What is Bidirectional Transmission (BiDi)?

Have you ever heard of the term BiDi (commonly read as "baidai")? BiDi means Bi-Directional.

For 40GBASE-SR4 and 100GBASE-SR4 multimode fiber optic (MMF) transmission, 12-fiber multi-fiber cables with MPO connectors are usually used.

Communication is performed using 4 of these 12 cores for transmission and the other 4 cores for reception.

On the other hand, the BiDi optical transceiver performs bi-directional transmission and reception over a single optical fiber.

Advantages of using BiDi optical transceivers

The optical fiber with MPO connector used in the SR4 optical transceiver is a cord-shaped cable in which 12 fibers are bundled, and is thicker and less flexible than 1-fiber.

Along with the increase in network traffic, the number of 100G optical transceivers accommodated in transmission equipment is also increasing. Dealing with it will be a challenge.

Also, every time the transmission equipment is upgraded, it is not easy to replace all the optical fiber groups that are stretched freely between the equipment, both in terms of work and cost, and it is not possible to continue using it for a certain period of time. is asked.
 

Each BiDi optical transceiver requires only two optical fibers with LC connectors, which eliminates the difficulty of handling optical fibers, and upgrades networks that were conventionally built with 10GBASE-SR SFP+ or 40G BiDi to 100G. Even in this case, there is an advantage that the optical fiber group can be used as it is.

Top: QSFP+ optical transceiver

Middle: 12-fiber with MPO connector

Bottom: 1-core optical fiber with LC connector

Structure of 100G QSFP28 BiDi Optical Transceiver

Figure 1 shows a block diagram of the QSFP28 100GBASE-SR4 optical transceiver.

Both the electrical side interface (CAUI4) and the optical side interface use 4 lanes for transmission and reception, and similarly, 4 optical fibers are required for transmission and reception (8 fibers in total).

Figure 2 shows the block diagram of the QSFP28 100GBASE-SR4 BiDi optical transceiver.

The electrical side interface is common to CAUI4, but the internal NRZ to PAM4 CODEC IC converts 4x25Gbps NRZ ↔ 2x50Gbps(25GBaud) PAM4. These two 50Gbps signals are transmitted by two Lasers (Laser1,2) and two PDs (PD1,2).

Two lasers and two PDs operate at different wavelengths (850nm and 900nm bands), and transmit and receive light with different wavelengths are bi-directionally communicated over a single optical fiber. Since the wavelengths are different, there is no interference between the transmitted light and the received light within one core.

Figure 1 QSFP28 100GBASE-SR4 optical transceiver

Figure 2 QSFP28 100GBASE-SR4 BiDi optical transceiver

Diversion of BiDi to 400G

BiDi has been put into practical use for 10G, 40G, and 100G. And now 400G has been standardized (IEEE802.3cm 400GBASE-SR4.2).

In 400GBASE-SR4.2, like 100GBASE-SR4 BiDi, 50 Gbps bi-directional communication is performed on one fiber, and 8 fibers are used to achieve 400G transmission.

For the 400G transceiver, considering connection with existing 100G equipment, an application (Breakout) that treats 400G as four independent 100G is also assumed.

A 100GBASE-SR4 BiDi optical transceiver can be used as a Breakout connection destination for a 400GBASE-SR4.2 optical transceiver.

Inquiry

Broadcom has a lineup of 40G and 100G BiDi optical transceivers.

40G BiDi : AFBR-79EBPZ

100G BiDi : AFBR-89BDDZ

We also have many other products, so please visit the Broadcom optical transceiver product website and contact us below.