Introduction

Today, 100G is one of the most widely used technology on the Telecom/Datacom market. But 5G application as well as the upgrade of service like 4K VR, Internet of Things (IoT), and cloud computing increases significantly the demand for bandwidth. Indeed, we can see a 26% annual growth rate of network traffic. Here comes the 400G Considered as the next generation mainstream port technology. The 400G technology provides the ability to significantly improve the network bandwidth by using the installed set-up of interconnection helping operators and customer to cope with the massive growth of data traffic.

Today, IEEE, ITU, OIF and MSA have already released standards for 400G and are working on 800G standards to cover the future growth of data traffic.

Skylane Optics and 400G?

Skylane Optics investigated on the coming trends for 400G transceivers technology and as for 100G application, the 400G transceivers have been developed following 2 main points being high density and low power consumption. 3 main formats are coming on the market, the CFP8, a bit smaller than CFP2, the OSFP having his own thermal management and the QSFP-DD being backward compatible with the current QSFP28.

Skylane Optics investigated on the coming trends for 400G transceivers technology and as for 100G application, the 400G transceivers have been developed following 2 main points being high density and low power consumption. 3 main formats are coming on the market, the CFP8, a bit smaller than CFP2, the OSFP having his own thermal management and the QSFP-DD being backward compatible with the current QSFP28.

Skylane Optics is then coming with a full range of transceiver for 400G application in order to cover all the applications and demand of the Telecom/datacom market.

The below schematics shows the different standards based on distances:

The below schematics shows the different standards based on distances:

Standard naming based on distance

More options are coming to cover all the datacenter needs and Skylane Optics remains attentive at every new technology.

400G Technology

Single Mode transceivers

Transceivers using 8x 50G PAM4 like FR8: The “8” indicates the use of 8 wavelengths with each one operating at 50G PAM4. The 8 wavelengths are multiplexed into one fiber through a duplex LC interface.

Some transceiver as the 2x FR4 also uses 8 lasers but is divided into 2 groups with four wavelengths. These 2 groups are multiplexed each into a fiber and the transceiver offers a 2x200G interface on dual CS connectors.

Some transceiver as the 2x FR4 also uses 8 lasers but is divided into 2 groups with four wavelengths. These 2 groups are multiplexed each into a fiber and the transceiver offers a 2x200G interface on dual CS connectors.

 

Transceivers using 4x100G PAM4: Those are the current market focus and use 4 lanes with 100G PAM4. Here we can group the transceivers into “Multi Fiber” and “Two fiber” types. The key element in these transceivers is the DSP with its gearbox function.

For instance, in the DR4 transceivers the DSP converts the 8x50G PAM4 electrical host signals into 4x 100G electrical lanes towards the optical engine. At the same time the DSP acts as a CDR. In a DR4 the optical engine (EML lasers or Silicon Photonics SIP based) generates and terminates the optical lanes. Each lane operates at 1310 and requires one fiber. In other words, the transceiver interface needs to have 8 fibers.

For instance, in the DR4 transceivers the DSP converts the 8x50G PAM4 electrical host signals into 4x 100G electrical lanes towards the optical engine. At the same time the DSP acts as a CDR. In a DR4 the optical engine (EML lasers or Silicon Photonics SIP based) generates and terminates the optical lanes. Each lane operates at 1310 and requires one fiber. In other words, the transceiver interface needs to have 8 fibers.

In the case of FR4 and LR4, The basic function of the DSP is the same as in the DR4, but now 4 wavelengths (CWDM4 grid) are being used instead of 4x 1310 signals and a multiplexer is added to combine these CWDM signals together. By this, the number of required fibers is reduced to 2 (TX + RX). The transceivers have duplex LC interfaces.

In the case of FR4 and LR4, The basic function of the DSP is the same as in the DR4, but now 4 wavelengths (CWDM4 grid) are being used instead of 4x 1310 signals and a multiplexer is added to combine these CWDM signals together. By this, the number of required fibers is reduced to 2 (TX + RX). The transceivers have duplex LC interfaces.

Multimode Short Reach (SR) transceivers

The main trend goes to SR8 (IEEE802.3cm) and SR4.2 (MSA BD4.2).

In case of the SR8, the “8” implies there are 8 optical channels on 8 separate fibers. A total of 16 fibers (8 Tx and 8 Rx) are needed as each optical channel operates at 50G PAM4. The SR8 module uses either an MPO-16 connector or a 2 row MPO-12 connector to connect to 8 fiber pairs. The most common implementations use 2 row MPO-12.

In case of the SR8, the “8” implies there are 8 optical channels on 8 separate fibers. A total of 16 fibers (8 Tx and 8 Rx) are needed as each optical channel operates at 50G PAM4. The SR8 module uses either an MPO-16 connector or a 2 row MPO-12 connector to connect to 8 fiber pairs. The most common implementations use 2 row MPO-12.

When talking about the SR4.2, the “4” implies there are 4 optical channels using 4 separate fibers and the “2” means that each channel uses 2 different wavelengths. A total of 8 fibers are needed as each optical channel operates at 2x50G PAM4. The wavelengths are bi-directional and multiplexed. The SR4.2 module uses an MPO-12 connector.

When talking about the SR4.2, the “4” implies there are 4 optical channels using 4 separate fibers and the “2” means that each channel uses 2 different wavelengths. A total of 8 fibers are needed as each optical channel operates at 2x50G PAM4. The wavelengths are bi-directional and multiplexed. The SR4.2 module uses an MPO-12 connector.

The big interest of the SR4.2 is to be able to re-use the existing cables placed in the current installations.

400G Optics Summary

Description Electrical interface Operating wavelength () Optical lane  Connector Distance
SR8 8x50G 850 8x50G MPO-16 100m
SR4.2 8x50G 850/910 8x50G Bidi MPO-12 100m
DR4 8x50G 1310 4x100G MPO-12 500m
DR4+ 8x50G 1310 4x100G MPO-12 2km
2x FR4 8x50G 2x (1271/1291/1311/1331) 8x50G CS 2km
FR4 8x50G 1271/1291/1311/1331 4x100G LC 2km
FR8 8x50G 1275/1277.5/1282.5/1285/1295/1300/1305/1310 8x50G LC 2km
LR4 8x50G 1271/1291/1311/1331 4x100G LC 10km
LR8 8x50G

1275/1277.5/1282.5/1285/1295/1300/1305/1310

8x50G LC 10km
ER4 8x50G 1295/1300/1305/1310 4x100G LC 40km
ER8 8x50G 1275/1277.5/1282.5/1285/1295/1300/1305/1310 8x50G LC 40km

Sources:

  • 400G and 100G PAM4 Transceiver Interfaces published by Dirk Lutz from Eoptolink
  • Arista 400G Architectures and Optics Overview

 

Cédric Doumont

Product Line Manager at Skylane Optics

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