## 4 The Deployment of WDM-PON Protection Schemes
### Power Budget Considerations for WDM-PON Protection Schemes  
The evolution of WDM-PON networks directs towards larger coverage of access areas, higher number of subscribers and wider available broadband for services [19]. The Power Budget (PB) in the WDM-PON network is an important parameter for the designing of optical telecommunication networks together with other considered features as a network type, a utilized technology, a network range, a traffic protection, and a mutual interconnection of network components.  
The available optical budget \(PB_{WDM}\) involving losses due to various components used in WDM-PON networks can be mathematically expressed as follows:  
\[PB_{WDM}=P_{Tmin}-R_{Smith}~{}[\text{dB}] \tag{5}\]  
where \(P_{Tmin}\) is the minimum transmitted power generated by the OLT laser source launched onto the optical fiber in [dBm], and \(R_{Smith}\) presents a minimum average power requested by the ONU receiver in [dBm] [5].  
The signal attenuation is given as a sum of losses from all components \(L_{WDM~{}comp}\) as  
\[\sum L_{WDM~{}comp}=\alpha\cdot FF+\alpha\cdot DF+L_{s}+m\cdot L_{\text{con}}+ L_{AWG}+L_{MUX/DEMUX}+SM~{}[\text{dB}] \tag{6}\]  
where \(FF\) presents a length of the feeder fiber in [km], and \(DF\) presents a length of the distribution fiber in [km]. In a case of the WDM-PON network, the (\(FF+DF\)) fiber length is taken from a 20 km to 100 km range. The specific attenuation \(\alpha\) gently differs for various utilized wavelengths in the WDM-PON network. For the power budget calculation, it can be considered \(\alpha\) = 0.25 [dB/km] at the 1550 nm central wavelength for a standard single-mode fiber. The loss due to splices is \(L_{s}\) = 0.2 [dB], whereby one splice is realized at each 5 km. The loss due to connectors is \(L_{con}\) = 1 [dB], whereby one connector is used at 10 km, and \(m\) is a number of connectors used. For the AWG element, a provision of the wavelength routing for eight different wavelengths around the 1550 nm central wavelength is supposed. The attenuation of this element is \(L_{AWG}\) = 5 [dB]. The losses due to multiplexers and demultiplexers are represented by \(L_{MUX/DEMUX}\) = 2 [dB]. The System Margin (SM) allocates a certain amount of power to additional sources of power penalty that may develop during a system lifetime because of a component degradation or other unforeseen events. A system margin is from the 3 to 10 dB range, and it is allocated during a process of network designs [31].  
Subsequently, the calculated optical power budget \(PB_{WDM~{}calc}\) in passive optical networks [5] is determined as follows:  
\[PB_{WDM~{}calc}=PB_{WDM}-\sum L_{WDM~{}comp}~{}[\text{dB}] \tag{7}\]  
For correct power budget considerations, both input and output power levels at OLT and ONU modules and simultaneously all kinds of attenuations occurring in the passive optical network should be known [5]. For evaluation of the total network availability for each considered WDM-PON protection scheme, a power budget and a number of subscribers due to their impacts on functionality and operation of given protection schemes must be necessarily included.