This document introduces bi-directional (bidi) optical transceivers that allow for sending and receiving optical signals over a single fiber strand, effectively reducing fiber usage by half and resulting in cost savings, especially in environments with many connectivity endpoints. Bidi transceivers operate in pairs using two different wavelengths for upstream and downstream communications and are particularly useful in scenarios with limited fiber availability. The document also discusses the economic benefits of bidi transceivers in campus environments, with examples of significant savings compared to standard 2-fiber transceivers.

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Fiberstore (FS.COM) | Introduction to BiDi Optical Transceivers 1
In the past few decades, a new class of pluggable optical transceivers have been developed that
send and receive optical signals end-to-end over a single fiber strand. This reduces by half the
amount of fiber required for that same total data transmission. This factor-of-two improvement can
lead to substantial cost savings especially in campus environments with large numbers of
connectivity endpoints.
Bi-Directional transceivers, called BiDi’s for short, use two different wavelengths to achieve
transmission in both directions on just one fiber. The modules are deployed in pairs, one for the
upstream (“U”) direction and another for the downstream (“D”). The standard defining these parts
is the IEEE 802.3ah Gigabit Ethernet 1000BASE-BXnn (nn= transmission reach in kilometers)
specification for point-to-point Ethernet in the First Mile (EFM) applications.
The value of the BiDi solution derives from the reduction in the use of fibers by a factor of two.
There are many situations in real-world networks where this reduction is extremely important if not
absolutely required. As mentioned above, the IEEE802.3ah specification defining BiDi’s mentions
point-to-point Ethernet in the First Mile (EFM) applications. In addition, BiDi transceivers can be of
great use in any situation where only limited fibers or limited conduit space is available. Other
common applications include: digital video and Closed Circuit TeleVision (CCTV) applications and
high-density switch-to-switch port interconnection.
BiDi Technology…how they work…
As mentioned above BiDi transceivers are deployed in matched pairs, one for the upstream (“U”)
direction and another for the downstream (“D”), each part transmitting at a different wavelength.
The figure below depicts the details of such a matched set of BiDi transceivers. In this example, the
two wavelengths utilized by the BiDi pair are 1310nm and 1490nm. Typically the “Upstream” or “U”
transceiver transmits at the shorter of the two wavelengths and the “Downstream” or “D” module
the longer wavelength.
Introduction to BiDi Optical
Transceivers

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Fiberstore (FS.COM) | Introduction to BiDi Optical Transceivers 2
The key additional technology present in BiDi’s that is not present in standard 2-fiber transceivers is
the “Diplexer”. The Diplexer acts simultaneously couples the locally transmitted wavelength onto
the single fiber while “splitting” off the received wavelength so it is directed at the receiver.
Economic Case for BiDi’s
The value of the BiDi solution derives from the reduction in the use of fibers by a factor of two.
There are many situations in real-world networks where this reduction is extremely important if not
absolutely required. As mentioned above, the IEEE802.3ah specification defining BiDi’s mentions
point-to-point Ethernet in the First Mile (EFM) applications. In addition, BiDi transceivers can be of
great use in any situation where only limited fibers or limited conduit space is available. Other
common applications include: digital video and Closed Circuit TeleVision (CCTV) applications and
high-density switch-to-switch port interconnection.
The simplest economic case for BiDi’s is probably a campus environment requiring fiber connectivity
to a large number of endpoints. For example, most universities campuses are spread over a fairly
wide area and required high-speed (read: fiber) connectivity between campus core resources (e.g.,
databases, computing resources, common internet access, etc.) and a large number of classrooms,
dorm rooms, and faculty and administrative offices. The following is a simple economic model to
demonstrate the savings possible in such an environment using BiDi versus standard 2-fiber
transceivers.
So, for a campus environment where average link length is greater than 800 feet, the BiDi solution is
the right decision. In an real world example, a large university campus lighting 400 GbE fiber links
with an average length of 1600 feet used BiDi’s to save $32,000 versus using 2-fiber transceivers.
FS.COM BiDi Offering
FS.COM offers BiDi transceivers in the SFP form-factor supporting 1GbE for all major switch brands
like Cisco, HP, Juniper, Extreme, Brocade, etc. We offer a 1Gbps SFP BiDi’s to cover a wide range of
distances including: 10km, 20km, 40km, 80km and 120km, all of which are ROHS compliant. To aid
in turn-up and maintenance of BiDi links, all FS.COM BiDi transceivers support Digital Diagnostics
Monitoring (DDM as defined in standard SFF-8472) allowing real-time monitoring of parameters of
the fiber SFP, such as optical output power, optical input power, temperature, laser bias current, and
transceiver supply voltage.

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Fiberstore (FS.COM) | Introduction to BiDi Optical Transceivers 3
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Notice: This document is for informational purposes only and does not set forth any warranty, expressed or
implied, concerning any equipment, equipment features, or service offered or to be offered by Fiberstore.
Fiberstore reserves the right to make changes to this document at any time, without notice, and assumes no
responsibility for its use. This information document describes features that may not be currently available.
Contact a Fiberstore sales team for information on feature and product availability.
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