Fig. 1: An all-fiber multimode source and mode sorter for photon pairs correlated in the fiber modes.
From: All-fiber source and sorter for multimode correlated photons
a Ultrashort pulses of 140fs (λpump = 695 nm) are coupled into a 1-km-long fiber. Pump photons are spontaneously annihilated and pairs of signal and idler photons are generated at two different spectral channels (λs = 542 nm, λi = 970 nm). At these wavelengths, the fiber (SMF-28) supports a few modes, where the modal distribution of the photon pairs is determined by the phase-matching condition of the fiber. After the first few tens of centimeters, the temporal spread of the pump pulse prevents SFWM. In the next 1-km of the fiber, the different modes are separated due to modal dispersion (inset). Higher spatial modes arrive after lower spatial modes, and shorter wavelengths arrive after longer wavelengths. At the output of the fiber, the signal and idler photons are spectrally separated by a dichroic mirror (DM), filtered by a bandpass filter (BPF), and their arrival times are registered using two single-photon detectors and a time-to-digital converter (TDC). An electronic delay of 70ns is introduced to the idler detector to compensate for the chromatic delay between the signal and idler photons. b Experimentally measured coincidence rate as a function of the pump average power for a 20-cm-long fiber, exhibiting a quadratic scaling.
