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arXiv:1810.02267 · OSA Continuum

Turn-key diode-pumped all-fiber broadband polarization-entangled photon source

Changjia Chen, Arash Riazi, Eric Y. Zhu, Mili Ng, Alexey V. Gladyshev, Peter G. Kazansky, Li Qian

Published Nov 2, 2018• 24 citations
arXivHTMLPDF

Abstract

In this letter, we report a compact, low-power laser diode-pumped, all-fiber polarization-entangled photon pair source based on periodically-poled silica fiber technology. The all-fiber source offers room-temperature, alignment-free, turn-key operation, with low power consumption, and is packaged into a fanless, portable enclosure. It features a broad biphoton spectrum of more than 100nm with a concurrence that is greater than 0.96 for polarization entanglement. The source is stable over at least 10 hours of continuous operation, achieving coincidence-to-accidental ratios of more than 2000 consistently over this time period.

DOI
10.1364/osac.1.000981

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In this letter, we report a compact, low-power laser diode-pumped, all-fiber polarization-entangled photon pair source based on periodically-poled silica fiber technology. The all-fiber source offers room-temperature, alignment-free, turn-key operation, with low power consumption, and is packaged into a fanless, portable enclosure. It features a broad biphoton spectrum of more than 100nm with a concurrence that is greater than 0.96 for polarization entanglement. The source is stable over at least 10 hours of continuous operation, achieving coincidence-to-accidental ratios of more than 2000 consistently over this time period.
In this Letter, we report a polarization-entangled photon-pair source based on type-II spontaneous parametric downconversion at telecom O-band in periodically poled silica fiber (PPSF). The photon-pair source exhibits more than 130 nm ( ∼ 24 T H z ) emission bandwidth centered at 1306.6 nm. The broad emission spectrum results in a short biphoton correlation time, and we experimentally demonstrate a Hong–Ou–Mandel interference dip with a full width of 26.6 fs at half-maximum. Owing to the low birefringence of the PPSF, the biphotons generated from type-II SPDC are polarization-entangled over the entire emission bandwidth, with a measured fidelity to a maximally entangled state greater than 95.4%. The biphoton source provides the broadest bandwidth entangled biphotons at O-band to our knowledge.
The time-energy entangled photon source is a core resource in quantum key distribution, quantum teleportation, and quantum metrology. The output of orthogonally polarized photon pairs can enhance the effective coincidence counts of the entangled source in these applications. Additionally, an all-fiber entangled source offers small size and high mobility advantages. However, most current orthogonally polarized all-fiber time-energy entangled sources are limited to a bandwidth of around 1 nm, which is detrimental to the effective utilization of channel resources in fiber networks and restricts precision in quantum metrology. To address this issue, we employ a fiber-coupled 775 nm narrow linewidth pump laser in a periodically poled lithium niobate (PPLN) waveguide to achieve type-II spontaneous parametric down-conversion (SPDC). This results in an all-fiber orthogonally polarized time-energy entangled photon source with a bandwidth greater than 7 nm. We measured the single counts, coincidence counts, coincidence to accidental coincidence ratio (CAR), single photon spectra, and joint spectral intensity of the entangled source, calculating the Schmidt number S = 7.8. Furthermore, we measured Hong-Ou-Mandel (HOM) interference by inserting two 2 nm bandpass filters, and the interference visibility remained around 95.8% after continuous operation for 3 hours. The experimental results indicate that while maintaining an all-fiber structure, this source possesses a broadband range, low noise, and high stability, providing efficient and reliable biphoton resources for applications in quantum communication, quantum networks, and precision metrology.
Entangled photons are a fundamental resource in quantum applications. Broadband entangled photon sources have been used in applications such as high-resolution quantum sensing and wavelength-multiplexed quantum communication. In particular, in fiber-based quantum applications such as long-distance quantum clock synchronization and quantum key distribution in deployed fiber networks, a practical entangled source that is robust and compatible with silica fiber is highly sought after. Periodically poled silica fiber (PPSF) has been demonstrated to be a promising resource of entangled photon-pairs. PPSF uses the induced second-order nonlinearity in poled fiber to generate polarization-entangled photon pairs based on type-II spontaneous parametric down-conversion. The negligible group birefringence of the PPSF ensures high-quality and broadband polarization entanglement without compensation, making it particularly suitable for these quantum applications. The PPSF-based source has a lot of potentials to be tapped because of its high entanglement quality, broadband emission bandwidth, simple structure, and its compatibility with the existing fiber infrastructure. In this thesis, I focus on the development of the PPSF-based entangled photon sources. I first investigate the design and the manufacturing process of the PPSF where I try to produce PPSF with improved performance and innovative properties. Next, I study the compensation-free nature of the PPSF-based polarization entanglement source and discuss the interplay between dispersion, birefringence, emission bandwidth, and polarization entanglement. Based on the theory, a commercial PPSF-based photon-pair source prototype is developed and patented. It has to my knowledge the simplest design of all polarization-entangled sources reported so far in the literature. Furthermore, I broaden the biphoton bandwidth by building a PPSF photon-pair source that emits biphotons at telecom O-band. With more than 24THz bandwidth, the biphotons generated in this source are the broadest of all O-band polarization-entangled photon sources reported to my knowledge. I also propose and experimentally demonstrate a polarization-frequency hyperentangled photon source using PPSF, which provides higher dimensionality by making use of entanglement in multiple degrees of freedom. Overall, this thesis contributes to the development of PPSF technology for practical quantum applications. I anticipate that the PPSF-based photon-pair source will play an important role in the era of quantum technology.
We demonstrate a novel alignment-free all-fiber source for generating telecom-band polarization-entangled photon pairs. Polarization entanglement is created by injecting two relatively delayed, orthogonally polarized pump pulses into a piece of dispersion-shifted fiber, where each one independently engages in four-photon scattering, and then removing any distinguishability between the correlated photon-pairs produced by each pulse at the fiber output. Our scheme uses a Michelson-interferometer configuration with Faraday mirrors to achieve practically desirable features such as ultra-stable performance and turnkey operation. Up to 91.7% two-photon-interference visibility is observed without subtracting the accidental coincidences that arise from background photons while operating the source at room temperature.