In this work we generate and detect single photons in optical fibers using the stimulated four-wave mixing (FWM)process. The results show an accurate generation of single
photons at four different linear states of polarization (SOPs), with angles 0, 45, 90 and -45 degrees.QuantTel - Quantum Secure Telecommunication

Almeida, Álvaro J.

Fernandes, Gil G.

Pinto, Armando N.

Repositório Institucional da Universidade de Aveiro

Single-Photon Source With Adjustable Linear SOPÁlvaro J. Almeida, Gil G. Fernandes and Armando N. PintoAbstract—In this work we generate and detect single photonsin optical fibers using the stimulated four-wave mixing (FWM)process. The results show an accurate generation of singlephotons at four different linear states of polarization (SOPs),with angles 0, 45, 90 and -45 degrees.Index Terms—Optical polarization, optical mixing.I. INTRODUCTIONIn order to achieve quantum secure telecommunicationswith enhanced security, single-photon sources are an emergingkey technology [1]. A single-photon source should presentproperties such as wavelength stability, high efficiency, gen-eration of a low number of photons, and it also should allowthe polarization control of the photons [1], [2].Stimulated Four-Wave Mixing (FWM) is a third-ordernonlinear process that occurs when light of two or morefrequencies (known as pump and signal fields) are launchedinto an optical fiber given rise to a new wave, known as idlerfield [3].Most of the quantum protocols require single-photonsources in order to transmit information between two differentlocations [4]. Recently, polarization encoded photons havebeen proposed in some quantum experiments to implementthese quantum protocols in optical fibers [4]. Typically, single-photon sources with different linear states of polarization(SOPs) are obtained using several highly attenuated lasers [5].In this paper we use the FWM process to obtain a source ofsingle photons with adjustable linear SOP.In section II, we present a description of the experimentalsetup, used to generate and detect single photons in fourdifferent linear SOPs. In this section we also present theobtained experimental results. The main results of this workare summarized in section III.II. SINGLE-PHOTON SOURCEIs this section we describe the proposed single-photonsource with adjustable linear SOP, and present the obtainedexperimental results.This work was partially supported by the Instituto de Telecomunicaçõesunder the Associated Laboratorial program supported by the Fundação para aCiência e Tecnologia (FCT) and European Union FEDER program, throughthe IT/LA project named: “QuantTel - Quantum Secure Telecommunications”.Álvaro J. Almeida is with the Instituto de Telecomunicações, 3810-193Aveiro, Portugal (e-mail: aalmeida@av.it.pt).Gil G. Fernandes is with the Departamento de Física, Universidade deAveiro, and the Instituto de Telecomunicações, 3810-193 Aveiro, Portugal (e-mail: gfernandes@av.it.pt).Armando N. Pinto is with the Departamento de Electrónica, Teleco-municações e Informática, Universidade de Aveiro and the Instituto deTelecomunicações, 3810-193 Aveiro, Portugal (e-mail: anp@ua.pt).A. Experimental SetupIn the experimental setup, see Fig. 1, a pump at λ1 froma tunable laser source (TLS), passes through a polarizationcontroller (PC1), before being coupled to another opticalsignal, at λ2, from a external cavity laser (ECL). This opticalsignal, λ2, is externally modulated to produce optical pulseswith a width at half maximum of 1.6 ns and a repetition rateof 555.6 kHz. The two optical fields, λ1 and λ2, pass through alinear polarizer (P1) and are launched into a dispersion-shiftedfiber (DSF), with a length equal to 305 m. Due to the FWMprocess, a new signal, the idler, is generated inside the DSFat λ3 = λ1λ2/(2λ2−λ1). At the fiber output, the three opticalfields pass through the PC4 in order to align the SOP of theidler photons with the linear polarizer P2. A filter F1 blocksthe pump and signal waves. At the exit of P2 the angle ofthe linear SOP is controlled using a rotatable key connector(RKC), θ1. The SOP of the idler photons is analyzed usinganother linear polarizer (P3), whose orientation is tuned usinga second RKC, θ2.The idler photons from P3 are detected with a Single-PhotonDetector Module (SPDM) operating in Geiger mode. The darkcount probability of the SPDM for a time gate, tg = 2.5 ns, isPdc < 5 ·10−5. The quantum detection efficiency is η= 10 %[6]. The average number of idler photons per pulse, n¯, wasmeasured during a period of time of 10 s [1].B. ResultsIn Fig. 2 we plot the average number of idler photonsper pulse as a function of the linear polarizer angle, ∆θ2,for the four different linear SOPs generated by our single-photon source. From Fig. 2 we can see that exists a maximumand a minimum for each linear SOP, and the phase differencePump 1549.32 nm Signal 1550.92 nm Coupler 50/50 DSF  (305 m) PC3 P1 Patern generator MZ  modulator PC2 PC1 Photon detector DC Voltage SOP analyzer F1 PC4 P2 2P3 1Single-photon source with adjustable linear SOP RKC RKC Fig. 1: Experimental setup used to generate and detect single photons at thelinear SOPs with angles 0, 45, 90 and -45 degrees. Details of the setup arepresented in the text.- 8 0 - 4 0 0 4 0 8 0 1 2 00 . 0 00 . 0 20 . 0 40 . 0 60 . 0 80 . 1 00 . 1 20 . 1 4Average number of photons per pulse∆θ2	Fig. 2: Average number of idler photons per pulse as a function of the angle(degrees), for the linear SOPs with angles 0, 45, 90 and -45 degrees. Thepump and signal optical powers at the fiber input were P1 = 3.39 mW, andP2 = 0.54 mW, respectively. The wavelengths for the pump and the signalwere λ1 = 1549.32 nm and λ2 = 1550.92 nm, respectively.between the maximum value for each linear SOP is 45 degrees.The maximum value, n¯ ∼ 0.14, is obtained when the polarizeris aligned with the SOP of the single-photon source, while theminimum, n¯ ∼ 0, is found when they are orthogonal.In order to obtain a theoretical approximation for theexperimental results, we can consider that the SOP at thepolarizer output is given by,sˆ= R (θ)MPR (−θ)sˆ(0) , (1)where R (θ) and MP are, respectively, the rotation and thelinear polarizer Mueller matrices in Stokes space [7], andsˆ(0) is the Stokes vector corresponding to the initial SOP.Assuming an initial SOP given by sˆ(0) = [1,0,0]T , where Tis the transpose, we obtain, s1s2s3= cos2(2θ)sin(2θ)cos(2θ)0 . (2)As the total optical power is given by P= |s0|2 = s21+ s22+ s23,where s1,s2 and s3 are the Stokes parameters [8], we have,P= [cos2(2θ)]2+[sin(2θ)cos(2θ)]2 = cos2(2θ) . (3)From (3) we can obtain a theoretical fit for the experimentalresults of the form,n¯= Acos2[∆θ2+φ] , (4)where A is the amplitude, ∆θ2 is the shift in the angle inrelation to the linear SOP of 0◦, and φ is the phase differencebetween the linear SOPs.In Fig. 3 we plot the average number of idler photons perpulse as a function of the angle ∆θ2, and the theoretical fitgiven by (4), for the linear SOPs with angles 0 and 45 degrees.From Fig. 3 we can see that the theoretical fit given by (4) isa good approximation to the experimental results.- 8 0 - 4 0 0 4 0 8 0 1 2 00 . 0 00 . 0 20 . 0 40 . 0 60 . 0 80 . 1 00 . 1 20 . 1 4∆θ2Average number of photons per pulse 	Fig. 3: Average number of idler photons per pulse as a function of the angle∆θ2, for the linear SOPs with angles 0 and 45 degrees. The circles and thesquares represents the measured values, and the solid lines represents thetheoretical fit given by (4). The optical powers and the wavelengths are thesame used in Fig. 2.III. CONCLUSIONWe have shown that it is possible to generate and detectsingle photons in well defined four linear SOPs. This can beused to implement a quantum protocol to authenticate classicalmessages with enhanced security.With our single-photon source we could select the linearSOP at the source using only one optical field.To improve the results, a better alignment between thekeys of the linear polarizers and the keys of the polarizationmaintaining fibers must be performed.REFERENCES[1] Antunes, P.; André, P.S; Pinto, A. N.; “A Simple and Inexpensive Single-Photon Source by Means of Four-Wave-Mixing and Attenuation”, ProcConf. on Telecommunications - ConfTele, Peniche, Portugal, pp. 255 -257, May, 2007.[2] Antunes, P.; André, P.S; Pinto, A. N.; “Single-Photon Source by Meansof Four-Wave Mixing Inside a Dispersion-Shifted Optical Fiber”, ProcOSA Frontiers in Optics, Rochester, New York, USA, October, 2006.[3] Govind, P., Agrawal; “Nonlinear Fiber Optics”, 4th ed., Academic Press,San Diego, California, USA, 2007.[4] Bouwmeester, D.; Ekert, A.; and Zeilinger, A.; “The Physics of QuantumInformation” Berlin: Spinger-Verlag, 2000.[5] Jie Chen; Guang Wu; Yao Li; E. Wu; and Heping Zeng; “Active polariza-tion stabilization in optical fibers suitable for quantum key distribution”,Opt. Express 15, 17928-17936, 2007.[6] Id Quantique, “Single-Photon Detector Module - Operating Guide, Ver-sion 2.2”, Carouge, Switzerland, 2005, unpublished.[7] Goldstein, D., “Polarized Light, Second Edition, Revised and Expanded”,Air Force Research Laboratory, Eglin Air Force Base, Florida, U.S.A.,2003.[8] J. N. Damask.; “Polarization Optics in Telecommunications”, SpringerSeries in Optical Sciences, 2005.

Single-photon source with adjustable linear SOP

http://ria.ua.pt/bitstream/10773/6281/1/paper.seons09_v1.0.pdf

Single-photon source with adjustable linear SOP

Abstract

Similar works

Full text

Available Versions

Repositório Institucional da Universidade de Aveiro