InGaAs SPAD – freerunning

The InGaAs Single-Photon Counter is based on a InGaAs/InP SPAD for the detection of near-infrared single photons up to 1700 nm. The module includes a front-end circuit for fast avalanche sensing and detector quenching and resetting.

BIOMEDICAL APPLICATION • Confocal Microscopy • Single Molecule

Spectroscopy • Ultra-Sensitive

Fluorescence • Time-correlated single

photon counting • Single Molecule Detection

INDUSTRIAL APPLICATION • Optical Testing of

integrated circuits • Metrology by Time of Flight

measurements • Fibre optics

characterization

QUANTUM APPLICATION • Quantum Cryptography • Quantum Optics • Single-photon source

characterisation

ASTRONOMY APPLICATION • Optical Range Finding,

LIDAR & LADAR • Astronomy Observations &

Adaptive Optics

High Photon Detection Efficiency Up to 40% at 5V excess bias (VEX)

Best-in class Timing Accuracy < 100ps FWHM (focused light)

Free running mode No gating

Fully programmable module SPAD excess bias, temperature and hold-off are user selectable

MODULE FEATURES • 25µm active-area diameter InGaAs/InP SPAD • Free Space and SMF-28 Fibre Pigtailed version  • Sensitivity from 900nm to 1700nm  • Available in different Grade depending on Dark

Counts specifications  • Adjustable PDE vs. DCR trade-off and hold-off time  • PC control interface via USB  • Control Unit is the same both for free running and

gated detection heads  

Overview The InGaAs Single-Photon Counter is a photon counting module based on an InGaAs/InP Single-Photon Avalanche Diode (SPAD) for the detection of near-infrared single photons up to 1700 nm. The module includes the front-end circuit for fast avalanche sensing and detector quenching and resetting. All the SPAD settings (excess bias, hold-off time and temperature) are user adjustable, by means of a PC interface. This enables the user to configure the module with optimal parameters in order to match the requirements of the different applications. Typical SPAD Photon Detection Efficiency (PDE) as a function of wavelength and excess bias is shown on the front page. Typical PDE @ 1550 nm as a function of the excess bias for fibre pigtailed modules and typical SPAD dark-counting rates (DCR) as a function of the applied excess bias and hold-off time are shown here below. 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. The module is composed by two parts connected together through a 2m wide-bandwidth cable:

• A Detection Head (DH) which comprises of an InGaAs/InP SPAD detector and the related fast electronics. Its small dimension allows for easy integration in all experimental setups.

• A Control Unit (CU) which contains the pulse generator (used only with gated mode detection heads), Peltier controller, communication system and power supplies for the entire module.

Detection module control The InGaAs module is controlled through a PC software interface. With this software it is possible to set all the detector’s parameters: temperature, excess bias and hold-off time. In this way it is possible to adjust the detector performances in terms of DCR, hold-off time and photon detection efficiency, in order to properly match the requirements of the user application. The PC interface also offers five different preset configurations in order to speed up the module configuration and help the user in exploiting its intrinsic performances: ü Lowest Noise sets almost the lowest achievable

DCR at the expense of detection efficiency and timing resolution;

ü Low Noise offers higher detection efficiency and still low DCR;

ü Better Timing allows to obtain high efficiency and a good temporal response (low jitter) with moderate DCR;

ü Best Timing gives you almost the best possible efficiency and timing jitter of the module at the expense of high DCR but still not the highest;

ü Advanced allows to set any SPAD or gate parameter as desired for reaching the optimum module configuration.

InGaAs/InP now in free-running mode! Normally the InGaAs SPADs have such high DCR and afterpulsing that are operated in gated

regime: 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.

In case of particularly good devices it is anyway possible to bias them also in free-running mode as with Silicon SPADs. The main difference is related to the following characteristics: InGaAs SPADs have an afterpulsing effect that is much higher; InGaAs SPADs afterpulsing time constants have values in the range of microseconds. As a consequence it is necessary to use hold-off times in the order of few or few tens of microseconds.

Now, due to the hold-off time the InGaAs/InP SPAD has a linear working range, which means that the number of detection events within a defined time period (T) depends linearly on the illumination intensity, only for photon fluxes much smaller than the reciprocal of the hold-off time. At large photon fluxes the number of detected photons deviates from linearity and saturates to a constant value, which is the reciprocal of the dead-time (THO). When the deviation from linearity is moderate, i.e. the counting rates are smaller than 1/(2𝑇!"), it is possible to evaluate the deviation from linearity and to correct the measured counting rates with the following equation (well known in literature):

𝑁!"# =𝑁!"#$%&'

1 − 𝑁!"#$%&'×𝑇!"

where THO is the hold-off time, Ncounted is the count rate as measured with a normal pulse counter and Nimp is the impinging photon counting rate.

Please note that the previous equations do not take into account the Photon Detection Efficiency of the InGaAs module. These formulas also strictly apply when the photon rate is uniformly distributed over time.

Hardware connections

The control unit is the same independently on the type of the Detection Head (free running or gated).

• PHOTON OUT output, SMA connector; a digital pulse is generated for each detected photon; the output is a NIM pulse. The falling edge of the pulse marks, with very low jitter, the photon arrival time;

• VALID GATE output, SMA connector; outputs the effective SPAD status: it is in the high logic level when the SPAD is ON or in the low logic level when the SPAD is OFF due to the hold-off. The output conforms to a LVTTL standard;

• TRIGGER OUT (USE ONLY when a GATED MODE detection head is attached) output, SMA connector; outputs the internal trigger reference signal used to periodically enable the SPAD. The pulses are LVTTL standard;

• TRIGGER IN (USE ONLY when a GATED MODE detection head is attached) input, SMA connector; if an external trigger is needed, then the signal must be connected to this input. The external trigger signal can be positive or negative up to ±5V and the internal comparator allows for a programmable threshold.

Specifications1

Parameter Notes Min Typ Max Units Active area diameter 25 µm Photon Detection Efficiency

Vex = 2.5V, λ=1550nm, T=233K (fibre pigtailed) 12 % Vex = 2.5V, λ=1550nm, T=233K (free space) 15 %

Single photon timing jitter (FWHM)

At VEX = 5 V (free space - unfocused) < 150 ps At VEX = 5 V (fibre pigtailed) < 150 ps

Excess Bias range 2 5 V SPAD temperature SW selectable @ 0.1 K 228 243 K

Hold-off time SW selectable @ 24 ns step 1 3000 µs Accuracy ± 3.5 ns

PHOTON OUT NIM output -800 0 mV Required Load (DC) 50 Ω

TRIGGER IN

Amplitude -2 2.5 V Threshold (SW selectable 18 mV step) -2 2.5 V Load Impedance (DC) 50 Ω Impulse width 2 ns

TRIGGER OUT VALID GATE

Output levels 0 3.3 V Required Load (DC) 50 Ω

Supply voltage 100 - 240 VAC @ 50 - 60 Hz

Optical input Free space or FC/PC fibre pigtailed (SMF-28)

1See the user-manual Specifications paragraph for the full list of module’s specifications. Module designed and built compliant with the European Union Directive 2011/65/CE (also known as RoHS 2).

Grades Specifications Dark Counts (c/s) TE Cooled @ 233°K and 2.5V excess bias

Module Type Grade C Grade B Grade A

Free space - 25µm active area ∅ < 10 kc/s < 20 kc/s (call MPD for availability)

< 40 kc/s (call MPD for availability)

Single Fibre coupled – SMF-28 < 10 kc/s < 20 kc/s (call MPD for availability)

< 40 kc/s (call MPD for availability)

Very low dark counts modules can be selected in order to meet customer requirements

Mechanical Dimensions

System requirements (software) • USB 1.1 or 2.0 interface • Microsoft Windows XP, Vista,7,8 32 or 64 bit versions • The SW is the same for both free-running or gated modules. It is also able to control both type of

modules at the same time.

Ordering Information The InGaAs module can be purchased as a KIT, which includes the Detection Head (either free space or fibre coupled), the Control Unit and the interconnection cable, or as individual components; in this latter case the user shall already have a KIT from a previous purchase.

A standard InGaAs KIT is usually shipped with the following parts:

• Control Unit; • Detection Head (either fibre-pigtailed or windowed); • Orange wide-bandwidth Cable for Control Unit to Detection Head connection; • USB key containing the installation software and the user manual in PDF® format; • SPAD test report. • Optical table Universal adaptor

Products can be ordered directly from Micro Photon Devices or its representatives. For a complete list of representatives, visit our website at www.micro-photon-devices.com. Custom designed products are available upon request. The ordering codes for the kit and for the single components are respectively:

Warranty A standard legal warranty according to local legislation applies following shipment. Any warranty is null and void if the module case has been opened or if the absolute maximum ratings are exceeded. Specifications are subject to change without any notice. Document version : v2.1.2 – June 2014.

Contacts Micro Photon Devices S.r.l, Via Stradivari 4, I-39100 Bolzano, Italy T: +39 0471 051212 F: +39 0471 501524 www.micro-photon-devices.com