The advancement of quantum technologies [1] heavily relies on the efficient generation and manipulation of the photon-pairs. Among the numerous methods available for photon-pairs generation, spontaneous four-wave mixing (SFWM) in photonic crystal fibers [2] has emerged as a promising technique due to its inherent advantages in scalability and integration within existing telecommunication infrastructures. Inhibited-coupling hollow-core photonic crystal fibers (IC-HCPCFs) filled with inert gases provide a unique platform for SFWM-based photon- pairs generation, offering several features including entanglement control [3], integrability into telecommunication networks and also Raman-free generation [4] which minimizes noise and enhances the purity of the generated photon-pairs resulting in record coincidence-to-accidental ratio (CAR) superior to 104[5]. Building upon these advantages, we have recently focused on enhancing the photon-pairs brightness. In our previous work, we demonstrated significant improvements in brightness through optimization of fiber parameters such length, effective area and dispersion [5]–[6] on one hand and the use of a GHz-repetition rate femtosecond laser [7] on another hand to get closer to the MHz-level. One of the remaining parameters to further improve the generation efficiency
(η)of IC-HCPCF based photon-pair source, and thereby conclude our investigation, is the pump pulse duration
(τp). Since
ηis inversely proportional to the pump pulse duration [8], shorter pulses are expected to yield larger brightness. In this work, we developed a homemade pulse compressor [9] based on a hybrid IC-HCPCF design [10], which was integrated as the first stage of our photon-pair generation set-up as shown in Fig. 1a. By engineering the fiber dispersion and by controlling the optical nonlinearities through the pressure of the filling gas (argon), we achieved a self-compression of input pulses from an ultrashort pulse laser (~280 fs pulse width,1030 nm wavelength, 2 MHz repetition rate) down to ~35 fs. Fig. 1b shows the pulse duration of the compressor output over an input energy range of
0.01μJto
0.7μJ. The energy transmission efficiency of the compressor was measured to exceed 80%. This compressor enables tunable pulse durations ranging from 280 fs down to 35 fs. As expected, the compression was accompanied by a spectral broadening from 8 nm to 41 nm (gaussian fit FWHM), primarly driven by self-phase modulation (see Fig. 1c). The compressed pulses were subsequently coupled into the photon-pair generation fiber (1 m of tubular lattice HCPCF with a 40 μm core, filled with xenon at 3.2 bar). As expected, when the pulse duration is reduced, the brightness increase scales as
1/τp(see Fig. 1d). For the shortest input duration of 35 fs, the brightness was enhanced by a factor of 7.7, which is in agreement with the expected value. Additionally, we observed a slight improvement in the CAR attributed to the increase in the number of coincidences (see Fig. 1e). Finally, the structuring of the spectral pump has led to a change in the joint spectral intensity (JSI) pattern (see inset of Fig. 1d). The implication of this change on the photon-correlation is under investigation.
Photon-pairs generated by spontaneous four-wave mixing (SFWM) in inhibited-coupling hollow-core photonic crystal fiber (IC-HCPCF) filled with an inert gas (Xenon) combine Raman free generation, high signal-to-noise ratio, entanglement control and integrability in the telecommunications network [1]. Furthermore, this technology proved to be a promising platform for both single photon and entangled photon-pairs sources. However, increasing the brightness of such platform is required. Recently, we demonstrated an enhancement of this photon -pairs source brightness by an order of magnitude to reach
B0=30kHzusing GHz-repetition rate femtosecond laser [2].
We demonstrate an all-fiber photon pair source for the critical telecom C-band. We achieve high pair generation rates in excess of 10 MHz while maintaining coincidence-to-accidental ratios (CARs) greater than 100. This is one of the brightest and lowest-noise photon pair sources ever demonstrated. We achieve the high pair rate through CW-pumped spontaneous four-wave mixing in dispersion-shifted fiber. We achieve the high CAR by cooling the fiber to 4 K to suppress the Raman generation and detecting the photons with low jitter and low dark count superconducting single-photon detectors.