# US 10,502,619 B2 · Characterization of single-photon detectors using a continuous wave laser source

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- Number: US 10,502,619 B2
- Document ID: US10502619B2
- Status: Granted
- Kind: B2
- Application number: 15/689,682
- Filed: 2017-08-29
- Published: 2017-12-14
- Granted: 2019-12-10
- Earliest claimed: 2010-07-13
- Assignees: AT&T Intellectual Property I, L.P.
- Applicants: AT&T Intellectual Property I, L.P.
- Inventors: Michael Brodsky; Cristian Antonelli; Jungmi Oh
- Web page: https://patentgrep.com/patent/US10502619B2

## CPC

- G01J 1/44: Electric circuits {(for command of an exposure part G03B7/02)}
- G01J 1/08: Arrangements of light sources specially adapted for photometry {standard sources, also using luminescent or radioactive material}
- G01J 1/42: using electric radiation detectors (optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10)
- G01J 2001/442: {Single-photon detection or photon counting}
- G01J 2001/4466: {Avalanche}
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)

## Abstract

Operational parameters of a single-photon detector are determined with a continuous wave laser source. At a fixed trigger, a dark count probability and a series of count probabilities at different optical powers are determined. A particular optical power is selected by using a wide-range variable attenuator to attenuate the optical power of the continuous wave laser. The dark count probability and the count probabilities are determined for different trigger rates. The operational parameters include efficiency, afterpulsing constant, and detrap time. The operational parameters are computed by fitting the computed dark count probabilities and count probabilities to a user-defined relationship.

## Claims

### Claim 1

An apparatus comprising:
a processor; and
a memory to store computer program instructions, the computer program instructions when executed on the processor cause the processor to perform operations comprising:
recording dark counts at a trigger rate with a single-photon detector;
computing a dark count probability for the trigger rate based on the dark counts;
recording counts at the trigger rate with the single-photon detector, the counts generated by a continuous wave laser at an optical power;
computing a count probability based on the counts; and
calculating an operating parameter of the single-photon detector by fitting the dark count probability and the count probability to a user-defined relationship defining a probability of detecting photons generated by a specific source in an absence of the dark counts and afterpulses,
wherein the calculating the operating parameter comprises calculating one of:
an efficiency η;
an afterpulsing constant Q0; and
a detrap time τ; and
wherein the probability of detecting the photons generated by the specific source in the absence of the dark counts is exponentially related to an average number of the photons per detector gate,
wherein the user-defined relationship comprises:
P
c
=
P
⁢
⁢
1
⁢
{
•
}
+
1
2
⁢
P
⁢
⁢
2
⁢
{
•
}
+
P
⁢
⁢
3
⁢
{
•
}
,
wherein
⁢
:
P
⁢
⁢
1
⁢
{
•
}
=
2
-
e
1
/
R
⁢
⁢
τ
-
(
1
-
P
dc
)
⁢
(
1
-
P
ph
)
⁢
(
1
-
Q
0
)
2
,
⁢
P
⁢
⁢
2
⁢
{
•
}
=
[
2
-
e
1
/
R
⁢
⁢
τ
-
(
1
-
P
dc
)
⁢
(
1
-
P
ph
)
⁢
(
1
-
Q
0
)
]
2
,
⁢
P
⁢
⁢
3
⁢
{
•
}
=
4
⁢
(
e
1
/
R
⁢
⁢
τ
-
1
)
⁡
[
1
-
(
1
-
P
dc
)
⁢
(
1
-
P
ph
)
]
,
⁢
P
ph
=
1
-
exp
⁡
(
-
μη
)
,
Pc is the count probability,
Pdc is the dark count probability,
μ is the average number of the photons per detector gate, and
R is the trigger rate.

### Claim 2 (depends on 1)

The apparatus of claim 1, the operations further comprising:
generating the optical power by attenuating a constant optical power generated by the continuous wave laser.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein a wavelength of the continuous wave laser ranges from approximately 1.3 microns to approximately 1.6 microns.

### Claim 4 (depends on 1)

The apparatus of claim 1, wherein the count probability is derived from evaluating a probability of an afterpulse occurring at a predetermined time interval after a photon count.

### Claim 5 (depends on 1)

The apparatus of claim 1, wherein the trigger rate is fixed.

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the trigger rate is variable.

### Claim 7 (depends on 1)

The apparatus of claim 1, wherein the continuous wave laser is turned off prior to the recording dark counts.

### Claim 8 (depends on 2)

The apparatus of claim 2, wherein the optical power is attenuated using a wide-range variable attenuator.

### Claim 9 (depends on 7)

The apparatus of claim 7, wherein the continuous wave laser is turned on after the recording dark counts.