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Optics Express

Measurement of dispersion properties in a short optical fiber for an efficient quantum frequency converter

Dongjin Lee, Junyeop Kim, Heedeuk Shin

Published Oct 4, 2024• 1 citation
Publisher

Abstract

Optical fibers have played a pivotal role in the long-distance transportation of quantum states and quantum key distribution due to their low loss. They have garnered attention for photon-pair generation and quantum frequency conversion due to their engineered dispersion properties. Accurate measurement of dispersion properties is essential for these applications. In this study, we introduce a new method to measure the dispersion properties of short optical fibers using Bragg-scattering four-wave mixing (BS-FWM). We successfully measured properties, including zero group-velocity-dispersion wavelength, dispersion slope, and the nonlinear coefficient, for fiber lengths ranging from 9.7 m to 392.7 m. Furthermore, we achieved efficient quantum frequency conversion with an efficiency of 83.8±0.8% using parameters extracted from a 53.9-m-long optical fiber. Our research offers a valuable resource for improving the performance of fiber-based photon-pair sources and quantum frequency converters and has potential implications for advancing fiber-based quantum information processing.

DOI
10.1364/oe.537030

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Optics Letters•Mar 11, 2013•66 citations
Optical fibers have played a pivotal role in the long-distance transportation of quantum states and quantum key distribution due to their low loss. They have garnered attention for photon-pair generation and quantum frequency conversion due to their engineered dispersion properties. Accurate measurement of dispersion properties is essential for these applications. In this study, we introduce a new method to measure the dispersion properties of short optical fibers using Bragg-scattering four-wave mixing (BS-FWM). We successfully measured properties, including zero group-velocity-dispersion wavelength, dispersion slope, and the nonlinear coefficient, for fiber lengths ranging from 9.7 m to 392.7 m. Furthermore, we achieved efficient quantum frequency conversion with an efficiency of 83.8±0.8% using parameters extracted from a 53.9-m-long optical fiber. Our research offers a valuable resource for improving the performance of fiber-based photon-pair sources and quantum frequency converters and has potential implications for advancing fiber-based quantum information processing.
We demonstrate an all-fiber broadband photon pair source based on four wave mixing (FWM) process in dispersion flattened highly non-linear fiber (DF-HNLF). The fiber exhibits a zero dispersion slope near 1550 nm, allowing phase-matched FWM over entire S, C, and L bands and thus efficient generation of signal and idler photons. A comparative theoretical study between conventional dispersion-shifted fiber (DSF) and DF-HNLF highlights the spectral range differences in the generation of photon pairs. We measure coincidence counts at three different sets of wavelengths. To study the effects of Raman scattering, which acts as noise source in these types of fibers, we calculate the correlationg(2)(τ)g^{(2)}(\tau)g(2)(τ)at different pump powers. We use stimulated emission tomography to characterize the generation of photon pairs across the S, C, and L bands. We show that DF-HNLF is an ideal medium for generating correlated photons over a broad spectral range (> ⁣ ⁣100 nm>\!\!100\,\text{nm}>100nm), making it suitable for frequency-multiplexed quantum communication systems. We estimate the photon pair generation efficiency to be 0.05mW−2/pulse\text{mW}^{-2}/\text{pulse}mW−2/pulse.
The authors consider, experimentally and theoretically, the quantum frequency translation (i.e., noiseless conversion) of quantum states of light, including single-photon states. This process is useful for allowing quantum optical systems (atoms, ions, cavities, fibers, detectors) operating at different wavelengths to communicate with each other. The authors recently developed the process of frequency translation in optical fiber through use of the Bragg scattering four-wave mixing process. The high nonlinearity and the ability to control dispersion in photonic crystal fiber (PCF) enable efficient translation between nearby photon channels within the visible to-near-infrared spectral range, useful in quantum networks. This offers an important advantage compared with frequency translation using second-order nonlinear optical crystals, which limits the translation process to widely separated frequencies only.
We present an experimental method for characterizing the (Green) cross-transfer functions of quantum frequency conversion (QFC) systems, which provide a complete spectral characterization of the underlying parametric interaction. We demonstrate the approach on a kilometer-scale fiber Bragg-scattering four-wave-mixing (BS-FWM) converter, retrieving its transfer functions directly from classical probe measurements. The reconstructed responses reveal clear departures from theory that we attribute primarily to longitudinal dispersion variations in the physical medium. Incorporating such variations in a numerical model yields quantitative agreement with experiment and accurately predicts single-photon conversion efficiencies measured independently in another experiment. The outlined method provides a practical route to characterizing and optimizing complex QFC systems using only classical probes, offering predictive insight directly relevant to applications in the quantum regime.
Efficient frequency conversion is crucial for interfacing photons with a variety of quantum systems ranging from matter qubits (color centers, quantum dots, atoms), optical fibers, detectors, that often operate at widely different wavelengths. Frequency conversion is also a resource to process quantum information.1, 2 Parametric processes such as sum frequency generation (SFG) and Bragg scattering four wave mixing (BS-FWM) offer a good versatility for such frequency conversion. It is well understood that those nonlinear processes have to be strong enough and satisfy phase matching to achieve a high conversion efficiency. While it is enough to consider those two aspects for moderate conversion efficiency up to 50%, the analysis is a bit more complicated when targeting efficiencies closely approaching unity. We are reviewing the pitfall that must be avoided to indeed reach near unity frequency transduction.
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.
In this Letter we demonstrate frequency conversion in the single-photon regime through Bragg-scattering four-wave mixing with near-unit efficiency in a 750 m long commercially available dispersion-engineered highly nonlinear fiber, where all photons and pump laser frequencies are in the low-loss telecommunications band. We achieve 99.1%±4.9% downconversion and 98.0%±5.0% upconversion of photons by 12 nm using a weak coherent state with an average input of 0.27 photons per detection gate window.