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100G QSFP28 LR4 DML version and EML version

Number of visits: Date:2017-6-20 18:30

Abstract:

There are two types of lasers in 100G QSFP28 LR4 product:EML(Electlro-absorption Modulated Laser)and DML(Directly Modulated Laser);


 

EML

DML

Chirping

Small

Large

Extinction Ratio

Large

Small

Optical Eye Diagram Performance

Large Standard Margin

Small Standard Margin

Jitter Performance

Small

Larger

Power Consumption

Large

Smaller

Cost

High

Low

Drive Cost

High

Low

Transmission Distance

40km

10km

Carrier-class Application

Supported

To be discussed

Global Supply Situation

Tight

In General


Comparing several aspects in the above chart no matter it is cost、power consumption or transmission distance ,we can target EML for carrier-class applications, and DML is suitable for data center applications IEEE802.3ba defines the standard for 100GBASE-LR4.From the whole OSI,the LR4 product series has w/o FEC capabilities on the PHY, and the BER requirements for optical module products should be less than 1E-12 to guarantee packet loss rates for communications.


100GBASE-LR4 requires a wide range of TX parameters - more than 4dB for ER requirements,so it leaves space for DML as well as EML.Compared to the ER requirements of ER4 greater than 8dB, so it can only use EML, and DML is not up to this modulation depth.


The only embarrassing thing to DML is the eye pattern.For EML lasers,the margin of 100GBASE-LR4 eye pattern template is at least 30% to 35% ,but 20% is already good for DML.Because the smaller DML eye diagram ER and larger jitter lead to eye template not as good as EML's, but still in the scope of the agreement.


EML Eye Diagram DML Eye Diagram


The reception portion is less differentiated because the receiver sensitivity defined by the IEEE802.3ba is OMA.From the following conversion formula, it is known that RX_SEN (OMA) is related to the magnitude of the emitted light ER value.So when the EML and DML ER are different, the RX_SEN (Pave) will be different, but converted to RX_SEN (OMA) value,they are in the same range.


RX_SEN(Pave) to RX_SEN(OMA):

ER=P1/P0;(1)

POMA=2*PAVE*(ER-1)/(ER+1);(2)


 

ER

RX_SEN(Pave)

RX_SEN(OMA)

DML

5dB

-11dBm

-10.8dBm

EML

10dB

-13dBm

-10.8dBm


Comparison of module power dissipation in full temperature range:


 

EML

DML

Power Consumption

3.5~4.5W

2.6~3.5W


SFF-8436 MSA defines the QSFP module power consumption level, the maximum is 3.5W.In other words,because of the power consumption relationship, the QSFP28 LR4 with EML laser may not be used in the case that the design margin of the equipment power supply is insufficient.


In general,DML LR4 products will gradually become the mainstream of 100GE applications.The only downside is that the application of OUT-4 has not yet been supported,mainly due to the higher rate of DFB lasers.If the DFB can be used at 28Gbps, the DML supported OUT-4 is just around the corner.

TypeInfo: Blog Articles

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