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Entry  Sat Jun 1 09:46:00 2019, Anjali, Update, 2micronLasers, Frequency noise measurement of 2 micron source 
    Reply  Fri Jun 7 16:32:59 2019, Anjali, Update, 2micronLasers, Frequency noise measurement of 2 micron source Lock_in_amplifier_moku_lab.jpgFM_noise.pdf
       Reply  Thu Jun 13 22:53:25 2019, Anjali, Update, 2micronLasers, Frequency noise measurement of 2 micron source FM_noise_new_.pdfMokulab.m
Message ID: 2362     Entry time: Thu Jun 13 22:53:25 2019     In reply to: 2360
Author: Anjali 
Type: Update 
Category: 2micronLasers 
Subject: Frequency noise measurement of 2 micron source 

There was a correction in the script I used to estimate the frequency noise from the inphase and quadrature component. Attachment #1 shows the frequency noise estimated after the correction. 

I have also attached the Matlab script ( I am not able to attach the zip file with data files). I remember, while saving the data, we gave the time duration as 70 s. But while processing the data only I realised that the  time domain data is captured only upto 2 s. Even in this case, I would expect the frequency axis to start from 0.5 Hz, but I don't see that in the FM noise plot. Kinldy let me know whther I am doing anything wrong in data proocessing. 

Quote:

Attachment # 1 show the schematic of the lock in amplifier configuration used in Moku lab. We saved the in phase and quadrature components.

In phase =cos\left ( \right \omega_o\tau+\Delta\phi(t))

quadrature =Sin\left ( \right \omega_o\tau+\Delta\phi(t))

where \omega_0  corresponds to 2 -micron , \tau is the delay time in the delay fiber  and \Delta\phi(t)=\phi(t) - \phi(t-\tau).

 \phi(t) is the phase noise of the laser. 

From the inphase and quadrature component \Delta \phi(t)value is extracted. So, we are actually extrating the combined effect of phase noise of laser as well the phase noise due to fiber length fluctuations due to environmental fluctuations. ASD of this is converted to frequency noise in Hz/rt Hz. Attachment # 2 shows the frequency noise estimated from two sets of measurements. This curve exhibit a 1/f characteristics from about 240 Hz upto 30 kHz

Quote:

[Anchal, Anjali]

We tried the Lock in amplifier in Moku lab for the frequency noise measurement. In this case, the output of the photo detector , after dc block and one stage of amplification, is fed into  input 1 of Moku. It gives out the inphase and quadrature component. We have saved the data. I will process the data offline and update later.

 

 

Attachment 1: FM_noise_new_.pdf  86 kB  Uploaded Thu Jun 13 23:54:18 2019  | Hide | Hide all
FM_noise_new_.pdf
Attachment 2: Mokulab.m  2 kB  Uploaded Thu Jun 13 23:59:46 2019  | Hide | Hide all
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clc
lam=2e-6;%wavelength
c=3e8;%velocity of light 
n=1.5;%refractive index of fiber
len=15;%length of delay fiber
omeg=2*pi*(c/lam);%optical frequency corresponds to 2-micron
tau=(len*n)/c;%time delay due to delay fier
Fs=500e3;%acquisition rate
... 27 more lines ...
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