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Journal of Contemporary Physics (Armenian Academy of Sciences)

Spectral distribution of photon pairs in a chirped waveguide

A. R. Tamazyan, Gagik Yu. Kryuchkyan

Published Jan 1, 2016• 0 citations
Publisher

Abstract

The spectra of two photon generation in the process of spontaneous parametric down conversion are studied in a waveguide containing the nonlinear segments with the spatial chirp. Three photon parametric interaction is investigated for the waveguide containing only a spatial fundamental mode. The peculiarities of spectra broadening of photon pair in the chirped waveguide are studied.

DOI
10.3103/s1068337216010035

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The spectra of two photon generation in the process of spontaneous parametric down conversion are studied in a waveguide containing the nonlinear segments with the spatial chirp. Three photon parametric interaction is investigated for the waveguide containing only a spatial fundamental mode. The peculiarities of spectra broadening of photon pair in the chirped waveguide are studied.
We study the generation of biphoton modally entangled states in such waveguide structures that lead to spectrum broadening. The process of spontaneous parametric down conversion (SPDC) has been considered for the biphoton generation. The main subject of our study is the dependence of the biphoton spectra on the structure spatial characteristics. The representation of the core structures as definite assembles of nonlinear layers allows us to find analytical description for biphoton spectrum. We show that chirped biphotons with discrete as well as continuous spectra can be generated depending on the waveguide structure. The conditions for spectrum discretization are obtained analytically. It is shown that the biphoton entangled states can be controlled by varying the parameters of the waveguide structure.
We present a study of the propagation of higher-order spatial modes in a waveguided parametric down-conversion photon-pair source. Observing the multimode photon-pair spectrum from a periodically poled KTiOPO(4) waveguide allowed us to isolate individual spatial modes through their distinctive spectral properties. We have measured directly the spatial distribution of each mode of the photon pairs, confirming the findings of our waveguide model, and demonstrated by coincidence measurements that the total parity of the modes is conserved in the nonlinear interaction. Furthermore, we show that we can combine the advantages of a waveguide source with the potential to generate spatially entangled photon pairs as in bulk-crystal down-converters.
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We describe properties of entangled photon pairs generated by spontaneous parametric down-conversion in periodically poled nonlinear crystals. These materials can serve as a useful bright source of photon pairs which properties can be tailored on demand. Especially photon pairs with broad spectra and sharp temporal features can be observed. Both uniform and chirped poling are considered. Spectral properties of the generated photons, photon fluxes, coincidence-count patterns in a Hong-Ou-Mandel interferometer, entropy of entanglement, as well as transverse profiles of intensities of the generated photon fields are discussed. Also the correlation area of two photons comprising a photon pair has been studied as it depends on parameters of periodical poling. Attention is also paid to structures with randomly distributed boundaries.
The propagation of several spatial modes has a significant impact on the structure of the emission from parametric down-conversion in a nonlinear waveguide. This manifests itself not only in the spatial correlations of the photon pairs but also, due to new phase-matching conditions, in the output spectrum, radically altering the degree of entanglement within each pair. Here we investigate both theoretically and experimentally the results of higher-order spatial-mode propagation in nonlinear waveguides. We derive conditions for the creation of pairs in these modes and present observations of higher-order mode propagation in both the spatial and spectral domains. Furthermore, we observe correlations between the different degrees of freedom and finally we discuss strategies for mitigating any detrimental effects and optimizing pair production in the fundamental mode.