Experimental Cryptography Using Continuous Polarization States - Quantum Communications and Cryptography - page 116

200
180
160
140
120
100
80
60
40
20
0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Optical power in µ W

Figure 5.6 DC detector calibration curve. Optical power corresponds to the power
on one photodiode, while the other is blocked.

The DC response of the detectors was calibrated by applying a known
intensity on one of the two diodes while blocking the other diode. The re-
sulting calibration curve is shown in Figure 5.6. The AC calibration is shown
in Figure 5.7. Both diodes were illuminated with the same amount of light,
and the AC response was recorded with a rf spectrum analyzer. The detectors

5.00E-008

4.00E-008

3.00E-008

2.00E-008

1.00E-008

0.00E-008

0 200 400 600 800 1000

Figure 5.7 AC detector output power vs. light intensity for an unmodulated S 1 beam.
This corresponds to a homodyne quadrature measurement of the vacuum field, thus
resulting in a linear power dependence of the detected noise signal.