Today we are going to talk about a segmentation closely related to the 5G theme – 100G optical transceivers. Recently, there has been a new landmark theme, which is ”100G optical transceiver”, what are the reasons?
What Are 100G Optical Transceivers?
1. The first explain is that the 100G ”G” refers to the optical signal transmission rate of units, rather than the 5G ”G” (Generation, 5th generation mobile communications).
2. Optical transceiver is one of optical devices to achieve high-speed conversion between optical signals. It includes the optical receiver, optical transmitter, laser, detector and other functional modules.
3. According to the packaging types (CFP / XFP / SFP / QSFP, etc.), the transmission rate (155Mbps ~ 200Gbps), optical link (CWDM / DWDM / PSM), mode (Single-mode / Multi-mode), Plug-in/out mode (Fixed / Hot-pluggable) and other categories, optical transceivers have various kinds of categories. If considering the operating temperature range, whether the number of self-diagnostic functions and performance classification elements, optical transceiver categories are more.
4. The basic structure of an optical transceiver includes a laser (TOSA) + driving circuit, a detector (ROSA) + receiving circuit, a multiplexer (MUX), a demultiplexer (DEMUX), an interface, an auxiliary circuit and a housing.
5. Driven by technological upgrading and cost reduction, the optical transceiver continues to be ”high speed, miniaturization and integration.” 100G optical transceivers use 25G laser chip technology. According to the different packaging methods, 100G optical transceivers are CFP / CFP2 / CFP4, CXP and QSFP28. QSFP28 is a new generation of 100G optical transceiver packaging, and has now become the mainstream packaging of optical transceivers.
6. 100G optical transceivers have different models and standards. Generally speaking, the transmission rate of optical signals is much higher than that of low-rate 10G and 25G products. Now they have become the star products in large-scale data centers and telecom markets.
Why Are 100G Optical Transceivers So Popular?
1. From the Market Segmentation Point of View
The optical transceiver market can be subdivided into Telecom, Datacom and Access markets. Access market generally use 10G and below the low-speed optical transceiver. North American data center market is undergoing 40G to 100G upgrading, the current high-speed optical transceiver is the main growth point. After 5G construction started, the telecommunications market for high-speed optical transceiver demand will be larger than the data center market.
2. The Relationship between Optical Transceivers and 5G
With the evolution of 5G technology, based on the requirement of higher base station density, there will be greater new demand and market space for high-rate optical transceivers. At present, LTE base stations of 4G mainly use 10G optical transceivers, and 25G / 100G optical transceivers are the preferred solutions of the front 5G optical transmission modules in the future.
(1) At present, the market demand for digital communications is growing rapidly: the demand for high-end optical transceivers in Internet data centers is accelerating, especially in overseas digital communications markets. In the data center server and switch, a large number of connections are using optical communication technology; data center network has become the driving force for the growth of optical transceivers. With the construction of large-scale data centers and the outbreak of traffic, the demand for optical transceivers in the data center has been shifted from 10G / 25G to 40G / 100G and 100G has become the mainstream since 2017.
(2) The rapid increase of optical transceiver industry profit in 2016 was mainly due to the sharp increase in the demand for 100G optical transceiver in North American cloud computing center. The demand for optical transceiver increased sharply, and 100G optical transceiver in the market was in short supply. It is estimated that the global 100G optical transceiver shipments in 2017 will reach 200-300 million.
(3) Telecommunication Network Market (Three Major Carrier Capital Expenditure Items): Optical communication is the cornerstone of 5G and the demand of 5G for high-rate optical transceivers increases. At present, LTE base stations of 4G mainly use 10G optical transceivers, and 25G / 100G optical transceivers are the preferred solutions of the 5G fronthaul optical transceivers in the future.
Each base station needs 12 25G / 100G optical transceivers: one base station has one BBU and connects to three RRUs, and each BBU uses three pairs of six optical transceivers, each pair uses two pairs of RRUs, for a total of 12 optical transceivers. Theoretically, due to the characteristics such as high frequency, high density and high connection of 5G, the domestic future needs to build nearly 10 million base stations, that is, the demand of hundreds of millions of optical transceivers, and the number of base stations in North America is 10 million, The demand for high-speed optical transceivers brought by 5G construction will be even greater. At present, there are many kinds of mature 100G optical transceivers in the market, like 100G QSFP28 CWDM4, 100G QSFP28 PSM4 and 100G CFP / CFP2 / CFP4 optical modules provided by Gigalight. They cover the mainstream form factors: CFP / CFP2 / CFP4 / QSFP28 and can be used for a variety of optical network bearer demand.
The continuous and rapid development of the Internet as well as the desire of people for higher speed optical networks facilitated the vigorous development of the entire optical communications industry and strongly promoted the independent R & D and innovation in many core technologies including optoelectronic devices technologies. 100g optical transceiver is regarded as the product of this big data era.
The first generation of 100G optical modules is CFP optical module with very large volume, then CFP2 and CFP4 optical modules appears. CFP4 optical module is the latest generation of 100G optical module, the width is only 1/4 of CFP optical module. Its package size is not same as the QSFP + optical module. The QSFP28 optical module has a smaller package size than the CFP4 optical module, which means the QSFP28 optical module has a higher port density on the switch. The following are several 100G QSFP28 series optical modules:
Main Types of QSFP28 Optical Transceivers
100G QSFP28 LR4 is a 100Gb/s transceiver module designed for optical communication applications compliant to 100GBASE-LR4 of the IEEE P802.3ba standard.
100G QSFP28 SR4 is a four-channel, pluggable, parallel, fiber-optic QSFP+ SR4 optical transceiver module for 100/40 Gigabit Ethernet, Infiniband DDR/EDR and 32GFC applications.
100G QSFP28 PSM4 is a four-channel, pluggable, parallel, fiber-optic QSFP28 PSM4 optical transceiver module for 100/40 Gigabit Ethernet and Infiniband DDR/EDR Applications.
100G QSFP28 CWDM4 is a 100Gb/s transceiver module which is designed for optical communication applications compliant with the QSFP MSA, CWDM4 MSA and portions of IEEE P802.3bm standard.
Of course, QSFP28 series also includes 100G QSFP28 active optical cables; these products have played an important role in the development of 100G.
Advantages of 100G QSFP28 Optical Transceivers
1. Power Consumption
The power consumption of QSFP28 typically is no more than 3.5W, while the power consumption of other 100G optical modules typically is between 6W and 24W. From this, the power consumption of QSFP28 optical modules is much lower power than other 100G optical modules.
Now the data center is mainly 10G network architecture, in which the interconnection solutions are mainly 10GBASE-SR optical module and duplex LC multimode fiber jumper. If the existing 10G network architecture based on the direct is upgraded to 40 / 100G network, it will save a lot of time and cost. Therefore, one of the major interconnection trends in data centers is to upgrade from 10G networks to 40 / 100G networks without changing existing duplex multimode infrastructure. In this case, the MPO / MTP branchable cable is undoubtedly the ideal solution for a 10G upgrade to 40 / 100G.
The QSFP28 uses the advanced 100G transport technology to provide the data center with a connection between the chassis switch and the core network, providing up to 150% greater panel bandwidth density than the 40G QSFP solution
Optical Module Test
When using optical modules, test performance is an essential step. Optical module is composed of transmitter and receiver, so when we test, it is generally divided into four steps, which mainly includes the transmitter and receiver test.
First, the transmitter part:
When testing, pay attention to the wavelength and shape of the transmitter output waveform, as well as the receiver’s jitter tolerance and bandwidth. When testing the transmitter, note the following:
1. The quality of the input signal used to test the transmitter must be good enough. In addition, the quality of the electrical measurements must also be confirmed by jitter and eye measurements. Eye diagram measurements are a common way to check the transmitter’s output waveform because the eye diagram contains a wealth of information that reflects the overall performance of the transmitter.
2.The output optical signal of the transmitter must be measured by the optical quality index such as eye pattern test, optical modulation amplitude and extinction ratio.
Second, the receiver part:
Unlike test transmitters, the quality of the optical signal must be sufficiently poor when testing the receiver that a light pressure eye pattern representing the worst signal must be created. This worst case optical signal must pass through jitter measurements and light Power test to calibrate.
1. Eye pattern test, this will ensure that the eye ”eye” is open. Eye diagram testing is usually done at the depth of the bit error rate;
2. Jitter test to test different types of jitter;
3. Jitter Tracking and Tolerance, testing the internal clock recovery circuit to track the jitter.
All in all, testing light modules is a complex undertaking, but it is also an indispensable step in ensuring good performance. Eye diagram measurement is a widely used measurement method that can effectively test the transmitter of an optical module. The optical module receiver test is more complex, but also requires more testing methods.
CWDM optical module adopts CWDM technology, which can combine optical signals with different wavelengths through an external wavelength division multiplexer. It saves fiber resources by transmitting through one optical fiber. At the same time, the receiving end needs to use the wave-demultiplexer to decompose the complex optical signal. In addition, CWDM optical modules can be plugged into switch or router SFP ports. This article will describe in detail what CWDM optical modules are and what are the differences between CWDM optical modules and other modules.
The Main Form Factors and Type of CWDM Optical Modules
There are three types of CWDM optical module form factors: SFP, SFP + and XFP. The transmission distance is generally as follows: 40KM, 80KM, 100KM, and 120KM.
CWDM optical modules can be divided into: CWDM SFP optical module, CWDM GBIC optical module, CWDM SFP + optical module, CWDM XFP optical module, CWDM X2 optical module, CWDMXENPAK optical module and CWDM LX-4 optical module.
The Differences between CWDM Optical Modules and Ordinary Optical Modules
CWDM optical modules are passive modules that do not emit laser. They generally use optical planar waveguide (PLC) technology; just a beam of light is divided into several beams of light. The ordinary optical modules belong to the photoelectric conversion device, which are active optical modules. Each module has two ports for receiving and transmitting, and the launch port inside is a laser.
CWDM Optical Modules VS DWDM Optical Modules: Which One to Choose?
The principle of DWDM optical modules is similar to CWDM optical modules, except that DWDM optical module are optical modules for dense wavelength division multiplexing, and has 40 common channels to choose from.
CWDM optical modules are widely used in schools, data centers, FTTH (Fiber to the Home), 1G and 2G Fiber Channel, metro Ethernet, security and protection systems and other fields.
DWDM optical modules are mainly used in long-distance optical synchronous digital transmission networks, such as Ethernet / Fiber Channel with 200km links and 80km links.
From a cost point of view, CWDM optical modules are cheaper than DWDM optical modules. CWDM optical modules provide a convenient and cost-effective solution for using Gigabit Ethernet and Fiber Channel.
DWDM optical modules, on the other hand, typically use denser channel spacing and are used for large optical networks over longer distances. If you want long-distance SFP modules, DWDM optical modules are the ideal choice.
The Differences between CWDM4 and PSM4
CWDM4 optical module transmission rate is 103.1Gbp, mainly used in computing, high frequency trading and other fields. Its cost is significantly higher than QSFP28 PSM4.
1. The optical transmitter: PSM4 needs four integrated silicon photonic modulator and a distributed feedback laser, and CWDM4 needs four CWDM direct modulation laser;
2. The connector: PSM4 needs a MPO connector with 8 fibers, CWDM4 needs duplex LC connector;
3. The optical fiber: PSM4 is a ribbon SMF (8 core), CWDM4 is a duplex SMF;
4. The transmission distance: PSM4 is 500 meters, CWDM4 is 2000 meters
5. The four wavelength of CWDM multiplexer: PSM4 does not need, but CWDM4 needs.
CWDM optical modules are multi-rate optical modules with 20-40km, 40-80km and 80-120km transmission distances. The optical modules of different wavelengths are marked with different colors to better meet customer requirements.
With the development of science and technology, the application of optical communications products in real life is becoming more and more widespread. The demand for network technology is also getting higher and higher. Therefore, 100G optical transceivers are gradually appearing on the market. The development of 5G and Data Center further make the 100G optical transceivers become the mainstream of the optical transceiver market gradually. Perhaps you have had a certain understanding of 100G optical transceivers, but if we analysis 100G optical transceivers from another point of view, you will find something different.
Development Background of 100G Optical Transceivers
For the earliest developed 100G optical transceiver, the form factor is CFP, developed in 2010. At that time, IEEE launched 100G optical transceiver SR10, LR4 and ER4 three standards, separately aiming at the 100m, 10Km and 40Km transmission. Followed by that, the IEEE standard added the new 100G SR4 project, but in 2013 did not reach consensus and vacancies. By 2016, the 100G optical transceivers used by various data centers were mostly the 25Gbps Serdes program, and the 100G optical transceivers that use the 50Gbps Serdes planned slowly appeared.
The Facing Problems for 100G Optical Transceivers
1. Channel Distance: The DWDM system supporting the 50GHz wavelength distance is very extensive. The 100G optical transceiver needs to meet the condition of supporting the 50GHz wavelength distance, therefore, the pattern of high spectral power should be used.
2. OSNR (optical signal-to-noise ratio): Under the same pattern, 100G optical transceivers requires10dB higher than 10G optical transceivers and 4dB higher than 40G optical transceivers. Therefore, a low OSNR tolerance code and high coding gain FEC algorithm are needed.
3. CD Margin: Under the same conditions, 100G optical transceiver dispersion tolerance only needs 1/100 of 10G optical transceiver, accounting for 16/100 of 40G optical transceiver. Therefore, 100G optical transceivers can use dispersion compensation technology, in the electric field or the optical domain compensation to complete the dispersion compensation for each wavelength.
4. PMD Tolerance: Under the same conditions, PMD (polarization mode dispersion) tolerance of 100G optical transceiver is 1/10 of 10G optical transceivers, accounting for 4/10 of 40G optical transceiver, so you need to choose coherent reception plus digital signal processing.
5. Nonlinear Effects: Compared with 10G / 40G optical transceiver, the nonlinear effects of 100G optical transceivers are messier.
The Types and Advantages of 100G Optical Transceivers
The main form factors of 100G optical transceiver include: CFP, CFP2, CFP4 and QSFP28. To compare their advantages, the main factor to consider is the costs and power consumption for Data Centers.
1. CFP optical transceiver supports all C-band wavelengths tunable and can complete the link detection, which use a common optical dual-binary modulation format ODB, convenient layout, power consumption is less than 24W.
2. The volume of CFP2 optical transceiver is one-half of CFP, its integration is 2 times CFP. It can complete the wide dynamic input range based on SOA to achieve stable admission sensitivity, support a full CFP optical transceiver, its low power consumption is lower than 9W.
3. The volume of CFP4 optical transceiver is one-half of CFP2, its integration is twice that of CFP2, front panel port density is also doubled compared with CFP2. CFP4 optical transceiver follows the MSA protocol, support the same rate as CFP/CFP2. Its transmission power increases significantly, but the power consumption drops significantly, only about half of the original, the system cost is lower than the CFP2. In addition, CFP4 optical transceiver uses 4 * 25 forms, through the 4 * 25G channel, complete 100G transmission. The transmission power is higher with higher stability.
4. The form factor of QSFP28 optical transceiver is smaller than the CFP4 optical transceiver. QSFP28 optical transceiver power consumption is generally not more than 3.5W, the use of QSFP28 optical transceiver can directly upgrade from 25G to 100G not through 40G, and therefore the cost is lower.
|Types||Standard||The Largest Transmission Distance||Connector||Channel||Wavelength||Fiber Types|
(CFP4 doesn’t support SR10)
Learning the contents of the 100G light module, above, do you have any further information? 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. Gigalight, as a veteran optical transceiver manufacturer with professional technology, advanced R & D capability and stable manufacturing capability, not only has many popular 100G optical transceiver products, like 100G QSFP28 CWDM4, 100G QSFP28 PSM4, CFP2 100G LR4, and etc. but also will release more new 100G optical transceivers in the first quarter of this year. More information about 100G optical transceivers, please visit the official website.
Mobile communication is an important driving force for the development of optical networks. It is also self-evident that the development of optical modules is of great importance. We know that the optical module market can be subdivided into the Telecom market, the Datacom market and the Access market. Among them, the Telecom market is the ”main battlefield” competed by the optical module industry. The biggest surprise for the future Telecom market is the evolution of 5G technology. Based on the requirement of 5G higher rate, higher capacity and higher base station density, there will be greater new demand and market space for high rate optical modules.
The Demands of Optical Transceivers for 5G Network
Although the current 5G is still in the standard stage, major equipment manufacturers have actively carried out joint trials with operators to strive to achieve 5G commercial use by 2020. ”5G is commercial, carrying is the first.” It is predicted that the future number of 5G base stations will exceed 10 million, which will bring the surge in demand for optical modules in quantity. Compared with 4G technology, 5G data transmission rate is 10 to 100 times that of 4G, which means that the number of optical modules used by a single base station will increase substantially when the optical module rate remains unchanged.
We simply use a formula to represent the demand of a 5G optical module: optical module requirement (F) = base station number (m) * single base station module requirement (n). In the 5G era, compared with 4G, m and n will be significantly improved. Therefore, under the 5G construction period, the optical module will become one of the most flexible segments in the 5G industry chain. In addition, the demand for optical modules for the construction of large-scale data centers will also increase with the outbreak of 5G traffic.
To sum up, it is helpful for optical module suppliers to get ahead in the 5G era when they grasp the demand for optical modules in 5G networks in advance. So what are the specific demands of 5G optical modules? What are the mature products in the industry can initially meet the needs of 5G load? We try to analyze in the following parts.
Why Will the 100G Optical Transceivers Become the Mainstream for 5G Network?
Compared with 4G networks, 5G rebuilds the BBU into a separate architecture of CU (Centralized Unit) and DU (Distributed Unit), so its bearer needs an additional layer of intermediate network. Fronthaul – middlehaul – backhaul, the three carrier network requirements for optical modules are different. For 5G fronthaul, the CPRI bandwidth per 10MHz single-antenna port is about 614.4Mbps under ideal transmission conditions. The typical 5G wireless bandwidth is 100M ~ 1G, the peak is 20G, the antenna port may be 64 or 128. After a simple conversion, 5G fronthaul network granularity should be 25Gbps, which has been generally accepted by the industry. It can be inferred that the future 50Gbps and 100Gbps of the 5G pre-transmission modules will be the mainstream. For 5G middlehaul, it will use DWDM ring network structure, transmission distance 10 ~ 40km, n * 25G technology. This means that 100G optical modules are highly likely candidates for 5G messenger. For 5G backhaul, either with the network can be merged, but also separate. According to the future OTN networking, n * 100G technology will be adopted; if there is no OTN networking and 200G / 400G optical module technology. But no matter what kind of technology, 100G and above ultra-high-speed optical module must become the mainstream for the 5G market.
In conclusion, the demand of the 100G optical module by the 5G network is very urgent. At present, there are many kinds of mature 100G optical transceivers in the market, like 100G QSFP28 CWDM4, 100G QSFP28 PSM4 and 100G CFP / CFP2 / CFP4 optical modules provided by Gigalight. They cover the mainstream form factors: CFP / CFP2 / CFP4 / QSFP28 and can be used for a variety of optical network bearer demand. In particular, 100G QSFP28 and 100G CFP4 have the advantages of more compact, high module integration, transmission efficiency, power consumption and cost-effectiveness.
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|
(CFP4 doesn’t support SR10)
|CPAK (Cisco 100G)||SR10/SR4/
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.