Single Fibre Bidirectional 'BiDi' Optics

Traditionally fibre optic communication utilises 2 cores or strands of fibre between devices to achieve full duplex transmission. One core is exclusively used for the transmit direction, the other core for the receive direction. However advances in optical technology now mean that both the transmit and receive directions can reside on a single core providing full duplex bi-directional communication with just half the infrastructure.

Single fibre optics, commonly referred to as 'BiDi', can achieve better utilisation of your fibre infrastructure.

Benefits includes :-

  • The potential to double capacity.
  • The possibility to serve twice as many customers.
  • Cost savings, only having to rollout and maintain half the amount of fibre.
  • The ability to maximise investment in existing infrastructure. Migrating to single fibre optics on links that are nearing capacity or where infrastructure needs to be freed up.

Single fibre transmission is achieved via the innovative use of Wave Division Multiplexing. WDM assigns each direction its own wavelength and this enables each to co-exist on the same fibre.

Single Fibre Bidirectional BiDi Optics

Single fibre optics are available as either a fixed option built into the equipment and designated at time of ordering or where the equipment employs a modular optic, in the form of an SFP, then these SFP's can be ordered as a single fibre variant.

Below shows a fixed single 'SC' connector integrated into a media converter card versus an SFP that presents a single 'LC' connector.

Single Fibre fixed 1x9 Optic vs SFP

If you'd like to take advantage of single fibre optics but find that it's not possible to change the fibre interface on your equipment then by using a suitable transponder you can effectively convert your duplex arrangement into a single fibre one. Our transponders provide Optical / Electrical / Optical conversion and are completely transparent to the protocols running over them. They simply sit between your equipment and the fibre infrastructure.

Single fibre optics need to be used in pairs with specific A & B ends. The 'A' end transmits at one wavelength and receives at another. The 'B' end is required to do the reverse. We must therefore make sure that the optics are 'married up' correctly to ensure proper operation.

One interesting development in the use of single fibre SFP's is the cSFP or Compact SFP. We can see from the above drawing that when a single fibre arrangement is provisioned within an SFP only half of the SFP is physically occupied. Why not occupy the other half with another single fibre package? The cSFP can do this, allowing us to feed 2 end points each over a single fibre.

Compact SFP cSFP 2 x Gigabit Ethernet SIngle Fibre BiDi


The CT-GSW-4448CM Enterprise switch utilises the cSFP.  This switch has the capability to provide up to 48 Gigabit fibre links. By making use of the cSFP format this density can be realised in only 1U of space.  Uplink and backhaul of traffic is achieved via an additional 4 dual rate 1/10Gbps SFP's.

GSW-4448CM cSFP BiDi Ethernet Switch

Single fibre BiDi optics are are not limited to Ethernet only applications. Single fibre optics can be provisioned in many other of our products -

CWDM / DWDM Multiplexers
Serial Fibre Optic modems - X.21, RS530, RS232, V.35, RS449
E1/T1, E3/DS3 Fibre Optic modems
Primary and Basic Rate ISDN (PRI/BRI)
Contact Closure and Digital I/O over Fibre
Analog Telephony / POTS over Fibre
Fibre Optic Multiplexers
SDH / PDH Multiplexers