Abstract Spontaneous four-wave mixing (SpFWM) in fiber optics has been investigated due to its high photon-pair generation rate and negligible connection loss to fiber optic systems. Photon pairs generated in the fundamental or sideband modes satisfy SpFWM’s phase matching condition, and the pair-generation efficiency of both modes has been considered nearly identical. Here, we directly compare the pair-generation efficiency of the fundamental and sideband modes. Dispersion in optical fiber varies unevenly, and SpFWM in the sideband mode is more sensitive to the medium’s dispersion properties than in the fundamental mode, inducing lower pair-generation efficiency. These strong non-uniformity effects in the sideband mode will affect the photon-pair generation and four-wave mixing based quantum and nonlinear applications.
Abstract Spontaneous four-wave mixing (SpFWM) in fiber optics has been investigated due to its high photon-pair generation rate and negligible connection loss to fiber optic systems. Photon pairs generated in the fundamental or sideband modes satisfy SpFWM’s phase matching condition, and the pair-generation efficiency of both modes has been considered nearly identical. Here, we directly compare the pair-generation efficiency of the fundamental and sideband modes. Dispersion in optical fiber varies unevenly, and SpFWM in the sideband mode is more sensitive to the medium’s dispersion properties than in the fundamental mode, inducing lower pair-generation efficiency. These strong non-uniformity effects in the sideband mode will affect the photon-pair generation and four-wave mixing based quantum and nonlinear applications.
A fiber-based photon-pair source in the telecom C-band is suitable for quantum information science including quantum communications.Spontaneous four-wave mixing effects are known to create photon pairs that are slightly detuned from the pump wavelength only in the anomalous groupvelocity-dispersion (GVD) regime.Here, we achieve high-quality photon-pair generation slightly detuned from the pump wavelength in the normal GVD regime through a dispersion shifted fiber, for the first time.The photon pairs in C-band exhibit strong temporal correlation with each other and excellent heralded anti-bunching property.This photon-pair generation scheme can be exploited as telecom-band quantum light sources for quantum information applications.A non-classical light source is one of the key elements of quantum information processing systems, and several types of these sources have been investigated, including molecules [1], trapped atoms [2], quantum dots [3], diamond vacancy centers [4], spontaneous parametric down-conversion (SPDC) [5], and spontaneous fourwave mixing (SFWM) [6]. Among these processes, the SPDC and the SFWM processes create quantumcorrelated photon pairs from one and two pump photons, respectively, and both processes require satisfying the energy conservation as well as phase matching [7].Typically, the nonlinear coefficient of SPDC in second-order nonlinear crystals is larger than that of SFWM in amorphous single mode optical fibers as SFWM is a third-order nonlinear process.In the case of several hundred meters long single-mode fibers, however, the SFWM conversion efficiency from pump beam to photon pairs can be similar with that of the SPDC process in nonlinear crystals.In addition, the fiber based photon-pair sources are able to be directly coupled to fiber systems with negligible coupling loss, but waveguide-to-fiber coupling efficiency of a periodically poled SPDC crystal is reported about 50% [8].The SFWM process has been studied intensively for the fiber-based photon generation [6, 9-20] for quantum information applications including quantum key distribution.Photon-pair generation via SFWM is active near the zero group-velocity-dispersion (GVD) wavelength, λ ZGVD , in the anomalous GVD regime [6, 9-15] or normal GVD regime [16][17][18][19][20].In the normal GVD regime, the wavelength of the generated photon pairs is significantly detuned from the pump wavelength.In this case, Raman noise can be avoided, but the generated photon pair do not exhibit telecom-band wavelength together.On the other hand, in the anomalous GVD regime, the wavelength of the generated photon pair is slightly detuned from the pump in the telecom C-band and is strongly power dependent [16].Since the wavelength of the generated pair is sensitive to the λ ZGVD of the generation medium, several types of commercial fibers which have λ ZGVD in the telecom C-band have been investigated as the telecom C-band pair sources.Even if commercial optical fibers have small tolerances in their physical properties, it is common to have sizeable λ ZGVD variance along an optical fiber [21,22].Therefore, the precise measurement of the GVD spectrum is required, but it is often tricky with short length optical fibers.One way to overcome this problem is engineering the dispersion of a commercial fiber by heating and pulling the fiber, but this method is an ambitious research field [19,20,23].On the other hand, if a slightly detuned pair can be generated in the normal GVD regime, the constraint for the λ ZGVD of medium can be weakened, but it has not been reported to the best of our knowledge because phases are mis-matched in this regime due to the Kerr effects of the media.
Abstract Effects of ultrafast nonlinear optics are shown to play a significant role in photon-pair generation by spontaneous four-wave mixing (FWM) of broadband photon packets in an optical fiber. When extended to this regime, the models of photon-pair generation can stay consistent with energy and photon-number conservation only when the frequency dependence of nonlinear wave coupling is included, giving rise to a shock-type waveform dynamics and a strong asymmetry in FWM sideband amplification. Resonant energy transfer from soliton transients to dispersive waves, accompanied by Cherenkov-type radiation, is shown to open a channel whereby FWM output photons are lost from entanglement generation pathways.
Summary form only given. Optical fibre (either classical or microstructured) is a favourable medium for realization of sources of entangled photons for quantum communications. Indeed the photon pairs are generated through spontaneous Four Wave Mixing (FWM) directly in the fibre core and can thus be connected easily and without loss to the optical telecommunication network.We have realized such a source and characterized its performance. Our measurements showed a photon pair generation rate lower than expected in theory. Further characterization showed, as can be seen in Fig. 1A, a widened pair spectrum and a diminution of the generation rate compared to the prediction of our model (Fig. 1B) [2]. Such features can be explained by taking in account the intrinsic inhomogeneity of the fibre, i.e. the core and cladding dimensions fluctuation along the fibre. Indeed, a small variation of the fibre diameter implies a slightly different dispersion, hence shifted photon pair frequencies. To depict these uniformities, we extended our model through a similar approach as in Ref. [3], considering the fibre as an assembly of homogeneous sections, each one with its own length and phase mismatch. Consequently, the joint spectral intensity of pairs describing their generation probability for a given couple of frequencies is more complex. In Fig. 1B, we show the result of our numerical simulation for a purely uniform fibre with parameters corresponding to our source [1,2], and in the case of a linear variation of the zero dispersion wavelength along the fibre. In this specific case, a new analytical solution that will be presented, can be derived from our model, and is also shown in Fig. 1B as a comparison.
Quantum entanglement has been an extremely active field of research, both theoretically and experimentally. Studies on entanglement are fundamental to improving our basic understanding of quantum mechanics. As our understanding of the phenomenon grows, so does interest in using it to advance various technological fields: communications, computing, and sensing, to name just a few. It is now known that entangled photon pairs can be generated through a process known as Spontaneous Four-Wave Mixing (SFWM). In this paper, we report the generation of entangled photon pairs in time intervals by spontaneous four-wave mixing in a nonlinear fiber optic ring resonator. The requirements for efficient SFWM are quite similar to those for classical FWM, but they require even greater precision, especially for quantum applications. To achieve a measurable pair generation rate, a high-intensity pump laser is essential. The nonlinear medium must have high nonlinearity and confinement. This technique is compatible with contemporary fiber, enabling compact, low-cost, and scalable implementations such as quantum memories.
We present a study of the spectral properties of photon pairs generated through the process of spontaneous four-wave mixing (SFWM) in single mode fiber. Our analysis assumes narrowband pumps, which are allowed to be frequency degenerate or nondegenerate. Based on this analysis, we derive conditions on the pump frequencies and on the fiber dispersion parameters which guarantee the generation of ultrabroadband photon pairs. Such photon pairs are characterized by (i) a very large degree of entanglement, and (ii) a very high degree of temporal synchronization between the signal and idler photons. Through a numerical exercise, we find that the use of photonic crystal fiber (PCF) facilitates the fulfilment of the conditions for ultrabroadband photon pair generation; in particular, the spectral region in which emission occurs can be adjusted to particular needs through an appropriate choice of the PCF parameters. In addition, we present a quantum interference effect, resulting from indistinguishable pathways to the same outcome, which can occur when pumping a SFWM source with multiple spectral lines.
Four-wave mixing in optical fibers has been proven to have many applications within processing of classical optical signals. In addition, recent developments in multimode fibers have made it possible to achieve the necessary phase-matching for efficient four-wave mixing over a very wide bandwidth. Thus, the combination of multimode fiber optics and four-wave mixing is very attractive for various applications. This is especially the case for applications in quantum communication, for example in photon-pair generation. This is the subject of this work, where we discuss the impact of fluctuations in core radius on the quality of the heralded single-photon states and demonstrate experimental results of intermodal spontaneous four-wave mixing for photon-pair generation.