Figure 1

(a) The C-PPSLT gratings with six different degrees of chirp $\alpha$, specified in units of $\mu {\mathrm{m}}^{-2}$. The poling period at the entrance face of each grating ($z=0$) is fixed at $\Lambda =9.824\mu \mathrm{m}$; the values at the exit face are indicated. For the grating with the lowest (highest) chirp, the poling period changes by about 0.02% (10%) over its length. (b) Setup used to image the emission-cone cross sections from the C-PPSLT gratings. A monochromatic ${\mathrm{Kr}}^{+}$-ion laser operated at ${\lambda }_p=406\mathrm{nm}$ pumps the C-PPSLT gratings. BPF represents a 10-nm bandpass filter at the degenerate wavelength ${\lambda }_0=812\mathrm{nm}$, and ICCD represents an intensified charge-coupled device camera, which is placed in the Fourier plane of an $f=100\mathrm{\text{−}}\mathrm{mm}$ lens. (c) The emission-cone cross sections from C-PPSLT gratings at the degenerate wavelength at different temperatures, for various values of the chirp parameter $\alpha$.Reuse & Permissions

Figure 2

Normalized interferogram $I(\tau )$ for collinear SPDC. Emission from a C-PPSLT grating with (a) $\alpha =0.2\times {10}^{-7}\mu {\mathrm{m}}^{-2}$ exhibits a FWHM of 130 fs and (b) $\alpha =9.7\times {10}^{-6}\mu {\mathrm{m}}^{-2}$ exhibits a FWHM of 7.87 fs. (c) The power spectral densities $|\varphi (\Omega ){|}^2$, plotted vs wavelength ${\lambda }_{s,i}$, for the data shown in (a) and (b). (d) The FWHM (squares) of the measured interferograms for gratings of different degrees of chirp are plotted on the left ordinate. The biphoton fluxes per milliwatt of pump power (circles) are plotted on the right ordinate. The lines connecting the experimental points are for guiding the eye.Reuse & Permissions

Figure 3

Normalized HOM coincidence interferograms (dips) for various values of the chirp parameter $\alpha$. The symbols represent the measured data points, whereas the solid curves are the corresponding numerical simulations using Eqs. (2, 4). The FWHM of the measured dips are 77, 19.1, and 7.16 fs for $\alpha =0.2\times {10}^{-7}$, $1.0\times {10}^{-6}$, and $9.7\times {10}^{-6}\mu {\mathrm{m}}^{-2}$, respectively.Reuse & Permissions

Figure 4

(a) Magnitude and (b) phase of the biphoton spectral density $\varphi (\Omega )$ as provided by Eq. (2), for $\alpha =9.7\times {10}^{-6}\mu {\mathrm{m}}^{-2}$. (c) Numerical simulation of the expected signal if these biphotons were employed in a HOM interferometer (solid blue curve) or in an SFG experiment (dashed red curve). The outcome of an SFG experiment is a direct measure of the biphoton wave packet square magnitude $|f(\tau ){|}^2$.Reuse & Permissions