MPD Technologies PDM-IR Bedienungsanleitung

MICRO PHOTON DEVICES

PDM-IR

900 nm – 1700 nm Infrared Photon

Detection Module

ã Micro Photon Devices S.r.l.

Via Stradivari, 4

39100 Bolzano (BZ), Italy

email info@micro-photon-devices.com

Phone +39 0471 051212 • Fax +39 0471 501524

PDM-IR User Manual Version 3.0.3 - September 2018

PDM-IR user manual v3.0.3

Table of Contents

1!INTRODUCTION 4!

2!THE INGAAS/INP SINGLE-PHOTON AVALANCHE DIODE 5!

2.1!Gated)Mode)Operation) 5!

2.2!Free)Running)Operation) 8!

2.3!Further)readings) 9!

3!PDM-IR HARDWARE CHARACTERISTICS 10!

3.1!Rear)Panel)10!

3.2!Mechanical)Dimension)11!

4!PDM-IR SPECIFICATIONS 13!

4.1!PDM-IR)Trigger)Section)14!

4.1.1!Internal Trigger 15!

4.1.2!Trigger In 16!

4.1.3!Aux In 16!

4.1.4!Logic Function 17!

4.2!PDM-IR)Gate)Section)18!

4.2.1!Gated mode with fixed gate width operation 19!

4.2.2!Gated mode with Free-gate operation 20!

4.2.3!Free running mode 20!

4.3!PDM-IR)SPAD)Section)21!

4.3.1!Temperature 22!

4.3.2!Excess Bias 22!

4.3.3!Hold Off 22!

4.4!PDM-IR)Counters)Section)23!

4.5!PDM-IR)Output)Section)23!

4.5.1!PHOTON OUT 24!

4.5.2!TTL AUX OUT 25!

4.5.3!NIM AUX OUT 25!

4.6!PDM-IR)LED)Status)25!

4.7!PDM-IR)propagation)delays)26!

5!PDM-IR SOFTWARE INTERFACE 28!

PDM-IR user manual v3.0.3

5.1!Installation)28!

5.2!Software)Interface)28!

5.2.1!Main Window: Trigger and Gate Section 28!

5.2.2!Main Window: SPAD Section 30!

5.2.3!Main Window: Output Section 31!

5.2.4!Main Window: Status Section 32!

5.2.5!Main Window: Counter Section 33!

5.2.6!Counter Window 34!

5.2.7!Module Selection Window 34!

5.2.8!Module Info Window 35!

5.2.9!Configurations Window 35!

5.2.10!Save configuration Window 36!

5.2.11!RunTime Menu 37!

6!SETUPS 38!

6.1!Basic)setups)38!

6.1.1!Photon Counting setup 38!

6.1.2!Photon Timing setup 40!

6.2!Advanced)setups)41!

6.2.1!Cross correlation setup with external sync 41!

6.2.2!Cross correlation setup without sync 43!

6.2.3!Long Decay Measurement 44!

7!SYSTEM REQUIREMENTS 47!

PDM-IR user manual v3.0.3

1 Introduction

The MPD PDM-IR, is built around a Peltier cooled InGaAs/InP Single-Photon Avalanche Diode (SPAD) for the

detection of near-infrared single photons from 900 nm up to 1700 nm.

The module includes a programmable frequency and pulse generator for gating the detector, a front-end

circuit for photodetector’s avalanche sensing, a fast circuit for detector’s avalanche current quenching and

operative bias voltage resetting and some sub-circuits for signal conditioning. All the main parameters and

delay paths are adjustable by the user through the software interface, in order to match the requirements of

different applications. The system can be conveniently used both for counting and timing measurements,

since the high-performance electronics guarantees a clean temporal response even with fast gate transitions.

PDM-IR can work either in free-runnging or in gated mode (see paragraph 2) and the optical interface can be

chosen between a free space and a pigtailed version as shown by Figure 1 and Figure 2.

Figure 1. PDM-IR free space version.

Figure 2. PDM-IR fiber pigtailed version.

PDM-IR user manual v3.0.3

2 The InGaAs/InP Single-Photon Avalanche Diode

The core of this module is a Single-Photon Avalanche Diode (SPAD), housed into the Detection Head. The

detector has a 25 μm diameter active area in case of the free space version or a 10 µm diameter SPAD when

pigtailed with a single-mode fiber. The diode is mounted on the top of a three-stage Peltier cooler. A SPAD is

a p-n junction, biased well above the breakdown voltage (VB), that stays in a meta-stable state with no

current flowing. At this bias, the electric field is so high that a single charge carrier injected in the depletion

layer can trigger a self-sustaining avalanche. The current rises swiftly (nanoseconds or sub nanosecond rise-

time) to a macroscopic steady level, in the milliAmpere range. If the primary carrier is photo-generated, the

leading edge of the avalanche pulse precisely marks the photon arrival time. The current continues to flow

until the avalanche is quenched by lowering the bias voltage down to or below VB. Then the bias voltage

must be restored, in order to detect another photon. These operations are usually performed by a suitable

circuit named Active Quenching Circuit (AQC).

The device primary source of internal noise consists in a random dark-counting rate (DCR) arising from free

carriers thermally generated. These events compete with photons in triggering the detector and thus impair

the signal to noise ratio. The Peltier cooler is therefore useful to lower the temperature of the detector in

order to diminish this effect.

2.1 Gated Mode Operation

Normally single photon detectors are operated in the so-called free-running mode, where the devices are

enabled immediately after the quenching of each avalanche current. This is true for Silicon SPADs but for

InGaAs SPADs, due to higher DCR, gated regime is also used, for further reducing these unwanted counts:

the detector is periodically enabled for a short time window called Gate, of duration

!"#

(Gate Width),

whereas it is usually held off at a bias slightly below the breakdown voltage.

The counting rate (CR) of a detector operated in free running, and not in gated mode, is simply the number

of counts generated by the module output (PHOTON OUT) divided by the integration time:

$% &'()*+,-./-$.(012

301+4,516.0-!6)+

When the detector is operated in gated mode, the photon-out count rate (CR) must be corrected considering

both the Gate Frequency, i.e. the frequency at which the SPAD is periodically enabled, and the Gate Width

(

!"#

), i.e. the time length during which the SPAD is turned on during each duty cycle. The correction is due

to the fact that photons (or dark-counts) may be absorbed during the times the SPAD is kept turned off and

PDM-IR user manual v3.0.3

so are not counted. The correction considers how many photons have been counted and for how long, during

the integration time, the SPAD has been kept really turned on. In order to calculate the true counting rate,

thus, the following formula must be used:

$%789: & ; <

!"# =>?-

<;$% A!

where T is the Gate Period, i.e. the reciprocal of the Gate Frequency.

In most of the applications, this formula can usually be approximated to:

$%789: C$% A!

!"# -----/.,------$% D! E <

that is the raw counts divided by the duty-cycle applied to the detector.

However, a secondary source of noise exists in SPADs: the afterpulsing. During the avalanche some carriers

are captured by deep levels in the junction depletion layer and subsequently released with a statistically

fluctuating delay. Released carriers can retrigger the avalanche, generating after-pulses correlated with a

previous avalanche pulse which sum up with the DCR. In order to mitigate these avalanche re-triggerings,

after each avalanche, during the subsequent gating occurrences, the detector is kept off for a user

programmable time, named hold-off time,

!F"

. In this way the trapped carriers can be released without

triggering further avalanches. The hold-off time is particularly useful when cooling the detector since the

afterpulsing effect worsens at low temperatures because the decay times of the trapped carriers increase.

The hold-off time is usually longer than the gate period T.

An example of a photon counter module, operated in gated mode and employing the hold-off feature, is

shown in Figure 3. The reference signal is TRIGGER GATE which sets the gate repetition rate (frequency). The

signal actually applied to the SPAD is GATE, it is synchronized with TRIGGER GATE and has a width that

corresponds to the TON of the SPAD. Initially GATE and TRIGGER GATE are synchronized and their pulses

correspond 1-to-1. When a photon is absorbed, it triggers the avalanche current which is marked, in this

example, by the falling edge of Photon Output pulse. Once the avalanche is detected it is immediately

quenched; the system does not wait for the end of the Gate window to bias below breakdown the SPAD.

Now GATE and TRIGGER GATE begin to differ. During the hold-off time, the TRIGGER GATE pulses are ignored,

and GATE remains low, keeping the photodetector OFF. The SPAD is enabled again when the hold off time is

over. Of course, if a photon arrives at the detector after the end of a previous hold-off but during the gate-

off time, it is not detected as shown in Figure 3. Finally, in case the hold-off ends inside a GATE pulse, the

latter is either skipped (as shown in Figure 3) or applied with a reduced width, i.e. only the remaining part of

TON following the end of the hold-off. For a complete description of what happens see paragraph 4.2.

PDM-IR user manual v3.0.3

Figure 3. Main waveform in the module in case of the gated mode operation: output of pulse generator (TRIGGER

GATE), pulses at the SPAD detector (GATE), hold off time keeping the detector off for the amount of time

(HOLD OFF) and photon output signal (PHOTON OUTPUT).

Now, because of the hold-off time, the measured counting rate CR is not equivalent to the actual rate of

photons but can be estimated by:

$%F" &$%

<; $% A!F"

In counting applications, the maximum count rate should be then limited at about

<G@H!F"B

, because for

higher values the correction factor becomes so high that even small errors in the equation’s parameters will

result in high errors in the CRHO counting-rate.

Since the MPD PDM-IR biases the SPAD in gated mode and applies the hold-off every time an avalanche is

detected, the two effects must be applied at the same time in order to obtain the correct photon counting

rate CRphoton from the measured counting rate CR. From simple mathematics, it turns out that the final

equation is the following:

$%IJKLKM & ; <

!"# =>?-

<; $%

<;$% D !F" A!

which can then be simplified to :

$%IJKLKM C$%

<;$% D !F" A!

!"# -----/.,----- $% D!

<;$% D!F" E <

Please note that the previous equations do not consider the Photon Detection Efficiency of the InGaAs SPAD.

These formulas also strictly apply when the photon rate is uniformly distributed over time while particular

care must be used when applied to specific cases like the one discussed in paragraph 6.1.2.

Figure 3 is, in addition, very helpful in explaining the VALID GATE output. This signal is generated in order to

properly trace which TRIGGER GATE pulse effectively enabled the SPAD, i.e., which are the pulses that were

PDM-IR user manual v3.0.3

not blanked during the hold-off time (VALID GATE is a digital signal with the same pattern of Gate). This

information is particularly useful when looking for the percentage of counts over the total number of

available valid gates. In fact, in timing measurements one must be careful not to exceed the single-photon

statistics, in order not to distort the TCSPC histogram (see paragraph 6.1.2).

2.2 Free Running Operation

As already discussed, normally single photon detectors are operated in the so-called free-running mode,

where the devices are enabled immediately after the quenching of each avalanche current. PDM-IR allows

the user the possibility to choose which type of module operation, and thus not only the gated mode but

also the free running mode is possible with PDM-IR. In this mode of operation, as shown in Figure 4, TRIGGER

GATE signal is no more useful because the SPAD is always enabled until an avalanche is triggered. After each

of them, the SPAD is disabled for the hold off time and then immediately and swiftly re-enabled.

Overall, as a suggestion, the gated mode is used to achieve the best Signal-to-Noise (SNR) ratios and timing

resolutions whenever the signal to be detected is synchronous with a reference signal (for example the laser

clock used to stimulate the signal emission) that can be used to synchronize the PDM-IR. Indeed, better S/N

ratio or dynamic range, in case of TCSPC measurements, are achieved by enabling the detector only for the

short windows where the signal is present and keeping the detector off whenever the signal is not present.

The free running mode is typically used instead whenever the signal to be detected is not synchronous with

a reference signal (like the stimulated emission of photons from a nonlinear crystal by a CW laser). Of course,

free-running mode can also be used whenever a synchronous signal has to be detected but the S/N ratio (or

the dynamic range) is, in this case, lower compared to the gated mode module since the detector is always

enabled and InGaAs/InP diodes have much higher noise and after pulsing, compared to the silicon diodes.

Figure 4. Main waveforms for PDM-IR module in case of the free running operation: TRIGGER GATE is not significative

and ignored, the SPAD detector enabling time (GATE), the off time in case of avalanche (HOLD OFF) and

photon output signal (PHOTON OUTPUT).

PDM-IR user manual v3.0.3

2.3 Further readings

Cova, S., Ghioni, M., Lacaita, A. L., Samori, C., and Zappa, F. “Avalanche photodiodes and quenching circuits

for single-photon detection”, Applied Optics, 35(12), 1956—1976 (1996).

http://dx.doi.org/10.1364/AO.35.001956

Cova, S., Ghioni, M., Zappa, F., Rech, I., and Gulinatti, A., “A view on progress of silicon single-photon

avalanche diodes and quenching circuits”, Proceedings of SPIE , 6372, pp. 63720I-1 - 63720I-12 (2006).

http://dx.doi.org/10.1117/12.685963

Alberto Tosi, Alberto Dalla Mora, Franco Zappa and Sergio Cova, “Single-photon avalanche diodes for the

near-infrared range: detector and circuit issues,” Journal of Modern Optics, 56:2-3, 299-308 (2008) -

http://dx.doi.org/10.1080/09500340802263075

Alberto Tosi, Alberto Dalla Mora, Simone Tisa, Fabio Acerbi, Franco Zappa and Sergio Cova , “InGaAs/InP

SPADs for near-infrared applications: device operating conditions and dedicated electronics,” Proc. SPIE

7681, Advanced Photon Counting Techniques IV, 76810R (April 28, 2010);

http://dx.doi.org/10.1117/12.850696

Alberto Tosi, Adriano Della Frera, Andrea Bahgat Shehata, and Carmelo Scarcella, “Fully programmable

single-photon detection module for InGaAs/InP single-photon avalanche diodes with clean and sub-

nanosecond gating transitions,” Rev. Sci. Instrum. 83, 013104 (2012)

http://dx.doi.org/10.1063/1.3675579

PDM-IR user manual v3.0.3

3 PDM-IR hardware characteristics

3.1 Rear Panel

The PDM-IR has USB, power, IOs connectors and LED lens on rear side as shown in Figure 5. A description of

each component can be found in Table 1.

Table 1. PDM-IR rear panel components

PHOTON OUT

RF output, requires 50 Ohm DC terminated transmission lines. The output is a NIM pulse,

which means that the low logic level is 0 V and the high logic level is -800 mV. The falling

edge of the pulse marks, with very low jitter, the photon detection time. See paragraph 4.5

for a complete electrical description of this signal.

NIM AUX OUT

RF output, requires 50 Ohm DC terminated transmission lines. The output is a NIM pulse,

which means that the low logic level is 0 V and the high logic level is -800 mV. Output signal

is user selectable. See paragraph 4.5 for the available possibilities and for a complete

electrical description of this signal.

TTL AUX OUT

RF output, requires 50 Ohm DC terminated transmission lines. Electric pulses of 3.3V LVTTL

are generated at this output. Output signal is user selectable. See paragraph 4.5 for the

available possibilities and for a complete electrical description of this signal.

AUX IN

RF input, 50 Ohm with fixed DC impedance. The trigger signal can be positive or negative and

the input internal threshold is fully programmable. See Table 4 for a complete electrical

description of this input.

TRIGGER IN

RF input, 50 Ohm with fixed DC impedance. The trigger signal can be positive or negative and

the input internal threshold is fully programmable. See Table 3 for a complete electrical

description of this input.

USB ❶

Connector for a USB type-B cable. Used for PC connection

POWER SUPPLY ❸

Jack for connecting the provided +12V power supply. It requires at least 15 W output power.

Use only power supply provided by MPD to avoid electronics damage.

STATUS LED ❷

This LED indicates the PDM-IR status. It can be Green, Orange, Red and Off. See paragraph

4.6 for a complete description of the possible statuses

Figure 5. PDM-IR rear panel with highlighted connectors.

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