BiDi Transceiver Overview

The primary difference between Bi-Directional (BiDi) transceivers and common optical transceivers is that BiDi transceivers combine the transmit and receive functions on to a single fiber (single-mode or multi-mode). That’s to say, unlike common optical transceivers which have two ports, BiDi transceivers have only one port (as shown in the following figure). They use wavelength division multiplexing (WDM) technology to send and receive both directions using different center wavelengths.

In the market, there are now three commonly used types of BiDi transceivers: BiDi SFP+ transceivers, BiDi XFP transceivers and QSFP BiDi transceivers. Both BiDi SFP+ transceivers and BiDi XFP transceivers are designed for Bi-Directional 10G serial optical data communications, while QSFP BiDi transceivers allow reuse of existing 10G fiber infrastructure for 40G connections. All these BiDi transceivers are widely used in telecommunication and data bidirectional communications applications. This article will introduce BiDi transceivers from the aspects of components, operating principle and economic advantages.

Inside a BiDi transceiver there is a component named bidirectional optical sub-assemblies (BOSA), which is composed of a sending laser diode, a receptor and a 2 channel WDM. At one end of the BOSA, there are electrical signals that are fed in and out respectively, and the other end is positioned a single fiber connector. In addition, a very short single-mode fiber could also be found inside the connection to the single fiber connector.

Unlike common two-fiber optical transceivers, the WDM couplers (also known as diplexers) equipped in the BiDi transceivers can help to combine and separate data transmitted over a single fiber according to the wavelengths of the light. Thus, BiDi transceivers can also be called WDM transceivers. To work effectively, BiDi transceivers must be used in matched pairs. Therefore, the diplexers could turn to match the expected wavelength of the transmitter and receiver transmitting data. To make it clearly, here is an example:

If paired BiDi transceivers are being used to connect Device A (Upstream) and Device B (Downstream), as shown in the figure below (Tx represents transmit, Rx represents receive), then:

Transceiver A’s diplexer must have a receiving wavelength of 1490nm and a transmit wavelength of 1310nm

Transceiver B’s diplexer must have a receiving wavelength of 1310nm and a transmit wavelength of 1490nm

The most obvious advantage of using BiDi transceivers is that they help to reduce the cost in fiber cabling infrastructure. This is because that BiDi transceivers decrease the number of fiber patch panel ports and the amount of tray space dedicated to fiber management. Moreover, they require less fiber cable.

Although the price of BiDi transceivers are higher than that of common transceivers in the market, BiDi transceivers utilize half the amount of fiber per unit of distance. For many networks, the cost savings of utilizing less fiber far exceed the higher purchase price of BiDi transceivers.

The deployment of BiDi transceivers instantly doubles the bandwidth capacity of the existing optical fiber infrastructure and helps customers to achieve economical and efficient performance for their fiber optic network.

Originally published at www.fiber-optical-networking.com.