Bi-Directional technology means a communication mode that processes data in both directions (send and receive) over optical fiber. Unlike traditional transceiver modules that use two fibers to transmit data (one is for sending, and one is for receiving), BiDi technology allows modules to transmit and receive data to/from the interconnected network devices (like network switches or routers) via a single optical fiber (as figure 1 shows), which enables users to simplify their cabling system, increase network capacity and reduce cost. With these benefits, BiDi fiber modules are of interest to 5G applications.
On the market, BiDi transceivers adopt two different interface designs, single fiber and dual fiber types.
Typically, most BiDi optical modules feature with one port and use LC simplex single mode fiber to transmit the data, such as 1G SFP BiDi, 10G SFP+ BiDi, 25G SFP28 BiDi and 50G QSFP28 transceiver modules (visit BiDi datasheet to learn more).
At present, these single fiber BiDi modules are usually deployed in applications like ISP networks, FTTX, or data center links that require 1/10/25/50Gbps transmission. They can be installed on switches, media converters, OEO converters to provide high speed and stability optical transmission systems. Here take SFP+ BiDi modules as examples to show the application of BiDi transceivers.
Scenario 1: A pair of 10G BiDi modules are linked via a single LC simplex fiber patch cable to build a direct 10G connection of two 10G switches.
SFP+ BiDi modules work on network switches.
Scenario 2: A pair of BiDi SFP+ transceivers are connected with two fiber media converters by an SMF, and then Ethernet cables are used to connect the media converter and the switch. Thus, the transmission of Ethernet to fiber is achieved.
SFP+ BiDi modules are deployed in media converters.
Scenario 3: BiDi SFP+ can be used to convert dual fiber to single fiber with OEO converters. Connections are shown in figure 4.
SFP+ BiDi modules are used with OEO converters.
In addition, 25/50G Bidi transceivers are welcomed by 5G networks since they can save fiber resources and support high bandwidth, ultra-low latency and high reliability for data transmissions.
40G QSFP+ BiDi optical transceivers use LC duplex interface design. As figure 5 shows, they support two 20Gbps channels, each transmitted and received simultaneously over two wavelengths (850nm and 900nm) on an LC duplex multimode fiber. This 40G transmission will reach 100m distance on OM3 and 150m on OM4 fiber.
QSFP+ BiDi Working Principle
QSFP+ 40G BiDi transceivers is a cost-effective solution for 10G to 40G upgrade. As figure 6 shows, generally users have to use MTP fiber cables to connect the 40G QSFP+ transceivers installed at two ends. But 10G connections are usually achieved by LC fibers. If users decide to upgrade 10G system to 40G, they need to upgrade their cabling system. But now, with QSFP+ BiDi optical transceivers, technicians can reuse the existing 10G LC fiber cabling, which results in zero-cost cabling migration in 10G to 40G upgrade.
Note that, BiDi modules must work in pairs. This means the TX and RX wavelengths of the interconnected BiDi transceivers must be matched. For example, SFP+ BiDi transceivers with 1310nm TX and 1490nm RX just work with SFP+ BiDi transceiver with 1490nm TX and 1310nm RX.
In the 5G area, the front/mid/back-haul transmission requires data transmission in a high-rate, low latency and high-reliability way to support services like telemedicine, autonomous driving and so on. Considering the saving of fiber resources and costs, 25/50G BiDi transceivers are suitable choices for delivering data in the physical layer of 5G communication.
In 5G front-haul transmission, each AAU (Active Antenna Unit) and DU (Distribute Unit) is achieved by fiber optical point-to-point connection, which requires lots of fibers. Besides, 5G requires at least a 10x improvement in download rate than 4G, which means a higher rate transmission is necessary. According to the two aspects, 25G BiDi transceivers are attractive solutions (visit 25G optics in 5G to learn more).
In 5G midhaul and backhaul transmissions, high-speed 50G BiDi modules with PAM4 transmitter prepare well for 100/200G rate applied in the convergence and core layers, so as to meet the load requirements of 5G bearers for large capacity and network slicing.
BiDi transceivers serve as an ideal and feasible solution to help end-users simplify the network cabling and increase network capacity. What's more, 25/50G bidi transceivers prepare well for delivering higher-rate and higher-reliability data transmission in 5G networks.
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