FOCS Physics 101
As our name suggests, OpticAmpere's fiber optic current sensors (FOCS) exploit Faraday rotation of plane polarized light to measure electric current through magnetic flux integration, but the quantum-level magneto-optical interactions which create Faraday rotation are described with the Zeeman effect, where a counter-clockwise planar rotation, or precession, of the naturally oscillating valence electrons within the dielectric fiber optic silica waveguide's lattice structure, which conducts the photon radiation comprising the polarized light which propagates as a wave-like electrical field (E), is induced by an external magnetic field (H), with the rotation - or precession - rate determined by the Larmor frequency, which is directly proportional to the strength of the magnetic field (H).
The longitudinal Zeeman effect occurs when a parallel interaction path of the polarized optical field (E) in the FOCS waveguide, with respect to the electric conductor's magnetic field (H) vector orientation, splits the spectral lines of the polarized light by exciting left and right circularly polarized modes within the polarized light waves (E) propagating through the fiber optic waveguide, at frequencies determined by the difference between the Larmor precession frequency corresponding to the magnetic field (H), and the natural frequency of the solid state optical waveguide's bound charges, which induces circular birefringence in the FOCS waveguide, resulting in Faraday rotation, or modal coupling between the birefringent fiber optic transmission axes, as modulated by the Verdet constant of the magneto-optical single mode birefringent fiber cable, for the ideal scenario of a FOCS installed at an angle exactly normal to the conductor path.
In practice, FOCS modules may be required to be installed at offset angles relative to the conductor, for a variety of mechanical or clearance reasons, or perhaps guaranteeing a six-sigma level of perpendicularity when installing is simply not possible.
OpticAmpere's FOCS modules operate using any offset angle with respect to the electrical conductor, as post-installation calibration factors the effect of observation angle between the optical field path of the FOCS module, and the magnetic field vector orientation of the electric conductor, into the fiber optic sensor output.
This introduces a transverse Zeeman effect in operation, which does not produce Faraday rotation, where linearly polarized modes are excited at both the Larmor-deviation and natural frequencies of the naturally oscillating valence electrons within the FOCS waveguide silica lattice structure, resulting in an elliptical state of polarization of the FOCS' atomic emission spectra, at the positive and negative Larmor frequency deviations from the natural frequency, where the ellipticity results from the combination of longitudinal and transverse Zeeman effects, as the vector superposition of right and left circularly polarized modes, excited by the longitudinal Zeeman effect, which induces circular birefringence in the FOCS, resulting in Faraday rotation, with the linear vertical polarized optical modes excited at the Larmor-deviation frequencies of the waveguide's naturally oscillating charges within the polarized optical field by the transverse Zeeman effect, results in an elliptical polarization state of the FOCS network's split spectral lines, at the positive and negative Larmor-deviation frequencies, with a linearly horizontal polarized spectral line emitted at the natural frequency, due only to the transverse zeeman effect.
