Fiber-assisted single-photon spectrograph

We demonstrate the implementation of a fiber-integrated spectrograph utilizing chromatic group velocity dispersion (GVD) in a single-mode fiber. By means of GVD we stretch an ultrafast pulse in time in order to spectrally resolve single photons in the time domain, detected by single-photon counting modules with very accurate temporal resolution. As a result, the spectrum of a very weak pulse is recovered from a precise time measurement with high signal-to-noise ratio. We demonstrate the potential of our technique by applying our scheme to analyzing the joint spectral intensity distribution of a parametric downconversion source at a telecommunication wavelength.