Modified script to plot multiple RIN curves.
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Time-Series-Analyzer/computeAndcompareRIN.m
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Time-Series-Analyzer/computeAndcompareRIN.m
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% Script to compute the Relative Intensity Noise of a laser by recording the y-t signal
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% by Mathias Neidig in 2012
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% modified for DyLab use by Karthik in 2024
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% The RIN is defined as
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%
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% RIN = 10* log10 [Single-sided power spectrum density / (average power)]
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%
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% and is given in [RIN] = dB/Hz
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clear all
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close all
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%% Set the directory where the data is
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dirDCData = 'C:\\Users\\Karthik\\Documents\\GitRepositories\\Calculations\\Time-Series-Analyzer\\Time-Series-Data\\20240915\\After_AOD\\DC_Coupling\\';
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dirACData = 'C:\\Users\\Karthik\\Documents\\GitRepositories\\Calculations\\Time-Series-Analyzer\\Time-Series-Data\\20240915\\After_AOD\\AC_Coupling\\';
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%% Load the files which contain: - the DC coupled y-t signal to obtain the averaged power
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% - the AC coupled y-t signal to obtain the fluctuations
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% - the AC coupled y-t signal with the beam blocked to obtain the background fluctuations
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%------------------------------------------------------------------------- %
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bgsignal = load( [ dirACData '20240915_Background_AC'] ); %
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dcsignal = load( [ dirDCData '20240915_1V_-3Mod_DC_PID_Inactive'] ); %
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acsignal_1 = load( [ dirACData '20240915_1V_-3Mod_AC_PID_Inactive'] ); %
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acsignal_2 = load( [ dirACData '20240915_1V_-3Mod_AC_PID_Active'] ); %
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label_0 = 'Background'; %
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label_1 = 'Power = 1 V, Modulation = -3.0 V, PID Inactive'; %
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label_2 = 'Power = 1 V, Modulation = -3.0 V, PID Active'; %
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%------------------------------------------------------------------------- %
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%% Read out the important parameters
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dcdata = dcsignal.A;
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acdata_1 = acsignal_1.A;
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acdata_2 = acsignal_2.A;
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bgdata = bgsignal.A;
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N = length(dcdata); % #samples
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f_s = 1/dcsignal.Tinterval; % Sample Frequency
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delta_f = f_s/N; % step size in frequency domain
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delta_t = 1/f_s; % time step
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%% Custom Control Parameters
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% Choose smoothing parameter; has to be odd
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%----------------%
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span = 21; %
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%----------------%
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%% Computes the RIN
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% compute the average power (voltage^2)
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average_P = mean(dcdata.*dcdata);
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% compute the power spectrum density FFT(A) x FFT*(A)/N^2 of the source & the bg
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psd_src_1 = fft(acdata_1) .* conj(fft(acdata_1))/N^2;
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psd_src_2 = fft(acdata_2) .* conj(fft(acdata_2))/N^2;
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psd_bg = fft(bgdata) .* conj(fft(bgdata))/N^2;
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% converts the psd to the single-sided psd --> psd is symmetric around zero --> omit
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% negative frequencies and put the power into the positive ones --> spsd
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for i = 1 : N/2+1
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if i>1
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spsd_src_1(i) = 2*psd_src_1(i);
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spsd_src_2(i) = 2*psd_src_2(i);
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spsd_bg(i) = 2*psd_bg(i);
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else
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spsd_src_1(i) = psd_src_1(i);
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spsd_src_2(i) = psd_src_2(i);
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spsd_bg(i) = psd_bg(i);
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end
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end
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% smooths the spsd by doing a moving average
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spsd_src_smooth_1 = smooth(spsd_src_1,span,'moving');
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spsd_src_smooth_2 = smooth(spsd_src_2,span,'moving');
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spsd_bg_smooth = smooth(spsd_bg, span,'moving');
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% calculates the RIN given in dB/Hz; the factor delta_f is needed to convert from dB/bin into dB/Hz
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RIN_src_smooth_1 = 10*log10(spsd_src_smooth_1/(average_P*delta_f));
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RIN_src_smooth_2 = 10*log10(spsd_src_smooth_2/(average_P*delta_f));
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RIN_bg_smooth = 10*log10(spsd_bg_smooth /(average_P*delta_f));
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% creates an array for the frequencies up to half the sampling frequency
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f = f_s/2 * linspace(0,1,N/2+1);
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f_smooth = smooth(f,span,'moving');
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%
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% Calculates the shot noise limit of the used PD given the wavelength of the light source and
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% incident average power
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PlanckConstant = 6.62607015E-34;
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SpeedOfLight = 299792458;
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WavelengthOfLaserLight = 1064E-9;
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FrequencyOfLaserLight = SpeedOfLight / WavelengthOfLaserLight;
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QuantumEfficiencyOfPD = 1;
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AverageIncidentPower = 0.001; % (in W)
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ShotNoiseLimit = 10*log10((2 * PlanckConstant * FrequencyOfLaserLight) / (QuantumEfficiencyOfPD * AverageIncidentPower));
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%% Plots the RIN
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% Plots the RIN vs frequency
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f_ = clf;
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figure(f_);
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set(gcf,'Position',[100 100 950 750])
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semilogx(f_smooth, RIN_bg_smooth, LineStyle = "-", Color = [.7 .7 .7])
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hold on
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semilogx(f_smooth,RIN_src_smooth_1,'r-')
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semilogx(f_smooth,RIN_src_smooth_2,'b-')
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ax = gca(f_);
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ax.XAxis.FontSize = 14;
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ax.YAxis.FontSize = 14;
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xlabel('Frequency [Hz]', FontSize=16)
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ylabel('RIN [dBc/Hz]', FontSize=16)
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xlim([10 5E6]);
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ylim([-140 -25]);
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title('\bf Intensity noise of Arm 1 of the ODT as measured by an Out-of-loop PD', FontSize=14)
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legend(label_0, label_1, label_2, 'Location','NorthWest', FontSize=12);
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grid on
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% optional: save the picture without editing wherever you want
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%------------------------------------------%
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% saveas(f_,'FileName','png'); %
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%------------------------------------------%
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