Coupler | Generic term for Splitters, Combiners and their amalgamated form. Used to split the power in one or more input fibres into 2 or more output fibres. Normally described by N x M where N is the number of input and M the number of output fibres. The ratio in which input power (Pi1 through PiN) is combined and output power (Po1 through PoM) is split can be different. | 
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Splitter | Used to split the power in one input fibre into 2 or more output fibres. Normally described by 1 x M where 1 is the number of input and M the number of output fibres. The ratio in which output power (Po1 through PoM) is split can be different. | 
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Combiner | Used to combine the power in 2 or more input fibres into 1 output fibre. Normally described by N x 1 where N is the number of input and 1 the number of output fibres. The ratio in which input power (Pi1through PiN) is combined can be different. | 
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Tap | Normally used to sample the light in a fibre for monitoring purposes i.e. a low ratio (PoT ~ 0.01 x Pi) splitter | 
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Tree coupler | 1 X M coupler | 
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X coupler | 2 x 2 coupler (or larger) | 
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Multiplexer (WDM) | Combines 2 or more signals of different wavelengths on separate fibres into 1 signal on 1 fibre | 
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Demultiplexer (WDM) | Separates the signal on one fibre into 2 or more signals of different wavelengths on separate fibres | 
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Excess Loss | The difference between the aggregate input power and output power i.e. a measure of the device's losses. Excess loss = Σ(Pi1, Pi2...PiM) - Σ(Po1, Po2...PoM) | |
Insertion Loss | The difference in power between a particular input and output fibre. Insertion Loss = Pox - Piy | |
