Tara and I re-measured the transfer function coupling the RIN to frequency noise at five different power levels.
We were having problems with the ACAV gain at low powers, so we chose appropriate attenuation through an OD filter to compensate.
The following plot shows the TF's measured, with their corresponding ACAV power levels:
The transfer functions measured at 2.2mW, and 1.9mW were measured with a .15 OD filter. Those measured at 1.77mW, 1.6mW, and 1.42mW were measured with a .10 OD filter.
As shown in the plot, the magnitudes of the transfer functions measured at different power levels match up quite nicely, confirming the validity of the transfer function. The phase plots are pretty consistent, with slight variation up to 20 degrees at higher frequencies.
I converted the above transfer function magnitudes to units of [Hz/Watt] and plotted the results with the calculation using Cerdonio's result:
The main source of error between the calculated and measured transfer function is from the voltage to power calibration. We will re-measure this and see if a result closer to the calculation is achieved. Since the measured transfer functions are all fairly consistent with each other in magnitude, I used the transfer function measured at 2.2mW and calculated the residuals for the calculation w/ Cerdonio's results:
I attached the raw data, where the first column of each .mat variable is frequency and the second is dB for magnitude variables and degrees for phase variables. |