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.
Raman-scattering noise in silica has been the key obstacle toward the realisation of high quality fiber-based photon-pair sources. Here, we experimentally demonstrate how to get past this limitation by dispersion tailoring a xenon-filled hollow-core photonic crystal fiber. The source operates at room temperature, and is designed to generate Raman-free photon-pairs at useful wavelength ranges, with idler in the telecom, and signal in the visible range. We achieve a coincidence-to-accidentals ratio as high as 2740 combined with an ultra low heralded second order coherence [Formula: see text], indicating a very high signal to noise ratio and a negligible multi-photon emission probability. Moreover, by gas-pressure tuning, we demonstrate the control of photon frequencies over a range as large as 13 THz, covering S-C and L telecom band for the idler photon. This work demonstrates that hollow-core photonic crystal fiber is an excellent platform to design high quality photon-pair sources, and could play a driving role in the emerging quantum technology.
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.
Fibered sources of photon pairs can be easily integrated into future quantum communication networks. However, in silica-core fibres, the broadband spectrum of spontaneous Raman scattering strongly contributes to uncorrelated noise photons degrading the quality of the source. To overcome the problem of the silica Raman scattering, a new architecture was recently proposed, with hollow-core photonic crystal fibers (LF-HCPF) whose core and cladding are filled with a non-linear liquid. As opposed to the Raman scattering spectrum of silica, which is broadband and continuous, the Raman scattering spectrum of liquids is composed of narrow lines. Thus, generating photon pairs between these narrow lines permits to avoid the spectral overlap between the SFWM pairs and the Raman photons. A near infra-red LF-HCPCF photon pair source has been demonstrated, featuring a three order of magnitude suppression of the Raman noise [1]. We have also demonstrated the first non-linear LF-PCF with a transmission band and a zero-dispersion-wavelength (ZDW) in the telecom wavelength range combined with a non-linearity of the same order of magnitude as the one of silica, as a first step towards a Raman-free photon pair source in the telecom band [2]. Injecting light on both sides of this fiber in a Sagnac loop configuration can then be used to obtain entanglement.