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Photonics North (PN)

Super-critical phase-matching in nonlinear optics

Rebecca Y. Saaltink, Lambert Giner, Robert W. Boyd, Ebrahim Karimi, Jeff S. Lundeen

Published Jun 1, 2015• 0 citations
Publisher

Abstract

Radially and azimuthally polarized beams display unique properties that make them an appealing alternative to linearly polarized beams for optical applications. This paper presents a novel geometry for spontaneous parametric down-conversion pumped by a Bessel-Gauss beam that will directly produce azimuthally and radially polarized photon pairs.

DOI
10.1109/pn.2015.7292541

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Radially and azimuthally polarized beams display unique properties that make them an appealing alternative to linearly polarized beams for optical applications. This paper presents a novel geometry for spontaneous parametric down-conversion pumped by a Bessel-Gauss beam that will directly produce azimuthally and radially polarized photon pairs.
We propose a method for directly producing radially and azimuthally polarized photon pairs through spontaneous parametric downconversion (SPDC). This method constitutes a novel geometry for SPDC, in which a radially polarized Bessel-Gauss pump beam is directed into a nonlinear crystal, with the central propagation direction parallel to the crystal axis. The phasematching conditions are controlled by changing the opening angle of the pump beam; as the crystal axis cannot be tuned, we refer to this process as super-critical phasematching. We model and plot the spatial and polarization output distributions for Type-I and Type-II super-critical phasematching.
We propose a method for directly producing radially and azimuthally polarized photon pairs through spontaneous parametric downconversion (SPDC). This method constitutes a novel geometry for SPDC, in which a radially polarized Bessel-Gauss pump beam is directed into a nonlinear crystal, with the central propagation direction parallel to the crystal axis. The phasematching conditions are controlled by changing the opening angle of the pump beam; as the crystal axis cannot be tuned, we refer to this process as super-critical phasematching. We model and plot the spatial and polarization output distributions for Type-I and Type-II super-critical phasematching.
We present two projects that exploit symmetry to produce and measure photon pairs. In the first project, we propose a method for directly producing radially and azimuthally polarized photon pairs through spontaneous parametric downconversion (SPDC). This method constitutes a novel geometry for SPDC in which a radially polarized Bessel-Gauss pump beam is directed into a nonlinear crystal, with the central propagation direction parallel to the crystal axis. We model and plot the spatial and polarization distributions for Type-I and Type-II phasematching. In the second project, we demonstrate experimentally a method to measure the polarization state of single photons through direct measurements performed on optimal quantum clones. We produce these optimal quantum clones on a non-polarizing beam splitter and interfere the outputs of this beam splitter in a displaced Sagnac interferometer. By performing orthogonal polarization measurements on these two photons, we reconstruct the density matrix for input states H and R.
An analysis of the output polarization of a noncollinear type I optical parametric downconversion source is presented. Such a source can be made by pumping a nonlinear crystal with an extraordinary-polarized beam to produce pairs of ordinary-polarized photons. A polarization map of the output light illustrates dramatic variation in the polarization direction at large scattering angles. The effect of this variation in polarization direction is seen on a map of the nonlinear conversion efficiency. The apparent ambiguity in the polarization for the particular case in which one of the outputs propagates along the crystal optic axis is also discussed.
Most modern quantum light sources are based on spontaneous parametric down-conversion (SPDC) in bulk non-linear crystals, with strict phase-matching requirements that limit their design flexibility and the range of two-photon states produced. Recent research has focused on generating quantum light via SPDC with metasurfaces [1], i.e. array of nanoresonators with sub-wavelength dimensions. At this scale, SPDC becomes independent of phase matching, allowing the use of materials with greater nonlinear susceptibility and enabling efficient photon generation with tailored properties for the angular and spectral distribution and polarization.