  A fiber-integrated spectrometer for single-photon pulses outside the
telecommunications wavelength range based upon frequency-to-time mapping,
implemented by chromatic group delay dispersion (GDD), and precise
temporally-resolved single-photon counting, is presented. A chirped fiber Bragg
grating provides low-loss GDD, mapping the frequency distribution of an input
pulse onto the temporal envelope of the output pulse. Time-resolved detection
with fast single-photon-counting modules enables monitoring of a wavelength
range from 825 nm to 835 nm with nearly uniform efficiency at 55 pm resolution
(24 GHz at 830 nm). To demonstrate the versatility of this technique, spectral
interference of heralded single photons and the joint spectral intensity
distribution of a photon-pair source are measured. This approach to
single-photon-level spectral measurements provides a route to realize
applications of time-frequency quantum optics at visible and near-infrared
wavelengths, where multiple spectral channels must be simultaneously monitored.
