectors

Common connector types are: SC / LC / MPO and so on. The traditional 10G interface often use SC / LC connectors in the form of dual-core interconnect single-income hair. LC connector and SC connector are similar, but the LC connector is smaller than the SC.

MPO connector is a multiple fiber push-on / push-off all-in-one adapter. In simple terms, it is the use of parallel technology, the number of transponders in a box and the final combination of multiple optical fibers. MPO is divided into MPO12 and MPO24;

MPO 12 is 12 cores with 4 receivers and 4 transmissions, using 12 optical fibers, there are 4 idle, so the standard is SR4 / LR4.

The MPO 24 is a 24-core, 12-wire, 12-wire, 24-wire optical fiber soldered into 12-core arrays, one for transmit and one for receive. Take CFP as an example, in each array, the middle 10 * 10G optical fiber is used to transmit traffic, while the two optical fibers at both ends are idle. A total of four of the two arrays are idle, so the format is SR10. CXP module is 12 transmit and 12 receive, there is no idle line.

Take QSFP28 as an example, if the module inside uses splitters and multiplexers to 4 way 28g data modulated onto a fiber, the external transceiver is a single pay-single LC interface, so for long-distance can save fiber. This kind of optical fiber transmission technology with multiple optical fibers is called wavelength division multiplexing (WDM). Generally, short-distance uses MPO type, long-distance uses LC interface type for saving fiber.

How to Interoperate for Different 100G Optical Transceivers

The same type of 100G modules can communicate with each other. For example: CXP can interoperate with CXP; CFP-SR10 can interoperate with CFP-SR10. Different 100G module types can communicate with each other under the same standard and the same interface type. For example, CFP / CFP2 / CFP4 can communicate with the QSFP28 in the same signal system and the same interface type. For example, CFP2-LR4 with the duplex LC interface can interoperate with QSFP28-LR4 when the interface is duplex LC.

CXP module can interoperate with CFP / CFP2 / CFP4 / QSFP28 optical transceiver only when SR10 is adopted. When CXP and CFP2-SR10 are interoperated, the CXCPs must be screened out 1, 12, 13 and 24 at the edge of the CXP. Because CXP is 12 channels, CFP2 is 10 channels.


From the development trend, QSFP28 optical transceiver and CFP series optical transceiver are 100G network hot solutions, and the use of CXP will be less and less. The following table summarizes the commonly-used 100G optical transceiver types.

Types Standard The Largest Transmission Distance Connector Channel Wavelength Fiber Types
CXP SR10 100m MPO24 12*10G 850nm MMF

(CFP4 doesn’t support SR10)

SR10 100m MPO24 10*10G 850nm MMF
LR4 10km Dual LC 4*25G 1310nm SMF
ER4 40km Dual LC 4*25G 1310nm SMF
ZR4 80km Dual LC 4*25G 1310nm SMF
QSFP28 SR4 100m MPO12 4*25G 850nm SMF
LR4 10km LC 4*28G 1310nm SMF
ER4 40km LC 4*25G 1310nm SMF
ZR4 80km LC 4*25G 1310nm SMF
CWDM4 2km Dual LC 4*25G 1310nm SMF
PSM4 2km MPO 4*25G 1310nm SMF
CPAK (Cisco 100G) SR10/SR4/


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The Key Technology for 100G CFP/CFP2 LR4 Optical Transceivers

The form factors of 100G CFP optical modules can be divided into CFP/CFP2/CFP4, and they can be divided into 100GBASE-SR10, 100GBASE-LR4, and 100GBASE-ER4 according to the transmission distance. All optical module transmission distance is decided by the optical output signal OSNR tolerance and chromatic dispersion tolerance decision. Generally speaking, it is determined by the laser and its drive performance.

At present, there are two types of optical modulation methods for implementing CFP 100GBASE-LR4 transmission in the mainstream market. One is a Direct Modulation Laser Modulation (DML) mode, that is, a direct modulation laser. And another one is an Electlro -Modulation Modulation (EML) mode, that is, modulation laser.

The following post will briefly introduce some key technical points of using the TEC circuit and EML modulation mode to realize the 100G CFP / CFP2 LR4 optical transceivers.

1. TEC Circuit

EML lasers need to work at a certain wavelength, the temperature jump will lead to a temperature drift effect, resulting in wavelength instability, drifting, so the stable working conditions of the laser is a relatively stable operating temperature (steady wavelength) This requires that we have to provide a high-precision TEC circuit, that is, a semiconductor refrigerator. The TEC is actually a PN junction made of two semiconductors of different materials. When a direct current passes through the PN junction, electrons and gaps in the two materials The hole produces an endothermic or exothermic effect during movement across the PN junction, effecting a cooling or heating laser effect, and TEC heating or cooling can be controlled by changing the current direction and size.

A high-precision op amp compares the target temperature we set with the temperature fed back by the thermistor, and the error voltage is amplified by a high-gain amplifier while compensating for the network’s contribution to the hot and cold ends of the laser The phase delay is compensated to drive the H-bridge output to control the size and direction of the TEC current. When the temperature drops below our target temperature, the H-bridge will reduce the TEC current or change the direction of the TEC current for cooling. Conversely, the final control loop Road will reach a dynamic equilibrium, the temperature will stabilize. Among them, the compensation circuit is the most critical part of the TEC temperature control circuit, that is PID proportional integral differential adjustment compensation network, which determines the TEC controller response speed and regulation accuracy.

2. EAM Regulation

EML lasers are essentially integrated devices for EAM (Electroabsorption Modulator) and LD (DFB lasers). The key core is the EML chip, which is the core of an electro-absorption modulated laser based on the Stark Effect (QCSE) design. The DML laser modulates the light intensity by directly controlling the laser current, which always works in an unstable state and is easily influenced by the outside world. In contrast, the EML laser mainly controls the optical signal by controlling the EAM, the light source will be more stable, and the transmission Relatively speaking, the characteristics and transmission effects will be better, especially in high frequency modulation and long distance.

In application, the LD pin injects a constant current to the laser to make the laser emit light, and the EAM changes the ratio of the laser light to obtain different intensity of light. The development of Ethernet technology has gone through a number of development stages from low speed to high speed.

The rate of development from 1M, 10M, 100M and 1G to 10G and 100G has led to more demand for it to evolve to a higher rate. I believe there will be new technologies have emerged to meet the growing demand for optical modules.

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QSFP28 PSM4, QSFP28 SR4 and QSFP28 LR4: Which One to Choose

The appearance of QSFP28 optical transceivers is the same as that of 40G QSFP + optical transceivers. The difference is that QSFP28 optical transceiver can transmit optical signals up to 100G. Therefore, QSFP28 optical transceivers have become the mainstream of 100G optical transceivers and are the preferred solution for 100G network upgrade. There are mainly four kinds of popular QSFP28 optical transceiver modules: QSFP28 SR4, QSFP28 LR4, QSFP28 CWDM4 and QSFP28 PSM4. In this article, we will focus on describing the differences between QSFP28 PSM4 optical transceiver, QSFP28 SR4 optical transceiver, and QSFP28 LR4 optical transceiver.


Difference between QSFP28 PSM4, QSFP28 SR4 and QSFP28 LR

1. Different Transmission Methods

As we all know, QSFP28 optical transceivers usually have four transmission channels, and each channel data rate is 25Gbp. This transmission method is very similar with 40G QSFP+ optical transceiver transmissions. QSFP28 SR4 optical transceiver and QSFP28 PSM4 optical transceiver both use 12-way MTP interface, realizing the 8-way fiber bidirectional 100G transmission. But the QSFP28 LR4 optical transceiver cannot do this, which is transmitted at the same time in two LC duplex fibers in one direction for 100G transmission.

2. Different Transmission Media and Transmission Distance

The QSFP28 SR4 optical transceiver operates at 850nm and is used with OM3 or OM4 multimode optical fibers and OM3 optical fiber. When using together, the maximum transmission distance of up to 70m, and OM4 fiber transmission distance up to 100m.

The QSFP28 LR4 optical transceiver is usually used with single-mode fiber, which operates at 1310 nm and has a maximum transmission distance of up to 10 km.

The QSFP28 PSM4 optical transceiver is generally used with a 12-way MTP interface and single-mode optical fiber with a transmission distance of up to 2km.

3. Different Cabling Structure

Optical transceiver transmission has playing a very important role in the optical fiber routing. Because the QSFP28 SR4 optical transceiver and the QSFP28 LR4 optical transceiver are used for short-distance transmission and long-distance transmission respectively, their wiring structures are different. The former requires multi-fiber cabling based on a 12-way MMF MTP interface, while the latter requires only a traditional two-fiber SMF cabling. In this case, the conversion between multimode fiber and single-mode fiber is very complicated because they use a completely different wiring structure.

Although the QSFP28 PSM4 optical transceiver operates in single-mode fiber, its wiring structure is the same as that of the QSFP28 SR4 optical transceiver. Using the QSFP28 PSM4 optical transceiver saves conversion costs between multimode and single-mode without changing existing cabling structures.

4. Different Working Principle

(1) Working Principle of QSFP28 PSM4 optical transceiver:

The QSFP28 PSM4 optical transceiver works in much the same way as the QSFP28 SR4 optical transceiver. The difference is that the QSFP28 PSM4 optical transceiver operates on single mode fiber while the QSFP28 SR4 optical transceiver operates on OM4 multimode fiber.

(2) Working Principle of QSFP28 SR4 optical transceiver:

QSFP28 SR4 optical transceiver transmits signals at the transmitting end; the electrical signals are converted into optical signals by the laser array and then transmitted in parallel on the ribbon multimode fiber. Upon reaching the receiving termination, the photodetector array converts the parallel optical signals into parallel Electrical signals.

(3) Working Principle of QSFP28 LR4 optical transceiver:

QSFP28 LR4 optical transceivers are typically used with LC single-mode fiber optic cables to convert 4 25Gbps electrical signals into 4 LAN WDM optical signals and then multiplexed into a single channel for 100G optical transmission. At the receiving end, the module demultiplexes the 100G optical inputs into 4 LAN WDM optical signals, which are then converted into 4 electrical signal output channels.

Types Connector Fiber Type Transmission Distance Wavelength Cabling
QSFP28 SR4 MPO MMF 100m 850nm 12-Way MPT
QSFP28 LR4 LC SMF 10km 1295.56/ 1300.05/1304.58/1309.14nm Duplex LC
QSFP28 PSM4 MTP SMF 2km 1310nm 12-Way MPT


The QSFP28 SR4 optical transceiver is suitable for 12-way MTP fiber cabling systems and also for short-distance transmission of OM3, OM4 multimode fiber. The QSFP28 PSM4 optical transceiver is also suitable for transmission with 12 MTP interfaces, but it is suitable for use with single-mode fibers and can transmit distances up to 500m. QSFP28 LR4 optical transceiver is for data transmission up to 2km. If you want to know more about 100G optical transceiver solution, you can visit Gigalight official website.

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