[Koji, Suresh]
In the previous measurement, the PDA 255 had most probably saturated at DC, since the maximum ouput voltage of PDA255 is 5V when it is driving a 50 Ohm load. It has a bandwidth of 0 to 50MHz and so can be reliably used to measure only the 11 MHz AM peak. In this band it has a conversion efficiency of 7000 V per Watt (optical power at 1064nm). [Conversion efficiency: From the data sheet we get 0.7 A/W of photocurrent at 1064nm and 10^4 V/A of transimpedance] The transimpedance at 55 MHz is not given in the data sheet. Even if PDA255 is driving a high impedance load, at high incident power levels the bandwidth will be reduced due to finite gain x bandwidth product of the opamps involved, so the conversion efficiency at 11 MHz would not be equal to that at DC.
So Koji repeated the measurement with a lower incident light level:
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V_DC = 1.07 V with 50 Ohm termination on the multimeter.
Peak height at 11 MHz on the spectrum analyzer (50 Ohm input termination) = 48.54 dBm
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Calculation:
a) RF_Power at 11 MHz : 48.45 dBm = 1.4 x 10^(8) W
b) RF_Power = [(V_rms)^2] / 50_ohm ==> V_rms = 8.4 x 10^(4) V
c) Optical Power at 11 MHz: [V_rms / 7000] = 1.2 x 10^(7) W
d) Optical Power at DC = [V_DC / 7000] = 1.46 x 10^(4) W
e) Intensity ratio: I_AM / I_c = 7.9 x 10^(4) . AM:Carrier amplitude ratio is half of the intensity ratio = 4.0 x 10^(4)
f) PM amplitude ratio from Mirko's measurement is 0.2
g) The PM to AM amplitude ratio is 506
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As the AM peak is highly dependent upon the drifting EOM position in yaw, it is quite likely that a higher PM/AM ratio could occur. But this measurement shows how small it could get if the current situation is allowed to continue.
Quote: 
[Mirko / Kiwamu]
We have reviewed the AM issue and confirmed the ratio of AM vs. PM had been about 6 x10^{3}.
The ratio sounds reasonably big, but in reality we still have some amount of offsets in the LSC demod signals.
Next week, Mirko will estimate the effect from a mismatch in the MC absolute length and the modulation frequency.
(Details)
Please correct us if something is wrong in the calculations.
According to the measurement done by Keiko (#5502):
DC = 5.2 V
AM @ 11 and 55 MHz =  56 dBm = 0.35 mV (in 50 Ohm system)
Therefore the intensity modulation is 0.35 mV / 5.2 V = 6.7 x 10^{5}
Since the AM index is half of the intensity modulation index, our AM index is now about 3.4 x 10^{5}
According to Mirko's OSA measurement, the PM index have been about 0.2.
As a result, PM/AM = 6 x 10^{3}
Quote from #5502 
Measured values;
* DC power = 5.2V which is assumed to be 0.74mW according to the PDA255 manual.
*AM_f1 and AM_f2 power = 55.9 dBm = 2.5 * 10^(9) W.


