PON is developed for different scenarios, which share some standard components. The main components are splitter/coupler and the Arrayed Waveguide Grating (AWG) that are shown in Figure 1. TDM-PON is using splitter/coupler for downstream and upstream, respectively. In WDM-PON splitter/coupler is being replaced by AWG in the remote node.

Figure 1. Passive splitter/ coupler in a TDM-PON and AWG in WDM-PON

Passive Optical Coupler (POC)

Multiple signals are being combined by the POC, received from different sources. POC can have one or more outputs, as shown in Figure 2.

Figure 2. A 2 x 2 coupler

Signal from input 1 is being coupled to output 1 with fraction alpha(α) (0<α<1). Meanwhile reminder is coupled to output 2. The same way signal from input 2 is being coupled. The fraction from input 2 (1-α) is coupled to output 1. Both outputs have signal combined from two inputs.

3-dB coupler is the 2×2 coupler with α=0.5 where the input signal is split in half between two output ports. Coupler can be wavelength independent – where coupling coefficient is the same for all the wavelengths, or wavelength selective – that works only with particular wavelengths.