**5. Comparison of EDFA and EYDWA for WDM/FSO network**

The FSO-WDM with eight input signals using EYDWA amplifier as a pre- or post-TT6Af an externally modulated WDM transmitter generating eight NRZ signals at 2.5 Gbit/s with input power of 10 dBm, the eight channels are multiplexed with a spacing set at 0.8 nm in the wavelength range 1550 to 1554.8 nm. Then the signal is ready to travel through 30 Km range of FSO. On the receiver's side, the avalanche photodiode (APD) is used followed by a low pass filter and a 3R regenerator. The performance is analyzed using BER analyzer which gives the related BER, power level and eye diagrams.

**Figures 6** and **7** shows the dependence of the gain and noise figure on frequency for both optical amplifiers EDFA and EYDWA, respectively. It is evident that the EYDWA amplifier also offers a better price/performance ratio (better gain of (32 dB and high NF of 11 dB) than comparable EDFA amplifier (Gain of 15 dB and better N Fof 5 dB) for WDM/FSO network applications. Most of the intrinsic advantages of EYDWAs come from their ability to provide high gain in very short optical paths than EDFA amplifier. This capability gives vendors more flexibility in the design of a compact amplifier.

#### **5.1 Concentration quenching affects**

The homogeneous up conversion tends to cause more impairment in the EDFA amplifier performance than in the EYDWA amplifier. **Figure 8** shows variation of gain as a function of the HUC coefficient [15]. It is observed that as this later increased; the gain spectrum decreased and showed larger variation especially for EDFA as compared as EYDWA amplifier. Furthermore for UHC coefficient higher of 2.10<sup>22</sup> m+3/s we can notice lowest results in term of gain for EDFA, however EYDWA amplifier provides the best results (high and flat gain). Also the maximum

**Figure 6.** *Gain and noise figure as a function of frequency for the erbium doped fiber amplifier (EDFA).*

**Figure 7.** *Gain and noise figure as a function of frequency for the Er-Yb doped waveguide amplifier (EYDWA).*

**Figure 8.** *Gain as a function of up-conversion coefficient for the EYDWA and EDFA.*

Q factor values occur for EYDWA amplifier and at lower HUC coefficient as compared as EDFA amplifier **Figure 9**.

### **5.2 Influence of length and erbium doping**

The critical turning point in the EYDWA technology is finding a compromise between the high erbium ytterbium co-doping levels, which helps create large gain in a short optical length [13]. The dependence of EYDWA performance on the length and erbium ion concentration is studied **Figures 10** and **11**.

For better performance the optimization has been done and it was reported of the system amplified (WDM- FSO) under medium rain and at 2.5 Gbit/s. The EYDWA

**Figure 9.** *Q factor as a function of up-conversion coefficient for the EYDWA and EDFA.*

**Figure 10.** *Curves of Q factor versus EYDWA length for WDM-FSO system under medium rain.*

amplifier can be reached higher FSO range (over 12 km) with acceptable quality factor (Q values of 6 and BER = 10<sup>9</sup> ) by increasing the erbium concentration (up to 6.1026 ions/m3 ) and with optimum waveguide length (over 3.5 cm). These results proved that we can achieve high gain with a short device length.

**Figure 11.**

*Curves of maximum gain versus erbium ion concentration for WDM- FSO system under medium rain.*
