Editing Electro-optic modulator (section)

==Polarization modulation==

Depending on the type and orientation of the nonlinear crystal, and on the direction of the applied electric field, the phase delay can depend on the polarization direction. A [[Pockels effect|Pockels cell]] can thus be seen as a voltage-controlled waveplate, and it can be used for modulating the polarization state. For a linear input polarization (often oriented at 45° to the crystal axis), the output polarization will in general be elliptical, rather than simply a linear polarization state with a rotated direction.

Polarization modulation in electro-optic crystals can also be used as a technique for time-resolved measurement of unknown electric fields.<ref>{{cite journal|last1=Consoli|first1=F.|last2=De Angelis|first2=R.|last3=Duvillaret|first3=L.|last4=Andreoli|first4=P. L.|last5=Cipriani|first5=M.|last6=Cristofari|first6=G.|last7=Di Giorgio|first7=G.|last8=Ingenito|first8=F.|last9=Verona|first9=C.|title=Time-resolved absolute measurements by electro-optic effect of giant electromagnetic pulses due to laser-plasma interaction in nanosecond regime|journal=Scientific Reports|date=15 June 2016|volume=6|issue=1|page=27889|doi=10.1038/srep27889|bibcode=2016NatSR...627889C|pmc=4908660|pmid=27301704}}</ref><ref>{{cite journal|last1=Robinson|first1=T. S.|last2=Consoli|first2=F.|last3=Giltrap|first3=S.|last4=Eardley|first4=S. J.|last5=Hicks|first5=G. S.|last6=Ditter|first6=E. J.|last7=Ettlinger|first7=O.|last8=Stuart|first8=N. H.|last9=Notley|first9=M.|last10=De Angelis|first10=R.|last11=Najmudin|first11=Z.|last12=Smith|first12=R. A.|title=Low-noise time-resolved optical sensing of electromagnetic pulses from petawatt laser-matter interactions|journal=Scientific Reports|date=20 April 2017|volume=7|issue=1|page=983|doi=10.1038/s41598-017-01063-1|bibcode=2017NatSR...7..983R|pmc=5430545|pmid=28428549}}</ref>
Compared to conventional techniques using conductive field probes and cabling for signal transport to read-out systems, electro-optical measurement is inherently noise resistant as signals are carried by fiber-optics, preventing distortion of the signal by electrical noise sources. The polarization change measured by such techniques is linearly dependent on the electric field applied to the crystal, hence providing absolute measurements of the field, without the need for numerical integration of voltage traces, as is the case for conductive probes sensitive to the time-derivative of the electric field.