Page 65 - rise 2017

0
-10
-20
Output power (mW) -40
-30

-50
-60
-70
-80
-90
1550 1555 1560 1565 1570 1575 1580
Wavelength (nm)

Figure 2: Output spectrum of the Q-switched EDFL at pump power of 39 mW

150

100

Volts (mV) 50 0

-50

-100
-125 -75 -25 25 75 125
Time (µs)

Figure 3: Typical oscilloscope trace of the Q-switching pulse at pump power of 96 mW

Figure 4 shows the relationship between the pulse repetition rate and pulse width with pump power.
As pump power increases from 39 mW to 96 mW, the repetition rate increases almost linearly from
44.33 kHz to 61.77 kHz. As pump power increases, more gain is provided to saturate the SA and thus
increases repetition rate. In contrast, pulse duration decreases from 9.51 µs to 5.57 µs as the pump
power increases. We observe a smaller change of pulse width with the pump power at higher pump
power. This is attributed that the SA is becoming saturated when more photons circulates inside the
laser cavity as the pump power increased. The minimum attainable pulse duration is 5.57 µs, which is
believed to be related to modulation depth of the SA. The pulse duration can be further decreased by
shortening the cavity length and improving the modulation depth of the SA.