Custom Dual 2x2 Half Duplex Switch (D22HC)
The dual 2x2 half duplex fiber optic switch is two half duplex 2x2 optical switches
in one switch with an extra path in state 2.
The following diagrams show the optical connections for the 2 states. The numbers
identify the fiber endpoints. If looking at it as 2 single half duplex 2x2s, fibers
1, 2, 7 and 8 make up one 2x2 while fibers 3, 4, 5 and 6 make up the other. Note
the extra path connecting fibers 2 and 6.
Although most applications do not require the connection between fibers 2 and 6
in state 2, it is often not an issue and in some cases may be a desired feature
(e.g. a loopback for self-testing of a transmitter/receiver pair).
Power Off Bypass Application Example
One application of a dual 2x2 half duplex fiber optic switch is to bypass a transmit/receive
module that is daisy changed with other modules (e.g. a token ring application).
In this application, selecting a reversed non-latching drive type allows the module
to be bypassed automatically when power is lost.
Below, the diagram illustrates how inserting a D22HC in a ring or daisy chain topology
allows a module to be optically disconnected from the ring or daisy chain while
keeping the other modules connected in the same topology. A "ring module" represents
any dual channel optical device intended to be connected in a ring or daisy chain.
In state 1, the top "ring module" is connected to the "ring" or daisy chain.
In state 2, the top "ring module" is disconnected from the "ring" or daisy chain.
Note that the extra path would have no negative effect since it is simply looping
a transmitter back to a receiver.
Of course the previous diagram could be expanded to have a D22HC providing power
off bypass protection to the other two modules as well.
For more information, see Switch Overview for information that applies to all switch products.