Self-calibrating Fiber Spectrometer for the Measurement of Broadband Downconverted Photon Pairs

We experimentally demonstrate a simple method to measure the biphoton joint spectrum by mapping the spectral information onto the temporal domain using a dispersive medium. Various top-hat spectral filters are used to limit the spectral (and hence, temporal) extent of the broadband downconversion photons measured. The sharp edges of the spectral filters are utilized as spectral markers for dispersion characterization of the dispersive medium. This method allows dispersion characterization and joint spectral measurement to be completed simultaneously. The joint spectrum (which extends beyond 100 nm, centered about 1.5 micron) of the type-II downconverted photon pairs generated from a poled optical fiber is obtained with this method.