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Nonlinear Frequency Generation and Conversion: Materials and Devices

Efficient difference frequency generation for quantum frequency conversion in a multimode PPLN-waveguide

Hans Huber, Martin Walochnik, Florian Elsen, Bernd Jungbluth, Peter Loosen

Published Mar 4, 2021• 0 citations
Publisher

Abstract

Converting single photons from one wavelength to another is of fundamental interest for future quantum communication and computing. Using commercially available lasers and a multimode PPLN waveguide a DFG scheme was set up. Phase-matching was shown in the fundamental transverse mode of the waveguide for wavelengths between 851 nm and 862 nm. The setup is capable of converting up to 87% of photons from 856 nm to 1526 nm in transverse fundamental mode. Simulations were performed showing that the quantum conversion efficiency at 856 nm is representative for powers down to thousands of photons per second.

DOI
10.1117/12.2578605

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Converting single photons from one wavelength to another is of fundamental interest for future quantum communication and computing. Using commercially available lasers and a multimode PPLN waveguide a DFG scheme was set up. Phase-matching was shown in the fundamental transverse mode of the waveguide for wavelengths between 851 nm and 862 nm. The setup is capable of converting up to 87% of photons from 856 nm to 1526 nm in transverse fundamental mode. Simulations were performed showing that the quantum conversion efficiency at 856 nm is representative for powers down to thousands of photons per second.
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Dense wavelength division multiplexing (DWDM) is a key technology for realizing high-capacity and flexible quantum communication networks. To enable the emerging quantum internet, quantum frequency conversion is also essential for bridging different quantum systems over optical fiber networks. In this work, aiming at a frequency-multiplexed quantum internet, we present a channel-selective quantum frequency conversion (CS-QFC) based on difference frequency generation in a PPLN waveguide, which has been widely used in conventional QFC experiments. The CS-QFC converts a frequency of a photon at a single frequency to any frequency in the DWDM channels by dynamically selecting one of the pump lights. In the experiment, we demonstrated the CS-QFC from 780 nm to around 1540 nm employing one of the pump lights around 1580 nm detuned with a spacing of 25 GHz. From the experiment using the laser light, we showed that the output-frequency tunability of our CS-QFC reaches 2.5 THz, which corresponds to the ability to establish a 100-ch DWDM dynamic link from a single quantum system. Using photon pairs, we performed an experiment in which photons were routed into seven of the DWDM channels. As a result, photons were converted to the channels corresponding to the pump frequencies, while keeping the nonclassical cross-correlation functions, and no crosstalk to the other channels was observed.
The principle of all-optical wavelength conversion based on the cascaded sum and difference frequency generation (SFG+DFG) in quasi-phase-matched (QPM) periodically poled LiNbO3 (PPLN) waveguides is introduced. The conversion efficiency of the wavelength converter is calculated. The influences of the powers and span of two pumps on the conversion efficiency are analyzed. Bandwidth of one pump wavelength is discussed. The tuning is about 0.5 nm. The signal pulse width is compressed about 0.68 times.
We report an experiment demonstrating quantum frequency conversion of weak light pulses compatible with atomic quantum memories to telecommunication wavelengths. We use a PPLN nonlinear waveguide to convert weak coherent states at the single photon level with a duration of 30 ns from a wavelength of 780 nm to 1552 nm. We measure a maximal waveguide internal (external) conversion efficiency η(int) = 0.41 (η(ext) = 0.25), and we show that the signal to noise ratio (SNR) is good enough to reduce the input photon number below 1. In addition, we show that the noise generated by the pump beam in the crystal is proportional to the spectral bandwidth of the device, suggesting that narrower filtering could significantly increase the SNR. Finally, we demonstrate that the quantum frequency converter can operate in the quantum regime by converting a time-bin qubit and measuring the qubit fidelity after conversion.
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In this paper we measure the efficiency of photon pair production from parametric downconversion at the photon counting level, generated in a laboratory prototype of PPLN waveguide at 1572 nm. The aim is to enhance the brightness of an heralded single photon source and to improve compactness for quantum communication applications, namely quantum key distribution. We observed a maximum of the conversion efficiency corresponding to 7.9 106 photon pairs/s for a pump power of 28 μW. This value is compared with the measured pairs production in a classical experiment of difference frequency generation, realized with the same sample by analogue classical detection. We highlight the advantages of using the waveguide versus a bulk PPLN for such applications and we foresee further possible improvements by adopting waveguide in a single photon level experimental setup.