text: """All-pass ring resonator example."""
  
  import EMpy
  import numpy
  import pylab
  
  wls = numpy.linspace(1.5e-6, 1.6e-6, 1000)
  K = EMpy.devices.Coupler(wls, numpy.sqrt(0.08), 1.0)
  l = 2 * numpy.pi * 5e-6
  SWG = EMpy.devices.SWG(400, 220, 125).solve(wls)
  APRR = EMpy.devices.APRR(K, SWG.neff, l).solve()
  
  pylab.plot(wls, numpy.unwrap(numpy.angle(APRR.THRU)), "r.-")
  pylab.axis("tight")
  pylab.xlabel("wavelength /m")
  pylab.ylabel("phase")
  pylab.show()
  