Tests of a two-photon technique for measuring polarization mode dispersionwith subfemtosecond precision

An investigation is made of a recently introduced quantum interferometric m ethod capable of measuring polarization mode dispersion (PMD) on sub-femtos econd scales, without the usual interferometric stability problems associat ed with such small time scales. The technique makes use of the extreme temp oral correlation of orthogonally polarized pairs of photons produced via ty pe-II phase-matched spontaneous parametric down-conversion. When sent into a simple polarization interferometer these photon pairs produce a sharp int erference feature seen in the coincidence rate. The PMD of a given sample i s determined from the shift of that interference feature as the sample is i nserted into the system. The stability and resolution of this technique is shown to be below 0.2 fs. We explore how this precision is improved by redu cing the length of the down-conversion crystal and increasing the spectral band pass of the system.