BiDi Fiber Optic Transceiver Overview

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As we all know, common optical
transceivers, like SFP+, SFP, normally require two fibers to achieve data
transmission between switches, firewalls, servers, routers, etc. The first
fiber is dedicated to receiving data from networking equipment, while the other
is to transmit data to the equipment. With the development of technology, a new
class of pluggable optical transceiver—BiDi
fiber optic transceiver has been developed to combine the transmit and
receive functions onto a single fiber (single-mode or multimode). The image
below shows the differences between common optical transceiver and BiDi
transceiver. How does BiDi transceiver achieve the transmission of optical
channels on a fiber propagating simultaneously in both directions? What are the
most commonly used BiDi transceivers available on the market? Is it worthwhile
to use this kind of transceiver which is much more expensive than standard
transceiver? The following test will provide more details from these three
aspects.

 

How Does BiDi Fiber Optic Transceiver
Work?

BiDi fiber optic transceiver is also
called as WDM transceiver, since it is fitted with WDM coupler, which helps to
combine and separate data transmitted over a single fiber based on the
wavelengths of light. Unlike common optical transceivers use two fibers for
duplex transmission, BiDi transceiver uses two different wavelengths to carry
the duplex signals separately. The optical signals for transmitting and
receiving are separately converted into signals of specific wavelengths as
shown in the following image. This is why BiDi transceiver module can achieve
the transmission of optical channels on a fiber propagating simultaneously in
both directions.

 

Three Commonly Used BiDi Transceiver
Types

Currently, there are a lot of fiber
optic transceivers designed with BiDi technology available on the market, but
the most commonly used ones are BiDi SFP, BiDi SFP+ and BiDi QSFP+. The
following part will introduce them one by one.

 

BiDi SFP: BiDi SFP (shown in image
below), compliant with the SFP multi-source (MSA), is specially used for the
high-performance integrated duplex data link over a single optical fiber. It
uses a long wavelength DFB laser diode, enabling data transmission up to 80 km
on a single fiber. Generally, BiDi transceiver can be produced with LC simplex
port which is used both for transmitting and receiving. Nowadays, it is one of
the most popular industry formats supported by many fiber optic component
vendors.

 

BiDi SFP+: Like BiDi SFP, BiDi SFP+
(see following image) is also connected by simplex LC fiber cable. Currently,
BiDi SFP+ transceivers using 1270 nm and 1330 nm for transmission are most
commonly used for 10G transmission. And it can achieve 10G data rate for the
link lengths of 10 km, 20 km, 40 km, and 80 km. When you select BiDi
transceivers, please take these two factors into consideration.

 

BiDi QSFP+: BiDi QSFP+ transceiver is a
latest product used for 40G short-reach data communication and interconnect
applications. Compliant with the QSFP MSA specification, it is terminated with
a duplex LC connector interface to transmit data over laser-optimized OM3 and
OM4 multimode fiber cables for the length of up to 100 m and 150 m
respectively, that is the same as the traditional QSFP-40G-SR4. This 40G
transceiver has two 20G channels, and each channel transmits and receives two
wavelengths over a single multimode fiber strand. The following picture is a
BiDi QSFP+ transceiver.

 

Why Should We Use BiDi Fiber Optic
Transceiver?

Generally, BiDi fiber optic
transceivers are much more expensive than common fiber optic transceivers. From
fiber-mart.com, a Cisco SFP-10G-SR is 16 dollars, while a cheapest Cisco BiDi
SFP+ transceiver is 50 dollars. Is it worthwhile to use this kind of transceiver?
The answer is definitely yes.

 

As we have mentioned above, compared to
traditional optical transceivers, BiDi transceivers uses fewer fibers (about 2
fibers) to support signal transmission, which can save an amount of money for
you. Take BiDi QSFP+ transceiver as an example, if you are building a new 40G
data center fabric in the traditional way, you would need to run 8-multimode
fiber strands between your access and aggression layer: a cost of $2000 per
port. However, with BiDi QSFP+ transceivers, you can get 40G performance using
just 2 fiber strands: a quarter of cabling. For a standard server rack (384
ports), that translates to a savings of more than $550,000.

 

Summary

Although the label price of BiDi fiber
optic transceiver is higher than standard optical transceiver, it is of much
more value in practical applications. With the existence of BiDi fiber optic
transceiver, the cost of fiber infrastructure will reduce, while the network
capacity will increase. But keep in mind that BiDi transceiver is usually
deployed in matched pairs to get the work most efficiently, since it uses two
different wavelengths for transmission.