from numpy import log, log10, pi
  
  #constants
  c = 3E8
  nu = c/1542E-9
  f = 1
  
  #allan deviation aimed
  sigma_y = 1E-17
  
  #PSD of frequency fluctuations (frequency flicker) in dB.Hz^-1
  Sy = 10*log10(sigma_y**2/(2*log(2)))
  
  #PSD of phase fluctuations in dB.rad^2.Hz^-1
  Sphi = Sy + 20*log10(nu) - 20*log10(f)
  
  #PSD of time delay fluctuations in dB.s^2.Hz^-1
  Sx = Sphi - 20*log10(2*pi*nu)
  
  #PSD of position fluctuations in dB.m^2.Hz^-1
  Su = Sphi + 20*log10(c) - 20*log10(2*pi*nu) -20*log10(2)