Field experiments ofquantumcryptosystem in96kminstalled fibers

Tetsuya Hasegawa, Takahiro Nishioka, Hirokazu Ishizuka, Junichi Abe, Ken Shimizu, M. Matsui

Published Jan 1, 2005• 0 citations

Abstract

We havesuccessfully demonstrated quantum cryptosystem in96kminstalled fibers between OsakaandKyoto, Japan withourdedicated QKD hardware suitable forfield experiments. Weconfirmed that keyrate is8.2bps andQBERis9.9%. Quantum cryptography hastheadvantage ofdetecting eavesdroppers andsecurity guaranteed byafundamental physical law,andisexpected asanabsolutely unbreakable cryptography. Although manylong-distance experiments23 within a laboratory havebeencarried out, aserious QKDfield experiment, except 67kmQKDexperiment' byGeneva Univ., hasnot beenreported yet. Infield experiments compared tothat inlaboratories, there areseveral difficulties tobeovercome, such asfluctuations bytemperature, losses/reflections atconnected points, operations between twodistant points andsoon. Inthis paper, wereport ourfield experiments ofquantum cryptosystem in96kminstalled fibers ofJGNIItestbed between OsakaandKyoto(see Fig. 1). Wehavedesigned compact 1550nmsingle photon detectors andoptics forportable useand electronic control units suitable forfield tests. Andthenwedeveloped atotal portable QKD system applicable toactual fiber networks. Ourdesign policy ofQKD system forfield experiments isthatitscomponents, especially detectors andoptics, are compact forportable use, thesystem canworkstable attwodistant points tofollow timing shifts resulted bytemperature fluctuations andsoforth. We also regarded flexibility asimportant. Therefore wedesigned electronic control units sothat wecould easily change detector's parameters, timing parameters orevenalaser repetition rate (I-IOMHz)whennecessary. Asforsingle photon detectors, wedesigned several parameters toattain about 10-6 darkcount probability andS/Nwhich canlead toabout 100kilometers QKD.Weoperated EPITAXXEPM239BAingated Geiger mode.Wechose anexcess bias voltage as7.1 V(breakdown voltage 44.9V), gate width asInsec(FWHM)andtemperature asabout 203KbyPeltier cooling. Inanother sample, anexcess bias voltage is5.8V(breakdown voltage 44.3V). Asaresult, wehavesuccessfully constructed compact low-noise detectors whosedarkcount probabilities are1.2x10.6, 1.Ox I0-6. Forfield experiments ofquantum cryptosystem, weusedthese compact detectors andourdedicated electronic control units. We adopted modified plugp ) D i __~~~~~~~~~~~~~~~~~~~~~~~~~~~(OIOS Ib A icboPD2 | 7 ~~~~~~~pWbi, cbh-mLAN-TCP/IP Fig.VI.aLAN) Fig. 1.JGNII fiber testbed between OsakaandKyoto Fig 2.Schematic diagram ofexperimental setup

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