Optical Transceiver Technology Trends of Data Center in 2022

With the rapid development of cloud computing, big data, ultra-high-definition video, artificial intelligence, and 5G industry applications, the frequency of network access and access methods continue to increase, and network data traffic grows rapidly, posing higher challenges to data center interconnection (DCI). Taking a data center with a spine-leaf CLOS architecture as an example, the typical optical interconnection scenarios are shown in Table 1. The first three scenarios are interconnection within the data center, and the fourth scenario is the interconnection among data centers.

Interconnection Scenarios		Typical Distance		Typical Requirements for Optical Modules
				Last Generation	At Present	Next Generation
Scenario 1	Server to TOR (within Data Center )	2m(within the rack) 30/50m（across racks）	within Machine Room	25G AOC/DOC	100G AOC/DAC	200G AOC/DAC
Scenario 2	TOR to Leaf (within Data Center)	≥70m/100m	within Building	100G SR4	400G SR8/SR4.2	800G PSM8/PSM4
Scenario 3	Leaf to Spine (within Data Center)	500m/2km	among Buildings	100G CWDM4	400G FR4/DR4	800G FR4/PSM4
Scenario 4	Among Data Centers	80-120m	among Campuses	100G DWDM	400G ZR/ZR+	800G ZR

Table1: Typical Optical Interconnection Scenarios of Data Centers

1. Optical Module Requirements for Internal Interconnection of Data Centers

The internal interconnection of the data center accounts for a large proportion of the overall traffic distribution of the data center. The typical requirements for optical modules are shown in Table 1, and there are development trends toward high speed, low power consumption, low cost, intelligence, etc.

(1)The Trend Toward High Speed

The internal interconnection within Amazon, Google, Microsoft, Facebook, and other North American ultra-large data centers has begun commercial deployment of 400Gb/s optical modules between 2019 and 2020. Domestic data centers are gradually transitioning from 100Gb/s to 400Gb/s transceivers, and the scale deployment is expected to be realized in 2022. As shown in Diagram 1, the throughput of data center switching chips are expected to reach 51.2Tb/s in 2023 and 102.4Tb/s after 2025. Higher rates of 800Gb/s and 1.6Tb/s will become important choices to realize high-bandwidth data exchange.

Diagram1: the developing trend of data center switch chip throughput

(2) The Trend Toward Low-consumption

As the capacity of switching chips continues to increase, the power consumption of optical modules has begun to exceed that of switching chips, becoming a key factor in network solutions. The early power consumption of 400Gb/s optical modules is 10~12W, and the long-term power consumption is expected to be 8~10W; the power consumption of 800Gb/s optical modules is about 16W. In addition, the industry expects to reduce the power consumption and cost of interconnecting SerDes by encapsulating the optical engine and the switching chip, and CPO (co-packaged optics) technology encapsulates electronic chips and optical engines together, which has become a research hotspot in the industry.

(3) The Trend Toward Low Cost

There are massive interconnection requirements in data centers, and low cost is one of the main driving forces for the continuous development of optical module technology solutions. First, the access cables in scenario one show a trend of diversification. Some solutions reduce the interconnection distance by adjusting the cabinet layout, and using lower-cost direct-attached copper cables (DAC) instead of optical cables; second, with the stable operating environment and fast replacement of data center optical modules, the industry is actively exploring solutions to lower costs by reducing requirements for temperature and long-term reliability and so on; thirdly, as the speed continues to increase, the sinking trend of coherent solutions is obvious, and non-coherent solutions are also striving to expand to long distances. The two schemes “meet” in some application scenarios, and the proportion of demand for different schemes in the “meeting” scenes will be closely related to factors including cost.

(4)The Trend Toward Intelligence

OTT has begun to pay attention to the enhancement of the operation and maintenance capabilities and quality improvement of optical modules. The health monitoring of optical modules and early warning of faults are realized through artificial intelligence, machine learning, and big data, which puts forward new requirements for the functional characteristics and specifications of optical transceivers.

Types of Optical Modules		Form Factor	Optical Interface Rate Gb/s	Electrical interface rate Gb/s	Transmission Distance	Number of Fibers	Typical Power Consumption
100Gb/s	VR	QSFP28	100	100	30/50m	1	＜3.5W
	SR4		4×25	4×25	70/100m	4
	PSM4		4×25	4×25	500m	4
	CWDM4		4×25	4×25	2km	1
	LR4		4×25	4×25	10km	1
200Gb/s	VR2	QSFP56	2×100	2×100	30/50m	2	＜6.5W
	SR4		4×50	4×50	70/100m	4
	FR4		4×50	4×50	2km	1
	LR4		4×50	4×50	10km	1
400Gb/s	VR4	QSFP-DD/OSFP	4×100	4×100	30/50m	4	＜12.0W
	SR8		8×50	8×50	100m	8
	SR4.2		8×50	8×50	100m	4
	DR4		4×100	4×100	500m	4
	FR4		4×100	4×100	2km	1
	LR4		4×100	4×100	10km	1
800Gb/s	VR8	QSFP-DD800 /OSFP /QSFP224 /CPO	8×100	8×100	30/50m	8	16W
	PSM8		8×100	8×100	70/100m	8
	DR8		8×100	8×100	500m	8
	DR4		4×200	8×100	500m	4
	2×FR4		8×100	8×100	2km	2
	FR4		4×200	8×100	2km	1

Table2:  Optical Module Requirements of Internal Data Center Interconnection

2. Optical Modules Used in the Interconnection Among Data Centers

In the early stage, it was mainly accessed through the Internet. With the increase in business traffic, the data traffic reached more than Tb/s, and problems such as network delay, congestion, and security required special interfaces to support. Data centers are energy-intensive industries. Due to the constraints of power supply and the surrounding environment, the scale of a single data center cannot be expanded infinitely. The extensive application of modern virtualization technology enables multiple physically separated data centers to work like a virtual data center, and large Internet companies can share the load among multiple data centers and services, effectively reducing the data center’s demand for power supply, and facilitating rapid deployment. In addition, in consideration of disaster recovery and backup, many large data centers are composed of multiple sites, between which a large number of low-latency data exchange channels are required. The above application scenarios all place strong demands on DCI. The DCI distance is generally several kilometers to tens of kilometers, or even more than 100 kilometers. Typical interconnection scenarios are as follows:

(a) DCI-Campus: Connect to a data center at a short distance. The transmission distance is usually about 2km, and further expands to a longer distance of 10km;

(b) DCI-Edge: Distributed data center in the connection area. The transmission distance is usually 80km~120km;

(c) Metro/Long Haul: It is further extended to the metropolitan area and long-distance transmission, and the distance can reach hundreds or thousands of kilometers. In order to make full use of optical fiber resources, dense wavelength division multiplexing (DWDM) technology is widely used, and different modulation codes can be used for different transmission distances. In addition, although not part of the DCI infrastructure, wireless networking is also being integrated into the data center network.

For DCI within 20km, depending on the connection bandwidth and fiber resources, CWDM or DWDM direct modulation and detection technology can be selected. For the transmission distance of 20km to 80km, DWDM coherent technology, and direct modulation and detection technology compete in terms of construction and operation cost, reliability, etc. For the transmission distance of 80km~120km, DWDM coherent technology is the mainstream solution. In order to further reduce technical complexity and cost, colored light and gray light modules based on direct modulation and detection technology are also being developed simultaneously. As for transmission distances of hundreds of kilometers and more, it is necessary to transmit higher-speed signals on each wavelength to increase the total interface bandwidth, and coherent technology is the mainstream solution.

Rate	Form Factor	Transmission Distance	Detection Technology	Modulation Mode	Reference Standard/Specification
100Gb/s	CFP2	80-120km	Coherence	QPSK	Open ZR+
	QSFP28	80-120km	Direct Modulation and Detection	PAM4	ColorZ
	QSFP28	80km	Direct Modulation and Detection	NRZ	_
400Gb/s	QSFP-DD	80-120km	Coherence	16QAM	OIF 400ZR
800Gb/s	QSFP-DD800	10km	Coherence	16QAM	OIF 800LR
	QSFP-DD800	80-120km	Coherence	16QAM	OIF 800ZR

Table3: Requirements for optical modules for interconnection among data centers

3. Optical module technology used in data center interconnection

100G QSFP28 and 400G QSFP-DD, OSFP optical transceivers based on single-wavelength 100Gb/s

Datacenter construction puts forward strong demands for high speed, small size, low cost, and low power consumption of optical modules. Single wave 100Gb/s technology can effectively take advantage of the bandwidth improvement and iterative evolution of photoelectric chips, as well as highly integrated processes and packaging, to achieve higher interface density and low cost while meeting the same bandwidth requirements and reducing optical complexity.

In terms of international standardization, IEEE802.3 and 100G Lambda MSA have released or established a series of 100/400Gb/s related standards based on single-wavelength 100Gb/s, as shown in Table 4. In terms of industry standards, CCSA is formulating “100Gb/s Single-Wavelength Optical Transceiver” industry standards, including distance specification of DR (500m), FR1 (2km), LR1 (10km), LR1-20 (20km), and ER1-30/40 (30/40km); YD/T 3538.3-2020: “400Gb/s Intensity Modulation Pluggable Optical Transceiver Part 3: 4×100Gb/s” has been released in 2020, containing distance specification of DR4 (500m) and FR4 (2km); at the same time, FiberMall is actively carrying out research topics such as 4×100Gb/s intensity modulation long-distance optical modules and high-speed optical devices of 100GBaud and above.

	Guideline	State	Operating Wavelength	Distance
100G VR	IEEE 802.3db	under research	842-948nm	30m(OM3) 50m (OM4/5)
100G SR	IEEE 802.3db	under research	844-863nm	60m(OM3) 100m (OM4/5)
100G DR	IEEE 802.3cd-2018	published	1304.5-1317.5nm	500m
100G FR1	IEEE 802.3cu-2021 100G Lambda MSA (100G-FR and 100G-LR Technical Specifications Rev 2.0)	published	1304.5-1317.5nm	2km
100G LR1		published	1304.5-1317.5nm	10km
100G LR1-20	100G Lambda MSA (100G-LR1-20,100G-ER1-30 and 100G-ER1-40 Technical Specifications Rev 1.1)	published	1304.5-1317.5nm	20km
100G ER1-30/40		published	1308.09-1310.19nm	30/40km
400G VR4	IEEE 802.3db	under research	824-948nm	30m(OM3) 50m (OM4/5)
400G SR4	IEEE 802.3db	under research	844-863nm	60m(OM3) 100m (OM4/5)
400G DR4	IEEE 802.3bs-2017	under research	1304.5-1317.5nm	500m
400G FR4	IEEE 802.3cu-2021 100G Lambda MSA (400G-FR4 Technical Specifications Rev 2.0)	published	1264.5-1277.5nm 1284.5-1297.5nm 1304.5-1317.5nm 1324.5-1337.5nm	2km
400G LR4-6	IEEE 802.3cu-2021	published	1264.5-1277.5nm 1284.5-1297.5nm 1304.5-1317.5nm 1324.5-1337.5nm	6km
400G LR4-10	100G Lambda MSA (400G-LR4-10 Technical Specification Rev1.0)	published	1264.5-1277.5nm 1284.5-1297.5nm 1304.5-1317.5nm 1324.5-1337.5nm	10km
400G ER4	100G Lambda MSA	under research	nLWDM	30/40km

Table4：Progress of 100/400Gb/s-related international standards based on single-wavelength 100Gb/s

In terms of form factor, QSFP-DD MSA and OSFP MSA have released specifications of 400Gb/s QSFP-DD and 400Gb/s OSFP  respectively, using an 8×56Gb/s electrical interface. The QSFP-DD MSA updated and released the 6.01 version of the specification including 400Gb/s QSFP112 in 2021. The QSFP112 MSA, led by Alibaba and Baidu, will soon release relevant specifications to promote data center interconnection applications.

（1）500m/2km 100/400Gb/s optical transceivers

As shown in the diagram below, the first-generation single-wavelength 100Gb/s based 400Gb/s optical module is mainly based on an 8×56Gb/s electrical interface, which requires DSP to realize 8:4 Gearbox rate conversion. The second-generation 400Gb/s optical module adopts a 4×112Gb/s electrical interface, which can simplify the connection between the switch chip and the optical module, thereby reducing power consumption and cost.

Diagram2: the first and second generation of 400Gb/s optical modules based on single-wavelength 100Gb/s

In terms of optical interface technology, the 400Gb/s 500m DR4 optical module based on single-mode fiber has come into commercial use, and there are three types of solutions: EML, DML, and silicon photonics. Among them, the EML solution is the traditional solution with the highest maturity. At the end of 2020, Lumentum released a 100Gb/s PAM4 DML chip to provide strong support for the DML solution, which requires temperature control to ensure bandwidth performance at standard temperature (0~70°C). In terms of electronic chips, the industry lacked single-wave 100Gbs/s PAM4 DML supporting electronic chips in the early days. At present, optical communication companies like Insica, and Aluksen have launched Driver and TIA-related products, but the maturity of the industry chain still needs to be further improved.

The investment and R&D enthusiasm for silicon photonics solutions is high. Intel, Lumentum, II-VI, Acacia, FiberMall, and other companies have launched 400Gb/s DR4 silicon photonics module products, and Alibaba has also released self-developed silicon photonics modules. The silicon photonics solutions of various manufacturers in the industry are not uniform, which brings certain challenges to the formation of scale advantages. Due to factors such as high coupling loss, high-power CW DFB lasers, and large-swing drivers, the silicon photonics solution is still far from industry expectations in terms of power consumption. In addition, there is also controversy in the industry on the choice of CWDM4 and PSM4 technical solutions in 500m application scenarios. Both have their own pros and cons, so various factors such as performance and cost need to be comprehensively considered.

	EML Solution	DML Solution	Silicon Photonics Solutions
Power Consumtion	Moderate	Low	Moderate
Cost	Moderate	Low	Depends on pass rate at scale
Maturity	High	Low	Moderate
Key technology	_	High bandwidth linear DML、DML Driver	Low power modulator
Solution	CWDM4	PSM4 or CWDM4	PSM4
Number of pigtails	2	8 or 2	8
Fiber splice	LC/UCD/SN/MDC	MPO/LC/UCD/SN/MDC	MPO/UCD/SN/MDC

Table5: Comparison of 400Gb/s 500m DR4 technical solutions

The 400Gb/s DR4+ optical module further expands the transmission distance to 2km, currently with the EML solution as the main solution. 100Gb/s DR and 100Gb/s FR1 optical modules mainly adopted the QSFP28 form factor, and are used in 500m and 2km breakout cable scenarios with 400Gb/s DR4 and 400Gb/s DR4+ optical modules respectively. The breakout scenario is currently used in large OTTs in North America. The advantage is that it can realize the practicability and flexibility of service signal interconnection and effectively improve port density; the disadvantage is that the maintenance is complicated and the types of modules are increased. The failure or replacement of any link will affect the other links. The 400Gb/s 2km FR4 application scenario mainly adopts the CWDM4 technical solution, which can greatly reduce the demand for optical fibers and achieve end-to-end cost advantages. At the same time, due to a large number of optical modules with different transmission distances, some domestic OTTs expect to use the 400Gb/s 2km FR4 solution to realize the unified bearer of 500m and 2km to reduce the complexity of operation and maintenance. At present, 100/400Gb/s optical module products based on single-wavelength 100Gb/s have been mass-produced by many manufacturers around the world.

Type	Form factor	Representative domestic and foreign manufacturers
		EML	Silicon photonics/DML
100G DR	QSFP28/ SFP56-DD	Cisco,Juniper,FiberMall,II-VI	Intel
100G FRI	QSFP28/ SFP56-DD	Cisco,Juniper,FiberMall	Intel
400G DR4	QSFP-DD	Cisco,Arista,Juniper,II-VI,FiberMall	Intel,II-VI, AOI(DML)
400G DR4+	QSFP-DD	Broadcom	Intel
400G FR4	QSFP-DD	Juniper,FiberMall,II-VI,Cisco,Arista	_

Table 6: Representative optical module manufacturers of 100Gb/s DR/FR1 and 400Gb/s DR4/DR4+/FR4

Device classification	Key chip	Representative manufaturer
		500m	2km
Optical chip	53GBaud detector	Broadcom、GCS	Broadcom、GCS
	53GBaud laser	Lumentum、II-VI、AOI(DML)	Mitsubishi、Lumentum、Broadcom(EML)
Electric chip	53GBaud linear TIA	Inphi、Broadcom、 Semtech、Macom	Inphi、Broadcom、 Semtech、Macom
	53GBaud linear Driver	Inphi、Broadcom、 Semtech、Macom	Inphi、Broadcom、 Semtech、Macom
	DSP	Inphi、Broadcom	Inphi、Broadcom
Silicon photonics integrated chip		Intel、Acaica、 Rockley	Intel、Acaica、 Rockley

Table7: Representative manufacturers of 100/400Gb/s 500m/2km optical module core photoelectric chip device

（2）10km/40km 100/400Gb/s optical transceivers

The mainstream technical solutions of 10km/40km 100/400Gb/s optical modules are shown in Table 8. The transmitting side of the 100Gb/s LR1 optical module uses a 53GBaud EML chip and has two form factor solutions: BOX and TO. The latter has the advantage of low cost, but the bandwidth margin is small and the pass rate is slightly lower. 53GBaud un-cooled EML has the advantages of low cost and low power consumption. It is currently used in scenarios of 2km and below, and the application of 10km needs to be further verified. The receiving side uses a 53GBaud PIN chip, with the coexistence of BOX and TO, airtight, and non-hermetic form factor, which may evolve to TO hermetic form factor and COB non-hermetic form factor in the future.

Module type	Form factor	Electrical interface	Optical interface	Optical chip	OSA Form factor
100Gb/s LR1	QSFP28	4x25G NRZ	1x 100G PAM4	EML+ PIN	TO/BOX
100Gb/s ER1	QSFP28	4x25G NRZ	1x 100G PAM4	EML+ APD	TO/BOX
400Gb/s LR4	QSFP-DD	8x50G PAM4	4x 100G PAM4	EML+ PIN	COB/BOX
400Gb/s ER4	QSFP-DD	8x50G PAM4	4x 100G PAM4	EML+ APD EML+(SOA+PIN)	BOX

Table8: 100/400Gb/s 10/40km mainstream technical solutions

The block diagram of the 100Gb/s LR1/ER1 optical module is shown in Figures (a) and (b) below. The transmitter uses a 53GBaud EML chip; the receiver uses a 53GBaud PIN/APD chip, and the 4:1 PAM4 DSP chip supports KP4 FEC. The block diagrams of 400Gb/s LR4 and ER4 optical modules are shown in Diagram (c) and (d) respectively. The 400Gb/s LR4 transmitter uses 4×53GBaud EML array chips (BOX/COB form factor), and the receiver uses a 4×53GBaud PIN Array chip (BOX/COB form factor; airtight and non-airtight coexistence); 400Gb/s ER4 transmitter adopts 4×53GBd EML array chip (BOX package), with wavelength selection to be determined; receiver solution is to be determined, with high-performance APD and SOA+PIN solutions being possible (BOX/COB package, coexistence of airtight and non-airtight form factor). The 400Gb/s LR4/ER4 optical module adopts an 8:4 PAM4 DSP chip and supports KP4 FEC. Compared with traditional solutions, 100/400Gb/s optical modules based on single-wavelength 100Gb/s technology can save multiple optical chips, thereby reducing cost, power consumption, and manufacturing complexity, and improving pass rate. The electronic chip adopts DSP with integrated Driver, CDR, and Gearbox functions, which reduces the design complexity and facilitates the product focus for chip designers.

Diagram3: 100/400Gb/s optical modules based on single wave 100Gb/s technology

At present, a number of domestic and foreign manufacturers have released mass-produced products and road signs based on single-wavelength 100Gb/s technology:

• 100Gb/s LR1 has been supplied by several module manufacturers in batches. With the gradual maturity of 53GBaud optical device packaging technology, the qualification rate of optical module products has gradually improved, and the current cost is expected to be better than that of the 100Gb/s LR4 solution;

• As for 400Gb/s LR4, a number of module manufacturers can provide Beta samples, and the cost is expected to be better than that of the 400Gb/s LR8 solution. With the gradual increase in the demand for 53GBaud optical chips in the future, there is a large room for cost reduction;

• 100Gb/s ER1 and 400Gb/s ER4 are currently under research by several module manufacturers. The 100Gb/s ER1 has made a preliminary breakthrough and can achieve 40km transmission in the laboratory environment. 400Gb/s ER4 is under research, and a prototype is expected to be launched by the end of 2022 based on the good foundation of the 100G ER1. Both 100Gb/s ER1 and 400Gb/s ER4 currently face challenges such as high optical coupling efficiency requirements at the transmitting end, high chip sensitivity requirements at the receiving end, and the need for screening.

Type	Form factor	Representative optical module manufacturers
		Airtightness	Non-airtightness
100G LR1	QSFP28	CIG、FiberMall、Juniper、 AOI、Cisco	II-VI
100G ER1	QSFP28	Sifotonics、AOI、FiberMall	_
400G LR4	QSFP-DD	SEDI、Juniper、FiberMall、AOI	Molex、CIG、II-VI
400G ER4	QSFP-DD	FiberMall、Cisco	_

Table9：Representative optical module manufacturers of 100Gb/s LR1/ER1 and 400Gb/s LR4/ER4

The core photoelectric chip devices of the single-wave 100Gb/s PAM4 technology are mainly produced by foreign manufacturers, and some domestic manufacturers have made progress at the current stage. The qualification rate of screening 53GBaud EML lasers from 25GBaud EML lasers is low, and chip structure design, material doping, etc. are needed to be optimized, so as to solve the challenges and problems of increasing bandwidth while ensuring reliability. The 53GBaud APD detector chip is relatively mature at home and abroad, and the domestic products have excellent performance. The PAM4 DSP chip has developed rapidly in China in the past two years with the 50Gb/s rate having samples in small batches and good test performance. The 100Gb/s and 400Gb/s products are in the research and development stage.

Device classification	Key chip	Representative manufaturer
		10km	40km
Optical chip	53GBaud EML	Mitsubishi、SEDI、Lumentum、Broadcom、NeoPhotonics	Mitsubishi、SEDI、Lumentum、Broadcom、NeoPhotonics
	53GBaud PIN	Kyosemi、GCS、Albis	_
	53GBaud APD	_	Macom
Electric chip	53GBaud linear TIA	Inphi、Semtech、Macom	Inphi、Semtech、Macom
	DSP	Inphi、Broadcom	Inphi、Broadcom

Table10： 100Gb/s 10/40km core optoelectronic chip device of the optical module

Device classification	Key chip	Representative manufaturer
		10km	40km
Optical device	53 GBaud CWDM EML	Mitsubishi,SEDI,lumentum,Broadcom,NeoPhotonics	_
	53 GBaud nLWDM EML	_	Mitsubishi,SEDI,lumentum,Broadcom,NeoPhotonics
	53 GBaud PIN	Kyosemi,GCS,Albis	_
	53 GBaud APD	_	Macom
Electric chip	53 GBaud linear TIA	Inphi,Semtech,Macom	Inphi,Semtech,Macom
	DSP	Inphi,Broadcom	Inphi,Broadcom

Table11：400Gb/s 10/40km core optoelectronic chip device of the optical module

In terms of application and deployment, 100Gb/s LR1 and 400Gb/s LR4 optical module products have basically grown into maturity, and shipments have gradually increased based on market demand; 100Gb/s ER1 and 400Gb/s ER4 are expected to become commercially available in mid-2022. 100/400Gb/s optical modules based on single-wavelength 100Gb/s technology have also begun to occupy an important position in the blueprint of operator deployment and equipment vendor integration, and there will be a large demand for them in the next few years. According to the mode of carriers’ bearer network, 30/40km optical modules are mainly used in wireless middle-haul and back-haul scenarios. When 100Gb/s ER1 has a cost advantage, it will become a strong contender with the existing 100Gb/s ER4. In the future, the market may support OTN 400Gb/s signal requirements on the basis of supporting Ethernet applications and further discussion is needed for enhancing the application space of 100Gb/s ER1 and 400Gb/s ER4.

(3)  50/100/400Gb/s 80~120km optical module

For the transmission distance of 80~120km, the coherent DWDM technology can solve the link dispersion problem through DSP, reduce the optical signal-to-noise ratio requirement, and have good performance. In order to further reduce power consumption, cost, and occupied space, the industry is also actively exploring DWDM color and gray light technology solutions with direct modulation and detection technology for 80~120km transmission distance.

Solution		Modulation code	Wave band	Channel Spacing	Channel number	FEC Type	Dispersion compensation	Power efficiency	Fiber capacity	Form factor	Relative cost
Colored light	Coherence	100G DQPSK	C	100 GHz	48/96	CFEC	FEC	18W/100G	4.8/9.6 Tb/s	QSFP-DD/ CFP2-DCO/ CFP	3
		400G 16QAM	C	100 GHz	48	CFEC	FEC	5W/100G	19.2 Tb/s	QSFP-DD/ CFP2-DCO/ OSFP/ CFP-16L	8
	Direct mudulation and detection	50G PAM4	C	50 GHz	80	KR4/KP4 /IFEC/SFEC	External dispersion compensation is required beyond ±100ps	4.5W/100G	4 Tb/s	QSFP28	1
		100G PAM4	C	100 GHz	80	KR4/KP4 /IFEC/SFEC	External dispersion compensation is required beyond ±40ps	4.5W/100G	8 Tb/s	QSFP28	1.5
Gray light	Direct mudulation and detection	4X25G NRZ	O	_	_	KR4	No dispersion compensation required	6.5W/100G	100 Gb/s	QSFP28	0.5

Table12：Comparison of 100G/400G 80~120km technical solutions

Conclusion:

The rapid development and construction of data centers have brought opportunities and vitality to the optical module market. At the same time, they have also raised new demands and higher challenges for optical modules such as high speed, high performance, low power consumption, low cost, and intelligence. Strengthening technological innovation, guiding market agglomeration, and strengthening industrial base support are effective means of coping with those challenges. All parties in the industry and the upstream and downstream industrial chain need to form a joint force and promote coordinated progress. In terms of technological innovation, R&D and innovation of technologies such as new materials, new designs, new processes, new packaging, and new frequency bands are used to meet the new demands for optical modules in various application scenarios.