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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 6 — Mar. 15, 2010
  • pp: 5906–5911
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Method for characterizing single photon detectors in saturation regime by cw laser

Jungmi Oh, Cristian Antonelli, Moshe Tur, and Misha Brodsky  »View Author Affiliations


Optics Express, Vol. 18, Issue 6, pp. 5906-5911 (2010)
http://dx.doi.org/10.1364/OE.18.005906


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Abstract

We derive an analytical expression for the count probability of a single photon detector for a wide range of input optical power that includes afterpulsing effects. We confirm the validity of the expression by fitting it to the data obtained from a saturated commercial Single Photon Detector by illuminating it with a cw laser. Detector efficiency and afterpulsing probability extracted from the fits agree with the manufacture specs for low repetition frequencies.

© 2010 OSA

1. Introduction

Photon counting by InGaAsP/InP diodes at 1550 nm wavelength was reported a quarter of century ago [1

1. B. F. Levine, D. G. Bethea, and J. C. Campbell, “Near room temperature 1.3 um single photon counting with a InGaAs avalanche photodiode,” Electron. Lett. 20(14), 596–598 (1984). [CrossRef]

]. Since then Single Photon Detectors (SPD) have found a range of applications from quantum information experiments [2

2. D. Stucki, G. Ribordy, A. Stefanov, H. Zbinden, J. G. Rarity, and T. Wall, “Photon counting for quantum key distribution with Peltier cooled InGaAs/InP APD’s,” J. Mod. Opt. 48(13), 1967–1981 (2001). [CrossRef]

] to fiber characterization techniques [3

3. M. Wegmuller, F. Scholder, and N. Gisin, “Photon counting OTDR for Local Birefringence and Fault Analysis in the Metro Environment,” J. Lightwave Technol. 22(2), 390–400 (2004). [CrossRef]

]. To ensure proper operation of SPDs, various approaches for testing SPD have been developed. Modern advanced methods such as the interleaved bias method [4

4. D. S. Bethune, W. P. Risk, and G. W. Pabst, “A high performance integrated single photon detector for telecom wavelengths,” J. Mod. Opt. 51, 1359–1368 (2004).

] and the time-interval analysis method [5

5. A. Yoshizawa, R. Kaji, and H. Tsuchida, “Quantum efficiency evaluation method for gated-mode single photon detector,” Electron. Lett. 38(23), 1468–1469 (2002). [CrossRef]

] permit extraction of both the afterpulsing probability and the detector efficiency. However, these methods rely on complicated timing control schemes and extremely low input power levels. Thus, they require expensive equipment such as electronic time delays, pulsed lasers, high dynamic range attenuators and sensitive power meters, and might not be suitable for field applications. An end-user of recent generation portable table-top instruments could benefit from a simple method that works at relatively high power levels and requires only a conventional cw laser.

In this letter, we demonstrate a new characterization method for Single Photon Detectors that utilizes a cw laser at modestly high power ranging from –61dBm to –53dBm (for our detectors this corresponds to the average number of photon per gate, μ, of 3 – 20). First, we measure probability of a count over a range of power and trigger rates for both pulsed and cw lasers. The data suggest higher afterpulsing probability at higher rates, which, unexpectedly, is accompanied by a slight decrease in detector efficiency. These tendencies are more pronounced with cw lasers than with pulsed lasers. Then, we fit the experimental results by a newly derived analytical expression using the detector efficiency and afterpulsing probability as fitting parameters. Our fits perfectly match the data within rms deviation of < 0.03%. Extracted efficiencies of 20%, and conditional afterpulsing probability in the range of 0.01 - 0.03 for 250 kHz trigger rate (device dependent) are similar to the values reported in manufacturer tests performed at the conventional low power regime of μ=0.1 [4

4. D. S. Bethune, W. P. Risk, and G. W. Pabst, “A high performance integrated single photon detector for telecom wavelengths,” J. Mod. Opt. 51, 1359–1368 (2004).

]. We found that in the cw regime the afterpulsing is somewhat stronger and decays faster with the characteristic time of 2.5-3μs, which is shorter than the 4-5μs measured for pulsed laser. This observation suggests that different processes dominate in the cw and pulsed regime. But when the trigger rates are below 200 kHz the results obtained by cw and pulsed methods are nearly identical.

2. Experimental setup

Figure 1
Fig. 1 The experimental setup.
shows our experimental setup. Light from a standard telecom 1549.32nm cw laser is fed via a 3dB coupler to a variable attenuator and into a detector under test. For our experiments we used several commercial SPDs, operating in a gated mode [68

8. X. Jiang, M. A. Itzler, R. Ben-Michael, and K. Slomkowski, “InGaAsP-InP avalanche photodiodes for single photon detection,” IEEE J. Sel. Top. Quantum Electron. 13(4), 895–905 (2007). [CrossRef]

]. To determine the effective detector gate and to compare our results with those obtained by the conventional pulsed laser method [4

4. D. S. Bethune, W. P. Risk, and G. W. Pabst, “A high performance integrated single photon detector for telecom wavelengths,” J. Mod. Opt. 51, 1359–1368 (2004).

] we connected a 1551nm pulsed laser source (idQuantique, id300) to the other input of the 3dB coupler. The laser optical pulse width is about 30ps. We used a double stage variable attenuator with a range of 85dB. Each stage was calibrated independently at relatively high power levels of −50dBm by using a power meter. The calibration enabled us to control the power precisely at levels below the sensitivity of our power meter. Thus, the average number of photons per detector gate, μ, was adjusted down to 0.02 for both cw and pulsed sources. The detector produces an electrical NIM pulse (Nuclear Instrumentation Module Standard) for each detection event. These NIM pulses were then integrated by an electronic counter.

In order to determine the average number of photons per detector gate in the cw regime, we measure the effective gate window of the detector, τg. Each counting cycle, a short 1ns-wide electrical bias pulse brings the diode above the breakdown voltage. Conventionally, the maximum efficiencyη0 achieved at the peak of the bias pulse is measured with a properly aligned narrow optical pulse [4

4. D. S. Bethune, W. P. Risk, and G. W. Pabst, “A high performance integrated single photon detector for telecom wavelengths,” J. Mod. Opt. 51, 1359–1368 (2004).

] and serves as the major spec for SPDs. On the other hand, cw light experience efficiency that changes during the bias pulse in a nonlinear fashion. To simplify calculations, we model the SPD in the cw regime as operating at its maximal efficiency value η0 for an effective gate window τg. To assess τgexperimentally, we first measure the probability of a count Pc over a wide power range of each cw and pulsed laser. The repetition rate of the detector is R=100kHz in both cases, and the pulsed laser is synchronized with the detector. Then we pick the values of the cw laser power Pcw and the average pulsed laser power Pp that equates the corresponding count probabilities Pc(Pcw)=Pc(Pp). Finally the gate window can be calculated as: τg=10(PpPcw10log10(R))/10, where the power values Pp and Pcw are in dBm. When averaged over the entire power range this procedure results in τgin a range of 0.49ns – 0.59ns for different detectors.

Figure 2
Fig. 2 Measured count probability Pc as a function of the average number of photons per gate μ for pulsed (●) and cw (□) laser. Hereτg=0.49ns.
plots measured count probabilities Pc(μ)as a function of the average number of photons per gate μcw=10(Pcw/10)1000×h×ν×τg and μp=10(Pp/10)1000×h×ν×R, where h is the Planck constant and ν is optical frequency. Here the value τg=0.49ns equates the measured count probabilities in the cw and the pulsed. Although here we determined the effective gate window τg by ourselves, it could preferably be provided by the manufacturer as one of the instrument’s specs.

3. Derivation of the detector count probability

The dependence shown in Fig. 2 saturates because avalanche SPDs are not sensitive to the number of registered photons. For the Poissonian photon statistics, this saturation was first described by a simple expression in [1

1. B. F. Levine, D. G. Bethea, and J. C. Campbell, “Near room temperature 1.3 um single photon counting with a InGaAs avalanche photodiode,” Electron. Lett. 20(14), 596–598 (1984). [CrossRef]

],
Pc=1(1Pdc)×exp(μη)
(1)
Here Pdc is the probability of a dark count, μ is the average number of photons per SPD gate and η is the detector efficiency. However, we find that our data deviates from such dependence in two ways. First, we find that the measured probability is somewhat higher at lower μ values, which suggests the presence of afterpulses [7

7. M. A. Itzler, R. Ben-Michael, C. F. Hsu, K. Slomkowski, A. Tosi, S. Cova, F. Zappa, and R. Ispasoiu, “Single photon avalanche diodes (SPADs) for 1.5 um photon counting applications,” J. Mod. Opt. 54(2), 283–304 (2007). [CrossRef]

,8

8. X. Jiang, M. A. Itzler, R. Ben-Michael, and K. Slomkowski, “InGaAsP-InP avalanche photodiodes for single photon detection,” IEEE J. Sel. Top. Quantum Electron. 13(4), 895–905 (2007). [CrossRef]

]. Second, the entire curve seems to be tilted toward higher μ indicating a slight decrease in efficiency. These two effects become more pronounced with higher repetition rates. To account for these deviations we modify the expression for the count probability to include the afterpulsing effect.

We characterize the afterpulsing effect by the conditional probability Q(t)of having an avalanche for the detector gate being open after a time interval t since the successful detection event. We further assume that this conditional probability decays exponentially with a time constant τ:Q(t)=Q0exp(tτ) [9

9. Y. Kang, H. X. Lu, Y.-H. Lo, D. S. Bethune, and W. P. Risk, “Dark count probability and quantum efficiency of avalanche photodiodes for single-photon detection,” Appl. Phys. Lett. 83(14), 2955 (2003). [CrossRef]

]. Then Qn is the conditional probability of the avalanche occurrence after exactly n clock cycles in the detector that is gated with the trigger rate R:
Qn=Q0exp(nRτ)
(2)
Within this model the overall probability of a registered event Pc can be found to be
Pc=2e1Rτ(1Pdc)(1Pph)(1Q0)2+12[2e1Rτ(1Pdc)(1Pph)(1Q0)]2+4(e1Rτ1)[1(1Pdc)(1Pph)]
(3)
Here Pph would be probability of detecting photons generated by the source under scrutiny in the absence of both dark counts and afterpulses. For a Poissonian source of single photons, such as attenuated coherent laser light, Pph=1exp(μη). As an aside, we would like to mention that if a low-power Poissonian source of photon pairs is available instead of attenuated laser light, then Eq. (3) still can be used, but withPph=1exp(μη(2η)).

The derivation of Eq. (3) is accomplished in two steps. The first step consists of evaluating the marginal probability of an afterpulse Pap:
Pap(n)=Pc(n1)Q1+(1Pc(n1))Pc(n2)Q2+(1Pc(n1))(1Pc(n2))Pc(n3)Q3+...
(4)
where the superscript n denotes that the corresponding probability is evaluated at the n-th time interval. Note that Qk is a conditional probability of an afterpulse given that no counts occur during the time t=k/R. Substitution of Eq. (2) into Eq. (4) yields:
Pap(n)=Pc(n1)Q1+Pap(n1)(1Pc(n1))Q1/Q0
(5)
After a some large number of trigger cycles the probabilities Pap(n) and Pc(n) reach their stationary values and can be replaced by Pap and Pc, respectively, in Eq. (5), which hence can be solved for Pap, yielding
Pap=PcQ11(1Pc)Q1/Q0
(6)
Finally, the second step of our derivation consists of extracting Pc from Pc=1(1Pdc)(1Pph)(1Pap), where Pap is given by Eq. (6). Note that for Q00 or τ0 (that is Q10) Eq. (6) yields Pap=0, hence Pc, as evaluated from Pc=1(1Pdc)(1Pph), reduces to the simple form given by Eq. (1).

4. Experimental results

Figure 3
Fig. 3 Count probability Pc versus average number of photons per gate μcw=0.120 for cw laser at different trigger rates of 100 kHz (□) and 1 MHz(○). Inset: a zoom in with more trigger rates. Data is shown by symbols, lines are fits.
shows the measured count probability for cw laser for the average incoming photon number μcw=10(Pcw/10)1000×h×f×τg ranging from 0.1 to 20. The data taken at each of the four different trigger rates is plotted in different symbols. Our calculation presented above shows that for each trigger rate R the experimental dependence of Pcon μcwcan be described by the expression in Eq. (3), computed with the corresponding values of R . This allows us to extract the efficiency for each trigger rate η(R), the afterpulsing constant Qo, and the detrap time τ by fitting Eq. (3) to the data.

We first measure the dark count probability Pdc. Then we perform a simultaneous fit to all four experimentally obtained dependencies of the count probability on the average photon number. By inserting the resulting parameters back into Eq. (3) we plot lines in Fig. 3. The high quality of the fits can be clearly seen. In fact, by using only a limited range of μcw=320 (corresponding to easily measurable interval of61dBmPcw53dBm) we obtained a nearly perfect match to our data within rms deviation of 3×104. Thus we conclude that the basic detector parameters can be extracted from measured photon counts at a relatively high number of incoming photons.

5. Conclusion

We presented a new method of extracting the SPD efficiency and the afterpulsing probability. The method consists of measuring photon counts at relatively high cw power at several repetition rates and fitting the data with a newly derived analytical expression. We show that the method produces good results for repetition rates below250kHz. Such a simple and reliable method could potentially help a service provider with maintenance and configuration of QKD systems.

References and links

1.

B. F. Levine, D. G. Bethea, and J. C. Campbell, “Near room temperature 1.3 um single photon counting with a InGaAs avalanche photodiode,” Electron. Lett. 20(14), 596–598 (1984). [CrossRef]

2.

D. Stucki, G. Ribordy, A. Stefanov, H. Zbinden, J. G. Rarity, and T. Wall, “Photon counting for quantum key distribution with Peltier cooled InGaAs/InP APD’s,” J. Mod. Opt. 48(13), 1967–1981 (2001). [CrossRef]

3.

M. Wegmuller, F. Scholder, and N. Gisin, “Photon counting OTDR for Local Birefringence and Fault Analysis in the Metro Environment,” J. Lightwave Technol. 22(2), 390–400 (2004). [CrossRef]

4.

D. S. Bethune, W. P. Risk, and G. W. Pabst, “A high performance integrated single photon detector for telecom wavelengths,” J. Mod. Opt. 51, 1359–1368 (2004).

5.

A. Yoshizawa, R. Kaji, and H. Tsuchida, “Quantum efficiency evaluation method for gated-mode single photon detector,” Electron. Lett. 38(23), 1468–1469 (2002). [CrossRef]

6.

PGA-600, www.princetonlightwave.com.

7.

M. A. Itzler, R. Ben-Michael, C. F. Hsu, K. Slomkowski, A. Tosi, S. Cova, F. Zappa, and R. Ispasoiu, “Single photon avalanche diodes (SPADs) for 1.5 um photon counting applications,” J. Mod. Opt. 54(2), 283–304 (2007). [CrossRef]

8.

X. Jiang, M. A. Itzler, R. Ben-Michael, and K. Slomkowski, “InGaAsP-InP avalanche photodiodes for single photon detection,” IEEE J. Sel. Top. Quantum Electron. 13(4), 895–905 (2007). [CrossRef]

9.

Y. Kang, H. X. Lu, Y.-H. Lo, D. S. Bethune, and W. P. Risk, “Dark count probability and quantum efficiency of avalanche photodiodes for single-photon detection,” Appl. Phys. Lett. 83(14), 2955 (2003). [CrossRef]

10.

J. Zhang, R. Thew, J. D. Gautier, N. Gisin, and H. Zbinden, “Comprehensive characterization of InGaAs/InP avalanche photodiodes at 1550 nm with an active quenching ASIC,” IEEE J. Quantum Electron. 45(7), 792–799 (2009). [CrossRef]

11.

S. V. Polyakov and A. L. Migdall, “High accuracy verification of a correlated-photon- based method for determining photoncounting detection efficiency,” Opt. Express 15(4), 1390–1407 (2007), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-4-1390. [CrossRef] [PubMed]

OCIS Codes
(060.2380) Fiber optics and optical communications : Fiber optics sources and detectors
(270.5290) Quantum optics : Photon statistics
(270.5570) Quantum optics : Quantum detectors

ToC Category:
Detectors

History
Original Manuscript: November 20, 2009
Revised Manuscript: January 12, 2010
Manuscript Accepted: January 25, 2010
Published: March 10, 2010

Citation
Jungmi Oh, Cristian Antonelli, Moshe Tur, and Misha Brodsky, "Method for characterizing single photon detectors in saturation regime by cw laser," Opt. Express 18, 5906-5911 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-6-5906


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References

  1. B. F. Levine, D. G. Bethea, and J. C. Campbell, “Near room temperature 1.3 um single photon counting with a InGaAs avalanche photodiode,” Electron. Lett. 20(14), 596–598 (1984). [CrossRef]
  2. D. Stucki, G. Ribordy, A. Stefanov, H. Zbinden, J. G. Rarity, and T. Wall, “Photon counting for quantum key distribution with Peltier cooled InGaAs/InP APD’s,” J. Mod. Opt. 48(13), 1967–1981 (2001). [CrossRef]
  3. M. Wegmuller, F. Scholder, and N. Gisin, “Photon counting OTDR for Local Birefringence and Fault Analysis in the Metro Environment,” J. Lightwave Technol. 22(2), 390–400 (2004). [CrossRef]
  4. D. S. Bethune, W. P. Risk, and G. W. Pabst, “A high performance integrated single photon detector for telecom wavelengths,” J. Mod. Opt. 51, 1359–1368 (2004).
  5. A. Yoshizawa, R. Kaji, and H. Tsuchida, “Quantum efficiency evaluation method for gated-mode single photon detector,” Electron. Lett. 38(23), 1468–1469 (2002). [CrossRef]
  6. PGA-600, www.princetonlightwave.com .
  7. M. A. Itzler, R. Ben-Michael, C. F. Hsu, K. Slomkowski, A. Tosi, S. Cova, F. Zappa, and R. Ispasoiu, “Single photon avalanche diodes (SPADs) for 1.5 um photon counting applications,” J. Mod. Opt. 54(2), 283–304 (2007). [CrossRef]
  8. X. Jiang, M. A. Itzler, R. Ben-Michael, and K. Slomkowski, “InGaAsP-InP avalanche photodiodes for single photon detection,” IEEE J. Sel. Top. Quantum Electron. 13(4), 895–905 (2007). [CrossRef]
  9. Y. Kang, H. X. Lu, Y.-H. Lo, D. S. Bethune, and W. P. Risk, “Dark count probability and quantum efficiency of avalanche photodiodes for single-photon detection,” Appl. Phys. Lett. 83(14), 2955 (2003). [CrossRef]
  10. J. Zhang, R. Thew, J. D. Gautier, N. Gisin, and H. Zbinden, “Comprehensive characterization of InGaAs/InP avalanche photodiodes at 1550 nm with an active quenching ASIC,” IEEE J. Quantum Electron. 45(7), 792–799 (2009). [CrossRef]
  11. S. V. Polyakov and A. L. Migdall, “High accuracy verification of a correlated-photon- based method for determining photoncounting detection efficiency,” Opt. Express 15(4), 1390–1407 (2007), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-4-1390 . [CrossRef] [PubMed]

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