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Quantum Computing, Communication, and Simulation

Optimized entangled photon pair generation via intermodal four-wave mixing in a telecommunication-length few-mode fiber

Seyedehnajmeh Montazeri, Mina Esmaeelpour

Published Mar 12, 2024• 0 citations
Publisher

Abstract

We report our recent progress in generating and verifying entangled photon pairs in a telecommunication-length few-mode fiber using spontaneous four-wave mixing in a non-degenerate pump configuration. We demonstrate through seeding the desired four-wave mixing effect for pair production in the presence of a strong mode-coupling when using integrated mode multiplexers known as photonic lanterns. The mode content and phase-matching requirements were validated through computations and experiments. We discuss the challenges and requirements for phase matching and photon visibility without modifying the fiber structure. This work represents our first steps toward an efficient tunable source of entangled photons for space division multiplexing applications.

DOI
10.1117/12.3003547

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We report our recent progress in generating and verifying entangled photon pairs in a telecommunication-length few-mode fiber using spontaneous four-wave mixing in a non-degenerate pump configuration. We demonstrate through seeding the desired four-wave mixing effect for pair production in the presence of a strong mode-coupling when using integrated mode multiplexers known as photonic lanterns. The mode content and phase-matching requirements were validated through computations and experiments. We discuss the challenges and requirements for phase matching and photon visibility without modifying the fiber structure. This work represents our first steps toward an efficient tunable source of entangled photons for space division multiplexing applications.
High degrees of security have been achieved in quantum communication over fiber using entangled photons. For communications applications, it is crucial to produce high-yield entangled photon pairs (EPPs) with the capacity to transmit them over telecommunication-length fiber distances and the ability to integrate and transmit them over existing classical communication systems. Since spatial division multiplexing (SDM) is currently being demonstrated to replace single-mode communication systems, it only makes sense to demonstrate the generation and transferring EPPs in various fiber modes suitable for generation and transmission in SDM fibers. We experimentally demonstrate EPP formation in a 25-km-long graded-index few-mode fiber (three modes) via the intermodal spontaneous four-wave mixing (SFWM) effect. Mode profile and phase matching condition have been confirmed through experiments.
We experimentally demonstrate the various intermodal and intramodal four-wave mixing processes in a few-mode fiber with three modes using non-degenerate pumps. We distinguish the processes by calculating their phase mismatch and identify the intermodal spontaneous four-wave mixing process that generates entangled photon pairs in various modes. We achieve this using continuous-wave beams and the seeding technique due to the low efficiency of the spontaneous four-wave mixing effect in the fiber. We seeded the Stokes and anti-Stokes waves and measured the spectral content of each mode while moving the seed away from the perfect phase-matched condition in the fiber under test. We observe that the closer the seed gets to the pumps, the higher the efficiency of the four-wave mixing process.
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.
We demonstrate intermodal spontaneous four-wave mixing in a 500 m graded-index few-mode fiber, generating correlated photon pairs in distinct spatial modes at room temperature and under cryogenic cooling. Two nondegenerate pumps at 1550 and 1551 nm are launched into the LP 01 and LP 11 spatial modes, enabling flexible phase matching and strong intermodal photon-pair correlations spanning the optical C band. Cooling the fiber to −160 ∘ C in a liquid-nitrogen-cooled cryogenic chamber substantially suppressed spontaneous Raman scattering without degrading the four-wave mixing process. Spectral and power-dependent measurements confirm quadratic photon-pair scaling with pump power and reduced linear Raman background at low temperature. Coincidence measurements show a coincidence-to-accidental ratio of 39±0.03 at −160 ∘ C, representing approximately a 40.8% improvement over room temperature. With photonic-lantern-based mode excitation and collection, the source exhibits low modal crosstalk and clean mode separation. This approach provides a practical route to low-noise, fiber-integrated photon-pair sources for scalable quantum photonics.
mode, respectively, via the spontaneous intermodal four-wave mixing in a 100-m-long few-mode fiber. We achieve a coincidence to accidental-coincidence ratio of 28, which clearly indicates the existence of quantum correlation. We also discuss the contribution of spontaneous Raman scattering to the background noise of photon pairs. Our source of photon pairs, compatible with the low-loss multiplexing and de-multiplexing components for space division multiplexing optical fiber communication, can be used for generating higher-dimensional entanglement.
Intermodal four-wave mixing (FWM) process in few-mode fibers (FMFs) could be utilized for entangled photon-pair generation. Previous studies mainly performed in single-mode fibers suffered from the significant Raman scattering background from the glass fiber. Therefore, the instantaneous Raman and FWM effects would compete; this could be avoided in FMFs if the modal dispersion is larger than the Raman gain spectra. Utilizing two pumps in different modes in FMFs will generate photon pairs in various modes. Here, we study the effect of pump spectral separation on the intermodal FWM power and bandwidth using a seeding technique. It is concluded that the further the pumps and intermodal FWM idler and signal are from each other spectrally, the smaller the photon efficiency and larger the bandwidth. Experimental results for two FMFs of different differential mode group delay values are presented.