## High performance photon-pair source based on a fiber-coupled periodically poled KTiOPO_{4} waveguide

Optics Express, Vol. 17, Issue 14, pp. 12019-12030 (2009)

http://dx.doi.org/10.1364/OE.17.012019

Acrobat PDF (418 KB)

### Abstract

We demonstrate efficient generation of photon pairs at 1316 nm in a fiber-coupled type-II phase-matched Rb-indiffused waveguide in periodically poled KTiOPO_{4}. The integrated waveguide source has a pair production rate of 2×10^{7}/s/mW in a 1.08-nm bandwidth, in good agreement with a theoretical model that takes into account the transversal momentum imparted on the phase matching function by the waveguide. We achieve a Hong-Ou-Mandel quantum-interference visibility of 98.2% after subtraction of accidental coincidences, representing the highest reported value for a waveguide-based photon-pair source.

© 2009 Optical Society of America

## 1. Introduction

1. K. Banaszek, A. B. U’Ren, and I. A. Walmsley, “Generation of correlated photons in controlled spatial modes by downconversion in nonlinear waveguides,” Opt. Lett. **26**, 1367–1369 (2001).
[CrossRef]

2. S. Tanzilli, H. de Riedmatten, W. Tittel, H. Zbinden, P. Baldi, M. De Micheli, D. B. Ostrowsky, and N. Gisin, “Highly efficient photon-pair source using periodically poled lithium niobate waveguide,” Electron. Lett. **37**, 26–28 (2001).
[CrossRef]

3. A. B. U’Ren, C. Silberhorn, K. Banaszek, and I. A. Walmsley, “Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks,” Phys. Rev. Lett. **93**, 093601 (2004).
[CrossRef] [PubMed]

4. T. Suhara, H. Okabe, and M. Fujimura, “Generation of polarization-entangled photons by type-II quasi-phase-matched waveguide nonlinear-optic device,” IEEE Photon. Technol. Lett. **19**, 1093–1095 (2007).
[CrossRef]

5. M. Fiorentino, S. M. Spillane, R. G. Beausoleil, T. D. Roberts, P. Battle, and M. W. Munro, “Spontaneous parametric down-conversion in periodically poled KTP waveguides and bulk crystals,” Opt. Express **15**, 7479–7488 (2007).
[CrossRef] [PubMed]

6. A. Martin, V. Cristofori, P. Aboussouan, H. Herrmann, W. Sohler, D. B. Ostrowsky, O. Alibart, and S. Tanzilli, “Integrated optical source of polarization entangled photons at 1310 nm,” Opt. Express **17**, 1033–1041 (2009).
[CrossRef] [PubMed]

7. W. Tittel, J. Brendel, H. Zbinden, and N. Gisin, “Quantum cryptography using entangled photons in energy-time Bell states,” Phys. Rev. Lett. **84**, 4737–4740 (2000).
[CrossRef] [PubMed]

8. T. Honjo, S. W. Nam, H. Takesue, Q. Zhang, H. Kamada, Y. Nishida, O. Tadanaga, M. Asobe, B. Baek, R. Hadfield, S. Miki, M. Fujiwara, M. Sasaki, Z. Wang, K. Inoue, and Y. Yamamoto, “Long-distance entanglement-based quantum key distribution over optical fiber,” Opt. Express **16**, 19118–19126 (2008).
[CrossRef]

9. H. Takesue, E. Diamanti, C. Langrock, M. M. Fejer, and Y. Yamamoto, “10-GHz clock differential phase shift quantum key distribution experiment,” Opt. Express **14**, 9522–9530 (2006).
[CrossRef] [PubMed]

*µ*m telecommunication fiber-optic infrastructure with minimal effects due to cross-talk and nonlinear spurious signals.

*et al*. reported [5

5. M. Fiorentino, S. M. Spillane, R. G. Beausoleil, T. D. Roberts, P. Battle, and M. W. Munro, “Spontaneous parametric down-conversion in periodically poled KTP waveguides and bulk crystals,” Opt. Express **15**, 7479–7488 (2007).
[CrossRef] [PubMed]

_{4}(PPKTP) waveguide over that of a bulk PPKTP crystal and attributed it to a much larger density of states for the waveguide. We investigate the origin of this significant increase in the density of states using a different theoretical model of waveguide SPDC generation. We modify the standard phase matching function of a nonlinear medium by including the transverse wave vector imposed by the cross-sectional index profile of the waveguide and arrive at the same analytical result as that found in [5

5. M. Fiorentino, S. M. Spillane, R. G. Beausoleil, T. D. Roberts, P. Battle, and M. W. Munro, “Spontaneous parametric down-conversion in periodically poled KTP waveguides and bulk crystals,” Opt. Express **15**, 7479–7488 (2007).
[CrossRef] [PubMed]

10. C. E. Kuklewicz, M. Fiorentino, G. Messin, F. N. C. Wong, and J. H. Shapiro, “High-flux source of polarization-entangled photons from a periodically poled KTiOPO_{4} parametric down-converter,” Phys. Rev. A **69**, 013807 (2004).
[CrossRef]

11. C. K. Hong, Z. Y. Ou, and L. Mandel, “Measurement of subpicosecond time intervals between two photons by interference,” Phys. Rev. Lett. **59**, 2044–2046 (1987).
[CrossRef] [PubMed]

## 2. Theory of SPDC in Waveguides

^{-12}to 10

^{-8}, depending on the type of crystal, the crystal length, collection angle and bandwidth. Moreover, in a bulk crystal the total output flux from a bulk crystal is linearly proportional to the pump power and is not dependent on pump focusing. On the other hand, several groups have demonstrated that a nonlinear waveguide yields a significantly higher SPDC efficiency [1

1. K. Banaszek, A. B. U’Ren, and I. A. Walmsley, “Generation of correlated photons in controlled spatial modes by downconversion in nonlinear waveguides,” Opt. Lett. **26**, 1367–1369 (2001).
[CrossRef]

2. S. Tanzilli, H. de Riedmatten, W. Tittel, H. Zbinden, P. Baldi, M. De Micheli, D. B. Ostrowsky, and N. Gisin, “Highly efficient photon-pair source using periodically poled lithium niobate waveguide,” Electron. Lett. **37**, 26–28 (2001).
[CrossRef]

3. A. B. U’Ren, C. Silberhorn, K. Banaszek, and I. A. Walmsley, “Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks,” Phys. Rev. Lett. **93**, 093601 (2004).
[CrossRef] [PubMed]

**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

6. A. Martin, V. Cristofori, P. Aboussouan, H. Herrmann, W. Sohler, D. B. Ostrowsky, O. Alibart, and S. Tanzilli, “Integrated optical source of polarization entangled photons at 1310 nm,” Opt. Express **17**, 1033–1041 (2009).
[CrossRef] [PubMed]

12. K. Sanaka, K. Kawahara, and T. Kuga, “New high-efficiency source of photon pairs for engineering quantum entanglement,” Phys. Rev. Lett. **86**, 5620–5623 (2001).
[CrossRef] [PubMed]

*et al*. made a direct comparison between the outputs from a waveguide on PPKTP and a bulk PPKTP crystal, showing a 50-fold enhancement in the case of the waveguide and in agreement with a semiclassical model based on the density of states of guided mode fields [5

**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

*P*within a bandwidth dλ

_{s}*is given by [5*

_{s}**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

*L*is the crystal length,

*P*is the pump power,

_{p}*n*is the waveguide modal index at wavelength λ

_{k}*for subscript*

_{k}*k*being signal

*s*, idler

*i*, or pump

*p*, and

*A*is the mode-overlap area of the three interacting fields. For type-II first-order quasi-phase matching (QPM) in PPKTP with a grating period Λ, the effective second-order nonlinear coefficient is

_{I}*d*

_{eff}=(2/

*π*)

*d*

_{24}and the momentum mismatch is

*k*is the wave vector

_{jz}*k*⃗

*in the material projected along the propagation axis*

_{j}*z*.

*A*, and therefore field confinement in a waveguide leads to an enhanced pair generation rate. The difference in the output flux between a waveguide and a bulk crystal is attributed to the larger density of states (excitation modes) in a waveguide [5

_{I}**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

13. D. A. Kleinman, “Theory of optical parametric noise” Phys. Rev. **174**, 1027–1041 (1968).
[CrossRef]

14. K. Koch, E. C. Cheung, G. T. Moore, S. H. Chakmakjian, and J. M. Liu, “Hot spots in parametric fluorescence with a pump beam of finite cross section,” IEEE J. Quantum Electron. **31**, 769–781 (1995).
[CrossRef]

*bandwidth is [15*

_{s}15. R. L. Byer and S. E. Harris, “Power and bandwidth of spontaneous parametric emission,” Phys. Rev. **168**, 1064–1068 (1968).
[CrossRef]

*ϕ*is the angle between the signal wave vector

_{s}*k*⃗

*and pump wave vector*

_{s}*k*⃗

*. Most of the signal output comes from a narrow signal cone, beyond which the phase-matching function*

_{p}*f*(

*λ*,

_{s}*ϕ*)=sinc

_{s}^{2}(Δ

*k*/2) is negligibly small to contribute. Consider the momentum mismatch for the longitudinal (

_{z}L*z*) component, as given by Eq. (2), and for the transverse component

*z*principal axis so that there is no walk-off due to double refraction and that

*k*=

_{pz}*k*. For signal and idler propagating at small angles relative to the pump,

_{p}*ϕ*,

_{s}*ϕ*≪1, the

_{i}*z*-component of the signal and idler wave vectors can be expressed in terms of their transverse wave numbers

*k*to second order:

_{jt}*k*=-

_{st}*k*. For the case of frequency-degenerate SPDC in type-II phase-matched PPKTP,

_{it}*λ*=

_{s}*λ*and

_{i}*n*≈

_{s}*n*, and therefore

_{i}*k*≈

_{s}*k*and

_{i}*ϕ*≈-

_{s}*ϕ*. The standard phase matching condition for collinear propagation is Δ

_{i}*k*=0 with

_{z}*k*=-

_{st}*k*so that Eq. (6) is simplified to

_{it}*f*(

*λ*,

_{s}*ϕ*), we can obtain the phase-matching angular bandwidth by setting Δ

_{s}*k*=

_{z}L*π*which yields a divergence angle for SPDC in a bulk crystal of

*w*×

_{x}*w*and a uniform index Δ

_{y}*n*higher than the surrounding nonlinear material. The transverse index profile of the material, including both the waveguide and its surrounding, is a boxcar function with width

*w*(

_{x}*w*) along the

_{y}*x*(

*y*) dimension. The 2D index profile induces a transverse momentum vector

*k*⃗

*that must be included in the transversal momentum mismatch of Eq. (4). Similar to the longitudinal grating momentum added by periodic poling in nonlinear crystals, we obtain the transversal grating vector*

_{gt}*k*⃗

*from the Fourier transform of the 2D index profile. For the ideal case of a uniform rectangular waveguide,*

_{g}*k*(

_{gx}*k*) is simply a sinc function centered at

_{gy}*k*=0 (

_{gx}*k*=0) with a half width of

_{gy}*π*/

*w*(

_{x}*π*/

*w*). We note that the transverse momentum of the signal field in its fundamental waveguide propagating mode is also bounded by |

_{y}*k*

_{sx,sy}|≤

*π*/

*w*

_{x,y}.

*C*is a constant over the range of possible

*k*, which is bounded by |

_{st}*k*|≤

_{st}*π*/

*w*for waveguide propagating modes. At the maximum value of

_{t}*k*=±

_{st}*π*/

*w*, we have

_{t}*C*≥2

*π*

^{2}/

*w*

^{2}

*. On the other hand, at the minimum value*

_{t}*k*=0,

_{st}*C*=

*k*

^{2}

*. Given that*

_{gt}*k*is a sinc function that has the first zero at ±2

_{gt}*π*/

*w*, it is always possible to find a

_{t}*k*for any value of

_{gt}*k*such that

_{st}*C*is a constant. In this case, the waveguide phase-matching function of Eq. (10) behaves similar to the normal bulk-crystal phase matching.

*k*waveguide-propagating range of ±

_{st}*π*/

*w*, we can now evaluate the spectral brightness of the output signal. Rewriting the angular integration over

_{st}*ϕ*in Cartesian coordinates, we have

_{s}*A*

_{wg}=

*w*is the cross-sectional area of the waveguide, and Δ

_{x}w_{y}*k*is given by Eq. (10). The combination of the constant C/2ks and the longitudinal grating momentum 2

_{z}*π*/Λ in Eq. (10) yields an effective grating momentum in the waveguide 2

*π*/Λ′=2

*π*/Λ+

*C*/2

*k*so that the sinc function dependence of the waveguide output remains the same as in the bulk crystal. The enhanced waveguide output is due to the factor 1/

_{s}*A*

_{wg}resulting from a much larger phase-matched

*k*range. The SPDC interaction remains phase matched within a large range of effective divergence of the signal field because such divergence is always compensated by the transverse grating momentum

_{st}*k*imposed by the waveguide.

_{gt}**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

*A*

_{wg}whereas [5

**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

*A*. In a waveguide with moderate confinement, the majority of the interacting fields lie within the rectangular cross section, and

_{I}*A*

_{wg}and

*A*are approximately the same. Applying the result of Eq. (13) to our PPKTP waveguide with an approximately 4

_{I}*µ*m×8

*µ*m rectangular cross section, we have

*A*

_{wg}=32

*µ*m

^{2}and estimate a pair generation rate of 2.1×10

^{7}pairs/s/mW of pump power over a bandwidth of 1.1 nm.

## 3. Fabrication of Fiber-Coupled PPKTP Waveguide

*µ*m wide index step of 0.02 in the lateral direction, and a diffusion profile along the

*Z*direction

*n*(

*z*)=

*n*

_{KTP}+0.02exp(-

*z*/

*d*), with

*d*=8

*µ*m. In a type-II phase-matched process, the pump field is polarized along the crystallographic

*Y*axis, while the signal and idler fields are polarized along the crystallographic

*Y*and

*Z*axes, respectively. All fields propagate along the

*X*axis of the crystal. We applied periodic poling to the KTP waveguide crystal with a grating period of 227

*µ*m, designed for type-II QPM with frequency-degenerate outputs at 1316 nm near room temperature. We used the Sellmeier equation for bulk KTP [16

16. J. D. Bierlein and H. Vanherzeele, “Potassium titanyl phospate: properties and new applications,” J. Opt. Soc. Am. B **6**, 622–633 (1989).
[CrossRef]

*n*=1.783,

_{p}*n*=1.749,

_{s}*n*=1.830, respectively.

_{i}*Y*and

*Z*axes of the PPKTP crystal. We measured at room temperature a fiber to waveguide coupling efficiency of ~49% for the input fiber (Coastal Connections PM630) and ~50% for the output fiber (Coastal Connections PM1310). We have characterized the PPKTP waveguide device by measuring its type-II phase-matched second harmonic generation (SHG) process. A 1310-nm diode laser served as the pump and we obtained SHG outputs over a range of waveguide temperatures. From the temperature tuning curve we estimate that frequency degenerate operation at the desired 1316 nm would occur in the room temperature range. Also, absolute-power SHG measurements yielded a nonlinear coefficient

*d*

_{eff}=(2/

*π*)

*d*

_{24}of ~2.1 pm/V.

## 4. Flux and Bandwidth Characterization

*d*

_{eff}using SHG allow a straightforward comparison with the brightness characterization of our waveguide SPDC source. Pumped by a cw diode laser at 658.0 nm, the fiber-coupled SPDC outputs were collimated and sent through a long-pass filter to block the pump, followed by a 10-nm band-pass filter centered at 1316.0 nm. We used a polarizing beam splitter (PBS) to separate the orthogonally polarized signal and idler beams and coupled them into their respective SMF-28 single-mode optical fibers. The signal-idler coincidences were measured using a pair of fiber-coupled InGaAs avalanche photodiode (APD) single-photon counters with a coincidence window of 2.5 ns. The InGaAs APDs operated in the Geiger mode with a gating frequency of 50 kHz, and a 20-ns duty in each cycle. Detector efficiencies were calibrated using a laser source at 1316 nm and a fiber variable attenuator to be 15.4% and 20.5% with corresponding dark counts of ~32.1 kHz and ~17.2 kHz, respectively. Taking into account the waveguide-to-fiber coupling, transmission efficiencies of optical components, the overall signal and idler detection efficiencies were estimated at η

*≃1.8% and η*

_{s}*≃2.8%.*

_{i}*P*in the waveguide. At low pump powers, the singles rate (after subtraction of dark counts) has a linear power dependence, as expected. At higher pump powers the saturation of the InGaAs APD detectors caused an undercount of the singles rate, as shown in Fig. 2 for pump powers greater than ~1 mW. The shaded region in Fig. 2 shows the singles rates and pump power levels with which there was no detector saturation. Using the standard time-delay technique [17] we also measured the accidental coincidences that can be subtracted from the raw coincidence data to yield the net detected coincidence rate

_{p}*R*in Fig. 2. Following the method in [2

_{c}2. S. Tanzilli, H. de Riedmatten, W. Tittel, H. Zbinden, P. Baldi, M. De Micheli, D. B. Ostrowsky, and N. Gisin, “Highly efficient photon-pair source using periodically poled lithium niobate waveguide,” Electron. Lett. **37**, 26–28 (2001).
[CrossRef]

*R*=

_{gen}*R*/η

_{c}*η*

_{s}

_{i}*P*, and we obtain a pair generation rate of ~2.0×10

_{p}^{7}pairs/s/mW of pump, in excellent agreement with our theoretical estimate of ~2.1×10

^{7}pairs/s/mW. Note that the theoretical and measured generation rates are total-flux values because we used a 10-nm bandwidth that was much larger than the expected phase-matching bandwidth of 1.1 nm. Excluding the dark counts of the detectors, the expected singles rate obtained from the net coincidence rate

*R*̃

_{s,i}=

*R*/η

_{c}_{i,s}is smaller than the measured rate because the measured singles included background photons that were primarily fluorescence photons. Over the 10-nm measurement bandwidth, which invariably included background photons outside of the phase-matching bandwidth, the ratio of total fluorescence photons to the total downconverted photons was 15±5%.

^{5}pairs/s/GHz/mW, which is of the same order of magnitude as the pair generation rate of a 3.6-cm-long type-II phase-matched periodically poled lithium niobate waveguide reported in [6

6. A. Martin, V. Cristofori, P. Aboussouan, H. Herrmann, W. Sohler, D. B. Ostrowsky, O. Alibart, and S. Tanzilli, “Integrated optical source of polarization entangled photons at 1310 nm,” Opt. Express **17**, 1033–1041 (2009).
[CrossRef] [PubMed]

**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

*Y*crystal axis to the downconverted signal photons is ~10%. A similar measurement for the other polarization and the idler photons shows a lower value. However, if we integrate the background counts over a bandwidth of 10 nm we obtain a ratio that is higher than the 15% we measured using only a 10-nm filter. This apparent discrepancy resulted from our arrangement of the filters. In this case, the narrowband fiber filter was connected directly to the waveguide output fiber, thus the strong residual pump produced additional background photons within the narrowband filter. To accurately measure the amount of fluorescence photons, we placed the narrowband filter after the pump-blocking long-pass filter. With the narrowband filter center wavelength fixed at 1316 nm, we changed the waveguide temperature to detune the signal and idler until their spectra were outside of the filter bandwidth. We then observed that the true ratio of total generated fluorescence photons to total downconverted photons within the phase-matching bandwidth was ~2%, which is consistent with the previously obtained ratio of 15±5% over the entire 10 nm bandwidth. We note that the amount of fluorescence photons in our source was much lower than those reported in previous PPKTP waveguides that were pumped at shorter wavelengths [1

1. K. Banaszek, A. B. U’Ren, and I. A. Walmsley, “Generation of correlated photons in controlled spatial modes by downconversion in nonlinear waveguides,” Opt. Lett. **26**, 1367–1369 (2001).
[CrossRef]

3. A. B. U’Ren, C. Silberhorn, K. Banaszek, and I. A. Walmsley, “Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks,” Phys. Rev. Lett. **93**, 093601 (2004).
[CrossRef] [PubMed]

**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

18. J. Chen, A. J. Pearlman, A. Ling, J. Fan, and A. Migdall, “A versatile waveguide source of photon pairs for chip-scale quantum information processing,” Opt. Express **17**, 6727–6740 (2009).
[CrossRef] [PubMed]

## 5. Hong-Ou-Mandel Interference Measurements

10. C. E. Kuklewicz, M. Fiorentino, G. Messin, F. N. C. Wong, and J. H. Shapiro, “High-flux source of polarization-entangled photons from a periodically poled KTiOPO_{4} parametric down-converter,” Phys. Rev. A **69**, 013807 (2004).
[CrossRef]

*λ*=658.0 nm, we found the signal and idler outputs were wavelength degenerate at a temperature of 19.5° C. Additional free-space filtering of the residual pump and fluorescence photons were provided by a long-pass filter and a 10-nm band-pass filter.

_{p}*P*=57

_{p}*µ*W, in which the raw coincidence counts (solid blue diamonds) and the separately measured accidental coincidences (open red squares) are plotted as a function of the path length difference between the two arms. After subtracting the accidental coincidences from the raw data in Fig. 5, we obtain a HOM quantum-interference visibility

*V*=(

*C*

_{max}-

*C*

_{min})/(

*C*

_{max}+

*C*

_{min})=98.2±1.0%, where

*C*

_{max}and

*C*

_{min}are the maximum and minimum coincidence counts with accidentals subtracted, respectively. To our knowledge, this is the highest HOM visibility ever reported for waveguide-based photon-pair sources. The 1% uncertainty of the measured visibility is mainly due to the uncertainty of the accidental coincidence rates caused by the high dark count rates of our InGaAs detectors and the long averaging times. The base-to-base width of the HOM dip is 2.3±0.13 mm, corresponding to a two-photon coherence time of 3.83±0.21 ps, or equivalently a two-photon bandwidth of 0.76±0.04 nm, as expected from the narrowband filter bandwidth of 0.79 nm.

*α*within a coincidence time window for small

*α*. With our system efficiency estimated at η ~1.1% for the HOM measurements,

*V*

_{HOM}is dominantly determined by the pumping level. In particular, low coincidence detection rates do not imply low pair generation rates. We verify this relationship by repeating the HOM quantum interference measurements at various pump powers. Figure 6 plots the measured HOM visibility (with accidentals subtracted) as a function of the mean pair number. As

*α*increased from 0.3% to 4.0%, the HOM visibility dropped from 98.2% to 85.5%, in good agreement with the prediction of Eq. (14) (solid line) that takes into account the effect of double-pair generation. In Fig. 6, we also plot the expected HOM visibility (dashed curve) by including contributions from all multi-pair events. We note that as

*α*increases, the experimental data drifts away from the staright line of Eq. (14) towards the more exact theoretical prediction. More importantly, Eq. (14) reveals a fundamental trade-off between the brightness and the quantum interference visibility of a photon-pair source, which allows the waveguide SPDC source to be operated according to the needs of specific applications. With single spatial-mode operation and low pumping levels, we have achieved a HOM quantum-interference visibility that is significantly higher than previous high-brightness waveguide sources [5

**15**, 7479–7488 (2007).
[CrossRef] [PubMed]

**17**, 1033–1041 (2009).
[CrossRef] [PubMed]

*µ*W, we measured a HOM visibility of

*V*

_{broadband}=84.2%. Assuming the difference between the broadband and narrowband visibilities was due to spectral indistinguishability, we estimate that the spectral overlap between signal and idler photons was ~92% without the narrowband filter. For the broadband case we expect the two-photon bandwidth to be determined by the SPDC phase-matching bandwidth. The observed base-to-base width of the HOM dip of 1.6 mm yields a two-photon coherence time of 2.67 ps, or a two-photon bandwidth of 1.08 nm, which is in excellent agreement with the phase-matching bandwidth calculated from Eq. (13).

## 6. Conclusions

## Acknowledgments

## References and links

1. | K. Banaszek, A. B. U’Ren, and I. A. Walmsley, “Generation of correlated photons in controlled spatial modes by downconversion in nonlinear waveguides,” Opt. Lett. |

2. | S. Tanzilli, H. de Riedmatten, W. Tittel, H. Zbinden, P. Baldi, M. De Micheli, D. B. Ostrowsky, and N. Gisin, “Highly efficient photon-pair source using periodically poled lithium niobate waveguide,” Electron. Lett. |

3. | A. B. U’Ren, C. Silberhorn, K. Banaszek, and I. A. Walmsley, “Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks,” Phys. Rev. Lett. |

4. | T. Suhara, H. Okabe, and M. Fujimura, “Generation of polarization-entangled photons by type-II quasi-phase-matched waveguide nonlinear-optic device,” IEEE Photon. Technol. Lett. |

5. | M. Fiorentino, S. M. Spillane, R. G. Beausoleil, T. D. Roberts, P. Battle, and M. W. Munro, “Spontaneous parametric down-conversion in periodically poled KTP waveguides and bulk crystals,” Opt. Express |

6. | A. Martin, V. Cristofori, P. Aboussouan, H. Herrmann, W. Sohler, D. B. Ostrowsky, O. Alibart, and S. Tanzilli, “Integrated optical source of polarization entangled photons at 1310 nm,” Opt. Express |

7. | W. Tittel, J. Brendel, H. Zbinden, and N. Gisin, “Quantum cryptography using entangled photons in energy-time Bell states,” Phys. Rev. Lett. |

8. | T. Honjo, S. W. Nam, H. Takesue, Q. Zhang, H. Kamada, Y. Nishida, O. Tadanaga, M. Asobe, B. Baek, R. Hadfield, S. Miki, M. Fujiwara, M. Sasaki, Z. Wang, K. Inoue, and Y. Yamamoto, “Long-distance entanglement-based quantum key distribution over optical fiber,” Opt. Express |

9. | H. Takesue, E. Diamanti, C. Langrock, M. M. Fejer, and Y. Yamamoto, “10-GHz clock differential phase shift quantum key distribution experiment,” Opt. Express |

10. | C. E. Kuklewicz, M. Fiorentino, G. Messin, F. N. C. Wong, and J. H. Shapiro, “High-flux source of polarization-entangled photons from a periodically poled KTiOPO |

11. | C. K. Hong, Z. Y. Ou, and L. Mandel, “Measurement of subpicosecond time intervals between two photons by interference,” Phys. Rev. Lett. |

12. | K. Sanaka, K. Kawahara, and T. Kuga, “New high-efficiency source of photon pairs for engineering quantum entanglement,” Phys. Rev. Lett. |

13. | D. A. Kleinman, “Theory of optical parametric noise” Phys. Rev. |

14. | K. Koch, E. C. Cheung, G. T. Moore, S. H. Chakmakjian, and J. M. Liu, “Hot spots in parametric fluorescence with a pump beam of finite cross section,” IEEE J. Quantum Electron. |

15. | R. L. Byer and S. E. Harris, “Power and bandwidth of spontaneous parametric emission,” Phys. Rev. |

16. | J. D. Bierlein and H. Vanherzeele, “Potassium titanyl phospate: properties and new applications,” J. Opt. Soc. Am. B |

17. | M. A. Albota and E. Dauler, “Single photon detection of degenerate photon pairs at 1.55 µm from a periodically poled lithium niobate parametric downconverter,” J. Mod. Opt. |

18. | J. Chen, A. J. Pearlman, A. Ling, J. Fan, and A. Migdall, “A versatile waveguide source of photon pairs for chip-scale quantum information processing,” Opt. Express |

**OCIS Codes**

(190.4410) Nonlinear optics : Nonlinear optics, parametric processes

(270.5290) Quantum optics : Photon statistics

(270.5585) Quantum optics : Quantum information and processing

**ToC Category:**

Quantum Optics

**History**

Original Manuscript: May 4, 2009

Revised Manuscript: June 24, 2009

Manuscript Accepted: June 25, 2009

Published: July 1, 2009

**Citation**

Tian Zhong, Franco N. Wong, Tony D. Roberts, and Philip Battle, "High performance photon-pair source based on a fiber-coupled periodically poled KTiOPO_{4} waveguide," Opt. Express **17**, 12019-12030 (2009)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-14-12019

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