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Message ID: 2312     Entry time: Mon Mar 25 09:40:16 2019
Author: Anjali 
Type: Noise Budget 
Category: 2micronLasers 
Subject: Noise budget for the frequency discriminator 
  • Different fiber parameters are very important in determining the thermal noise of the fiber. I was considering SM1950 fiber for the calculations, but all the characteristic parameters for this fiber are not known.
  • Glenn ( IEEE Journal of Quantum Electronics25(6), 1218-1224 ) and Jing Dong (Applied Physics Letters108(2), 021108) had given the set of fiber parameters. Attachment #1 shows the comparison of thermoconductive noise of the fiber with fiber parameters taken from Glenn and Jing Dong. The parameters from Jing Dong are for Corning standard SMF 28 fibers and they are the recent resuts compared to Glenn. Hence I think it would be good to follow the parameters given in Jing Dong's paper.
  • It is also found that the thermal noise of fiber has contributions from the thermoconductive noise (https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=255919) and thermomechanical noise (https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5614023) . Thermoconductive noise  (in rad/rtHz) predicts a frequency independent characteristics at lower frequencies where as thermomechanical noise (in rad/rtHz) has a 1/f characteristics over a certain frequency range. The thermomechanical noise is of concern only over a certain frequency range it is given by the ratio of velocity of sound with the total length of the fiber. This indicates that, in the case of thermomechanical noise, the fluctuation of concern is much slower than the time it takes for the sound wave to travel across the length of the fiber. 
  • Attachment #2 shows the noise budget including the thermomechanical noise of the fiber. With 10 m length of the fiber, the thermoconductive noise is of concern for frequencies lower than 364 Hz . Thus a low pass transfer function is assumed with corner frquency of 364 Hz in the calculation of thermomechanical noise. 
Attachment 1: Comparison_of_thermoconductive_noise_in_Hz_per_rtHz.pdf  31 kB  Uploaded Mon Mar 25 10:48:02 2019  | Hide | Hide all
Attachment 2: Noise_budget_with_thermomechanical_noise.pdf  44 kB  Uploaded Mon Mar 25 11:12:07 2019  | Hide | Hide all
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