The authors present a new method of measuring the frequency structure of single photons through using group-velocity dispersion to map frequency to time. At telecoms wavelengths this can be done with low loss in fiber, but here the authors were working around 800 nm, where fiber attenuation is too high to provide sufficient cumulative dispersion. Instead, they used a chirped fiber Bragg grating spliced to a circulator to create a device with large group delay dispersion between 825–835 nm. Hence, they were able to characterize in detail the spectra of photon-pairs from parametric downconversion, as well as monitoring many frequency channels simultaneously. The technique is likely to find use in time-frequency quantum communications and optical quantum state engineering.
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