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Message ID: 1891     Entry time: Wed Aug 12 12:08:16 2009
Author: Stephanie 
Type: Update 
Category: General 
Subject: Multiply Resonant EOM Update 

I measured the magnitude of modulation as a function of frequency using the optical spectrum analyzer and an oscilloscope while generating signals using a Marconi signal generator; the results are shown in the attached plot and are compared to the expected modulation given the measured transfer function of the circuit and the nominal modulation index of the EOM used (13 mrad/V). Using the oscilloscope, I found the resonant peaks to be at 11.11 MHz, 29.57 MHz, and 54.70 MHz. There are several different colors on the plot; this is because I had to take the data in several different segments and had to switch to measuring a different sideband partway through the measurment. I also separately found the modulation at each resonant peak for each sideband. The magnitude of modulation was measured  by finding the ratio between the magnitude of the carrier and sideband powers using an oscilloscope, and calculating the magnitude of modulation from this. This method was also used to quantify the dependence of modulation magnitude on input power at each resonant peak; these results are also attached. These same results can also be plotted as modulation magnitude as a function of voltage into the resonant circuit; this is also attached (I'm not sure which is more useful).

In order to produce these results (get the measurements in mrad/V) it was necessary to measure the gain of the amplifier. I used the signal generator to input signals of varying power and measured the output signal voltage using the oscilloscope; I then repeated this process at each resonant frequency. From this I was able to calculate the gain of the amplifier to be 28.1 dB at 11.11 MHz, 27.4 dB at 29.57 MHz, and 25.7 dB at 54.70 MHz. These values are in the same ballpark as the values in the Mini Circuits data sheet (all values are ~25-28 MHz).

Attachment 1: Modulation.png  12 kB  | Hide | Hide all
Modulation.png
Attachment 2: Linearity.png  16 kB  | Hide | Hide all
Linearity.png
Attachment 3: Linearity_V.png  15 kB  | Hide | Hide all
Linearity_V.png
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