3. Experimental Results
In order to demonstrate the UWB generation approach, an experiment has been carried out
according to Fig. 1. The pump laser was externally modulated with a quasi-Gaussian pulse train.
The electrical signal that is introduced into the EOM has a fixed pattern of one B1[ and sixty-three
B0[, summing up a total of 64 bits with a bit rate of 12.5 Gb/s. Fig. 3(a) shows the equivalent pulse to
the input of the EOM and Fig. 3(b) plots the optical output of the EOM corresponding to the time
varying optical pump signal. It is important to mention that the EOM is biased in a negative region so
an inverted pulse is obtained which is essential to guarantee the saturation of the SOA1 with high
level of power coming from the pump signal.
As it was shown in Fig. 1, the pump signal is introduced into Port 1 ðP1Þ, the probe signal into the
port P4 and the system output is obtained at port P2 where a PD is connected to detect the RF signal.
As previously mentioned, it was important to control the operation currents for SOA1 and SOA2. In
this case, the operation current for SOA1 ðI1Þ is set at 300 mA, but the value for I2 is gradually
modified in order to measure the resulting waveform and spectrum through a digital communication
analyzer (DCA) and an electrical spectrum analyzer (ESA). First, a current of 300 mA is applied to
SOA2. Such current value corresponds to an operation region in the transfer function with negative
slope. As expected, the output pulse is inverted leading to the generation of a quasi-Gaussian
pulse as shown in Fig. 4(a). The corresponding spectrum is visualized in Fig. 4(b).