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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Measurement of femtosecond time delay in optical materials using type-III parametric downconversion

Alexander V. Sergienko, Yanhua H. Shih

Published Aug 24, 2005• 0 citations
Publisher

Abstract

Correlated pairs of photons generated in Type-II nonlinear spontaneous parametric down conversion (SPDC) were used to develop a new approach for the measurement of time delay between two orthogonally polarized waves (linear or circular) in optical materials with femtosecond time resolution. This technique can be used to improve the accuracy of measurement of polarization properties of optical fibers, birefringent materials including nonlinear crystals, waveguides, Pockel’s cells and Faraday rotators in the visible and IR spectrum.

DOI
10.1109/cleoe.1994.636708

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Correlated pairs of photons generated in Type-II nonlinear spontaneous parametric down conversion (SPDC) were used to develop a new approach for the measurement of time delay between two orthogonally polarized waves (linear or circular) in optical materials with femtosecond time resolution. This technique can be used to improve the accuracy of measurement of polarization properties of optical fibers, birefringent materials including nonlinear crystals, waveguides, Pockel’s cells and Faraday rotators in the visible and IR spectrum.
Correlated pairs of photons generated in nonlinear type-II spontaneous parametric downconversion (SPDC) can be used to develop a new approach for directly measuring the group-velocity difference between two orthogonally polarized wave packets propagating inside optical materials or fibers with femtosecond time resolution. This technique can be used to improve the accuracy of polarization-mode-dispersion measurement in single-mode and high-birefringence fibers, fiber sensors, and birefringent materials, including nonlinear crystals, waveguides, Pockels cells, and Faraday rotators, in the visible and IR spectra.
Polarization correlation measurement of two-photon state generated in type-II spontaneous parametric downconversion (SPDC) has been performed in a single input port beam splitter configuration. Two orthogonally polarized entangled photons with degenerate k vectors were directed to the single input port 50%-50% beam splitter. Polarization were measured with linear and circular polarization entangled state by the use of two polarization analyzers followed by two photon counting detectors. A strong correlation of polarization has been observed. The type of two-photon state generated in Type-II SPDC was tested. A strong dependence of the polarization correlation upon the spectral bandwidth of the detector spectral filter was found and a different correlation between linear and circular polarization entangled state were observed. It seems that the standard theoretical models for SPDC need to be improved in order to provide a comprehensive treatment for the result of the experiment.
An investigation is made of a recently introduced quantum interferometric method capable of measuring polarization mode dispersion (PMD) on sub-femtosecond scales, without the usual interferometric stability problems associated with such small time scales.The technique makes use of the extreme temporal correlation of orthogonally polarized pairs of photons produced via type-II phase-matched spontaneous parametric down-conversion.When sent into a simple polarization interferometer these photon pairs produce a sharp interference feature seen in the coincidence rate.The PMD of a given sample is determined from the shift of that interference feature as the sample is inserted 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 reducing the length of the down-conversion crystal and increasing the spectral band pass of the system.
Polarization-entangled photon pairs can be efficiently prepared into pure Bell states with a high fidelity via type-II spontaneous parametric down-conversion (SPDC) of narrow-band pump light. However, the use of femtosecond pump pulses to generate multiphoton states with precise timing often requires spectral filtering to maintain a high quality of polarization entanglement. This typically reduces the efficiency of photon pair collection. We experimentally map the polarization correlations of photon pairs from such a source over a range of down-converted wavelengths with a high spectral resolution and find strong polarization correlations everywhere. A spectrally dependent imbalance between contributions from the two possible decay paths of SPDC is identified as the reason for a reduction in entanglement quality observed with femtosecond pump pulses. Our spectral measurements allow us to predict the polarization correlations for arbitrary filter profiles when the frequency degree of freedom of the photon pairs is ignored.
A two-photon wave packet (a biphoton) produced by type-II parametric downconversion is studied in a simple beam-splitting experiment for its natural shape in space–time. The measured triangular shape of a two-photon correlation function is the signature of a rectangular-shaped biphoton. Inserting a birefringent sample into the beam causes a displacement of the vertex of the notch pattern, which can be used to measure the optical delay between the ordinary and the extraordinary rays in the sample with femtosecond resolution.