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Conference on Lasers and Electro-Optics

New technique for the measurement of polarization-mode dispersion in optical materials and fibers

Alexander V. Sergienko, Yanhua H. Shih

Published May 21, 1995• 0 citations
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Abstract

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.

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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.

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Optics Express•Sep 8, 2017•34 citations
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.
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.
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.
We propose and analyze a generic technique to engineer the two-photon quantum state generated by spontaneous parametric downconversion (SPDC) in nonlinear photonic nanowires using any suitable material system. Through dispersion engineering in nanowires, the group velocity of each photon involved in the SPDC process can be tuned such that pure heralded single photons or maximally polarization entangled photons can be directly generated on a chip. Implementations in III–V semiconductor and ferroelectric waveguides demonstrate minimal frequency correlations with Schmidt numbers of ∼1 for heralded single photons, and maximal entanglement with concurrences of ∼1 for polarization entangled photons.
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.
Quantum sources that provide broadband biphotons entangled in both polarization and time-energy degrees of freedom are a rich quantum resource that finds many applications in quantum communication, sensing, and metrology. Creating such a source while maintaining high entanglement quality over a broad spectral range is a challenge, which conventionally requires various compensation steps to erase temporal, spectral, or spatial distinguishabilities. Here, we point out that in fact compensation is not always necessary. The key to generate broadband polarization-entangled biphotons via type-II spontaneous parametric downcoversion (SPDC) without compensation is to use nonlinear materials with sufficiently low group birefringence that the biphoton bandwidth becomes dispersion-limited. Most nonlinear crystals or waveguides cannot meet this condition, but it is easily met in fiber-based systems. We reveal the interplay of group birefringence and dispersion on SPDC bandwidth and polarization entanglement quality. We show that periodically poled silica fiber (PPSF) is an ideal medium to generate high-concurrence (>0.977) polarization-entangled photons over a broad spectral range (>77nm), directly and without compensation. This is the highest polarization-entanglement concurrence reported that is maintained over a broad spectral range from a compensation-free source.