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Degenerate correlated photon pairs (DCPPs) have been widely used in quantum information science,especially in the areas of quantum computation,quantum state control and precision measurement,which are typically generated in a (2) nonlinear crystal through the spontaneous parametric down-conversion.However,such a source is not compatible with optical fiber as large coupling losses occur when the pairs are launched into it,which restricts its direct application to quantum information processing system.More recently,DCPP generation from spontaneous four-wave mixing in (3) optical fiber has aroused strong interest,due to its advantages of compatibility with existing fiber networks and free of alignment.The process of generating DCPP in fiber can be described as follows:two pump photons at different frequencies p1 and p2 scatter through the (3) nonlinearity to create a pair of identical photons at the mean frequency c,such that p1+p2=2c.Because the collinear tensor component xxxx(3) in a Kerr nonlinear medium is 3 times as large as the tensor component xyxy(3),the co-polarized four-wave mixing is preferred,which means the two pump photons and new-born twin photons are both co-polarized.Therefore,it is very challenging to deterministically separate the fiber-based DCPP,since the twin photons share the same properties in all degrees of freedom:frequency,polarization and spatial.Sagnac fiber loop (SFL),composed of a piece of nonlinear fiber and 50/50 coupler,is presented as the splitter for DCPP based on the reversed Hong-Ou-Mandel quantum interference of counter-propagating DCPPs.The SFL can be configured as a total reflector,total transmitter or equally transmissive and reflective state,which sets the differential phases of counter-propagating DCPPs meeting at 50/50 coupler to be ,0 and -,respectively.In order to satisfy the differential phase requirement for completely splitting the DCPP,the SFL is always set to be equally transmissive and reflective state,however,the polarization-mode matching of counter-propagating DCPPs is not easily achieved due to the disturbance of fiber birefringence.According to the Jones matrix derivation of DCPP propagating in the SFL,the polarization mode of counter-propagating DCPPs when interference at 50/50 coupler is automatically matched,if the SFL is set as a total reflector or total transmitter.In experimental scheme,utilizing the SFL as a total reflector,the 1.1 nm bandwidth and 1544.53 nm central wavelength DCPPs are generated by two pulsed light beams pumping the 300 m dispersion-shifted fiber in the SFL.Using the two pieces of single mode fiber connecting the 300 m dispersion-shifted fiber and 50/50 coupler,whose length difference is fixed at 3.3 m,the differential phase of counter-propagating DCPPs highly dependent on the dispersion properties of single mode fiber is managed at 2 for fully distributing DCPPs into which degrades the fidelity of DCPP source.The measured ratio of coincidence to accidental-coincidence of DCPPs from one port is approximately 1.8:1,which indicates that the coincidence counts mainly originate from accidental coincidence counts and extra coincidence counts from photon bunching and there are not any DCPPs outputting from one port.Meanwhile,the ratio of best measured coincidence to accidental-coincidence of DCPPs from two ports reaches 47:1,when the average power of two pumps is fixed at 0.026 mW.The experimental results demonstrate that the high purity and fully spatial separation DCPPs are successfully prepared in optical fibers,which is a very useful tool for realizing various quantum information systems.How the spatial state of outputting DCPPs depends on the length difference between single-mode fiber and detuning wavelength is also discussed in detail.
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Keywords:
- narrow-band degenerate correlated photon pairs /
- Sagnac fiber loop /
- spontaneous four-wave mixing /
- dispersion
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[13] Li X Y, Yang L, Ma X X, Cui L, Ou Z Y, Yu D Y 2009 Phys. Rev. A 79 033817
[14] Yang L, Sun F W, Zhao N B, Li X Y 2014 Opt. Express 22 2553
[15] Li X Y, Voss P L, Chen J, Lee K F, Kumar P 2005 Opt. Express 13 2236
[16] Takesue H, Inoue K 2005 Opt. Express 13 7832
[17] Yang L, Li X Y, Wang B S 2008 Acta Phys. Sin. 57 4933 (in Chinese) [杨磊, 李小英, 王宝善2008 57 4933]
[18] Ribordy G, Gautier J D, Zbinden H, Gisin N 1998 Appl. Opt. 37 2272
[19] Ou Z Y, Rhee J K, Wang L J 1999 Phys. Rev. A 60 593
[20] Li X Y, Ma X X, Quan L M, Yang L, Cui L, Guo X S 2010 J. Opt. Soc. Am. B 27 1857
[21] Cui L, Li X Y, Fan H Y, Yang L, Ma X X 2009 Chin. Phys. Lett. 26 044209
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[1] Shi Y H 2003 Rep. Prog. Phys. 66 1009
[2] Bouwmeester D, Pan J W, Mattle K, Eibl M, Weinfurter H, Zeilinger A 1997 Nature 390 575
[3] Knill E, Laflamme R, Milburn G J 2001 Nature 409 46
[4] Nasr M B, Saleh B E A, Sergienko A V, Teich M C 2003 Phys. Rev. Lett. 91 083601
[5] Fraine A, Simon D S, Minaeva O, Egorov R, Sergienko A V 2011 Opt. Express 91 22820
[6] Hong C K, Ou Z Y, Mandel L 1987 Phys. Rev. Lett. 59 2044
[7] Fan J, Dogariu A, Wang L J 2005 Opt. Lett. 30 1530
[8] Fan J, Migdall A 2005 Opt. Express 13 5777
[9] Chen J, Lee K F, Liang C, Kumar P 2006 Opt. Lett. 31 2798
[10] Chen J, Lee K F, Kumar P 2007 Phys. Rev. A 76 031804R
[11] Lin Q, Yaman F, Agrawal G P 2007 Phys. Rev. A 75 023803
[12] Mortimore D B 1988 J. Lightwave Technol. 6 121
[13] Li X Y, Yang L, Ma X X, Cui L, Ou Z Y, Yu D Y 2009 Phys. Rev. A 79 033817
[14] Yang L, Sun F W, Zhao N B, Li X Y 2014 Opt. Express 22 2553
[15] Li X Y, Voss P L, Chen J, Lee K F, Kumar P 2005 Opt. Express 13 2236
[16] Takesue H, Inoue K 2005 Opt. Express 13 7832
[17] Yang L, Li X Y, Wang B S 2008 Acta Phys. Sin. 57 4933 (in Chinese) [杨磊, 李小英, 王宝善2008 57 4933]
[18] Ribordy G, Gautier J D, Zbinden H, Gisin N 1998 Appl. Opt. 37 2272
[19] Ou Z Y, Rhee J K, Wang L J 1999 Phys. Rev. A 60 593
[20] Li X Y, Ma X X, Quan L M, Yang L, Cui L, Guo X S 2010 J. Opt. Soc. Am. B 27 1857
[21] Cui L, Li X Y, Fan H Y, Yang L, Ma X X 2009 Chin. Phys. Lett. 26 044209
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