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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-11 parametric downconversion

Alexander V. Sergienko, Y. H. Shih

Published Jan 1, 1994• 0 citations
Publisher

Abstract

Correlated pairs of photons generated in nonlinear Type II spontaneous parametric downconversion can be used to develop a new approach for the measurement of time delay between orthogonally polarized wave packets with femtosecond time resolution. This technique does not require the use of sophisticated and expensive femtosecond laser sources.

DOI
10.1364/cleo_europe.1994.cfb7

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Correlated pairs of photons generated in nonlinear Type II spontaneous parametric downconversion can be used to develop a new approach for the measurement of time delay between orthogonally polarized wave packets with femtosecond time resolution. This technique does not require the use of sophisticated and expensive femtosecond laser sources.
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.
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.
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.
Summary form only given. Pairs of entangled photons display a complex quantum state that cannot be represented through a product of single-particle states. The spontaneous parametric down-conversion (SPDC) process, that takes place when a laser pulse pumps a second-order nonlinear crystal has become recently a convenient source of such nonclassical states of light in quantum optics experiments. Nonstationary effects are mainly observed when the pump pulse temporal duration is significantly shorter than the characteristic interaction time in the nonlinear crystal. We introduce a nonstationary theory of SPDC to describe the results of fourth-order quantum-interference experiments when no spectral filtering is applied to the down-converted fields. Experiments involving nonlinear SPDC crystals with three different lengths were performed. The ultraviolet laser pulses were obtained from a Ti:sapphire femtosecond laser with a second-harmonic generator. These pulses were used to pump nonlinear crystals to initiate the process of nonstationary spdc and generate orthogonally-polarized photon pairs. These pairs then went into a polarization interferometer, and the coincidence counts of the detectors at the two output ports of the interferometer were recorded.