**3. RSOA devices static characteristics**

Optical gain measurements depending on the input current and optical power were realized. Figure 4 shows the experimental setup which is used to perform static measurements. The required wavelength controlled by an external cavity laser is launched into the RSOA through an optical circulator (OC). A combined power meter and attenuator is used to control the input power to the RSOA. An optical spectrum analyser and a power

Next Generation of Optical Access Network Based on Reflective-SOA 9

Fig. 5. Confinement effect on 700 µm long RSOA depending on the current (a) and the

 = 20 % = 80 %

from a device point of view in order to compare similar operating conditions.

Two optical confinement values have been studied and low optical confinement (Г~20 %) enables the fabrication of high gain devices. It was the consequence of the LSHB reduction inside the active material which leads to an overall higher gain. However, the length (L) also affects the single pass gain (Gs). Again two effects are in competition inside the active zone: the exponential growth of Gs with the length and the non-homogenous carrier density distribution (which leads to strong saturation effect). Therefore a trade-off needs to be found in order to balance these two effects. By increasing the length, the forward and backward amplifications are also increased up to an optimum point. Devices that are too long induce high saturation and reduce the optical gain. Figure 6 (a) shows the optical gain versus the current density in different RSOA cavity lengths. The current density (J) is more relevant

Optical gain (dB)

*b)*


Output power (dBm)


Output power (dBm)

 L = 300 µm L = 500 µm L = 700 µm L = 850 µm

*L = 700 µm, I = 150 mA*

 = 20 % = 80 %

Fig. 6. Length effect on 20% optical confinement RSOA depending on the current density (a)

Gain (dB)

*Γ = 20%, Pin = ‐25 dBm Γ = 20%, J = 10 kA/cm2*

)

 L = 300 µm L = 500 µm L = 700 µm L = 850 µm

output power (b)


Gain (dB)

Optical gain (dB)

*a)*

**3.2 Saturation effect in long RSOA** 

20 40 60 80 100 120 140 160 180 200 220

*L = 700 µm, Pin = ‐25 dBm*

Current (mA)

and on the output power (b) for J = 10 kA/cm2

0 5 10 15 20 25 30 35 40

*a) b)*

Current density (kA/cm<sup>2</sup>

meter are used in order to determine the static performances of the device, such as optical gain, gain peak, bandwidth and ripple, noise figure and output saturation power. The impacts of these several parameters (Γ and L) are experimentally studied in the next subsections.

Fig. 4. Static experimental setup
