Non-collinear generation of ultra-broadband parametric fluorescence photon pairs using chirped quasi-phase matching slab waveguides

We previously reported a scheme for collinear emission of high-efficiency and
ultra-broadband photon pairs using chirped quasi-phase matching (QPM) periodically poled
stoichiometric lithium tantalate (PPSLT) ridge waveguides. However, collinearly emitted photon
pairs cannot be directly adopted for applications that are based on two-photon interference,
such as quantum optical coherence tomography (QOCT). In this work, we developed a chirped
QPM device with a slab waveguide structure. This device was designed to produce spatially
separable (photon pair non-collinear emission) parametric fluorescence photon pairs with an
ultra-broadband bandwidth in an extremely efficient manner. Using a non-chirped QPM slab
waveguide, we observed a photon pair spectrum with a full-width-at-half-maximum (FWHM)
bandwidth of 26 nm. When using a 3% chirped QPM slab waveguide, the FWHM bandwidth of
the spectrum increased to 190 nm, and the base-to-base width is 308 nm. We also confirmed a
generation efficiency of 2.4×106 pairs/(µW·s) using the non-chirped device, and a efficiency of
8×105 pairs/(µW·s) using the 3% chirped device under non-collinear emission conditions after
single-mode fiber coupling. This is, to the best of our knowledge, the first report of frequency
correlated photon pairs generation using slab waveguide device as a source. In addition, using
slab waveguides as photon pair sources, we performed two-photon interference experiments
with the non-chirped device and obtained a Hong–Ou–Mandel (HOM) dip with a FWHM of 7.7
µm and visibility of 98%. When using the 3% chirped device as photon pair source, the HOM
measurement gave a 2 µm FWHM dip and 74% visibility.