5.2.3 Measurement Result
In this characterization, we used the actual modulator structure for the pump probe
measurement in the setup described above, however, the measured response was not
limited by the device parasitics. After propagating through the SiGe modulator with
suitable delays, the probe and reference beams were simultaneously incident on a slow
detector. The amplitude of the difference frequency (1 MHz) was detected using a
high-frequency lock-in amplifier. This signal is proportional to the transmission of the
modulator. The energies of the pump and probe pulses were 650fJ and 20fJ,
respectively.
The response of the modulator depends strongly on the pump wavelength and
bias voltage, Typically, the modulator transmission varies abruptly over a few
picoseconds and recovers to its initial transmission value within several tens of
picoseconds. Fig 5.11 shows the relative transmission variation of the modulator,
immediately after perturbation from the pump pulse vs. the bias voltage for various
pump wavelengths. For low bias voltage (typically below 4 V), the modulator
response is weak. For large bias voltage, the response depends on the pump
wavelength. It can be seen that at 1.4µm wavelength, the transmission variation is
strongest.
81
0
2
4
6
8
10
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
0.05
0.06
1380nm
1390nm
1400nm
1410nm
1420nm
1440nm
1450nm
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