Apparatus for electronically analyzing modulated light beams

Claim 2

Apparatus for measuring an electrical current represented by a time-dependent quantity phi (t) comprising: means for producing a beam of linearly polarized light, means for periodically varying the intensity of said polarized light beam at a frequency omega , a magneto-optical element through which the current is passed to produce a corresponding time-dependent magnetic field, said intensity-varied polarized light beam being directed through said magneto-optical element which thereby effects a rotation of the polarization plane through an angle proportional to the time-dependent magnetic field, an optical divider through which said light beam is passed after passing through said magneto-optical element, said optical divider serving to split said light beam into first and second partial light beams, first and second polarizers through which said first and second partial light beams are respectively passed and whose respective polarization planes differ from each other by an angle of substantially 45*, a first photo-detector into which said first partial light beam is directed after passing through said first polarizer and from which a corresponding first electrical signal is produced, a second photo-detector into which said second partial light beam is directed after passing through said second polarizer and from which a corresponding second electrical signal is produced, means producing a third electrical signal having a periodically varied amplitude corresponding to the periodic variation in the intensity of said polarized light beam, means combining said first and third electrical signals to produce a fourth electrical signal, means combining said second and third electrical signals to produce a fifth electrical signal, first and second filters through which said fourth and fifth electrical signals are respectively passed, said filters having a flat pass characteristic in the frequency range omega + OR - (d phi /dt)max. and one of said filters having a 90* phaseshifter device connected therewith, and an additive network combining the outputs from said filters for producing a final output electrical signal constituting a measurement of the time-dependent current.

Claim 3

Apparatus as defined in claim 1 for measuring a generally sinusoidal time-dependent current wherein the phase constant ( delta 1) of the fundamental oscillation (q1 sin omega t) of the function of the periodic variation of the intensity of said polarized light beam is made equal to zero.

Claim 4

Apparatus as defined in claim 1 for measuring a generally sinusoidal time-dependent current wherein the frequency omega at which the intensity of said polarized light beam is varied is greater than twice the value of the maximum variation in time of the argument (d phi /dt)max. of the time-dependent current.

Claim 5

Apparatus as defined in claim 1 for measuring a generally sinusoidal time-dependent current wherein the amplitude of said third electrical signal is equal to the amplitudes of said first and second electrical signals.

Claim 6

Apparatus as defined in claim 1 for measuring a generally sinusoidal time-dependent current wherein said filters are of the band-pass type and wherein the frequency omega at which the intensity of said polarized light beam is varied is greater than twice the value of the maximum variation in time of the argument (d phi /dt)max. of the time-dependent current.

Claim 7

Apparatus as defined in claim 1 for measuring a generally time-dependent current wherein one of said filters and the 90* phase-shifter device connected therewith are integrated into a common network.

Claim 8

Apparatus as defined in claim 1 for measuring a generally sinusoidal time-dependent current wherein said means for periodically varying the intensity of said polarized light beam is constituted by a chopper inTerposed in the path of said beam and which serves to periodically interrupt said beam.

Claim 9

Apparatus for measuring an electrical current represented by a time-dependent quantity phi (t) comprising: means for producing a beam of linearly polarized light, means for periodically varying the intensity of said polarized light beam at a frequency omega , a magneto-optical element including a coil through which the current is passed to produce a corresponding time-dependent magnetic field, a first optical divider into which said polarized light beam of variable intensity is passed and which serves to split said light beam into first and second partial light beams, said first partial light beam being directed through said magneto-optical element which thereby effects a rotation of the polarization plane through an angle proportional to the time-dependent magnetic field, a second optical divider through which said second partial light beam is passed after passing through said magneto-optical element, said second optical divider serving to split said second partial light beam into third and fourth partial light beams, first and second polarizers through which said third and fourth partial light beams are respectively passed and whose respective polarization planes differ from each other by an angle of substantially 45* , a first photo-detector into which said third partial light beam is directed after passing through said first polarizer and from which a corresponding first electrical signal is produced, a second photo-detector into which said fourth partial light beam is directed after passing through said second polarizer and from which a corresponding second electrical signal is produced, a third photo-detector into which said second partial light beam is directed and from which a corresponding third electrical signal is produced, means for combining said first and third electrical signals to produce a fourth electrical signal, means for combining said second and third electrical signals to produce a fifth electrical signal, first and second filters through which said fourth and fifth electrical signals are respectively passed, said filters having a flat pass characteristic in the frequency range omega + or - (d phi /d)max. and one of said filters having a 90* phase-shifter device connected therewith, and an additive network combining the outputs from said filters for producing a final output electrical signal constituting a measurement of the time-dependent current.

Claim 10

Apparatus for measuring an electrical current represented by a time-dependent quantity phi (t) comprising: means for producing a beam of linearly polarized light, means for periodically varying the intensity of said polarized light beam at a frequency omega , a magneto-optical element including a coil through which the current is passed to produce a corresponding time-dependent magnetic field, a first optical divider into which said polarized light beam of variable intensity is passed and which serves to split said light beam into first and second partial light beams, said first partial light beam being directed through said magneto-optical element which thereby effects a rotation of the polarization plane through an angle proportional to the time-dependent magnetic field, a second optical divider through which said second partial light beam is passed after passing through said magneto-optical element, said second optical divider serving to split said second partial light beam into third and fourth partial light beams, first and second polarizers through which said third and fourth partial light beams are respectively passed and whose respective polarization planes differ from each other by an angle of substantially 45* , a first photo-detector into which said third partial light beam is directed after passing through said first polarizer and from which a corresponding first electrical signal is produced, a second photo-detector into which said fourth partial light beam is directed after passing through said second polarizer and from which a corresponding second electrical signal is produced, a third photo-detector into which said second partial light beam is directed and from which a corresponding third electrical signal is produced, means for combining said first and third electrical signals to produce a fourth electrical signal, means for combining said second and third electrical signals to produce a fifth electrical signal, first and second filters through which said fourth and fifth electrical signals are respectively passed, said filters having a flat pass characteristic in the frequency range omega + or - (d phi /d)max. and one of said filters having a 90* phase-shifter device connected therewith, and an additive network combining the outputs from said filters for producing a final output electrical signal constituting a measurement of the time-dependent current.