We present a comprehensive numerical investigation of entangled photon pair generation via spontaneous four-wave mixing (SFWM) in hollow-core photonic crystal fibers (HC-PCFs). By analyzing various fiber geometries, dispersion profiles, and anti-resonant characteristics, we identify optimal configurations that enhance photon-pair generation efficiency. Our study highlights the crucial roles of group velocity dispersion engineering, pump parameters, and phase-matching conditions in shaping the joint spectral amplitude (JSA) of the emitted photons. Utilizing gas-filled or evacuated HC-PCFs significantly reduces Raman noise by minimizing field overlap with the glass, while maintaining strong nonlinear interactions. The results reveal practical regimes for improving spectral purity and heralding efficiency. These findings provide practical design guidelines for scalable, low-noise quantum light sources suitable for quantum communication technologies. We bridge fiber design and nonlinear optics to create a predictive model and practical design charts for application-specific quantum light sources.
We present a comprehensive numerical investigation of entangled photon pair generation via spontaneous four-wave mixing (SFWM) in hollow-core photonic crystal fibers (HC-PCFs). By analyzing various fiber geometries, dispersion profiles, and anti-resonant characteristics, we identify optimal configurations that enhance photon-pair generation efficiency. Our study highlights the crucial roles of group velocity dispersion engineering, pump parameters, and phase-matching conditions in shaping the joint spectral amplitude (JSA) of the emitted photons. Utilizing gas-filled or evacuated HC-PCFs significantly reduces Raman noise by minimizing field overlap with the glass, while maintaining strong nonlinear interactions. The results reveal practical regimes for improving spectral purity and heralding efficiency. These findings provide practical design guidelines for scalable, low-noise quantum light sources suitable for quantum communication technologies.
We present a comprehensive numerical investigation of entangled photon pair generation via spontaneous four-wave mixing (SFWM) in hollow-core photonic crystal fibers (HC-PCFs). By analyzing various fiber geometries, dispersion profiles, and anti-resonant characteristics, we identify optimal configurations that enhance photon-pair generation efficiency. Our study highlights the crucial roles of group velocity dispersion engineering, pump parameters, and phase-matching conditions in shaping the joint spectral amplitude (JSA) of the emitted photons. Utilizing gas-filled or evacuated HC-PCFs significantly reduces Raman noise by minimizing field overlap with the glass, while maintaining strong nonlinear interactions. The results reveal practical regimes for improving spectral purity and heralding efficiency. These findings provide practical design guidelines for scalable, low-noise quantum light sources suitable for quantum communication technologies.
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.
Spectrally pure photons heralded from unentangled photon pair sources are crucial for any quantum optical system reliant on the multiplexing of heralded photons from independent sources. Generation of unentangled photon pairs in gas-filled hollow-core photonic crystal fibers specifically remains an attractive architecture for integration into quantum-optical fiber networks. The dispersion design offered by selection of fiber microstructures and gas pressure allows considerable control over the group-velocity profile which dictates the wavelengths of photon pairs that can be generated without spectral entanglement. Here, we expand on this design flexibility, which has previously been implemented for four-wave mixing, by modeling the use of a static, periodically poled electric field to achieve an effective quasi-phase-matched three-wave mixing nonlinearity that creates spontaneous parametric downconversion. Electric-field-induced quasi-phase-matched spontaneous parametric downconversion enables control of phase matching conditions that is independent of the group velocity, allowing phase matching at arbitrary wavelengths without affecting the entanglement of photons at those wavelengths. This decoupling of entanglement engineering and phase matching facilitates spectrally pure photon pair generation with efficiency and wavelength-tunability that is otherwise unprecedented.
Based on the dispersion property of a given photonic crystal fiber (PCF), we study how to directly generate photon pairs with minimized frequency correlation via pulse-pumped spontaneous four-wave mixing. After illustrating why the intensity correlation function g (2) of individual signal (idler) photons can be used to reliably characterize the frequency correlation of photon pairs, we numerically investigate the dependence of g (2) under various kinds of experimental conditions. The results show that to minimize the frequency correlation, the experimental parameters should be properly optimized by balancing the influences of the high-order dispersion and the intrinsic sinc oscillation of phase matching function, apart from the satisfaction of the specified phase matching condition and the usage of transform-limited pump pulses. To verify the calculated results, we conduct two series of experiments by regulating the pump to respectively satisfy the asymmetric and symmetric group velocity matching conditions in our 0.6 m-long PCF. In both cases, the measured values of g (2) are less than the calculated results due to the inhomogeneity of the PCF; however, the experimental results qualitatively agree with the numerical simulations. Our investigation is very useful in fiber-based quantum state engineering.
We report on the experimental characterization of a novel nonlinear liquid-filled hollow-core photonic crystal fiber for the generation of photon pairs at a telecommunication wavelength through spontaneous four-wave mixing (SFWM). We show that the optimization procedure in view of this application links the choice of the nonlinear liquid to the design parameters of the fiber, and we give an example of such an optimization at telecom wavelengths. Combining the modeling of the fiber and classical characterization techniques at these wavelengths, we identify for the chosen fiber and liquid combination SFWM phase-matching frequency ranges with no Raman scattering noise contamination. This is a first step toward obtaining a telecom band fibered photon-pair source with a high signal-to-noise ratio.